Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session 2WG: Workshop on Transverse Spin and the Transverse Structure of the Nucleon |
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Chair: Toshi-Aki Shibata, Tokyo Institute of Technology Room: Kings 2 |
Tuesday, October 13, 2009 2:00PM - 2:30PM |
2WG.00001: Transversity at HERMES Invited Speaker: A brief introduction to the transversity distribution function, denoted $\delta q$ or $h_1$, will be presented. Access to $h_1$ can be gained by measurement of Fourier moments of single-spin asymmetries in semi-inclusive production of mesons on a transversely polarized hydrogen target. Other transverse momentum dependent functions can also be accessed through various azimuthal moments. Preliminary results from HERMES will be presented. The experimental results from COMPASS will also be shown for comparison. An additional observable, the pion yield difference, will also be presented, as this observable has negligible contribution from vector meson decay. [Preview Abstract] |
Tuesday, October 13, 2009 2:30PM - 3:00PM |
2WG.00002: Transverse Spin Measurements at RHIC Invited Speaker: Large single transverse spin asymmetries, $A_N$, for inclusive hadron production were first observed by the E704 collaboration at Fermi National Laboratory in polarized proton-proton collisions at a center of mass energy of $ \sqrt{s} = 20 $ \, GeV. Different mechanisms have been suggested to explain the origin of large single transverse spin asymmetries in hard scattering processes: Collins has shown that correlations between transverse quark spin and transverse hadron momentum in the final state hadron fragmentation process can give rise to single transverse spin asymmetries. Alternatively, Sivers has identified correlations between the initial state transverse proton spin and the intrinsic transverse momentum of quarks as possible source for the observed single spin asymmetries. At RHIC large $A_N$ for inclusive hadrons have been observed to persist at center of mass energies of $62.4$ \, GeV and $200$ \, GeV. In addition to precise measurements of $A_N$ for inclusive hadrons new ideas have been explored to explicitly separate single spin asymmetries from the Collins and Sivers mechanisms through measurements at RHIC. Examples include Sivers asymmetries in back-to-back correlation of opposing jet hemispheres, Sivers asymmetries in Drell Yan and jet-photon production and Collins- like asymmetries in di-hadron interference fragmentation. Present status and future plans based on increased luminosity and detector upgrades at RHIC will be presented. [Preview Abstract] |
Tuesday, October 13, 2009 3:00PM - 3:30PM |
2WG.00003: Theory of Transverse Spin and Transverse Structure of the Nucleon Invited Speaker: Large single transverse spin asymmetries (SSA) observed in various collision processes opened a new window to disentangle QCD dynamics and quark-gluon substructure of the nucleon. Since SSA is a ``naively T-odd'' observable, it can only occur as an interference between the scattering amplitudes which have different complex phases in a time-reversal invariant theory like QCD. A conventional framework for hard inclusive processes, i.e. perturbative QCD in the twist-2 level, can only give rise to a negligible asymmetry and thus can not explain the observed data. Understanding the origin of the large SSAs requires the extention of the framework of the QCD hard processes, and by now QCD mechanisms leading to large SSAs have been clarified in greater detail. These mechanisms based on different perspectives introduce new concepts describing the nucleon structure not present in the conventional parton model, such as ``parton's intrinsic transverse momentum'' and ``multi-parton correlations.'' Precise and unambiguous definition of these ideas requires much more careful theoretical analyses than the twist-2 case, in particular, in connection with the universality of the parton distribution/fragmentation functions, gauge invariance and factorization properties of the cross sections. In the literature, QCD mechanisms for SSAs are often classified into two categories. One is based on the (naively) ``T-odd'' distribution and fragmentation functions in the transverse momentum dependent (TMD) factorization approach. Sivers and Collins functions are typical examples for this one. The other one is based on the twist-3 quark-gluon (more generally, multi-parton such as triple-gluon) correlation functions in the collinear factorization approaches. The former mechanism can describe SSAs in