Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session C10: Light Mesons and Baryons |
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Sponsoring Units: DNP GHP Chair: Leonard Gamberg, Pennsylvania State University Room: 250B |
Saturday, April 16, 2016 1:30PM - 1:42PM |
C10.00001: Radiative decay of $\eta^{\prime}$ in CLAS Georgie Mbianda Njencheu, Moskov Amaryan, Ilya Larin We would present preliminary experimental results of the radiative decay of $\eta^{\prime}\rightarrow\pi^{+}\pi^{-}\gamma$ based on CLAS data collected during the photoproduction experiment $\gamma p\rightarrow p\eta^{\prime}$ for the center-of-mass energy from 1.96 to 2.72 $GeV$ at Jefferson Lab. The analysis is based on the highest statistics collected in this channel in comparison to other experiments reported so far. This analysis could provide an important test of the box anomaly, also accessible via the Primakoff reaction of $\pi^{-}\gamma^{*}\rightarrow\pi^{-}\pi^{0}$. [Preview Abstract] |
Saturday, April 16, 2016 1:42PM - 1:54PM |
C10.00002: Photoproduction of the $f_1(1285)$ Meson. Reinhard Schumacher The $f_1(1285)$ meson with mass $1281.0 \pm 0.8$ MeV/$c^2$ and width $18.4 \pm 1.4$ MeV (FWHM) was measured for the first time in photoproduction from a proton target using CLAS at Jefferson Lab. Differential cross sections were obtained via the $\eta\pi^{+}\pi^{-}$, $K^+\bar{K}^0\pi^-$, and $K^-K^0\pi^+$ decay channels from threshold up to a center-of-mass energy of 2.8 GeV and are compared to model predictions. An amplitude analysis of the $\eta\pi^{+}\pi^{-}$ final-state Dalitz distribution is consistent with identification as the axial-vector $J^P=1^+$ $f_1(1285)$, rather than the pseudoscalar $0^-$ $\eta(1295)$. The production mechanism is most consistent with $s$-channel decay of a high-mass $N^*$ state, and not with $t$-channel meson exchange. Decays of the $f_1(1285)$ to $\eta \pi \pi$ are clearly dominated the intermediate states $a_0^\pm(980)\pi^\mp$. The branching ratios $\Gamma(a_0\pi (no \bar{K} K)) / \Gamma(\eta\pi\pi (all))$, $\Gamma(K \bar{K} \pi)/\Gamma(\eta\pi\pi) $ and $\Gamma(\gamma\rho^0)/\Gamma(\eta\pi\pi)$ were obtained and will be compared to world averages. [Preview Abstract] |
Saturday, April 16, 2016 1:54PM - 2:06PM |
C10.00003: Resolving Difficulties of a Single-Channel Partial-Wave Analysis Brian Hunt, D. Mark Manley The goal of our research is to determine better the properties of nucleon resonances using techniques of a global multichannel partial-wave analysis. Currently, many predicted resonances have not been found, while the properties of several known resonances are relatively uncertain. To resolve these issues, one must analyze many different reactions in a multichannel fit. Other groups generally approach this problem by generating an energy-dependent fit from the start. This is a fit where all channels are analyzed together. The method is powerful, but due to the complex nature of resonances, certain model-dependent assumptions have to be introduced from the start. The current work tries to resolve these issues by first generating single-energy solutions in which experimental data are analyzed in narrow energy bins. The single-energy solutions can then be used to constrain the energy-dependent solution in a comparatively unbiased manner. Our work focuses on adding three new single-energy solutions into the global fit. These reactions are $\gamma p \rightarrow \eta p$, $\gamma n \rightarrow \eta n$, and $\gamma p \rightarrow K^+ \Lambda$. During this talk, I will discuss the difficulties of this approach, our methods to overcome these difficulties, and a few preliminary results. [Preview Abstract] |
Saturday, April 16, 2016 2:06PM - 2:18PM |
C10.00004: Spin density matrix elements for radiative decays of the omega meson in photoproduction at 5 GeV Fridah Mokaya The photoproduction of $\omega$(782) meson on the nucleon at high energies is well described by a sum of t-channel exchanges. In the high energy limit of diffractive scattering, where Pomeron exchange dominates the total cross section, the helicity of the incident photon is transferred directly to the vector meson. At intermediate energies, other Regge exchanges compete with the Pomeron, leading to a complex energy dependence in the spin density matrix for vector mesons like the omega. High statistics measurements of the spin density matrix elements for the reaction $\gamma$p\rightarrow$\omega$p, $\omega$\rightarrow$\pi$$^0$$\gamma$ are presented based on data taken with the Radphi experiment at Jefferson Lab in the energy range 4.4 - 5.5 GeV. The results binned in E$_{\gamma}$ and $\vert$t$\vert$ are analysed in both the Gottfried Jackson and s-channel helicity frames and compared to a model with the Pomeron and other Regge exchanges contributing to the omega meson photoproduction amplitude. [Preview Abstract] |
Saturday, April 16, 2016 2:18PM - 2:30PM |
