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 ED: Mini-symposium on Orbital Motion of Quarks in Hard Scattering I |
Hide Abstracts |
Sponsoring Units: DNP JPS Chair: Volker Burkert, Thomas Jefferson National Accelerator Facility Room: Ritz-Carlton Hotel Salon 1 |
Wednesday, September 21, 2005 9:00AM - 9:30AM |
ED.00001: Target Spin Asymmetries from CLAS/JLab Invited Speaker: The CLAS detector at Jefferson lab was used to measure
semi-inclusive deep-inelastic scattering of 5.7 GeV electrons
from
longitudinally polarized protons in an NH$_3$ target. The target
single spin asymmetry is observed to have a significant
azimuthal
angle dependence for $\pi^+$, $\pi^0$, and $\pi^-$, which have
been fit with a combination of $\sin(\phi)$ and $\sin(2\phi)$
terms,
sensitive to the product of the spin-dependent Collins
fragmentation function and twist-3 and twist-2 transverse
momentum
dependent quark distribution functions, respectively. The data
suggest non-zero quark transverse polarization in a
longitudinally
polarized target, in agreement with a prediction in the quark
chiral soliton model. Studies
of the double spin asymmetries $A_{LL}$ in the same data set
support the applicability of factorization in the kinematic
region
studied ($W>2$ GeV, $Q^2>1.1$ GeV$^2$, and $0.4 |
Wednesday, September 21, 2005 9:30AM - 9:45AM |
ED.00002: Pion Photoproduction in the Photon Frame Ronald Gilman, Andrei Afanasev Exclusive photoreactions have been interpreted to indicate the importance of orbital angular momentum in the reaction spin dynamics, such as in the proton electromagnetic form factors. Of recent interest is the observation that $K^+\Lambda^0$ electroproduction polarizes the lambda in the photon spin direction (D. S. Carmen et al., Phys. Rev. Lett. 90, 131804 (2004).). This result shows that helicity is not conserved, and that orbital angular momentum is again important. We have reanalyzed previously published pion photoproduction data (K. Wijesooriya et al., Phys. Rev. C 66, 034614 (2002).) in the photon frame to investigate whether it too displays any simple behavior. It does not. This work was supported in part by the U.S. Department of Energy contract DE-AC05-84ER40150 under which the Southeastern Universities Research Association (SURA) operates the Thomas Jefferson National Accelerator Facility, and by the National Science Foundation grant PHY 03-54871 to Rutgers University. [Preview Abstract] |
Wednesday, September 21, 2005 9:45AM - 10:00AM |
ED.00003: Azimuthal dependence in unpolarized proton-induced Drell-Yan process Lingyan Zhu, Jen-Chieh Peng, Paul Reimer For unpolarized Drell-Yan process, a $\cos(2\phi)$ azimuthal distribution could arise from the presence of a chiral-odd, transverse-momentum dependent quark distribution function, $h_1^{\perp}$. In quark-diquark model, $h_1^{\perp}$ is equal to the Sivers function. Both the Sivers function and the $h_1^{\perp}$ are predicted to undergo a sign-change in the Drell-Yan process as compared to the Semi-Inclusive Deep-Inelastic scattering. A significant $\cos(2\phi)$ distribution has been observed in pion-induced Drell-Yan process and has been interpreted in terms of the $h_1^{\perp}$ distribution function. Additional information on the origin of the $cos(2\phi)$ dependence could be obtained from an analysis of the unpolarized proton-induced Drell-Yan data. Preliminary results from an analysis of the Fermilab E866 800 GeV p+p and p+d Drell-Yan data for the $\cos(2\phi)$ azimuthal distribution will be presented. [Preview Abstract] |
Wednesday, September 21, 2005 10:00AM - 10:15AM |
ED.00004: Transverse momentum distribution of Drell-Yan pair in transversely polarized proton-proton collision Kazuhiro Tanaka, Hiroyuki Kawamura, Jiro Kodaira, Hirotaka Shimizu We discuss the QCD predictions for the transverse momentum ($Q_T$) distribution of Drell-Yan pair, produced in collisions of transversely polarized protons. We compute the 1-loop QCD corrections to transversely polarized Drell-Yan process at a measured $Q_T$ and azimuthal angle of the produced lepton in the dimensional regularization scheme. We also include soft gluon effects at small $Q_T$ by all-order resummation of logarithmically enhanced contributions up to next-to-leading logarithmic accuracy. We demonstrate that the soft gluon resummation leads to a well- defined, finite prediction of the cross section for all region of $Q_T$. We show the numerical results of the cross section using the transversity distributions $\delta q(x,Q^2 )$ which satisfy the Soffer inequality. We also discuss role of nonperturbative corrections related to the intrinsic transverse momentum distributions of partons inside protons, and present the results for the transverse double-spin asymmetry $A_{TT}$. [Preview Abstract] |
