Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session EG: Electromagnetic Interactions |
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Chair: Latifa Elouadrhiri, Thomas Jefferson National Accelerator Laboratory Room: King's 3 |
Thursday, October 9, 2014 7:00PM - 7:15PM |
EG.00001: Precision Measurement of $\pi^{0}$ Lifetime via the Primakoff Effect Liping Gan As the lightest particle in the hadron spectrum, $\pi^{0}$ plays an important role in understanding the fundamental symmetries of QCD at low-energy. The $\pi^{0} \to \gamma \gamma$ decay width offers a key test of the QCD predictions based on the chiral anomaly and spontaneous chiral symmetry breaking. The theoretical calculations over the last decade have reached 1{\%} precision in the decay amplitude of the $\pi^{0}$ into two photons. The experimental measurement of this parameter with a comparable precision will be an important test of QCD. The PrimEx collaboration at Jefferson Lab has developed and performed experiments to measure the $\pi^{0}$ radiative decay width via the Primakoff effect. The published result from the first experiment (PrimEx-I) has a 2.8{\%} total uncertainty. The second experiment (PrimEx-II) was carried out with the final goal of 1.4{\%} precision. The preliminary result of PrimEx-II will be presented. [Preview Abstract] |
Thursday, October 9, 2014 7:15PM - 7:30PM |
EG.00002: PEN experiment: a measurement of $\pi^+\to e^+\nu_e(\gamma)$ branching ratio Emil Frlez The experimental $\pi^+\to e^+\nu_e(\gamma)$ decay branching ratio currently provides the most accurate test of lepton universality. The PEN experiment at PSI, Switzerland, aims to improve the present world average experimental precision of $\Delta B/B = 3.3\cdot 10^{-3}$ to $\sim$$5\cdot 10^{-4}$ using a stopped pion beam. During runs in 2008-2010, PEN has acquired over $2\cdot 10^7$ $\pi_{e2}$ events. The experiment includes active beam detectors (degrader, mini TPC, target), central MWPC tracking with a plastic scintillator hodoscope, and a spherical pure CsI electromagnetic shower calorimeter. We will present a progress report on the PEN analysis. In addition to $\pi_{e2}$ and the normalizing $\pi\to\mu\to e$ process, we will discuss radiative pion and muon decays, decays in flight, as well as accidental and hadronic backgrounds. [Preview Abstract] |
Thursday, October 9, 2014 7:30PM - 7:45PM |
EG.00003: ABSTRACT WITHDRAWN |
Thursday, October 9, 2014 7:45PM - 8:00PM |
EG.00004: Photoproduction of scalar mesons using CLAS at JLab Shloka Chandavar, Kenneth Hicks, Dennis Weygand The search for glueballs has been ongoing for decades. The lightest glueball has been predicted by quenched lattice QCD to have a mass in the range of 1.0-1.7 GeV and $J^{PC}=0^{++}$. The mixing of glueball states with neighbouring meson states complicates their identification. The $f_{0}(1500)$ is one of several candidates for the lightest glueball, whose presence in the $K_{s}^{0}K_{s}^{0}$ channel is investigated in photoproduction using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. This is done by studying the reaction, $\gamma p\rightarrow f_{J}p\rightarrow K_{s}^{0}K_{s}^{0}p\rightarrow2(\pi^{+}\pi^{-})p$ using data from the g12 experiment. A brief description of this analysis, along with a preliminary partial wave analysis results will be presented. [Preview Abstract] |
Thursday, October 9, 2014 8:00PM - 8:15PM |
EG.00005: Pion-Mass Dependence of the Nucleon Polarisabilities: A Reappraisal Daniel R. Phillips, Harald W. Griesshammer, Judith A. McGovern The static electric and magnetic scalar dipole polarisabilities and the four spin polarisabilities parametrise the nucleon's two-photon response. At next-to-next-to-leading order in Chiral Effective Field Theory ($\chi$EFT) with dynamical $\Delta(1232)$s, they have recently been extracted from Compton scattering data; ongoing experiments at HI$\gamma$S, MAMI and MAXlab test proton-neutron differences and chiral symmetry breaking. Comparing lattice QCD simulations at pion masses $m_\pi > 220$MeV to data and $\chi$EFT predictions requires a reliable extrapolation to the physical point. Since $\chi$EFT provides a systematically improvable, model-independent parametrisation of the polarisabilities, it is well-suited for that task. The relative theoretical uncertainties increase with increasing $m_\pi$: the magnitudes of the polarisabilities decrease; the $\chi$EFT expansion parameter itself increases; and the $\Delta(1232)$ becomes more important, leading to a re-ordering of contributions. After a review of $\chi$EFT, this presentation offers a method to quantitatively assess error-bands for chiral lattice extrapolations which can also be applied to other cases. Published errors appear to be underestimated. [Preview Abstract] |
