Light Cone 2015

21 Sept 2015, 08:00 → 25 Sept 2015, 18:00 Europe/Rome

Aula Bruno Touschek (Laboratori Nazionali di Frascati)

LC2015 belongs to a conference series that started in 1991 under the supervision of the International Light Cone Advisory Committee and showed, year by year, to play a vital role in promoting the research towards a rigorous description of hadrons and nuclei, based on Light-Cone quantization methods.

A strong relation with the experimental activity represents an important commitment of the Light-Cone community, with the ambition ''to assist in the development of crucial experimental tests at hadron facilities''.

To emphasize this goal, the LC2015 venue will be the INFN National Laboratories in Frascati.
In anticipation of opportunities afforded by new facilities, such as the 12 GeV upgrade of Th. Jefferson Natl. Lab, the FAIR facility at GSI, J-PARC, and other facilities around the globe, we aim to have a scientific program that could have a stimulating impact on the forefront research development of nuclear, hadron and particle physics.
In particular, LC2015 will address the following topics:

• Hadron Physics in present and future facilities
• AdS/CFT - Theory and applications
• Few-body problems on the Light Cone
• Relativistic models of nuclear and hadronic structures
• Nonperturbative methods in quantum field theory
• Light-front field theory in QCD and QED
• Lattice Gauge Theories

     Conference Chairs

 

Barbara Pasquini Dipartimento di Fisica Universita' di Pavia Via Bassi 6, 27100 Pavia Tel +390382987450 Fax +390382526938

Giovanni Salmè INFN Sezione di Roma Piazzale Aldo Moro 6, 00185 Roma Tel. +390649914872 Fax +39064454749

 

Participants


 

Slides IMG_9847_elaborata.jpg IMG_9848_elaborata.jpg

Monday, 21 September

08:00 → 08:45 Registration

08:45 → 09:00 Welcome

Slides Welcome-information.pdf

09:00 → 11:00 1.

Convener: Prof. Chueng Ji (NCSU)

09:00 TMD phenomenology

The Transverse Momentum Dependent Partonic Distributions (TMD-PDFs) and Fragmentation Functions (TMD-FFs) should reveal new properties of the 3-dimensional structure of nucleons and of the quark hadronization process. Many experimental data are now available and much progress has been made in their phenomenological interpretation. A short summary of the situation is presented.

Speaker: Mauro Anselmino (TO)

Slides Light_Cone_2015.pdf

09:30 Exploring the Glue that Binds Us All: Science of the Electron Ion Collider in the US

Deep Inelastic Scatting is arguably the best experimental technique employed by physicists to study the fundamental structure of nucleons and nuclei. Much of what we know about the quark gluon structure of the nucleons and nuclei comes form experiment performed in polarized and unpolarized fixed-target experiments around the world, and those performed at DESY using the HERA collider. However many important questions related to the gluon’s role in QCD still remain unanswered. Many of these relate to collective behavior of partons (mostly gluons) in (polarized) nucleons and in nuclei at high energy. Without understanding those, we simply can not say we understand QCD, the theory of strong interactions in the Standard Model, completely. The missing experimental data that will guide our understanding of QCD and address those questions, will require high-energy polarized electron-nucleon, and electron-nuclear collisions with a wide range in the size of the nuclei. High-energy and polarization are critical for addressing this in a future collider. The Electron Ion Collider (EIC) being considered in the US is planned with precisely this in mind. Further, the systematic study of the nucleon and its spin properties, including the position and momentum correlations amongst the parsons inside the nucleons (resulting in possible tomographic images of the nucleons) will require a sufficiently high luminosity. I will summarize the gluon related open questions in QCD and present the capabilities of the EIC in addressing them. I will also present the present status of the EIC project, and invite you to support it and get involved.

Speaker: Abhay Deshpande (Stony Brook University)

Slides EIC-LC2015.pdf

10:00 Quark and gluon orbital angular momentum: where are we?

The orbital angular momentum of quarks and gluons contributes significantly to the proton spin budget and attracted a lot of attention in the recent years, both theoretically and experimentally. We summarize the various definitions of parton orbital angular momentum together with their relations with parton distributions functions. In particular, we highlight current theoretical puzzles and give some prospects.

Speaker: Dr Cedric Lorce (IPNO and LPT Orsay, Universite Paris-Sud)

Slides Lorce_LightCone2015.pptx

10:30 Quark Orbital Angular Momentum

Definitions of orbital angular momentum based on Wigner distributions are used to discuss the connection between the Ji definition of the quark orbital angular momentum and that of Jaffe and Manohar. The difference between these two definitions can be interpreted as the change in the quark orbital angular momentum as it leaves the target in a DIS experiment. The mechanism responsible for that change is similar to the mechanism that causes transverse single-spin asymmetries in semi-inclusive deep inelastic scattering. A sum rule for quark orbital angular momentum based on a twist 3 GPD is also discussed.

Speaker: Prof. Matthias Burkardt (New Mexico State University)

Slides Burkardt_LC2015.pdf

11:00 → 11:45 Coffee break

11:45 → 13:15 2.

Convener: Sergio Scopetta (PG)

11:45 Integrated and unintegrated PDFs and GPDs from effective two-body light-cone wave functions

We introduce a classification scheme for parton distribution models and we model generalized parton distributions (GPDs), their form factors, and parton distribution functions (PDFs), integrated and unintegrated ones, in terms of unintegrated double distributions that are obtained from the parton number conserved overlap of effective light-cone wave functions. For a so-called "spherical" model we present general expressions for all twist-two related non-perturbative quantities in terms of one effective light-cone wave function, including chiral-odd GPDs. We also discuss the Regge improvement of such quark models from the $s$-channel point of view and study the relations between zero-skewness GPDs and unintegrated PDFs on a more general ground.

Speaker: Dr Dieter Mueller (Ruhr-University Bochum)

Slides Dieter_Mueller_LC2015.pdf

12:15 Theory of Double Parton Scattering

Double parton scattering (DPS) is the process in which two distinct pairs of partons hard scatter in an individual proton-proton collision. It can be an important background to single scattering processes suppressed by small or multiple coupling constants (e.g. new physics signals), and can reveal novel information about the proton structure. I review recent developments in the endeavour to describe this process theoretically using a 'hard scattering factorisation' framework.

Speaker: Dr Jonathan Gaunt (DESY)

Slides LCQCDtalkGaunt.pdf

12:45 Valon model for double parton distributions

We explore ansatze for parton distributions of the proton following the idea of the valon model, where the Fock components have the form f1(x_1)f1(x_2)...fn(x_n)delta(1-x_1-x_2-...-x_n). Upon integration, double and single parton distributions are generated from the n-particle distributions. We show that the construction leads to preservation of the Gaunt-Stirling sum rules, thus providing distributions with the required features which can be used in phenomenological studies.

Speaker: Wojciech Broniowski (Jan Kochanowski U. and Institute on Nuclear Physics PAN, Poland)

Slides frascati.pdf

13:15 → 14:30 Lunch break

14:30 → 16:00 3.

Convener: Dr Daniele Binosi (ECT*-Fondazione Bruno Kessler)

14:30 Hadron Physics from Superconformal Quantum Mechanics in the Light-Front and its Holographic Embedding

Relativistic bound-state equations for mesons and baryons are constructed in a semiclassical approximation to light-front QCD from a superconformal algebra which relates baryon and meson spectra. This procedure uniquely determines the confinement potential for arbitrary spin and its embedding in AdS space. The specific breaking of dilatation invariance within the supersymmetric algebra explains hadronic properties common to light mesons and baryons, such as the observed mass pattern in the radial and orbital excitations, as well as their distinctive and systematic features. The lowest-lying state, the the pi-meson, is massless in the chiral limit and has no supersymmetric partner. Quark masses break conformal invariance, but the basic underlying supersymmetric mechanism gives remarkable connections across the entire spectrum of light and heavy-light hadrons. We also explore the consequences of extending supersymmetry to double-heavy mesons and baryons.

Speaker: Prof. Guy de Teramond (University of Costa Rica)

Slides DeTeramond-Frascati_2015.pdf

15:00 Hadron phenomenology from first-principle QCD studies

One of the longstanding challenges of QCD is to furnish quantitatively accurate ab-initio predictions for the observable properties of hadrons. In this talk we present a significant step for bridging this gap, based on the synergy between Schwinger-Dyson equations and large-volume lattice simulations.

