Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session CB: Mini-Symposium on Studying the Orbital Structure of the Proton with Di-Jets at RHIC |
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Chair: Werner Vogelsang, Brookhaven National Laboratory Room: Newport News Marriott at City Center Grand Salon III |
Friday, October 12, 2007 9:00AM - 9:36AM |
CB.00001: Transverse momentum and transverse spin in hadronic scattering Invited Speaker: In this talk, I will present a theoretical overview of the transverse momentum and transverse spin physics in hadronic reactions. [Preview Abstract] |
Friday, October 12, 2007 9:36AM - 9:48AM |
CB.00002: HERMES Measurement of the Collins and Sivers Asymmetries from a Transversely Polarized Hydrogen Target Edward Kinney In 2005 the HERMES collaboration published first evidence for azimuthal single-spin asymmetries in semi-inclusive production of charged pions on a transversely polarised hydrogen target. The measured asymmetries are caused by both the Collins and the Sivers mechanisms. Their distinctive Fourier components provide signals to previously unmeasured quantities: the transversity quark distribution in conjunction with the Collins fragmentation function (Collins mechanism/asymmetry) and the Sivers parton distribution (Sivers mechanism/asymmetry). The transversity distribution will provide new insight into the relativistic nature of the quarks inside the nucleon while the Collins fragmentation function describes spin-orbit correlations in the hadron formation process. The Sivers function is related to the orbital motion of the quarks within the proton and its correlation with the proton's spin direction. New results will be presented for the Collins and Sivers asymmetries for charged pion, neutral pion, and charged kaon production. The new measurements include the entire HERMES data set collected from the transversely polarized hydrogen target. [Preview Abstract] |
Friday, October 12, 2007 9:48AM - 10:00AM |
CB.00003: Sivers Transverse Single Spin Asymmetries for Di-jet Production in $\sqrt{s}$ = 200 GeV Polarized Proton-Proton Collisions at STAR Issam Qattan Deep inelastic scattering experiments with polarized beams and targets have established that no more than ~30\% of the proton's spin can be attributed to a net preferential spin alignment of quarks and antiquarks. The rest of the spin must arise from some combination of gluon spin alignment and parton orbital angular momentum. One possible manifestation of the orbital contributions is the Sivers effect [1]: a correlation between the transverse momentum direction of partons in the initial state and the transverse spin orientation of the parent proton. We will present the first measurements, from the STAR Collaboration at RHIC, of single spin asymmetries sensitive to the Sivers effect for di-jet production in collisions of transversely polarized proton beams. The data span a wide range in jet pseudorapidity, thereby probing parton transverse momentum preferences in both the valence and (gluon-dominated) sea regions. We will present final results for a sample of ~3 million di-jet events from the 2006 RHIC run based on partial jet reconstruction from the electromagnetic calorimeter contribution to jet energies, as recorded online at the trigger level, as well as the status of full offline jet reconstruction incorporating charged-particle tracks. [1] D. Sivers, Phys. Rev. Lett. D41, 83 (1990) [Preview Abstract] |
Friday, October 12, 2007 10:00AM - 10:12AM |
CB.00004: ABSTRACT WITHDRAWN |
Friday, October 12, 2007 10:12AM - 10:24AM |
CB.00005: Studies of Spin-Orbit Correlations with Longitudinally Polarized Target at CLAS12 Kawtar Hafidi Azimuthal distributions of final state particles in semi-inclusive deep inelastic scattering (SIDIS) provide access to the orbital motion of quarks and play a key role in the study of transverse momentum dependent (TMD) parton distributions. A comprehensive program to study the transverse momentum dependence of valence-quark transverse and longitudinal spin distributions through measurements of single-spin and double-spin azimuthal asymmetries in the SIDIS of pions using the upgraded JLab 11 GeV polarized electron beam and the CLAS12 detector with longitudinally polarized proton and deuteron targets has recently been proposed. The sin(2$\phi)$ azimuthal moment of the target-spin-dependent part of the cross section, in particular, will provide direct information on spin-orbit correlations because the leading twist TMD parton distribution is related to the interference between states with different orbital angular momenta. The p$_{T}$ dependence of the double spin asymmetry will provide information on the transverse momentum dependence of the quark helicity distributions that is complimentary to the single-spin asymmetry measurements. [Preview Abstract] |
Friday, October 12, 2007 10:24AM - 10:36AM |
