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- Indico Weeks View
In this presentation, I will discuss selected highlights in electromagnetic hadron physics since the last edition of EINN held remotely in 2021
I give a broad overview of recent theory developments and open questions for a subset of topics discussed at this conference. The focus lies on different ways of 'imaging' the nucleon, from form factors to parton distributions.
The Muon g$-$2 experiment at Fermilab aims to measure the anomalous magnetic moment of the muon, $a_\mu = (g-2)/2$, with a final accuracy of 140 parts per billion, representing one of the most precise tests of the Standard Model. The experiment's first result from the 2018 dataset, Run 1, was published in 2021 and confirmed the previous result obtained at Brookhaven National Laboratory with a similar sensitivity. We present here the result based on the 2019 and 2020 datasets, Runs 2 and 3, which contain a factor of four more data than in Run 1, thus entering a new sensitivity regime to g$-$2.
We discuss the experimental and the analysis improvements with respect to Run 1 result and the experiment's future prospects for the next years.
Over twenty years ago, in an experiment at Brookhaven National Laboratory, physicists detected what seemed to be a discrepancy between measurements of the muon’s magnetic moment and theoretical calculations of what that measurement should be, raising the tantalizing possibility of physical particles or forces as yet undiscovered. The Fermilab team has announced 2021 and then in 2023 that their precise measurement supports this possibility. The reported significance for new physics was first 4.2 sigma and according to the latest result it is 5.1 sigma, just slightly above the discovery level of 5 sigma. However, an extensive new calculation of the muon's magnetic moment using lattice QCD by the BMW-collaboration reduces the gap between theory and experimental measurements. The lattice result appeared in Nature on the day of the first Fermilab announcement. In this talk both the theoretical and experimental aspects are summarized with two possible narratives: a) probable discovery or b) Standard Model re-enforced. Some details of the lattice calculation are also shown.
Heavy quarkonium production serves as a powerful tool to investigate the gluonic structure of the nucleon. The latest generation of experiments being conducted at Jefferson Lab in the 12 GeV era use near-threshold J/ψ production to explore the mass structure of the nucleon. In this presentation, I will focus on both current and forthcoming experiments aimed at unraveling the proton’s gluonic gravitational form factors. I will discuss the new and upcoming results from J/ ψ -007 in Hall C, GlueX, and CLAS12, with a particular emphasis on the recent experimental determination of the proton's gluonic gravitational form factors and mass radius. Additionally, I will explore future opportunities with the SoLID experiment at Jefferson Lab and with ePIC at the EIC.
We present a brief report on our ongoing efforts to calculate the transverse single-nucleon spin asymmetry of single-inclusive jet production in lepton-nucleon collisions at NLO accuracy within the collinear twist-3 factorization framework. This observable can very well be measured at a future Electron-Ion Collider (EIC). Such data will give new insight into both the partonic structure of the nucleon as well as the QCD dynamics inside the nucleon.
We present our results on transverse momentum dependent factorization and resummation at sub-leading power in Drell-Yan and semi-inclusive deep inelastic scattering. In these processes the sub-leading power contributions to the cross section enter as a kinematic power correction to the leptonic tensor, and the kinematic, intrinsic, and dynamic sub-leading contributions to the hadronic tensor. By consistently treating the power counting of the interactions, we demonstrate renormalization group consistency. We calculate the anomalous dimensions of the kinematic, intrinsic, and dynamical sub-leading correlation functions at one loop and find the evolution equations. Additionally we calculate the hard and soft functions associated with each of these contributions and and compare them to the leading power results. We also calculate the one loop soft function associated with the intrinsic and kinematic sub-leading transverse momentum dependent distributions and compare them to the leading power results. Using this information, we establish the factorization formalism at sub-leading power for these processes at the one-loop level. We also focus on the matching of the large and small transverse momentum contributions in semi-inclusive deep inelastic scattering processes and Drell Yan. We pay special attention to azimuthal modulations of unpolarized cross sections such as the Cahn effect. Finally we present our findings on the QCD equation of motion relations beyond tree level.
We present results for the nucleon axial and pseudoscalar form factors extrapolated at the continuum limit using three $N_f = 2 + 1 + 1$ twisted mass fermion ensembles with all quark masses tuned to their physical values. Convergence to the ground state matrix elements is assessed using multi-state fits. We study the momentum dependence of the three form factors and check the partially conserved axial-vector current (PCAC) hypothesis and the pion pole dominance (PPD). We show that in the continuum limit, the PCAC and PPD relations are satisfied. We also show that the Goldberger-Treimann relation is approximately fulfilled and determine the Goldberger-Treiman discrepancy.
An overview of the progress preparing the Electron-Ion Collider (EIC) for construction. The presentation addresses the EIC design requirements, conceptual design, and construction schedule. Current efforts to promote international engagement and collaboration will be described, including opportunities for contributions to the design and construction of the accelerators and collaboration on the experimental program.