Thursday, October 9, 2014 8:15PM - 8:30PM |
EG.00006: Measuring the electromagnetic polarizability of the charged pion at Jefferson Lab Hall D Rory Miskimen The electromagnetic polarizability of the charged pion is arguably among the most important tests of low-energy QCD unresolved by experiment. Beyond providing a test of ChPT, a precision measurement of the charged pion polarizabilty (CPP) has significant ramifications for predictions of hadronic light-by-light scattering in (g-2)$_\mu$. The goal of the Jefferson Lab CPP experiment E-12-13-008 is to make a precision measurement of the charged pion polarizability at the level of $\approx 10$\% through measurements of $\gamma \gamma \rightarrow \pi^+ \pi^-$ cross sections. The CPP experiment will utilize the Hall D GlueX forward drift chambers, time-of-flight counters, and forward calorimeter to detect forward going $\pi^+ \pi^-$ pairs produced by linearly-polarized tagged photons incident on a nuclear target. A system of forward angle MWPCs and iron absorbers is under development for muon identification in the experiment. This talk will summarize the present state of experiment and theory, and present the status of instrumentation development for the experiment. [Preview Abstract] |
Thursday, October 9, 2014 8:30PM - 8:45PM |
EG.00007: Compton Scattering and the Nucleon Polarizabilities in the A2 Collaboration at MAMI Evangeline Downie There has been an upsurge in interest in Compton Scattering experiments as a means to understand the internal structure and dynamics of the nucleon. The new PDG value of $\beta$, the proton magnetic polarizability, changed noticeably, with no new data, simply new theoretical treatment of the existing data set. This indicates that the existing data is insufficient to constrain our extraction of these fundamental constants, which are important in areas of physics such as the proton radius determination, and neutron star physics. In the A2 Collaboration of the Institut fuer Kernphysik in Mainz, we use the MAMI accelerator with the Glasgow Mainz Photon Tagger to produce a quasi-monoenergetic, linearly polarized photon beam and apply it to a liquid hydrogen target. The reaction products detected in the Crystal Ball and TAPS large acceptance spectrometer array allow clean separation of the low-cross-section hadronic Compton scattering process. In so doing, we have produced the firs t measurement of the photon asymmetry in Compton scattering on the proton below the pion production threshold. Preliminary results show a demonstrable effect due to the polarizabilities. We will cover the experimental results and future prospects of the A2 polarizability program. [Preview Abstract] |
Thursday, October 9, 2014 8:45PM - 9:00PM |
EG.00008: Initial State Helicity Correlation in Wide Angle Compton Scattering Jixie Zhang, Donal Day, Dustin Keller, Oscar Rondon The applicability of pQCD to exclusive reactions at medium energies is a subject of considerable interest. Real Compton scattering (RCS) has the potential to provide insight to this unsettled issue. In pQCD, three active quarks and two hard gluons are involved when describing RCS. But the cross sections do not agree with the pQCD predictions. In contrast, a handbag dominance model, involving only one single quark coupling to the spectator through generalized parton distributions (GPDs) does a good job of matching the cross section data. A measurement of the longitudinal polarization transfer parameter $K_{LL}$ was found inconsistent with predictions of pQCD yet consistent with calculations within the hand-bag mechanism. Further Miller's handbag approach, which including quark and hadron helicity flip, contradicts pQCD and others which demands that $K_{LL} = A_{LL}$, the initial state helicity correlation asymmetry, by finding that $K_{LL} \neq A_{LL}$. The first ever measurement of $A_{LL}$ has been proposed to run in Jefferson Lab's Hall C. This experiment will utilize an untagged bremsstrahlung photon beam and the longitudinally polarized UVA/JLAB proton target. After a brief introduction to the physics, the experiment will be described and the expected results presented. [Preview Abstract] |
Thursday, October 9, 2014 9:00PM - 9:15PM |
