Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session B6: Hadronic Physics |
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Sponsoring Units: GHP Chair: Igor Strakovsky, George Washington University Room: Key 2 |
Saturday, April 11, 2015 10:45AM - 10:57AM |
B6.00001: Preliminary Results of Polarization Observables $T$ and $F$ in the $\vec p(\vec \gamma,\pi^0)p$ Reaction from CLAS Hao Jiang The theory which describes the interaction of quarks is Quantum Chromodynamics (QCD), but how quarks are bound inside a nucleon is not yet well understood. Pion photoproduction experiments reveal important information about the nucleon excited states and the dynamics of the quarks within it and thus provide a useful tool in the study of QCD. Detailed information about this reaction can be obtained in experiments which utilize polarized photon beams and polarized targets. Pion photoproduction in the $\gamma p \to \pi^0 p$ reaction has been measured in the FROST experiment at the Thomas Jefferson National Accelerator Facility. In this experiment circularly polarized photons with energies up to 3~GeV impinged on a transversely polarized frozen-spin target. Final-state protons were detected in the CEBAF Large Acceptance Spectrometer. Preliminary results of the polarization observables $T$ and $F$ have been extracted. The data generally agree with predictions of present partial wave analyses, but also show marked differences. The data will constrain further partial wave analyses and improve the extraction of proton resonance properties. This work is supported in parts by the U.S. National Science Foundation: NSF PHY-1205782. [Preview Abstract] |
Saturday, April 11, 2015 10:57AM - 11:09AM |
B6.00002: ABSTRACT WITHDRAWN |
Saturday, April 11, 2015 11:09AM - 11:21AM |
B6.00003: ABSTRACT WITHDRAWN |
Saturday, April 11, 2015 11:21AM - 11:33AM |
B6.00004: Light Meson Decays from Photon-Induced Reactions with CLAS Michael Kunkel Photo-production experiments with the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Laboratory produce data sets with unprecedented statistics of light mesons. With these data sets, measurements of transition form factors for $\eta$, $\omega$, and $\eta^\prime$ via conversion decays can be performed using a line shape analysis on the invariant mass of the final state dileptons. Tests of fundamental symmetries and information on the light quark mass difference can be performed using a Dalitz plot analysis of the meson decay. In addition, the data allows for a search for dark matter, such as the heavy photon via conversion decays of light mesons and physics beyond the Standard Model can be searched for via invisible decays of $\eta$ mesons. An overview of the first results and future prospects will be given. [Preview Abstract] |
Saturday, April 11, 2015 11:33AM - 11:45AM |
B6.00005: Timelike Compton Scattering Arthur Mkrtchyan, Ibrahim Albayrak, Tanja Horn, Pawel Nadel-Turonski Deeply Virtual Comtpon Scattering (DVCS) is deemed the simplest and cleanest way to access the Generalized Parton Distributions (GPDs) of the nucleon. The DVCS process interferes with the Bethe-Heitler process allowing one to access the DVCS amplitudes. The imaginary part of the Compton amplitude is now relatively well understood, primarily through measurements of DVCS. However, much less is known about the real part of the amplitude. Time-like Compton Scattering (TCS) is the inverse process of DVCS and provides a new and promising way for probing the real part of the amplitude, and so constraining GPDs. Comparing data from Time-like Compton Scattering and the space-like DVCS process will also allow for testing the universality of GPDs. First studies of TCS using real tagged and quasi-real untagged photons were carried out at Jefferson Lab 6 GeV. In this talk, preliminary results on asymmetries and extraction of the real part of the CFF using photoproduction data and a comparison to electroproduction data will be presented. We will also discuss future plans for dilepton production at Jefferson Lab 12 GeV. [Preview Abstract] |
Saturday, April 11, 2015 11:45AM - 11:57AM |
