Session X13: Instrumentation: JLAB

Simulation of a hadron calorimeter for Jefferson Lab Hall-A Super Bigbite Spectrometer

A ``shashlik'' hadron calorimeter is being designed for the new Super Bigbite Spectrometer in Jefferson Lab Hall-A. The calorimeter will be used in nucleon-coincidence form-factor experiments after Jefferson Lab's 12 GeV upgrade. A Geant4 simulation has been developed to optimize hadron-detection efficiency, time and spatial resolution in a momentum range of 2-10 GeV/c. Significant efforts were made to implement the simulation as realistically as possible. Simulation has been validated by measuring detector-response time resolution for cosmic ray muons in hadron calorimeter blocks of a similar design, used in the COMPASS experiment. Tests with a short decay-time combination, ELJEN 232 scintillator and ELJEN 299-27 wavelength shifter (WLS), were also conducted to study their suitability. The results of these tests indicate that the simulation is able to predict time resolution with better than 5\% precision and the ELJEN scintillator WLS combination is suitable for the hadron calorimeter. Simulation indicates $\sim$1.5 ns FWHM time resolution, 5-3 cm spatial resolution and more than 90\% hadron detection efficiency in the momentum range of 2-10 GeV/c.   

Large Gas Electron Multiplier Trackers for Super Bigbite Spectrometer at Jefferson lab Hall A

The 12 GeV upgrade at Jefferson Lab (JLAB) makes many exciting nuclear experiments possible. These experiments also require new high performance instrumentation. The Super Bigbite Spectrometer (SBS) was proposed to perform a series of high precision nucleon form factor experiments at large momentum transfer. The SBS will be capable of operating at a very high luminosity and provide a large solid angle acceptance of 76 msr. SBS will be equipped with a double focal plane polarimeter. Thus, SBS will have three large trackers made of Gas Electron Multiplier (GEM) chambers. The first, second, and third trackers will consist of six, four, and four tracking layers respectively. When completed in 2017, the SBS GEM trackers will form one of the largest sets of GEM chambers in the world. The GEM trackers allow the SBS to operate under high background rates over 500 kHz/cm$^2$, while providing an excellent spatial resolution of 70 $\mu$m. The first tracker will be constructed at the Istituto Nazionale di Fisica Nucleare in Italy, while the second and third trackers will be built at the University of Virginia. In 2012, the first UVa SBS GEM chamber prototype was successfully constructed and tested. The GEM chamber construction details and test results will be presented in this talk.   

Quartz Detector for the SuperHMS Spectrometer at Hall-C Jefferson Lab

We have developed and constructed a quartz hodoscope to be part of the trigger system for the Super High Momentum Spectrometer (SHMS). The SHMS spectrometer will play a central role in carrying out the 12-GeVphysics program at Hall-C Jefferson Lab. The hodoscope consists of twenty one fused silica bars. Each bar is 125-cm long, 5.5-cm wide, and 2.5-cm thick. It is viewed by a UV-sensitive PMT on each end. The quartz hodoscope task is to provide a clean detection of charged particles, a high level of background suppression, and an accurate tracking efficiency determination. We present results of tests leading to the construction of the hodoscope, as well performance test results of the completed detectors such as detection efficiency and position resolution.   

A Novel Spin-Light Polarimeter for the Electron Ion Collider

High precision polarimetry is a pre-requisite for the suite of precision experiments being planned for the proposed Electron Ion Collider. A novel polarimeter based on the asymmetry in the spacial distribution of the spin light component of synchrotron radiation will make for a fine addition to the existing-conventional M{\o}ller and Compton polarimeters. The spin light polarimeter consists of a set of wiggler magnet along the beam that generate synchrotron radiation. The spacial distribution of synchrotron radiation will be measured by an ionization chamber. The up-down (below and above the wiggle) spacial asymmetry in the transverse plain is used to quantify the polarization of the beam. As a part of the design process, the fringe fields of the wiggler magnet was simulated using a 2-D magnetic field simulation toolkit called Poisson Superfish, which is maintained by Los Alamos National Laboratory. The effects of the fringe field was found to be negligible. Lastly, a full fledged GEANT-4 simulation was built to study the response of the ionization chamber. The results from all the simulations carried out, the preliminary design parameters of the polarimeter and its impact will be discussed.   

Design of a Noble Gas Cerenkov for the Super High Momentum Spectrometer for 12 GeV at Jefferson Lab

The 12 GeV upgrade of the accelerator and the associated experimental facilities at Jefferson Lab will provide innumerable new opportunities for nuclear science. In Hall~C the new Super High Momentum Spectrometer (SHMS) will provide excellent angular and momentum resolution up to a maximum central momentum of 11 GeV/c and a diverse set of directed studies, from the spin structure of the neutron to multi-nucleon correlations in nuclei, are planned. These and other approved experiments demand robust particle identification. As part of the electron identification and pion rejection package, a 2 meter long, 4-mirror noble gas Cerenkov counter is being built. The design principles, expected performance and status of the project will be presented.   

Studies of single-photoelectron response and of performance in high magnetic field of a multianode H8500C-03 photomultiplier tube

Several approved experiments at Jefferson Laboratory for the 12 GeV era will require threshold Cerenkov detectors to function optimally in high magnetic field, up to 250 Gauss. A magnetic field resistant photon detector with good resolution for single photoelectron signals is necessary for the proper functionality of such Cerenkov detectors. We recently performed extensive studies of single photoelectron response and of performance in high magnetic field (up to 300 gauss) of the multianode photomultiplier tube H8500C-03. We mapped in great detail the effect of a longitudinal and transverse high magnetic field on both large signals, up to 60 photoelectrons, and on single photoelectron signals. We were thus able to disentangle the loss of photoelectrons extracted from the photocathode which would lead to the loss of an event from the losses during the amplification stage on the dynode chain which could be corrected by use of external amplification. Our measurements show that H8500C-03 is a viable choice for an efficient detection of Cerenkov photons in a high magnetic field environment.