Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session M16: Sub-Nucleonic Degrees of Freedom II |
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Sponsoring Units: DNP Chair: Jim Thomas, Lawrence Berkeley National Laboratory Room: Hyatt Regency Jacksonville Riverfront City Terrace 12 |
Sunday, April 15, 2007 3:15PM - 3:27PM |
M16.00001: Improving the measurements of the flavor asymmetry of the nucleon Rusty Towell Fermilab E866/NuSea performed the first measurements of Drell-yan cross section ratio of p+p to p+d collisions over a large kinematic range, allowing the extraction of the ratio of anti-down to anti-up quarks in the proton. After reviewing E866 results, improvements that can be made on these measurements by taking advantage of the Fermilab Main Injector will be discussed. The lower energy of the Main Injector provides a higher Drell-Yan cross section, allowing the extension of all measurements to higher Bjorken-x. E906 is an approved experiment that plans to make these measurements in the near future. [Preview Abstract] |
Sunday, April 15, 2007 3:27PM - 3:39PM |
M16.00002: Probing QCD Structure of NN Interaction in Hard Disintegration of the Nucleon Pair Carlos Granados, Misak Sargsian We investigate high energy photo-disintegration of pp and pn pairs from the $^3He$ nucleus in $90^0$ center of mass scattering in the two nucleon system. These processes are unique in their ability to provide very large center of mass energy in the produced NN system at photon energies larger than few GeV. We study these reactions within QCD hard rescattering mechanism[1] and reduced amplitude approximation[2]. In both cases quark degrees of freedom are explicitly invoked to calculate the scattering amplitude. Our calculations show that the explicit account of quark degrees of freedom results to the prediction that pp pairs have larger strength of photodisintegration than the pn pairs. This is strikingly different from low energy predictions, in which due to dominance of meson exchange currents the $pp$ has only $3\%$ of the $pn$ photodisintegration strength. We discuss how these reactions can be used to probe the hadron-quark transition in NN interactions.\\ \noindent [1] L.L.~Frankfurt, G.A.~Miller, M.M.~Sargsian and M.I.~Strikman, Phys.\ Rev.\ Lett.\ {\bf 84}, 3045 (2000).\\ \noindent [2] S.J.~Brodsky and J.R.~Hiller, Phys.\ Rev.\ C {\bf 28}, 475 (1983);Phys.\ Rev.\ C {\bf 30}, 412(E) (1984). [Preview Abstract] |
Sunday, April 15, 2007 3:39PM - 3:51PM |
M16.00003: Strangeness and threshold of phase changes Johann Rafelski, Jean Letessier Expansion of the fireball of deconfined matter facilitates formation of an over-saturated strange quark phase space. The excess abundance of strangeness is compensating the suppression of this semi-heavy quark yield by its quark mass. The dynamical yield of strangeness means that the effective number of flavors varies between 2 and 3, rather than 2+1 used in equilibrium LGT. In addition, the dynamical expansion of colored quanta pushes against the confining vacuum structure, with a resulting supercooling of the transition temperature. These nonequilibrium effects alter measured phase boundary compared to theoretical (lattice) evaluation. The phase diagram derived from the analysis of hadron production shows two boundaries, one corresponding to the expected transition between confined and deconfined matter, with a downward temperature shift due to dynamical effects, and the other, at a high quark density, which appears to involve heavy effective quarks, at relatively large temperatures. [Preview Abstract] |
Sunday, April 15, 2007 3:51PM - 4:03PM |
M16.00004: Nuclear Shadowing and Select d+Au Observables Adeola Adeluyi, George Fai Much of the complexity of the description of d+Au collisions in the framework of perturbative Quantum Chromodynamics (pQCD) derives from effects of the nuclear environment. Here we investigate the effects of the most recent available nuclear shadowing parametrization, the Hirai-Kumano-Nagai (HKN) nuclear parton distribution functions (nPDFs) and the updated Albino-Kniehl-Kramer (AKK) fragmentation functions on three select d+Au collision observables. We compare our results to available experimental data from the STAR and BRAHMS collaborations. [Preview Abstract] |
Sunday, April 15, 2007 4:03PM - 4:15PM |
M16.00005: Measurements of A$_{LL}$ in Inclusive Charged Pion Production at the STAR Experiment. Adam Kocoloski The STAR Spin program at RHIC contributes to world knowledge of the polarized gluon distribution function $\Delta $G through measurements of double spin asymmetries A$_{LL}$ in various final state channels of longitudinally polarized p+p collisions. The channels p+p$\to \pi ^{+/-}$+X have large production cross-sections and the difference of the two asymmetries is particularly sensitive to models with different signs of $\Delta $G. Moreover, STAR has already developed techniques to identify charged pions and calculate their production cross-sections over a broad kinematic range, making these inclusive final states excellent candidates for analysis given the integrated luminosities that have been recorded to date. This contribution will present measurements of A$_{LL}$ for inclusive charged pion production extracted from 2 pb$^{-1}$ of data taken at $\surd $s=200 GeV and $\sim $50{\%} beam polarizations during the 2005 RHIC run. The asymmetries are calculated over the transverse momentum region 2$<$p$_{T}<$10 GeV/c and compared with theoretical predictions incorporating several gluon polarization scenarios. The 2006 RHIC data allows for more precise and refined measurements. Analysis progress will be discussed, followed by an outlook for the future. [Preview Abstract] |