B6.00006: Strangeness asymmetry in the proton Mary Alberg Strangeness asymmetry in the proton may arise from fluctuations of the proton into meson-baryon pairs. The leading contributions to proton strangeness are from the $K \Lambda$, $K \Sigma$, $K^*\Lambda$ and $K^*\Sigma$ states. We use a Fock state expansion of the proton in terms of these pairs to represent the strange meson cloud. We determine the strangeness distributions of the proton in a hybrid convolution model, in which the fluctuations are represented either by light-cone wave functions or meson-baryon splitting functions. For the parton distributions of the $s(\bar{s}$) quarks in the bare baryons(mesons) of the Fock states, we use light cone wave functions or our statistical model, which expands the bare hadrons in terms of quark-gluon states. The momentum distributions of the $s$ and $\bar{s}$ quarks in each Fock state differ because they are constituents of different hadrons. We present our results for proton strangeness asymmetry, and compare them to NuTeV and to global parton distributions. [Preview Abstract] |
Saturday, April 11, 2015 11:57AM - 12:09PM |
B6.00007: Exploring hadron structure through exclusive kaon electroproduction Marco Carmignotto, Indra Sapkota, Tanja Horn Exclusive pion and kaon electroproduction are important tools in the study of hadron structure, and in particular for our understanding of the dominant reaction mechanism in exclusive reactions. The dependence of the cross section on the Mandelstam variable $-t$ provides important information about the role of the $t$-channel meson exchange, which is also needed for the extraction of meson form factors. Increasing the photon virtuality, $Q^2$, makes one more sensitive to the partonic picture, where soft non-perturbative and hard physics have been shown to factorize. In that regime, Generalized Parton Distributions (GPDs) provide the most complete description of the non-perturbative physics. The additional flavor degree of freedom in the p(e,e'K+)$\Lambda $ and p(e,e'K+)$\Sigma $0 reactions provides a unique opportunity to study the reaction mechanism underlying strangeness production and the transition from hadronic to partonic degrees of freedom in exclusive processes. In this talk I will present the current status and discuss the outlook on future studies of strange quarks with kaon electroproduction as well as the particle identification requirements for each of these stages. [Preview Abstract] |
Saturday, April 11, 2015 12:09PM - 12:21PM |
B6.00008: Studies of partonic distributions using semi-inclusive production of Kaons Fatiha Benmokhtar Measurements towards the studies of partonic distributions using semi-inclusive production of Kaons will be performed in Hall B of Jefferson lab. Multiplicities for several hadron species ($\pi^{\mathrm{+}}$, $\pi ^{\mathrm{-}}$, $\pi^{\mathrm{0}}$, K$^{\mathrm{+}}$,K$^{\mathrm{-}}$,K$^{\mathrm{0}}$s ) using both hydrogen and deuterium targets will be extracted. The goal is the control of the fragmentation functions used in the extraction of the individual quark and antiquark contributions to the nucleon spin. In addition, the shape of the strange parton distribution functions for several $z$ and $Q^{2}$ bins with three independent measurements ($\pi^{\mathrm{+}} \quad + \quad \pi ^{\mathrm{-}}$, K$^{\mathrm{+}} \quad +$K$^{\mathrm{-}}$ and K$^{\mathrm{0}}$s ) will be extracted. A good charged Kaon identification for the whole momentum range and to enhance the existing particle identification, a RICH detector for CLAS12 is under construction. [Preview Abstract] |
Saturday, April 11, 2015 12:21PM - 12:33PM |
B6.00009: Luminosity Monitoring at the OLYMPUS Two-Photon Exchange Experiment Colton O'Connor OLYMPUS collected data mainly in 2012 with beams of positrons or electrons incident on a gaseous hydrogen target. Since several models of two-photon exchange in the literature predict similar cross section ratios at many values of $Q^2$, OLYMPUS seeks results with less than 1\% uncertainty in order to select among them. Estimates from beam and target parameters indicate that approximately 4.5 fb$^{-1}$ were collected, providing sufficient statistics. But the relative luminosity obtained with each beam species must be known more precisely, and to that end multiple independent detector systems were used to monitor the luminosity in real time. This talk will detail our methods and show comparisons between detector systems. [Preview Abstract] |
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