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1. Proton form factor ratio \mu_p G_E^p/G_M^p from double spin asymmetry

   Liyanage, A. ; Armstrong, W. ; Kang, H. ; Maxwell, J. ; Mulholland, J. ; Ndukum, L. ; Ahmidouch, A. ; Albayrak, I. ; Asaturyan, A. ; Ates, O. ; et al ( March 2020 , Physical review)

   The ratio of the electric to magnetic form factors of the proton, μpGEp/GMp, has been measured for elastic electron-proton scattering with polarized beam and target up to four-momentum transfer squared Q2=5.66(GeV/c)2 using double spin asymmetry for target spin orientation aligned nearly perpendicular to the beam momentum direction. This measurement of μpGEp/GMp agrees with the Q2 dependence of previous recoil polarization data and reconfirms the discrepancy at high Q2 between the Rosenbluth and the polarization-transfer method with a different measurement technique and systematic uncertainties uncorrelated to those of the recoil-polarization measurements. The form factor ratio at Q2=2.06(GeV/c)2 has been measured as μpGEp/GMp=0.720±0.176stat±0.039sys, which is in agreement with an earlier measurement using the polarized target technique at similar kinematics. The form factor ratio at Q2=5.66(GeV/c)2 has been determined as μpGEp/GMp=0.244±0.353stat±0.013sys, which represents the highest Q2 measurement reached using double spin asymmetries with polarized target to date. 

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2. Global Analysis of SSAs and the Impact of the EIC and SoLID on Tensor Charge Extractions

   https://doi.org/10.21468/SciPostPhysProc.8.044  

   Pitonyak, Daniel ( January 2022 , SciPost Physics Proceedings)

   Single transverse-spin asymmetries (SSAs) give great insight into the 3-dimensional structure of hadrons. We report on the first global QCD analysis of SSAs in semi-inclusive deep-inelastic scattering, electron-positron annihilation, Drell-Yan, and single-inclusive proton-proton collisions. One byproduct of the analysis is an extraction of the transversity function, from which the nucleon tensor charges can be computed, and we find, for the first time, agreement with lattice QCD for these quantities. Based on this analysis, we perform an impact study of future data on extractions of the nucleon tensor charges. 

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3. Study of Drell-Yan dimuon production in proton-lead collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 8.16 TeV

   https://doi.org/10.1007/JHEP05(2021)182  

   Sirunyan, A. M. ; Tumasyan, A. ; Adam, W. ; Ambrogi, F. ; Bergauer, T. ; Dragicevic, M. ; Erö, J. ; Escalante Del Valle, A. ; Frühwirth, R. ; Jeitler, M. ; et al ( May 2021 , Journal of High Energy Physics)

   null (Ed.)

   A bstract Differential cross sections for the Drell-Yan process, including Z boson production, using the dimuon decay channel are measured in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of 8.16 TeV. A data sample recorded with the CMS detector at the LHC is used, corresponding to an integrated luminosity of 173 nb − 1 . The differential cross section as a function of the dimuon mass is measured in the range 15–600 GeV, for the first time in proton-nucleus collisions. It is also reported as a function of dimuon rapidity over the mass ranges 15–60 GeV and 60–120 GeV, and ratios for the p-going over the Pb-going beam directions are built. In both mass ranges, the differential cross sections as functions of the dimuon transverse momentum p T and of a geometric variable ϕ * are measured, where ϕ * highly correlates with p T but is determined with higher precision. In the Z mass region, the rapidity dependence of the data indicate a modification of the distribution of partons within a lead nucleus as compared to the proton case. The data are more precise than predictions based upon current models of parton distributions. 

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4. Inclusive photon production at forward rapidities in pp and p–Pb collisions at $$\sqrt{{{s}}_{\textrm{NN}}}={5.02}$$ TeV

   https://doi.org/10.1140/epjc/s10052-023-11729-y  

   Acharya, S. ; Adamová, D. ; Adler, A. ; Aglieri Rinella, G. ; Agnello, M. ; Agrawal, N. ; Ahammed, Z. ; Ahmad, S. ; Ahn, S. U. ; Ahuja, I. ; et al ( July 2023 , The European Physical Journal C)

   A study of multiplicity and pseudorapidity distributions of inclusive photons measured in pp and p–Pb collisions at a center-of-mass energy per nucleon–nucleon collision of$$\sqrt{s_{\textrm{NN}}}~=~5.02$$$\sqrt{s_{\text{NN}}}=5.02$ TeV using the ALICE detector in the forward pseudorapidity region 2.3 $$<~\eta _\textrm{lab} ~<$$$<{\eta }_{\text{lab}}<$ 3.9 is presented. Measurements in p–Pb collisions are reported for two beam configurations in which the directions of the proton and lead ion beam were reversed. The pseudorapidity distributions in p–Pb collisions are obtained for seven centrality classes which are defined based on different event activity estimators, i.e., the charged-particle multiplicity measured at midrapidity as well as the energy deposited in a calorimeter at beam rapidity. The inclusive photon multiplicity distributions for both pp and p–Pb collisions are described by double negative binomial distributions. The pseudorapidity distributions of inclusive photons are compared to those of charged particles at midrapidity in pp collisions and for different centrality classes in p–Pb collisions. The results are compared to predictions from various Monte Carlo event generators. None of the generators considered in this paper reproduces the inclusive photon multiplicity distributions in the reported multiplicity range. The pseudorapidity distributions are, however, better described by the same generators.

    

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5. Two-Photon Exchange Effects in Semi-Inclusive Deep-Inelastic Scattering on a Nucleon

   A. Afanasev, Stinson Lee ( January 2021 , APS)

   Deep-inelastic scattering of electrons on a nucleon is a primary source of information about parton distribution functions (PDF) and transverse momentum distributions (TMD). The calculation of the QED corrections to SIDIS with any predetermined accuracy is crucial for studies of the 3D structure of the nucleon at JLab and future Electron Ion Collider (EIC). A majority of approved physics experiments that will be running with 12-GeV electron beams at JLab to study the nucleon structure require per-cent level accuracies in the measurements of differential cross sections and polarization asymmetries. Neglecting electromagnetic corrections may lead to significant mis-interpretation of data. Analysis of T-odd singe spin asymmetries (SSA) in SIDIS, p (e, e'h) X, is based on an assumption that purely electromagnetic T-odd effects are negligible. 

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