Speaker: Dr Joannis Papavassiliou (Universtiy of Valencia)

Slides LC_Papavassiliou.pdf

15:30 Proton structure in high-energy high-multiplicity p-p collisions

Ridge-like correlations in high-energy proton-proton collisions reported by the CMS collaboration suggest a collective flow that resembles the one in heavy-ion collisions. If the hydrodynamic description is valid then the effect results from the initial anisotropy of the colliding matter, which depends on the distribution of matter in protons. Following recent theoretical developments, we propose several phenomenological models of the proton structure and estimate the associated anisotropy coefficients in p-p collisions using the Monte Carlo Glauber model[1]. Our estimates suggest that the initial anisotropy in some models appears capable of accounting for the p-p ridge effect, with potentially discernible differences in dependence on multiplicity. [1] P. Kubiczek, S. D. Glazek, arXiv:1505.04155 [hep-ph].

Speaker: Prof. Stanislaw Glazek (University of Warsaw)

Slides SDGlazek-LC2015-Frascati20150921.pdf

16:00 → 16:30 Coffee break

16:30 → 18:10 4.

Convener: Alessandro Bacchetta (PV)

16:30 Double parton scattering and 3D proton structure: a light-front analysis

We present a calculation of the effective cross section σ_eff , an important ingredient in the theoretical description of double parton scattering in proton-proton collisions. The theoretical approach makes use of a Light-Front quark model as framework to calculate the double parton distribution functions at low-resolution scale. QCD evolution is implemented to reach the experimental resolution scale. The obtained σ_eff , when averaged over the longitudinal momentum fractions of the interacting partons, x_i in the valence region, is consistent with the present experimental scenario. However the complete result shows a strong dependence of σ_eff on x_i, a feature not easily seen in the available data, probably because of their low accuracy. Measurements of σ_eff in restricted x_i regions are addressed to obtain a first indication of double parton correlations, a novel and interesting aspect of the three dimensional structure of the nucleon.

Speaker: Matteo Rinaldi (PG)

Slides LC_rinaldi_last_port_plus.pdf

16:50 Gravitational form factor, transverse spin sum rule and longitudinal momentum density in the transverse plane in a light front quark-diquark model of nucleons

In lightcone framework, longitudinal angular momentum operator is kinematical but the transverse angular momentum operator is dynamical and thus understanding the transverse spin and transverse angular momentum of the proton is more complicated than longitudinal spin and angular momentum and frame dependent. Here, we evaluate the gravitational form factors for a transversely polarized proton from the energy momentum tensor and evaluate the Pauli-Lubanski operator to verify a sum rule for the transverse spin in a light front scalar quark-diquark model with the light front wave functions constructed from a soft-wall AdS/QCD model. Further, the Fourier transform of the gravitational form factor $A(Q^2)$ in the impact parameter space gives the longitudinal momentum density in the transverse impact parameter space. The longitudinal momentum densities in the transverse impact parameter space are discussed for both unpolarized and transversely polarized nucleons in the quark-diquark model. For the unpolarized nucleon, the distribution is axially symmetric whereas for the transversely polarized nucleon the distribution becomes distorted and our analysis shows that the distortion is dipolar in nature.

Speaker: Dr Dipankar Chakrabarti (Indian Institute of Technology Kanpur, India)

Slides Frascati.pdf

17:10 Understanding Transverse Momentum Dependent Functions from data.

The role of TMDs in understanding the 3D-structure of hadrons has drawn a lot of interest in both the theoretical and experimental communities. In order to extract TMDs, it is necessary to understand what information is contained in the different sets of data that are available. In this talk, I will discuss the advantages and limitations of some of the most recent experimental data, in the context of TMD-extraction.

Speaker: Jose Osvaldo Gonzalez Hernandez (TO)

Slides gonzalez.pdf

17:30 Internal stucture of the pion inspired by AdS/QCD correspondence

The Light-Front Wave Functions (LFWFs) represent a perfect starting point for describing the partonic structure of hadrons. In this work we use the results for the LFWFs of the pion coming from the AdS/QCD correspondence, in the context of a soft-wall model. We study the parton distribution function (PDF) and the electromagnetic form factor (FF) of the pion and for the first time we implement the analysis of the unpolarized transverse momentum dependent parton distribution (TMD) $f_1(x,\mathbf{k}_\bot)$. The correspondence has also been used to investigate the transition of the QCD coupling from high to low scales. In our analysis we obtain a value for the physical mass scale parameter $\kappa$ which can also be used to calculate the QCD effective coupling predicted by this approach.

Speaker: Ms Sabrina Cotogno (Vrije Universiteit Amsterdam and Nikhef)

Slides LC2015.pdf

17:50 The pion renormalized light-cone wave function

An approximate light-cone wave function for the pion effective quark-antiquark Fock sector corresponding to a small value of the renormalization group parameter $\lambda$ will be presented. This wave function will be used to obtain wave functions of higher pion sectors for larger $\lambda$ by the W-transformation [1]. The approximate wave function is motivated by the LF-holography [2] in harmony with the quadratic confinement potential in the front form of Hamiltonian dynamics [3], and thus also with the linear confining potential in the instant form. The S-wave and P-wave contributions to the wave functions will be discussed in the context of the pion diffractive scattering on platinum, using the experimental data of the E791 Experiment [4]. [1] S. D. Głazek, Acta Phys. Pol. B42, 1933 (2011) [2] S. J. Brodsky and G. F. de Téramond, Phys. Rev. D77, 056007 (2008) [3] A. P. Trawiński, et al., Phys.Rev. D90, 074017 (2014) [4] E791 Collaboration, Phys. Rev. Lett. 86, 4768 (2001)

Speaker: Mr Arkadiusz P. Trawinski (University of Warsaw)

Slides LC2015-Trawinski.pdf

18:10 → 19:00 POSTER SESSION

18:10 A comparative study of nucleon structure in light-front quark models in AdS/QCD

We present the nucleon electromagnetic form factors, using the light-front wave functions of a quark-diquark model for the nucleon predicted by the soft-wall model of AdS/QCD. The results are compared with the soft-wall AdS/QCD model. Then we show a comparitive study of the nucleon charge and anomalous magnetization densities in the transverse plane. Flavor decompositions of the form factors and transverse densities are also discussed. We also present a comparison of the generalized parton distributions(GPDs) calculated in the both models.

Speaker: Mr CHANDAN MONDAL (INDIAN INSTITUTE OF TECHNOLOGY KANPUR)

Poster Mondal.pdf

18:10 Canonical Quantization and Lorentz Symmetry for the LC Gauge in QED

The LC gauge condition A_0-A_3=0 is considered within the canonical quantization procedure with different temporal parameters: x^0, x^+ and x^-, respectively. Though this gauge condition is Lorentz noncovariant, the symmetry for the Lorentz boost along the x^3 axis remains unbroken. This longitudinal boost plays a crucial role for the modified quantization procedure at the hypersurface x^{+}=0, where the standard Dirac procedure for constrained systems fails. The Feynman propagators with chronological ordering in x^0, x^+ and x^-, respectively, contain the Mandelstam-Leibbrandt prescription for the noncovariant pole.

Speaker: Dr Elżbieta Dzimida-Chmielewska (University of Bialystok)

18:10 Electronic Helicity Flipping via Podolsky in the Light Front

The generalized elecrodynamics proposed by Podolsky is based on the Lagrangian density \begin{equation*} {\cal L}_{\text{o}}=-\frac{1}{4}F^{\mu \nu }F_{\mu \nu }+\frac{a^{2}}{2}\partial _{\nu }F^{\mu \nu }\partial ^{\lambda }F_{\mu \lambda }, \end{equation*}% in which $a$ is a constant with dimension of length. This Lagrangian density generates a linear field theory, with gauge symmetry of the type $U(1)$, that reduces to the Maxwell theory when we let $a=0$. Evidently this is a higher order theory since the equations of movement contain fourth order derivatives of the vector potential. As in the Maxwell's theory, Podolsky's theory also pesents positive definite energy in the electrostatic case that, nonetheless, is finite for a point charge. This last result clearly shows that the force between two point charges is no longer of Coulomb type, a point that deserves to be closely looked at. In this work we focus on the Podolsky's electrodynamics on the light front. As a consequence, it is shown that the electron's helicity is flipped.

Speaker: Jorge Sales (Universidade Estadual de Santa Cruz, DCET-PPGMC)

18:10 Light Front Fermion Field Quantization with Explicit Lorentz Symmetry

A novel quantization procedure with the explicit Lorentz symmetry is applied for a fermion field in $D=3+1$ dimensions. The Wightman function for a free fermion field is evaluated in terms of the covariant singular function $\Delta_{+}(x)$. The singularities at the LF hypersurface $x^{+}=0$ appear whenever the "bad" component $\psi_{-}$ is considered. Accordingly the anti-commutator function cannot follow from the canonical Dirac method for constrained systems. The chronological ordering in $x^{+}$ temporal variable leads to the Feynman propagator with a well-known addition of non-covariant term. The Yukawa model in $D=3+1$ dimensions is considered for the Gaussian effective potential with the point-splitting regularization with a space-like separation.

