Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session GF: Spin Structure of the Nucleon at High Energy |
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Sponsoring Units: DNP Chair: Les Bland, Brookhaven National Laboratory Room: Gaylord Opryland Hermitage C |
Saturday, October 28, 2006 9:00AM - 9:12AM |
GF.00001: Double Longitudinal Spin Asymmetry for Inclusive Jet Production in Polarized p+p Collisions at 200 GeV Murad Sarsour The STAR experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory is measuring polarized pp collisions at a center of mass energy of $\sqrt{s} = 200$ GeV to determine the polarized gluon distribution in the proton, $\Delta G$, in the kinematic range $0.03 < x_g < 0.3$, via spin asymmetry measurements. Data were collected during 2005, at sampled luminosity of $\sim$\,3 pb$^{-1}$, with 40-50\% beam polarization. We present run 2005 preliminary results for the double longitudinal spin asymmetry for inclusive jet production at mid-rapidity, along with results from 2003/04. Comparisons to theoretical calculations using deep-inelastic scattering parameterizations for gluon polarization in the nucleon are also presented. [Preview Abstract] |
Saturday, October 28, 2006 9:12AM - 9:24AM |
GF.00002: Constraining the Gluon Contribution to the Proton's Spin by Measuring the Double Longitudinal Spin Asymmetry in Neutral Pion Production in Polarized p+p Collisions Kieran Boyle The quark contribution to the proton's spin measured with polarized DIS fixed target experiments was found to be only 20-30 \%. This has raised interest in measuring the gluon contribution, $\Delta g$, directly. Using the PHENIX Detector at the Relativistic Heavy Ion Collider (RHIC), we study longitudinally polarized proton collisions. The double longitudinal spin asymmetry in $\pi^{0}$ production, $A_{LL}^ {\pi^{0}}$, is related to $\Delta g$. RHIC has recently completed its second long polarized proton run. In 2005, 46\% average polarization and 2.7 pb$^{-1}$ integrated luminosity was achieved while in 2006, 60\% average polarization and 7.5 pb$^{- 1}$ was achieved. The current status of our analysis of $A_{LL}^ {\pi^{0}}$ will be presented. [Preview Abstract] |
Saturday, October 28, 2006 9:24AM - 9:36AM |
GF.00003: Longitudinal Spin Asymmetry and Cross Section of Inclusive Pi0 Production in Polarized p+p Collisions at 200 GeV Frank Simon One goal of the polarized p+p program at RHIC, the first high-energy polarized p+p collider, is the study of the gluon polarization in the proton via spin asymmetry measurements in a variety of processes. Due to its large acceptance tracking and electromagnetic calorimetry the STAR detector is an ideal tool for these studies. We present the first measurement of the cross section and the double longitudinal spin asymmetry of inclusive Pi0 production in polarized p+p collisions at mid-rapidity with the STAR detector, using the barrel electromagnetic calorimeter. The measured cross section is compared to NLO pQCD calculations, and can provide constraints on fragmentation functions. The comparison of the measured unpolarized cross section to theory is crucial in order to validate model calculations used to extract the gluon polarization from the observed asymmetries. The double longitudinal spin asymmetry is compared to NLO pQCD calculations based on different assumptions for the gluon polarization in the nucleon to provide constraints on $\Delta$g/g. Although at present the asymmetry result is still limited by statistics, it provides a proof of principle for future analysis with higher integrated luminosity and increased acceptance. [Preview Abstract] |
Saturday, October 28, 2006 9:36AM - 9:48AM |
GF.00004: Longitudinal Double Spin Asymmetry and Cross Section for $\eta$ production at mid-rapidity in polarized p+p collisions at $\sqrt{s_{NN}} = 200$ GeV Joseph Seele Longitudinal double spin asymmetries, $A_{LL}$, measured for inclusive hadron production in polarized proton-proton collisions at high energies have been shown to be sensitive to the gluon helicity distribution, $\Delta g$. A recent measurement of the longitudinal double spin asymmetry for neutral pion production at RHIC by the PHENIX experiment (Phys. Rev. Lett. 93, 202002 (2004)) has provided a significant constraint on the gluon helicity distribution of the nucleon. The extraction of $\Delta g$ from these data depends on the experimental knowledge of the relevant fragmentation functions. However, the measurement of $A_{LL}$ for different hadrons with independent experimental uncertainties and different fragmentation functions will further constrain the uncertainties present in global analyses of data. The measurement of the longitudinal double spin asymmetry for $\eta$ production will provide such a constraint. The PHENIX spectrometer has been used to measure the production of $\eta$ particles at mid-rapidity ($|\eta| < 0.35$). The results for the $A_{LL}$ and cross section for $\eta$ production in polarized p+p collision at $\sqrt{s_{NN}}=200$ GeV at RHIC will be presented. [Preview Abstract] |
