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 KF: Mini-Symposium on Hadron Structure and QCD in High Energy Processes III |
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Chair: Yuji Goto, RIKEN Room: Kohala 3 |
Saturday, October 17, 2009 9:00AM - 9:30AM |
KF.00001: Experimental quest for the proton spin structure -- past, present and future Invited Speaker: For the last 20 years there have been many great discoveries are made experimentally and theoretically, concerning on the spin structure of the nucleons, the fundamental bound states of the strong interaction. Motivated largely from the ``Spin Puzzle,'' many experimental plans emerged in early 90$^{th}$ to measure the gluon contribution to the proton spin, by hoping to solve the puzzle with gluons. After more than 10 years, the recent experimental outcomes from RHIC and other polarized deep-inelastic interactions set a stringent limit on the gluon polarization. Although further studies must be continues on the glues, the simplest solution to the spin puzzle seems to be fail, i.e., the spin structure of the proton is much richer than we thought. The scientific focus is now moving to the new direction. Keys are in our own findings on the way, namely, discoveries of finite Collins and Sivers effects and progress on deeply virtual Compton scattering both in theoretical and experimental sides. Based on these new discoveries, we now need to rebuild the long range plan toward the complete understanding of the proton spin structure. Discussions are planed to give the general overview of the past, and to hint future experiments utilizing the existing facilities and the electron icon collider. [Preview Abstract] |
Saturday, October 17, 2009 9:30AM - 9:45AM |
KF.00002: The Proton Spin Puzzle: Recent Results and Prospects from STAR at RHIC William Christie Polarized deep-inelastic lepton-nucleon scattering measurements have shown that a surprisingly small fraction of the proton spin is carried by quark and anti-quark spins. This observation has renewed the interest in proton spin structure, which is currently being pursued by experiments worldwide. One of the main objectives of the STAR experiment at Relativistic Heavy Ion Collider is to determine the polarization of gluons, Delta G, in the polarized proton. Our measurements use proton-proton collisions at high center-of-mass energies. STAR measurements of inclusive jet and pion probes, using data collected in the years 2003-2006 at 200 GeV center-of-mass energy, have placed constraints on Delta G for gluon momentum fractions, x, over the range of about 0.03 $<$ x $<$ 0.3. STAR has just completed a data taking period with substantially better statistics and has recorded also a first data sample at a higher beam collision energy of 500 GeV. The new 200 GeV data is expected to better constrain Delta G and, using correlated probes such as di-jets and photon-jets, to give insight also in its x-dependence. The 500 GeV data form the start of a program to delineate quark polarization by using leptonic decays of W-bosons as probes. I will present a summary of recent results and will discuss expectations from the 2009 data taking period as well as prospects for the further future. [Preview Abstract] |
Saturday, October 17, 2009 9:45AM - 10:00AM |
KF.00003: Measurements of the Gluon Polarization in the Nucleon at COMPASS Takahiro Iwata, Shigeru Ishimoto, Kaori Kondo, Norihiro Doshita, Takeo Hasegawa, Naoaki Horikawa, Tatsuro Matsuda, Takuma Michigami The gluon polarization in the nucleon has been investigated in COMPASS at CERN with a polarized muon beam and a longitudinally polarized deuteron target. The gluon polarization was determined by longitudinal double spin asymmetries for the photon-gluon-fusion (PGF) process. Identifying the PGF by detecting either a charm hadron( ``open charm''), namely D$^{0}$ meson decaying into charged K $\pi $, or two light hadrons with high Pt( ``high Pt hadron''), the gluon polarization values were extracted with a help of LO-QCD. In this talk, the final result from open charm events taken from 2002 to 2006 (all the deuteron data) and the recent results from high Pt hadrons taken from 2002 to 2004 will be presented. The former case, which is expected to be ideal process with less physical background, shows negative polarization with relatively large error due to limited statistics. While, the results from the high Pt hadron events giving smaller errors show small gluon polarization values around 0.1 for the gluon's Bjorken-x. [Preview Abstract] |
Saturday, October 17, 2009 10:00AM - 10:15AM |
