Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session EF: Mini-Symposium on Baryon Resonances and Meson Production II |
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Chair: Mark Paris, Jefferson Lab Room: Newport News Marriott at City Center Pearl Salon II |
Friday, October 12, 2007 2:00PM - 2:12PM |
EF.00001: Roper transition form factor from Lattice QCD Huey-Wen Lin, Robert Edwards Experiments at Jefferson Laboratory, MIT-Bates, LEGS, Mainz, Bonn, GRAAL, and Spring-8 offer new opportunities to understand in detail how nucleon resonance ($N^*$) properties emerge from the nonperturbative aspects of QCD. Preliminary data from CLAS collaboration, which cover a large range of photon virtuality $Q^2$ shows interesting behavior with respect to $Q^2$ dependence: in the region $Q^2 \le 1.5 \mbox{ GeV}^2$, both the transverse amplitude, $A_{1/2}(Q^2)$, and the longitudinal amplitude, $S_{1/2}(Q^2)$, decrease rapidly. In this work, we attempt to use first-principles lattice QCD (for the first time) to provide a model-independent study of the Roper-nucleon transition form factor. [Preview Abstract] |
Friday, October 12, 2007 2:12PM - 2:24PM |
EF.00002: High resolution hypernuclear spectroscopy in a wide mass region Lulin Yuan High resolution hypernuclear spectroscopy for medium heavy and heavy hypernuclei will enable us to extract the spin dependent $\Lambda$-N interaction beyond p-shell and help us understand the role of strangeness in dense nuclear matter. In the light mass region, hypernuclear spectroscopy by electroproduction will help us understand the effect of Charge Symmetry Broken (CSB) by studying neutron rich hypernuclei and reveal new nuclear structure aspects induced by strangeness. The preliminary results from JLab HKS experiment, which was carried out in 2005, has demonstrated the ability of hypernuclear electroproduction in obtaining high resolution spectroscopy by utilizing high precision electron beam. In this talk, I will present the current updated spectra of $^{12}_\Lambda$B, $^{28}_\Lambda$Al and $^{7}_\Lambda$He. The experimental setup and spectrometer calibration procedure will also be described. [Preview Abstract] |
Friday, October 12, 2007 2:24PM - 2:36PM |
EF.00003: Baryon Resonance Form Factors at High Momentum Transfer Paul Stoler The results of baryon resonance form factor measurements at high momentum transfer conducted at Jefferson Lab's Hall C and CLAS will be summarized. Special focus will be on the recent measurements of form factors for the $\Delta(1232)$ and $S_{11}(1535)$ resonances, which reach a maximum $Q^2$ of 7 GeV$^2$/c$^2$. The latest results of these experiments will be presented and the connections with other exclusive reactions such as elastic scattering form factors and high $-t$ Compton scattering in terms of common nucleon structure will be shown, and their connection with current theoretical models will be emphasized. [Preview Abstract] |
Friday, October 12, 2007 2:36PM - 2:48PM |
EF.00004: Electroexcitation of the $S_{11}(1535)$ and $D_{13}(1520)$ up to $Q^2 = 4.2~GeV^2$ from CLAS data. Inna Aznauryan, Volker Burkert, Victor Mokeev We present the helicity amplitudes for the electroexcitation
of the resonances $S_{11}(1535)$ and $D_{13}(1520)$ on protons
extracted from CLAS data on the $\pi$, 2$\pi$, and $\eta$
electroproduction at $ Q < 1~GeV^2$ and from $\pi^+$ data at
$1.7 |
Friday, October 12, 2007 2:48PM - 3:00PM |
EF.00005: Current status of a coupled-channel partial wave analysis using data from CLAS at Jefferson Lab Matthew Bellis, Michael McCracken, Curtis Meyer, Michael Williams The non-strange baryon spectrum has been mapped out predominantly by studying $N\pi$ elastic scattering with phase-shift analysis as the tool of choice. While there has been much success with these experimental techniques, the results have fueled debates in the community, most notably regarding the missing baryons problem. Theoretical solutions to this discrepancy appeal to a diquark-system within the baryons or a coupling to states other than $N\pi$. The CLAS detector at Jefferson Lab has turned out high-statistics, photoproduction datasets which are optimal for resolving these issues. However, new analytical techniques may be required to deal with this rich physics sector. The baryon resonances are photoproduced off liquid hydrogen and the CLAS detector allows us to measure a variety of final states. We will have access to $n\pi^+, p\pi^0, p\pi^+\pi^-, p\omega, p\eta, p\eta', \Lambda K^+$ and $\Sigma K^+$ final states. A robust software package has been developed that allows for the fitting of these states individually and in a coupled-channel mode. New techniques have been applied to background subtraction which brings an added level of consistency to the analysis. Polarization information from other experiments is incorporated at fit time to help distinguish potentially ambiguous physics processes by using information outside of the CLAS datasets. An overview of these tools will be presented as well as the current state of the analysis. [Preview Abstract] |