C10.00005: Elastic Lambda-proton Scattering in CLAS John Price The $\Lambda$-proton reaction is important to our understanding of the structure of the proton and the nature of the strong nuclear force. Most previous measurements used bubble chambers with kaon beams to produce the $\Lambda$ “beam”, which then interacted with a second proton inside the chamber. The $\Lambda$ can also be produced in the process $\gamma p\to K^+\Lambda$, which has been studied at Jefferson Lab by the CLAS Collaboration. The long decay length of the $\Lambda$ allows it to interact with a second proton in the target, leading to the process $\Lambda p\to\Lambda p$. The large acceptance of CLAS makes it a good choice for the study of this final state. A data-mining project was initiated with the CLAS g12 run, which used a tagged photon beam with 3.6<$E_\gamma$<5.4 GeV incident on a 40-cm liquid hydrogen target. The apparent non-conservation of baryon number in the final state leads to a very stringent cut which results in a good signal for this process. Future work will look at the possibility of increasing the detection rate for this process, using the upgraded CLAS12 detector, along with possible improvements to the target design. This talk will discuss the motivation for this work, the analysis and initial results, and the possibilities for future studies. [Preview Abstract] |
Saturday, April 16, 2016 2:30PM - 2:42PM |
C10.00006: Coherent $\omega$-Meson Photoproduction off Deuteron Taya Chetry, Kenneth Hicks Coherent $\omega$ photoproduction from the deuteron has been studied using CLAS at Jefferson Lab, Virginia, as a function of the photon energy and the 4-momentum transfer. Tagged photons with beam energies between 0.8 and 3.6 GeV were produced using the bremsstrahlung process incident on a deuterium target, during the run period g10. The final state particles detected are an energetic deuteron and a pair of charged pions. These events were constrained to have neutral pion missing mass, to ensure an exclusive reaction where an $\omega$-meson decays into a $\pi^+$, a $\pi^-$ and a $\pi^0$. This study allows to test models of hadronic scattering of $\omega$-mesons from the nucleon, as it is not possible to produce beams of $\omega$-mesons. A preliminary differential cross section of the $\omega$-meson in the coherent process is presented. In addition, this final state is useful to investigate a possible $d^*$ dibaryon resonance that has been seen in other reaction channels at CLAS, as well as being seen earlier in partial-wave analysis of pion-deuteron scattering at a mass of about 2145 MeV. [Preview Abstract] |
Saturday, April 16, 2016 2:42PM - 2:54PM |
C10.00007: Beam Spin Asymmetry in Exclusive $\omega$ Photoproduction off the Bound Proton Philip Cole, Olga Cortes In this talk, we present preliminary results for the polarization observable beam-spin asymmetry, $\Sigma$, of the $\vec{\gamma}d\rightarrow\omega p (n)$ reaction, where the $\omega$ meson was identified through its $\omega\rightarrow \pi^+\pi^-\pi^0$ decay. The data were taken during the E06-103 experiment with the CLAS detector in Hall B at Jefferson Laboratory. The experiment used the Hall-B Coherent Bremsstrahlung Facility to provide a high quality beam of linearly-polarized photons in the energy range from $1.1$ to $2.3$ GeV. We determined the beam-spin asymmetry of the $\omega$'s photoproduced off quasi-free protons in deuterium. We studied the evolution of $\Sigma$ with photon energy and center-of-mass angle. This observable provides information on the underlying mechanisms responsible for $s$- and $t$-channel processes. Further, since the $\omega$ meson is an isoscalar ($I_\omega=0$), the reaction of interest serves as an ideal isospin filter, as only $N^*$ states may contribute to the production process. Our results, together with studies of other reaction channels, serve to constrain the missing resonances predicted by QCD-inspired models of the nucleon's internal structure. [Preview Abstract] |
Saturday, April 16, 2016 2:54PM - 3:06PM |
C10.00008: The current status of the GlueX experiment at Jefferson Lab Matthew Shepherd The GlueX experiment is designed to search for and study light hybrid mesons utilizing a 9~GeV linearly polarized photon beam that is derived from the 12~GeV electron beam of the recently upgraded CEBAF at Jefferson Lab. Construction of the GlueX detector was completed in winter 2015 with initial detector commissioning utilizing low-energy polarized photons occurring in spring 2015. During spring 2016, continued detector commissioning and initial running at the full design energy are planned. In this talk the current status of the GlueX detector performance and data collection will be discussed. The prospects for first physics results, future run plans, and long term upgrades will be briefly presented. [Preview Abstract] |
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