Bulletin of the American Physical Society
6th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Sunday–Friday, November 26–December 1 2023; Hawaii, the Big Island
Session D03: Electromagnetic Form Factors I |
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Chair: Tyler Kutz, Massachusetts Institute of Technology Room: Hilton Waikoloa Village Kings 3 |
Wednesday, November 29, 2023 9:00AM - 9:15AM |
D03.00001: The Neutron Magnetic Form Factor Experiment on the SuperBigBite Spectrometer at Jefferson Lab Maria T Satnik The Neutron Magnetic Form Factor, GnM, gives insight into the magnetic moment distribution of the neutron. Experiment E12-09-019 in Hall A at Jefferson Lab took data to measure GnM at high Q2 up to Q2 = 13.6 (GeV/c)2 on the newly built SuperBigBite Spectrometer (SBS) apparatus. Electrons from quasi-elastic electron scattering on a deuterium target are measured in coincidence with the struck nucleon in a large hadron calorimeter. Simultaneous measurements of protons and neutrons allows utilization of a ratio method, causing many systematic uncertainties to cancel. The results from this experiment will significantly extend the range into large Q2 for the GnM world data. The experiment was conducted from Fall 2021 through Spring 2022 and was the commissioning experiment for the detectors. Calibrations of these new detectors constitutes a significant portion of the data analysis. The heavy gas Cherenkov detector (GRINCH) consists of 510 1-inch photomultipier tubes and C4F8 heavy gas to aid in pion and electron identification in the high background environment. In this talk, I will give an overview of the GnM experiment, show calibrations for GRINCH, and report my analysis progress towards physics results for my assigned kinematic settings. |
Wednesday, November 29, 2023 9:15AM - 9:30AM |
D03.00002: Methodology and Progress of SBS-GMn Physics Analysis Provakar Datta Nucleon elastic form factors help us understand the nucleon structure by probing its four-current distributions. But very little is known of the neutron's magnetic form factor, $G^{n}_{M}$, for $Q^2 > 4$ $(GeV/c)^2$. To shed some light on this area, the $SBS$-$G_M^n$ experiment (E12-09-019) ran in Jefferson Lab's experimental Hall A from fall 2021 to February 2022 and took data for several high precision measurements of $G_M^n$ in the range 3 ≤ $Q^2$ ≤ 13.6 $(GeV/c)^2$ using ``ratio" method. Systematic errors are greatly reduced by the use of ``ratio" method in which $G_M^n$ is extracted from the ratio of neutron-coincident to proton-coincident quasi-elastic electron scattering from deuteron. Despite various challenges the data taking was successful and significant progress on detector calibration and physics analysis has been made so far. In this talk, I will discuss our methodology and present our progress of physics analysis including preliminary data/MC comparisons that were achieved by using our simulation, digitization, and reconstruction machinery, preliminary nucleon detection efficiency analysis, and preliminary raw elastic yield extractions. I will also show realistic projections of the final uncertainties on $G_M^n$, emphasizing the high-$Q^2$ data points. |
Wednesday, November 29, 2023 9:30AM - 9:45AM |
D03.00003: JLab Hall-A Magnetic Form Factor of the Neutron (GnM) Experiment Analysis Update Anuruddha D Rathnayake, David Hamilton, Alexandre Camsonne, Brian Quinn, Bogdan Wojtsekhowski, Nilanga Liyanage The Measurement of the Magnetic Form Factor of the Neutron (GnM) experiment (E12-09-019) took place from October 2021 through February 2022 in Hall-A at Jefferson Lab. The ``ratio method" was used in this experiment, which involved detecting both neutron-tagged d(e,e'n) and proton-tagged d(e,e'p) quasi-elastic electron scattering off a deuteron target. The experiment explored five kinematic points ranging from 3.5 GeV2/c2 to 13.5 GeV2/c2, with beam energies reaching up to 9.91 GeV. This measurement is part of the Super Bigbite Spectrometer (SBS) project, which is an ongoing experiment series in Hall-A at Jefferson