KF.00004: Polarized gluon distribution from DIS and collider data Masanori Hirai, Shunzo Kumano We investigate the determination of the polarized gluon distribution by a global analysis using the DIS and the collider data. The polarized gluon distribution gives an important information about gluon contribution to the nucleon spin, however it has still large uncertainty. In the DIS experiments, the J-Lab provides the precise data in the large-$x$ and low- $Q^2$ region. The data is useful to determining the gluon distribution because the higher order contribution of the gluon is rather large at low $Q^2$. In addition, the collider experiment at the RHIC has measured the $\pi^0$ production process. Since the process is sensitive to the gluon distribution, the data has the strong constraint power on the determination. Therefore, we include these data in the global analysis. The DIS data suggest the positive value in the medium and large-$x$ region, however the RHIC data require the negative value in the small-$x$ region. So, the gluon distribution changes the sign around $x \sim 0.1$ at $Q^2=1$ GeV$^2$ We will discuss the behavior of the gluon distribution from the DIS and Collider data in the analysis. [Preview Abstract] |
Saturday, October 17, 2009 10:15AM - 10:30AM |
KF.00005: Dijet Cross Section and Longitudinal Double Spin Asymmetry Measurements in Polarized Proton-Proton Collisions at 200 GeV at STAR Matthew Walker The polarized gluon distribution function of the proton, $\Delta g(x)$, has been constrained by inclusive measurements from polarized proton-proton collisions at RHIC. Correlation measurements, such as the dijet measurement, provide access to the leading order parton kinematics, which provides sensitivity to the shape of $\Delta g(x)$. STAR's large acceptance electromagnetic calorimetry and tracking make it well suited for this measurement. The status of the dijet cross-section analysis from the 2005 and 2006 RHIC data sets and of the longitudinal double spin asymmetry analysis from the 2006 data set, all at mid-rapidity, will be presented. [Preview Abstract] |
Saturday, October 17, 2009 10:30AM - 10:45AM |
KF.00006: Probing the Spin Structure of the Proton via Heavy Flavor Production at PHENIX Han Liu At RHIC energy, heavy flavor production is dominated by gluon gluon fusion. So measurements of spin asymmetries in heavy flavor production are expected to provide valuable new information about the spin structure of the nucleon. In particular, the longitudinal double spin asymmetries ($A_{LL}$) will allow us to directly probe the polarized gluon distribution $\Delta G(x)$ and the dynamics of spin dependent QCD hard-scattering beyond light hadrons and jet productions. The transverse single spin asymmetries ($A_N$) are sensitive to the gluon Sivers function which is related to the orbital angular momentum of gluons inside the proton. Furthermore, $A_N$ in J/$\psi$ production can give us more insight on the production mechanism of quarkonia. The latest PHENIX results on $A_LL$ and $A_N$ of J/$\psi$ and open heavy flavor will be presented in this talk. [Preview Abstract] |
Saturday, October 17, 2009 10:45AM - 11:00AM |
KF.00007: Study of \textit{J/$\psi $} spin alignment in proton-proton collisions at $\surd s$ = 200 GeV in the PHENIX experiment at RHIC Kohei Shoji Non-relativisitic QCD calculations using Color Octet Models (COMs) succeed in describing the production cross section of heavy quarkonia measured by CDF and other experiments. However, these models can not reproduce the experimental data for \textit{J/$\psi $} spin alignment (polarization). The understanding of the heavy quarkonium production mechanism cannot proceed without additional experimental measurements. The \textit{J/$\psi $} spin alignment is experimentally determined by measuring the decay angular distribution of leptons in the \textit{J/$\psi $} center of mass system. The anisotropy in the helicity frame was measured at CDF; however, the necessity of analyzing data with respect to another frame like Collins-Soper was recently discussed because the proper polarization axis which is sensitive to the interesting physics phenomenon is not known well. Moreover, measurements of not only the polar angular distribution but also the azimuthal one are important. Proton-proton collision experiments are in progress at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory. The PHENIX experiment at RHIC has muon spectrometers which can detect decay muons from \textit{J/$\psi $} at forward and backward rapidity, 1.2$<\vert $\textit{$\eta $}$\vert <$2.2. We present the status of our \textit{J/$\psi $} spin alignment study in proton-proton collisions at $\surd s$ = 200 GeV. [Preview Abstract] |
Saturday, October 17, 2009 11:00AM - 11:15AM |
KF.00008: Transverse Spin Structure of the Proton Studied by HERMES Toshi-Aki Shibata HERMES is a deep inelastic scattering experiment at DESY-HERA. It uses the polarized electron/positron beam of 27.5 GeV and polarized gas targets such as hydrogen and deuterium, along with unpolarized high density gas targets. One of the major aims of HERMES is to explore the spin structure of the nucleon. The ``Proton spin problem'' was initiated by the discovery of EMC that quark spin contribution to the proton spin is small. The spin of the nucleon, which is 1/2, may consist of contributions of quark spin and gluon spin, and also of orbital angular momenta of quarks and gluons. One way to look into the spin structure of the nucleon is helicity distributions of the partons in the nucleon. The other way, which is developping rapidly, is to study transverse spin structure of the nucleon using a transversely polarized nucleon target. Sivers and Collins asymmetries from azimuthal angular dependence are typical examples. In this talk, the update of transverse spin structure of the nucleon at HERMES is presented. [Preview Abstract] |
