Sebastian successfully defended his thesis titled “The Two-Photon-Exchange Contribution to Electron-Neutron Elastic Scattering and Extraction of GMn at Q2 = 4.5 GeV2 in Hall A at Jefferson Lab” on Friday, July 19, 2024. After completing his Ph.D., Sebastian will start a new position as Staff Scientist 2 at Los Alamos National Laboratory, in the Intelligence and Space Research Division.
The thesis can be found here: Thesis PDF
Professor Puckett traveled to Jefferson Lab in July 2024 to defend an experiment proposal developed with Professors Jan Bernauer of Stony Brook University and Axel Schmidt of George Washington University at the 52nd meeting of Jefferson Lab’s Program Advisory Committee (PAC52). PAC52 approved the proposal with an “A-” scientific rating. The proposal was to add a short (two days of beam time), opportunistic, high-precision measurement to the upcoming experiment E12-07-109 in Hall A at JLab (of which Professor Puckett is also a co-spokesperson). This short “add-on” measurement to an upcoming experiment would improve the precision of the polarization transfer data for the proton form factor ratio as measured in electron-proton scattering by a factor of four at a squared four-momentum transfer of 3.7 GeV2. This improvement is necessary to enable a precise comparison to a planned future measurement using positron beams at the same or similar momentum transfer, aimed at resolving the long-standing discrepancy between cross section and polarization measurements in the determination of the proton’s form factor ratio. The precision goals are driven by the expected magnitude of two-photon-exchange contributions widely thought to be responsible for the discrepancy.
The experiment proposal as submitted to PAC52 can be found here.
Professor Puckett’s presentation to PAC52 can be found here.
The figure below shows the approved measurement compared to existing data and a planned future positron measurement at the same Q2:
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Professor Puckett gave an invited talk on the status of the ongoing data analyses from the completed SBS neutron form factor experiments at the joint Hall A/C summer workshop on July 15.
The meeting agenda can be found here.
Professor Puckett’s slides can be found here.
The “50 Years of Quantum Chromodynamics” invited review by the European Physical Journal C is now published online at the following link:
https://doi.org/10.1140/epjc/s10052-023-11949-2
Professor Puckett contributed section 10.1 on nucleon electromagnetic form factors. The review is a comprehensive history and introduction to research in QCD intended to serve as a useful reference for researchers in the field from beginning graduate students to senior physicists, as well as a snapshot of current research and future directions in the field.
Professor Puckett and UConn physics graduate students Provakar Datta and Sebastian Seeds were part of a strong contingent of Hall A SBS Collaborators at the recent APS DNP/JPS meeting on the big island of Hawaii, reporting on the progress of various data analyses and the preparations for upcoming experiments. This was the 6th Joint Meeting of the American Physical Society’s Division of Nuclear Physics (APS DNP) and the Physical Society of Japan (JPS). More information about the meeting, including the abstracts and authors, can be found at the meeting website.
Professor Puckett and UConn graduate students Provakar Datta, Sebastian Seeds, and Kip Hunt participated in the Super BigBite Spectrometer (SBS) Collaboration Meeting at Jefferson Lab on July 17-18, 2023. In the two-day meeting, talks were presented on the status of ongoing experiments, SBS equipment developments, data analysis of completed experiments, preparations for upcoming experiments, and ideas for future experiments using SBS equipment. Additionally, on the first day, Dr. Anatoly Radyushkin gave a seminar on recent developments in the calculation of the nucleon’s quark distributions in lattice gauge theory. At the end of the meeting, an “end of run party” for the first two completed experiments was held at the SURA Residence Facility.
Professor Puckett was at Jefferson Lab the week of January 23-27 to give an invited talk on the science that would be enabled by a potential future energy upgrade of CEBAF to 22 GeV, for the Jefferson Lab Users’ Organization Board of Directors Meeting, and for the Hall A Winter Collaboration Meeting.
The invited talk at the high-energy workshop can be viewed here.