Speaker: Dr Jan Żochowski (University of Białystok)

18:10 On $0^{--}$ glueballs

The spectrum of the glueball with $J^{PC}=0^{--}$ is computed using different bottom-up holographic models of QCD. The results indicate a lowest-lying state lighter than in the determination by other methods, with mass $m \simeq 2.8$ GeV. The in-medium properties of this gluonium are investigated, and stability against thermal and density effects is compared to other hadronic systems. Production and decay modes are identified, useful for searching the $J^{PC}=0^{--}$ glueball.

Speaker: Loredana Bellantuono (BA)

18:10 PION LIGHT-FRONT WAVE FUNCTION FROM LATTICE RESULTS

In this work, we study the pion valence wave function by starting with an analytic parametrisations of the vertex function and running quark mass fitted to lattice-QCD results. We also investigate the pion electromagnetic structure of the pion, which is a pseudoscalar meson composed of a quark-antiquark bound state, i.e., $|u \ \bar{d}>$ with total spin zero and negative parity. Our proposal is to obtain a wave function from the Lattice-QCD results, which describes the internal structure of the pion. In particular we calculate observables like the electromagnetic form factor and mean square radius. We compute the wave function by using a model with a running constituent quark mass. Specifically, we performed the calculations in the Light-Front formalism with a Bethe-Salpeter (BS) amplitude model with constituent quarks, which forms the pion composite state. The calculations will be compared with other models in the literature, which present different form for the pion light-front wave function. We take care of the Dirac matrix spinor structure of the BS amplitude. In a first approximation, we disregarded the Dirac structure, and make the first estimates for the wave function. Due to presence of poles also in the quark mass function, we approximated it by a constant of $\Sigma^2=0.300 \ GeV^2$, but this was only as a first step in our study of the wave function. For this purpose, we analyzed the poles of the Bethe-Salpeter amplitude in the momentum, which are integrated via Cauchy's theorem to eliminate te relative light-front time between the quarks, and in this way we derived the valence wave function.

Speaker: Mrs Clayton Santos Mello (Instituto Tecnológico de Aeronáutica)

18:10 Relaxation of a strongly coupled plasma: a holographic description

Methods based on the gauge/gravity duality are useful tools for the study of strong interactions phenomenology. In particular, the holographic approach seems effective in describing relaxation processes of strongly coupled systems, taken initially out of equilibrium. I examine the case of a boost-invariant fluid, focusing on the production of a far-from-equilibrium configuration and on the relaxation to the hydrodynamic regime. A physical realization of this kind of system is the strongly-coupled QCD plasma obtained in relativistic heavy ion collisions. I describe how the effective temperature, entropy density, energy density and pressure can be computed, and analyze their temporal evolution. An estimate of the equilibration time is obtained.

Speaker: Loredana Bellantuono (BA)

19:00 → 20:00 Welcome Reception

Tuesday, 22 September

09:00 → 11:00 5.

Convener: Maria Paola Lombardo (PI)

09:00 Hadron Reaction and Spectroscopy Studies at JPAC

Hadron spectroscopy plays an important role in determining workings of QCD. I will discuss recent developments in theory and phenomenology and the emerging challenges and opportunities given the forthcoming high precision data from the Jefferson Lab and other facilities.

Speaker: Prof. Szczepaniak Adam (Indiana University and Jefferson Lab)

Slides LC-Frascati-2015-szczepaniak.pdf

09:30 Hadron Spectroscopy from Lattice QCD

I will review recent progress in lattice hadron spectroscopy with an emphasis on resonances and scattering states. New theoretical ideas will be discussed and results from heavy and light quark systems presented. Some challenges and puzzles in hadron spectroscopy will be highlighted.

Speaker: Dr Sinead Ryan (Trinity College Dublin)

Slides SRyan_LightCone.pdf

10:00 The hadron spectroscopy program at Jefferson Lab

Understanding the hadron spectrum is one of the fundamental issues in modern particle physics. We know that existing hadron configurations include baryons, made of three quarks, and mesons, made of quark-antiquark pairs. However most of the mass of the hadrons is not due to the mass of these elementary constituents but to the force that binds them. Studying the hadron spectrum is therefore a tool to explore one of the fundamental forces in nature, the strong force, and Quantum Chromo Dynamics (QCD), the theory that describes it. This investigation can provide an answer to fundamental questions as what is the origin of the mass of hadrons, what is the origin of quark confinement, what are the relevant degrees of freedom to describe these complex systems and how the transition between the elementary constituents, quarks and gluons, and baryons and mesons occurs. For these reasons, hadron spectroscopy represents a central part of the Jefferson Lab physics program. In this talk I will review selected results from the experiments that were completed during the 6 GeV era of the laboratory life and outline the program planned with the 12 GeV upgrade.

Speaker: Raffaella De Vita (GE)

Slides devita_lightcone2015.pdf

10:30 An asymptotic solution of large-N QCD, for the glueball and meson spectrum and the collinear S-matrix

We work out the constraints that the renormalization group imposes on two- and three-point, and certain multi-point correlators and S-matrix amplitudes, in large-N QCD and, more generally, in any large-N confining asymptotically free gauge theory. We construct a twistorial string theory that implies the QCD large-N glueball and meson spectrum and collinear S-matrix, that satisfies the aforementioned constraints as opposed to all the previously known string-inspired models, including those based on gauge/gravity duality. In particular we predict the spectrum of odd-spin glueballs, yet to be observed, but in the experimental reach of GlueX or of other experiments.

Speaker: Marco Bochicchio (ROMA1)

Slides Bochicchio_.pdf

11:00 → 11:45 Coffee break

11:45 → 13:15 6.

Convener: Dr Joannis Papavassiliou (Universtiy of Valencia)

11:45 Elastic and transition form factors of nucleon resonances in Dyson-Schwinger Equations

The elastic and transition form factors of nucleon excited states provide vital information about their structure and composition. They are a measurable and physical manifestation of the nature of the hadrons' constituents and the dynamics that binds them together. In this respect, two emergent phenomena of Quantum Chromodynamics (QCD), confinement and dynamical chiral symmetry breaking, appear to play an important role; and Dyson-Schwinger equations (DSEs) have been established as a nonperturbative quantum field theoretical approach for the study of continuum strong QCD which is able to connect such emergent phenomena with the behaviour of form factors. In this presentation, I will provide examples of the contemporary application of DSEs to the study of elastic and transition form factors of N*-states, paying particular attention to the electromagnetic transition form factors of the nucleon's first radial (the Roper resonance) and first spin (the Delta resonance) excitations. In connection with the proton-Delta transition, the momentum-dependence of the magnetic transition form factor in the Jones-Scadron convention matches that of the nucleon's magnetic form factor once the momentum transfer enters the domain upon which meson-cloud contributions are negligible. From this, it follows naturally that the Ash form factor connected with the proton-Delta transition should fall faster than the nucleon's magnetic form factor. The electric quadrupole ratio (unlike the coulomb ratio) is a keen measure of diquark and orbital angular momentum correlations, the zero in which is obscured by meson-cloud effects on the domain currently accessible to experiment. In connection with the proton-Roper transition, our analysis indicates that the observed Roper resonance is at heart of the nucleon's first radial excitation and consists of a well-defined dressed-quark core augmented by a meson-cloud that reduces its (Breit-Wigner) mass by approximately 20%. Our analysis shows that a meson-cloud obscures the dressed-quark core from long-wavelength probes; but that it is revealed to probes with moderate and/or large momentum transfer. This feature is typical of nucleon-resonance transitions; and hence measurements of resonance electro-production on this domain can serve as an incisive probe of quark-gluon dynamics within the Standard Model, assisting greatly in mapping the evolution between the nonperturbative and perturbative domains of QCD.

Speaker: Dr Jorge Segovia (University of Salamanca)

Slides slides_LightCone_JorgeSegovia.pdf

12:15 Quark-hadron duality: connecting the perturbative and non-perturbative QCD regimes

The intriguing phenomenon of quark-hadron duality reflects the non-trivial relationship between observables at low energies in the region dominated by resonances and those in the deep inelastic scattering regime: averaged over the appropriate energy intervals the behavior of low-energy observables mimics that of high-energy, deep inelastic scattering ones. Quark-hadron duality has been intensively studied as it contains information about the relationship between the QCD confinement and asymptotic freedom, about the transition between the perturbative and non-perturbative regimes in QCD. In this talk I will give an overview of the experimental signatures of quark-hadron duality and of theoretical approaches to understanding this phenomenon.

