Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session JE: Mini-symposium on Orbital Motion of Quarks in Hard Scattering |
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Sponsoring Units: DNP JPS Chair: Toshi-Aki Shibata, Tokyo Institute of Technology Room: Ritz-Carlton Hotel Amphitheatre |
Thursday, September 22, 2005 9:00AM - 9:30AM |
JE.00001: Measurements of quark transversity and orbital motion in hard scattering Invited Speaker: The spin structure of nucleon has been one of the most important topics of QCD for about two decades. Recent results in hard scattering processes from the various experiments shed light on `quark transverse motion' for understanding the structure of nucleon. It implies that parton distribution and fragmentation functions are extended so that the transverse momentum of the parton is incorporated into the framework. \\ Single spin azimuthal asymmetries of hadron production in polarized lepton deep inelastic scattering at HERMES, JLab and COMPASS offer an access to such distribution functions, quark transversity and Sivers function, in conjunction with the corresponding fragmentation function. Measurements in hadron collisions such as at a proton collider at RHIC are also essential approaches to study these quantities. \\ One of the novel fragmentation function, Collins function, could be extracted in electron-position collider experiments. The expected results from BELLE would be a key for the extraction of the quark transversity from the experimental observables in other experiments. \\ Generalized parton distribution (GPD) has been proposed to unify the standard quark distribution functions and the nucleon form factors. It was also pointed that the 2nd moment of GPDs is related with orbital angular moment of the parton and can be extracted from hard exclusive productions, such as deeply virtual compton scattering (DVCS). The measurements of hard exclusive photon or meson productions have been performed at HERMES and JLab. \\ Recent experimental progress on these topics and its interpretation are presented. [Preview Abstract] |
Thursday, September 22, 2005 9:30AM - 9:45AM |
JE.00002: GPDs and single-spin asymmetries Matthias Burkardt Generalized parton distributions (GPDs) contain a wealth of information about hadron structure. I will focus on the connection between GPDs and impact parameter dependent parton distributions. For transversely polarized targets, the distribution of partons as a function of the impact parameter shows a significant deviation from axial symmetry. Together with attractive final state interactions this provides a very intuitive explanation for the observed single-spin asymmetry (Sivers effect) in semi-inclusive deep-inelastic scattering experiments (HERMES). Chirally odd GPS describe the quark transversity distribution for an unpolarized target. The same mechanism that gives rise to the Sivers effect may also give rise to the Boer-Mulders effect, except that sign and magnitude are now governed by chirally odd GPDs. The same linear combination of chirally odd GPDs that governs the quark transversity distribution for an unpolarized target can also be used to determine the correlation between quark angular momentum and transversity. [Preview Abstract] |
Thursday, September 22, 2005 9:45AM - 10:00AM |
JE.00003: GPD extraction - Experimental aspects Wolf-Dieter Nowak Generalized Parton Distributions are very briefly introduced. The observables in Deeply Virtual Compton Scattering and Deeply Virtual Meson Production are explained, and the complementary ways they offer to access various GPDs. First experimental results from HERMES and JLAB are reviewed and a collaborative effort is recommended towards a global analysis of GPDs. [Preview Abstract] |
Thursday, September 22, 2005 10:00AM - 10:15AM |
JE.00004: Study of Generalized Parton Distributions at Jefferson Lab Latifa Elouadrhiri Generalized Parton Distributions (GPDs) provide a rich and unifying picture of the nucleon structure. The GPDs can be accessed through hard scattering processes such as Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP). Experiments are starting to test these concepts. I will present first results from experiments conducted at Jefferson Lab and outline the future program with 12 GeV upgrade. [Preview Abstract] |
Thursday, September 22, 2005 10:15AM - 10:30AM |
JE.00005: Generalized Parton Distributions in Nuclei Simonetta Liuti We will present an analysis of the structure of generalized parton distributions in spin $0$ nuclei within a microscopic approach for nuclear dynamics. GPDs can be used on one side as tools to unravel the deep inelastic transverse structure of nuclei in terms of both transverse spatial and transverse momentum degrees of freedom. On the other hand, one can obtain information on GPDs themselves by observing how they become modified in the nuclear environment. Our study encompasses several nuclear observables: from Color Transparency, to nucleon overlap probabilties, to Mellin moments in nuclei, with particular emphasis on the behavior with the four-momentum transfer $t$ of the total momentum carried by quarks in a nucleus. The latter provides an important element for the evaluation of nuclear hadronization phenomena which are vital for interpreting current and future data at RHIC, HERMES and Jefferson Lab. [Preview Abstract] |
Thursday, September 22, 2005 10:30AM - 10:45AM |
JE.00006: Study of nucleon spin structure with a transversely polarized target in COMPASS Takahiro Iwata The nucleon spin structure is studied in COMPASS at CERN by the measurement of the double spin asymmetry of the semi inclusive deep inelastic scattering of a polarized muon at 160 GeV/c off a polarized $^{6}$LiD target. The target can be polarized transversely, as well as longitudinally, with respect to the longitudinally polarized muon beam. This allows the measurement of the Collins and Sivers asymmetries and two-hadron production asymmetries. The Collins and the two-hadron production asymmetries have a connection to the transverse spin distribution function $\Delta _T q\left( x \right)$ , referred to as transversity. Approximately 20{\%} of the beam-time in 2002, 2003 and 2004 was spent in the transverse configuration. The preliminary results of the analysis of the data obtained in 2002 and 2003 are presented. [Preview Abstract] |
