Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session 2WJ: Polarized Drell-Yan Physics at Fermilab |
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Chair: Toshi-Aki Shibata, Tokyo Institute of Technology Room: Kona 3 |
Tuesday, October 7, 2014 2:00PM - 2:30PM |
2WJ.00001: Single transverse-spin asymmetry in QCD Invited Speaker: Yuji Koike So far large single transverse-spin asymmetries (SSA) have been observed in many high-energy processes such as semi-inclusive deep inelastic scattering and proton-proton collisions. Since the conventional parton model and perturbative QCD can not accomodate such large SSAs, the framework for QCD hard processes had to be extended to understand the mechanism of SSA. In this extended frameworks of QCD, intrinsic transverse momentum of partons and the multi-parton (quark-gluon and pure-gluonic) correlations in the hadrons, which were absent in the conventional framework, play a crucial role to cause SSAs, and well-defined formulation of these effects has been a big challenge for QCD theorists. Study on these effects has greatly promoted our understanding on QCD dynamics and hadron structure. In this talk, I will present an overview on these theoretical activity, emphasizing the important role of the Drell-Yan process. [Preview Abstract] |
Tuesday, October 7, 2014 2:30PM - 3:00PM |
2WJ.00002: Nucleon spin decomposition and orbital angular momentum in the nucleon Invited Speaker: Masashi Wakamatsu To get a complete decomposition of nucleon spin is a fundamentally important homework of QCD. In fact, if our researches end up without accomplishing this task, a tremendous efforts since the 1st discovery of the nucleon spin crisis would end in the air. We now have a general agreement that there are at least two physically inequivalent gauge-invariant decompositions of the nucleon. In these two decompositions, the intrinsic spin parts of quarks and gluons are just common. What discriminate these two decompositions are the orbital angular momentum (OAM) parts. The OAMs of quarks and gluons appearing in the first decomposition are the so-called ``mechanical'' OAMs, while those appearing in the second decomposition are the generalized (gauge-invariant) ``canonical'' ones. By this reason, these decompositions are broadly called the ``mechanical'' and ``canonical'' decompositions of the nucleon spin. Still, there remains several issues, which have not reached a complete consensus among the experts. (See the latest recent [1-2]). In the present talk, I will mainly concentrate on the practically most important issue, i.e. which decomposition is more favorable from the observational viewpoint. There are two often-claimed advantages of canonical decomposition. First, each piece of this decomposition satisfies the SU(2) commutation relation or angular momentum algebra. Second, the canonical OAM rather than the mechanical OAM is compatible with free partonic picture of constituent orbital motion. In the present talk, I will show that both these claims are not necessarily true, and push forward a viewpoint that the ``mechanical'' decomposition is more physical in that it has more direct connection with observables. I also emphasize that the nucleon spin decomposition accessed by the lattice QCD analyses is the ``mechanical'' decomposition not the ``canonical'' one. The recent lattice QCD studies of the nucleon spin decomposition are also briefly overviewed.\\[4pt] [1] E.~Leader and C.~Lorc\'{e}, arXiv : 1309.4235 [hep-ph] (2013).\\[0pt] [2] M.~Wakamatsu, Int. J. Mod. Phys. A29, 1430012 (2014). [Preview Abstract] |
Tuesday, October 7, 2014 3:00PM - 3:30PM |
2WJ.00003: Probing Valence Quark's Sivers' Distribution with Polarized-Beam Drell-Yan Invited Speaker: Paul E. Reimer The E-906/SeaQuest experiment at Fermilab is collecting unpolarized Drell-Yan and $J/\psi$ data. These data will elucidate aspects of the antiquark distributions in nucleon and nuclear structure, including the the flavor asymmetry in the light quark sea and the EMC effect in the sea distributions. Presently, neither the beam nor the target is polarized in SeaQuest. With little or no modification to the spectrometer, the addition of either a polarized target or beam will unleash exciting new opportunities to examine the spin structure of the valence (polarized beam) and sea (polarized target) quark structure of the proton, including the valence and sea quark Sivers' distributions. QCD predicts that the Sivers' distribution measured with polarized Drell-Yan is equal in magnitude but opposite in sign to the Sivers' distribution measured by semi-inclusive DIS. After a review of SeaQuest's current physics program and spectrometer status, this talk will focus on the achievements that will be made with the addition of a polarized beam from the Fermilab Main Injector, including a precise determination of the Sivers' distribution of a wide range of $x_{\textrm{Bj}}$ necessary for this comparison. [Preview Abstract] |
