Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session X12: Hadronic Physics II |
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Sponsoring Units: DNP Chair: Kenneth Hicks, Ohio University Room: Marriott Tampa Waterside Room 11 |
Tuesday, April 19, 2005 10:45AM - 10:57AM |
X12.00001: A Pomeron-Quark Vertex that Has The Correct Property under The Charge Conjugation Lon-chang Liu High-energy $pp$ scattering suggests that its leading-order dynamics is associated with the exchange of a Pomeron between two quarks. One extensively used model for the Pomeron-quark coupling is the $\gamma_{\mu}$ coupling model where the Pomeron couples to a quark like an isoscalar photon [P.V. Landshoff and O. Nachtmann, Z. Phys.C35, 45 (1987); A. Donnachie and P.V. Landshoff, Phys. Lett. B185, 403 (1987)]. The model has, however, an intrinsic difficulty, namely, the $\gamma_{\mu}$ coupling is odd under charge conjugation while the Pomeron exchange is even under the charge conjugation [M.A. Pichkowsky and T.-S. H. Lee, Phys. Rev. D56, 1644 (1997)]. I show that the Pomeron-quark coupling behaves like a tensor coupling which has the correct transformation property under the charge conjugation. [Lon-chang Liu, Proc. of The 10th International Baryons Conference, Palaiseau, France, 2004]. I further show why the $\gamma_{\mu}$ model can have empirical success inspite of its difficulty at the basic level. [Preview Abstract] |
Tuesday, April 19, 2005 10:57AM - 11:09AM |
X12.00002: Some Aspects of Semileptonic Decay of Baryons Muslema Pervin, Simon Capstick, Winston Roberts We calculate baryon semileptonic decay form factors and rates in a quark model. Our calculations are carried out using two different bases for the baryon wave functions, the usual harmonic oscillator basis, along with the Sturmian basis. We also examine decays to excited states, and find that the branching ratio for the decays of the $\Lambda_c$ to excited $\Lambda$ is not insignificant. [Preview Abstract] |
Tuesday, April 19, 2005 11:09AM - 11:21AM |
X12.00003: Study of $\eta N$ scattering length by means of ($p,^{3}$He) nuclear reactions leading to the formation of $\eta$-mesic nucleus Q. Haider, L.C. Liu Because $\eta N$ scattering length is not directly measurable, its value is strongly model dependent$^{1}$. A good knowledge of this scattering length is, however, valuable to the modeling of various hadronic interactions where $\eta$ is produced. Since low energy $\eta N$ interaction is attractive and $\eta$-mesic nuclei can exist$^{2}$, we suggest to use the $p+A\rightarrow ^{3}$He $+(A-2)_{\eta}$ reaction to probe the $\eta N$ scattering length. In our model, the $\eta$ is first produced via $p+d\rightarrow \eta + ^{3}$He reaction, and then captured by the residual nucleus of nucleon number $A-2$. As a stronger scattering length allows $\eta$ to be bound onto lighter nuclei, the smallest value of $(A-2)$ for which $\eta$-nucleus bound states can exist will set an upper limit for the scattering length. Our choice of having $^{3}$He in the final state is for the purpose of significantly reducing background events. This suggestion will soon be implemented in an experiment at Juelich, Germany. We will present our predictions for $^{16}$O and $^{12}$C as target nuclei, leading to $^{14}$N$_{\eta}$ and $^{10}$B$_{\eta}$, respectively. Sensitivity of the $\eta$-mesic nucleus formation to the $\eta N$ scattering length will also be discussed.\\ $^{1}$ Q. Haider and L.C. Liu, Phys. Rev. {\bf C 66}, 045208 (2002).\\ $^{2}$ Q. Haider and L.C. Liu, Phys. Lett. {\bf B 172}, 257 (1986). [Preview Abstract] |
Tuesday, April 19, 2005 11:21AM - 11:33AM |
X12.00004: Measurement of the $^{3}$He and Neutron Spin Structure at Low Q$^{2}$ Vincent Sulkosky The Gerasimov-Drell-Hearn (GDH) sum rule was originally derived for real photon absorption (corresponding to Q$^{2}$=0) and has been generalized to finite Q$^{2}$. The goal of Jefferson Lab experiment E97-110 is to perform a precise measurement of the generalized GDH integral and the moments of the neutron spin structure functions in order to study their Q$^{2}$ dependence between 0.02 and 0.3 (GeV/c)$^{2}$. This Q$^{2}$ range will allow us to test the dynamics of Chiral Perturbation Theory, extrapolate to the integral's real photon point for $^{3}$He and the neutron, and will complement a previous experiment at higher Q$^{2}$. The measurement will provide new constraints on the $^{3}$He and neutron spin structure and contribute to the understanding of the nucleon resonances. The acquisition of data was completed using the Jefferson Lab high polarization continuous-wave electron beam, the Hall A polarized $^{3}$He target, and one of the Hall A septum magnets, which allow measurements at forward angles of 6 and 9 degrees. The status and prospects will be discussed. [Preview Abstract] |
Tuesday, April 19, 2005 11:33AM - 11:45AM |
X12.00005: The Double-Longitudinal Spin Asymmetry in Charged Pion Production at PHENIX: Determining the Sign of $\Delta g$ Christine Aidala The Relativistic Heavy Ion Collider (RHIC) began colliding polarized protons in 2001. Early measurements of the double- longitudinal asymmetry ($A_{LL}$) in the production of neutral pions, sensitive to $\Delta g$, the gluon's contribution to the spin of the proton, have been performed by the PHENIX experiment. Because a significant fraction of pion production in the presently accessible kinematic region is due to gluon-gluon scattering, the factorized polarized cross section contains $\Delta g$ twice, and thus the current measurement is not sensitive to the sign of the gluon contribution. Pion production at higher transverse momentum ($p_T$) will be dominated instead by quark-gluon scattering. The difference between $A_{LL}$ of positive and negative pions at high $p_T$ will be particularly sensitive to the sign of $\Delta g$. The current status of the charged pion $A_{LL}$ analysis using PHENIX data from the 2003 and 2004 polarized proton runs at RHIC will be presented. [Preview Abstract] |
Tuesday, April 19, 2005 11:45AM - 11:57AM |
X12.00006: FNAL E906: Extending Dimuon Measurements to New Kinematic Regions Rusty Towell Fermilab E866/NuSea performed the first measurements of the absolute Drell-Yan cross section in 800 GeV/c p+p and p+d collisions over a broad kinematic region. It also measured the 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 quark 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] |
Tuesday, April 19, 2005 11:57AM - 12:09PM |
X12.00007: Techniques for evaluating parallel random number generator Shu-Ju Tu, Ephraim Fischbach We have developed two statistical schemes to quantify random number generators used in parallel computation. The first method is based on the GRIP (Geometric Random Inner Products) formalism that applies geometric probability theory to evaluate the average scalar products for the random vectors distributed in geometric objects. We explicitly used the GRIP tests to compare some parallel random number generators. A visualization technique to evaluate the quality of the parallel random number generators was also developed. The method is based on the quantum noise simulation in cone beam computed tomography imaging. The Feldkamp algorithm was applied to reconstruct the phantom images containing quantum noise simulated from parallel random number generators. A mathematical phantom was analytically sampled and the results indicated that regular geometrical patterns can be observed in the reconstructed images produced from correlated random number sequences. [Preview Abstract] |
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