EG.00009: Using Polarized Compton Scattering to Extract Proton Spin Polarizabilities Philippe Martel The MAMI A2 collaboration has recently taken data on the Compton scattering beam-target asymmetry $\Sigma_{2z}$ using a circularly polarized photon beam with a longitudinally polarized target. These data accompany previous A2 data using a transversely polarized target to obtain $\Sigma_{2x}$ and a linearly polarized photon beam on an unpolarized target to obtain $\Sigma_{3}$. The goal of this Compton scattering program at A2 is the extraction of the proton spin polarizabilities, parameters which describe the response of the proton spin to a scattering photon. Third order terms in the energy expansion of the Compton scattering amplitude, the spin polarizabilities provide a valuable test of nucleon structure, dispersion and effective field theories, and lattice calculations. While values have been determined for two linear combinations of the spin polarizabilities, their independent extraction requires the use of such complimentary data sets on different Compton scattering observables. These data were taken with the MAMI A2 Bremsstrahlung beam, either a frozen-spin butanol or an unpolarized hydrogen target, and the Crystal Ball and TAPS detectors. We will report on the $\Sigma_{2x}$ measurements, supplemented by preliminary $\Sigma_{3}$ and $\Sigma_{2z}$ measurements. [Preview Abstract] |
Thursday, October 9, 2014 9:15PM - 9:30PM |
EG.00010: Dilepton and photon production spectra above Tc calculated with a lattice quark propagator Taekwang Kim, Masayuki Asakawa, Masakiyo Kitazawa We analyze the production rates of dileptons and photons from the deconfined medium using a quark propagator obtained from a first principle lattice QCD numerical simulation. We calculate the dilepton and photon production rates non-perturbatively at two temperatures in the deconfined phase with the quark propagator measured on the lattice. The photon-quark vertex is determined gauge-invariantly, so as to satisfy the Ward-Takahashi identity. The obtained dilepton production spectra show enhancements of order 10 or so compared with these from free quark systems at low invariant masses and van Hove singularity. These spectra could explain the discrepancy in the dilepton production yields in the low mass region between the PHENIX result and theoretical predictions. The result on the photon production rate will also be reported. [Preview Abstract] |
Thursday, October 9, 2014 9:30PM - 9:45PM |
EG.00011: Status of the TREK/E36 Experiment at J-PARC Michael Kohl The TREK/E36 experiment is scheduled to run in 2015 at the J-PARC K1.1BR kaon beamline. The experiment uses a scintillating fiber target to stop a beam of up to $10^6$ positive kaons per second. The kaon decay products are detected with a large-acceptance toroidal spectrometer capable of tracking charged particles with high resolution, combined with a photon calorimeter with large solid angle and redundant particle identification systems. With the aim to test lepton universality in the $K_{e2}/K_{\mu2}$ ratio with high precision, the experiment is highly sensitive to new physics beyond the Standard Model. A further goal of E36 is to search for light new particles with masses up to a few hundred MeV/c$^2$ such as sterile neutrinos or U(1) bosons, which could be associated with dark matter or explain established muon-related anomalies. An overview of the planned experiment and the current project status will be presented. [Preview Abstract] |
Thursday, October 9, 2014 9:45PM - 10:00PM |
EG.00012: Quark distributions at $x>1$ Nadia Fomin Inclusive lepton scattering has been used to measure nuclear structure functions from a Q$^2$ of a few to 200 GeV$^2$. We have previously used target-mass corrections to remove scaling violations for finite Q$^2$, yielding excellent agreement between almost all existing data sets. We will present our ongoing analysis of nuclear structure functions at high $x$ in terms of QCD and discuss possible sources of remaining disagreement. [Preview Abstract] |
Thursday, October 9, 2014 10:00PM - 10:15PM |
EG.00013: Quasielastic Transverse and Longitudinal Response Functions in the range 0.55 GeV/c$\leq \mid \overrightarrow{q}\mid\leq$1.0 GeV/c Hamza Atac In order to determine the Coulomb sum in nuclei, a precision measurement of inclusive electron scattering cross sections in the quasi-elastic region was performed at Jefferson Lab. Incident electrons with energies ranging from 0.4 GeV to 4 GeV scattered from $^{4}He$,$^{12}C$,$^{56}Fe$ and $^{208}Pb$ nuclei at four scattering angles ($15^{\circ},60^{\circ},90^{\circ},120^{\circ}$) and scattered energies ranging from 0.1 GeV to 4 GeV. The Rosenbluth separation method is used to extract the transverse and longitudinal response functions at three-momentum transfers in the range 0.55 GeV/c$\leq \mid \overrightarrow{q}\mid\leq$1.0 GeV/c. The Coulomb Sum is obtained for $^{56}Fe$ and $^{12}C$, and compared to predictions. We will discuss the impact of our results on short range nucleon-nucleon correlations and the possible modification of the nucleon electromagnetic properties in the nuclear medium. [Preview Abstract] |
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