Student Abstracts: Physics at LBNL

Z-axis and photomultiplier calibration for the KAMLAND detector. AIDAN CRAIG (UC Berkeley, Berkeley, CA 94720) AIDAN CRAIG (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
Ever since the 1998 report of a deficiency in atmospheric neutrino flux by the SuperKamiokande detector, neutrino physics has sought an explanation for the shortage of detected neutrinos from the sun, reactors, and other neutrino sources. The most popular answer to this puzzle has involved neutrino flavor oscillation, which would itself require non-zero neutrino mass eigenstates. The KAMLAND experiment, itself the successor to SuperKamiokande, seeks to provide a definitive measurement of the neutrino oscillation parameters sin2B and DM2 by measuring electron antineutrino flux from several reactors around Japan, as well as the difference in azimuthal and solar neutrino fluxes. Unprecedented precision is to be achieved from the combination of a relatively long baseline (approx. 150 km), as well as an extremely large detector volume of 1150 cu. meters of liquid pseudocumine scintillator. As such, the experimentally determined neutrino energy spectrum will allow physicists to distinguish between the Large Mixing angle, Small Mixing Angle, and the "just so" Vacuum models of MSW-enhanced oscillation put forth to explain the undercount. Given the notoriously weak coupling of neutrinos to normal matter, proper calibration of the detector will be vital, both to better characterize neutrino energies and to eliminate radioactive background, particularly from solar neutrino data. This is to be accomplished through the deployment of radio- and photo-active sources of known energy along a Z-axis and eventually a 4-pi deployment mechanism, along with a event reconstruction scheme requiring detailed information about phototube time response within the detector.

Luminosity Calculation and Data Quality Analysis of Peripheral Collisions. DREW FORMAN (Yale University, New Haven, CT 06520) FALK MEISSNER (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
The STAR experiment searches for signatures of the quark-gluon plasma (QGP) formation and investigates the behavior of strongly interacting matter at high energy density. In the experiment two beams of gold ions, traveling at relativistic speeds, intersect to produce collisions. Two properties of these beams, cross-section and luminosity, are fundamental to the experiment and need to be accurately calculated. The cross section is known from theoretical computation, however the luminosity must be determined using the equation N = rLe, where N is the number of events, r is the cross section of the gold beams, L the luminosity, and e the efficiency of the detector. With r now known and e found through monte-carlo computer similations, the Luminosity can be calculated by determining the number of events in the experiment. However, events during which the beam lines were unstable or the detectors had inconsistent readouts must be eliminated from the count and subsequent luminosity calculation. To remove such events, a detailed analysis of several variables must be made both over time and over each of the 2000 event data files. Large fluctuations in the variables of the beams coordinate position (x,y,and z vertexes) would reveal unstable beamline tuning and possible bad data. More importantly, a disparity among the detector readouts, specifically the ZCD (Zero degree Calorimiter) and the TPC (Time Projection Chamber) would signify unusable events.

Exploring the Limitations of the Dipole Approximation with Electron Time of Flight Technology. . SIERRA LAIDMAN (Bryn Mawr College, Bryn Mawr, PA 19010) FRED SCHLACHTER (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
Single photoionization is a process in which a photon collides with an atom or molecule and an electron with a certain kinetic energy is emitted, leaving behind a residual ion. The dipole approximation describes the angular emission of these electrons. It assumes that the electromagnetic field of the radiation, expressed as a Taylor-series expansion, can be simplified by using only the first term of the series. It has been known for some time that the dipole approximation becomes inaccurate at high photon energies, and it has recently been determined that there are discrepancies at lower energies as well. In order to enhance our understanding of these limitations, we measured the electron emissions of nitrogen and neon using the latest technology. Beamline 8.0.1 at the Advanced Light Source was used with an electron Time-of-Flight (TOF) end station. Data were collected over a broad range of photon energies (254 - 664 eV) using five analyzers placed at different angles. We also collected the spectra at 15 rotation angles, between 0 degrees and -90 degrees, about the axis of the photon beam. The data from this experiment will likely take a year to fully analyze, but preliminary analysis seems to indicate that these results confirm that the dipole approximation breaks down at photon energies well below 1 keV and that this breakdown is greatly enhanced in molecules just above the core-level ionization threshold.