Speaker: Dr Simona Malace (Jefferson Lab)

Slides duality_lc2015_malace.pdf

12:45 Covariant Spectator Theory and Hadron structure

We use the Covariant Spectator Theory (CST) \cite{FG}, which can be viewed as a reorganization of the Bethe-Salpeter equation (BSE) that works in Minkowski space, to develop a dynamical quark model that can describe the structure and the mass spectrum of both, heavy and light quark systems. We study mesonic structure and spectra. Treating mesons as effective qq states, our focus is on the nonrelativistic bound-state problem in momentum space and on the electromagnetic pion form factor. The quark-quark interaction kernel is used to calculate the quark self-energy in a consistent way, resulting in a momentum dependent quark mass function. The kernel includes a confining term that in the nonrelativistic limit reduces to a linear potential. Chiral symmetry is satisfied.

Speaker: Prof. Teresa Pena (IST Lisboa)

Slides Pena.pdf

13:15 → 14:30 Lunch break

14:30 → 16:00 7.

Convener: Prof. Tobias Frederico (Instituto Tecnologico de Aeronautica)

14:30 Solving the inhomogeneous Bethe-Salpeter Equation in Minkowski space

The inhomogeneous Bethe-Salpeter Equation for an interacting system, composed by two massive scalars exchanging a massive scalar, is numerically investigated in ladder approximation, directly in Minkowski space, by using an approach based on the Nakanishi integral representation. In this contribution, the results obtained for the scattering lengths and phase-shifts will be presented and compared with the analogous quantities recently obtained within a totally different framework. Moreover, a highly non trivial issue related to the abrupt change in the width of the support of the Nakanishi weight function, when the zero-energy limit is approached, will be discussed.

Speaker: Michele Viviani (PI)

Slides lc15_viviani.pdf

15:00 On non-perturbative renormalization in the truncated Yukawa model

In the framework of the Light-Front Tamm-Dancoff method, we applied the sector-dependent renormalization scheme to the quenched Yukawa model. A review of the results obtained in this way is given. The Yukawa model incorporated spin is studied in the truncation N=3 (one fermion and two mesons), whereas the spinless Yukawa model is truncated up to a higher value N=4. The eigenvector equation is reduced to a linear system of integral equations for the Fock components. We use the Pauli-Villars regularization. The following results were found. (i) The renormalization removes divergences: the results becomes stable relative to increase of the Pauli-Villars masses, like in the perturbation theory and in contrast to some other non-perturbative schemes. (ii) Comparison, in the scalar Yukawa model, of the N=3 and N=4 truncations shows the convergence of the (dominating) low Fock sectors and of the electromagnetic form factor relative to increase of truncation. This indicates that we are approaching to the true non-perturbative solution. (iii) In the N=3 truncation, the determinant of the system of equations for the Fock components vs. coupling constant $\alpha$ crosses zero at a critical value $\alpha=\alpha_c$. The non-renormalized solution obtains a pole ~$1/(\alpha-\alpha_c)$. The renormalization of coupling constant removes also this singularity: the renormalized wave functions becomes regular at $\alpha=\alpha_c$. These properties support the expectation that the Light-Front Tamm-Dancoff method complemented with the sector-dependent renormalization scheme can be an efficient tool in practical finding the non-perturbative solutions in field theory.

Speaker: Prof. Vladimir Karmanov (Lebedev Physical Institute)

Slides Karmanov_LC2015.pdf

15:30 Triviality of the light-front vacuum and zero modes

We use algebraic methods to reconcile the triviality of the vacuum in different light-front field theories with the inequivalence of vacuua in different canonical theories. We show how the inequivalence arises by extending the vacuum functional from the light-font Fock algebra to the algebra of local observables. This extension leads to an identification of a sub-algebra of the light-front Fock algebra where it is possible to realize Poincar\'e invariance and define local observables. While zero modes play no role in the structure of this sub algebra, they may be needed to treat local operator products, which are in this algebra.

Speaker: Prof. Wayne Polyzou (The University of Iowa)

Slides polyzou_lc_2015.pdf

16:00 → 16:30 Coffee break

16:30 → 17:50 PARALLEL SESSION I

Convener: Wojciech Broniowski (Jan Kochanowski U. and Institute on Nuclear Physics PAN, Poland)

16:30 On Shell Optical Potential at very High Energies

We analyze the usefulness of the optical potential as suggested by the double spectral Mandelstam representation at very high energies. Its particular meaning regarding the analysis of Nucleon-Nucleon scattering data up to the maximum available measured energies and implications in heavy-ions collisions is also discussed.

Speaker: Prof. Enrique Ruiz Arriola (Universidad de Granada)

Slides ruiz-arriola-LC2015.pdf

16:50 Nakanishi representation for two fermions bound state in Minkowski space.

We use the Nakanishi Integral Representation to solve the Bethe-Salpeter equation for two fermions bound state with a scalar exchanging, in Minkowski space. In this formulation we use the Light-Cone projection to obtain an equation for the Nakanishi weight function. Further, we investigate the validity of the Nakanishi uniqueness theorem for the weight functions for the Fermions system.

Speaker: Mr Wayne de Paula (Instituto Tecnológico de Aeronáutica)

Slides LightCone_dePaula.pdf

17:10 Light-Front Quark Model Analysis of Meson-Photon Transition Form Factor

Hadronic distribution amplitudes (DAs) provide essential information on the QCD interaction of quarks, antiquarks and gluons inside the hadrons and play an essential role in applying QCD to hard exclusive processes such as the pion-photon transition form factor (TTF). As the discrepancy of $Q^2F_{\pi\gamma}(Q^2)$ data between the BaBar and Belle measurements has not been resolved yet, more studies on the meson-photon TTF are called for. In particular, the pion-photon TTF still motivates more theoretical studies using various forms of pion DAs. The general agreement on the analysis of the pion DA is that the broader the pion DA the steeper the slope of $Q^2F_{\pi\gamma}(Q^2)$ as $Q^2$ is getting larger. For instance, the flat pion DA $\phi(x)=1$ shows the agreement with the BaBar data which kept rising over the Belle data as $Q^2$ gets larger. However, the flat pion DA $\phi(x)=1$ is severely different from the twist-2 asymptotic DA $\phi(x)=6x(1-x)$ which has been frequently discussed based on the collinear factorization and QCD scaling. Contrary to the pion-photon TFF,} the subsequent BaBar data for the $(\eta,\eta')\to\gamma^*\gamma$ TFFs have shown the consistency predicted by the perturbative QCD, where the use of flat DA for $\eta$ and $\eta'$ distributions appears strongly disfavored by the datasets of $\eta(\eta')-\gamma$ TFFs. Thus, the careful analysis of $(\eta,\eta')\to\gamma^*\gamma$ transitions is especially important under the circumstance of a prolonged dispute over the pion-photon TFF results. In this talk, we investigate the $P\to\gamma^*\gamma (P=\pi^0,\eta,\eta')$ transitions using the light-front quark model (LFQM) based on the QCD motivated effective LF Hamiltonian. We shall also show both timelike and spacelike TFF using the analytic continuation method of changing $Q^2\to -Q^2$ in the form factor. The $\eta-\eta'$ mixing scheme is analyzed to obtain the optimum values of the $\eta(\eta')-\gamma$ TFFs and compared with the current available experimental data.

Speaker: Prof. Ho-Meoyng Choi (Kyungpook National University)

Slides LC2015-Choi.pdf

17:30 Deuteron electromagnetic form factors in AdS/QCD

We present a high-quality description of the deuteron electromagnetic form factors in a soft-wall AdS/QCD approach [1]. We propose an effective action describing the dynamics of the deuteron in the presence of an external vector field. Based on this action the deuteron electromagnetic form factors are calculated, displaying the correct (1/Q2)**5 power scaling for large Q2 values. This finding is consistent with quark counting rules and the earlier observation that this result holds in confining gauge/gravity duals. The Q2 dependence of the deuteron form factors is defined by a single and universal scale parameter kappa, which is fixed from data. [1] T. Gutsche, V. E. Lyubovitskij, I. Schmidt and A. Vega, ``Nuclear physics in soft-wall AdS/QCD: Deuteron electromagnetic form factors,'' Phys. Rev. D 91, 114001 (2015) [arXiv:1501.02738 [hep-ph]].