The design of the electron-ion collider (EIC) at Brookhaven National Laboratory
is well underway, aiming at a peak electron-proton luminosity of 10^34 cm^-2
sec^-1. This high luminosity and wide center-of-mass energy range from 29 to
141 GeV (e-p) require innovative solutions to maximize the performance of the
machine, which makes the EIC one of the most challenging accelerator projects
to date. The complexity of the EIC will be discussed, and the project status
and plans will be presented.
Understanding the properties of nuclear matter and its emergence through the underlying partonic structure and dynamics of quarks and gluons requires a new experimental facility in hadronic physics known as the Electron-Ion Collider (EIC).
The EIC will address some of the most profound questions concerning the emergence of nuclear properties by precisely imaging gluons and quarks inside protons
and nuclei, such as the distribution of gluons and quarks in space and momentum, their role in building the nucleon spin and the properties of gluons in nuclei at
high energies.
A new detector collaboration has been formed around one of two possible interaction regions, the ePIC collaboration. This presentation will present the requirements for the ePIC detector, present in detail its design philosophy, and discuss the overall status and plans.
In global extractions of Transverse momentum dependent (TMD) distributions, the limit of small transverse distances is constrained using the matching to collinear parton density functions (PDF). Naturally, the TMDPDFs depend on the baseline PDF set used certain features of the former might be due to the latter, rather than genuinely due to TMD behaviour f the partons. To shed light on the issue, we study the influence of the PDF choice on the determination of unpolarized TMDPDFs and the description of TMD Drell-Yan-pair and Z-boson production data. We find that the selection of a PDF essentially biases the extraction of TMDPDFs, impacting the quality and shape of the distributions. This bias is alleviated once the PDF uncertainty is taken into account, making the non-perturbative TMD profile is flavor-dependent. This drives an improvement of the agreement between theory and experiment, substantially increase the uncertainty in extracted TMD distributions, and should be taken into account in future global analyses.
We review the current status of the nucleon's helicity PDFs. We describe
recent progress on "global" analysis of the distributions, highlighting
advances on the theoretical side especially in terms of higher-order
perturbative calculations. We discuss the relevance of these advances
for the spin program at the future EIC.
We present results for the axial, tensor, and scalar charges of the nucleon using lattice QCD simulations of twisted mass fermions with two degenerate light, a strange, and a charm quark, with masses tuned to their physical values (physical point simulations). The axial charge is well known experimentally and therefore provides for an important benchmark of our methodology, while the scalar and tensor charges are less well known and their determination from first principles can provide input for precision measurements probing the existence of novel scalar and tensor interactions. Our results are obtained at three values of the lattice spacing, allowing for a first extrapolation to the continuum limit directly at the physical point.
The gravitational form factors (GFFs) of hadrons are related to the matrix elements of the energy-momentum tensor of QCD. In recent years, the proton and pion GFFs have been constrained for the first time from experimental measurements. We compute the quark and gluon GFFs of the pion and the nucleon in the kinematic region $0 < -t < 2~\text{GeV}^2$ on a clover improved lattice QCD ensemble with $a=0.091~\text{fm}$ and $m_{\pi} = 170~\text{MeV}$, employing non-perturbative renormalization via the RI-MOM scheme. Our results for the pion GFFs agree with chiPT predictions, while from fits to the proton GFFs, we obtain estimates for its total $D$-term, and for its energy and mechanical distributions.
On behalf of the ePIC Collaboration
The future Electron-Ion Collider (EIC) at Brookhaven National Laboratory will collide polarized electrons with polarized proton/ions. The electron Proton and Ion Collider (ePIC) detector is being designed as the day one EIC detector. The EIC physics program requires precision tracking and particle identification (PID) capabilities that extend over a large kinematic acceptance. To meet these challenges ePIC is being designed as a highly integrated detector. One critical component of the detector is the tracking system, consisting of silicon layers near the interaction region, and then transitioning into large area micropattern gas detectors (MPGDs) further from the integration region. In the current ePIC design, the MPGDs play a critical role in providing fast timing hit points for pattern recognition and signal to background discrimination, which are needed for track reconstruction. Additionally, MPGDs located near PID subsystems could provide a precision space point measurement to better determine the angle that the particle enters the PID subsystem, ultimately leading to better Cherenkov ring reconstruction and PID performance.
An overview of the current ePIC tracking system and its projected performance will be presented.
The ePIC detector is being designed as a general-purpose detector for the Electron-Ion Collider (EIC) to deliver the full physics program. One of the key challenges at the EIC is particle identification (PID), which requires excellent separation of pions, kaons, and protons over a wide phase space with significant pion/electron suppression. To address this challenge, ePIC utilises multiple advanced particle identification technologies.
The talk will cover the PID subsystems of the ePIC detector, which comprise a of time-of-flight (TOF) detector for low-momentum PID and several high-momentum particle-identification systems that use DIRC and RICH techniques to exploit Cherenkov light emission from charged particles.