Ultrafast Time-Resolved X-Ray Science at the ALS. DAVID LE SAGE (University of California at Berkeley, Berkeley, Ca 94720) ROGER FALCONE (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
The group that I did research with this summer conducts ultrafast time-resolved x-ray diffraction and absorption experiments on materials undergoing structural phase transitions. These experiments are conducted at the Advanced Light Source (ALS) synchrotron at the Lawrence Berkeley National Laboratory (LBNL). The group uses 100 fs laser pulses to induce ultrafast phase transitions in the material being studied. These laser pulses are synchronized with X-ray pulses from the ALS, which are used to probe the sample at various times before and after the laser pulse arrives. An x-ray streak camera with single-shot time resolution better than 1 ps is then used to collect the x-ray data. The streak camera is triggered by the laser pulse with a GaAs photoconductive switch, resulting in a camera timing jitter of less than 2 ps. With this time resolution, it is possible to directly probe the structural dynamics of materials undergoing phase transitions, and to make measurements on states of the material that can only exist for a brief period of time after laser excitation. I personally assisted in several experiments of this nature during my summer research appointment, and helped to assess the possibility of increasing the resolution of the streak camera.

Development and Redesign of an Effective Educational Particle Physics Website. LAURA OCHOA-FRONGIA (U.C. Berkeley, Berkeley, CA 94720) DR. R. MICHAEL BARNETT (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
Particle physics is a subject virtually untaught in high schools in the United States, largely because an extensive mathematical and physical background is required to grasp the complex theories and principles. A joint venture between Lawrence Berkeley National Laboratory (LBL) and Fermilab conceived the original "Run II Discovery" website featuring an investigation of the existence of the Higgs boson. After analyzing the website, it was deemed that a new structure and motivation were needed to effectively bring particle physics to pre-collegiate audience. By engineering a site that is a self-contained goal-oriented research simulation, students and teachers are given all the tools to learn a considerable amount of particle physics without encountering the heavy math that often prevents the instruction of this subject in high schools. The new website contains background on the field and a tutorial to aid the students in analyzing real data from Fermilab's Tevatron and Monte Carlo simulations. The goal of exposing younger students to advanced research topics is to increase scientific curiosity, and diversify the high school curriculum. The redesigned website, which is pending approval, will replace the first draft at http://quarknet.fnal.gov/run2/.

Using the Electron Time of Flight Technique to Analyze the Limitations of the Dipole Approximation. MONICA PANGILINAN (Cornell University, Ithaca, NY 14853) FRED SCHLACHTER (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
Understanding the electronic structure of atoms and molecules is fundamental in determining their basic properties as well as the interactions that occur with different particles such as light. Theoretical models of electronic structures use the dipole approximation to simplify x-ray interactions with atoms and molecules. This approximation takes the exponential describing x-ray radiation and truncates everything but the first term. However, at both extremes of the photon energy, the dipole approximation is inaccurate. The electron time-of-flight technique is used to measure the time required for electrons emitted by photoionization to travel a fixed distance. Photoionization is a process describing the collision of a photon with an atom or molecule that produces a free electron and a residual ion. Using the electron time-of-flight technique, five analyzers were used to detect the electrons produced from neon and nitrogen gas at fifteen different chamber angles. From the spectrum produced, the dipole and nondipole parameters were experimentally determined at moderate photon energy values to examine whether nondipole effects must be taken into consideration at energy values far from the extremes. Results indicate that nondipole effects must be taken into consideration at energy values close to the core-level ionization threshold. Furthermore, other molecules and atoms were tested before and show the same conclusions, leading us to believe that these effects are universal. As a result, new theoretical models must be made that use higher order terms that were previously truncated.

ATLAS at LBNL. JAMES REED (University of Illinois, Champaign-Urbana, IL 61820) DR. M. GILCHRIESE (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
I worked on the strips components of the inner detector of the ATLAS project. We were in the testing phase doing temperature studies of noise and gain. The chips on the module were injected with a constant input charge while the threshold on each chip was raised. In a perfect world once the threshold reached the input voltage, the occupancy would drop to zero (It would read "no hit" instead of "hit"). However, do to noise, the response curve fit to a complimentary error function - nicknamed an "S-curve." I first learned a bit of C++ and then ROOT, then I wrote macros which extracted the S-curves from each channel of a chip and averaged them for each of 12 chips producing 12 different S-curve averages for each chip. These were used to compare the behavior of each chip with respect to the others. The two separate sets (streams 0 and 1) of chips (chips 0-5 and 6-11) were corresponding well within each stream, but across streams the chips did not match up as well (i.e. chip 2 was offset from any of the chips in stream 1). Upon examination with an IR camera, a temperature difference was found between the two sets of chips. A gap between the aluminum mounting and the module at stream 1 was responsible for the decreased thermal conduction. This was fixed by moving the place where the module was fastened to the aluminum mounting. The module is now functioning very well and we are finishing up testing.

