Session GJ: Hadronic Structure Measurements and Instrumentation III

Reducing the background levels of GEM detectors in high rate environments of SBS experiments at JLab

The Gas Electron Multiplier (GEM) detectors built at UVa are used for both front and rear tracking systems for SBS experiments at JLab. These detectors meet all critical requirements of the SBS program, including being able to handle rates as high as 500 kHz/cm2, and providing an excellent spatial resolution of 70 µm. However, a high background resulting from the intense low energy photon environment in SBS leads to reduced efficiency of the GEM detectors. Our research focuses on reducing the background hits created in the GEM detector due to radiation interaction with the chamber components through photoelectric effect, Compton scattering, and pair production processes. To achieve this, a Geant4 simulation of a 10cm x 10cm GEM module has been developed to optimize the cathode foil structure by varying its material, thickness, and effective area to lower the background rates. Prototype 10cm x 10cm GEM modules are constructed with different Cathode foil structures and data is taken while the prototypes are exposed to an X-ray beam in the detector lab at UVa to validate the simulated results.   

Optimization of High Voltage Distribution of Gas Electron Multiplier (GEM) Detectors for High Particle Rate at Jefferson Lab

Measurement of the Neutron Magnetic Form Factor, GMn, experiment was completed in February 2022 at the Jefferson Laboratory. During the experiment large area Gas Electron Multiplier (GEM) Detectors had to be operated under unprecedented high hit rates exceeding 100 kHz/cm2. This resulted in high drain currents from high voltage divider leading to modified potential differences applied to the detector and lowered efficiencies. To rectify this a number of modifications were applied to the high voltage distribution of the detector. All modifications were tested using a 50 cm x 60 cm GEM chamber exposed to an X-ray beam at the University of Virginia. Initial modifications were tested at beam condition during the experiment in which the detector efficiency improved significantly. Modified high voltage schemes and characterization measurements will be valuable for future high rate GEM detector operations. Final modifications are to be tested during the upcoming experiment, Measurement of the Neutron Electric Form Factor, GEn. Preliminary results relevant to detector efficiency from the GEn experiment and from a simulated high rate environment at University of Virginia will be presented.   

The Polarized 3He Target for the JLab SBS GEn Experiment, E12-09-016

The Super Bigbite Spectrometer (SBS) program at JLab will measure the elastic nucleon form factors at high momentum transfer, including a measurement of the neutron electric form factor GEn using the double-polarization technique with both a polarized electron beam and a polarized ³He target.  In order to obtain adequate statistics, the polarized ³He target will operate with a polarization-weighted luminosity approximately a factor of three above any previous polarized ³He target used in an electron-scattering experiment.  The target itself consists of a double-chambered glass cell, filled to approximately 7 atm of ³He at room temperature, with a long cylindrical "target chamber" 60 cm in length.  In order to maintain high polarization with electron beam currents up to 60uA, the target cells contain roughly 6 STP liters of ³He, twice the quantity of ³He used in previous targets at JLab.  This cell is polarized using alkali-hybrid spin-exchange optical pumping using up to 200W of near-infrared light from high-power diode-laser arrays.  The target system used in the experiment includes multiple Helmholtz coils which create a magnetic “holding field” that determines the polarization direction. The system also includes another set of coils, the RF coils, used for NMR, and components for performing EPR spectroscopy that are used for absolute polarization measurements. To shield against stray magnetic fields associated with the SBS system’s magnets, a large soft-iron enclosure surrounds the target system. In addition to a description of the SBS GEn target system, data from bench tests of individual ³He target cells will be presented.

    

Jlab Hall-A's Magnetic Form Factor of the Neutron (GMn) Experiment and Improvements Made to the Gas Electron Multiplier Detectors' Tracking Algorithms

 The Measurement of the Magnetic Form Factor of the neutron (G_Mⁿ) experiment (E12-09-019) ran from October 2021 through February 2022 in Hall-A of the Jefferson Lab. The  "ratio method" was used in this experiment which involved the detection of both neutron tagged, d(e,e'n) and proton tagged, d(e,e'p), quasi-elastic electron scattering off a deuteron target. This  experiment explored five kinematic points ranging from 3.5 GeV²/c² to 13.5 GeV²/c² with beam energies going up to 9.91 GeV. This measurement is part of Super Bigbite Spectrometer (SBS) project  which provides a large solid angle acceptance and the capability to operate at high luminosity using Gas Electron Multiplier (GEM) detector based particle trackers. In the G_Mⁿ experiment, GEM trackers were used in the BigBite Spectrometer (electron arm) which determined the q vector of the scattering reaction. Background rates exceeding  100 KHz/cm² were experienced especially by the front most GEM detectors. Tracking efficiency goes down  under these conditions due to the pileup of events both in space and time. Several techniques are under development to cleanup these pileup events and to extract good events and reject  background events, before performing the track reconstruction analysis.   

The Gas Ring Cherenkov Detector for Jefferson Lab, Hall A

The Gas Ring Cherenkov Detector (GRINCH) is a new heavy gas Cherenkov threshold detector developed for the Super Bigbite (SBS) program in Hall A in Jefferson Lab. The purpose of the GRINCH is to distinguish between pions and electrons during electromagnetic form factor experiments. Consisting of 510 1-inch photomultipier tubes and filled with C₄F₈O heavy gas, this novel detector is designed to run in very high background rates. The GRINCH began commissioning with beam during the Gⁿ_M experimental run in January 2022. This talk will give an overview of the GRINCH detector, analysis of its performance during the commissioning period using cluster finding methods, and its future in Hall A experiments.     

Characterization of a Charged Particle Thermal Kinetic Inductance Detector (CP-TKID) Prototype

Precision nuclear physics experiments have long played an important role in searches for physics Beyond the Standard Model (BSM). The traditional particle detection technologies of many of these experiments, semiconductor and scintillation detectors, face fundamental performance limitations that greatly restrict the sensitivity achievable. A new detector paradigm for charged particle detection has the potential to dramatically improve sensitivity in BSM searches. We are working toward this goal by adapting Thermal Kinetic Inductance Detectors (TKIDs) for external charged particle detection. These cryogenic detectors, used in X-ray and gamma spectroscopy as well as dark matter searches, have shown photon energy resolutions on the order of tens of eV and can be multiplexed to create large area detectors. However, TKIDs have not yet been developed for non-embedded charged particle detection. We have designed a Charged Particle TKID (CP-TKID) prototype to optimized for the  detection of the neutron beta decay electron.  In this talk, we will discuss these prototype design constraints and the characterization of its response using an optical source.    

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Starting from Fall 2021 up until Spring 2024, the schedule of Jefferson Lab's experimental Hall A is filled with the Super BigBite Spectrometer (SBS) collaboration experiments. The BigBite spectrometer and the Super BigBite spectrometer were built exclusively for the SBS experiments to detect scattered electrons and hadrons, respectively. A major portion of the detector R$\&$D was focused on building several layers of world's largest Gas Electron Multipliers (GEMs), which are being used in both the spectrometers for high precision tracking. Entirely new spectrometers, multiple GEM layers with active area up to $60$x$200\,\,\text{cm}^2$, and very high luminosity of SBS experiments ($\approx 10^{38}\,\,\text{cm}^{-2}\text{s}^{-1}$) make tracking and reconstruction very challenging. In this presentation, I will give an overview of the reconstruction machinery we use for SBS experiments and will also talk briefly about some of the biggest reconstruction and tracking related challenges we faced during SBS-$G_M^n$ run and how we handled them.