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 BG: Sub-nucleonic Degrees of Freedom |
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Sponsoring Units: DNP JPS Chair: Toru Sugitate, Hiroshima University Room: Ritz-Carlton Hotel Plantation 2 |
Monday, September 19, 2005 7:00PM - 7:15PM |
BG.00001: Effect of bound nucleon internal structure change on nuclear structure functions Kazuo Tsushima, Koichi Saito, Fernando Steffens Effect of bound nucleon internal structure change on nuclear structure functions is investigated based on local quark-hadron duality. The bound nucleon structure functions calculated for charged-lepton and (anti)neutrino scattering are all enhanced in symmetric nuclear matter at large Bjorken-$x$ ($x \agt 0.85$) relative to those in a free nucleon. This implies that a part of the enhancement observed in the nuclear structure function $F_2$ (in the resonance region) at large Bjorken-$x$ (the EMC effect) is due to the effect of the bound nucleon internal structure change. However, the $x$ dependence for the charged-lepton and (anti)neutrino scattering is different. The former [latter] is enhanced [quenched] in the region $0.8 \alt x \alt 0.9$ [$0.7 \alt x \alt 0.85$] due to the difference of the contribution from axial vector form factor. Because of these differences charge symmetry breaking in parton distributions will be enhanced in nuclei. [Preview Abstract] |
Monday, September 19, 2005 7:15PM - 7:30PM |
BG.00002: Measurement of inclusive jet yields in polarized $p+p$ collisions at $\sqrt s =$200 GeV. Michael Miller At RHIC, the STAR detector is uniquely capable of full jet reconstruction in
$p+p$ collisions. The calibration of the jet energy scale and transverse energy
resolution are critical to many physics analyses including, but not limited
to, extraction of the gluon polarization ($\Delta G)$ via measurement of jet
production in \textit{polarized} $p+p$ collisions (see J. Kiryluk, this meeting). Measurement of
\textit{unpolarized} jet cross sections at RHIC may provide significant additional constraints
to previously measured large-$x$ parton distributions. We present preliminary
measurements of inclusive jet yields in the transverse energy region
5$ |
Monday, September 19, 2005 7:30PM - 7:45PM |
BG.00003: The STAR Endcap Electromagnetic Calorimeter - 2005 Operation J. Sowinski An Endcap ElectroMagnetic Calorimeter (EEMC) has been built and installed on the west poletip of the STAR detector at RHIC. The EEMC is a Pb-scintillator sampling calorimeter covering the full azimuth for pseudorapidities of 1.1 $<\eta <$ 2 (37$^{\circ}>\theta>$ 15$^{\circ}$). The calorimeter is 21 radiation lengths thick at normal incidence and its 24 layers give a sampling fraction of ~5\%. The active area is divided into 720 projective towers, each read out by its own phototube to provide deposited energy. A copy of the signal from the first 2 and last layer of the towers are read out by individual channels on multi-anode PMTs as pre- and post-shower detectors. At a depth of $\sim$5 radiation lengths there is a shower maximum detector constructed of two planes of crossed triangular scintillator strips (pitch 5mm) each read out by a channel on a MAPMT. All 9360 PMT channels are digitized every 100 ns and buffered awaiting data transfer on receipt of a trigger. The tower energy signals are passed to trigger for decision on the highest tower above a threshold or a summed phi patch (1/6th) above a threshold. The detector was fully instrumented for the first time in the 2005 run. Operation and performance of the detector in the run for triggering, minimum-ionizing-particles and $\pi^0$ reconstruction will be discussed. [Preview Abstract] |
Monday, September 19, 2005 7:45PM - 8:00PM |