Lab. The primary goals of the SBS program is to measure nucleon form factors with unprecedentedly high Q2 and high precision. The ratio method for extracting GnM benefits from significantly reduced systematic uncertainties, as many of them cancel out when taking the cross-section ratio of d(e,e'n) and d(e,e'p) reactions. However, some uncertainties, such as neutron and proton detection efficiencies, inelastic background contribution, nuclear corrections, radiative corrections, and neutron and proton misidentification, still need to be studied and quantified. This talk will provide an introduction to the SBS nucleon form factor program and the GnM experiment, followed by an account of the progress made in the analysis of the GnM experiment. |
Wednesday, November 29, 2023 9:45AM - 10:00AM |
D03.00004: Neutron Elastic Form Factor Ratio from Recoil Polarization Sarashowati Dhital, Angel Christopher, David Hamilton, Michael Kohl, Jesmin Najeer, Tanvi Patel, Manjukrishna Suresh, Will Tiremen, Bogdan Wojtsekhowski The GEn-RP experiment with the Super-Bigbite Spectrometer (SBS) setup at Hall-A, Jefferson Lab, measures the ratio of electric to magnetic elastic form factors of the neutron, GEn/GMn using two recoil polarimetry techniques at Q2= 4.5 (Gev/c)2 in quasi-elastic electron-deuterium scattering. Both high-momentum, small-angle neutrons produced during elastic scattering and high-momentum, small-angle protons produced by np-pn (charge exchange) are used to analyze the neutron polarization components upon precessing through a known magnetic field. In addition, low-momentum, large-angle protons produced during np-np elastic scattering are detected, as a proof-of-principle measurement of the analyzing power. This experiment will yield GEn/GMn at the highest kinematic point yet recorded with recoil polarization and the experimental figure-of-merit information on the polarimetry along with the analyzing powers will be used to optimize future measurements of GEn/GMn to reach higher Q2 values using recoil polarimetry techniques. |
Wednesday, November 29, 2023 10:00AM - 10:15AM |
D03.00005: Measurement of the Neutron Electromagnetic Form Factor with Large Acceptance at High Rates Sean Jeffas, Nilanga Liyanage, Gordon D Cates, Bogdan Wojtsekhowski, Todd D Averett, Andrew J Puckett The neutron electromagnetic form factors, GEn and GMn, give important insights into the neutron structure. In previous experiments the proton electromagnetic form factors, GEp, was measured up to Q2 = 8.5 GeV2, and GMp was measured up to Q2 = 30 GeV2, while GEn has only been measured up to Q2 = 3.4 GeV2. The Super BigBite Spectrometer (SBS) program at JLab will measure the neutron form factor ratio, GEn/GMn, at Q2 values of 2.9, 6.6, and 9.7 GeV2 by scattering a polarized electron beam with a polarized 3He target, used here as an effective polarized neutron target, and measuring the double spin asymmetry of the cross section. Measurements of Q2 = 2.9 and 6.6 GeV2 was completed in December 2022, and Q2 = 9.7 GeV2 will be complete in October 2023. The analysis of this data is especially challenging due to the unprecedented high-rate background environment caused by the open nature of the spectrometer with a direct line of sight from tracking detectors to the target. Early analysis details for cuts and corrections needed for GEn extraction under these high-rate conditions at all Q2 points will be presented. |
Wednesday, November 29, 2023 10:15AM - 10:30AM |