Tuesday, October 7, 2014 3:30PM - 4:00PM |
2WJ.00004: COFFEE BREAK
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Tuesday, October 7, 2014 4:00PM - 4:30PM |
2WJ.00005: Spin and Beam Dynamics at the Fermilab Main Injector Invited Speaker: Christine Aidala Initial studies performed by the Spin@Fermi collaboration for producing and maintaining a polarized proton beam at 120 GeV using a single Siberian snake in the Fermilab Main Injector have been promising. More detailed studies incorporating a single Siberian snake into the Main Injector lattice and a partial snake as well as pulsed quadrupoles into the Booster lattice are presently underway. The resulting beam and spin dynamics given specific new equipment configurations are being examined. The current status of these simulation studies will be presented. [Preview Abstract] |
Tuesday, October 7, 2014 4:30PM - 5:00PM |
2WJ.00006: Drell Yan at FNAL with a Polarized Target Invited Speaker: Andi Klein One of the continuing puzzles in QCD is the origin of the nucleon spin. All of the existing experimental data suggest that the contributions from the quark and gluon spins account only for about 50{\%} of the nucleon spin. In order to account for the remaining 50{\%}, one has to include the orbital angular momentum of the quarks and gluons. One way to establish if quarks carry significant angular momentum, is to perform a measurement of the Sivers function, which describes the correlation of the spin direction of the nucleon with the transverse momentum of the quark. We will describe the E1039 experiment at Fermilab, which will measure the Sivers asymmetry of the sea quarks via the Drell Yan process, using a 120 GeV unpolarized proton beam on a transversely polarized NH$_{\mathrm{3}}$ target. [Preview Abstract] |
Tuesday, October 7, 2014 5:00PM - 5:30PM |
2WJ.00007: Opportunities with polarized beam {\&} target Invited Speaker: Yoshiyuki Miyachi Single spin asymmetries in Drell-Yan (DY) scattering, which are going to be measured in the present and planned polarized DY experiments, gain further insight into the internal structure of the nucleon. For the novel Sivers distribution function, the possible sign change in DY and Semi-Inclusive Deep-Inelastic-Scattering (SIDIS) may be confirmed for the first time, which is a critical test of the transverse momentum dependent (TMD) factorization in QCD, and precise information on the sea quarks, which are less sensitive in DIS, will be obtained. Since DY is one of the cleanest hard scattering processes, where no hadron fragmentation involved, it does not require information on hadron fragmentation functions (FF) to extract TMD PDF from the observed azimuthal amplitudes, where TMD PDF appears along with a corresponding FF in the case of SIDIS. Various azimuthal amplitudes of un-polarized cross section and singly-polarized or doubly-polarized cross section asymmetries in SIDIS have been measured. Double spin asymmetry in DY where beam and target are polarized is another unique tool to study TMD PDFs directly and it is a complementary measurement to SIDIS toward the complete description of the nucleon. Single spin asymmetries of the W-production cross section in the polarized proton-proton collision, recently measured at the RHIC/spin program, indicate the possible quark flavor symmetry violation in the polarized light-sea. Similar flavor asymmetry in the un-polarized light-sea, known as violation of the Gottfried sum rule, is currently studied at the on-going DY experiment SeaQuest at Fermilab. The observed flavor asymmetries can be a key to understand non-perturbative structure of the nucleon. With double spin asymmetry measurements in longitudinally polarized DY the flavor asymmetry in the polarized sea can be confirmed. In the presentation, physics cases which can be studied in doubly polarized DY and related topics will be discussed. [Preview Abstract] |
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