Saturday, October 28, 2006 9:48AM - 10:00AM |
GF.00005: Accessing the Gluon Polarization through the Double-Helicity Asymmetry in PHENIX Christine Aidala The RHIC spin program with its use of strongly interacting probes provides a unique opportunity that allows the direct study of gluon polarization within the nucleon. Among a variety of experimental channels the double-helicity asymmetry ($A_{LL}$) of charged pions seems to be an especially interesting probe. Charged pion asymmetry measurements will be an important component in upcoming global analyses, which will allow determination of the gluon polarization over a wide range in $x$. Comparison of differential cross section measurements to next-to-leading order (NLO) pQCD calculations has been essential to confirm our understanding of hard scattering at RHIC energies and the applicability of NLO pQCD in interpreting polarized processes. Quark-gluon scattering dominates mid-rapidity pion production at RHIC at transverse momenta above ~5 GeV/$c$; in this kinematic region the favored and unfavored fragmentation functions for each pion species provide relevant information. Relative differences among $A_{LL}$ of positive, neutral, and negative pions at high transverse momentum are sensitive to the sign of $\Delta g$. The current status of the charged pion $A_{LL}$ and cross section analyses using PHENIX data from the 2005 polarized proton run at RHIC will be presented. [Preview Abstract] |
Saturday, October 28, 2006 10:00AM - 10:12AM |
GF.00006: Double Longitudinal Spin Asymmetries of Inclusive Charged Pion Production in Polarized p+p Collisions at 200 GeV Adam Kocoloski A primary goal of the STAR Spin program at RHIC is the measurement of the polarized gluon distribution function $\Delta $G, which can be obtained from a global analysis incorporating measurements of the double spin asymmetry A$_{LL}$ in various final state channels of polarized p+p collisions. Final states with large production cross sections such as inclusive jet and hadron production are analyzed as the program moves towards the measurement of A$_{LL}$ in the theoretically clean channel of prompt photon production. The channels p+p$\to \pi ^{+/-}$+X are unique in that the ordering of the measurements of A$_{LL}$ in these two channels is sensitive to the sign of $\Delta $G. Moreover, STAR has already established the procedure for the identification of charged pions and the calculation of their production cross-sections over a broad kinematic range. This contribution will present first measurements of double longitudinal spin asymmetries for inclusive charged pion production extracted from 3 pb$^{-1}$ of data at $\surd $s=200 GeV and 50{\%} beam polarizations. The asymmetries are calculated over the transverse momentum region 2$<$p$_{T}<$12 GeV/c and compared with theoretical predictions incorporating several gluon polarization scenarios. A systematic bias introduced by the selection of charged pions from events satisfying electromagnetic energy triggers will be discussed and estimated using Monte Carlo. [Preview Abstract] |
Saturday, October 28, 2006 10:12AM - 10:24AM |
GF.00007: Longitudinal Double Spin Asymmetry and Cross Section for Direct Photon Production at Mid-rapidity in Polarized $pp$ Collisions at $\sqrt{s} = 200$ GeV Robert Bennett Inclusive direct photon production in $\sqrt{s}=200 GeV$ $pp$ collisions at RHIC, is one of the important channels PHENIX will employ to determine the polarized gluon distribution. To establish the usability of this process, we first present the comparison of its total cross section measured using our data, recorded in 2003 (Run-3) and 2005 (Run-5), with the perturbative QCD calculations at next-to-leading order. The extraction of the cross section relies on two techniques: First purifying our sample by considering only isolated photons as direct photon candidates and second by a statistical subtraction of weighted spectra of known sources of indirect photons from the total photon event sample. We then proceed to evaluate the double helicity spin asymmetries from these data sets, and to extract the polarized gluon distribution, $\Delta G$, using the known polarized quark distribution functions obtained from deep inelastic scattering. Final results from Run-3, based on luminosity of $240$ $nb^{-1}$ and polarization of 27\%, and the status of Run-5 analysis, $2.7$ $pb^{-1}$ and polarization 45\%, will be presented in this talk. [Preview Abstract] |
