Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session S18: Undergraduate Session I |
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Sponsoring Units: SPS Chair: Gary White, Society of Physics Students/American Institute of Physics Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), Director's Row 46 |
Monday, April 14, 2008 2:06PM - 2:30PM |
S18.00001: SPS Outstanding Student Award for Undergraduate Research Talk: Lifetime Measurements and Deformation in 79Sr Yun Kyoung Ryu, Robert Kaye, S.R. Arora, S.L. Tabor, J. Doring, Y. Sun, T.D. Baldwin, D.B. Campbell, C. Chandler, M.W. Cooper, S.M. Gerbick, M. Wiedeking , C.R. Hoffman, J. Pavan, O. Grubor-Urosevic, L.A. Riley High-spin states in $^{79}$Sr were produced following the $^{54}$Fe($^{28}$Si, 2\textit{pn}) fusion-evaporation reaction using a beam kinetic energy of 90 MeV at the Florida State University (FSU) Tandem-Linac particle accelerator facility, and the resulting de-exciting $\gamma $ rays were detected with the FSU array of 10 Compton-suppressed high-purity Ge detectors comprised of three Clover detectors and seven single-crystal detectors.~ The synthesized nuclei were stopped completely in the target, resulting in Doppler-shifted $\gamma $-ray line shapes that could be analyzed using the Doppler-shift attenuation method. The experimental line shapes were acquired at detection angles of 35\r{ } and 145\r{ }, and the resulting Doppler-shifted peaks were analyzed to extract the lifetime of their parent states.~ In all, 23 lifetimes were measured in three separate band structures using this method, and then used to infer transition quadrupole moments ($Q_{t})$ and quadrupole deformations ($\beta _{2})$ using the rotational model. The resulting $Q_{t}$ values indicated a high degree of collectivity and deformation in all three observed sequences of excited states (bands) with only a modest decline in collectivity with increasing angular momentum.~ The results show good qualitative agreement with the predictions of both cranked Woods-Saxon (CWS) and projected shell model (PSM) calculations.~ In addition, the pattern of excited energy states and their de-exciting gamma-ray transitions (level scheme) was re-examined and compared to the most recent study of $^{79}$Sr using $\gamma -\gamma $ coincidence measurements, intensity measurements, and directional correlation of oriented nuclei (DCO) ratios in addition to the lifetime measurements.~ Overall, the level scheme was verified, with the exception of the re-arrangement of one transition.~ The band based on the intrinsic $d_{5/2}$ single-particle orbital from the shell model, was found to have the largest average deformation ($\beta _{2}$,ave = 0.41) among the three observed bands, in agreement with the CWS and PSM theoretical predictions [Preview Abstract] |
Monday, April 14, 2008 2:30PM - 2:42PM |
S18.00002: Search for QCD Hawking Radiation in Heavy Ion Collisions Laura Stiles, Michael Murray A wide variety of measurements at RHIC, for example v$_{2}$ and energy loss, suggest that the partonic matter created in heavy collisions thermalizes early. One possible mechanism for this is the creation of the QCD analogue to gravitational black holes [1]. Such objects have no memory of their creation and radiate with a characteristic temperature, T, that can depend only on their energy, charge, and angular momentum. This hypothesis is consistent with the growth of multiplicity with $\surd $s in e+e- collisions and thermal temperature observed at LEP. For central heavy ion collisions the angular momentum of the system is approximately zero and the model predicts a universal dependence of the chemical freezeout temperature on the ratios of charge to transverse energy. To test this prediction against BRAHMS data, We have fitted data on $\pi $, K, p and $\bar {p}$ from central Au + Au collisions at several rapidities and energies, using the THERMUS code. The experimental dependence of the temperature on the ratio of charge to transverse energy will be compared to the Hawking radiation predictions. By comparing data sets at different energy, centrality and rapidity we can select systems with the same ratio of baryon number to energy but different rapidities. This may allow us to test for any effect of angular momentum on temperature. [1] P. Castorina, D. Kharzeev and H. Satz, Eur. Phys. J. C 52, 187 (2007) [Preview Abstract] |
Monday, April 14, 2008 2:42PM - 2:54PM |
