Student Abstracts: Physics at TJNAF

A Proton Detector Array For Deeply Virtual Compton Scattering. MICHAEL MASKELL (Old Dominion University, Norfolk, VA 23529) CHARLES HYDE-WRIGHT (Thomas Jefferson National Accelerator Facility, Newport News, VA 23606) .
A Deeply Virtual Compton Scattering (DVCS) experiment involves scattering an electron off of a proton and observing the paths of the proton, electron, and the photon emitted. In order to perform such an experiment, three detectors are required, one for each particle. For the DVCS experiment at TJNAF, a 100-element, semiannular proton detector array will be used. The core of each element is the scintillator material that actually does the detecting. For cost effectiveness, plastic scintillators will be used in this experiment. The design of the detectors must take into consideration protection of the scintillator material, maximizing light collection from each individual scintillator, minimizing light collection from neigboring scintillators, and preventing magnetic fields from altering the paths of collected photons. The scintillators must be wrapped to protect them from contaminants such as skin oils, which can attack them, as well as to prevent leakage of light from one block to the next. A reflective mylar wrapping will provide this layer of protection, and help direct more light into the photomultiplier tubes by reflecting stray photons back to the tubes. To shield the photomultiplier tubes from external magnetic fields, the tubes will be encased in a mu-metal shield. The base plate will be made of Aluminum, with a mu-metal plate attached to provide additional shielding, particularly from the fringe fields produced by the mu-metal tube. Following this basic design for each of the 100 elements of the proton detector array should allow the array to perform with the desired accuracy.

Hybrid Calorimeter Algorithm Development for PrimEx Experiment. EUGENE MOTOYAMA (Massachusetts Institute of Technology, Cambridge, MA 02139) ASHOT GASPARIAN (Thomas Jefferson National Accelerator Facility, Newport News, VA 23606) .
The PrimEx Collaboration seeks to measure the lifetime of the pi0 meson (neutral pion) at high precision. The decay rate of the pion is considered to be the most fundamental prediction of low-energy quantum chromodynamics (QCD). Pions will be produced by the Primakoff Effect: a few GeV photon interacts with the coulomb field of a nucleus to produce a pion. The pion then decays almost immediately (~10^-16 seconds) into two photons. The decay photons will be detected by an electromagnetic hybrid calorimeter (HYCAL), an array of lead tungstate and lead glass crystals. An algorithm is needed to calculate the angular separation of the two decay photons (and thus the invariant mass of the pion) from the energies deposited in HYCAL. A GEANT Monte Carlo simulation of the experiment is used to test and develop the algorithm to achieve the best angular resolution. The development of the algorithm is essential to the PrimEx project.

Pulsewidth Calculations Using a Photodetector and Two-photon Absorption Measurements Compared to Interferometric Autocorrelation. ANDREA MUNRO (University of Washington, Seattle, WA 98195) MICHELLE SHINN (Thomas Jefferson National Accelerator Facility, Newport News, VA 23606) .
We attempted to determine through experimentation, that two-photon absorption would be the ultrafast pulsewidth measuring technique best suited to be used as a reliable diagnostic for the Free Electron Laser at Jefferson Lab. Two-photon absorption was to be compared with interferometric autocorrelation as methods of pulsewidht measurement that allowed for a large bandwidth and relative ease in alignment. Experimenting parasitically we were unable to collect data that would allow us to draw useful conclusions about our hypothesis. I did learn the inherent difficulties of experimentation and this experience increase my interest in both laser technology and in becoming an experimentalist.

Detection of Pions and Kaons in Meson Electroproduction. NADIA NOVIKOFF (Houston Baptist University, Houston, TX 77478) ROLF ENT (Thomas Jefferson National Accelerator Facility, Newport News, VA 23606) .
We performed numerous tests to determine if it is possible to separate and then detect pions and kaons emitted by meson electroproduction using an HMS Aerogel Cherenkov detector in Hall C. The case of interest was that of the accelerator beam passing through a hydrogen target, producing a meson that subsequently passes through an aerogel Cherenkov detector, after which the electrons are detected by the SOS and the pions and kaons by the HMS spectrometers. The aerogel detector would contain sixteen photomultiplier tubes and aerogel of a refraction index of either 1.015 or 1.030. We found that it would be possible to separate pions and kaons in this manner, particularly using aerogel with a refraction index of 1.015. We also tested the photomultiplier tubes to be placed in the aerogel Cherenkov detector for gain.

Particle Detection Using Very Thin Scintillator Counters. GUY RON (Tel Aviv University, Tel Aviv, Israel, -- 69978) BOGDAN WOJTSEKHOWSKI (Thomas Jefferson National Accelerator Facility, Newport News, VA 23606) .
Very thin (1.5 mm & 3 mm) scintillator counters were tested using both Monte Carlo and experimental techniques. The thin detector plane is needed for use in the Big Bite spectrometer in JLAB's Hall A. Results of the tests indicate that these detector configurations are acceptable for the Big Bite detector and allow an approximation of the expected efficiency for the scintillator plane. This paper presents an overview of the tests performed, recommends the use of 1.5 mm detectors and proposes a construction method.

Shiftwork Automation Using the Tcl Language. TIMOTHY THARP (DePauw, Greencastle, IN 46135) STEVE WOOD (Thomas Jefferson National Accelerator Facility, Newport News, VA 23606) .
My work this summer has been invested in improving the shiftwork environment to make setting up and watching over experimental runs easier on the shift personnel. The purpose of this paper is to be a complete and informative reference and report of two new systems I helped install and program this summer. The first project involved creating GUI's (Graphical User Interfaces) that interface with hardware. I did this using the Tcl (``tickle'') language to control a set of relays. These relays short the reset signal line of a specific computer to ground which results in a hard reset of the computer. The second project takes information from the data acquisition system and displays it in a GUI. This display has been useful in keeping track of the rates of photo-multiplier tube (PMT) counts, and will hopefully aid in monitoring experiments to make sure the PMT's are working correctly.