Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session MK: Form Factors |
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Chair: Stefan Diehl, University of Connecticut Room: Arlington |
Wednesday, October 13, 2021 4:00PM - 4:12PM |
MK.00001: Neutron Magnetic Form Factor GnM Measurement at High Q2 with CLAS12 Lamya Baashen The neutron magnetic form factor GnM is a fundamental absorvable, but there are few high-precision measurements of GnM for Q2 > 5 GeV. The upgrade of CEBAF with the CLAS12 detector in Hall B at Jefferson Lab (JLab) provides the opportunity to measure GnM at higher Q2 . The ratio of quasi-elastic e-n to e-p scattering on a deuteron target is used to extract GnM. This method reduces our sensitivity to systematic uncertainties like detector acceptance, live-time corrections, etc. High-statistics data were collected with the CLAS12 Forward Detector (FD) in quasi-elastic (QE) kinematics. Measuring quasi-elastic e-n requires determining the neutron detection efficiency (NDE) of the electromagnetic calorimeter. A liquid hydrogen target is used to produce tagged neutrons from the p (e,e'π+)n reaction to measure NDE. A preliminary result for the NDE reached a maximum value of ∽ 74% at high neutron momentum. We have also developed algorithms to select the quasi-elastic e-p and e-n events. |
Wednesday, October 13, 2021 4:12PM - 4:24PM |
MK.00002: The measurement of the elastic magnetic form factor of the neutron GnM using the newly constructed "Super Bigbite Spectrometer" experimental setup at the Jefferson Lab Anuruddha D Rathnayake The 12 GeV beam upgrade of the Jefferson lab accelerator and the newly designed Super BigBite Spectrometer (SBS) in Hall-A, make possible a new generation of experiments to measure nucleon elastic electromagnetic form factors with high precision at high Q2 values to over 10 GeV2/c2. The very first experiment of the SBS program is the measurement of magnetic form factor of the neutron (GnM) using the ratio method which involves the detection of both neutron tagged, d(e,e'n) and proton tagged, d(e,e'p), quasi-elastic scattering from a deuteron target. The experiment explores several kinematic points ranging from 3.5 GeV2/c2 to 13.5 GeV2/c2 with beam energies going up to 11 GeV. The concept of the Super BigBite Spectrometer, which provides a large solid angle acceptance and the capability to operate at high luminosity, relies on Gas Electron Multiplier (GEM) detector-based particle trackers. The GEM trackers will be used in both BigBite Spectrometer (the electron arm) and Super BigBite Spectrometer (the hadron arm.) This talk will give an overview of the GnM experiment and will report on the recently completed characterization activities of the GEM tracker layers and their performance for the upcoming GnM experiment. |
Wednesday, October 13, 2021 4:24PM - 4:36PM |
MK.00003: Measurement of the Neutron Electromagnetic Form Factor Ratio at High Q2 Sean Jeffas The neutron electromagnetic form factors, GEn and GMn, give important insights into the neutron structure. Previous experiments measured the proton electromagnetic form factors GEp up to Q2 = 8 GeV2 and GMp up to Q2 = 10.2 GeV2, while GEn has only been measured up to Q2 = 3.5 GeV2. The proton electric form factor data showed unexpected features at high Q2 values, where no GEn data is available. The SBS program at JLab plans to measure GEn/GMn at Q2 values of 1.5, 3.8, 6.8, and 10.2 GeV2 by colliding a polarized electron beam with a polarized 3He target, used here as an effective polarized neutron target, and measuring the transverse asymmetry of the cross section. GEn values can be extracted using high Q2 GMn data from a companion experiment. Scattered electrons will be measured in the BigBite spectrometer upgraded with the addition of a Gas Electron Multiplier (GEM) based tracker. Scattered neutrons are magnetically separated from scattered protons and will be detected in an array of scintillators. At our highest Q2 point we expect to be able to calculate the form factor ratio with an accuracy better than Δ(GEn/GMn) = 0.20, which corresponds to ΔGEn = 3 x 10-4 with accurate measurements of GMn. |
Wednesday, October 13, 2021 4:36PM - 4:48PM |
MK.00004: GEn-Recoil Polarimetry Experiment Using the SBS Experimental Setup at Jefferson Lab John A Boyd A series of experiments to measure nucleon electromagnetic form factors (EMFFs) to high four-momentum transfer $Q^2$ values is underway at Jefferson Lab (JLab) using the Super BigBite Spectrometer (SBS). SBS is a large-acceptance spectrometer designed to handle high fluxes and high-momentum particles produced by JLab's 11\,GeV/c electron beam. One experiment in this program is GEn-RP: a measurement of the neutron EMFF ratio $G_E^n/G_M^n$ using recoil polarimetry at $Q^2 = 4.5$\,(GeV/c)$^2$. In GEn-RP, electrons elastically scatter off neutrons in a liquid deuteron target. The electrons are detected by the BigBite (BB) spectrometer while the neutron and its polarization are determined in the SBS. Two polarimetry techniques are employed: charge-exchange $np$ → $pn$ and conventional $np$ → $np$ scattering. This is the first proof-of-principle validation of the charge-exchange method against the conventional approach through direct comparison. The primary trackers in both BB and SBS are gaseous electron multipliers (GEMs). A combination of ''X--Y" and new, rotated-basis ''U--V" GEMs break analytical ambiguity created by high rates and improve tracking efficiencies. These GEMs are critical tracking components for all present and future high-impact experiments of the SBS program. |
Wednesday, October 13, 2021 4:48PM - 5:00PM |
MK.00005: Measurement of the neutral pion transition form factor at low Q2 at Jefferson Lab Ilya Larin, Rory A Miskimen, Ashot Gasparian, Liping Gan, Daniel S Dale, Dipangkar Dutta, Tyler J Hague, Sergey R Gevorkyan The neutral pion transition form factor (TFF) plays an important role in tests of low energy QCD, and in the determination of the hadronic-light-by-light (HLbL) scattering contribution to the muon anomalous magnetic moment, (g-2). Several measurements of this form factor exist in the large space-like Q2 region, but the low Q2 space-like region remains largely unexplored. |
Wednesday, October 13, 2021 5:00PM - 5:12PM |
MK.00006: Elastic Electron Scattering from 3He and 3H Mirror Nuclei Leiqaa Kurbany The cross section for elastic electron-nucleus scattering from a spin-1/2 particle is described by two nuclear form factors, fundamental quantities that describe the electromagnetic structure of the nucleus. By going to low energy and forward angle, the effect of the magnetic form factor GM(Q2) can be minimized, which allows for an extraction of the charge form factor GE(Q2) without having to do a Rosenbluth type experiment. The RMS radius of the nucleus is proportional to the slope, dGE/dQ2, as Q2 →0, so by measuring the electric form factor of a target at very low Q2, we can extrapolate and extract the nucleus radius. |
Wednesday, October 13, 2021 5:12PM - 5:24PM |
MK.00007: Resonant Form Factors from Two-Body Transition Amplitudes Keegan H Sherman, Raul A Briceno, Andrew W Jackura, Felipe G Ortega-Gama Due to the short lifetime of hadronic resonant states, constraining their structure has historically proven difficult; however, such information can be accessed through transition amplitudes that couple two-body states via an external current. Here I present an exact analytic representation for the on-shell form of these amplitudes in terms of generic form factors and known kinematic functions [Phys. Rev. D 103, 114512]. I will then show how it is possible to access the elastic form factors of resonances from this analytic representation. This framework combined with the finite-volume formalism presented in [Phys. Rev. D 100, 034511] constitutes a complete pipeline for extracting elastic resonant form factors from lattice QCD calculations. |
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