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 FC: Mini-Symposium on New insight into Hadronic Structure from Space-like and Time-like Form Factors |
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Chair: Gordon Cates, University of Virginia Room: Kohala 3 |
Friday, October 10, 2014 9:00AM - 9:30AM |
FC.00001: Modern Insights into Elastic Nucleon Form Factors Invited Speaker: Seamus Riordan The electromagnetic elastic form factors of the nucleon provide experimental access to the underlying charge and magnetic moment distributions arranged by the strong nuclear force. These form factors provide excellent testing grounds for QCD and QCD-inspired models and are fundamentally important in understanding non-perturbative strong force physics. By studying them over a broad range of momentum transfers, they provide insight into the underlying mechanisms relevant to the generation of nucleon structure. At low $Q^2$ there is presently a controversy regarding the charge radius measurements of the proton. At high $Q^2$, scaling of the form factors are presently being studied in the context of a transition from soft QCD processes. In this talk I will provide an overview of what we learn about nucleon form factors within leading models and calculations, provide an overview of the present experimental status, and summarize plans for future measurements. [Preview Abstract] |
Friday, October 10, 2014 9:30AM - 9:45AM |
FC.00002: Uncovering dressed-quarks and the correlations between them Craig Roberts The last five years have brought considerable progress in the study of the bound-state problem in continuum quantum field theory. I will highlight a subset of that progress; viz., that made within the context of Dyson Schwinger equation analyses of cold, sparse hadrons, with a particular focus on exposing the dressing of quarks and how correlations within them have a dramatic effect on nucleon observables. [Preview Abstract] |
Friday, October 10, 2014 9:45AM - 10:00AM |
FC.00003: Dressed Quark Mass Dependence of Pion and Kaon Form Factors Yu Ninomiya, Wolfgang Bentz, Ian Clo\"et The structure of hadrons is described well by the Nambu--Jona-Lasinio (NJL) model, which is a chiral effective quark theory of QCD. In this work we explore the electromagnetic structure of the pion and kaon using the three-flavor NJL model, including effects of confinement and a pion cloud at the quark level. In the calculation there is only one free parameter, which we take as the dressed light quark ($u$ and $d$) mass. In the regime where the dressed light quark mass is approximately $0.25\,$GeV, we find that the calculated values of the kaon decay constant, current quark masses, and quark condensates are consistent with experiment and QCD based analyses. We also investigate the dressed light quark mass dependence of the pion and kaon electromagnetic form factors, where comparison with empirical data and QCD predictions also favors a dressed light quark mass near $0.25\,$GeV. [Preview Abstract] |
Friday, October 10, 2014 10:00AM - 10:15AM |
FC.00004: Meson vector couplings and SU(4) flavor symmetry Kadir Utku Can, Guray Erkol, Makoto Oka, Toru T. Takahashi Meson-exchange models use SU(4) flavor symmetry to determine the coupling constants in constructing the effective Lagrangian. We extract the vector form factors and electric charge radii of light and charmed mesons in $2+1$-flavor Lattice QCD, which allow us to study the SU(4) flavor symmetry and its breaking. We compare our results with those from other theoretical approaches such as QCD sum rules. [Preview Abstract] |
Friday, October 10, 2014 10:15AM - 10:30AM |
FC.00005: Charge distribution in the neutron at short distances Sergey Abrahamyan Elastic form-factors are a fundamental property of the nucleon, and provide critical information on the nucleon's transverse spatial structure. Furthermore, by combining knowledge of the neutron electromagnetic form factors with the corresponding form factors of the proton, it is possible to gain understanding of the flavor structure of the nucleon. In this talk we present final results of the JLab experiment E02-013, comprising four measurements of the ratio of the neutron's electric and magnetic form factors, $G_E^n/G_M^n$, at four values of the four-momentum transfer Q$^2$ = 1.2,\,1.7,\,2.5\ and 3.4\, GeV$^2$. We note that the result at $\rm 1.2\,GeV^2$ has not been previously reported. In E02-013, a double-polarization asymmetry was measured in the reaction $^3\vec{\rm He}(\vec e,e^{\prime}\,n)p\,p$ in order to determine the ratio $G_E^n/G_M^n$. We present key aspects of the experimental approach that was used, as well as essential features of the data analysis such as exclusive quasi-elastic event selection, hadron charge identification and analysis of FSI effects. [Preview Abstract] |
Friday, October 10, 2014 10:30AM - 10:45AM |
FC.00006: Two-photon exchange in elastic $ep$ scattering and the status of the OLYMPUS experiment Douglas Hasell Two-photon exchange in elastic $ep$ scattering is believed to explain the observed discrepancy in the proton electric to magnetic form factor ratio, $\mu_{p}G_{E}^{p}/G_{M}^{p}$, measured by Rosenbluth separation and by polarization transfer methods. To quantitatively determine the contribution of two-photon exchange to elastic scattering the OLYMPUS experiment was proposed and operated at the DESY laboratory in Hamburg, Germany to measure the ratio in the elastic scattering cross sections, $\sigma_{e^{+}p}/\sigma_{e^{-}p}$. The OLYMPUS experiment used the positron and electron beams of the DORIS storage ring at a beam energy of 2.01~GeV incident on a windowless, internal, hydrogen gas target. A left/right symmetric detector measured the rates for elastic scattering over a broad kinematic range together with a redundant set of luminosity monitors. Approximately 4.45~fb$^{-1}$ of integrated luminosity was collected. The current status of the OLYMPUS analysis will be presented. [Preview Abstract] |