Sunday, April 15, 2007 4:15PM - 4:27PM |
M16.00006: Longitudinal Spin Asymmetry and Cross Section for Inclusive $\pi ^{0}$ Production in Polarized p+p Collisions at STAR Alan Hoffman The primary 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. The STAR detector, with its large-acceptance tracking and calorimetry, is an ideal tool for these studies. We present the most recent measurement of the cross section and the double longitudinal spin asymmetry for inclusive $\pi ^{0}$ production in polarized p+p collisions at mid-rapidity, using the STAR detector's barrel electromagnetic calorimeter. The measured cross section is compared to next-to-leading order perturbative QCD calculations. The agreement of NLO pQCD evaluations and the measured unpolarized cross section supports the use of this framework in extracting gluon polarization from the polarized measurements. 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. Results from RHIC run 5 are presented as well as the current status of the RHIC run 6 analysis. [Preview Abstract] |
Sunday, April 15, 2007 4:27PM - 4:39PM |
M16.00007: Di-Jet Measurement to Constrain Event Kinematics in Longitudinal Polarized Proton-Proton Collisions at STAR Tai Sakuma The polarized gluon distribution in the proton, the delta G, is of particular interest to the STAR Spin program. While initial studies have focused on inclusive pion and jet analyses, the recent improvements in RHIC luminosity and polarization enable di-jet analysis as the first correlation analysis to constrain initial event kinematics. With it's large acceptance electromagnetic calorimetery and tracking system, STAR is well suited for this measurement. We report progress towards measurement of di-jet cross section and A{\_}LL in polarized p+p collisions at 200 GeV for RHIC 2005 and 2006 run. [Preview Abstract] |
Sunday, April 15, 2007 4:39PM - 4:51PM |
M16.00008: Progress toward using non-photonic electrons in polarized p+p collisions to measure the gluon spin structure function Priscilla Kurnadi One of the main goals of the RHIC spin program is to measure the gluon spin structure function $\Delta G$ in the proton. So far, STAR has focused efforts on inclusive measurements such as pion and jet production in polarized $pp$ collisions. However, as improvements in both beam and detector have allowed for increased luminosity and statistics in the available data, other probes are becoming viable. One such probe is the non-photonic electrons from semi-leptonic decays of heavy flavor quarks. In $pp$ collisions, production of heavy quark pairs is dominated by gluon-gluon fusion, $gg \rightarrow q\bar{q}$. A study of these non-photonic electrons in polarized $pp$ collisions will provide insight into $\Delta G$. This talk will provide an overview of what has been done to date on the detection of non-photonic electrons towards an $A_{LL}$ measurement. The talk will include a summary of the electron identification procedures using the STAR Time Projection Chamber (TPC), Barrel Electromagnetic Calorimeter (BEMC), and Barrel Shower Maximum Detector (BSMD). A status update on the measurement of non-photonic electron yield in polarized $pp$ collisions at the center of mass energy of 200 GeV from the 2006 run will be presented. [Preview Abstract] |
Sunday, April 15, 2007 4:51PM - 5:03PM |
M16.00009: Double Longitudinal Spin Asymmetry Measurement for Inclusive Jet Production at STAR David Staszak A primary objective of the RHIC Spin physics program is the determination of the polarized gluon distribution function, $\Delta G$, in the nucleon. Measurements of the double longitudinal asymmetry $A_{LL}$ in 200 GeV polarized protons, from which $\Delta G$ can be extracted, have been presented previously by STAR in a number of channels from data collected in 2003 through 2005. The inclusive jet channel is of particular importance because it provides both a relatively large cross section and a direct probe into the initial state parton dynamics. STAR's previous inclusive jet results have constrained the allowed models of gluon polarization. The p+p data from run 2006 represent a sample of 9 $pb^{-1}$ integrated luminosity and $\sim 60\%$ polarized beams. We will present progress towards the $A_{LL}$ measurement from the run 2006 data set as well as our recent results from runs 2005 and 2003/4. [Preview Abstract] |
Sunday, April 15, 2007 5:03PM - 5:15PM |
M16.00010: Diffractive DIS in ep and eA Cyrille Marquet The discovery of diffractive deep inelastic scattering (DDIS) at HERA has opened the way for new experimental tests of QCD. In particular, as diffractive events are sensitive to infrared physics even in the weak coupling regime, it was realized that diffractive observables are good places for testing the saturation regime of QCD. We present preliminary results in the context of DDIS off nuclei, including potential CGC signatures. [Preview Abstract] |
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