Speaker: Dr Valery Lyubovitskij (Tuebingen University, Germany)

Slides lyubovitskij_LC2015.pdf

16:30 → 17:50 PARALLEL SESSION II

Convener: Bernard Bakker (VU University)

16:30 Asymptotic freedom of gluons in Hamiltonian dynamics

Asymptotic freedom of gluons in QCD is obtained in the leading terms of their renormalized Hamiltonian in the Fock space. We calculate the three-gluon interaction term in the front-form Hamiltonian for gluons using the renormalization group procedure for effective particles (RGPEP). The resulting three-gluon vertex is a function of the scale parameter, $s$, that has an interpretation of the size of effective gluons. The corresponding Hamiltonian running coupling constant, $g_{\lambda}$, depending on the associated momentum scale $\lambda=1/s$, is calculated in the series expansion in powers of $g_0=g_{λ_0}$ up to the terms of third order, assuming some small value for $g_0$ at some large $\lambda_0$. The third-order QCD solution of the RGPEP equation to be discussed, provides an explicit example of how asymptotic freedom of gluons is exhibited in the scale-dependence of Hamiltonians as operators in the Fock space. References: [1] Asymptotic freedom in the front-form Hamiltonian for quantum chromodynamics of gluons, M. Gomez-Rocha, S. D. Glazek, arXiv:1505.06688. [2] Nonperturbative QCD: A Weak coupling treatment on the light front, K.G. Wilson, T.S. Walhout, A. Harindranath, W.-M. Zhang, R.J. Perry, S.D. Glazek. Phys.Rev. D49 (1994) 6720-6766 [3] Dynamics of effective gluons, S. D. Glazek, Phys. Rev. D63, 116006, 29p (2001). [4] Perturbative formulae for relativistic interactions of effective particles, S. D. Glazek, Acta Phys. Pol. B43, 1843, 20p (2012).

Speaker: Dr Maria Gomez-Rocha (University of Graz)

Slides Frascati_mgr.pdf

16:50 The electron in three-dimensional momentum space

We study the electron at order alpha as a system composed by an electron and a photon within the framework of light-front quantization. We derive the leading-twist transverse-momentum dependent distribution functions for both the electron and photon in the dressed electron, using different gauge prescriptions. In particular, we discuss the light-cone gauge and the Feynman gauge, applying both the formalism of light-front wave function overlap representation and the diagrammatic approach. Furthermore, we present a detailed discussion of the role of the Wilson lines to obtain gauge-independent results.

Speaker: Luca Mantovani (PV)

Slides Mantovani_Frascati_2015.pptx

17:10 Light - Front Wave Function for Hadrons with arbitrary twist

Based on the matching of soft wall AdS / QCD models and Light - Front QCD for electromagnetic form factors, we derive a phenomenological wave function for hadrons with arbitrary twist dimension. We discuss a couple of examples of hadron properties calculated with this wave function.

Speaker: Dr Alfredo Vega (Universidad de Valparaiso)

Slides Light_Cone_2015_(Alfredo_Vega).pdf

17:30 Light Front Perturbation without Spurious Singularities

A new form of the light front Feynman propagators is proposed. It contains no energy denominators. Instead the dependence on the longitudinal subinterval x^2_L = 2 x^{+} x^{-} is explicit and a new formalism for doing the perturbative calculations is invented. These novel propagators are implemented for the one-loop scattering matrix for a massive scalar field. The consistency with results for the standard covariant Feynman diagrams is obtained and no spurious singularities are encountered at any step. Some remarks on the calculations with fermion and gauge fields in QED and QCD are added.

Speaker: Dr Jerzy A. Przeszowski (Faculty of Physics, University of Bialystok)

Slides jprzeszowski.pdf

17:50 → 19:10 POSTER SESSION

See on Monday 21 for Abstracts

Wednesday, 23 September

09:00 → 11:00 8.

Convener: Prof. James Vary (Iowa State University)

09:00 Scattering Solutions of the Bethe-Salpeter equation in Minkowski and Euclidean spaces

The solutions of the Bethe-Salpeter equation in Minkoswki space are mandatory for computing some physical quantities like elastic and transition form factors, scattering of-shell amplitudes etc. They are however plagued with the singularities of the free propagators, of the interaction kernel and of the amplitude itself making rather difficult its numerical computation. This difficulty was overcome in the 50's with the use of the "Wick rotation", which transforms the Minkowski into an Euclidean metric and allowed to obtain some observables invariant in this transformation. The Euclidean Quantum Field Theory is nowadays a basic ingredient in all the lattice calculations. We will see that this procedure is not always legitimate - at least in the original framework where its was formulated - without a detailed knowledge of the analytic structure of the Bethe-Salpeter amplitude in the complex momentum plane. We will present two methods to obtain the Minkowski solutions for bound and scattering states. The first one is based on the Nakanishi integral transform and the projection of the Bethe-Salpeter equation into the Light Front. The second method is based on a careful analysis of the singularities and a direct solution of the original equation. In particular we will show the possibility to extract the scattering lenght from a purely euclidean solution. This approach is directly applicable in Euclidean Lattice calculations and provides a direct way to obtain the scattering length without making use of the Luscher formula.

Speaker: Dr Jaume Carbonell (CNRS/IPN Orsay)

Slides Carbonell_LCM_2015.pdf

09:30 Electromagnetic properties of the nucleon in the covariant Faddeev approach

The covariant three-body Faddeev approach and its application to nucleon and delta properties are briefly reviewed. I will discuss results for mass spectra as well as nucleon and delta elastic and transition form factors, together with the role of electromagnetic gauge invariance and vector-meson dominance. I will also talk about some recent work on Compton scattering, pion-cloud effects and the road towards timelike form factors.

Speaker: Dr Gernot Eichmann (University of Giessen)

Slides eichmann-lightcone-2015.pdf

10:00 Inverting the Nakanishi weight function for a bound-state

We report our attempts in extracting the Nakanishi weight function for a S-wave bound-state using a model for the Bethe-Salpeter amplitude from a given form of the weight function. Both the Bethe-Salpeter amplitude in Euclidean space and the valence light-front wave function are written in terms of the Nakanishi integral representation, and through that we formulate an inhomogeneous integral equation problem to solve for the weight function. This linear problem is ill-defined and for the matrix inversion, we study the stability of the resulting weight function by truncation on the small eigenvalues. Reasonable numerical accuracy is found when the weight function is obtained starting from the valence light-front wave function, while using the Euclidean Bethe-Salpeter amplitude the numerical solution compared with the exact Nakanishi weight function model shows much less accuracy. Our work suggests the possibility to build the Bethe-Salpeter amplitude from the light-front valence wave function, which will be useful for building covariant models, e.g., for hadrons. Work done in collaboration with J. Carbonell and V. Karmanov.

Speaker: Prof. Tobias Frederico (Instituto Tecnologico de Aeronautica)

Slides FredericoLC2015.pdf

10:30 The renormalization group equations revisited in the light of finite field theories.

The analysis of physical observables in terms of energy/momentum scales necessitates to disantangle spurious scales originating from the divergence of ill-defined integrals from the physical scales inherent to the dynamics of a given system. The use of finite field theories is thus of particular interest in this separation. We shall investigate this question in the light of the recently proposed Taylor-Lagrange regularization scheme applied to light-front dynamics. We calculate the coefficients of the renormalization group equation in this scheme and compare them with the standard derivation using dimensional regularization in different renormalization schemes. We find that the renormalization group equations should be mass-dependent in any renormalization scheme, in contrast to what is usually assumed.

Speaker: Dr Jean-Francois MATHIOT (Laboratoire de Physique Corpusculaire)

Slides Mathiot.pdf

11:00 → 11:45 Coffee Break

11:45 → 13:15 9.

Convener: Prof. Stanislaw Glazek (University of Warsaw)

11:45 Pauli-Villars regularization of non-Abelian gauge theories

As an extension of earlier work on QED, we construct a BRST-invariant Lagrangian for SU(N) Yang-Mills theory, regulated by the inclusion of massive Pauli-Villars (PV) gluons. The underlying gauge symmetry for massless PV gluons is generalized to accommodate the PV-index-changing currents that are required by the regularization. Auxiliary adjoint scalars are used, in a mechanism due to Stueckelberg, to attribute mass to the PV gluons. The addition of Faddeev-Popov ghosts then establishes a residual BRST symmetry. Further extension to QCD is also considered. Although there are drawbacks to the approach, in particular the computational load of a large number of PV fields and a nonlocal interaction of the ghost fields, this formulation could provide a foundation for renormalizable nonperturbative solutions of light-front QCD in an arbitrary covariant gauge.

Speaker: John Hiller (University of Minnesota-Duluth)

Slides hiller-lc2015.pdf

12:15 Two-dimensional light-front massless fields and solvable models

One of the apparent problems of light front field theory has been a lack of description of two-dimensional massless fields. We show how both the massless scalar and fermion fields can be recovered as massless limits of the two-dimensional massive fields and consistenly quantized without any loss of physical information. Bosonization of the ligh-front (LF) fermion field then follows in a straightforward manner. Solvable models can also be studied directly in the LF formulation. We discuss the operator solution of the Thirring and Thirring-Wess models including the exact (nonperturbative) form of their correlation functions. A few remarks concerning the LF Schwinger model and the LF version of conformal symmetry conclude our contribution.

