Sar WorS 2019 - Sardinian Workshop on Spin studies

8 Jul 2019, 09:00 → 10 Jul 2019, 17:00 Europe/Rome

Aula Rossa (Cittadella dei Musei)

Umberto D'Alesio (CA)

A Workshop on the 3D structure of the nucleon: quark and gluon TMDs from SIDIS, pp collisions, e+e- annihilation processes and related quarkonium production.

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The main aim of the workshop is to bring together, in a lively and informal environment, experts in the study of Transverse Momentum Dependent parton distributions and fragmentation functions (TMDs), to discuss the state of the art and provide new ideas and perspectives in the field, both on the theory and the experimental side. The workshop will focus on open issues and new tools to investigate the 3D structure of the nucleon as well as the fragmentation mechanism within a TMD approach.

Presentations will be the starting point for a more in-depth common discussion on the main topics of the workshop and for a fruitful and educated brain storming among participants.

The number of participants is limited to about 25, and the number of presentations, upon invitation only, to around 20. The venue is “Aula Rossa” at the Cittadella dei Musei, Piazza Arsenale, 1 (Cagliari).

The workshop is supported and sponsored by Fondazione Sardegna under the project “Quarkonium at LHC energies”, CUP F71I17000160002 (University of Cagliari), University and INFN Cagliari and the “3DSPIN” ERC project, n. 647981 (University of Pavia).

Monday, 8 July

09:30 → 09:40 Welcome

09:40 → 10:20 COMPASS studies of TMDs; recent results and future perspectives

COMPASS is a fixed target experiment in operation at CERN since 2002 with a wide physics programme. An important part of this programme is the study of transverse spin and momentum dependent parton distribution and fragmentation functions. A review of recent results on TMDs obtained using both muon or hadron beams scattering off unpolarised and polarized targets will be given. The future 2021 approved run with a muon beam scattering off a transversely polarized deuteron target, as well as the further future plans of the COMPASS++/AMBER Collaboration will also be discussed.

Speaker: Andrea Bressan (TS)

2019SARWAR_bressan.pptx

10:20 → 11:00 The 3D nucleon structure program at JLab

In the recent years, it has been realized that in DIS reactions, single and dihadron semi-inclusive and hard exclusive production, provide a variety of spin and azimuthal angle dependent observables sensitive to the dynamics of quark-gluon interactions. New parton distributions and fragmentation functions have been introduced to describe the rich complexity of the hadron structure and move towards a multi-dimensional imaging of the underlying parton correlations. Besides the hard probe scale, these functions explicitly depend on the parton transverse degrees of freedom at the scale of confinement. Studies of the parton distribution functions which encode transverse momentum (TMDs) or transverse position (GPDs) promise to open a unprecedented gateway to the unique dynamics of the strongly interacting force. This work presents a selection of available observations and upcoming measurements planned at Jefferson Lab to address the mysteries of the nucleon structure from a modern point of view.

Speaker: Marco Contalbrigo (FE)

Contalbrigo_JLab.pdf

11:00 → 11:30 Coffee Break

11:30 → 12:10 Describing unpolarized SIDIS data at order $\alpha_s$

I will discuss a view on the issues of describing unpolarised SIDIS data in their entire spectrum, as well as possible solutions.

Speaker: Dr Jose Osvaldo Gonzalez Hernandez (TO)

cagliari2019_gonzalez.pdf

12:10 → 12:50 TMDs from SIDIS data: role of different choices in phenomenological analyses

In this talk we will assess the role of the different choices on TMD functions parametrisations in phenomenological analyses.

As an example, the latest Sivers extraction from SIDIS data is presented. Motivated by the latest COMPASS measurement, a new, thorough study of uncertainties affecting the extracted quark Sivers function, along with a critical assessment of visibility of TMD signals in SIDIS data, has been performed. We will see that, even within a simple and transparent parametrisation, a satisfactory description of experimental data is obtained.

Finally, a preliminary study on transversity function and its impact on the tensor charge will be discussed.

Speaker: Carlo Flore (CA)

flore_SarWorS.pdf

12:50 → 14:00 Lunch

14:00 → 14:25 Improving the perturbative accuracy of TMD PDF extractions: formalism

Speaker: Valerio Bertone (Università degli studi di Pavia)

bertone_SarWorS_08_07_2019.pdf

14:25 → 14:50 Improving the perturbative accuracy of TMD PDF extractions: preliminary results

In this contribution we present our recent preliminary results on the extraction of the unpolarised transverse-momentum dependent (TMD) parton distribution functions (PDFs) from a study of Drell-Yan and Z-boson production data. We consider a wide dataset that includes low-energy data from the FNAL and high-energy data from Tevatron and the LHC. In particular, we highlight the challenges of including the most recent LHC data and theoretical uncertainties in the analysis.