This talk will cover some of the electromagnetic calorimetry plans for the ePIC detector with a concentration on the design of the central barrel calorimeter based on the current GlueX BCAL at JLab. The requirements (as specified in the ePIC Project) include energy resolution of 10%/$\sqrt{E} \oplus (2-3)$% and electron-pion suppression great than $10^3$, which will be comfortably met by a novel imaging calorimeter that combines AstroPix silicon sensors for position resolution and lead-scintillating-fiber matrix for energy resolution. Specific Canadian contributions to the EIC effort will also be presented.
The Mainz Energy-Recovery Superconducting Accelerator MESA, currently under construction at the Institute of Nuclear Physics at Mainz, provides the basis for precision experiments in the areas of nuclear, hadron, and particle physics. In this talk, we report on the comprehensive physics program of the three fixed-target experiments prepared for MESA: (i) MAGIX, (ii) P2, and (iii) DarkMESA.
MAGIX will make use of MESA’s innovative energy recovery technique, which enables very high beam intensities. The setup is equipped with a gas jet target, surrrounded by two high-resolution magnetic spectrometers. The combination of a high-intensity electron beam with such a window-less gas jet target is innovative and will allow for instance for determinations of the proton radius, searches for dark sector particles, and measurements of reactions of relevance for nuclear astrophysics.
The P2 experiment will be operated in the external beam mode of MESA and will measure the parity-violating spin asymmetry, which in turn yields a measurement of the electroweak mixing angle at low momentum transfer. The comparison of such a measurement with the Standard Model (SM) prediction will allow to test extensions of the SM at scales of up to 50 TeV. Furthermore, the neutron skin of nculei can be extracted.
Finally, the DarkMESA beam dump experiment, located behind the beam dumo of P2, will search for hypothetical light dark matter particles
Dark matter exploration is become a central or side topic of many experiments at particle accelerators. Even if this approach, up-to-now, has not produced evidences, it helped in setting stringent limits on the characteristics of dark matter.
In this panorama is inserted the Positron Annihilation into Dark Matter Experiment (PADME) ongoing at the Laboratori Nazionali di Frascati of INFN. PADME was conceived to search a Dark Photon signal [2] by studying the missing-mass spectrum of single photon final states resulting from positron annihilations with the electrons of a fixed target. Actually, the PADME approach allows to look for any new particle produced in $e^+ e^-$ collisions through a virtual off-shell photon such as long lived Axion-Like-Particles (ALPs), proto-phobic X bosons, Dark Higgs ...
After the detector commissioning and the beam-line optimization, the PADME collaboration had different periods of data acquisition and and some results have been already published [3].
In the second half of 2022 a special data taking was conducted with the scope to confirm/disprove the particle nature of the X17 anomaly observed in the ATOMKI nuclear physics experiments studying de-excitation via $e^+ e^-$ emission of several light nuclei [4].
About $10^{10}$ positrons have been stopped on the target for each of the 47 beam energy values in the range 262 - 298 MeV. This precise energy scan was intended to study the reaction $e^+ e^-\rightarrow X17→e^+ e^-$.
The talk will give an overview of the scientific program of the experiment and of the data analyses ongoing.
[1] P. Agrawal et al., Eur. Phys. J. C 81 (2021) 11, 1015.
[2] P. Albicocco et al., JINST 17 (2022) 08, P08032.
[3] F. Bossi et al., Phys. Rev. D 107 (2023) 1, 012008.
[4] L. Darmé et al., Phys. Rev. D 106 (2022) 11, 115036.
A summary of experimental measurements unveiling spin-dependent nucleon structure prior to the arrival of the Electron-Ion Collider is given. Results from fixed-target experiments at Jefferson Lab, CERN, and DESY and collider experiments from RHIC will be presented. The measurements will be discussed in the context of transverse proton or parton spin and transverse parton momenta (TMDs), and their (spin-orbit) correlations, and generalized parton distributions (GPDs), the latter of which map the proton in transverse position space. The GPDs and TMDs provide complementary pathways to mapping multi-dimensional nucleon structure.
In the first part of the talk, I will review the recent progress on nucleon parton distributions in the global QCD analysis. In the second part, I will discuss the important role of epistemic uncertainties on PDFs in the increasingly common situation when other experimental and theoretical uncertainties are small. The AI techniques may complicate, rather than simplify, estimation of such uncertainties. Future comparisons of nucleon and other PDFs against predictions from lattice and nonperturbative QCD must balance between the precision and replicability of results.
In this talk, I will report on recent progress in Quantum Monte Carlo calculations of electron and neutrino interactions with nuclei in a wide range of energy and momentum transfer and their connections to current experimental efforts in fundamental symmetries and neutrino physics.