Speaker: L. Martinovic

Slides martinovic.pdf

12:45 Light-Front Quantization of the Restricted Gauge Theory of $~QCD_{2}~$

In this talk, we study the light-front quantization of the restricted gauge theory of $~QCD_{2}~$ $~\grave{a}~$ la Cho et al., using Hamiltonian, path integral and BRST quantization procedures.

Speaker: Prof. Daya Shankar Kulshreshtha (Department of Physics and Astrophysics, University of Delhi, Delhi-110007, India)

Slides Daya.pdf

13:15 → 14:30 Lunch

14:30 → 22:30 Excursion and Social Dinner

Thursday, 24 September

09:00 → 11:00 10.

Convener: Dr Cedric Lorce (IPNO and LPT Orsay, Universite Paris-Sud)

09:00 Extraction of TMDs from experimental data

I will review the current status of the extraction of Transverse Momentum Distributions (TMDs) from experimental data. We are gaining an ever increasing knowledge about TMDs, both unpolarized and polarized, but we are still far from a precise determination of these quantities. Central issues are currently related to the implementation of TMD evolution in the extractions. To make further progress, new experimental data are also needed.

Speaker: Alessandro Bacchetta (PV)

Slides Bacchetta_Frascati_2015.pdf

09:30 Deeply virtual Compton scattering: sensitivities to the three Compton form factors

In scalar QED the number of Compton form factors is known to be five. The case where the incoming photon is virtual, namely produced by electron scattering, while the final photon is real, the physical amplitudes depend on only three of them. We study the sensitivity of the differential cross section to the subleading Compton form factors.

Speaker: Bernard Bakker (VU University)

Slides Talk-Bakker.pdf

10:00 Hermes results on 3D imaging of the nucleon

In the context of rapid theoretical developments in non-perturbative QCD, a formalism of Transverse Momentum Dependent parton distribution functions (TMDs) and of Generalized Parton Distributions (GPDs) was introduced in the last two decades, providing a more comprehensive multi-dimensional description of the nucleon. TMDs and GPDs allow in fact for complementary descriptions of the nucleon in three dimensions (nucleon tomography), spanned by the quarks longitudinal momenta and, respectively, by the their transverse momenta components and transverse spatial coordinates. They thus contribute, with different approaches, to the full phase-space description of the nucleon structure. Furthermore, they provide complementary insights into the yet unmeasured quark orbital angular momentum. Experimentally, TMDs and GPDs can be accessed through the analysis of specific azimuthal asymmetries measured, respectively, in semi-inclusive deep-inelastic scattering and hard exclusive processes, such as hard leptoproduction of real photons or mesons. The HERMES experiment has collected wealth of data on scattering of a longitudinally polarized lepton (electron or positron) beam from HERA off unpolarized, longitudinally and transversely polarized internal gas targets. Collected data allowed to measure a variety of asymmetries with respect to beam charge, beam helicity and target polarization. A selection of HERMES results on observables sensitive to TMDs and GPDs will be presented.

Speaker: Mr Luciano Libero Pappalardo (FE)

Slides Pappalardo_LC2015.pdf

10:30 Flavor Asymmetry of the Proton Sea in Chiral Effective Theory

While the leading nonanalytic behavior in chiral effective theory must be universal, there has been a puzzling factor 4/3 difference in the coefficient of the leading nonanalytic contribution to the vertex renormalization constant of the nucleon or equivalently that of the pion for more than a decade. We have recently resolved this lingering factor difference by carefully analyzing the vertex renormalization constant with both pseudovector and pseudoscalar coupling theories and demonstrated how one may correctly achieve the equivalence between these two theories. We discuss this resolution with respect to the phenomenological application to the flavor asymmetry in the proton sea from the chiral effective theory. The on-shell splitting function of the pion from the nucleon has a direct consequence for the analysis of the leading neutron production at HERA as well as the proposed measurement of tagged deep inelastic scattering (TDIS) at JLab.

Speaker: Prof. Chueng-Ryong Ji (NCSU)

Slides LC2015-Frascati-Ji.pdf

11:00 → 11:45 Coffee break

11:45 → 13:15 11.

Convener: Patrizia Rossi (LNF)

11:45 Sketching the pion's valence-quark Generalised Parton Distribution

In order to learn effectively from measurements of Generalised Parton Distributions (GPDs), it is desirable to compute them using a framework that can potentially connect empirical information with basic features of the Standard Model. We sketch an approach to such computations, based upon a rainbow-ladder (RL) truncation of QCD's Dyson-Schwinger equations and exemplified via the pion's valence dressed-quark GPD. Our analysis focuses primarily on vanishing skewness, although we also capitalise on the symmetry-preserving nature of the RL truncation by connecting the considered pion GPD with the pion's valence-quark parton Distribution Amplitude. We explain that the impulse-approximation used hitherto to define the pion's valence dressed-quark GPD is generally invalid owing to omission of contributions from the gluons which bind dressed-quarks into the pion. A simple correction enables us to identify a practicable improvement to the approximation for the pion GPD at vanishing skewness, expressed as the Radon transform of a single amplitude. Therewith we obtain results for the associated impact-parameter dependent distribution, which provides a qualitatively sound picture of the pion's dressed-quark structure at an hadronic scale. We evolve the distributions to the scale 2\,GeV, so as to facilitate comparisons in future with results from experiment or other nonperturbative methods.

Speaker: Dr Hervé Moutarde (Irfu, CEA-Saclay)

Slides moutarde_lightcone_2015_09_24.pdf

12:15 Light-front dynamics and the 3He spectral function

After the 12 GeV upgrade, several experiments involving 3He nuclear targets will be performed at JLab to extract information on the parton structure of the neutron. The parton transverse momentum distributions (TMDs) (see, e.g. [1,2]) in the neutron will be studied through polarized SIDIS experiments off 3He, where a high-energy pion is detected in coincidence with the scattered electron [3]. To reliably disentangle the nuclear and the partonic degrees of freedom an accurate theoretical description of the process is needed. In Ref. [4] the plane wave impulse approximation was adopted. In a recent paper [5] the spectator SIDIS process off 3He was studied and the final state interaction (FSI) between the hadronizing quark and the detected deuteron was taken into account through a distorted spin-dependent spectral function. We are now studying the standard SIDIS process, where the FSI between the observed pion and the remnant is again taken into account through a distorted spin-dependent spectral function [6}. In these studies the description of the nuclear dynamics is non-relativistic. This talk addresses an approach for the relativistic description of the nuclear dynamics based on the Light-front Hamiltonian Dynamics [7]. The key quantity we consider is the LF spectral function, where both normalization and momentum sum rule can be satisfied at the same time. Preliminary results will be discussed. Among them, a study of the role played by relativity in the EMC effect on 3He, for which JLab data have been taken at 6 GeV [8]. Our final goal is to evaluate SIDIS cross sections off 3He taking into account both the relativity and the FSI between the observed pion and the remnant, through our LF spin-dependent spectral function. REFERENCES [1] V. Barone, A. Drago, P. G. Ratcliffe, Phys. Rept. 359, 1 (2002). [2] A. Bacchetta et al., Phys. Rev. D70, 117504 (2004). [3] G. Cates et al., E12-09-018, JLAB approved experiment, hallaweb.jlab.org/collab/PAC/PAC38//E12-09-018-SIDIS.pdf [4] S. Scopetta, Phys. Rev. D 75, 054005 (2007). [5] L.P. Kaptari, A. Del Dotto, E. Pace, G. Salme` and S. Scopetta, Phys. Rev. C 89, 035206 (2014). [6] A. Del Dotto, L. Kaptari, E. Pace, G. Salme` and S. Scopetta, in preparation. [7] E. Pace, G. Salme`, S. Scopetta, A. Del Dotto and M. Rinaldi, Few Body Syst. 54, 1079 (2013); A. Del Dotto, L.P. Kaptari, E. Pace, G., Sergio Scopetta, Few-Body Syst. 55, 877 (2014). [8] J. Seely, A. Daniel, D. Gaskell, J. Arrington, N. Fomin, P. Solvignon, R. Asaturyan and F. Benmokhtar et al., Phys. Rev. Lett. 103, 202301 (2009).