Speaker: Chiara Bissolotti (P)

2019_SarWors_Bissolotti.pdf

14:50 → 16:00 Discussion

Tuesday, 9 July

09:30 → 10:10 Hadron production in electron-positron annihilation

Fragmentation functions, describing the formation of hadrons from partons, are an indispensable tool in the interpretation of hadron-production data, e.g., in the investigation of nucleon structure via semi-inclusive deep-inelastic scattering. The cleanest process to access fragmentation functions is hadron production in electron-positron annihilation. In this review a selection of recent results on hadron production in electron-positron annihilation will be discussed, supplemented with an outlook on what can be expected in the nearer future.

Speaker: Gunar Schnell (University of the Basque Country UPV/EHU)

Sar WorS 2019 - Gunar Schnell.pdf

10:10 → 10:35 Transverse $\Lambda$ polarisation in $e^+e^-$ collisions

We discuss how recent data from the Belle Collaboration on transverse $\Lambda$ polarisation measured in $e^+e^-$ annihilation processes could be used to extract, for the first time, the polarising fragmentation function. This, giving the probability that an unpolarised parton fragments into a transversely polarised spin-1/2 hadron, represents one of the 8 leading-twist transverse momentum dependent fragmentation functions. Preliminary results will be shown.

Speaker: Marco Zaccheddu (Istituto Nazionale di Fisica Nucleare)

pres_marco_zaccheddu.pdf

10:35 → 11:00 The impact of the errors of collinear functions in describing unintegrated SIDIS data.

Describing qT-dependent SIDIS distributions requires consideration of two different regimes which involve two different factorization schemes. In both cases, the necessary ingredients include parton distribution and fragmentation functions (PDFs and FF), which are traditionally extracted in statistical analyses with collinear observables. In this talk I will present examples of how the errors in the extraction of collinear PDFs and FFs may affect the successful description of the qT-dependent SIDIS distributions.

Speaker: Andrea Simonelli (Università di Torino e INFN)

Slide Sar Wors 2019_Simonelli.pdf

11:00 → 11:30 Coffee Break

11:30 → 12:10 Effect of flavor-dependent partonic transverse momentum on precision measurements at hadron colliders

The electroweak working group at the LHC is actively working to analyse (and, possibly, reduce) all kind of theoretical and experimental uncertainties affecting precision electroweak observables. The resummation of soft and collinear radiation to all orders has a considerable impact on selected observables (i.e. mW). I will first present a concise review of the different frameworks (SCET, TMD, qt resummation, parton branching) presently available to take into account this kind of effect. Then, I will give an overview of recent results concerning the impact of a possible flavour dependence of the intrinsic quark transverse momentum on the direct determination of the boson mass. I will show that these effects are comparable in size to other nonperturbative effects commonly included in phenomenological analyses and should thus be included in precise theoretical predictions for present and future hadron colliders.

Speaker: Dr Giuseppe Bozzi (PV)

bozzi.pdf

12:10 → 12:50 Kinematical analysis of non-collinearity

The Drell-Yan process and electron-positron annihilation offer a natural arena for studies of non-collinearity. We [1] show how covariantly defined variables for these processes and also for semi-inclusive deep inelastic scattering are suited to get a feeling for the magnitude of intrinsic tranverse momenta.

[1] P.J. Mulders and C. Van Hulse ArXiv:1903.11467 [hep-ph]

Speaker: Piet Mulders (Nikhef Theory Group and VU)

2019-Cagliari-fragmentation.pdf

12:50 → 14:00 Lunch

14:00 → 14:40 Hadro-production of Z-bosons in the Parton Branching Approach to TMDs

Transverse Momentum Dependent (TMD) parton distributions obtained from the Parton Branching (PB) method are combined with next-to-leading-order (NLO) calculations of Drell-Yan (DY) production. We apply the MC-at-NLO method for the hard process calculation and matching with the PB TMDs. We compute predictions for the transverse momentum, rapidity and phi-* spectra of Z bosons. We find that the theoretical uncertainties of the predictions are dominated by the renormalization and factorization scale dependence, while the impact of TMD uncertainties is moderate. The theoretical predictions agree well, within uncertainties, with measurements at the Large Hadron Collider (LHC). In particular, we study the region of lowest transverse momenta at the LHC, and comment on its sensitivity to nonperturbative TMD contributions.

Speaker: Prof. Francesco Hautmann (U. of Oxford / U. of Antwerp)

14:40 → 15:40 Discussion

Wednesday, 10 July

09:30 → 10:10 Gluon TMDs in J/psi + jet production at an EIC

The process e + p -> e + J/psi + jet + X, where the proton can be polarized, is computed in the transverse momentum-dependent (TMD) factorization framework. This framework is applicable in the regime where the J/psi - jet pair is produced almost back-to-back in the transverse plane, such that its total transverse momentum is a measure of the primordial k_t of the parton. We show that in the kinematical regime of our interest, and at the energies of the planned Electron-Ion Collider (EIC), the contribution of the quark channel is strongly suppressed, such that the cross section can be analyzed solely in function of gluon TMDs. We demonstrate how these gluon TMDs could be disentangled using the various azimuthal asymmetries in the cross section, and comment on the influence of the different production mechanisms of the quarkonium (Color Singlet Model vs Non-Relativistic QCD) on our results.

