Student Abstracts: Physics at SLAC

Goniometer Control System for Coherent Bremsstrahlung Production. VICTOR ACOSTA (Augsburg College, Minneapolis, MN 55454) PERRY ANTHONY (Stanford Linear Accelerator Center, Stanford, CA 94025).
A system for the generation of a high-intensity, quasi-monochromatic photon beam is discussed. The theory behind coherent bremsstrahlung photon beam production is analyzed and developed. The mechanics of a goniometer control system are presented. The software developed for remote control of the goniometer is also discussed. Finally, the results from various performance measurements are included.

Automatic Alignment of X-Ray Beams. ZACHARY ANDERSON (Carnegie Mellon University, Pittsburgh, PA 15213) ANA GONZALEZ (Stanford Linear Accelerator Center, Stanford, CA 94025).
Protein crystals and other biological samples diffract weakly in X-rays. It is therefore important that the X-ray beam be very stable. Cubic smoothing splines were fit to ion chamber counts versus the vertical position of the sample. The extrema, inflection points about the maximum, and other information about the spline were calculated to determine whether the data corresponded to a beam profile. The algorithm developed here correctly identified the absence of a beam profile in all data gathered over the course of a year from four beam lines at the Stanford Synchrotron Radiation Laboratory. This algorithm is effective and can be adapted to other beam lines.

Electroweak Forward-Backward Asymmetry in Mu-Pairs at BaBar. DIANA CARVER (University of Texas at Austin, Austin, TX 78712) STEPHEN R. WAGNER (Stanford Linear Accelerator Center, Stanford, CA 94025).
Using $e^+e^-$ data collected on or near the $\Upsilon(4s)$ at BaBar, some systematic errors involved in the forward-backward asymmetry in $\mu$-pairs were studied. The error due to uncertainty in the boost to the center-of-mass frame appears to be acceptable. The background due to Bhabha events passing our cuts is higher than expected, and will need to be addressed further.

LectureSLAC-PUB-9380. CYNTHIA CORREA (Harvard University, Cambridge, MA 02138) GRZEGORZ MADEJSKI (Stanford Linear Accelerator Center, Stanford, CA 94025).
We report results of hard X-Ray observations of the clusters Coma, Abell 496, Abell 754, Abell 1060, Abell 1367, Abell 2256 and Abell 3558 using RXTE data from the NASA HEASARC public archive. Specifically we searched for clusters with hard x-ray emission that can be fitted by a power law because this would indicate that the cluster is a source of non-thermal emission. We are assuming the emission mechanism proposed by Vahé Petrosian where the inter cluster space contains clouds of relativistic electrons that by themselves create a magnetic field and emit radio synchrotron radiation. These relativistic electrons Inverse-Compton scatter Microwave Background photons up to hard x-ray energies. The clusters that were found to be sources of non-thermal hard x-rays are Coma, Abell 496, Abell 754 and Abell 1060.

Characterization of Ti:Sapphire Laser Rods for Installation in the Polarized Light Source. SEAN CORUM (Augustana Collge, Sioux Falls, SD 57197) DR. AXEL BRACHMANN (Stanford Linear Accelerator Center, Stanford, CA 94025).
The Flash:Ti laser in the Polarized Light Source at the Stanford Linear Accelerator Center (SLAC) is used to obtain spin polarized electrons for high-energy particle physics experiments. The Flash:Ti laser utilizes titanium-doped sapphire (Ti:Sapphire) crystals to produce laser light. The properties of these crystals, or laser rods, greatly affect the quality of the laser beam produced (e.g. power and jitter), which in turn affects the overall quality and reliability of the particle physics experiments at SLAC. In this interest, seven Ti:Sapphire laser rods were tested for absorption and transmission properties as a function of angular position (i.e. the rod was rotated along its geometrical axis). 833 nm light from a diode laser was linearly polarized and passed through the rods to test for transmission properties. The time-averaged power output of the emitted light was measured with a photodiode/powermeter apparatus. Similarly, the absorption properties of the rods were tested by passing linearly polarized light from a 543 nm green He:Ne laser through the rods. The rod with the best combination of absorption and transmission properties was selected for installation in the Polarized Light Source at the Stanford Linear Accelerator Center.

Preliminary Study of D0->Kpipi0 Decays with Dalitz Plots. MOIRA GRESHAM (Reed College, Portland, OR 97202) RAY COWAN (Stanford Linear Accelerator Center, Stanford, CA 94025).
Particle physicists study the smallest particles and most basic rules of their interactions in humankind's current scope. The Charm Analysis Working Group (CWG) of the BaBar Collaboration studies decays involving the charm quark. They currently study mixing in D decays, an interesting and poorly understood phenomenon in current physics models. We, as part of the CWG, investigated the plausibility of using Dalitz plots and the BaBar analysis framework to study mixing in Wrong Sign (WS) D0->Kpipi0 decays. Others in the CWG have studied mixing in the 2-body decay, D0->Kpi. The 3-body decay analyzed with the RooFitDalitz analysis package and Dalitz plots provides more information and another way of separating Doubly Cabibbo Suppressed Decays (DCSD) from mixing -- which share the same end products. Through doing many simulations, we have demonstrated the usefulness of this approach. We selected D0->Kpipi0 events from Simulation Production run #4 (SP4) and BaBar's run 1 and run 2. We made Dalitz plots with this data. Now that we better understand Dalitz plots and software, we plan to select WS D0->Kpipi0 events and perform rate fits as discussed in BaBar Analysis Document (BAD) #443, as well as fits for several different decay times and resonances, in order to further distinguish DCSD from mixing.

