Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session HF: Nucleon and Meson Excited State Structure |
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Chair: Charles Horowitz, Indiana University Room: Kearney |
Friday, November 5, 2010 10:30AM - 10:42AM |
HF.00001: The Search for a $\pi_1(1400)$ Exotic Meson in the $\gamma p\to\Delta^{++}\eta\pi^-$ System with CLAS Diane Schott The reaction $\gamma p\to\Delta^{++}X\to p\pi^+\pi^-(\eta)$ is being studied, with the CLAS detector in Hall B at Jefferson Lab. The resonance spectrum, $X$, shows contributions from $a_0(980)$ and $a_2(1320)$ in the intermediate states. A PWA of the resonance spectrum has been started and will conclude if there is a $\pi_1(1400)$ present under the $a_2(1320)$ distribution. The presence of the $\Delta^{++}$ restricts the isospin of the possible $X$ states, leaving the PWA with a smaller combination of partial waves, making it ideal to look for the $\pi_1(1400)$. The $\pi_1(1400)$ has been produced with the use of hadron-production previously but has yet to be conclusive with photo-production. The experimental moments have been calculated and the PWA has been started. We will discuss the data trends, along with the PWA technique being implemented. [Preview Abstract] |
Friday, November 5, 2010 10:42AM - 10:54AM |
HF.00002: Mass-independent PWA of $K^{+} \Lambda$ Photoproduction: Data, Scope, and Techniques Michael McCracken The photoproduced $K^{+}\Lambda$ system presents a unique opportunity to study the excited nucleon spectrum for several reasons. The $K^{+}\Lambda$ final state couples only to iso-spin- $\frac{1}{2}$ intermediate states, allowing for a simpler interpretation of resonant contributions. Furthermore, the self-analyzing nature of the $\Lambda\rightarrow p \pi^{-}$ decay allows for measurement of the $\Lambda$ polarization. Several recent experiments have exploited this feature to produce measurements of both single- and double-polarization observables for the reaction. As such, this $K^{+}\Lambda$ photoproduction is a strong candidate for a so-called \textit{complete} set of observables from which the transition amplitudes can be determined. Recent large-statistics measurements of the differential cross section, $\Lambda$ recoil polarization, and beam-$\Lambda$ polarization transfer made by the CLAS Collaboration, warrant new partial-wave techniques. We present our method for and preliminary results of the mass-independent partial-wave analysis of the $\gamma p \rightarrow K^{+}\Lambda$ reaction. Methods for constraining fits to other observables, including beam and target asymmetries and polarization transfer observables, are described. We discuss the differences in methodology between this and previous mass-dependent analyses, as well as techniques for applying the mass-independent technique to resolve ambiguities in previous analyses of the reaction. [Preview Abstract] |
Friday, November 5, 2010 10:54AM - 11:06AM |
HF.00003: 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 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. Jefferson Lab data from CLAS on photon beam asymmetry for both the $\pi^0$ and $\pi^+$ reactions have been taken for up to about E = 2.1 GeV. The kinematic range of these measurements complements the world database and provides finer energy and angular resolution than any previous measurements. Preliminary results in the photon energy range from 0.975 to 2.0 GeV will be presented. [Preview Abstract] |
Friday, November 5, 2010 11:06AM - 11:18AM |
HF.00004: Beam asymmetry in $\eta$, $\eta^\prime$, and $\omega$ meson photoproduction from the proton Patrick Collins The CLAS g8b running period using linearly polarized photons on a proton target allowed for the extracton of beam asymmetry in $\eta$, $\eta^\prime$, and $\omega$ meson photoproduction at photon energies up to 2.1 GeV Our analysis aims for providing tight constraints on the coupling of baryon resonances to these channels. The excitation spectrum of the proton is comprised of many broad overlapping resonances. One excellent tool in helping understand the spectrum is $\eta$, $\eta^\prime$, and $\omega$ meson photoproduction from the proton. Because these mesons have isospin 0, these channels can be seen as an ``isospin filter'' for the nucleon resonance spectrum. Differential cross section data has been the primary tool used to study these channels. There have been a comparatively smaller number of beam asymmetry measurements for $\eta$ and $\omega$, and none for $\eta^\prime$ The new $\eta$ and $\omega$ beam asymmetry data from CLAS have considerably finer binning in both energy and production angle and extend to higher $E_\gamma$. This data will provide better constraints for the presence of $N^\ast$($I$=$\frac{1}{2}$) production in these channels, providing further insight into the nucleon excitation spectrum, where ``missing'' resonance states are of particular interest. [Preview Abstract] |
Friday, November 5, 2010 11:18AM - 11:30AM |