Speaker: Pieter Maria Taels (Istituto Nazionale di Fisica Nucleare)

ptaelsSarWors2019.pdf

10:10 → 10:50 Linearly Polarized Gluon Distribution in J/psi Production at the EIC

We calculate the cos 2φ asymmetry in J/ψ production in electron-proton collision for the kinematics
of the planned electron-ion collider (EIC). This directly probes the Weisz¨acker-Williams (WW) type
linearly polarized gluon distribution. Assuming generalized factorization, we calculate the asymmetry
at next-to-leading-order (NLO) when the energy fraction of the J/ψ satisfies z < 1 and the dominating
subprocess is γ∗ + g → c + ¯c + g. We use non-relativistic QCD based color singlet (CS) model for J/ψ
production. We investigate the small x region which will be accessible at the EIC. We present the
upper bound of the asymmetry, as well as estimate it using a (i) Gaussian type parametrization for the
TMDs and (ii) McLerran-Venugopalan (MV) model at small x. We find small but sizable asymmetry
in all the three cases.

Speaker: Prof. Asmita Mukherjee (IIT Bombay)

SarWors.pdf

10:50 → 11:20 Coffee Break

11:20 → 12:00 Probing gluon TMDs through quarkonia production

In the last years a big progress has been made in the quark sector of TMDs, but the gluon sector is so far much less developed, due to the difficulty to cleanly probe gluons in high-energy processes.
A very promising way to access them, but also challenging, is through quarkonia production. However, a solid theoretical framework is still lacking.
In this talk I will present new developments towards a new formalism which, based on the effective field theory approach, allows to establish the needed factorization theorems to properly access gluon TMDs in quarkonia production.

Speaker: Miguel G. Echevarria (PV)

Echevarria_SarWorS2019.pdf

12:00 → 12:40 Single-Spin Asymmetry in $J/\psi$ Production in Proton-Proton Collision

Among the eight leading twist gluon TMDs, gluon Sivers function (GSF) has been the limelight in hadron physics. GSF is not yet known fully, though attempts have been made. The $J/\psi$ production has been advertised to probe the gluon TMDs. In this talk, we present the calculation of single-spin asymmetry (SSA) in $pp^\uparrow\to J/\psi+X$ process to probe the unknown GSF within the generalized parton model (GPM) framework. The non-relativistic QCD (NRQCD) framework is employed for calculating color singlet and color octet states of $J/\psi$. Finally, we compare the unpolarized differential cross section with PHENIX and CDF data in the low $P_T$ region.

Speaker: Rajesh Sangem (Istituto Nazionale di Fisica Nucleare)

RajeshSarWors19.pdf

12:40 → 13:05 Transverse-momentum-dependent gluon distribution in a spectator model

While significant steps toward the formal definition of quark TMDs and their extraction from experimental data through global fits has been made in the last years, the gluon-TMD field represents a largely unexplored territory. Pursuing the goal of extendending our knowledge of this sector, we present analytic expressions for all $T$-even gluon TMDs at twist-2, calculated in a spectator model for the parent nucleon. At variance with respect to previous works, our approach encodes a flexible parametrization for the spectator-mass spectral density, allowing us to improve the description in the small-$x$ region. We build a common framework where valence, sea quark and gluon densities are concurrently generated. Our results can be used to predict the behavior of observables sensitive to gluon-TMD dynamics.

Speaker: Dr Francesco Giovanni Celiberto (University of Pavia and INFN)

talk_Sar_WorS_2019_Celiberto.pdf

13:05 → 14:10 Lunch

14:10 → 14:50 Recent results on Quarkonia at forward rapidity with ALICE at the LHC

ALICE is the experiment specifically designed for the study of the Quark-Gluon Plasma (QGP) in heavy-ion collisions at the CERN LHC. Heavy-ion collisions help us to understand quarkonium suppression and regeneration mechanisms in the presence of the QGP. However, a modification of heavy quarkonium production can also take place in proton-nucleus collisions, where a QGP is not expected to be created and only cold nuclear matter (CNM) effects, such as nuclear absorption, parton shadowing and parton energy loss in initial and final states occur. The study of proton-nucleus collisions is therefore important to disentangle the effects of QGP from the CNM ones, and to provide essential input to understand nucleus-nucleus collisions. Finally, proton-proton collisions give insight to the different quarkonium production mechanisms and provide the baseline for the nuclear modification factor of quarkonium production in proton-nucleus and nucleus-nucleus collisions.
ALICE has produced a large amount of results on quarkonia both at forward and mid rapidity at various energies and colliding systems (pp, p-Pb, Pb-Pb and Xe-Xe) during the LHC Run1 and Run2 periods. In this talk, recent results on multiplicity dependent study of quarkonia in pp and p-Pb collisions will be discussed. Latest ALICE results of quarkonium nuclear modification factor, elliptic flow and polarization using the 2018 Pb-Pb data sample will also be presented. The results will be compared with other LHC results and theoretical predictions.

Speaker: Biswarup Paul (Istituto Nazionale di Fisica Nucleare)

Sar_Wors_2019_Biswarup_Paul.pdf

14:50 → 15:50 Discussion

15:50 → 16:00 Closing