Bulletin of the American Physical Society
Joint Fall 2017 Meeting of the Texas Section of the APS, Texas Section of the AAPT, and Zone 13 of the Society of Physics Students
Volume 62, Number 16
Friday–Saturday, October 20–21, 2017; The University of Texas at Dallas, Richardson, Texas
Session N2: Particle IV |
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Chair: Joe Izen, University of Texas at Dallas Room: DGAC 1.102B |
Saturday, October 21, 2017 2:30PM - 2:42PM |
N2.00001: Fluctuations of net-particle distributions in Pb-Pb collisions measured with the ALICE detector at the LHC Surya Prakash Pathak Heavy Ion Collisions at the LHC provide a tool to study the phase transition from hadronic matter to a deconfined phase of quarks and gluons. Lattice QCD calculations suggest that the chiral crossover transition and the hadronic freeze-out conditions can be tested by measuring cumulants of conserved charge distributions, which are directly related to the quark number susceptibilities in lattice QCD. We will present experimental results of the mean $(c_{1})$ and the variance $(c_{2})$ of net-proton, net-kaon and net-pion distributions, which serve as proxies for net-baryon, net-strangeness and net-charge distributions, respectively. The data were measured as a function of centrality and pseudo-rapidity in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV using the ALICE experiment at the LHC. The results will be compared with Skellam expectations and discussed in the context of quantum number conservation and chemical freeze-out. [Preview Abstract] |
Saturday, October 21, 2017 2:42PM - 2:54PM |
N2.00002: Fluctuations of net-Lambda distributions in Au+Au collisions measured as a function of collision energy with the STAR detector at RHIC Nalinda Kulathunga Chemical freeze-out parameters (temperature and baryochemical potential) in the QCD phase diagram can be extracted using measured moments of multiplicity distributions of conserved charges. Previously, net-Kaons were used as a proxy for net-strangeness, but we approach the problem using net-Lambda ($\Lambda - \bar{\Lambda}$) cumulants as they are subject to strangeness and baryon number conservation laws. We show the first three cumulants $(C_{1}, C_{2}, C_{3})$ and cumulant ratios $(C_{2}/C_{1}, C_{3}/C_{2})$ of net-Lambda and compare them to Poisson baseline and negative binomial expectation for four beam energies ($\sqrt{s_{NN}} = 19, 27, 39$ and $62$ GeV Au$+$Au collisions). Deviations from the Poisson baseline are considered interesting as a part of searches for enhanced fluctuations possibly resulting from the existence of a critical point in the nuclear matter phase diagram. The results are compared to previous STAR measurements of net-Proton and net-Kaon cumulants. [Preview Abstract] |
Saturday, October 21, 2017 2:54PM - 3:06PM |
N2.00003: Using Defect Creation for Directional Sensitivity and Dark Matter Signal Discrimination in Phonon-Mediated Detectors Fedja Kadribasic We examine two potential applications of defect formation for dark matter detectors - directionality and nuclear-electron recoil discrimination. Numerical simulations of classical interatomic potentials, alongside more precise density functional theory simulations and experiments, predict an angular dependence in the defect formation energy threshold that varies by around 20 eV from minimum to maximum. Additionally, they predict a nonisotropic, nonlinear energy loss in semiconductor detector materials that never produces phonons due to the nonzero energy required to form defects. Next-generation dark matter and coherent neutrino nuclear scattering, such as SuperCDMS and MINER, are poised to reach the resolutions necessary to detect these effects. Once these detectors are calibrated at these low recoil energies, we argue that the anisotropy in defect formation in single-electron resolution semiconductor detectors allows for very effective directional sensitivity to dark matter signals for masses below 1 GeV/c$^2$. Additionally, defect creation from nuclear recoil interactions distorts the expected spectra in such a way that, statistically, one can discriminate nuclear recoils from electron recoils with only phonon measurements, especially in the mass range below 10 GeV/c$^2$. [Preview Abstract] |
Saturday, October 21, 2017 3:06PM - 3:18PM |
N2.00004: Characterization of a High-Sensitivity Radon Emanation System Daniel Jardin, Ray Bunker Radon is an important background consideration for rare-event searches such as dark matter direct detection and neutrinoless double-beta decay experiments. Materials of construction for these experiments often require screening of ultra-low radon levels, sometimes as few as tens of atoms in equilibrium. Radon emanation is one of the most sensitive and robust ways of making these measurements. A system for low-level measurements has been commissioned at the Pacific Northwest National Laboratory (PNNL) that achieves high sensitivity through use of custom high-efficiency ultra-low-background proportional counters. The system includes small and large radon emanation chambers coupled to a custom-built gas handling system with a cryogenic radon trap. The emanation system and detection method will be described, and characterization of backgrounds and efficiencies using a calibrated radon source will be discussed. [Preview Abstract] |
Saturday, October 21, 2017 3:18PM - 3:30PM |
N2.00005: Effect of radiation and temperature on resonance properties of polyurethane-coated wire bonds. Yenho Chen, Joe Izen Aluminum wedge wire bonds are used in the silicon pixel detectors that compose the innermost section of the Large Hadron Collider (LHC). Wire bonds are susceptible to failure due to mechanical oscillations from periodic Lorentz forces and condensation induced corrosion. The proposed solution is to coat wire bonds with a thin layer of polyurethane (PU) for structural reinforcement and oscillation dampening. Coating robustness is evaluated by exposing samples to the lifetime radiation dosages expected in the High Luminosity LHC and by thermal-cycling to test for radiation-induced intolerance to thermal expansion. Mechanical properties of wire bonds were tested by exciting PU-coated wire bonds with 50{\%} duty cycle square wave currents in a 1.0T field. Wire bonds were configured to simulate the most vulnerable endcap disk geometry. Resonance characteristics were measured up to anticipated lifetime doses. [Preview Abstract] |
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