The theory of the strong force, Quantum Chromodynamics, describes the proton in terms of quarks and gluons. The proton is a bound state of two up and one down quark, but quantum theory predicts that in addition there is an infinite number of quark-antiquark pairs. Both light and heavy quarks, whose mass is respectively smaller or bigger than the proton’s, are revealed inside the proton in high-energy collisions. However, it is unclear whether heavy quarks also exist as a part of the static nucleon wave-function: so-called intrinsic heavy quarks. It has been argued for long that the proton could have a sizable intrinsic component of the lightest heavy quark, the charm quark. Innumerable efforts to establish intrinsic charm in the proton have remained inconclusive. We provide first evidence for intrinsic charm by exploiting a high- precision determination of the quark-gluon content of the nucleon based on machine learning and a large experimental dataset. We disentangle the intrinsic charm component from charm-anticharm pairs arising from high-energy radiation. We establish the existence of intrinsic charm at the 3σ level, with a momentum distribution in remarkable agreement with model predictions. We confirm these findings by comparing to very recent data on Z production with charm jets from the LHCb experiment.
In this contribution, I will present a recomputation of the evolution kernels of generalised parton distributions (GPDs) at one-loop accuracy for all of the three possible leading-twist polarisations: unpolarised, longitudinally polarised, and transversely/linearly polarised.
I will discuss the analytic and numerical properties of these kernels presenting a number of numerical results for the evolution of GPDs deriving from the their implementation in a public code.
We present the first direct lattice QCD calculation of the x-dependent pion distribution amplitudes on domain wall gauge ensembles at physical pion mass. We use the large momentum effective theory to directly calculate the x-dependence of meson DAs with several recently developed self-consistent precision control methods. We perform a leading renormalon resummation to remove linear corrections in $1/P_z$, and resum the renormalization group logarithms to include higher order large log terms at small quark momenta $xP_z$ and anti-quark momenta $(1-x)P_z$. Such techniques guarantee the precision of our calculation in mid-$x$ region. Finally, constraining with short-distance factorization analysis, we are able to model the endpoint regions of DA more reliably in all region. Measurements of both pion and kaon DAs on HISQ ensembles at physical pion mass are also analyzed for comparison, from which we examine the chiral symmetry breaking effect on meson DAs.
Generalized Parton Distributions (GPDs) are nowadays the object of an intense effort of research, in the perspective of understanding nucleon structure. They describe the correlations between the longitudinal momentum and the transverse spatial position of the partons inside the nucleon and they can give access to the contribution of the orbital momentum of the quarks and gluons to the nucleon spin.
Deeply Virtual Compton scattering (DVCS), the electroproduction on the nucleon, at the partonic level, of a real photon, is the process more directly interpretable in terms of GPDs of the nucleon. Depending on the target nucleon (proton or neutron) and on the DVCS observable extracted (cross sections, target- or beam-spin asymmetries, …), different sensitivity to the various GPDs for each quark flavor can be exploited. Gluon GPDs can also be accessed by probing specific kinematic regimes. And, besides DVCS, other exclusive reactions, such as Timelike Compton Scattering, Double DVCS, or the exclusive electroproduction of mesons, can provide information on GPDs.
This talk will provide an overview on recent and new, promising, GPD-related experimental results, mainly obtained at Jefferson Lab on fixed target experiments with a 12-GeV electron beam, for various target types and final states. These data open the way to a “tomographic” representation of the structure of the nucleon, allowing the extraction of transverse space densities of the quarks at fixed longitudinal momentum, as well as providing an insight on the distribution of forces inside the nucleon.
The perspectives for future GPD experiments at the Electron-Ion Collider (EIC) with the ePIC detector will also be outlined: these experiments will pave the way to perform the tomography of the nucleon in terms of its sea-quarks and gluons content.
Beam polarimetry will play an important role in meeting the goals of the planned EIC physics program. However, the EIC beam properties will make achieving the level of precision required challenging for both electron and hadron beam polarimetry.
In this talk, I will give a brief overview of the techniques used to measure electron and hadron beam polarization at high energies, and discuss the plans for meeting the EIC beam polarimetry requirements.
Precise measurements of the electron-hadron cross sections are the corner stone of scientific program at the future Electron-Ion Collider, hence the high demands towards the EIC luminosity measurements – at least a 1% accuracy is required for the absolute luminosity determination and only a 0.01% uncertainty for the relative, bunch-to-bunch, luminosity measurements. As was demonstrated at HERA – the first electron-hadron collider – the bremsstrahlung process can be successfully used to precisely measure the luminosity of high energy 𝑒𝑝 collisions. Such a technique can be also used at the EIC, but it poses major challenges, and a wide range of the electron beam energies and a large variety of hadron species, from protons to gold nuclei, will only increase that challenge. I will describe conceptual detector designs and measurement techniques being studied to overcome these huge challenges and to meet the target performance.
In this presentation, we delve into the calculation of perturbative corrections for the Deeply Virtual Compton Scattering process within a unique kinematic domain, specifically where $t \gg \Lambda^2_{\rm QCD}$, with $t$ representing the change in nucleon momentum following scattering. Working within this unconventional domain necessitated a distinctive approach, particularly dealing with non-zero values of $t$. Our calculation unveiled a previously undisclosed connection between Generalized Parton Distributions (GPD) and the chiral, as well as trace, anomalies of QCD. Of particular interest is the emergence of anomalies as infrared singularities when $t$ approaches zero. Subsequently, we validate factorization up to one-loop order by systematically incorporating these singularity-related anomalies into the GPDs. This development not only expands the horizons of GPD research to encompass quantum anomalies but also opens up novel avenues for exploring their implications in both high-energy exclusive processes and the domain of lattice QCD investigations.