D03.00006: GEn-Recoil Polarimetry Experiment in Jefferson Lab SBS Program Xinzhan Bai, Bhasitha Thuthimal Dharmasena Purijjala Lindagawa Gedara, Nilanga Liyanage, Bogdan Wojtsekhowski, David Hamilton, Michael Kohl, William Tireman The Super BigBite Spectrometer (SBS) program at JLab aims to measure nucleon electromagnetic form factors (EMFFs) at high momentum transfers. The GEn-RP experiment will measure the neutron EMFF ratio GEn/GMn through recoil polarimetry at Q2 = 4.5 (GeV/c)². This involves the elastic scattering of electrons off neutrons in a liquid deuterium target. The BigBite (BB) spectrometer detects electrons, while SBS tracks and determines the neutron's polarization. Two polarimetry techniques are used: charge-exchange np → pn with a passive Fe analyzer, and conventional np → np scattering with an active CH analyzer. GEn-RP acts as the initial validation of the charge-exchange method, by directly comparing it to the conventional approach. This experiment will serve to optimize future high Q2 experiments that measure GEn/GMn. In the experiment, BB and SBS utilize gas electron multiplier detectors (GEMs) for particle tracking. A set of in-line GEM trackers and recoil-polarimeter GEM trackers will be used. Installation and testing of GEM tracking detectors are ongoing at JLab. Experiment readiness of the tracking detector layers will be presented. |
Wednesday, November 29, 2023 10:30AM - 10:45AM |
D03.00007: The SBS-Gep Experiment and its Novel Detectors Jimmy Caylor Nucleon elastic form factors give important insights into the neutron structure. The Super Bigbite Spectrometer (SBS) program at Jefferson Lab will measure the elastic nucleon form factors at high momentum transfer, including a measurement of the proton electromagnetic form factor GEp at up to 12 GeV2. Little is known about the proton form factor at high momentum transfer, no data has been measured for GEp at Q2 > 8.5 GeV2. The approved experiment, E12-07-109, will use the recoil polarization technique and aims to make precision measurements at Q2 = 5.5, 8, and 12 GeV2 and will start in the fall of 2024. Work is underway to construct a new electromagnetic calorimeter capable of withstanding the high radiation load necessary for a precision measurement. The 1656 lead glass crystals will be placed in a custom oven capable of annealing the crystals at 220 deg C. An overview of the SBS-GEp experimental method and the development of multiple novel detectors, including the progress of the electromagnetic calorimeter and the completion of a small-scale test will be discussed. |
Wednesday, November 29, 2023 10:45AM - 11:00AM |
D03.00008: High-Q2 Measurement of Proton Electromagnetic Form Factor Ratio GEp/GMp using the Super BigBite Spectrometer Andrew J Puckett, Bogdan Wojtsekhowski, Mark Jones, Evaristo Cisbani, Lubomir Pentchev, Nilanga Liyanage Previous measurements of the proton electromagnetic form factor ratio GEp/GMp using the polarization transfer method upended long-held notions regarding the proton's structure and exposed the limits of applicability of the widely-used one-photon-exchange approximation in the interpretation of electron-nucleus scattering experiments at high energies. Nucleon form factor measurements at large values of momentum transfer Q2 continue to be of high interest for constraining the theoretical modeling of the nucleon in the challenging region of transition between non-perturbative and perturbative QCD, and for revealing the relevant degrees of freedom in explaining and predicting the nucleon's short-distance structure. The family of experiments in Jefferson Lab's (JLab's) experimental Hall A known as the Super BigBite Spectrometer (SBS) program was designed to study two-particle coincidence reactions in "hard" electron-nucleus scattering by combining moderately large solid angle acceptance with large momentum bite and high-luminosity capability at forward scattering angles. Among the major goals of the SBS program is to measure the electric and magnetic form factors of proton and neutron to Q2 ≥ 10 GeV2 with unprecedented precision. The SBS program started in 2021 with several experiments focused on neutron form factors, and is approximately 50% complete as of this writing. The planned measurements of the proton GE/GM ratio to Q2 = 12 GeV2 using the polarization transfer method, designated a "high impact experiment" by JLab's Program Advisory Committee, are currently scheduled to run in 2024. In this talk, I will give an overview of these measurements and the status of preparations for the upcoming experiment run. |
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