Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session BG: Hadronic Physics |
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Sponsoring Units: DNP Chair: Volker Oberacker, Vanderbilt University Room: Gaylord Opryland Hermitage D |
Thursday, October 26, 2006 2:00PM - 2:12PM |
BG.00001: First Observation of the $f_1(1285)$ / $\eta(1295)$ Meson in Photoproduction Ryan Dickson A meson of mass $m_x=1281$ MeV and a FWHM of $\Gamma_x=18$ MeV is seen in photoproduction off the proton using real photons in the energy range between 1.8 GeV and 4.0 GeV. The decay modes seen in the Jefferson Lab CLAS spectrometer are $x\rightarrow\eta\pi^{+}\pi^{-}$ and $x\rightarrow K^+\bar{K}\pi^-$, with a large fraction going through $a_0(980)\pi$. The state is not seen in the $x\rightarrow\rho^0\gamma$ decay channel, with an upper limit on the branching fraction $(B.R.) < 0.62\% \hspace{0.5cm} (95\% c.l.)$. This non-observation is inconsistent with the known nearby state $f_1(1285) 1^+$ which has a PDG-given $B.R.$ of $5.5 \pm 1.3 \%$ to $\rho^0\gamma$. This could mark the first direct observance of the $\eta(1295) 0^-$, albeit with a width that is much narrower than obtained through partial wave analysis of earlier hadronic production experiments. This presentation will emphasize the experimental production of this meson and the search for its $\rho^0\gamma$ decay mode. [Preview Abstract] |
Thursday, October 26, 2006 2:12PM - 2:24PM |
BG.00002: $K^*$ vector meson photoproduction on a proton target at Jefferson Lab Lei Guo It has been pointed out that the $K^*Y$ channels could provide some unique opportunities in searching for those missing resonances which couple to the $KY$ and $N\pi$ channels weakly. Compared with the $KY$ channels, the photoproduction of $K^*$ vector meson has not been studied in as much details mainly due to the lack of data. The CLAS Collaboration at Jefferson Lab conducted a photoproduction experiment on a proton target using a tagged photon beam with an energy range of 1.6-3.8~GeV during May-July 2004. With an integrated luminosity of about 75 $pb^{-1}$, this experiment provides the largest data set for photon-proton reactions ever collected. The two reactions $\gamma p \rightarrow K^{*+}\Lambda\rightarrow K^+p\pi^-(\pi^0)$ and $\gamma p \rightarrow K^{*0}\Sigma^+\rightarrow K^+\pi^-(\Sigma^+)$ have been investigated. The comparison of the two channels could provide insight into the contributions of the controversial $\kappa$ meson. The preliminary results of the cross section measurement and angular distributions for the photon energy range of 2.0-3.8~GeV will be presented and compared with theoretical calculations. [Preview Abstract] |
Thursday, October 26, 2006 2:24PM - 2:36PM |
BG.00003: $\Sigma(1385)$ photoproduction on a proton target at Jefferson Lab Lei Guo Previous investigation of the $J^P=\frac{3}{2}^-$ $\Lambda(1520)$ decay in the Gottfried-Jackson (GJ) frame has suggested the dominance of $K$ exchange in the eletroproduction data ($e p \rightarrow e' K^+ \Lambda(1520)$) as opposed to the strong contribution of $K^*$ exchange in the photoproduction data ($\gamma p \rightarrow K^+ \Lambda(1520)$). In the case of the $\Sigma(1385) (J^P=\frac{3}{2}^+)$, there has been no such study in the literature, probably due to the lack of available data. The recent large statistics ($L=75 pb^{-1}$) photon-proton reaction data collected by the CLAS Collaboration at Jefferson Lab has made possible the detailed study of the $\Sigma(1385)$ photoproduction through the reaction $\gamma p \rightarrow K^+\Sigma(1385)\rightarrow K^+\Lambda(\pi^0)$. Preliminary cross section results for the photon energy range of 1.5-3.8~$GeV$, as well as the angular distribution of the $\Sigma(1385)$ decay in the GJ frame will be presented. The results could provide new constraints on the hadro-dynamic models for hyperon production, and help determine the production mechanisms of the $\Sigma(1385)$ in photoproduction. [Preview Abstract] |
Thursday, October 26, 2006 2:36PM - 2:48PM |
BG.00004: Photoproduction of the $\phi $(1020) Meson Near Threshold David Tedeschi The differential cross section for the photoproduction of the $\phi $(1020) near threshold (E$_{\gamma }$ = 1.57 GeV) is sensitive to production mechanisms other than diffraction. Moreover, at large momentum transfer, the production of $\phi $-mesons becomes a test of quark and gluon degrees of freedom. We have performed a measurement of $\phi $-meson photoproduction on the proton at The Thomas Jefferson National Accelerator Facility using a liquid hydrogen target and the CEBAF Large Acceptance Spectrometer (CLAS). The energy of the tagged, bremsstrahlung photons ranged from $\phi $-threshold to 3.6 GeV, and the $\phi $(1020) was identified in the channels $\phi \to $K$^{+}$K$^{-}$ and $\phi \to $K$_{s}$K$_{l}$. Preliminary differential cross sections (d$\sigma $/dt) will be presented. An analysis of the energy dependence of the cross section at low and high momentum transfer will also be discussed. [Preview Abstract] |