Friday, October 12, 2007 3:00PM - 3:12PM |
EF.00006: Beam asymmetry in $\eta$ meson photoproduction from the proton Patrick Collins The excitation spectrum of the proton is comprised of many broad overlapping resonances. Due to this feature, investigations of individual resonances are challenging. One excellent tool in helping understand the spectrum is $\eta$ meson photoproduction from the proton. Because this meson has isospin zero, it can be seen as an ``isospin filter'' for the nucleon resonance spectrum. Differential cross section data has been the primary tool used to study $\eta$ meson photoproduction. There have been a comparatively smaller number of beam asymmetry measurements for $\eta$ photoproduction. However, these beam asymmetries cover the energy range up to only about $E_{\gamma}$ = 1.5 GeV. I will present preliminary Jefferson Lab CLAS data on beam asymmetry for the $\eta$ meson for energies up to about $E_ {\gamma}$ = 2.1 GeV. I will also discuss how the new measurements will be useful in understanding the structure and excited states of the proton. [Preview Abstract] |
Friday, October 12, 2007 3:12PM - 3:24PM |
EF.00007: Photoproduction of omega with linearly polarized photons at CLAS Lu Cheng, Franz Klein The CLAS-g8 running period with linearly polarized photons allowed for the extracton of beam and parity asymmetry for the $\omega p$ channel at photon energies between threshold and 2.1 GeV. Although our analysis aims for providing tight constraints on baryon resonances decaying into $\omega N$, a by-product is the separation of contributions of natural and unnatural parity- exchange mechanisms. Such a measurement is considered as an important step to parametrize the t-channel background for resonant production. The vector meson is identified in the decay mode $\omega\to\pi^+\pi^-\pi^0$. The recoil proton was detected in coincidence with two charged pions and the missing $\pi^0$ identified via missing mass. The three-pion mass spectrum shows a strong $\omega$ signal that is enhanced in the forward direction as expected from diffractive and pion-exchange processes. The extracted spin density matrix elements confirm the dominating pion-exchange mechanism for the lower energy points. However, the (preliminary) cross section and asymmetries are not fully consistent with t-channel processes: the cross section enhancement at $\cos\theta_{cm}\simeq 90^\circ$ and the modulation of the angular distribution of the decay pions indicate the presence of resonant production. [Preview Abstract] |
Friday, October 12, 2007 3:24PM - 3:36PM |
EF.00008: Current status of a partial wave analysis of the $\gamma p \rightarrow p \omega$ reaction using data from CLAS at Jefferson Lab Mike Williams Relativistic quark models predict strong couplings to $p\omega$ ---relative to $N\pi$---for some of the {\em missing} $N^*$ states. Previous searches for these states in $\gamma p \rightarrow p \omega$ have relied solely on differential cross section measurements. I will present final differential cross section and $\omega$ recoil polarization measurements obtained from the CLAS g11a dataset. Measurements have been made in 112 $\sqrt{s}$ bins over the range $1.72 GeV < \sqrt{s} < 2.84 GeV$. The quark model predictions, along with the added constraint of the recoil polarization measurements, make $\omega$ photoproduction a perfect candidate for a partial wave analysis. Preliminary PWA results will be presented, including comparisons of published models to our recoil polarization measurements. [Preview Abstract] |
Friday, October 12, 2007 3:36PM - 3:48PM |
