Session RD: Instrumentation for Electron Scattering Experiments

Performance of the PREX-II Apparatus

The PREX-II and CREX experiments at the Thomas Jefferson National Accelerator Facility will measure the neutral weak form factors for $^{208}$Pb and $^{48}$Ca respectively at one judiciously chosen Q$^2$ value each that enhance the sensitivities to their respective neutron RMS radii. The results of these experiments will constrain the density dependence of the symmetry energy of neutron-rich matter, with implications for three-neutron forces and the properties of neutron stars. The experimental designs require dense isotopically pure targets capable of withstanding high luminosity, radiation hard detectors, precision electronics and diagnostic tracking detectors to calibrate the acceptance and absolute momentum scale and precision polarimetry. We will report on the performance of various subsystems and the projected sensitivity of the data collected to date.   

Polarized Electron Beam for the PREX-II Experiment

PREX and CREX are parity violating electron scattering experiments currently running at Jefferson Lab. These experiments aim to map the weak charge distribution in nuclei and thus constrain nuclear structure models with implications for the equation of state of highly dense matter, neutron stars, and gravitational waves produced in neutron star collisions. One common crucial component of these experiments is control of helicity correlated false asymmetries in the polarized electron beam. To achieve the parity quality beam necessary for the small systematic uncertainties required in PREX-II, innovative techniques in the electron source were required. A key technology is the newly installed RTP Pockels cell system in the laser optics of the polarized electron source. This talk will describe the development of the this new RTP Pockels cell system in the injector source with precision nano-meter level control capabilities which helped achieve parity quality beam for PREX-II and CREX.   

Focal Plane Detector Package for PREX-II

The Pb Radius Experiment, PREX, aims to make a high precision, statistics limited measurement of a sub-ppm parity violating asymmetry.  To achieve this goal in relatively short time requires high (GHz-level) scattered flux rates on the main integrating detectors.  As a result, the PREX-II main detectors employ radiation-hard, high-purity Spectrosil 2000 fused-silica tiles as an active Cerenkov medium for counting electrons.  Each tile is optically polished and coupled to a photo-multiplier tube with a quartz window for UV light transmission.  The focal plane detector packages also each include three 10x20 cm$^2$ active area GEM tracking planes for Q$^2$ normalization, and two auxiliary quartz detectors for monitoring parity non-violating asymmetry backgrounds from any residual transverse polarization of the electron beam.  Detailed studies of expected flux rates, detector photo-electron yields, and pmt gains have been made in order to optimize the detector design as well as test and minimize the systematic uncertainty associated with pmt non-linearity.  In this talk, we will present the design of the PREX-II focal plane detector package and report on the key performance parameters achieved during the experiment.   

Use of gemdetectors for the proton polarimeter trackers of the super bigbite spectrometer in JLAB.

The jefferson lab's 12 gev beam upgrade and the newly designed super bigbite spectrometer make possible a new generation of experiments to measure nucleon form factors, which is essential for our understanding of The structure of the nucleon,with high precision at high qvalues over 10 gev. The concept of the super bigbite spectrometer, which provides large solid angle and the capability to operate at high luminosity, is based on new gas electron multiplier (gem) detector based particle trackers. The sbs gem chambers are expected to provide a good position resolution of 70 $\mu $\sout{\textsc{m, while operating in high rate conditions up to 0.5 mhz/mm. A set of 44 gem detector modules, each with an active area of 60x50 cm, has been built in the gem detector lab at uva for the proton polarimeter trackers of sbs. This talk will report on the assembly and commissioning of the 60x200 cmgem tracker layers for the sbs polarimeter using the gem modules.}}   

Commissioning of the Gas Electron Multiplier System for the E12-17-004 Neutron Polarimeter

A large set of Gas Electron Multiplier (GEM) detectors is being commissioned for a novel neutron polarimeter based on elastic and charge-exchange recoil proton detection in experiment E12-17-004 under preparation for the Super-Bigbite Spectrometer (SBS) program at Jefferson Lab. The status of the commissioning activity and performance of the GEM detectors will be presented.   

A Novel Neutron Polarimeter for the E12-17-004 Experiment

A novel neutron polarimeter design has been conceived for the E12-17-004 experiment prepared for the Super-Bigbite program at JLab to measure the neutron electric-to-magnetic form factor ratio via neutron recoil polarization in quasielastic electron-deuteron scattering. Three analyzing processes are pursued: $np$ elastic scattering with detection of small-angle neutrons and tracking of large-angle protons, as well as charge-exchange $np$ scattering with tracking of forward-angle protons. The concept and layout of the experiment and expected performance of the polarimeter is presented.   

Software and simulation framework for the Super Bigbite Spectrometer

Super Bigbite Spectrometer is a new instrument in preparation to take data in Hall A at Jefferson Laboratory starting in 2021. It will consist of a large aperture magnet with a modular detector package, and will be combined together with another arm (that will vary depending on the measurement). Its core physics program consists in the measurement of the nucleon form factors at large values of $Q^2$, but it is versatile enough to perform other measurements such as semi-inclusive DIS or even tagged DIS. Those measurements have in common to require high luminosity, which, combined with the large solid angle and open geometry, induces large trigger and background rates, which makes those measurements particularly challenging. Overcoming those challenges will require a lot of preparation including simulations to both evaluate actual experimental conditions and prepare pseudodata samples to develop the analysis chain. In this talk I will review the simulation and software framework, their capabilities and potential further developments. I will also illustrate the experimental challenge we have to face and overcome with the example of the tracking for the measurement of the proton electric form factor $G_E^p$.