Thursday, October 26, 2006 2:48PM - 3:00PM |
BG.00005: The Search for Missing Baryon Resonances in the Reaction $\rm\gamma p\to p\pi^0\eta$ Volker Crede The problem of so-called {\it missing} baryon resonances will be discussed on the basis of recent experimental results of the Crystal-Barrel experiment (CB-TAPS Collaboration) and discussion will be given on planned double-polarization experiments at the e$^-$~accelerator ELSA in Bonn. The Crystal-Barrel detector is the ideal instrument to study various multi-photon final states over the full dynamical range due to its almost 4$\pi$ coverage of the solid angle and its excellent energy resolution. Resonance production and even decay cascades of the type $\rm\gamma p\to\Delta^{*}\to\Delta\eta\to p\pi^0\eta$ have been observed. Indications for at least one $\Delta$~resonance around 1900 MeV/$c^2$ have been seen. The latter is particularly interesting if it had negative parity because a confirmation of this state would be in contradiction with current constituent quark models. Constraints provided by polarization observables are important because analyses of unpolarized data often result in ambiguous solutions. For the upcoming data-taking, circularly- and linearly-polarized photons will be used incident on the Bonn frozen-spin butanol target providing longitudinal polarization. Studies of the sensitivity of polarization observables to baryon resonances will be discussed. [Preview Abstract] |
Thursday, October 26, 2006 3:00PM - 3:12PM |
BG.00006: Measurement of $\pi^{+}\pi^{-}$ Photoproduction In Double-Polarization Experiments using CLAS Charles Hanretty Discussion will be given on an upcoming double-polarization experiment using a tagged-photon beam and the CLAS spectrometer at Jefferson Lab in Newport News, VA. Constituent quark models (CQMs) predict numerous baryon resonances that have not been experimentally verified and are thus ``missing.'' CQMs also predict a strong coupling of these states to $\rm\gamma p$ as well as to $\rm p\eta$ or $\Delta\pi$ making photoproduction experiments a promising method to find these missing resonances. Previous analyses show that constraints provided by polarization observables are important because analyses of unpolarized data often result in ambiguous solutions. A linearly- and circularly-polarized photon beam will be incident on a polarized butanol target in Hall B's CLAS detector. This detector allows for the use of a longitudinally- or transversely-polarized frozen spin target (FROST) giving rise to nine double-polarization observables in $\pi^+\pi^-$ production. Studies of the sensitivity of these observables to baryon resonances will be discussed. [Preview Abstract] |
Thursday, October 26, 2006 3:12PM - 3:24PM |
BG.00007: Search for New Forms of Hadronic Matter in Photoproduction Lukasz Blaszczyk Discussion will be given of an upcoming experiment at Jefferson Lab, in Hall B, scheduled for mid 2007. Recent experimental results for gluonic hybrid candidates as well as theoretical predictions suggest photoproduction is ideal in the search for gluonic matter. The CEBAF Large Acceptance Spectrometer (CLAS) detector at Jefferson Lab in Newport News, VA offers an excellent opportunity to study meson spectroscopy at photon beam energies up to 5.7GeV. The g12 HyCLAS experiment will collect the largest set of photoproduction data in meson spectroscopy to date, over an order of magnitude more than previous photoproduction experiments at CLAS. This will lead to substantial yields for the purpose of Partial Wave Analysis. [Preview Abstract] |
Thursday, October 26, 2006 3:24PM - 3:36PM |
BG.00008: The search for the $\Phi(1860)^{--}$ pentaquark with CLAS Maurik Holtrop, Hovanes Egiyan, J\"{o}rn Langheinrich A search for a narrow exotic resonance, the $\Phi(1860)^{--}$, is being conducted in the EG3 experiment with the CLAS detector at Jefferson Lab. The $\Phi(1860)^{--}$ is predicted to be the $S=-2$ exotic state in the pentaquark anti-decuplet. Evidence for this state has been cited by the NA49 experiment, but has not been confirmed so far. The search is conducted by looking for the decay $\Phi(1860)^{--} \to \Xi^{-}\pi^{-}$, which can use the detached vertices of the $\Xi^{-} \to \Lambda \pi^{-}$ and $\Lambda \to p \pi^{-}$ decay chain, a new technique for CLAS. We will report on the ongoing analysis. [Preview Abstract] |
Thursday, October 26, 2006 3:36PM - 3:48PM |