S18.00003: Measuring the transverse position of forward neutrons at the Large Hadron Collider Navid Terhani, Aradalan Dehdasht One way to study the quark-gluon matter produced in heavy ion collisions is to measure the deflection of very forward neutrons. In CMS this can be achieved with the Zero Degree Calorimeters, ZDCs, if we add a hodoscope of cerenkov or silicon detectors. The ideal position for such a detector is at shower maximum, i.e. the point where the number of secondary particles produced by the incoming neutrons is greatest. Fortunately for us this point is between the electromagnetic and hadronic parts of the ZDCs. Such an upgrade must be very compact and robust. I will describe a possible design for such a detector based on an 8*8 grid of 1cm tiles and a multi-anode PMT. I will present a model of such a detector and give estimates of its performance. [Preview Abstract] |
Monday, April 14, 2008 2:54PM - 3:06PM |
S18.00004: Neutron Flow at the Large Hadron Collidor Jessica Snyder One of the most exciting recent results in high-energy nuclear physics is the discovery that nucleus-nucleus collisions at the Relativistic Heavy Ion Collider, RHIC, produce an almost perfect fluid of quarks and gluons. This state was identified thanks to the strong collective ``flow'' of particles observed. In 2009 the Large Hadron Collider, LHC, will study lead-lead colllisions at an energy 28 times larger. At such high energies, it is possible that the collective properties of the produced matter resemble more that of a weakly interacting quark-gluon gas rather than the liquid-like state observed at RHIC. This would result in a different flow strength. Flow measurements at the LHC can be carried out by measuring the pattern of spectator neutrons emitted along the beam axis, using two detectors inserted between the electromagnetic and hadronic sections of the CMS Zero Degree Calorimeters (ZDCs). I will present results of GEANT simulations of such a detector, including estimates of its capabilities to measure neutron flow. [Preview Abstract] |
Monday, April 14, 2008 3:06PM - 3:18PM |
S18.00005: Accurate Energy Calibrations from Cosmic Ray Measurements Amy DeLine, Joseph Finck, Artemis Spyrou, Michael Thoennessen, Paul DeYoung The Modular Neutron Array, located at the NSCL at Michigan State University, is used in conjunction with the MSU/FSU Sweeper Magnet to study the breakup of neutron-rich nuclei. Fragmentation reactions create particle-unstable nuclei near the neutron dripline which spontaneously breakup by the decay of one or two neutrons with energies that reflect the nuclear structure of unbound excited and ground states. The neutrons continue forward into MoNA where their position and time are recorded, and the charged fragments' position and energy are measured by the array of detectors following the Sweeper Magnet. In such experiments it is important to be able to identify one-and two-neutron events hitting MoNA. For this reason an accurate energy calibration of the MoNA bars is crucial. The present work focuses on performing an energy calibration from cosmic ray measurements. The application of different gates on the cosmic ray spectra allowed the selection of events that correspond to different energy depositions in a MoNA bar, at energies between 18 and 32 MeV. [Preview Abstract] |
Monday, April 14, 2008 3:18PM - 3:30PM |
S18.00006: CDMS Veto Stability Study and Calibration Gabriel Caceres Most experiments searching for dark matter particles have been led deep underground to minimize the background produced by cosmic rays. The Cryogenic Dark Matter Search (CDMS) lies $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ mile underground in the Soudan Mine in Minnesota. Even though the muon rate is lowered by a factor of $\sim 10^5$, the rate is still high enough to produce background signals. To solve this problem, scintillator panels have been placed around the detector to veto cosmic induced events. This work studies the behavior over time of the scintillator veto panels. By analyzing and tracking the response to a LED pulser system, the stability was determined to be within 3{\%}. The absolute energy scale of the spectrum was then calibrated using radioactive sources, as well as the muon distribution. Knowing the absolute energy scale and where the veto trigger threshold lies provides useful information for calculating the amount of background that can be rejected. [Preview Abstract] |
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