the small-$p_T$ region ($p_T \ll Q$) as a leading-twist effect, while the latter one describes SSAs in the large $p_T$ region as a twist-3 effect. Both approaches have been applied to study SSAs in various processes, such as semi-inclusive deep-inelestic-scattering (SIDIS), Drell-Yan processes, $p^{\uparrow} p \to h X$ ($h=\pi,\ K\, D$ etc) etc, for which experimental measurements are ongoing at DESY, CERN, J-Lab and BNL-RHIC etc. Although the starting points of the analysis and the applicable kinematic region for these two mechanisms are different, they are shown to give identical SSAs in the intermediate region of $p_T$ for the ``Sivers'' type SSA. Universality of the TMD functions and the factorization property with TMD functions have been studied in detail. Gauge invariance and the factorization property of the twist-3 cross section in the latter approach is also understood. In this talk, I will first review recent developments in the theoretical frameworks for SSAs described above, and then I will present our recent works on SSAs based on the twist-3 mechanisms. I will discuss the azimuthal structure of the twist-3 single-spin-dependent cross section for SIDIS and $A_N$ for $p^{\uparrow} p\to h X$ including all kinds of pole contributions. [Preview Abstract] |
Tuesday, October 13, 2009 3:30PM - 4:00PM |
2WG.00004: COFFEE BREAK
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Tuesday, October 13, 2009 4:00PM - 4:30PM |
2WG.00005: Jefferson Lab Neutron Transversity Experiments (E06-010) Invited Speaker: Jefferson Lab Hall A ``Neutron Transversity'' experiment (E06-010) collected data between Oct. 2008 and Feb. 2009. An electron beam of 5.9 GeV energy was used to scatter from a transversely polarized neutron (3He) target. The scattered electrons were detected in coincidence with charged hadrons (pion or Kaon) in deep inelastic kinematics of x:0.1-0.4 with an average Q2 of 2.2 GeV2. The measured target single-spin asymmetries in semi-inclusive reactions allowed access to the quark transversity distributions as well as the T-odd Sivers distributions. The most recent status of physics analysis will be reported. [Preview Abstract] |
Tuesday, October 13, 2009 4:30PM - 5:00PM |
2WG.00006: Prospects in neutron transverse spin study with polarized 3He at 12 GeV Jefferson Laboratory Invited Speaker: Due to the unique ground state spin structure of the 3He nucleus, polarized 3He nuclear targets have been used widely in experiments ranging from measurements of the neutron electric and magnetic form factors to the study of the neutron spin structure. In this talk, I will discuss the recently completed neutron transversity experiment in Hall A at Jefferson Laboratory using a vertically polarized 3He target. This is the first time that a polarized 3He target has been used in probing the neutron transverse spin structure. I will focus in my talk the future prospects of neutron transverse spin study at 12-GeV Jefferson Laboratory after the energy upgrade. The work is supported by a U.S. Department of Energy grant DE-FG02-03ER41231. [Preview Abstract] |
Tuesday, October 13, 2009 5:00PM - 5:30PM |
2WG.00007: Drell-Yan Process and Transversity Invited Speaker: Boer-Mulders function, Sivers function and transversity are known as transverse momentum dependent parton distribution functions of the nucleon, {\bf TMD}. They have received much attention in recent years as they provide new perspectives on the hadron structure and QCD. Azimuthal distribution of cross section in Drell-Yan scattering, where quark and anti-quark annihilate and produce a charged lepton pair, has been measured in various experiments. A unique feature of the Drell-Yan process is that no fragmentation functions are involved to study TMD, unlike in deep inelastic scattering where hadron production is required. The azimuthal distribution in the Drell-Yan cross section would provide direct information on the Boer-Mulders function, and be complementing to the related measurements in the deep inelastic scattering. Sivers function and transversity play a role in transversely polarized Drell-Yan scattering. Single spin asymmetry of the Drell-Yan cross section is sensitive to the Sivers function, and the double spin asymmetry is proportional to the product of transversity distributions. Polarized Drell-Yan experiments have been planned at various laboratories. The experimental results related TMD from the Drell-Yan scattering experiments and future prospects will be discussed. [Preview Abstract] |
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