Wednesday, September 21, 2005 10:15AM - 10:30AM |
ED.00005: Dilepton production near partonic threshold in transversely polarized $\bar{p}p$ scatterings Hiroshi Yokoya, Hirotaka Shimizu, George Sterman, Werner Vogelsang Recently, it has been suggested that collisions of transversely polarized protons and antiprotons at the GSI could be used to determine the nucleon's transversity densities from measurements of the double-spin asymmetry for the Drell-Yan process. We investigate the QCD higher-order corrections, in this kinematic regime, in terms of available fixed-order contributions as well as of all-order soft-gluon resummations. We find these corrections are large, especially at large invariant mass regions. We examine the resummation formula with physically motivated cut-off which keep it away from the region where non-peturbative dynamics take place. We find that this reduce the large enhancements, moderately at lower scale collision, but rather at higher scale collisions. The unpolarized dilepton cross section for the GSI kinematics may therefore provide information on the relation of perturbative and nonperturbative dynamics in hadronic scattering. The spin asymmetry turns out to be rather robust, relatively insensitive to higher orders, resummation, and the cut-offs. [Preview Abstract] |
Wednesday, September 21, 2005 10:30AM - 10:45AM |
ED.00006: Twist-3 Mechnism for Single Spin Asymmetry Reexamined Yuji Koike, Kazuhiro Tanaka In the framework of the collinear factorization, single transverse spin asymmety (SSA) is a twist-3 observable which represents quark-gluon correlations in a hadron. In this talk, we present a lightcone-gauge calculation of SSA for the direct-photon production in the pp collision which is relevant for the RHIC-SPIN program. Some time ago, Qiu and Sterman presented a Feynman-gauge calculation for the quantity. The derivation of the cross section for SSA involves identification of the pole contribution in the Feynmann diagram, and expressing SSA in terms of gauge invariant correlation functions is quite involved. So it is interesting to reexamine the result in a different gauge. After identifying the relation between different representations of the twist-3 distribution functions for the transversely polarized nucleon, we show how each pole contribution can be identified and expressed in terms of the gauge invariant functions in the lightcone gauge. [Preview Abstract] |
Wednesday, September 21, 2005 10:45AM - 11:00AM |
ED.00007: Transverse Spin Results from STAR William Christie One of the main objectives of the Spin physics program at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory is to study transverse spin effects. Measurements of large Feynman x (xF) neutral pion production in polarized proton collisions at sqrt(s) = 200 GeV has been reported by STAR. Cross section measurements at eta = 3.3, 3.8, and 4.0 were found to be consistent with next-to-leading order perturbative QCD calculations. The analyzing power was found to be large and positive at xF$>$0.3, and consistent with phenomenological calculations based on the Collins effect, the Sivers effect, and initial-state higher twist contributions. This contribution will summarize these measurements, as well as give an outlook of future STAR semi-inclusive measurements to determine the Transversity and Sivers distribution functions. [Preview Abstract] |
Wednesday, September 21, 2005 11:00AM - 11:15AM |
ED.00008: Double Longitudinal Asymmetry in Jet k$_{t}$ Measured in Di-hadron Correlations in Polarized p+p Collisions at $\sqrt s $= 200GeV in the PHENIX Experiment at RHIC Robert Hobbs By measuring the azimuthal correlations between two high p$_{t}$ hadrons, one can extract jet properties such as the fragmentation transverse momentum j$_{t}$ and the ``intrinsic'' transverse momentum k$_{t}$.~ In longitudinally polarized p+p collisions, differences in the extracted average k$_{t}$ for like and un-like helicity combinations (double asymmetry) may give information on the relationship between the polarization and the partonic transverse momentum, and thus the orbital angular momentum of the hard-scattered partons.~ This method is similar to a technique previously suggested by Meng Ta-chung et al. in the Drell-Yan channel.~ In this talk we present the physics technique, the analysis method and the current status of the analysis for $\pi ^{0}$ - hadron azimuthal correlations in PHENIX with data from RHIC in 2003, 2004 and 2005. [Preview Abstract] |
Wednesday, September 21, 2005 11:15AM - 11:30AM |
