Investigating the Electromagnetic Structure of the Nucleon and Light Nuclei at Jefferson Lab

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The primary objective of this research project is to continue collaborative efforts at the Thomas Jefferson National Accelerator Facility ("Jefferson Lab") in Newport News, Virginia, which are specifically aimed at probing the structure of the nucleon using a high energy electron beam. This work will be accomplished in collaboration with the Super BigBite Spectrometer (SBS) Collaboration in Hall A at Jefferson Lab. During this grant period, Jefferson Lab will be emerging from the past transition "upgrade period" phase - having upgraded the beam energy from 6 GeV to 12 GeV - and beginning to utilize equipment specifically designed and built for the higher energy. This proposal includes a plan to ensure continued scientific contributions and student training with the early-running Hall A experiments (experiments focusing not only on nucleon structure, but also on that of light nuclei - particularly the triton three-nucleon system), but with primary emphasis remaining on preparation/development projects associated with a series of specific later-running SBS experiments that will probe nucleon structure functions at very high momentum transfers. The driving physics goals of all aspects of this project are related to improving understanding of the transition from the 'strong (non-perturbative) QCD' regime of relatively large distance scales of approximately 1 to a few fermis (where hadronic degrees of freedom are most appropriate), to the 'perturbative QCD' regime of much shorter distance scales.******Sarty has been working with Jefferson Lab's Hall A Collaboration for two decades, and during the past few years of equipment development for the lab's upgrade, Sarty and his students contributed to design/testing projects for Hall A's SBS group of experiments. The SBS experiments are designed to probe nucleon structure at very high momentum transfer; the hallmark experiment of this group being E12-07-109 ("Large Acceptance Proton Form Factor Ratio Measurements at 13 and 15 GeV/c^2 using Recoil Polarization Method"). This SBS group of experiments requires the construction of new equipment - a spectrometer, calorimeters, detectors - which will be completed by the collaboration during this granting period. Sarty's group has taken a lead role in preparing one part of the SBS detection system: a scintillator-based Coordinate Detector (CDet) to provide required fast timing and accurate position for the scattered electron detection - critical aspects needed for the very high radiation background environment of the E12-07-109 experiment. The CDet will consist of 0.5mm tall (4cm thick) scintillator strips, stacked to form two planes roughly 3m x 1m in size, for a total of 2352 channels of readout; Sarty's group will continue its work to ensure the CDet is constructed and an appropriate data acquisition system is ready for use when it is needed for SBS nucleon structure experiments at the end of the granting period.