BG.00004: High pt pi0 measurements in pp collisions at mid-rapidity with PHENIX detector at RHIC Alexander Bazilevsky Hadron production at large transverse momenta in pp collisions provides an important testing ground for QCD and helps to constrain fragmentation mechanism. PHENIX has reported pi0 cross section in pp collisions in the pt range 1-13 GeV/c, which is described well by NLO pQCD calculations [1]. In heavy ion collisions, high pt particle production allows us to study the modification of hard scattering processes in high-density medium. Extending the measured pt range is crucial in understanding medium-induced energy loss mechanism. We discuss technique to measure high pt pi0s based on PHENIX capability of triggering on high pt photons. At pi0 pt more than $\sim$15 GeV/c two decay photons start merging in the EMCal. Finely granulated EMCal allows us to extend the pi0 measurements to pt$>$25 GeV/c using detailed shower profile analysis to discriminate between single and merged photons. We will present pi0 spectrum up to $\sim$25 GeV/c measured in Run 2005 pp collisions and comparison to NLO pQCD calculations. \newline \newline [1] S.S. Adler et al., Phys. Rev. Lett. 91, 241803 (2003). [Preview Abstract] |
Monday, September 19, 2005 8:00PM - 8:15PM |
BG.00005: Measurement of Lambda polarization in longitudinally polarized proton-proton collisions at $\sqrt{s}$ =200 GeV Qinghua Xu Measurements of Lambda polarization in polarized proton-proton collisions can give insight into polarized fragmentation functions, which are still not well constrained by existing data. Over the past several years, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has been developing the capability to collide polarized protons. This contribution reports on the measurement of $\Lambda$ polarization in longitudinally polarized proton-proton collisions at $\sqrt{s}$ = 200 GeV from the data taken in 2003 and 2004. The $\Lambda$ candidates are reconstructed at mid-rapidity with the Time Projection Chamber (TPC) of the Solenoid Tracker At RHIC (STAR). Their mean momentum fraction xF is about 8 $10^-3$ and their mean transverse momentum pT is about 1.4 GeV/c. The $\Lambda$ polarization is extracted from the asymmetry of counts in intervals of the decay angle in the Lambda rest frame for different helicity states of the colliding proton beams. In this method the detector acceptance largely cancels. Preliminary results for $\Lambda$ polarization will be given. [Preview Abstract] |
Monday, September 19, 2005 8:15PM - 8:30PM |
BG.00006: Multiparticle Measurement in Polarized Proton-Proton Collisions at PHENIX Kenichi Nakano Polarized deep inelastic lepton-hadron scattering experiments revealed that the contribution of the quark spin to the proton spin is only 20-30\%. The remaining component can be carried by the gluon spin and the angular momenta of quarks and gluons. One of the goals of the PHENIX experiment is to obtain the contribution of the gluon spin to the proton spin. With longitudinally polarized proton-proton collisions at RHIC, particles produced with high transverse momentum are measured. The PHENIX experiment has already shown results with single particle production processes. We are analyzing photons and charged particles to measure jet production process. It will give us information on event structure and higher statistics in higher-transverse-momentum region than that in single particle measurements. We need studies for better jet identification methods with a limited acceptance of the PHENIX Central Arms which cannot detect all particles from jets. In this talk, the status of data analysis and studies with event generators will be presented. [Preview Abstract] |
Monday, September 19, 2005 8:30PM - 8:45PM |
BG.00007: Measurement of the double longitudinal spin asymmetry in inclusive jet production in polarized proton-proton collisions at $\sqrt{s} = 200$ GeV. Joanna Kiryluk One of the main objectives of the spin physics program at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory is the precise determination of the polarized gluon distribution in the nucleon over a wide kinematic range, $0.01 < x_g < 0.3$, by measurements of double longitudinal spin asymmetries in collisions of polarized protons at $\sqrt{s} = 200\,\mathrm{GeV}$ and $\sqrt{s} = 500\,\mathrm{GeV}$. This contribution reports on preliminary results for the double longitudinal spin asymmetry $A_{LL}$ in inclusive jet production in polarized proton proton collsions at $\sqrt{s} = 200\,\mathrm{GeV}$. The data amount to 0.5 inverse pb and the jet transverse energies are in the range of $5 < E_T < 20\,\mathrm{GeV}$. An outlook of future STAR measurements to determine the gluon polarization in the nucleon will be provided. [Preview Abstract] |