Thursday, September 22, 2005 10:45AM - 11:00AM |
JE.00007: Accessing quark orbital motion in semi-inclusive DIS experiments at Jefferson Lab Hall A and Hall C. Xiaodong Jiang A program of semi-inclusive deep-inelastic scattering experiments at Jefferson Lab Hall A and Hall C has been developed to access quark orbital motion in a nucleon. This program includes: 1. Single-spin asymmetry $A^n_{UT}$ measurements in Jefferson Lab Hall A through $\vec{n}(e,e^\prime \pi^\pm)$ reactions on a transversely polarized $^3$He target to access quark transversity distributions in the neutron. 2. Single-spin asymmetry $A^p_{UT}$ measurements through $\vec{p}(e,e^\prime \pi^\pm)$ reactions on a transversely polarized proton target in Jefferson Lab Hall C to access quark transversity distributions in the proton. 3. Double-spin asymmetry $A^p_{LT}$ measurements with a longitudinally polarized electron beam scattered off a transversely polarized proton target in $\vec{p}({\vec e},e^\prime \pi^\pm)$ reactions in Jefferson Lab Hall C to access the leading-twist quark transverse-momentum dependent distribution functions $g^q_{1T}(x)$. [Preview Abstract] |
Thursday, September 22, 2005 11:00AM - 11:15AM |
JE.00008: Factorization for Semi-inclusive Processes Feng Yuan In this talk, I will address the important question for the semi-inclusive processes: the factorization. I will demonstrate the QCD factorization works for these processes, and the cross sections can be factorized into transverse momentum dependent parton distributions and/or fragmentation functions, soft and hard factors. [Preview Abstract] |
Thursday, September 22, 2005 11:15AM - 11:30AM |
JE.00009: Single-spin asymmetries of two hadron production in polarized deep inelastic scattering at HERMES Tomohiro Kobayashi HERMES has been taking data with a 27.6GeV positron beam at HERA and polarized gas targets (H, D). A pion pair produced in DIS was detected. Single spin asymmetries in the azimuthal distribution around the virtual photon direction have been measured. These asymmetries can be explained in terms of quark transversity distribution in conjunction with the interference fragmentations. The transversity is one of the three fundamental leading twist distribution functions. The other ones are the unpolarized quark number density and the helicity distribution function. Until recent years, the transversity has not been measured due to experimental difficulties arising from its chiral odd nature. It requires other chiral odd object in the process such as the interference fragmentation function. First results for these measurements will be shown. [Preview Abstract] |
Thursday, September 22, 2005 11:30AM - 11:45AM |
JE.00010: Measurements of chiral-odd fragmentation functions at Belle Akio Ogawa The Collins fragmentation function connects the transverse quark spin with a measurable azimuthal dependence of the produced hadrons around the quark's momentum axis. Therefore, it can be used as a transverse spin analyzer in semi-inclusive DIS and proton-proton collisions. While in those measurements the Collins function appears convoluted with the so far unknown quark transversity distribution, it is directly accessible in e+e- collisions, where one measures a combination of a quark and an antiquark fragmentation function. We present measurements of azimuthal asymmetries for certain charge combinations of hadrons in which it is possible to minimize other systematic effects that could obscure the effect of spin-dependent fragmentation. [Preview Abstract] |
Thursday, September 22, 2005 11:45AM - 12:00PM |
JE.00011: Single Spin Asymmetry with a Transversely Polarized Hydrogen Target at HERMES Toshi-Aki Shibata Single spin asymmetry in meson productions with a transversely polarized hydrogen target was measured by HERMES experiment at DESY-HERA. Deep inelastic scattering of the 27.6 GeV positron off an internal hydrogen gas target was used. In addition to the scattered positron, produced hardons were detected. Pions, kaons and protons were identified with Ring Imaging Cherenkov Couonter(RICH). Azimuthal angle dependence of produced mesons was analysed in terms of Collins effect and Sivers effect. The separation of these effects became possible for the first time because of semi-inclusive measurement. Collins effect provides an access to a new, so far unmeasured structure function from which one can extract the transversity quark distribution. Sivers effect might have a link to the orbital motion of quark. The orbital angular momentum of quarks in the proton could contribute to the proton spin. In view of `nucleon spin problem' started by EMC, the orbital angular momentum of quarks is an important subject to be studied. [Preview Abstract] |
Thursday, September 22, 2005 12:00PM - 12:15PM |
JE.00012: Transversity in single spin and azimuthal asymmetries Leonard Gamberg One of the persistent challenges confronting the QCD improved parton model is to account for the large azimuthal and single spin asymmetries that emerge in semi-inclusive electro-production, and di-lepton production in Drell Yan scattering. Going beyond the collinear approximation in PQCD recent progress has been achieved in characterizing these asymmetries in terms of absorptive scattering. Central to this understanding are the correlations between transverse momentum and transverse spin in QCD hard scattering. These asymmetries provide a window to explore novel quark distribution and fragmentation functions which constitute essential information about the spin, transversity and generalized momentum structure of hadrons. Along with the chiral odd transversity time-reversal even (\textit{T-even}) distribution function, existence of the time reversal odd (\textit{T-odd}) distribution and fragmentation functions can provide an explanation for the substantial asymmetries that have been observed in these scattering processes. [Preview Abstract] |
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