BG.00009: $\Theta^{+}$ Search in CLAS with $\gamma d\rightarrow pK^{0}_{s}K^{-}(p)$ Nathan Baltzell, David Tedeschi A search for photo-production of the $\Theta^{+}(1540)$ pentaquark in the $pK^{0}$ decay mode was performed with the CLAS detector at Jefferson Lab. About $20,000$ $\gamma d\rightarrow pK^{0}_{s}K^{-}(p)$ events with photon beam energies $1.6-3.6GeV$ were fully reconstructed and kinematically fitted. To investigate the resonant backgrounds, a phenomological model including hyperon and meson production has been developed and fitted to the data w ith a maximum-likelihood method. The model results serve as a background to evaluate the existence of a pentaquark signal in the invariant mass of the $pK^{0}$ system. The cross-section upper limit on $\Theta^{+}$ photo-production in this channel will be reported. [Preview Abstract] |
Thursday, October 26, 2006 3:48PM - 4:00PM |
BG.00010: The Light-Front Quark Model and Exotic Matter Martin DeWitt, Chueng Ji According to the Standard Model of particle physics, much of the matter we see is made up of quarks bound together by the strong force. Although a theory of the strong force, Quantum Chromodynamics (QCD), has existed for many years, it has not been possible to solve it exactly. As such, models based on the essential characteristics of the strong force, which have been gleaned from approximate solutions of QCD, have been very useful in understanding the properties of bound states of quarks. The light-front quark model (LFQM) has generally been successful in predicting the properties of two-body (quark-antiquark) bound states called mesons. While experimental data on mesons with certain quantum numbers have matched well with the model predictions, the $^3P_0$ (scalar) mesons have not. In fact, more scalar states have been observed experimentally than should exist if they were all two-body bound states. It is suspected that other ``exotic'' forms of matter, which have been predicted by QCD but have never been directly confirmed in experiments, are complicating the scalar meson spectrum. These exotic states have the same quantum numbers as the scalar mesons, and are thus allowed to mix with them. The result is that the states observed experimentally are actually quantum-mechanical superpositions of the scalar mesons and these other exotic forms of matter, thus making them difficult to clearly identify. I will discuss how the LFQM is used to predict the properties of mesons in general, as well as how it can be used to shed light on the more complicated structure of the scalar states. [Preview Abstract] |
Thursday, October 26, 2006 4:00PM - 4:12PM |
BG.00011: A Unitary and Relativistic Model for $\pi \eta N$ and $\pi \pi N$ Photoproduction Alvin Kiswandhi, Simon Capstick, T.-S. Harry Lee We investigate $\pi \eta N$ photoproduction by using a unitary and relativistic model based on the effective Lagrangian approach. Unitarity is ensured by using the Lippmann-Schwinger equation to iterate the vertices and dress the propagators to all orders, and by including all possible two-body and quasi-two-body intermediate channels. The approach we present here has also been used to investigate $\pi \pi N$ photoproduction. A comparison of our calculation to an existing $\pi \pi N$ photoproduction study is made, and shown to produce consistent results. This agreement convinces us that our ongoing study of $\pi \eta N$ photoproduction will produce similar interesting results. [Preview Abstract] |
Thursday, October 26, 2006 4:12PM - 4:24PM |
BG.00012: Hybrid and Conventional Baryons as Four-Body Systems in the Flux-Tube Model Simon Capstick, Anton Souslov In the strong-coupling limit baryons can be viewed as constituent quarks connected by gluon flux tubes in a Y-shaped configuration. A previous study of the spectrum of hybrid and conventional baryons separated the motion of the gluonic degrees of freedom and that of the quarks using an adiabatic approximation, and showed that the motion of the gluon flux can be approximated by the motion of the junction of the three flux tubes. The calculation described here goes beyond the adiabatic approximation to solve directly for the states of a four-body system comprised of three quarks and a massive junction connected to the quarks by linear strings. Results for the spectrum and properties of hybrid baryons are shown, along with the effects of the motion of the flux on conventional baryons. [Preview Abstract] |
Thursday, October 26, 2006 4:24PM - 4:36PM |
BG.00013: Extrapolations of Lattice Meson Form Factors T. Brian Bunton, Fu-Jiun Jiang, Brian C. Tiburzi We use chiral perturbation theory to study the extrapolations necessary to make physical predictions from lattice QCD data for properties of pseudoscalar mesons. We focus on the quark mass, momentum, lattice spacing, and volume dependence and apply our results to simulations employing mixed actions of Ginsparg-Wilson valence quarks and staggered sea quarks. As an example, to determine charge radii at quark masses on the lattices currently used, we find that the chiral and continuum extrapolations dominate the systematic error. [Preview Abstract] |
