Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session W15: Hadronic Physics |
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Sponsoring Units: DNP Chair: Bernd Surrow, MIT Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), St. Louis H |
Tuesday, April 15, 2008 10:45AM - 10:57AM |
W15.00001: New Results on $\Upsilon$ Production Using p+p and p+d Interactions Paul Reimer, Lingyan Zhu, Jen-Chieh Peng The NuSea/E866 experiment at Fermilab has completed a high statistics measurement of $\Upsilon$ production using an 800 GeV/c proton beam on liquid hydrogen and deuterium targets. The dominance of the gluon-gluon fusion process for $\Upsilon$ production at this energy implies that the cross section ratio, $\sigma(p + d \rightarrow \Upsilon)$, is sensitive to the gluon content in the neutron relative to that in the proton. Over the kinematic region $0 < x_F < 0.6$, this ratio is found to be consistent with unity, in striking contrast to the behavior of the Drell-Yan cross section ratio $\sigma(p + d)_{DY}/2\sigma(p + p)_{DY}$. This is consistent with no charge symmetry breaking effect in the gluon distributions, showing that the gluon distributions in the proton and neutron are very similar. The $\Upsilon$ production cross sections are also compared with the $(p + d)$ and $(p + Cu)$ cross sections from earlier measurements. [Preview Abstract] |
Tuesday, April 15, 2008 10:57AM - 11:09AM |
W15.00002: New program for decay pion spectroscopy of light hypernuclei at JLAB Liguang Tang The unique beam parameters (high intensity, small emittance, and fine beam bunch time structure) of the CW electron beam at Jefferson Laboratory and the well established HKS spectrometer system for hypernuclear spectroscopy opens new opportunity for a high precision decay pion spectroscopy program. The decay pion contains information that offers wide range of hypernuclear and nuclear physics, from precise determination of binding energy of the ground state of light hypernuclei to study YN interaction, investigation of highly exotic hypernuclei to study mechanism for exotic nuclei, to probing the detailed low lying nuclear structure with the nuclear ``impurity'' -insertion of a $\Lambda$ into the nucleus. Combination of the CEBAF beam (electro-production of hypernuclei) and the HKS system makes the program capable to reach a high energy resolution of $\sigma\sim55$ keV thus rich physics can be learned from the decay pions from two body mesonic hypernuclear decay. The physics and experimental technique will be presented. [Preview Abstract] |
Tuesday, April 15, 2008 11:09AM - 11:21AM |
W15.00003: Beam Spin Asymmetry Measurements from Deeply Virtual Meson Production Bo Zhao, Rita De Masi, Michel Gar\c con, Kyungseon Joo, Valery Kubarovsky, Paul Stoler, Maurizio Ungaro The study of pseudoscalar meson production allows one to access the properties of the polarized Generalized Parton Distributions(GPDs), which is a part of the analysis for e1-dvcs experiment. This experiment was run at Jefferson Lab during the spring of 2005 with the CLAS detector, using a 5.7 GeV longitudinally polarized electron beam impinging on a liquid Hydrogen target. In this presentation, the results of the beam spin asymmetry measurements from the $\eta$ and $\pi^{0}$ channels will be discussed. [Preview Abstract] |
Tuesday, April 15, 2008 11:21AM - 11:33AM |
W15.00004: Quark Dressing and Constituent Mass Behavior for Heavy Quark Mesons Nicholas Souchlas, Pieter Maris, Peter Tandy We explore the effects of quark dressing upon the masses and electroweak decay constants of ground state pseudoscalar and vector quarkonia and heavy-light mesons. Quark masses are varied from the u/d region to the b-quark region. The effectiveness of a constituent mass approximation is evaluated. Residual effects of dressing are clearly evident in the values of the decay constants in the c- and b-quark regions. This fully covariant study is made with a consistent ladder-rainbow truncation for the Bethe-Salpeter and Dyson-Schwinger equations. [Preview Abstract] |
Tuesday, April 15, 2008 11:33AM - 11:45AM |
