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 KA: QCD Beyond Three Quarks |
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Sponsoring Units: DNP JPS Chair: Peter Bosted, Thomas Jefferson National Accelerator Facility Room: Ritz-Carlton Hotel Salon 4 |
Thursday, September 22, 2005 2:00PM - 2:45PM |
KA.00001: Experimental status of the pentaquark searches Invited Speaker: Since the LEPS at SPring-8 collaboration reported the first evidence for the $\Theta^+$ which has a quark configuration of $uudd\bar{s}$, extensive experimental efforts have been made to confirm the existence of the $\Theta^+$ and other pentaquarks. In my talk, I will report on the experimental evidences and counter evidences for the pentaquarks. Results from recent dedicated experiments will be extensively covered. [Preview Abstract] |
Thursday, September 22, 2005 2:45PM - 3:30PM |
KA.00002: Determination of nuclear parton distribution functions and their uncertainties Invited Speaker: Data of nuclear structure function F$_{2}$ and Drell-Yan cross-section ratios are analyzed for obtaining nuclear parton distribution functions, and their uncertainties are estimated by the Hessian method. Valence-quark distributions are determined well by the F$_{2}$ data in the large-x region. Their small-x behavior is constrained by baryon-number and charge conservations. Antiquark distributions are determined in the small-x region (x$\sim $0.01) by the F$_{2 }$data and in the region x$\sim $0.1 by the Drell-Yan data; however, their nuclear modifications are not obvious in the large-x region. Current data are not enough to determine nuclear gluon distributions because they have large uncertainties in the whole x region. A useful code could be obtained from our web site for calculating nuclear parton distribution functions. [Preview Abstract] |
Thursday, September 22, 2005 3:30PM - 4:15PM |
KA.00003: The Search for Color Transparency - A Color Coherence Effects in Nuclear Physics Invited Speaker: Mapping the transition of the strong interaction from the hadronic degrees of freedom to the partonic degrees of freedom of quantum chromodynamics (QCD), is an important goal in intermediate energy nuclear and particle physics. The need for such a mapping arises from the fact that at low energies the nucleon-meson picture is very successful in describing the overall features of the strong interaction, while at high energies perturbative QCD (pQCD) with its quark-gluon degrees of freedom allows extremely precise description of the interaction. Unfortunately, there is no clear understanding of how these two regimes are connected. One of the popular approaches used to study the transition between these two regions involves searching for the onset of various phenomena which are naturally predicted in pQCD. One such phenomena is Color Transparency (CT), which refers to the suppression of final (and initial) state interactions of hadrons with the nuclear medium in exclusive processes at high momentum transfers. I will review the status of the experimental search for CT covering experiments spanning over a decade. I will also show preliminary results from a few recently completed experiments at Jefferson Lab (JLab) and talk about future experiments being planned at JLab following the proposed upgrade to 12 GeV. This work is supported by the U.S. Department of Energy under contract number DE-FG02-03ER41231. [Preview Abstract] |
Thursday, September 22, 2005 4:15PM - 5:00PM |
KA.00004: Hadronization within the Nuclear Environment Invited Speaker: Details of the hadronization process remain difficult to probe. Experimentally one can only detect the fully formed hadron. Studies of parton fragmentation from high energy collisions are explained by semi-empirical models, but are typically insensitive to details of the formation process. By studying the fragmentation process within the nuclear medium, one can hope to explore the time-development of the hadronic state, that is, the dynamics of confinement. Recent high-energy experiments at RHIC have provided new measurements of fragmentation within both cold and hot partonic matter. Since the properties of the hot matter are deduced from the produced hadrons, a more detailed understanding of the hadronization process may allow one to learn more precise information about the state formed in the heavy-ion collision. Measurements from $d-Au$ collisions are forthcoming which test the modifcation of hadronization in cold nuclear matter, and at the same time, the $B$-factories are determining the basic fragmentation functions to an unparalled precision. Semi-inclusive deep inelastic scattering of leptons from nuclei provides a unique window on the hadronization process in cold nuclear matter since the momentum of the initially struck parton is experimentally determined; in addition, initial state hadronic effects are largely suppressed. The influence of the nuclear medium on the production of hadrons has been recently studied in the Hermes experiment at DESY in semi-inclusive deep-inelastic scattering of 27.6~GeV positrons off deuterium, helium, neon, nitrogen and krypton targets. Differential multiplicities for the heavier nuclei relative to deuterium have been determined for $\pi^+$, $\pi^0$, $\pi^-$, $K^+$, $K^-$, $p$ and $\bar p$, as a function of the virtual photon energy $\nu$, the fraction $z$ of the energy transfered to the hadron, the hadron transverse momentum squared, $p_T^2$, and the four-momentum squared of the virtual photon, $-Q^2$. New measurements of two-hadron attenuation will also be presented. Strong nuclear effects are seen, which depend also on hadron identity and nuclear size. Results will be compared to predictions of theoretical models which seek to explain hadron formation within the nuclear medium, and compared with recent results from RHIC. [Preview Abstract] |
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