Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session KC: 3D Parton Structure of Hadrons: Transverse Momentum Distributions I |
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Chair: Christopher Dilks, Duke University Room: Studio 2 |
Wednesday, October 13, 2021 11:30AM - 11:42AM |
KC.00001: Semi-Inclusive Deep Inelastic Scattering on Transversely Polarized Neutrons Using the BigBite and Super BigBite Spectrometers in Jefferson Lab's Hall A Andrew J Puckett Transverse target single-spin asymmetries (SSAs) in the single-hadron semi-inclusive lepton-nucleon deep inelastic scattering (SIDIS) process have attracted increasing attention since the discovery of non-zero Collins and Sivers effects in SIDIS on transversely polarized protons by the HERMES and COMPASS collaborations about a decade ago. Qualitatively, the Collins effect measures the correlation between the transverse polarization of the struck quark and that of the target nucleon, while the Sivers effect measures the correlation between the transverse momentum of the struck quark and that of the target nucleon. To go beyond initial exploration and discovery of these effects to precision measurement and detailed mapping of the asymmetries requires high-luminosity facilities with high-performance polarized targets and excellent particle detection, tracking, and identification capabilities. Experiment E12-09-018 was approved by the Jefferson Lab Program Advisory Committee for 64 days of beam time to measure SIDIS SSAs on a high-luminosity polarized helium-3 target in JLab's Hall A, using the newly constructed Super BigBite Spectrometer for hadron detection, and the upgraded BigBite spectrometer for electron detection. In this talk, I will present an overview of the experiment, its status, and its expected physics results. |
Wednesday, October 13, 2021 11:42AM - 11:54AM |
KC.00002: Recent HERMES results on spin asymmetries in semi-inclusive deep-inelastic scattering Gunar Schnell After 50 years of investigations, the nucleon is still far from being understood and continues to represent a unique test bench for QCD. Despite the enormous progresses achieved in five decades of deep-inelastic scattering (DIS) experiments, a number of crucial open questions are still on the carpet and subject of intense theoretical and experimental studies. In the last two decades, semi-inclusive DIS was established as a unique tool for the study of the non-collinear structure of nucleons, involving the parton transverse momentum pT as an additional degree of freedom. Requiring the detection of at least one final state-hadron in coincidence with the scattered lepton, it opened the way not only to measure of the chiral-odd transversity distribution, the last missing leading-twist collinear parton distribution function, but also to a variety of new pT-dependent PDFs, known as TMDs. Describing correlations between the quark transverse momentum and the quark or the nucleon spin, TMDs account for a number of intriguing effects observed in polarized and unpolarized reactions, and allow for a 3-dimensional description of the nucleon in momentum space. Furthermore, they could provide insights into the yet unmeasured quark orbital angular momentum. |
Wednesday, October 13, 2021 11:54AM - 12:06PM |
KC.00003: Investigating Transversity and Fragmentation Functions with Hadrons in Jets at STAR James L Drachenberg The Solenoidal Tracker at RHIC (STAR) collaboration investigates nucleon spin structure through collisions of spin-polarized beams of protons. One way STAR accesses the transversity distribution function is through the “Collins mechanism,” measuring spin-dependent azimuthal distributions of hadrons within jets from transversely polarized proton collisions. Data from STAR provide access to transversity over a range of x complementary to semi-inclusive deep inelastic scattering (SIDIS) experiments but at much higher Q2. STAR data at √s = 500 GeV and preliminary results at 200 GeV suggest that the universality of the Collins mechanism extends to proton-proton collisions, as it does in SIDIS and e+e-. The STAR data provide unique insight to the in-jet transverse momentum dependence of the Collins asymmetry, crucial for a deeper understanding of the Collins fragmentation function. Furthermore, spin-averaged multiplicities of hadrons-in-jets from the same datasets will provide unique insight into unpolarized fragmentation functions. The STAR Collins asymmetry data will be presented and discussed in context with recent global transversity analyses and model calculations. |
Wednesday, October 13, 2021 12:06PM - 12:18PM |