At the Hall A Meeting, Professor Puckett and his graduate students Provakar Datta and Sebastian Seeds all gave invited talks, see below:
Professor Puckett’s talk
Provakar Datta’s talk
Sebastian Seeds’ talk
Graduate students from the SBS collaboration won the first (Provakar Datta, UConn) and 3rd (Maria Satnik, College of William and Mary) prizes and an honorable mention (Sebastian Seeds, UConn) in the graduate student poster competition at the Jefferson Lab Users’ Organization annual meeting.
Links to the posters and short video overviews of the posters can be found at the following link:
Current UConn PhD students and group members Provakar Datta and Sebastian Seeds were accepted to the National Nuclear Physics Summer School (NNPSS) to take place at MIT this July.
From Oct. 2021-Feb. 2022, experiments E12-09-019 and E12-20-008 were completed in Jefferson Lab’s Experimental Hall A. Data were collected that will determine the neutron’s magnetic form factor (GMN) in a previously unexplored Q2 regime up to 13.6 (GeV/c)2 with unprecedented precision. These experiments were the first large-scale deployment and operation of Gas Electron Multipliers (GEMs) in the high-luminosity, high-radiation, high-background-rate environment in Hall A. The GEMs were used in this experiment for charged-particle tracking through the BigBite Spectrometer. Given the large channel count and the high occupancy of the BigBite GEMs in Hall A (approximately 42,000 readout strips with up to 30-40% of these firing in every event), the SBS GMN run produced 2 petabytes of raw data (or typically about 1 GB/s during beam-on conditions). This is roughly 5 times as much raw data produced in four months of beam time in Hall A as the previous 25 years of Hall A running combined. The UConn group was one of the most actively involved in the preparation and execution of the experiment, developed the Monte Carlo simulation, event reconstruction and data analysis software, and is now leading the analysis of the collected data. Two UConn Ph.D. students will write their doctoral dissertation on the analysis of the SBS GMN dataset.
Figure 1 shows the collected Q^2 points for the extraction of GMN and the projected accuracy based on the data obtained, compared to existing data, selected theoretical models, and the projected Q2 coverage and precision of a measurement in Hall B with similar physics goals, but qualitatively different sources of systematic uncertainty.
The example event distributions shown below were obtained at an incident electron beam energy of 6 GeV and Q2 = 4.5 GeV2:
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Figure 2 (above) shows the invariant mass distributions for reconstructed electrons in BigBite, from the hydrogen (left) and deuterium (right) targets, before and after applying cuts on the angle between the reconstructed momentum transfer direction and the reconstructed scattering angle of the nucleon (proton or neutron) detected in the SBS hadron calorimeter (HCAL). The hydrogen distribution shows a clear peak at the proton mass corresponding to elastic scattering, and the angular correlation cut removes most of the inelastic background, while keeping most of the events in the elastic proton peak. The deuterium distribution is “smeared” by the Fermi momentum of the bound nucleons in deuterium, and the distributions of events passing the angular correlation cut under the hypothesis that the detected nucleon is a proton (red) or neutron (blue) illustrate the relatively clean selection of quasi-elastic scattering and rejection of most inelastic events using the SBS dipole magnet and hadron calorimeter.
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Figure 3 (above) illustrates the method for nucleon charge identification using the SBS dipole magnet and the SBS hadron calorimeter. The plot shows the difference in vertical position between the detected nucleon at HCAL and the expected position predicted from the reconstructed electron kinematics assuming elastic (or quasi-elastic) scattering. The distributions are shown for hydrogen and deuterium targets for three different SBS magnetic field settings (magnet off, 70% of maximum field, 100% of maximum field). The hydrogen distributions show a single peak corresponding to elastic electron-proton scattering, that moves as the SBS magnetic deflection is varied. The deuterium distribution with field off shows a single nucleon (proton plus neutron) peak, smeared by Fermi motion. The deuterium distributions with SBS field on show a clear separation into proton (deflected) and neutron (undeflected) peaks, with protons undergoing the same average deflection as seen with the hydrogen target.
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