HF.00005: Exclusive $\pi^{\circ}$ and $\eta$ electro-production at high $Q^2$ in the resonance region Mark Jones At Jefferson Lab in Hall C, measurements of exclusive $p(e,e^{\prime}p)X$ with $X=\pi^{\circ}$,$\eta$ cross sections were performed for a beam energy of 5.5~GeV. Electrons were detected in the Short Orbit Spectrometer (SOS) at angles of 47.5$^{\circ}$ and 70$^{\circ}$ with a range of invariant mass, W, between meson threshold and 1.8~GeV. The outgoing protons were detected at a range of angles and momentum so that all center of mass angles were covered for most of the W range. The $p(e,e^{\prime}p)\pi^{\circ}$ data was centered at $Q^2 = 6.4 $ and 7.7 GeV$^2$ and the magnetic transition form factor, $G_M^{\star}$, for the $\Delta(1235)$ resonance was extracted from the cross section data. The $p(e,e^{\prime}p)\eta$ data is dominated by the $S_{11}(1535)$ resonance and the helicity conserving transition amplitude, $A_{1/2}$, for the $S_{11}$ was extracted at $Q^2 = 5.7 $ and 7.0 GeV$^2$. These results are at the highest $Q^2$ ever measured and will be discussed in the context of current theoretical models. [Preview Abstract] |
Friday, November 5, 2010 11:30AM - 11:42AM |
HF.00006: $\Sigma^{+}$(1189) Hyperon Polarization in Photo-production Chandra Nepali, Moskov Amaryan, Gagik Gavalian Since the considerable measurement of $\Lambda^{0}$ hyperon polarization in reaction with unpolarized proton beam on unpolarized target, the polarization of different hyperons have been measured at different energies with different beam on different target. We have measured the polarization of $\Sigma^{+}$(1189)hyperon in photo-production and result will be presented. The data set collected on hydrogen target in the photon energy range from 1.5-3.6 GeV on CLAS are used for this analysis. [Preview Abstract] |
Friday, November 5, 2010 11:42AM - 11:54AM |
HF.00007: Crystal Ball Experiment at MAMI Recent Results William Briscoe The Crystal Ball $4\pi$ spectrometer was first installed at the A2 Tagged Photon Facility at the Mainz Microtron in Mainz, Germany in 2003. Since then, a series of highly successful experiments have been performed that study a spectrum of topics from the accurate determination of the $\eta$ slope parameter to photon asymmetries in $\pi^0$ threshold photoproduction. The high quality of these results is made possible by the large solid-angle coverage of the combined Crystal Ball and TAPS spectrometers in conjunction with the Edinburgh Particle Identification Detector and two Multi-Wire Proportional Chambers from Pavia for charged particle identification and tracking. The successful upgrade of MAMI and the Glasgow Photon Tagger to 1.6 GeV has lead to an expansion of the program. More recently, a frozen-spin polarized proton target has been installed and double-polarization measurements have begun. An overview of the Crystal Ball experimental program will be described and a selection of preliminary results will be shown. [Preview Abstract] |
Friday, November 5, 2010 11:54AM - 12:06PM |
HF.00008: Photoproduction at Relativistic Heavy Ion Collider with STAR Yury Gorbunov Relativistic heavy ions carry strong transverse electromagnetic fields which can be treated as sources of quasi-real virtual photons. The ions interact through photon-Pomeron and photon-photon collisions at impact parameter more than twice the nuclear radius, so hadronic interactions are suppressed. We present recent results of the STAR experiment at RHIC on $\rho^0(770)$ production in AuAu collisions at various energies. STAR is also sensitive to the interference between two production modes: either ion can be the photon emitter or the target. We observed the coherent photoproduction of $\pi^+\pi^-\pi+\pi^-$, which maybe attributed to one of the poorly known excited states of $\rho^0$. As well in this talk we will present preliminary results based on data collected during run 10. [Preview Abstract] |
Friday, November 5, 2010 12:06PM - 12:18PM |
HF.00009: New Partial-Wave Analysis Results for $\eta N$ and $K \Lambda$ Manoj Shrestha, D. Mark Manley Previous measurements of $\eta N$ and $K \Lambda$ resonance couplings were based mainly on simplistic energy-dependent partial-wave analyses that violated unitarity. In this talk, new results will be presented based on a unitary multichannel partial-wave analysis that includes the channels $\pi N$, $\pi \pi N$, $\gamma N$, $\eta N$, and $K \Lambda$. Partial-wave amplitudes for the isospin-1/2 reactions $\pi N \to \eta N$ and $\pi N \to K \Lambda$ were first obtained at c.m. energies up to 2.1 GeV from single-energy partial-wave analyses of available world data. Then the amplitudes were incorporated into a global energy-dependent fit in order to obtain resonance parameters and energy-dependent amplitudes consistent with S-matrix unitarity. We will discuss the more important amplitudes and compare results from our energy-dependent solution with observables. These results present an important step into developing a partial-wave description of $\eta N$ and $K \Lambda$ photoproduction that is fully consistent with information determined from hadronic scattering reactions. [Preview Abstract] |
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