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 CF: Mini-Symposium on Baryon Resonances and Meson Production I |
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Chair: T.-S. Harry Lee, Argonne National Laboratory Room: Newport News Marriott at City Center Pearl Salon II |
Friday, October 12, 2007 9:00AM - 9:36AM |
CF.00001: Nucleon resonance and electromagnetic meson production reaction Invited Speaker: Accurate determination of the $N^*$ parameters is a crucial step toward the understanding of hadron structure and reaction in terms of QCD in the non-perturbative region. Now precise and extensive data of photo and electroproduction of mesons are available from the intensive experimental efforts, which make it possible to extract accurate parameters of the excited baryons $N^*$. In the past years, the $N\Delta$ transition has been studied using various theoretical approaches. It is now recognized that the meson cloud effects play an important role in understanding transition form factors. Above the $\Delta(1232)$ resonance, the meson production reaction becomes highly inelastic. In order to extract $N^*$ parameters from the data it is challenging but necessary to establish an approach to take into account the coupled channel effects of the various meson production channels. In this talk I will briefly review theoretical approaches to analyze the meson production reactions beyond the delta region. In particular, the coupled channel model of EBAC and the resonance parameters in this approach will be discussed. Recent results on the $N^*$ parameters from the analysis of single pion production reaction will be shown. A plan to extend the present EBAC analysis by incorporating the data of inelastic reactions in collaboration with experimentalists will be discussed. [Preview Abstract] |
Friday, October 12, 2007 9:36AM - 9:48AM |
CF.00002: Dynamical coupled-channel approach to omega meson production with pions and photons Mark Paris, T.-S. Harry Lee, Toru Sato A dynamical coupled-channel formalism is employed in the study of pion and photon induced omega meson production. We consider center-of-mass energies in the region from threshold to 2 GeV. Extensive optimization on parallel processors has been used to determine the parameters of the model hadronic Lagrangian. Non-resonant and resonance parameters are extracted from a least-squares global fit to the available observed differential cross section for $\pi N\to\omega N$ and $\gamma N\to\omega N$. The extracted strong and electromagnetic couplings are then used to calculate the electroproduction data. The importance of coupled-channel and off-shell effects is emphasized in comparisons to approximate $K$ matrix and other models. [Preview Abstract] |
Friday, October 12, 2007 9:48AM - 10:00AM |
CF.00003: Partial-wave analysis and spectroscopy. From pion-nucleon scattering to pion electroproduction up to W = 2.5 GeV Richard Arndt, Bill Briscoe, Igor Strakovsky, Ron Workman We have analysed data on piN elastic scattering along with the single pion photo- and electroproduction channels. The main focus is a study of low-lying resonances. Fits to electromagnetic pion production have been used to extract multipoles as functions of Q2. Our results are compared to other recent determinations. [Preview Abstract] |
Friday, October 12, 2007 10:00AM - 10:12AM |
CF.00004: $\pi^{0}$ electroproduction in the resonance region. Nikolay Markov, Maurizio Ungaro, Cole Smith, Kyungseon Joo We report the analysis of single $\pi^{0}$ electroproduction in the resonance region to study the electromagnetic excitation of nucleon resonances. The study is aimed at understanding of the internal structure and dynamics of the nucleon. The experiment was performed using an unpolarzied cryogenic hydrogen target and 2.0 GeV polarized electron beam during the e1f run period with CLAS at Jeffeson Lab. The new measurements will produce a data base with high statistics and large kinematic coverage for the hadronic invariant mass W up to 1.9 GeV in the momentum transfer $Q^{2}$ range of 0.3 - 1.0 GeV$^{2}$. Preliminary partial wave analysis results will be presented and compared with the various model calculations. [Preview Abstract] |
Friday, October 12, 2007 10:12AM - 10:24AM |
CF.00005: Dynamical Coupled-channel analysis of pion electroproduction data in the $W \leq 2 $ GeV resonance region L.C. Smith, B, Julia-Diaz, T.-S. H. Lee, A. Matsuyama, T. Sato Within a dynamical coupled-channel model developed recently at EBAC, we have analyzed single pion electroproduction data from CLAS. The channels included are $\gamma N$, $\pi N$, $eta N$ and $\pi\pi N$ which has $\pi\Delta$, $\rho N$, and $\sigma N$ resonant components. The hadronic parameters of the model have been determined from fitting the $\pi N$ scattering data up to $W=2$ GeV. The determined $\gamma^* N \rightarrow N^*$ form factors for all low-lying $N^*$ states will be presented. The relations with the analysis based on the unitary isobar models will be discussed. [Preview Abstract] |
Friday, October 12, 2007 10:24AM - 10:36AM |