Friday, October 10, 2014 10:45AM - 11:00AM |
FC.00007: First Precision Measurements of EM Form Factors of Pions, Kaons, Protons, and Hyperons, and Evidence for Diquark Correlations Kamal Seth Precision measurements of electromagnetic form factors of pion, kaon, proton, and charged and neutral hyperons at large timelike momentum transfers of 14 and 17 GeV$^2$ have been made. The measurements for lambda, sigma zero, sigma plus, cascade zero, cascade minus, and omega minus are the world's first, and their systematics is studied. The most dramatic result consists of the nearly factor two difference between the form factors of the lambda and sigma zero hyperons, which have the same uds quark construct, but different isospin. The result is explained in terms of the diquark correlations anticipated by Jaffe and Wilczek. [Preview Abstract] |
Friday, October 10, 2014 11:00AM - 11:15AM |
FC.00008: Tests of new physics explanations for the proton radius puzzle Carl Carlson An explanation for the discrepancy in the muonic vs. electronic measurements of the proton charge radius could be the existence of new, lepton universality violating interactions. If true, these must affect other measurements involving muons. Fine tuning could keep the muonic (g-2) discrepancy small. However, signals in other muonic reactions must appear, for example noticeable corrections to muonic K decay. We will explore some of these processes and show that the expected size of signals would be large enough to see. [Preview Abstract] |
Friday, October 10, 2014 11:15AM - 11:30AM |
FC.00009: Status of the MUSE Measurement of the Proton Radius at PSI Ronald Gilman It is a puzzle that the proton radius appears to be different when measured with muons vs.\ with electrons. The MUon Scattering Experiment (MUSE) at the Paul Scherrer Institut (PSI) $\pi$M1 beam line utilizes a mixed $e/\mu/\pi$ beam to measure $\mu^{\pm}p$ and $e^{\pm}p$ elastic scattering. The experiment will study the proton electromagnetic form factors at low $Q^2$, in the region most sensitive to the proton radius. The goal is to determine whether the charge radius is indeed the same for muons and electrons, with measurements at the same time in a single experiment. I will describe test measurements done for the MUSE experiment and discuss the status of the project. [Preview Abstract] |
Friday, October 10, 2014 11:30AM - 11:45AM |
FC.00010: Truncation Errors and Proton Radius Extractions from Form Factor Data Katherine Mesick The MUon Scattering Experiment (MUSE) Collaboration plans to extract the proton charge radius from new $\mathcal{O}(0.1\%)$ measurements of the $\mu^{\pm} p$ and $e^{\pm} p$ electromagnetic form factors in the region of $Q^2 = 0.002 - 0.07$ GeV$^2$. The aim is to determine if there is a fundamental difference between $e$ and $\mu$, adding new insight into the proton radius puzzle -- the $\sim$7$\sigma$ discrepancy between the charge radius as determined from muonic hydrogen and that from atomic hydrogen spectroscopy and $ep$ elastic scattering form factor data. One important consideration in extracting the radius from form factor data is errors in the fitting procedure, one of which is a so-called truncation offset, which results from the truncation of a series expansion to fit a finite range of $Q^2$ data. The truncation offset resulting from a Taylor series expansion and from an inverse polynomial series will be compared and discussed. An example of how the MUSE experiment plans to extract the proton radius and the anticipated significance will also be presented. [Preview Abstract] |
Friday, October 10, 2014 11:45AM - 12:00PM |
FC.00011: Laser spectroscopy of ground-state hyperfine splitting energy of muonic hydrogen Katsuhiko Ishida, Masaharu Sato, Masahiko Iwasaki, Yue Ma, Teiichiro Matsuzaki, Yu Oishi, Shinji Okada, Satoshi Wada, Norihito Saito, Katsumi Midorikawa, Yasuyuki Matsuda, Kazuo Tanaka, Sotaro Kanda We propose a new measurement of the ground-state hyperfine splitting of muonic hydrogen by laser spectroscopy with the accuracy of $\sim$2 ppm. The hyperfine splitting energy is connected to the Zemach radius [1], which is a convolution of the spatial distribution of the charge and the magnetic moment within the proton. This can provide new insights on ``Proton radius puzzle'' [2]. When the laser with the resonance frequency of the hyperfine splitting energy is irradiated, the spin-flip transition is induced from the spin-singlet to the spin-triplet hyperfine sub-levels. Since the muon spin in the spin-triplet state can be polarized by a circularly-polarized laser, we can search for the resonance frequency with the muon decay asymmetry by the decay-electron detection. The transition energy is about 0.182 eV, which corresponds to the laser wavelength of 6.7 $\mu$m. The experiment becomes feasible by a narrow-bandwidth tunable mid-infrared laser recently developed in RIKEN. In this contribution, we present the physics motivation, the experimental principle and its feasibility.\\[4pt] [1] A. Dupays et al., Phys. Rev. A68, 052503 (2003).\\[0pt] [2] R. Pohl et al., Nature 466, 213 (2010). [Preview Abstract] |
Friday, October 10, 2014 12:00PM - 12:15PM |
FC.00012: Accurate calulation of nucleon form factor in lattice QCD Eigo Shintani We present the accurate lattice calculation of nucleon form factor in $N_f=2$ Wilson-clover fermion. In this calculation, we evaluate the nucleon isovector and axial-vector form factor with the new numerical technique, so-called all-mode-averaging, in order to enhance the statistical accuracy in Monte-Carlo simulation. We investigate the systematic effect on the lattice, for instance excited state contamination, large pion mass dependence, finite size effect and lattice artifact, around 200 MeV pion in 3--4 fm lattice box. We also perform the convergence test of baryon chiral perturbation theory using lattice results. [Preview Abstract] |
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