Speaker: Emanuele Pace (ROMA2)

Slides Pace2015.pdf

12:45 Studies of the 3D Structure of the Nucleon at JLab

The quark-gluon dynamics manifests itself in a set of non-perturbative functions describing all possible spin-spin and spin-orbit correlations. The Transverse Momentum Dependent parton distributions (TMDs) and Generalized Parton Distributions (GPDs) carry information not only on the longitudinal but also on the transverse momentum and position of partons, providing rich and direct information on the orbital motion of quarks. Single and Dihadron semi-inclusive and hard exclusive production, both in current and target fragmentation regions, provide a variety of spin and azimuthal angle dependent observables, sensitive to the dynamics of quark-gluon interactions. Studies of the 3D PDFs are currently driving the upgrades of several existing facilities (JLab, COMPASS and RHIC), and the design and construction of new facilities worldwide (EIC, FAIR, and JPARC). In this talk, we present an overview of the current status and some future measurements of the orbital structure of nucleons and nuclei at Jefferson Lab.

Speaker: Dr Harut Avakian (JLab)

Slides avakian-frascati-lc2015.ppt

13:15 → 14:30 Lunch

14:30 → 16:00 12.

Convener: Gunnar Bali (University of Regensburg)

14:30 Proton spin structure from large momentum effective theory

Understanding the spin structure of the proton has been an important goal in hadron physics. One of the well-known spin sum rule, the Jaffe-Manohar sum rule, is motivated from a free-field expression of QCD angular momentum and has a natural partonic interpretation. However, this natural partonic sum rule exhibits a gauge dependence in its individual contributions (apart from the quark spin). I will explain how these individual contributions arise from gauge-invariant, but frame-dependent operator matrix elements in the spirit of the large momentum effective theory, which also provides a practical possibility to compute the partonic orbital angular momentum in the proton. I will also explain how to compute parton distribution functions following the same spirit.

Speaker: Jianhui Zhang (Regensburg University)

Slides proton_spin_JHZ.pdf

15:00 Parton distribution functions from lattice QCD

Recent results on nucleon observables using simulations of Quantum Chromodynamics (QCD) with a range of quark masses that include their physical values are presented. We use a discretization of the theory known as twisted mass QCD, which allows for an automatic O(a^2) improvement without requiring improvement of the operators. The simulations use lattice spacings a<0.1fm and are performed by the European Twisted Mass Collaboration. We focus in particular on results on the nucleon generalized form factors and parton distribution functions.

Speaker: Prof. Constantia Alexandrou (University of Cyprus &amp; Cyprus Institute)

Slides Alexandrou.pdf

15:30 Radon transform and light-cone distributions

The Radon transform applications for relations between various light-cone distributions is considered. The contributions of different channels to the inverse Radon transform for Double Distributions are extracted. The relations between fracture and dihadron fragmentation functions are analyzed. The transverse momentum dependencies for exclusive and semi-inclusive processes are compared.

Speaker: Prof. Oleg Teryaev (JINR)

Slides teryaev.pdf

16:00 → 16:30 Coffee break

16:30 → 17:50 PARALLEL SESSION IV

Convener: John Hiller (University of Minnesota Duluth)

16:30 Hidden Conformal Symmetry of Maxwell's Theory in $d\neq 4$

In this work, we define a modified non-local conformal transformation compatible with BRST formalism for $U(1)$ gauge field, which is a symmetry of the Maxwell's theory in any dimension. We prove the invariance by explicitly showing that the gauge invariant transverse two point function, the classical action, and equation of motion are unchanged under such transfomation.

Speaker: Ms Kelly Chiu (SLAC)

Slides Chiu+.pdf

16:50 Light-Front Quantization of the Vector Schwinger Model \\ with a Photon Mass Term in Faddeevian Regularization

In this talk, we study the light-front quantization of the vector Schwinger model with photon mass term in Faddeevian Regularization, describing two-dimensional electrodynamics with mass-less fermions but with a mass term for the $ U(1)$ gauge field \cite{13}-\cite{15}. This theory is seen to be gauge-non-invariant (GNI). We then construct a gauge-invariant (GI) theory corresponding to this GNI theory using Stueckelberg mechanism and then recover the physical content of the original GNI theory from the newly constructed GI theory under some special gauge-fixing conditions (GFC's). We then study LFQ of this new GI theory using Hamiltonian, path integral and BRST formulations.

Speaker: Dr Usha Kulshreshtha (Department of Physics, Kirori Mal College, University of Delhi, Delhi-110007, India)

Slides Usha-Frascati-Rome-LC2015.pdf

17:10 Light-front $\phi^4_{1+1}$ theory using a many-boson symmetric-polynomial basis.

We extend earlier work on fully symmetric polynomials for three-boson wave functions to arbitrarily many bosons and apply these to a light-front analysis of the low-mass eigenstates of $\phi^4$ theory in 1+1 dimensions. The basis-function approach allows the resolution in each Fock sector to be independently optimized, which can be more efficient than the preset discrete Fock states in DLCQ. The approach also allows for a direct calculation of the expectation value of the field.

Speaker: Sophia Chabysheva (University of Minnesota-Duluth)

Slides chabysheva-lc2015.pdf

17:30 True muonium on the light front

The true muonium (μ^+μ^-) bound state presents an interesting test of light-cone quantization techniques. In addition to the standard problems of solving these non-perturbative calculations, true muonium requires correct treatment of e^+e^- Fock state contributions. Having previously produced a crude model of true muonium using the method of iterated resolvents [1], current work has focused on the inclusion of the box diagrams that should improve the cutoff dependent issues of the model. Further, a parallel computer code allowing for decreased numerical uncertainties is in development. This talk will focus on the current state of these efforts to develop a model of true muonium testable at near-term experiments. [1] H. Lamm and R.F. Lebed, “True Muonium (μ^+μ^−) on the Light Front,” J. Phys. G 41 125003 (2014).

Speaker: Mr Henry Lamm (Arizona State University)

Slides LightCone_Lamm_Talk.pdf

16:30 → 18:10 PARALLL SESSION III

Convener: Dr Harut Avagyan (Jefferson Lab)

16:30 OAM measurements from DVCS at JLab

Deeply-Virtual Compton scattering provides the cleanest access to the 3D imaging of the nucleon structure encoded in the Generalized Parton Distributions, that correlate the fraction of the total nucleon momentum carried by a constituent to its position in the transverse plane. Besides the information on the spatial imaging of the nucleon, GPDs provide an access, through the Ji relation, to the quark contribution to the nucleon total angular momentum. An accurate estimate of such a contribution will lead to a better understanding of the origin of the proton spin. Jefferson Lab has been an ideal environment for the study of exclusive processes, thanks to the combination of the high-intensity and high-polarization electron beam provided by the CEBAF, with the complementary equipments of the three experimental halls. This has allowed high-precision measurements of the DVCS observables in a wide kinematic region, with focus on those observables that provide access to the GPDs entering the Ji relation. These studies will be further widened by the projected data from the 12-GeV era, which will improve the existing measurements both in terms of precision and phase-space coverage. The important results on the proton DVCS obtained during the 6-GeV era will be discussed, together with the upcoming experiments approved for the 12-GeV upgrade, that foresees measurements with both proton and neutron targets and that, when combined, will lead to the extraction of the GPDs for separate quark flavors.

Speaker: Dr Silvia Pisano (LNF)

Slides pisanos_lightcone2015.pdf

16:50 Parton Distributions and One-Loop Matching

Recent researches showed that the light-cone parton distributions can be accessed by investigating the quasi distributions which are space-like correlation functions, hence can be directly simulated on the lattice. In this talk, I will show the one-loop matching between the light-cone and quasi PDFs, GPDs. The matching condition is essential to extract the light-cone distribution from the quasi distributions. I will also discuss the light-cone and quasi heavy meson distribution amplitude which is perturbatively calculable through NRQCD refactorization.

Speaker: Dr Xiaonu Xiong (INFN, Sezione di Pavia, Pavia, 27100)

Slides LaMET_Xiong_LC2015.pdf

17:10 T-odd gluon TMDs inside a transversely polarized hadron

The limit of high gluon density is currently under active investigation, both from the theoretical and the experimental side, since gluons play an increasingly important role as the energy of the relevant scattering process increases. Thus it is our aim to better understand this limit in order to get valuable information on the 3-dimensional structure of hadrons. In this talk I will analyze the three leading power T-odd gluon TMDs inside a transversely polarized target in the perturbative regions, i.e., at large transverse momentum and the saturation regime. I will show that all of three gluon TMDs can be dynamically generated by the Qiu-Sterman function at large transverse momentum. Moreover, when a close loop gauge link in the fundamental representation appears in these T-odd gluon TMDs, they turn out to be identical at small x, and can as well be related to the spin dependent odderon.