Search for a Novel Antihypernucleus. DAVID SCHMIERER (University of Pennsylvania, Philadelphia, PA 19104) DAVID HARDTKE (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
I searched for the lightest antihypernucleus, which is known as the antihypertriton. The search for a novel antihypernucleus was made possible by the STAR (Solenoidal Tracker At RHIC) experiment. Antihypertriton is composed of an antiproton, antineutron, and an antilambda particle. Antihypertriton is unstable and was therefore searched for by the identification of its decay products, which are antihelium 3 and a pion. The identification of antihypertriton required extensive studies of the background signal. The first step in searching for antihypertriton was to simulate its production and test the analysis software on this data. In addition, simulations of background were made in order to study ways to reduce background in the real data. Following the simulation studies I looked at year one STAR data where 29 antihelium 3 tracks had already been identified. However, the data yielded too much background to conclusively identify any antihypertriton production. Subsequently a mixed event background was produced by embedding real antihelium 3 tracks in STAR events that have none. The analysis of the mixed event background permitted us to set an upper limit on the production of antihypertriton. We calculated the ratio of antihypertriton to antihelium 3 to be < 1.4 with a 90% confidence level and in fact expect this ratio to be < 0.9. Although my search for antihypertriton did not identify any production, it shows nonetheless that such a search is feasible and will be worthwhile pursing in the future when STAR collects more data.

Neutron Activation Analysis. CHUE VUE (CSUFresno, Fresno, CA 93704) ERIC B NORMAN (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
Neutron activation analysis (NAA) is a useful technique for identifying the elemental composition of materials in a non-destructive way. This can be done by irradiating a sample with neutrons and then studying the decays of the radioactive nuclei that are produced. Sensitivities of the method are sufficient enough to measure certain elements down to extremely low concentrations (parts per billion). NAA can be performed to determine the concentration of several different elements within a single sample of a material. Since neutrons have no charge they only interact with the nucleus of an atom, not the electrons. In addition, this technique sees all the elements in a sample, regardless of their chemical form or oxidation State. The basic requirement to carry out analysis of samples by NAA are: the detailed knowledge of the reactions that occur when neutrons interact with the target nuclei, a source of neutrons, and an instrument that can detect gamma rays accurately. Because of its accuracy and precision, NAA is widely performed in many different fields of sciences. In this project we neutron activated zinc (Zn), iridium (Ir), potassium bromide (KBr), molybdenum (Mo), calcium fluoride (CaF2), and a banana. The spectra were obtained, identified and will be posted on the internet for use in high school basic nuclear science curriculum. With this web site and access to the internet, teachers and students can use actual experimental results to back up theory and technique that had long been studied and used by many scientists. The goal is that by doing this, nuclear science will be less abstract and more understandable.

Airflows Through Large Horizontal Apertures. WILLIAM WATTS (City College of San Francisco, San Francisco, CA 94112) DR. DAVID LORENZETTI (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
Data collected from experiments does not sufficiently characterize airflows through large horizontal apertures that connect multiple zones. Experimental work must be done to fill gaps in data to allow for the accurate modification of building simulation programs, such as COMIS and CONTAM. Two chambers connected by a vertical shaft were used in this experiment to replicate two floors in a building. Outside air was driven into the top chamber, exiting the bottom chamber, to model the effect of air infiltration in buildings. The bottom chamber was heated in order to induce a buoyancy driven flow that opposed the mechanically driven external flow. Tracer gas was injected in the bottom chamber and measured with uniformly distributed sample tubes in each chamber to determine the size of the buoyancy driven and mechanically driven flows. Sufficient data was not gathered to fill experimental gaps due to the inability to achieve a well-mixed temperature in the heated chamber.

Thermal Qualification of ATLAS Pixel Detector Disk Sectors. WILLIAM WISE (Harvard, Cambridge, MA 02138) MURDOCK GILCHRIESE (Ernest Orlando Lawrence Berkley National Laboratory, Berkley, CA 94720) .
Two prototypes of ATLAS pixel disk sectors were tested to determine if they met thermal requirements. Sector temperature was determined after thermal cycling, thermal shock, pressure, irradiation, and loss of coolant tests, and compared to the sector baseline temperature. The hottest point on either sector after testing was 9.5 degrees Celsius above coolant temperature. This is well within ATLAS specifications, which require that all points on the sectors be less than 15 degrees above coolant temperature. Therefore, these two sector prototypes thermally qualify for use within the ATLAS detector.