W15.00005: Parity Determination of the $\Lambda(1405)$ Kei Moriya, Reinhard Schumacher The $\Lambda(1405)$ is a well-established hyperon state just below N $\bar{\mathrm{K}}$ threshold. Previous studies of its spin and parity have been inconclusive, but consistent with $J=1/2$. Using the CLAS system at Jefferson Lab, we collected an event sample of $\sim 1.8 \times 10^5$ reconstructed $\Lambda(1405)$ hyperons photoproduced off the proton, with photon energies between 1.5 and 3.9 GeV. We present preliminary results of the first definitive measurement of the parity of the $\Lambda(1405)$ using the method of Byers and Fenster. The method relies on our observation that the $\Lambda(1405)$ is produced polarized in this reaction. Determination of the polarization axis of the $\Sigma^+$ hyperon from the decay of a $J=1/2$ $\Lambda(1405)$ to $\Sigma^+ \pi^-$ then reveals the parity of the parent state. [Preview Abstract] |
Tuesday, April 15, 2008 11:45AM - 11:57AM |
W15.00006: Line Shapes of Exotic $c \bar{c}$ Mesons Meng Lu, Eric Braaten The B-factory experiments have discovered a series of charmonium-like mesons, including the $X(3872)$ and the first manifestly exotic meson $Z^+(4430)$. The proximity of the masses of these two mesons to thresholds for pairs of charm mesons has motivated their interpretations as charm meson molecules. Given these interpretations, we investigate the invariant mass distributions (line shapes) of $X(3872)$ and $Z^+(4430)$ by taking advantage of the universality of $S$-wave bound states with small binding energies and by including the effects from the nonzero widths of their constituents. We isolate the dependence of the line shapes on the details of QCD into constant factors. We make quantitative predictions of the line shapes for the $X(3872)$ and the $Z^+(4430)$ with an emphasis on the difference between the line shapes in decay modes containing a charmonium and those containing two charm mesons. [Preview Abstract] |
Tuesday, April 15, 2008 11:57AM - 12:09PM |
W15.00007: Estimate of $\langle \bar q q \bar q q \rangle$ from the V-A Current-Current Correlator Trang Nguyen, Peter Tandy In QCD, the difference of the current-current correlators for vector and axial vector currents, in a color singlet and flavor non-singlet channel, is zero to all orders in perturbation theory if the quarks are massless. As an example of the efficiency of this so-called V-A correlator in probing nonperturbative phenomena, its leading ultraviolet term is proportional to the scalar 4-quark condensate $\langle \bar q q \bar q q \rangle$. This condensate is a key ingredient in QCD sum rule analyses of hadronic properties and, in the absence of independent information, it is often assumed that vacuum saturation holds, namely $\langle \bar q q \bar q q \rangle \approx \langle \bar q q \rangle^2$. We describe here an independent estimate based upon direct evaluation of the current-current correlators within a ladder-rainbow truncated model of QCD. Our results indicate that $\langle \bar q q \bar q q \rangle$ is significantly larger than what vacuum saturation would suggest. [Preview Abstract] |
Tuesday, April 15, 2008 12:09PM - 12:21PM |
W15.00008: Strangeness Production on the Neutron in the Deuteron with Polarized Photons: $\vec{\gamma} n \rightarrow K^+ \vec{\Sigma}^-$ Edwin Munevar, Barry Berman As in the case of atomic systems, the measurement of the excited spectrum of nucleons provides valuable information about their internal composition. The study of the extra excited states of the nucleon (missing resonances) predicted by the constituent quark model but not found experimentally are key in the understanding of the nucleon structure. The experimental search for these missing states is believed to be more effective using strangeness channels because they offer the possibility of determining several spin observables. A recent experiment done using the CLAS system at JLab, based on a liquid deuterium target and a polarized photon beam covering from threshold to 2.5 GeV provides high-quality data (about 52 billion triggers) in strangeness production on the neutron. These neutron channels are important for constraining phenomenological models. A brief description of this experiment along with a very preliminary analysis for the $\vec{\gamma} n \rightarrow K^+ \vec{\Sigma}^-$ reaction will be presented [Preview Abstract] |
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