CB.00006: Transvers Quark Spin Effects in Hard Processes Leonard Gamberg The connection between quark orbital angular momentum and final state interaction for transversely polarized quarks in unpolarized hadrons suggests significant $\cos 2\phi$ azimuthal asymmetries in semi-inclusive deep inelastic scattering (SIDIS), $e\ p\rightarrow e^\prime \ H\ X $, and in inclusive charged di- hadron production, $e^+\ e^-\rightarrow H\ H\ X$, as well as in di-lepton production in Drell Yan scattering, $p\ \bar {p} \rightarrow \ell^+ \ \ell^- \ X$. When the transverse momentum of the reaction $P_{T}$ is on the order of or less than $\Lambda_{\rm qcd}$, that is where $P_T\sim k_T$, where $k_T$ is intrinsic transverse quark momentum, these effects are characterized in term of naive time reversal odd (so called ``$T$-odd'') transverse momentum dependent (TMD) parton distribution and fragmentation functions. At these moderate transverse momentum scales we estimate the size of the $\cos 2\phi$ azimuthal asymmetry in SIDIS, Drell Yan and $e^+\ e^-$ annihilation, within the parton motivated spectator framework. In SIDIS and Drell Yan scattering we consider this so called ``Boer-Mulders'' effect for a future experiments at the upgraded CLAS-12 GeV detector at Jefferson LAB and for proton-proton and anti-proton experiments at RHIC,JPARC, and GSI. In $e^+\ e^-$ annihilation, we consider this asymmetry in terms of the Collins effect for kaons at BELLE. [Preview Abstract] |
Friday, October 12, 2007 10:36AM - 10:48AM |
CB.00007: Photon-Hadron Correlations in p-p Collisions with the PHENIX Detector Matthew Nguyen Hard scattering in the $\gamma$-jet channel is thought to be a clean observable for energy-loss studies in heavy-ion collisions and spin asymmetries in polarized proton collisions. The measurement of photon-hadron correlations in unpolarized p+p collisions is an important baseline. pQCD calculations describe direct photon production reasonably at in the relevant $x_{T}$ range, however theoretical uncertainties are non-negligible. Initial and final state radiation present at Next-to-Leading Order may complicate the interpretation of experimental results. Moreover, non-perturbative quantities which influence the yield of photon-hadron pairs, particularly the gluon distribution function and photon fragmentation function, are poorly constrained by the world data in the kinematic range of interest. Photon-hadron correlation data from RHIC at $\sqrt{s}$ = 200 GeV should serve as a benchmark with which to compare data in polarized p-p and nuclear collisions where $\gamma$-jet data represent experimental signatures of possible gluon spin effects and Quark-Gluon Plasma formation, respectively. Recent PHENIX data will be presented. [Preview Abstract] |
Friday, October 12, 2007 10:48AM - 11:00AM |
CB.00008: Latest HERMES Measurements of Hard Exclusive Processes Steve Gliske Hard exclusive processes provide access to the unknown generalized parton distributions (GPDs) which extend our description of the nucleon structure beyond the standard parton distributions. Azimuthal asymmtries in Deeply Virtual Compton Scattering from a transversely-polarized target have been measured for the first time by HERMES. These asymmetries are sensitive to the GPD $E$ which is related via the Ji sum rule to the total angular momentum of quarks within the proton. By comparing these asymmetries with model calculations, model dependent constraints are obtained on $J_u$ and $J_d$. Second, the first measurement of the transverse-target spin asymmetry for exclusive $\rho^0$ production will be shown. This observableprovides further access to the GPD $E$, but a factorization theorem for exclusive meson production has only been proven for longitudinally polarized photons. Fortunately $s$-channel helicity conservation (SCHC) has been shown to hold well in exclusive $\rho^0$ production. The asymmetry for the production of longitudinally polarized $\rho^0$ mesons was isolated through the angular distribution of the decay products, and assuming SCHC this is equal to the longitudinal-photon asymmetry. The results will be compared with theoretical calculations. [Preview Abstract] |
Friday, October 12, 2007 11:00AM - 11:12AM |