Monday, September 19, 2005 8:45PM - 9:00PM |
BG.00008: Measurement of the transverse-spin asymmetries in \textit{pp} elastic Hiromi Okada The single transverse-spin asymmetry (analyzing power $A_N$) for pp elastic scattering is expected to reach a peak of $0.045$ in the Coulomb Nuclear Interference (CNI) region at very small momentum transfer $-t$ of $0.003$ $(\rm{GeV/\textit{c})^2}$. During the 2004 RHIC run, we completed a measurement of $A_N$ in the CNI region by detecting the recoil protons from pp elastic scattering using a polarized hydrogen gas jet target and the 100 GeV RHIC proton beam. In this talk, we will show the first measurements of the $A_N$ absolute value and shape in the $-t$ range from 0.0015 to 0.032 $(\rm {GeV/\textit{c})^2}$ with a precision better than $0.005$ for each $A_N$ data point. The recoil protons were detected with an array of Si detectors. The absolute target polarization as monitored by a Breit-Rabi polarimeter was stable at $0.924\pm 0.018$. At the same time, exploiting the polarization of target and beam, we have also measured the double transverse-spin asymmetry ($A_{NN}$). These results allow us to further investigate the spin dependence of elastic \textit{pp} scattering in the very low $-t$ region. [Preview Abstract] |
Monday, September 19, 2005 9:00PM - 9:15PM |
BG.00009: Measurement of the nuclear transparency in \textbf{A($e$,$e^\prime \pi^+$) reactions}$^1$ B. Clasie$^2$, D. Dutta$^3$, H. Gao$^{2,3}$, X. Qian$^3$ Color transparency is a phenomenon predicted by QCD in which hadrons produced at large $Q^2$ can pass through the nuclear medium with little or no interaction. Results will be presented from E01-107, an experiment that was successfully completed at Hall C at Jefferson Laboratory in 2004, where the pion electroproduction cross section from $Q^2 = 1.1~ \mathrm{to} ~4.8~ (\mathrm{GeV})^2$ was measured. The nuclear transparency is formed by the ratio of $(\sigma_A/\sigma_H)$ from the data and $(\sigma_A/\sigma_H)$ from a model of electroproduction from nuclei that does not include $\pi -N$ final state interactions. A signature of color transparency is the enhancement of the nuclear transparency at large $Q^2$ compared with predictions based on Glauber multiple scattering theory. An effect as large as $\approx 40\%$ due to color transparency is predicted in this $Q^2$ range by some models. This experiment will provide the first nuclear transparency data from ($e$,$e^\prime \pi^+$) reactions and seek unambiguous evidence for the existence of the color transparency effect. This work is supported by the US department of Energy under contract number DE-FC02-94ER40818 and DE-FG02-03ER41231 and Duke University. \newline $^{1}$On behalf of the Jefferson Laboratory E01-107 collaboration $^{2}$Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA\\ $^{3}$Triangle Universities Nuclear Laboratory, Duke University, Durham, NC 277 [Preview Abstract] |
Monday, September 19, 2005 9:15PM - 9:30PM |
BG.00010: Measurement of the Polarization of the Strange-quark Sea in the Proton Ahmed El Alaloui The polarization of the strange quarks in the proton is of particular interest in understanding the origin of its spin. An explanation of the small net contribution to the proton spin from the quark spins observed experimentally, under the assumption of SU(3) symmetry, implies a significant negative value for this quantity. Such a value would explain the violation of the Ellis-Jaffe sum rule in inclusive deep-inelastic scattering (DIS). The total strange quark helicity density $\Delta S\equiv[\Delta s(x)+\Delta \overline{s}(x)]$ carries no isospin. It can extracted from measurements of scattering from deuterium alone, an isoscalar target. Measurements of the inclusive double spin asymmetries probe the helicity density of the non-strange sea. Using semi-inclusive asymmetries for charged kaons as the second data set it is possible to extract $\Delta S$ directly. By measuring the charged kaon multiplicities at HERMES kinematics, the fragmentation functions needed for the extraction can be obtained without resort to other experiments. The only symmetry assumed is charge-conjugation invariance. Results of a direct leading-order extraction of $\Delta S$ using this approach with DIS data from the HERMES experiment at the HERA accelerator will be presented. [Preview Abstract] |