Speaker: Dr Miguel Echevarria (Nikhef / VU University Amsterdam)

Slides Echevarria_LightCone2015.pdf

17:30 Gluon TMDs in quarkonia production

Production of quarkonia bound states from hadronic collisions can be a useful handle to map the probability density distributions for gluons inside protons. We derive the factorization theorem for the pT-spectrum of color-singlet quarkonia production in terms of gluon transverse-momentum-dependent parton distribution functions (TMD PDFs). With this tool we predict cross sections up to NNLL level of accuracy for the LHC and the AFTER@LHC experiments, exploring different configurations for the gluon and the target polarization. After completing a framework in which evolution of TMDs is incorporated, we will be able to extract new information about the non-perturbative structure of the (un)polarized gluon TMD PDFs from future experimental measurements.

Speaker: Mr Andrea Signori (VU University Amsterdam / Nikhef)

Slides Signori_LC2015.pdf

17:50 Universality of a New Soft Phase Factor

The Wilson line in a TMD is needed for gauge invariance, but quantum field theory lays no restriction on the specific path layout except for its endpoints. However, there is no reason to assume that different path structures would lead to equivalent results. Care has to be taken when splitting complicated structures into separate path segments, especially when the path contains obstructions such as cusps or self-intersections. We will present a new Wilson line structure that can be considered as a soft factor and pure phase, and which is constructed to be universal by definition. This structure is carefully chosen in order to avoid any obstructions or phase factors originating from infinity cuts.

Speaker: Dr Frederik Van der Veken (University of Antwerp)

Slides Light_Cone_2015.pdf

18:10 → 19:00 POSTER SESSION

See on Monday 21 for Abstracts

Friday, 25 September

09:00 → 10:30 13.

Convener: Adam Szczepaniak (Indiana University)

09:00 Hadron structure from lattice QCD

I review recent hadron structure results of the Regensburg group.

Speaker: Prof. Gunnar Bali Bali (University of Regensburg)

Slides talk.pdf

09:30 Jefferson Lab: Present and Future

The Continuous Electron Beam Accelerator Facility (CEBAF) and associated experimental equipment at Jefferson Lab comprise a unique facility for nuclear physics research whose upgrade is presently underway, with completion expected in 2017. The upgraded facility will accelerate electron beams to 11 GeV for experiments in the existing Halls A, B and C. In addition, a 12 GeV beam can be provided to a new experimental Hall D to generate a 9 GeV tagged photon beam. This upgrade will enable a new experimental program with substantial discovery potential to address important topics in hadronic, nuclear, and electroweak physics. Further in the future, it is envisioned that the Laboratory will evolve into an electron-ion colliding beam facility (EIC). In this talk the status of the 12 GeV upgrade and the associated experimental program will be presented as well as a brief overview of the EIC project.

Speaker: Dr Patrizia Rossi (Jefferson Lab)

Slides Rossi_LightCone-2015__indico.pdf

10:00 Search for Light Dark Matter at accelerators

In the last few years interest for Light Dark Matter (LDM) in the MeV - GeV range has been increasingly growing. Direct detection of non-relativistic dark matter particles from the Galactic halo mainly focused to higher masses(> 10 GeV) being insensitive to few-GeV or lighter DM, whose nuclear scattering transfers invisibly small kinetic energy to a recoiling nucleus. On the other hand availability of high intensity, high precision and moderate energy electron beams allow for testing different LDM scenarios leaving to accelerator-based experiments the opportunity to explore an equally promising but uncovered territory. In this talk I will review the latest experimental results for LDM searches as well as the new experiments proposed in different laboratories.

Speaker: Dr Marco Battaglieri (Istituto Nazionale di Fisica Nucleare)

Slides LC2015-battaglieri.pdf

10:30 → 11:15 Coffee break

11:15 → 13:00 14.

Conveners: Giovanni Salme' (ROMA1), Marco Mirazita (LNF)

11:15 Overview of COMPASS Experimental Program for GPDs and TMDs

COMPASS is a fixed target experiment at the CERN SPS taking data since 2002. A major part of the COMPASS program at CERN is dedicated to the investigation of the 3 dimensional structure of the nucleon which can be reached measuring the spin and transverse momentum dependent distributions (TMDs) and generalized parton distributions (GPDs). TMDs have been investigated at COMPASS in semi-inclusive processes (SIDIS) using scattering of 160 GeV longitudinally polarized muons on transversely polarized targets. This includes the measurements of the Collins and Sivers asymmetries observed in production of single pions or kaons on both proton and deuteron targets, as well as all the other six asymmetries in the case of non identified hadrons. The large statistics cumulated with the proton target allows multidimensional analysis to investigate for example Q2 evolution. The similarity of Collins effects induced by single and di-hadron production will be discussed. New results on the Sivers gluon asymmetry on protons and deuterons will also be given. Finally the first-ever polarized Drell-Yan experiment using scattering of 190 GeV pions on a transversely polarized target which is presently performed at COMPASS in 2015 will be presented. This will allow the measurement of the TMDs functions in both SIDIS and DY and the study of their universality in the same kinematical domain with a same apparatus. GPDs are experimentally accessible via lepton-induced exclusive reactions, in particular the Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP). A complete measurement of the eight asymmetries for exclusive rho0 and omega productions have already been performed by COMPASS at the same time than the SIDIS studies using the transversely polarized target but without any recoil particle detection. Results which involve GPD H and E and also chiral-odd or transverse GPDs will be presented. In 2016 and 2017 DVCS and DVMP will be investigated using the muon beam of 160 GeV and a 2.5 m long liquid hydrogen target. In order to optimize the selection of exclusive reactions at those energies, the target will be surrounded by a newly built barrel-shaped time-of-flight system to detect the recoiling particles. The option to change simultaneously the charge and polarization of the muon beam in the DVCS process will allow to access both real and imaginary parts of the Compton form factor related to the dominant GPD H. Moreover the xBj-dependence of the nucleon transverse size will be investigated via the pure DVCS or meson cross sections. In parallel to the DVCS and DVMP, SIDIS measurements will provide clean cross section data for the extraction of multiplicities and possibly of the Boer Mulders function from the azimuthal modulations.

Speaker: Franco Bradamante (TS)

Slides Bradamante_Lightcone_2015.pptx

11:45 Basis Light Front Quantization - Recent Results and Future Prospects

Light-front Hamiltonian field theory has advanced to the stage of becoming a viable non-perturbative method for solving forefront problems in strong interaction physics. Physics drivers include hadron mass spectroscopy, generalized parton distribution functions, spin structures of the hadrons, inelastic strength functions, hadronization, particle production by strong external time-dependent fields in relativistic heavy ion collisions, and many more. I will review selected recent results with Basis Light Front Quantization (BLFQ) that include Fermion-Antifermion bound states in QED and in QCD. I will then present a selection of near-term projects/plans and their challenges. Computational resources on leadership class supercomputers play an essential role in these projects/plans.

Speaker: James Vary (Iowa State University)

Slides Vary_LC2015_Frascati_final.pdf

12:15 New Results for Hadron Physics from Light-Front Holography and Superconformal Algebra

Light-front holography provides a precise relation between the bound-state amplitudes in the fifth dimension of AdS space and the boost-invariant light-front wavefunctions describing the internal structure of hadrons in physical space-time. The resulting valence Fock-state wavefunctions of the light-front QCD Hamiltonian satisfy a relativistic equation of motion, analogous to the nonrelativistic radial Schr\"odinger equation, with an effective confining potential. If one requires that the effective action which underlies the QCD Lagrangian to remain conformally invariant and extends the formalism of de Alfaro, Fubini and Furlan to light front Hamiltonian theory, the potential has a unique form of a harmonic oscillator potential, and a mass gap arises. The result is a nonperturbative relativistic light-front wave equation which incorporates color confinement and other essential spectroscopic and dynamical features of hadron physics, including a massless pion for zero quark mass and linear Regge trajectories with the same slope in the radial quantum number n and orbital angular momentum L. One can also construct an effective QCD light-front Hamiltonian for both mesons and baryons based on superconformal algebra. The superconformal construction is shown to be equivalent to a semiclassical approximation to light-front QCD and its embedding in AdS space. The specific breaking of conformal invariance determines a unique effective confinement potential. The generalized supercharges connect the baryon and meson spectra to each other in a remarkable manner. We also show how the mass scale underlying confinement and hadron masses determines the scale controlling the evolution of the perturbative QCD coupling. The relation between scales is obtained by matching the nonperturbative dynamics, as described by an effective conformal theory mapped to the light-front and its embedding in AdS space, to the perturbative QCD regime. The result is an effective coupling defined at all momenta.

Speaker: Prof. Stanley Brodsky (SLAC National Accelerator Laboratory, Stanford University)

Slides SJB_LC2015_Animated.pdf