Saturday, October 17, 2009 11:15AM - 11:30AM |
KF.00009: Transverse Spin Asymmetries in Back-to-Back Di-Hadron Correlations in the PHENIX Experiment at RHIC John Lajoie The measurement of transverse single spin asymmetries gives us an opportunity to probe the parton structure of transversely polarized nucleons. We present an analysis of single nucleon transverse spin asymmetries using di-hadron correlations in transversely polarized p+p collisions as measured by the PHENIX experiment. The Sivers effect predicts that a non-zero k$_{t}$ in transversely polarized nucleons can lead a very small azimuthal asymmetry in back-to-back di-jets events. Because the PHENIX detectors do not have full phase space coverage it is problematic to fully reconstruct jets. Instead, we use di-hadron correlations in our analysis and measure the sum of two leading back-to-back hadrons' transverse momentum as q$_{t}$, which contains contributions both from partonic k$_{t}$ and fragmentation. Because of this, such measurements may also include contributions from spin-dependent fragmentation. We present yields and asymmetries of the projection of q$_{t}$ on the direction perpendicular to the spin orientation, which is the most sensitive to the small asymmetry due to Sivers effect. These correlations are performed for both midrapidity di-hadron pairs, as well as correlations between midrapidty hadrons and hadrons detected at forward rapidity in the PHENIX muon arms. These measurements offer the potential to elucidate the origin of large transverse single-spin asymmetries observed at RHIC. [Preview Abstract] |
Saturday, October 17, 2009 11:30AM - 11:45AM |
KF.00010: Transverse single spin asymmetries of single electrons from open heavy flavor decay in transversely polarized p+p collisions Seishi Dairaku The measurements of transverse single spin asymmetries ($A_N$) give us a good opportunity to advance our understanding of hadron structure. A number of mechanisms based on QCD for explaining $A_N$ have been proposed, and measurements in different processes have played complementary and important roles in attempts to understand $A_N$. Using the PHENIX Detector at the Relativistic Heavy Ion Collider (RHIC), we study open heavy flavour production with single electrons in transversely polarized p+p collisions. At RHIC energy, heavy flavor production is dominated by gluon fusion process, so there is no chance to observe any large transverse single spin asymmetry of single electrons from open heavy flavor decay which may be explained in terms of the Collins effect because the gluon's transversity is zero. Therefore, the measurement of transverse single spin asymmetries of single electrons from heavy flavor decay at RHIC serve as a clean probe of the gluon Sivers effect. In 2006, the PHENIX experiment has collected 2.7 pb$^{-1}$ integrated luminosity in transversely polarized p+p collisions at $\sqrt{s}$=200GeV. Present status of the analysis of $A_N$ of single electrons from heavy flavor decay at mid-rapidity will be presented. [Preview Abstract] |
Saturday, October 17, 2009 11:45AM - 12:00PM |
KF.00011: Beam Asymmetry for the $\vec{\gamma}\, n \rightarrow K^{^+} \vec{\Sigma}^{^-}$ Reaction Edwin Munevar, Barry Berman Strangeness channels have been shown to be important for the experimental search for missing resonances. They are uniquely suited because they allow the possibility of determining several spin observables. A recent experiment performed at Jefferson Lab (g13 run period) [1], using a liquid deuterium target with linearly and circularly polarized tagged photon beams covering energies from threshold to 2.3 GeV, and using the CLAS detector, provides high-quality data (about 50 billion triggers) with good kinematic coverage and many experimental observables available for each reaction channel. We have analyzed these data to measure strangeness photoproduction on the neutron. In particular, we are interested in the exclusive analysis of the $\vec{\gamma}\, n\rightarrow K^{^+} \vec{\Sigma}^{^-}$ reaction. A preliminary first exclusive measurement of the photon beam asymmetry for this reaction will be presented. \\[4pt] [1] P. Nadel-Turo\'nski \emph{et al., Kaon Production on the Deuteron Using Polarized Photons}, PAC30 Proposal: PR-06-103, 2006. [Preview Abstract] |
Saturday, October 17, 2009 12:00PM - 12:15PM |
KF.00012: Transversity results and polarized Drell-Yan measurement at COMPASS Norihiro Doshita The recent results of the transversity measurement at COMPASS will be presented. And the Drell-Yan measurement with a transversal polarized target as a COMPASS future program will be shown. [Preview Abstract] |
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