In this talk I present our work on the calculation of exclusive single jet and dijet production cross sections in polarized DIS. The NLO accuracy results are obtained with our extension of the dipole subtraction method to account for initial state polarized processes. In the case of single jet production, we also reach NNLO accuracy by applying the projection-to-Born (P2B) subtraction method. We consider the case of pure photon exchange as well as full neutral-current (NC) and charged-current (CC) processes where the weak boson W± and Z are involved. The calculation is fully implemented in our Monte Carlo code POLDIS, which is used to study the phenomenological implications of the results obtained in the kinematics of the future Electron-Ion Collider (EIC) and how they will impact on our knowledge on the spin decomposition of hadrons.
Charged-current quasielastic neutrino scattering is the signal process in neutrino oscillation experiments and requires precise theoretical prediction for the analysis of modern and future experimental data, starting with the nucleon axial-vector form factor. In this talk, I compare a new MINERvA measurement of this form factor with lattice-QCD calculations and deuterium bubble-chamber data, provide uncertainty projections for future extractions, and present recent calculations of radiative corrections to charged-current processes. The exchange of photons with nuclear medium modifies (anti)neutrino and electron scattering cross sections. We study the distortion of (anti)neutrino-nucleus and charged lepton-nucleus cross sections and estimate the QED-medium effects on the final-state kinematics and scattering cross sections. We find new permille-to-percent level effects, which were never accounted for in either (anti)neutrino-nucleus or electron-nucleus scattering.
A deeper understanding of the nucleon structure can be achieved through the study of Generalized Parton Distributions (GPDs).
The particularity of GPDs is that they convey an image of the nucleon structure where the longitudinal momentum and the
transverse spatial position of the partons inside the nucleon are correlated. Moreover, GPDs allow the quantification,
via Ji's sum rule, of the contribution of the orbital angular momentum of the quarks to the nucleon spin, important
to the understanding of the origins of the nucleon spin. Deeply Virtual Compton scattering (DVCS), the electroproduction of a
real photon off the nucleon at the quark level, is the golden process directly interpretable in terms of GPDs of the nucleon.
The GPDs are accessed in DVCS mainly through the measurements of single- or double- spin asymmetries. Combining measurements
of asymmetries from DVCS experiments on both the neutron and the proton will allow performing the flavor separation of relevant
quark GPDs via linear combinations of proton and neutron GPDs. This talk will mainly focus on recent DVCS off the neutron from
deuterium measurement from the CLAS12 experiment at Jefferson Lab with the upgraded ~11 GeV CEBAF polarized electron beam.
This process emphasizes mainly, in the kinematic range covered at Jefferson Lab, the access to the GPD E of the neutron which
is the least constraind GPD up till now. Details on the data analysis along with preliminary results on Beam Spin Asymmetries will be
presented.
The investigation of nucleon elastic electromagnetic form factors (EMFFs) at large momentum transfer has generated a large and increasing amount of experimental and theoretical interest over the last several decades. EMFFs provide precision benchmarks for theoretical modeling of nucleon structure and ab initio predictions in lattice QCD. Additionally, precise knowledge of the form factors at large Q^2 values is required as input to the interpretation of many other experiments in nuclear and hadronic physics, including studies of the Generalized Parton Distributions (GPDs) in Deeply Virtual Compton Scattering (DVCS). The experimental study of nucleon EMFFs at very large Q^2 is presently a unique worldwide capability of the Continuous Electron Beam Accelerator Facility at Jefferson Lab (JLab). The Super BigBite Spectrometer (SBS) Collaboration is presently carrying out a comprehensive program of high-Q^2 measurements of proton and neutron form factors in JLab's Hall A. The program started in October 2021, is approximately 50% complete as of this writing, and will continue to occupy Hall A through early 2025. In terms of luminosity and access to relevant kinematics for the measurement of polarization observables in elastic electron-nucleon scattering, the existing 11 GeV CEBAF and a proposed upgraded CEBAF to 22+ GeV are superior to the planned Electron-Ion Collider (EIC). However, the high center-of-mass energies available at the planned EIC allow for a significantly higher Q^2 reach than will ever conceivably be accessible in fixed-target experiments. Moreover, the detector and luminosity requirements for currently envisioned measurements of DVCS and other hard exclusive processes at the EIC are similar to those required for elastic form factor measurements. As such, the EIC can make a unique contribution to the knowledge of elastic electron-nucleon scattering cross sections at very large Q^2, albeit only for longitudinally polarized virtual photons. In this talk, I will review the current status of the SBS form factor program, including ongoing and planned experiments, the analysis of partially collected data, and the preliminary results of already completed experiments. I will also discuss the challenges involved in such measurements, and the prospects for extending their Q^2 reach beyond the SBS program, at the planned Electron-Ion Collider (EIC) and elsewhere.