Saturday, October 28, 2006 10:24AM - 10:36AM |
GF.00008: Di-final state measurements to constrain event kinematics in longitudinally polarized p+p collisions at STAR Tai Sakuma A primary motivation of the RHIC spin program is the extraction of the gluon helicity distribution (Delta-G) from polarized p+p collisions. Initial studies have focused on measurements of inclusive final states, such as pions and jets. Steady improvements in RHIC integrated luminosity and polarization open more exclusive final states such as di-jets and di-hadrons, allowing tighter constrains on initial state parton kinematics. With it's large acceptance electromagnetic calorimetery and tracking, STAR is particularly well suited for this measurement. We report progress towards measurement of di-jet and di-hadron final state A{\_}LL extracted from $\sim $6 pb-1 of polarized p+p collisions at 200 GeV. In particular, we focus on data vs MC comparisons that provide insight into the level of constraint of the event kinematics. [Preview Abstract] |
Saturday, October 28, 2006 10:36AM - 10:48AM |
GF.00009: Transverse Quark Spin Effects in Azimuthal Asymmetries in SIDIS and Drell Yan 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 pion production in semi-inclusive deep inelastic scattering (SIDIS) ($e\ p\rightarrow e^\prime \ X \ \pi$) and in di-lepton production in Drell Yan ($p\ \bar{p}\rightarrow \ell^+ \ \ell^- \ X$) scattering. When 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 and Drell Yan scattering in the parton spectator framework. In the former case we consider this so called ``Boer-Mulders'' effect for a proposed experiment at the upgraded CLAS-12 GeV detector at Jefferson LAB. In the latter case we consider this asymmetry for proton anti-proton experiments. [Preview Abstract] |
Saturday, October 28, 2006 10:48AM - 11:00AM |
GF.00010: Determination of the Collins Function from Di-Hadron Fragementation in $e^{+}e^{-}$ Annhiliation Matthias Grosse Perdekamp, David Mertens, Ralf Seidl The Collins function connects transverse quark spin with an observable azimuthal asymmetry of final state hadrons around the intial quark momentum direction. The Belle experiment has carried out a first measurement of Collins asymmetries for pion pairs produced in $e^{+}e^{-}$ annihilation. We will present an extraction and parametrization of the favored and disfavored Collins fragmentation functions from the Belle fragmentation data as functions of the fractional hadron energy. We will discuss the sensitivity of the Belle data in discriminating between different possible functional forms for the Collins fragmetation function. [Preview Abstract] |
Saturday, October 28, 2006 11:00AM - 11:12AM |
GF.00011: Transverse Single Spin Asymmetries for identified charged hadrons in p+p collisions at $\sqrt s $=200 and 62 GeV. J.H. Lee, F. Videbaek The transverse single-spin asymmetries of identified charged hadrons, \textbf{$\pi $, } of K , p and pbar, have been measured at mid and forward rapidities in polarized proton-proton collisions at $\sqrt s $=200 GeV and for \textbf{$\pi $}$^{-}$ at $\sqrt s $=62 GeV. The data were obtained with the two magnetic spectrometers in the BRAHMS experiment at RHIC. The data cover a Feynman-x (x$_{F})$ range 0-0.35 at 200 GeV and 0-0.6 at 62 GeV in 0.5 $<$ p$_{T} \quad <$ 3 GeV/c. The dependence on p$_{T }$and x$_{F}$ are discussed in the context of theoretical models based on pQCD. In addition, inclusive cross sections at forward rapidities are compared to NLO pQCD calculations. This work is supported by the Division of Nuclear Physics of the Office of Science of the US DOE. [Preview Abstract] |
Saturday, October 28, 2006 11:12AM - 11:24AM |
GF.00012: Measurement of Sivers Transverse Spin Asymmetries for Di-Jet Production in 200 GeV Polarized Proton Collisions at STAR Steven Vigdor Hard-scattering collisions of transversely polarized protons may be preferentially initiated by partons with transverse momentum $(\vec {k}_T )$ directed toward one side of the plane formed by the proton's momentum and spin vectors [1]. Parton orbital angular momentum within the proton is a prerequisite for this so-called Sivers effect. We report the first measurement of the Sivers asymmetry in collisions of transversely polarized proton beams, using di-jet production data acquired with the STAR detector during the 2006 RHIC run. A non-zero Sivers function would be manifested directly by a spin-dependent change in the distribution of the