Monday, September 19, 2005 9:30PM - 9:45PM |
BG.00011: Strangeness form factors of the proton: Results from the G0 forward angle measurement Lars Hannelius The G0 experiment at Jefferson Lab has recently concluded its first phase: a measurement of the parity-violating (PV) asymmetry in polarized electron-proton scattering over a four-momentum transfer range $0.12 < Q^2 < 1.0$ GeV$^2$ at a beam energy of 3 GeV. This PV asymmetry, which arises through the interference of the electromagnetic and neutral weak interactions, can be related to the strangeness vector current matrix element $\langle N | \bar s \gamma_\mu s | N \rangle$, and thereby provide information about the non-perturbative $\bar ss$ sea in the nucleon. In particular, the G0 measurement yields a linear combination of the proton's strangeness electric and magnetic form factors $G_{E,M}^s$ in each of 18 $Q^2$ bins. In this talk I will give a brief overview of PV electron-proton scattering, the G0 experimental apparatus, the data analysis, and then present results from the G0 forward angle measurement. [Preview Abstract] |
Monday, September 19, 2005 9:45PM - 10:00PM |
BG.00012: Quark model calculation of spin-transfer observables for $\bar{p}p\rightarrow \bar{\Lambda}\Lambda$ Mary Alberg, Ernest Henley, Peter Kunz, Lawrence Wilets The reaction $\bar{p}p \rightarrow\bar{\Lambda}\Lambda$ provides a test for models of strangeness production. Models of the strangeness production mechanism have been developed in terms of meson-baryon or quark-gluon degrees of freedom. Although both types of model have been successful in reproducing the measurements of PS185 for unpolarized proton targets, their predictions for the spin- transfer observables $D_{nn}$ and $K_{nn}$ are in disagreement with recent measurements for a polarized target. We have carried out an improved DWBA calculation of cross sections and spin observables for this reaction using a quark model for the strangeness production mechanism. Our initial state interaction is determined by a good fit to $\bar{p}p$ elastic scattering data in a momentum range corresponding to the $\bar{\Lambda}\Lambda$ production experiment. The reaction mechanism includes effective scalar and vector quark annihilation and creation contributions. The free parameters of the calculation include the strengths of the scalar and vector exchanges, a quark cluster size parameter, and parameters of the unknown $\bar{\Lambda}\Lambda$ interaction. Comparison with the published experimental results from PS185 is made, including both observables and spin density matrix parameters. This work is supported in part by the U.S. National Science Foundation, Award No. 0070942, and the U.S. Department of Energy. [Preview Abstract] |
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BG.00013: Experimental Study of Duality in SIDIS at JLab Peter Bosted Measurements of semi-inclusive deep-inelastic scattering have been made using an unpolarized electron beam of energy 5.5 GeV scattering from both proton and deuteron targets. Measurements were made with $\pi^+$ or $\pi^-$ detected in coincidence with the electrons. The dependence of hadron kinematic variable was studied for $0.3 < z < 1$ and $0 < p_t < 0.5$ GeV for average electron kinematic vvariables $x=0.32$ and $W=2.5$ GeV. The $x$-dependence was also studied in the range $0.2 < x < 0.5$ for average $z= 0.55$. Although the electron-pion missing mass $W^\prime<2$ GeV for these data, they are reasonably consistent (for $z < 0.7$) with expectations from higher energy data assuming factorization of quark densities functions and current fragmentation functions. [Preview Abstract] |
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