The transversity distribution function of quarks, $h_1^{q}(x)$, encapsulates the transverse spin structure of the proton at leading twist, where $x$ represents the longitudinal momentum fraction carried by the quark $q$. Extracting $h_1^{q}(x)$ poses a formidable challenge due to its chiral-odd nature. Measurements of final-state hadron pairs in transversely polarized proton-proton ($p^\uparrow p$) collisions directly probe collinear quark transversity through its coupling with a chiral-odd interference fragmentation function (IFF), $H_1^{\sphericalangle, q}$. This coupling leads to an experimentally measurable azimuthal correlation asymmetry, $A_{UT}$.
To extract $h_1^{q}(x)$ from $A_{UT}$ asymmetry measurements, precise knowledge of IFF and unpolarized di-hadron fragmentation functions is needed.
The former is provided from $e^{+}e^{-}$ experiments, owing to the factorization and universality of the physics mechanism in the collinear framework.
On the other hand, the latter is largely unknown but can be extracted from unpolarized di-hadron cross-section measurements in pp collisions.
In this presentation, we will present preliminary results of $A_{UT}$ using $p^\uparrow p$ data collected in 2015 at $\sqrt{s}=200\,$GeV and in 2017 at $\sqrt{s}=510\,$GeV, and the unpolarized cross section using $pp$ data collected in 2012 for $\pi^+\pi^-$ pairs at $\sqrt{s} = 200$ GeV by the STAR experiment. The presentation will also discuss prospects for additional data at both $\sqrt{s}=200\,$GeV and $\sqrt{s}=510\,$GeV.
During the past several decades a large quantity of high-quality mesonic photo- and electro-production data have been measured at electromagnetic facilities worldwide. By contrast, meson-beam data for these same final states are mostly outdated, largely of poorer quality, or even non-existent, especially those involving spin asymmetries and polarizations. Thus, existing meson beam results provide inadequate input to interpret, analyze, and exploit the potential of the new electromagnetic data. To achieve full benefit of these high-precision electromagnetic data, new high-statistics data from measurements with meson beams, with good angle and energy coverage for a wide range of reactions, are critically needed to advance our knowledge in baryon and meson spectroscopy and other related areas of hadron physics. To address this situation, new, state-of-the-art meson-beam facilities are needed. This presentation summarizes unresolved issues in hadron physics and outlines the opportunities and advances that are possible with facilities such as the EIC.
Over the last decades, tremendous progress has been made in understanding the 3D partonic structure of strongly-interacting systems like the nucleon in terms of generalized parton distributions (GPDs) and transverse-momentum-dependent parton distributions (TMDs). In this presentation, we briefly describe the status of this field and highlight some recent developments.
Fragmentation functions describe the formation of confined, final state hadrons out of asymptotically-free, high-energetic partons. They therefore help us understand the process of confinement. Additionally, they are also the most important tool to learn about the flavor, spin and transverse momentum of the fragmenting partons and thus access the corresponding parton distribution functions in semi-inclusive DIS or hadronic collisions. In addition to these two processes, fragmentation functions can be probed in electron-positron annihilation, particularly at the B factories, where the absence of hadrons in the initial state provide the cleanest environment to study hadronization.
The latest status of fragmentation function measurements will be reported.
Many interactions with nuclei can be described in terms of convolutions of universal parton distributions. These parton distributions describe the way quarks and gluons conspire to create the hadrons. Over the past decade these distributions have been inferred from matrix elements calculating with Lattice QCD. These matrix elements are similar convolutions of the parton distribution as cross sections. Even more the Lattice QCD matrix elements can be included as prior information in global analysis of experimental cross sections. The complementary information gives improved results than either could individually.
AMBER is a new fixed-target experiment at the CERN/SPS for the study of
Hadron Physics, thanks to a versatile beamline capable of providing muon and hadron beams over a wide energy range and a multipurpose modular spectrometer. The emergence of hadron mass phenomenom, central for our undertanding of QCD, can be experimentally addressed from the AMBER measurements of hadron radii, polarizabilities, form factors and distribution functions.
The pion and kaon induced Drell-Yan processes will be measured, providing input for the extraction of these ligh mesons parton distribution functions and studies of their transverse motion dependence. Sea to valence separation is accessed from the use of both beam charges. A measurement of direct photon production in meson-nucleon collisions allows to infer on the gluon contribution. A first-ever measurement of the kaon polarizabilities, accessed from the Primakoff reaction, complements the
characterization of kaons in the low energy regime.
A rich program on hadron spectroscopy in the light and strange meson sector is proposed. Additionally a series of unique hadron charge radii measurements are planned. The already approved high energy muon-proton elastic scattering study will address the long standing issue of the proton charge radius. The pion and kaon charge radii may be accessed from the elastic scattering on the electron cloud of target nuclei in inverse
kinematics.