EF.00009: Current status of a partial wave analysis of the $\gamma p \rightarrow K^{+} \Lambda$ reaction using data from CLAS at Jefferson Lab Michael McCracken Couplings of $N^{*}$ states to two-body final state have been predicted using relativized quark-model calculations. Though these predictions give couplings to the $K^{+} \Lambda$ final state that are small relative to the couplings of other final states, the $K^{+} \Lambda$ channel is an interesting application of partial wave analysis techniques because it couples only to the iso-spin $\frac{1}{2}$ $N^{*}$ states and the self-analyzing $\Lambda$ decay to $p \pi^{-}$ allows study of the $\Lambda$ polarization. We have isolated some $1.6\times10^{6}$ $\gamma p \rightarrow K^{+} \Lambda$ signal events in the CLAS g11a dataset. The signal is remarkably clean with less than 2\% background to total ratio across 95\% of the observed W range ($1.63 GeV < W < 2.84 GeV$). I will present preliminary differential cross-section and recoil polarization results from this channel which are consistent with both previous CLAS measurements and world data. I will also present the status of the partial wave analysis of the $K^{+} \Lambda$ channel. We fit using information from the g11a run ($\frac{d\sigma}{dt}$, $\Lambda$ recoil polarization) as well as double polarization observables from the CLAS g1c run to constrain possible physics models. These polarization observables are a particularly powerful constraint on non-resonant (t-channel) processes. [Preview Abstract] |
Friday, October 12, 2007 3:48PM - 4:00PM |
EF.00010: $\phi$-meson Photoproduction By Using a Beam of Linearly-Polarized Julian Salamanca, Philip Cole The observables afforded by linearly-polarized photons are of interest in delineating the contributions of the various hadronic processes giving rise to vector meson photoproduction. And in particular, I shall describe how phi meson production affords an incisive tool for exploring the nature of the parity exchange at threshold energies, the strangeness content of proton, as well as extracting signatures for the violation of Okubo-Zweig-Iizuka observation (OZI rule). Our goal will be measure the $\vec{\gamma} p \rightarrow \phi p $ reaction, with $\phi \rightarrow K^{+}K^{-}$, in the photon energy range of 1.7 to 2.1 GeV by using the Coherent Linear Bremsstrahlung Facility in Hall B of Jefferson Laboratory (Newport News, VA). The data were collected during the g8b run in the summer of 2005. [Preview Abstract] |
Friday, October 12, 2007 4:00PM - 4:12PM |
EF.00011: Measurement of inclusive $\Lambda(1520)$ photoproduction on deuteron Kenneth Hicks, Tsutomu Mibe, Stepan Stepanyan The possible observation of the $\gamma n \rightarrow K^- \Theta^+$ reaction in LEPS and non-observation of the reaction $\gamma p \rightarrow \bar{K^0} \Theta^+$ in CLAS would require a large isospin asymmetry in the cross section. In 2005, Nam, Hosaka and Kim proposed a large isospin asymmetry in the cross section due to the possible absence of a contact term (Kroll-Ruderman term) in production from the neutron of a $\Theta^+$ with spin 3/2. The $\Lambda(1520)$ is a well-established excited hyperon with spin and parity $J^{P}=3/2^-$. If a large isospin asymmetry exists in the $\Theta^+$ photoproduction ($\sigma_n(\Theta^+) >> \sigma_p(\Theta^+)$), then a similar but opposite cross section asymmetry is predicted in the photoproduction of $\Lambda(1520)$ from the proton and neutron ($\sigma_n(\Lambda^*) << \sigma_p(\Lambda^*)$). This talk will report the measurement of differential cross sections and decay angular distributions for the inclusive reaction $\gamma d \rightarrow \Lambda(1520) X$ at Jefferson Laboratory using the CLAS detector. Data for $\Lambda(1520)$ photoproduction from both proton and neutron targets will be discussed. [Preview Abstract] |
Friday, October 12, 2007 4:12PM - 4:24PM |
EF.00012: Upsilon Production in STAR Pibero Djawotho In the hot and dense matter produced in relativistic heavy-ion collisions, the creation of a quark-gluon plasma is expected to modify the production of quarkonia, significantly suppressing their yields. However, the ground state of the Upsilon is not expected to melt at RHIC energies and thus can be used as a standard candle. As a baseline for any estimate of suppression, the production in p+p collisions is mandatory. We present preliminary results on Upsilon measurements in p+p collisions at sqrt(s)=200 GeV via the dielectron decay channel in the midrapidity region. A dedicated trigger was used to enhance the Upsilon samples. We compare the results to perturbative calculations and previous measurements as well as present prospects for future analyses and measurements at STAR. [Preview Abstract] |
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