Assessment of Hall A VDC Analysis Software Performance through Monte Carlo Simulation. AMY ORSBORN (Case Western Reserve University Cleveland, OH 44106) JENS-OLE HANSEN (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)

The High Resolution Spectrometers (HRS) employed by Hall A at the Thomas Jefferson National Accelerator Facility (JLab) rely on vertical drift chambers (VDCs) for particle tracking. In order to reconstruct particle paths, data from these VDCs are analyzed using custom analysis software ('the analyzer') that builds upon the ROOT data analysis framework [1]. To test the software's abilities and find methods for improvement, it is useful to examine simulated data. In this paper, a Monte Carlo simulation of the VDC wire chambers was carried out. The simulation was based on an existing framework [2], which was expanded and improved as part of this project. Realistic effects were incorporated into the simulation to test the analyzer's resolution and tracking limits. Data from this simulation were analyzed, and results were compared with the simulated data to assess analyzer performance. The effects of angle estimation in the track reconstruction algorithm, VDC drift time resolution, random wire firing, and coincident tracks on analyzer performance were examined. It was found that track angle estimation reduces error in track position and slope linear fits by approximately 10% with a drift time resolution of 4.5 ns. In simulations with a drift time resolution of 4.5 ns, a 0.5% probability of random wire firing, 99.999% wire efficiency, and angle estimation incorporated, the overall tracking efficiency remained above 90% for all triggering rates ranging from 2 kHz to 700 kHz. Tracking efficiency in reconstructed multi-track events was shown to be below 90% for all rates, falling below 80% for trigger rates above 500 kHz. The simulation may still be improved via the addition of more natural effects such as delta and cosmic rays. Preliminary simulation results show a high level of confidence in trigger track reconstruction but significant failures in the analyzer's processing and identification of multiple tracks. Further analysis of analyzer performance with reconstructed and generated multi-track events is necessary to identify problems in the algorithm's treatment of multiple track events.

Meson Form Factor and the Convolution Product. LESLIE UPTON (Hampton University Hampton, VA 23668) PAUL GUEYE (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)

At Thomas Jefferson National Accelerator Facility, experiments are performed to extract unobserved key information on the constituents of nuclei through measurements of meson form factor data. The current method requires the knowledge of cross sections. However, this method is currently not accurate enough. The focus of this study is to develop and validate a technique to accurately extract meson form factors based on the combination of the convolution product and Lyapunov stability. Three independent functions f(Q2), g(W) and h(t) mix to form the cross section. The intent is to extract the analytical functions that combined to exactly reproduce the behavior of the cross section by using a deconvolution technique. Finally, the Lyapunov stability algorithm will be applied to insure a unique solution. Using [1], non-linear and polynomial regressions for the data were calculated. The data was used to determine the functions for f(Q2), g(W) and h(t). These analytical expressions will be used to confirm the exact meson form factor extraction technique. If this technique proves successful, there will be major implications within nuclear physics, medical imaging, and even statistics.

Particle Identification in BigBite Spectrometer for G_En Experiment. KYLE DAMBORSKY (Tulane University New Orleans, LA 70118) BOGDAN WOJTSEKHOWSKI (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)

Electron/Pion identification is one of the critical tasks of the detector system in the upcoming G_En experiment at Thomas Jefferson National Accelerator Facility (JLab). Due to the high-energy nature of the electron beam and its collision with a target, multiple pions are produced. These pions produce an excessive counting rate and disrupt the detection of similarly charged electrons whose momenta are to be measured. To reject the pion counts, a lead glass calorimeter is used in the BigBite spectrometer to explore the longitudinal profile of the electromagnetic shower created by the particles. The calorimeter consists of a preshower detector array and a total absorption array, both comprised of lead glass counters. From their distinct shower profiles, pion and electron events can be discerned and an online rejection factor of up to 50 could be achieved, thereby creating a clean trigger apparatus for the _En experiment. Each of these counters passed an extensive examination using cosmic rays, as well as hermicity tests before being added to the BigBite spectrometer, yielding 53 usable detectors. These detectors will be installed in the preshower array of BigBite. Also, a Monte Carlo simulation of the probability of a particle interacting with the lead glass detector was conducted. The average dark current of the usable detectors was -2 nA, while the average voltage required for a 5 mV output signal was found to be -1.5 kV. These results will be used as a starting point for a precise calibration of the BigBite spectrometer in Hall A. The results from the initial stage of a Monte Carlo simulation, eventually meant to model the electromagentic shower inside of a lead glass block, showed that 95.5% of all incident events interact with the preshower detector, 100% of all incident events interact with the total absorption detector, and 100% interact with the entire shower detector. The 100% is only within the tolerance of the written program, which is accurate to two decimal places. This data gives a good estimate as to the expected efficiency of the shower detector.

Reconstructing Parton Distribution Functions From Their Moments. SCARLET NORBERG (Kent State University kent, OH 44243) DAVID RICHARDS (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)

Parton Distribution Functions (PDFs) are used to describe what the inside of the nucleon looks like and to determine the effective degrees of freedom of Quantum Chromodynamics (QCD). One way to determine the PDFs is to compute or to measure their moments. However, if only the first few moments are known it is important to explore the extent to which the shape of the PDF can be recovered. Using the computer-algebra package Maple, we took a known PDF and computed its moments; we then examined the extent at which we could recover the shape of the PDF with a given number of moments. The goal of this project is to show if moments can be taken and PDFs can be found with reasonably amount of accuracy. What one realizes immediately is that one more moment is needed then parameters. Some parameters were discovered using this method and discovering the shape of the PDF. We did discover though despite our best efforts the parameters we got did not give us back the moments we had initial had. They were close but there were still discrepancies. Also, the accuracy of getting the PDF parameters is not very good. There is no way to get the shape of the PDF, if all that is known is a limited number of moments.

Testing and Reparing Detectors for the Møller Polarimeter. APRIL COOK (Monmouth College Monmouth, IL 61462) DAVE GASKELL (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)

The Møller Polarimeter is used to measure the polarization of the electron beam passing through the beam line on its way to the main target in Hall C at JLab. A key component of the detector system is 32 small detectors, made up of a piece of scintillator attached to a photomultiplier tube (PMT). The electron beam hits this wall of detectors and excites the atoms and molecules in the scintillator, which then decay and emit photons. The photons then travel through the PMT and produce a pulse that is sent to a data acquisition (DAQ) program. After several years of use, these PMT's are not working properly and need to be replaced. Before they are repaired, the detectors are tested to see what data they produce at their broken state. Cobalt-60 (Co-60) is then placed directly on the scintillator, to produce signals. After their initial tests, new PMT's are glued onto the same scintillators, using special ultraviolet (UV) curing glue. The new detectors are wrapped tightly with aluminized Mylar and black electrical tape to keep ambient light out. After they are fixed, the detectors are tested again using the same Co-60 source. The signals produced after repairs are compared to the previous data to ensure that they are working better. The detectors have improved since their repairs. They have larger signals at much lower voltages. This will significantly improve the effectiveness of the Møller Polarimeter.