Finally, AMBER measures the antiproton production cross section in proton on Helium and proton on Hydrogen targets. A beam energy scan in the range 60 to 250 GeV is performed. The precise knowledge of these cross sections is a necessary input for the interpretation of antiproton cosmic fluxes in the context of Dark Matter searches.
The Generalized Parton Distributions (GPDs) paradigm has profoundly renewed the understanding of the nucleon structure. As describing the correlations between partons, GPDs allow us to access static and dynamical information about the nucleon structure, ultimately learning about the mechanics of Quantum Chromodynamics. This comprises the total angular momentum of the nucleon carried by the quarks, the distribution of forces experienced by partons inside the nucleon or the gravitational form factors of the nucleon. This presentation will focus on the new experimental results about GPDs from the 12 GeV CEBAF (Continuous Electron Beam Accelerator Facility) and the future measurement projects with an emphasis on the possibilities offered by the perspective of positron beams at CEBAF.
The polarizabilities of a composite system such as the proton are elementary structure constants. They describe its response to an external electromagnetic (EM) field and quantify the deformation of the charge and magnetization distributions inside the proton caused by the electric or magnetic field, respectively. When studied through the virtual Compton scattering process, the virtuality of the photon gives access to the generalized polarizabilities and allows to map out the resulting deformation of the densities in a proton subject to an EM field. These measurements provide unique access to the underlying system dynamics and are a key for decoding the proton structure in terms of the theory of the strong interaction that binds its elementary quark and gluon constituents together. Of particular interest are puzzling measurements of the proton's electric generalized polarizability, that have challenged the theoretical predictions in recent years. This talk will present an overview on the topic, followed by the discussion of new results and of future prospects.
I will present some recent lattice QCD results on parton distribution functions, generalized parton distribution functions and distribution amplitudes. I will focus on results obtained using perturbative matching coefficients computed beyond the next-to-leading order in the strong coupling, specifically using next-to-next-to-leading order matching coefficients as well as incorporating various resummations.
Generalized parton distributions (GPDs) are important quantities that characterize the 3-D structure of hadrons and complement the information extracted from TMDs. They provide information about the partons’ momentum distribution and also on their distribution in position space. The non-perturbative part of the cross-section of high-energy processes may be expanded in terms of the process's large energy scale. This gives rise to a tower of distribution functions labeled by their twist (mass dimension minus spin). The leading twist (twist-2) contributions have been at the center of experimental measurements, theoretical investigations, and lattice QCD calculations. It has been recognized that twist-3 contributions to distribution functions can be sizable and should not be neglected. However, it is challenging to disentangle them experimentally from their leading counterparts, posing limitations on the structure of the proton.
Most of the information from lattice QCD is on the Mellin moments of GPDs, namely form factors and their generalizations. Calculating the x-dependence of GPDs from lattice QCD has become feasible in the last few years due to novel approaches. In this work, we employ the approach of quasi-distributions, which relies on matrix elements of fast-moving hadrons coupled to non-local operators. The quasi-distributions are matched to the light-cone distributions using Large Momentum Effective Theory (LaMET). The approach has been extensively used for twist-2 PDFs, and is now extended to twist-2 GPDs. More recently, the feasibility of the approach for twist-3 PDFs and GPDs was discussed. In this talk, we present an overview of selected results on x-dependent GPDs. This demonstrates the potential of lattice QCD calculations to complement other theoretical and experimental efforts toward the 3-D structure of hadrons.
In this presentation we would like to determine the properties of the lightest resonance in
the baryonic sector of QCD: the Delta(1232) resonance. Using two-hadron operators we calculate the finite volume QCD energy spectrum of $\pi-N$ in the $p$-wave. Using Luescher formalism we can predict the mass and the width of the delta resonance. In our analysis we probe the Luescher formula by including several volumes and pion masses down to the physical point. Having results from so many different parameters we are in a position to perform controlled chiral extrapolation of the delta resonance parameters.
We investigate contributions of excited states to nucleon matrix elements by studying the two- and three-point functions using nucleon and pion-nucleon interpolating fields. This study is made using twisted mass fermion ensembles with pion masses 346 MeV and 131 MeV. We construct an improved nucleon interpolating field with the generalized eigenvalue problem of two-point functions, and use it to study three-point functions. This method itself is also discussed in more details. We compare results obtained using these two ensembles and show preliminary results for nucleon charges.