Thursday, October 26, 2006 4:36PM - 4:48PM |
BG.00014: A PWA of $p\omega$ in photoproduction using CLAS Mike Williams We will present results of a partial wave analsysis, (PWA), on the reaction $\gamma p\rightarrow p\omega$ with the $\omega$ decaying to $\pi^{+}\pi^{-}\pi^{\circ}$. The decay of the $\omega$ into its three pseudoscalar final state provides information on the polarization of the $\omega$ which in turn provides an additional handle in the PWA analysis. These data are analalyzed using a covariant tensor formalism which provides a natural mechnaism for including both $t$-channel contributuions as well as background terms in the PWA. The results of such an analysis are a decomposition of into the $s$-wave contributions to the final state. The mass dependence of the intensity and phase of these partial waves can be used to deduce information about the baryon resonances that couple to $p\omega$ final states. [Preview Abstract] |
Thursday, October 26, 2006 4:48PM - 5:00PM |
BG.00015: A Coupled Partial Wave Analysis of $p\eta$ and $p\eta'$ in photoproduction using CLAS Zebulun Krahn In late 2004, a very large photoproduction data set was collected using the CLAS detector at Jefferson Lab. This data set contains several hundred thousand events of the type $\gamma p \rightarrow \eta p $ and $\gamma p \rightarrow \eta\prime p $. Results of a coupled partial wave analysis, (pwa), of these two data sets will be presented. The pwa analysis uses a covariant tensor formalism with the aim of disentangling resonance structure in the $\eta p$ and $\eta\prime p$ systems. Such a formalism also allows a method to handle $t$-channel contributions to the cross sections. In addition, the use of a coupled channel approach takes advantage of the fact that given sufficient phase space, all intermediate states that couple to $\eta$ must also couple to $\eta\prime$. Given both the different acceptances and systematic errors for the two data sets, this provides for a more contrained method of pulling out partial waves from the two data sets. [Preview Abstract] |
Thursday, October 26, 2006 5:00PM - 5:12PM |
BG.00016: A PWA of $p\pi^{+}\pi^{-}$ in photoproduction using CLAS Matthew Bellis While the Constituent Quark Model does an excellent job of catagorizing much of the observed baryon spectrum, there are multiplets which are conspicuously absent from the experimental data. With much of this data coming from $N\pi \rightarrow N\pi$ scattering and a small predicted coupling to $N\pi$, it is perhaps not surprising they have not yet been seen. The CLAS detector allows us to make a comprehensive search for these missing resonances in states that do not have $N\pi$ in either the intial or final state. We are engaged in a PWA of multiple final states using a covariant tensor formalism in a mass-independant approach. This allows us to extract the amplitudes for intermediate $s-$channel processes as well as measure the $t-$channel contribution. Resonances will be observed by motion in both intensity and phase. This talk will discuss the current status of the analysis of one of these channels: $\gamma p \rightarrow p \pi^+ \pi^-$. We use isobars to model the intermediate $\Delta^{++}, \Delta^{0}$ and $\rho^{0}$ states. Differential and total cross sections will also be shown. [Preview Abstract] |
Thursday, October 26, 2006 5:12PM - 5:24PM |
BG.00017: Implementation of Vertex Reconstruction in the Search for Resonances in the 1610-1770 MeV Invariant Mass Region Ezekiel Walker In recent years, there has been considerable activity in the realm of baryon spectroscopy. A collaboration between Petersburg Nuclear Physics Institute (PNPI), Institute for Theoretical and Experimental Physics (ITEP), and Abilene Christian University (ACU), is aimed at increasing the understanding of the 1610-1770 MeV invariant mass region. ACU is particularly interested in the N*(1710) resonance, a poorly defined excited state of the nucleon. Utilizing GEANT4 and ROOT, two powerful simulation and analysis programs, ACU is simulating the $\pi ^{-}$p -$> \quad {\rm K}\Lambda $ reaction to help find the optimum design parameters for the experiment. In order to reconstruct the $\pi ^{-}$p -$> \quad {\rm K}\Lambda $ events, a vertex reconstruction algorithm was designed, tested, and implemented. An overview of the design process, capabilities, limitations, and current results will be discussed. [Preview Abstract] |
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