ED.00009: Measurement of Transverse Single-Spin Asymmetries in Neutral Pion and Charged Hadron Production at PHENIX Waled Emam A number of experiments studied polarized proton collisions at center of mass energies $\sqrt{s} \leq 20$ GeV and observed large transverse single-spin asymmetries for pion production at high $x_F$ and moderate transverse momentum ($0.5 \leq p_T \leq 2.0$ GeV/c). At high center of mass energy of 200 GeV the $\pi^0 $ asymmetry at high $x_F$ was found to persist. On the other hand, a 20-GeV measurement of the asymmetry in $\pi^0$ production at $-0.15 < x_F < +0.15$ and $1 < p_T < 4$ GeV/c was found to be consistent with zero. These asymmetries can be generated by spin-dependent effects such as the Collins fragmentation function and the Sivers function. The PHENIX experiment, one of the large experiments being conducted at the Relativistic Heavy Ion Collider (RHIC), has measured the transverse single-spin asymmetries for mid-rapidity production of neutral pions and non-identified charged hadrons in polarized proton-proton collisions. From data collected during the 2001-2 run at $\sqrt{s} = 200$ Gev, $0.5 < p_T < 5.0$ GeV/c, and $x_F$ close to zero, the asymmetries seen are consistent with zero within statistical errors of a few percent. [Preview Abstract] |
Wednesday, September 21, 2005 11:30AM - 11:45AM |
ED.00010: New Prospects for Transverse Physics with the PHENIX detector Mickey Chiu PHENIX has made measurements of the transverse single spin asymmetry $A_N$ for pi-zero and non-identified charged hadrons near $x_F~\sim~0$ at collider energies, and measurements of pi-zero $A_N$ and pi+/pi- have also been made at the same $\sqrt{s}$ but at $x_F$ up to 0.6 by the STAR and Brahms collaborations. Asymmetries as large as $\sim~30\%$ have been found. Currently, these large asymmetries are thought to come either from higher-twist contributions, modifications to the parton distribution functions (Sivers), modifications to the fragmentation functions (Collins), or even perhaps some combination of the three. Future progress will require separating these effects. We discuss future prospects with the PHENIX detector for reducing these ambiguities in inclusive single spin asymmetries by looking at correlations between hadrons from the same and from back to back jets. [Preview Abstract] |
Wednesday, September 21, 2005 11:45AM - 12:00PM |
ED.00011: Measurement of the single transverse-spin asymmetry of forward neutrons in p-p collisions at RHIC-PHENIX Manabu Togawa The Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory (BNL) has been operated with polarized proton beams colliding at the center of mass energy $\sqrt{s}$=200 GeV. In the RUN2 (2001-2002), a large single transverse spin asymmetry $A_{N}$ (-10\%) of the forward neutrons measured at the 12 o'clock interaction point experiment. In the ISR experiment, it is $\sqrt{s}$=30.6 to 62.7 GeV in p-p collisions, the cross-section of forward neutron production was measured to be lager than at mid-rapidity. Our understanding of this effect is based on pion exchange. The forward neutron asymmetry can shed new light to understand such forward physics. Trough the 2003-2005, PHENIX experiment has measured the forward neutrons by ZDC(Zero Degree Calorimeter) with SMD(Shower Max Detector) which is position sensitive detector. The energy resolution of ZDC is twice better than that of the hadron calorimeter which was used in the 12 o'clock experiment. In this talk, we will report the measurement of neutron asymmetry by the PHENIX experiment and discuss the physics implication of the neutron asymmetry. [Preview Abstract] |
Wednesday, September 21, 2005 12:00PM - 12:15PM |
ED.00012: Polarization Measurement of 100GeV Proton Beams at RHIC with CNI $\vec {p}$C Polarimeter Itaru Nakagawa The polarization measurement through elastic ($\vec {p}$,C) reaction plays a crucial role in the polarized proton beam operation of Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The analyzing power of the reaction reaches its maximum in the Coulomb Nuclear Interference (CNI) region (0.001 $< \quad t \quad <$ 0.01 (GeV/c)$^{2})$, although it is still as small as 4{\%}. Despite the size of asymmetry, a few percent statistical accuracy can be achieved within 20 seconds at proton beam intensity of $60\times 10^{11}$, because of a large reaction cross section. The polarimeter thus serves realtime feedbacks to an accelerator tuning and experiments. The polarimeter consisted of ultra thin (3.5 $\mu $g/cm$^{2})$ carbon ribbon targets and six silicon strip detectors per beam. Each detector is segmented into 12 strips with 2 mm pitches. Independent measurements of total 72 channels will provide a chance of detailed systematic studies. In this talk, I will describe recent upgrades and improvements of the polarimeter and analysis for Run05. [Preview Abstract] |
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