In its report, the DPAP observed that ``there is significant support in the community and from the panel for a second general-purpose detector system to be installed in IR8 when resources are available.'' Such a detector would unlock the full discovery potential of the EIC by providing cross checks of results from ePIC, and reduce the combined systematic uncertainties. And in combination with a novel IR design, it could provide new and unique physics opportunities. In particular, the 2nd focus that has been incorporated into IR8 will greatly enhance far-forward detection, making it possible to detector protons and light nuclei all the way down to $p_T$ = 0, and significantly improve the ability to detect nuclear breakup. The latter would enhance the ability to veto breakup in exclusive and diffractive scattering on nuclei, and even make it possible to study the level structure (gamma spectroscopy) of isotopes produced in electron-ion collisions. Improved veto efficiency would make measurements like coherent diffraction on heavy nuclei much less challenging, and open the way for coherent DVCS not only on He, but also heavier nuclei such as $^{12}$C, $^{16}$O, or even Ca, and in the future maybe polarized $^7$Li.The combination of excellent low-t acceptance and coverage of the low-$Q^2$ region in-between photoproduction and 1 GeV$^2$, could also open up the possibility to study the elusive but important double-DVCS process at lower $x$, where rates are high. To fully take advantage of these and other new opportunities, the design of the IR and central detector should from the outset be designed to maximize the synergies. For instance, a higher magnetic field and improved tracking resolution would help studies of coherent diffraction, a high-resolution barrel EMcal would be important for DVCS on nuclei, and purpose-built and fully optimized muon detection would be necessary for double-DVCS - but also advantageous for, $\textit{e.g.}$, charmonium production.
The STAR experiment at the Relativistic Heavy-Ion Collider has recently released findings regarding exclusive coherent and incoherent photoproduction of $J/\psi$ mesons in Au+Au ultra-peripheral collisions (UPCs). In this talk, I will delve into the preliminary findings and examine how they influence our understanding of nuclear parton density within heavy nuclei and the event-by-event density fluctuation. The data will be rigorously assessed through quantitative comparisons with various models. Furthermore, I will outline prospective avenues for future research opportunities in UPCs.
Machine learning and AI are rapidly growing areas of research offering various avenues for exploration in high-energy nuclear physics. Novel tools including generative modeling, regression, and classification are poised to have a significant impact on theoretical and experimental research efforts. In this talk, I will review recent progress in the context of hadron structure, spin physics, uncertainty quantification, and simulations of collider experiments.
Different parts of the QCD phase diagram in the plane temperature - baryon density are expected
to be relevant for early stages of the Universe, neutron stars, heavy ion collision experiments.
From theoretical point of view a lot of information about the QCD phase diagram and QCD thermodynamics
can be extracted using lattice ab-initio methods. In this talk I present an overview of
the lattice studies of QCD phase diagram, current status of the field and possible future directions.
Quantum computing is rapidly emerging as a new method of scientific computing. It has the potential to solve problems much faster than it is possible with classical computers. Examples are applications in logistics, drug design, medicine finances and many more. In addition, with quantum computers problems can be tackled that are very hard or even impossible to address with classical computers.
After providing an introduction to quantum computing we will discuss why quantum computing can lead to a quantum advantage. We then give several real world examples of applications which can already now be computed on existing quantum computers.
The study of baryonic excited states provides fundamental information on the internal structure of the nucleon and on the degrees of freedom that are relevant for QCD at low energies. N* are composite states and are sensitive to details of the how quarks are confined. Meson photo-and electro-production reactions have provided complementary information on light quark baryon spectroscopy for several decades, but a crucial step forward has been the advent of large solid angle detectors, together with polarized beam and targets, which gave access to single and double polarization observables. The Q2 dependence of excited baryons electro-couplings has also been measured, gaining insight into the internal structure of baryons.
The CLAS12 energy upgrade opened an “exciting” new era in baryon spectroscopy, including the search for hybrid hadrons, in which gluons appear as constituent components beyond the valence quarks.
We present a data-driven analysis of the S-wave $\pi\pi\to\pi\pi$ and $\pi K \to \pi K$ reactions using the partial-wave dispersion relation. The contributions from the left-hand cuts are accounted for in a model-independent way using the Taylor expansion in a suitably constructed conformal variable. The fits are performed to experimental and lattice data. Our central result is the hadronic Omnes functions, which allows us to find the poles associated with the lightest scalar resonances $\sigma/f_0(500)$ and $\kappa/K^*_0(700)$ for the physical and unphysical pion mass values.
The obtained coupled channel $\{\pi\pi, K\bar{K}\}$ Omnes matrix is used to describe the double-virtual photon-photon scattering to two pions, which is required for the dispersive implementation of the $f_0(980)$ resonance to $(g-2)_\mu$. In addition, we consider the $a_0(980)$ resonance. Since the hadronic data in the $I=1 \{\pi\eta, K\bar{K}\}$ channel is not available, the Omnes function is obtained using the fits to the different sets of experimental data on two-photon fusion processes with $\pi\eta$ and $K\bar {K}$ final states.
The US Nuclear Physics community recently completed its Long Range Plan process. The US Nuclear Science Advisory Committee (NSAC), a federal advisory committee appointed jointly by the US Department of Energy, Office of Science, and Directorate for Mathematical and Physical Sciences, the US National Science Foundation, approved the 2023 Long Range Plan "A New Era of Discovery - 2023 Long Range Plan for Nuclear Science" on October 4, 2023. In this report, several fundamental questions in hadron physics have been identified. In this talk, I will discuss how these questions will be addressed in the coming decade and beyond both at existing facilities, and new facilities under construction including new detector(s) proposed for the existing facilities. Synergies with other subfields of nuclear physics, and physics in general will be touched upon as well.