KC.00004: Transverse Single Spin Asymmetry of Heavy Flavor Electrons in 200 GeV p+p↑ Collisions at Midrapidity from PHENIX Dillon Fitzgerald Understanding the transverse spin and momentum structure of the proton is of great interest to the nuclear physics community and it is one of the main goals of the spin physics program at the Relativistic Heavy Ion Collider (RHIC). Transverse single spin asymmetry measurements for particles produced in proton-proton collisions provide insight into initial and final state spin-momentum and spin-spin correlations of partons within hadrons. In particular, electrons from heavy flavor decays provide access to initial state spin-momentum correlations of gluons in the proton. Electrons are measured at midrapidity at PHENIX using the central arm spectrometers which consist of an electromagnetic calorimeter, a ring-imaging Cherenkov detector, as well as drift and pad chambers. In addition, the silicon vertex detector is used in order to veto background from conversion electrons. Recent results for the transverse single spin asymmetry of heavy flavor electrons from the 2015 running period (200 GeV p+p↑) will be presented. |
Wednesday, October 13, 2021 12:18PM - 12:30PM |
KC.00005: Phenomenology of Transverse Momentum Distributions within the Jefferson Lab Angular Momentum (JAM) Collaboration framework Alexei Prokudin, Nobuo Sato, Daniel Pitonyak, Leonard Gamberg, Eric Moffat, Patrick C Barry, Wally Melnitchouk I will present highlights of recent developement of TMD phenomenology and extraction of TMD distribution and fragmentation functions within JAM framework. |
Wednesday, October 13, 2021 12:30PM - 12:42PM |
KC.00006: Update on the JAM Global Analysis of SSAs Daniel Pitonyak, Michel J Malda, Joshua A Miller, Alexei Prokudin, Nobuo Sato The analysis of single transverse-spin asymmetries (SSAs) gives us tremendous insight into the internal structure of hadrons. For example, the Sivers and Collins effects in semi-inclusive deep-inelastic scattering (SIDIS), Sivers effect in Drell-Yan, and the Collins effect in electron-positron annihilation have been widely investigated over many years in order to perform 3D momentum-space tomography. In addition, observables like AN in proton-proton collisions are of interest due to their sensitivity to quark-gluon correlations. In this talk I will discuss results, and give an update on, our global fit of SSA data from SIDIS, Drell-Yan, e+e− annihilation into hadron pairs, and proton-proton collisions. This includes the impact of new HERMES and STAR data on our analysis as well as lattice data for the tensor charge. I will also mention future directions for the JAM global analysis of SSAs. |
Wednesday, October 13, 2021 12:42PM - 12:54PM |
KC.00007: Improved Theory for Azimuthal Asymmetries in Semi-Inclusive DIS Markus A Ebert, Anjie Gao, Iain W Stewart Fully differential measurements of the Semi-Inclusive DIS (SIDIS) process with polarized beams provide important information on the three-dimensional structure of hadrons. In particular, azimuthal asymmetries of the fragmenting hadron probe interesting new correlations between partons in the system through novel hadronic distribution functions. In the framework of factorization for transverse momentum distributions (TMDs) some key asymmetries start at subleading order in the power expansion, where the formalism needed to fully relate observables and distributions is not yet under control, being primarily at tree level in the parton model. In this talk I utilize the soft collinear effective theory formalism to answer a few open questions, including providing generalized definitions of the distribution functions that are valid beyond tree level, giving a proof of completeness of the basis of functions, and providing a description of soft dynamical effects. These results enable a QCD description of SIDIS azimuthal asymmetries beyond tree level, and hence provide a framework for systematically improvable relations to the underlying distributions. |
Wednesday, October 13, 2021 12:54PM - 1:06PM |
KC.00008: Abstract Withdrawn
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Wednesday, October 13, 2021 1:06PM - 1:18PM |
KC.00009: Online Reconstruction on GPUs for J/ψ TSSA Study at SpinQuest Catherine Ayuso The E1039/SpinQuest experiment is a transversely polarized fixed target experiment at Fermi National Accelerator Laboratory aiming to explore the sea quark and gluon Sivers functions via the measurement of the transverse single spin asymmetry (TSSA) for a number of physics processes including J/ψ, ψ' and Drell-Yan production. The experiment employs a 120-GeV extracted proton beam colliding with transversely-polarized NH3 and ND3 cryogenic targets and its spectrometer is optimized to detect the oppositely-charged muon pair output of these processes. In pursuit of these asymmetry measurements, we are developing an advanced graphical processing unit (GPU) based multi-threaded framework that allows for an efficient parallelization of the online data processing flow and track reconstruction along with diagnostics and visualization tools. In this talk, I will report the plans to complete the optimization of the offline track reconstruction in GPU by this early autumn to reach real-time data visualization and monitoring. Moreover, I will present results estimating the anticipated precision of TSSA measurement via J/ψ production from the first SpinQuest production data. |
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