Testing Fiber Optic Cables at 300 and 4.2 K. FAWN HUISMAN (Reed College, Portland, OR 97202) JOHN WEISEND (Stanford Linear Accelerator Center, Stanford, CA 94025).
Strange "cavity lights" have been observed in Superconducting Radio Frequency (SCRF) Cavities. In order to understand this phenomenon a spectral analysis of the light is necessary. However, the extreme conditions presented within the cavity require the equipment to function at cryogenic temperatures. Ocean optics P600 UV/VIS fiber optic cables were studied at 300 K and 4.2 K to determine whether or not they would be appropriate for cryogenic temperatures. At 300 K the performance of different lengths of cable, the effect of a lens and the effect of a junction were investigated by taking spectra of red, green, and yellow LEDs at a variety of distances from where the source and the cable/spectrometer were aligned. It was found that there was significant attenuation of the signal between the spectrometer alone and the spectrometer with any combination of cables. The lens reduced the number of locations where a readable signal was produced, but the intensity increased greatly when the lens was aligned with the light source. The junction did not seem to make a difference except when there was a large angle between the light source and the cable. At 4.2 K a 4 m cable and a lens were submerged in liquid Helium to test their capabilities at cryogenic temperatures. The fiber optic cable was found unsuitable for use as it did not function at 4.2 K, and the signal was essentially lost. However, the lens survived.

Amplifying High-Frequency Acoustic Signals. CARMEN KUNZ (San Jose State University, San Jose, CA 95192) JOE FRISCH (Stanford Linear Accelerator Center, Stanford, CA 94025).
In search of the hypothetical Higgs boson, a prototype electron accelerator structure has been developed for use in the Next Linear Collider (NLC), SLAC's proposed version of the machine necessary to create the predicted particle. The Next Linear Test Accelerator (NLCTA), designed to provide 0.5GeV - 1TeV center-of-mass collision energy, generates electromagnetic breakdowns inside its copper structure while the beam is running. The sparks vaporize the surface of the copper, and will eventually ruin the accelerator. They also create high-frequency (hf) acoustic signals (100 kHz - 1 MHz). Acoustic sensors have been placed on the structure, however current knowledge regarding sound propagation in copper limits spark location to within one centimeter. A system was needed that simulates the sparks so further study of acoustic propagation can be pursued; the goal is locate them to within one millimeter. Various tests were done in order to identify an appropriate hf signal source, and to identify appropriate acoustic sensors to use. A high-voltage spark generator and the same sensors used on the actual structure proved most useful for the system. Two high-pass filters were also fabricated in order to measure signals that might be created above 2MHz. The 11-gain filter was used on the acoustic simulation system that was developed, and the 100-gain filter will be used on the NLCTA.

Power density spectral analysis as a method of compact object determination in X-ray binary systems. JOHN LEE (Taylor University, Upland, IN 46989) PABLO SAZ PARKINSON (Stanford Linear Accelerator Center, Stanford, CA 94025).
Mass determinations and X-ray energy spectral analyses are among the methods used to distinguish between the types of compact objects present in X-ray binary systems. We test a method of distinguishing between neutron stars and black holes proposed by Sunyaev and Revnivtsev where power density spectra are used, particularly in the 500-1000Hz range. Sunyaev and Revnivtsev found that only neutron stars appear to have significant power in this frequency range. We apply this criterion to 12 X-ray binary systems (six neutron stars and six black holes) using USA data and cannot reproduce Sunyaev and Revnivtsev's result. The reason for this discrepancy is most likely a USA instrumental effect which manifests itself as excess power in the frequency range of interest. Future work on correcting this problem should provide more accurate analyses that may yield a different result.

Spectral Analysis of the Black Hole Candidate 4U 1630-47. RISHIK SAXENA (University of California at Berkeley, Berkeley, CA 94702) DEREK TOURNEAR (Stanford Linear Accelerator Center, Stanford, CA 94025).
We performed spectral analysis on the 1999 X-ray outburst of the soft X-ray transient black hole candidate (BHC) 4U 1630-47, in order to learn about physical processes (such as changes in inner disk radius of the accretion disk) that manifest themselves as changes of state. This source goes through an outburst every 600 - 690 days, which is a very short time period compared with other transient X-ray sources. The overall shape of the outburst's light curve was very similar to that of the 1996 outburst, but noticeably different from that of the 1998 outburst. We fitted 47 observations of the outburst to a model consisting of a disk blackbody, inverse Comptonization power law, and Gaussian component, multiplied by an absorption constant and an overall normalization constant. We found that the BHC progressed from a low state to high, and then back to low during its outburst. This pattern is common to persistent sources, not transient sources. We also found that when the source is in the low state, the flux and hardness are anticorrelated, as is predicted by theory. However, when 4U 1630-47 is in the high state, it is unclear whether or not the flux and hardness are correlated as theory says they should be.

Building a Pulse Detector using the Frequency Resolved Optical Gating Technique. JOSE VALLIN (San Jose State University, San Jose, CA 95192) PAUL BOLTON (Stanford Linear Accelerator Center, Stanford, CA 94025).
We show how to construct a diagnostic optical layout known as Frequency Resolved Optical Gating (FROG) for an infrared mode-locked laser by using the nonlinear effect known as second harmonic generation (SHG). In this paper, we explain the principle of operation and the theory upon which this diagnostic is based. Moreover, we described the procedure used to measure the duration and frequency components of a pulse. This process consists of calibrating the scales of a two-dimensional image, time delay vs. frequency, known as FROG spectrogram or FROG trace. This calibration of the time delay scale yields the correspondence between a pixel and time delay. Similarly, the calibration of the frequency scale yields the correspondence between a pixel, and frequency.