CF.00006: Extractions of Resonance Parameters with Speed-Plot and Time-Delayed methods Nobuhiko Suzuki, Toru Sato, Tsung-Shung Lee Within several exactly soluable multi-channel multi-resonance models, the conditions under which the Speed-Plot and Time-Delayed Methods are valid in extracting resonances from the scattering amplitudes are studied. We then apply the methods to extract the nucleon resonances from the $\pi N$ amplitudes generated from a recently constructed dynamical coupled-channel model of $\pi N$ scattering up to $W=2$ GeV. The results comparing our findings and the values of Particle Data Group will be presented and discussed. [Preview Abstract] |
Friday, October 12, 2007 10:36AM - 10:48AM |
CF.00007: Photon beam asymmetries for $\pi^0$ and $\pi^+$ photoproduction from the proton Michael Dugger Pion photoproduction data have been vital to uncovering details of the nucleon resonance spectrum. The pions, as the lightest mesons, are copiously produced in the strong interaction. However, while pion photoproduction data is an important fundamental tool in baryon spectroscopy, the existing data set still remains relatively limited, and the existing database is dominated by measurements of the differential cross sections. I will present preliminary Jefferson Lab data from CLAS on photon beam asymmetry for both the $\pi^0$ and $\pi^+$ reactions for energies up to about E = 2.1 GeV. The kinematic range of these measurements both complements and extends the world database for these reactions. [Preview Abstract] |
Friday, October 12, 2007 10:48AM - 11:00AM |
CF.00008: Electroexcitation of the Roper Resonance at $Q^2 < 4.2 GeV^2$. Inna Aznauryan, Volker Burkert, Victor Mokeev The helicity amplitudes of the electroexcitation of the Roper
resonance on proton are extracted at $1.7 |
Friday, October 12, 2007 11:00AM - 11:12AM |
CF.00009: The Double Spin Asymmetry for Exclusive $\pi^{+}$ Production With CLAS Joshua Pierce The eg1b run was conducted using CLAS at Jefferson Lab using a 1.6 GeV - 5.6 GeV longitudinally polarized electron beam and polarized nuclear targets (composed of NH$_{3}$ and ND$_{3}$). This analysis is of the double spin asymmetry $A_{et}$ in the exclusive production of positive pions from a polarized proton ($ep\rightarrow e\pi^{+}n$). The double spin asymmetry was measured as a function of the four kinematic variables $W$, $Q^{2}$, $\cos\theta ^{*}$ (the angle between the direction of the virtual photon and the produced pion), and $\phi^{*}$ (the angle between the lepton interaction plane and the hadron interaction plane). The value of this asymmetry can be used to determine the spin structure of the resonances. A brief description of the experimental setup will be given, and preliminary results will be shown. [Preview Abstract] |
Friday, October 12, 2007 11:12AM - 11:24AM |
CF.00010: Exclusive $\pi^{-}$ Production from Deuterium Jixie Zhang As part of a complete study of baryon resonances, data on the n$\to $p$\pi ^{-}$ channel is clearly important. However, there are very few data available for this channel because of the difficulty inherent in obtaining a neutron target. To overcome this limitation, the CLAS collaboration at Jefferson Lab has constructed a low momentum recoil detector (BoNuS) based on GEMs for use with a deuteron target. By tagging the spectator proton (p$_{s})$, one can isolate events in which the electron scatters from the neutron. In 2005 electron scattering data were taken with beam energies of 2.1, 4.2 and 5.3 GeV using a 7 atm deuterium target in conjunction with the BoNuS and CLAS detectors. We will present preliminary results for events in which at least two of the three final state hadrons in the ed $\to$ e$^{\prime} $p$_{s}$p$\pi^{-}$ channel are detected. [Preview Abstract] |
Friday, October 12, 2007 11:24AM - 11:36AM |
CF.00011: Phenomenological studies of CLAS data on double charge pion electroproduction Victor Mokeev, Volker Burkert Comprehensive studies of unpolarized $\pi^{-} \pi^{+} p$ electroproduction cross-sections, for the first time available from CLAS [1,2], were carried out within the framework of phenomenological approach [3]. Analysis of these data allowed us to establish all important mechanisms, contributing to this exclusive channel in $N^{*}$ excitation region at photon virtualities from 0.2 to 1.5 GeV$^2$. Electrocouplings for $P_{11}(1440)$, $D_{13}(1520)$ states at $Q^{2}$ $<$ 0.6$GeV^2$ were obtained from the analysis of CLAS data [1]. The contributions from various mechanisms in terms of both amplitudes and single differential cross-sections were determined from the data fit. This information is of particular interest for $N^{*}$ studies in coupled channel approaches under development at EBAC [4]. \newline $[1]$ G.V.Fedotov, et. al., Bull. of Russian Academy of Science,71,328 (2007). \newline [2] M.Ripani, et. al., Phys. Rev.,91,0222002 (2003). \newline [3] V.I.Mokeev, et. al., Int. Workshop on the Physics of Excited Baryons (NSTAR05) Tallahassee, Florida, 10-15 Oct 2005, ed by V.Crede, P.Eugenio and S.Capstick, p.47. \newline [4] A.Matsuyama, et.al., Phys.Rep.,439,193 (2007); B.Julia-Diaz, et.al., arXiv:0704.1615. [Preview Abstract] |
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