Student Abstracts: Physics at BNL

Non invasive measurement of ultrashort bunch lengths of relativistic charge particles using the electro-optic technique. MUSTAFA AMIN (University of Texas, Arlington, TX 76010) T.TSANG (Brookhaven National Laboratory, Upton, NY 11973) .
An Electro-optic probe based on the Linear Pockels effect provides a non invasive way of measuring the bunch length of charge particles down to the femtosecond time scale. The transient electric field induced by a relativistic charge bunch changes the dielectric properties of an EO crystal placed near the charge beam. The polarization state of an optical beam probing the crystal is modulated during its passage through the crystal by the electric field of the charged particles. The optical beam can then be analyzed to reconstruct the temporal profile of the electric field at the crystal and hence infer the pulse length. In this work an effort is made to understand the relation between the applied electric field, the rotation of the index ellipsoid and Electro-optic modulation of light passing through an anisotropic crystal. General expressions for the rotation of the index ellipsoid, Electro-optic retardation and intensity modulation are derived. The rotation of the index ellipsoid and retardation of an optical beam in LiNbO3 induced by a relativistic charge bunch is discussed.

On Radiation Levels at the PHOBOS Detector. JOEL CORBO (Massachusetts Institute of Technology, Cambridge, MA 02139) ALAN CARROLL (Brookhaven National Laboratory, Upton, NY 11973) .
Because of its large number of silicon-based sensors, the PHOBOS detector is very sensitive to radiation levels, and a great deal of time is spent monitoring these levels with thermoluminescent dosimeters (TLDs), beam loss monitors (BLMs), and chipmunks. It was noted that there is an asymmetry between the radiation levels on the two sides of the beampipe. A calculation was done to show that it is possible that alpha particles generated by the gold ion beam might be causing this asymmetry. It was also noted that there is a very steep falloff of radiation levels near the beampipe. A study using TLDs verified that this falloff is exponential and that it falls to background levels at approximately 15 cm from the beampipe. Finally, a study was done using radiation data from the chipmunks and beam data from RHIC to calculate "beam quality", a measure of whether the radiation levels present are acceptable based on the beam currents and energy.

A new Muon Trigger for the Measurement of the Quark Distribution Functions in the Proton with the PHENIX Detector. HAROLD HAGGARD (Reed College, Portland, OR 97202) MATTHIAS GROSSE-PERDEKAMP (Brookhaven National Laboratory, Upton, NY 11973) .
Results from the first polarized Deep Inelastic Scattering (DIS) measurements led to the so called "proton spin crisis", the observation that quarks only carry a small fraction of the proton spin. Parton Distribution Functions (PDF) describe the contributions of the various constituents of the Proton to its overall spin and are well understood over a large range in x Bjorken. Direct measurements of the PDF at low x will constrain both DG (the gluon contribution) and DS (the quark contribution) in the near future. Measurements of asymmetries in W± production at RHIC will allow discrimination between a flavor symmetric and flavor-broken picture of the polarized (and unpolarized) light sea quarks. The Relativistic Heavy Ion Collider (RHIC) will produce polarized proton-proton collisions with center of mass energies up to 500 GeV. These energies along with two large muon spectrometers provide the Pioneering High Energy Nuclear Interaction eXperiment (PHENIX) with high sensitivity to the production and decay of W±, an excellent channel for measuring the quark and anti-quark distributions. Monte Carlo simulations of both W± decay and hadronic jet background yielded a muon rate that is larger than PHENIX can accept online. A method for reducing this rate, by placing a detector near the interaction point to distinguish jet showers from W events, was studied and shows promise.

A New Electron for Gluon Polarization Measurements Through Heavy Flavor Production in PHENIX. SUSAN KANE (Rensselaer Polytechnic Institute, Troy, NY 12180) MATTHIAS GROSSE PERDEKAMP (Brookhaven National Laboratory, Upton, NY 11973) .
In the endeavor to better understand the universe, physicists strive to understand the smallest "elements" of matter. The make-up and behavior of these particles affect everything around us, even the distribution and motion of the galaxies. In an attempt to better understand one of the four fundamental forces, the so-called strong nuclear force, physicists examine the spin-dependent structure of the proton. The Relativistic Heavy Ion Collider will collide two beams of polarized proton beams, starting in November. At full luminosity, protons will collide an average of 1.2 times every 106 ns. At high collision rates, the amount of data generated in the detectors exceeds the capacity of the data acquisition system. Using fast event selection electronics and processors, triggers, the data volume can be reduced without loosing the quality of the information. For the PHENIX detector we have studied how to use information from the Electromagnetic Calorimeter, and the Ring-Imaging Cherenkov Counter to filter out the interesting physics events thus reducing the raw rate by a factor of 5000.

Accelerator Orbit Simulation. BRENDAN LYON (Jamestown Community College, Jamestown, NY 14702) ALFREDO LUCCIO (Brookhaven National Laboratory, Upton, NY 11973) .
Computer simulations are necessary tools to apply theory to a subject matter being studied. It is applicable to particle accelerators especially because it deals with theory on a microscopic scale. With modern physics, it is possible to determine trajectories of particles (in this case, electrons) due to magnetic fields of quadrupole and sector magnets. Using a program called MAD, developed by CERN, we generate the necessary lattices for a particular accelerator, for example, an accelerator with bends or no bends. These FODO lattices represent force vectors of individual elements (quadrupoles) with respect to the experimental particle distribution. By applying each individual lattice to the distribution, we generate output files using C/C++ programming, which represents the same distribution with different positions and velocities. Output files are visualized using a Linux based graphing tool called Gnuplot, and Data Visualization Explorer (DX). Our major disadvantage is the output files are represented by two-dimensional slices; therefore, we are unable to fully use DX's three-dimensional rendering capabilities. In addition, we also investigated certain attributes of the distribution such as beta components, which represent the relative maxima of the distribution's envelope, energy distribution, and charge densities.

Validating Performance of the PHOBOS Silicon Detector Through Noise Values. MARC RAFELSKI (University of Arizona, Tucson, AZ 85721) MARK BAKER (Brookhaven National Laboratory, Upton, NY 11973) .
In order to further the understanding of the evolution of the Universe and Quark Gluon Plasma, the detector must send non-defective data to be analyzed. Thus, the performance of the PHOBOS silicon detector is of utmost importance to the experiment. It is imperative that we know the condition of the silicon sub detectors. The programs written in this research do exactly that; validate the performance through average noise values of the sub detectors. Through these programs, it is evident if something were to go wrong. If the detector suddenly had radiation damage due to higher luminosity runs at RHIC, or some other problems, the shift crew would be made aware of the problem right away. This allows for quick validation of the performance of the detector before more lengthy analyses down the road. The result is a graphical program that displays the average noise values of the seven sub detectors, and would show increased noise values if there were any problems. If the noise increased, the PHOBOS collaboration would be immediately aware of the situation and could deal with it appropriately. The work on the noise of the detector aided in the processing of data for the analysis, which yielded a paper during the internship. The paper is called Energy Dependence of Particle Multiplicities in Central Au + Au Collisions. This paper was submitted to Physical Review Letters.