azimuthal opening angle between the two reconstructed jets [2]. We present a preliminary analysis reconstructing the jet thrust axes only from the electromagnetic calorimeter component of the jet energies, recorded online at trigger level for a sample of $\sim $ 3 million di-jet events. By selecting subsets of events within particular phase space regions, we can emphasize quark- or gluon-dominated Sivers functions. In addition to experimental results, we present model simulations that demonstrate the correlations among various measures of the Sivers asymmetries, and their sensitivity to the shape of the underlying $\vec {k}_T $ distribution. [1] D. Sivers, Phys. Rev. D\textbf{41}, 83 (1990) and Phys. Rev. D\textbf{43}, 261 (1991). [2] D. Boer and W. Vogelsang, Phys. Rev. D\textbf{69,} 094025 (2004). [Preview Abstract] |
Saturday, October 28, 2006 11:24AM - 11:36AM |
GF.00013: Measurement of dipion azimuthal angular correlations intransversely polarized pp collisions at $\sqrt{S}=62.4$ GeV in Center of Mass using PHENIX detector at RHIC. Nathan Means It has been recently suggested that observation of azimuthal asymmetry in back-to-back jets produced in single transverse polarized pp collisions at RHIC would be a direct evidence for non-zero transverse momentum in the nucleon [Boer and Vogelsang]. The connection of this transverse momentum and the orbital angular momentum of the partons in the nucleons has also been discussed in the literature. PHENIX is a multipurpose detector at RHIC with electromagnetic calorimetry ($d\phi \times d\eta$=$0.01 \times 0.01$) in the diagonally opposite $d\phi = \frac{\pi}{2}$ regions around the horizontal plane, and a pseudorapidity range of $|\eta| = 0.35$. This enables PHENIX excellent measurement of $\pi^{0}$'s which may be the remnants of produced the jet in pp collisions. In the recently finished run (RHIC Run-6) we added the Muon Piston Calorimeter (MPC), a new PbWO$_{4}$ crystal calorimeter, which covers the pseudorapidity range 3.1 to 3.6 and $\phi = 2\pi$. With these two EM calorimeters we plan to make the back-to-back angular correlation measurements in double pion production from the transverse spin proton-proton collisions. About 20 nb$^{-1}$ of data with an average beam polarization of 57\% were collected in Run-6. I will present the status of this analysis from Run-6 data. [Preview Abstract] |
Saturday, October 28, 2006 11:36AM - 11:48AM |
GF.00014: Perspective of $\Lambda$ hyperon production in semi-inclusive DIS with an 11 GeV electron beam at Jefferson Lab Xiaodong Jiang, Hai-jiang Lu With the planned energy upgrade and the large acceptance CLAS12 detector operated at the high luminosity of $10^{35}$ cm$^{-2}$s$^{-1}$, Jefferson Lab provides unique opportunities to study $\Lambda^0$ hyperon productions in semi-inclusive DIS reactions in the current fragmentation regime ($x_F>0$, $z>0.5$). Based on the LUND model and the recent HERMES data, we carried out numerical estimations of the following physics observables: 1. lepton to $\Lambda$ longitudinal spin transfer, 2. beam-target double-spin asymmetries, 3. nucleon to $\Lambda$ spin transfer, 4. Induced $\Lambda$ polarization on an unpolarized target, 5. transverse $\Lambda$ polarization on a transversely polarized target. The projected statistical accuracies will be compared with existing theory models and recent data from the COMPASS and the HERMES collaborations. [Preview Abstract] |
Saturday, October 28, 2006 11:48AM - 12:00PM |
GF.00015: Realistic Simulation of W Boson Production in the PHENIX Muon Spectrometers Kristin Kiriluk The separate contributions of $\bar{u}$ and $\bar{d}$ quarks to the proton spin are at present known only from lepton SIDIS double spin asymmetries, in which they are extracted using the ``hadron tagging'' technique. Single spin asymmetries of leptons from W bosons produced in longitudinally polarized $pp$ collisions are directly sensitive to the sea quark polarizations; a detailed understanding of the final hadronic state is not required[1]. The PHENIX collaboration at RHIC plans to determine the $W^+$ and $W^-$ boson production cross sections and single spin asymmetries at $\sqrt{s} = 500$~GeV by detecting decay muons at forward and backward rapidities. In order to understand resolution, backgrounds, and efficiency effects, the PHENIX spectrometer simulation PISA was used to study the planned measurements and determine realistic expectations of the yields and the sensitivity to the light quark polarizations. \newline [1] G.~Bunce {\it et al.,} {\sl Ann.\ Rev.\ Nucl.\ Part.\ Sci. }{\bf 50} (2000) 525. [Preview Abstract] |
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