CB.00009: k$_{T}$ Asymmetry in Longitudinally Polarized pp Collisions at PHENIX Douglas Fields Researchers in the PHENIX experiment at RHIC have developed a method for measuring the average net pair transverse momentum of hard scattered jets at central rapidity. The method is based on the azimuthal correlation between a leading high p$_{T}$ neutral pion and another charged hadron. The widths of the resulting near- and far-side peaks can then be related to the fragmentation transverse momentum, j$_{T}$ (the transverse momentum of the fragmented hadron relative to the hard-scattered parton) and the net pair transverse momentum, k$_{T}$. The net pair transverse momentum can be produced from parton intrinsic transverse momentum inside the proton, from soft gluon emission, or from next-to-leading order processes of the perturbative QCD. In addition, one could consider the possibility that spin-correlated transverse momentum (orbital angular momentum) may contribute to k$_{T}$. Spin-dependent parton transverse momentum adds to k$_{T}$ an amount dependent upon the helicity combination of the colliding protons, and upon the impact parameter of the collision. However, integration over impact parameter should leave a residual effect that is dependent only on the helicity combination, a signal that is examined in the present data from past RHIC runs. [Preview Abstract] |
Friday, October 12, 2007 11:12AM - 11:24AM |
CB.00010: Transverse Spin Dependent Identified Hadron Cross-sections in $p$$^\uparrow$+$p$ Collisions at $\sqrt{s} = 62.4$ and $200$ GeV J.H. Lee, Flemming Videbaek Transverse spin dependence of particle production, Single Spin Asymmetries (SSAs), at the energy regime where pQCD is applicable are expected to be negligibly small in the lowest-order QCD approximation, whereas experimentally large SSAs have been observed at high Feynman-$x$($x_F$). Recently, new measurements of SSAs have been available from semi-inclusive deep-inelastic scattering and $p^\uparrow$+$p$ at RHIC providing more insight into the fundamental mechanisms of SSAs as well as the relevant hadron structure. The BRAHMS experiment at RHIC has unique capabilities to explore the high-$x_F$ kinematic region with particle identification. Measurements of cross-sections and single spin asymmetries of identified charged hadrons, $\pi^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$, from transversely polarized proton collisions at $\sqrt{s} = 62.4$ and 200 GeV are presented. The results are discussed in the context of theoretical models based on pQCD. The energy and flavor dependent SSAs combined with the cross-sections at high-$x_F$ bring new insight into the perturbative Quantum Chromodynamical description of partonic dynamics at RHIC. [Preview Abstract] |
Friday, October 12, 2007 11:24AM - 11:36AM |
CB.00011: Transverse Single Spin Asymmetry Measurement with J/$\Psi$ in Polarized p+p Collisions at RHIC Han Liu The measurement of transverse single spin asymmetries($A_N$) gives us an opportunity to probe the quark and gluon structure of transversely polarized nucleons. PHENIX experiment has collected 2.7 pb$^{-1}$ data in transversely polarized p+p collisions at $\sqrt{s}$=200GeV in 2006 run. At RHIC energy, J/$\Psi$ production is dominated by gluon-gluon fusion, thus Collins effect has minimum impact on $A_N$ as the gluon's transversity is zero. Therefore, the measurement of $A_N$ in J/$\Psi$ production offers a good opportunity to gain information on gluon's Sivers effect. Results from 2006 for J/$\Psi$ $A_N$ at forward rapidity will be presented. [Preview Abstract] |
Friday, October 12, 2007 11:36AM - 11:48AM |
CB.00012: ABSTRACT WITHDRAWN |
Friday, October 12, 2007 11:48AM - 12:00PM |
CB.00013: Single Transverse Spin Asymmetries in Drell Yan Production at RHIC Les Bland, Gerry Bunce, Matthias Grosse Perdekamp, Ming Liu, Beau Meredith, Werner Vogelsang, Feng Yuan We present the physics and experimental feasibility of single transverse spin asymmetry measurements in Drell Yan di-lepton production in polarized proton-proton collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The measurement will be sensitive to Sivers quark distributions and test recent fundamental theory predictions that the Sivers effect will be observed to be process dependent. [Preview Abstract] |
Friday, October 12, 2007 12:00PM - 12:12PM |
CB.00014: Transverse single spin asymmetry for dihadron production in polarized $\sqrt{s}=200$ GeV $pp$ collisions at PHENIX Ruizhe Yang Due to the chiral-odd nature of the transverse quark spin distribution functions of the proton, they can only be accessed when coupled to another chiral-odd function such as itself in Drell-Yan, the Collins fragmentation function in inclusive hadron production, or the di-hadron fragmentation function (also called interference fragmentation function) in di-hadron production. Using the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC), the single spin asymmetry of di-hadron production is being studied in transversely polarized proton proton collisions. This single spin asymmetry can be used to extract quark transversity distribution functions with the interference fragmentation function which will be measured in $e^+e^-$ collisions by the BELLE detector at KEK. First data for this measurement was collected in 2006, with 2.7 pb$^-1$ integrated luminosity and 57\% polarization. The current status of the di-hadron single spin asymmetry will be reported. [Preview Abstract] |
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