Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session X14: Hadron Structure |
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Sponsoring Units: GHP Chair: Volker Crede, Florida State University Room: 102 |
Tuesday, April 8, 2014 10:45AM - 10:57AM |
X14.00001: Phenomenology of light hadrons in a chiral effective theory Timothy Hobbs, John Londergan, Chueng-Ryong Ji, Wally Melnitchouk We present the results of a recent calculation of the pion production cross section as might be determined in proposed Jefferson Lab measurements involving spectator tagging in single-inclusive proton electroproduction on a fixed neutron target. Estimates are computed assuming the Sullivan process as the dominant mechanism, and chiral effective Lagrangians provide a description of the relevant hadronic interactions. We also assess the role of the $\Delta$ isobar in generating the light quark sea asymmetry using $\chi$-PT. [Preview Abstract] |
Tuesday, April 8, 2014 10:57AM - 11:09AM |
X14.00002: Polarization Observables for Double-Pion Photoproduction using a Linearly Polarized Photon Beam and a Transversely Polarized Target from FROST P. Roy, V. Crede One of the prominent ways to understand quark-gluon interactions in baryons in the low-energy regime is studying the baryon spectrum. The present world database of baryon resonances is inadequate to interpret the spectrum in terms of the relevant degrees of freedom. Double-pion photoproduction, which dominates the total photoabsorption cross section above 1.7 GeV, serves as an important reaction to get access to the higher mass resonances. Cross sections and polarization observables for the double-pion reaction will provide information about the scattering amplitudes and assist in isolating the resonant contributions to the reaction. Here we report on the analysis technique and preliminary results on polarization observables obtained from the study of $\pi^{+}\pi^{-}$ photoproduction using a transversely polarized FROzen Spin butanol Target (FROST) and a linearly polarized photon beam. The experiment was conducted at Jefferson Lab using the CLAS spectrometer. The coherent edge of the linearly polarized beam ranged from 0.9 to 2.1 GeV and we were able to bin the data in 3 kinematic variables. A salient feature of this analysis was the use of an event-based quality factor technique to separate signal from background that originated from bound nucleons present in the target. [Preview Abstract] |
Tuesday, April 8, 2014 11:09AM - 11:21AM |
X14.00003: MOVED TO M7.008 |
Tuesday, April 8, 2014 11:21AM - 11:33AM |
X14.00004: Analysis of anti-Kaon-induced Cascade baryon production Benjamin Jackson, Kanzo Nakayama, Helmut Haberzettl, Yongseok Oh In preparation for the forthcoming experiments on multi-strangeness baryon production at JLab and JPARC, we analyze the general features of Cascade production in both the anti-kaon- and photon-induced reactions. Particular attention is paid to the spin structure of the reaction amplitude for producing Cascade resonances with the emphasis on identifying the spin observables required to determine the production amplitude as well as the spin-parity of the resonance. For the production of Cascade resonances with spin higher than 1/2, the spin-density-matrix formalism is proven to be particularly useful. The $\gamma N \to K K \Xi$ and $\bar{K}N \to K \Xi$ reactions are investigated within a simple model. Emphasis will be placed on the results of the model calculations. [Preview Abstract] |
Tuesday, April 8, 2014 11:33AM - 11:45AM |
X14.00005: Decays of Scalar Mesons in the Light-Front Quark Model Martin DeWitt The light-front quark model (LFQM) is used to investigate the structure of the scalar mesons, mainly focusing on the three heavy isoscalar states $f_0(1370)$, $f_0(1500)$, and $f_0(1710)$. The spectrum of scalar mesons is computed by diagonalizing a relativized, QCD-inspired model Hamiltonian. The masses are then used to perform a mixing analysis which assumes that the heavy isoscalars are mixtures of $n\bar{n}=\left(\frac{u\bar{u}+d\bar{d}}{\sqrt{2}}\right)$, $s\bar{s}$, and $gg$. The resulting quark--glue content is used along with the meson wave--functions determined from the spectrum to compute the decay rates for $f_0\rightarrow\pi\pi$, $f_0\rightarrow K\bar{K}$, and $f_0\rightarrow\eta\eta$. When the glueball contribution to the decays is ignored, the results are in poor agreement with the available data. However, when the effect of including the glueball contribution is considered, a solution is found that matches the data quite well. In this solution, the $f_0(1710)$ is mostly glueball, while the $f_0(1500)$ and $f_0(1370)$ are dominantly mixtures of $n\bar{n}$ and $s\bar{s}$. [Preview Abstract] |
Tuesday, April 8, 2014 11:45AM - 11:57AM |
X14.00006: Measurement of two-photon exchange effects in CLAS Dipak Rimal, Brian Raue, Dasuni Adikaram, Lawrence Weinstein There is a significant discrepancy between the Rosenbluth and the polarization transfer measurements of the proton's electric to magnetic form factor ratio $\frac{G^{p}_{E}}{G^{p}_{E}}$. One possible explanation of this discrepancy is the contribution from two-photon exchange (TPE) effects, which are not typically accounted for in standard radiative corrections. The ratio of positron-proton to electron-proton elastic scattering cross sections, $R = \frac{\sigma (e^{+}p)}{\sigma(e^{-}p)}$, provides a model independent measurement of the TPE contribution to elastic electron-proton scattering. We measured this ratio at Jefferson Lab using a mixed electron-positron beam. Both electrons and positrons were elastically scattered from a liquid hydrogen target. The resulting scattered particles were detected in CLAS. The experimental details and results will be discussed. [Preview Abstract] |
Tuesday, April 8, 2014 11:57AM - 12:09PM |
X14.00007: Positron-proton to electron-proton elastic cross section ratios from CLAS Dasuni Adikaram, Dipak Rimal, Larry Weinstein, Brian Raue There is a significant discrepancy between the ratio of the electromagnetic form factors of the proton measured by the Rosenbluth and the polarization transfer technique. The most likely explanation of this discrepancy is the inclusion of two-photon exchange (TPE) amplitude contributions to the elastic electron-proton cross section. The CLAS TPE experiment measured the TPE contribution in the wide range of $Q^2$ and $\varepsilon$ range using a comparison of positron-proton to electron-proton elastic cross sections ($R = \sigma(e^+p)/\sigma(e^-p$)). Preliminary results will be presented, along with the estimations of systematic uncertainties. A detailed comparison of new results with previous $R$ measurements and theoretical calculations will be presented. Implications of the CLAS TPE measurements on the elastic electron-proton cross section will be also discussed. [Preview Abstract] |
Tuesday, April 8, 2014 12:09PM - 12:21PM |
X14.00008: A Radiative Event Generator for OLYMPUS Axel Schmidt The OLYMPUS Experiment, which completed data taking in 2013, will determine the ratio of positron-proton to electron-proton elastic scattering cross sections over a range of momentum transfer from 0.4 to 2.2 (GeV/$c$)$^2$. A deviation in this ratio from unity is evidence of two-photon exchange, which is a possible explanation for the discrepancy in measurements of the proton's electromagnetic form factors. However, the ratio is also sensitive to other radiative effects, such as the interference of lepton and proton bremsstrahlung. To isolate the contribution of hard two-photon exchange, the OLYMPUS MIT group has developed a Monte Carlo radiative generator, so that the various contributions to the cross section ratio can be studied by simulation. With this method, radiative effects can be properly convolved with detector-specific properties such as acceptance and efficiency. It is a goal of the collaboration to make this generator publicly available so that unbiased comparisons can be made between OLYMPUS and other two-photon exchange experiments. The MIT generator will be presented in detail along with a description of radiative corrections in the OLYMPUS analysis. [Preview Abstract] |
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