Bulletin of the American Physical Society
83rd Annual Meeting of the APS Southeastern Section
Volume 61, Number 19
Thursday–Saturday, November 10–12, 2016; Charlottesville, Virginia
Session B3: Nuclear Physics I |
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Chair: Xiaochao Zheng, University of Virginia Room: Monroe Room |
Thursday, November 10, 2016 10:45AM - 10:57AM |
B3.00001: Polarized Electron Source for the MOLLER Experiment Caryn Palatchi The MOLLER experiment at Jefferson Laboratory will be part of a new generation of ultra high precision electroweak experiments. It will measure the Moller (electron-electron scattering) parity-violating asymmetry, providing an unprecedented precision on the electroweak mixing angle. To achieve such small uncertainties, innovative techniques in the electron source are required to switch the beam helicity more quickly than previously achievable. The key technology is the Pockels cell in the laser optics of the polarized electron source. RTP crystals, which do not suffer from piezo-electric ringing, have been demonstrated to achieve almost an order of magnitude faster transition times than commonly used KD*P crystal cells. This talk will detail the design modifications made to the RTP cell in order to achieve beam quality which is comparable to traditional KD*P controlled accelerator beams. The specific challenges for this use of the RTP system, including laser and crystal constraints, will be discussed. [Preview Abstract] |
Thursday, November 10, 2016 10:57AM - 11:09AM |
B3.00002: A New Strangeness Fit to World Parity-Violating Electron Scattering Data Benjamin Gilbert A global experimental effort to determine the strangeness content of nuclei, including experiments such as G0, SAMPLE, HAPPEx, and A4, have presented results on the precision frontier for parity-violating electron scattering. In particular, the kinematics of these experiments are in the low momentum-transfer region ($Q^2 $ \textless \hspace{1mm} 1), to allow more robust extrapolation to the static ($Q^2$ = 0) properties of the nucleon. The combination of these results into a global fit presents a new opportunity to comment on the globally observed strangeness content in nuclei. The process for constructing this fit faces certain challenges, with electromagnetic form factor model dependence standing out in particular. A novel fit including the most recent data for $^1$H, $^2$H, and $^4$He target parity-violating electron scattering experiments will also be presented, suggesting small but non-zero electromagnetic strangeness contributions. [Preview Abstract] |
Thursday, November 10, 2016 11:09AM - 11:21AM |
B3.00003: Experimental study of the $^3$He and neutron spin structure at low $Q^2$ using a polarized $^3$He target Nguyen Ton The Jefferson Lab (JLab) Hall A E97110 experiment performed a precise measurement of the neutron spin structure functions at low $Q^2$ by using a polarized $^3$He target as an effective polarized neutron target. The goals of the experiment are to make a bench-mark test of Chiral Perturbation Theory calculations and to check the Gerasimov-Drell-Hearn (GDH) sum rule by extrapolating the integral to the real photon point. The data were taken in two experimental run periods. The first period covered the lowest $Q^2$ points but with a defective equipment which complicates the data analysis. The second period covered higher $Q^2$ point, with a properly working equipment. The elastic carbon cross section measurement used for spectrometer optics and systematics studies will be discussed for the first run period along with the future plans for the analysis. [Preview Abstract] |
Thursday, November 10, 2016 11:21AM - 11:33AM |
B3.00004: Predictions for 5.02A TeV Pb$+$Pb Collisions from A Multi-Phase Transport Model Zi-Wei Lin, Guo-Liang Ma A multi-phase transport (AMPT) model [1] aims to provide a kinetic description of essential stages of high-energy heavy ion collisions. Currently the string melting version of the AMPT model consists of a fluctuating initial condition, parton elastic scatterings, quark coalescence for hadronization, and hadronic interactions. In this talk I will show our predictions for 5.02A TeV Pb$+$Pb collisions at the Large Hadron Collider [2]. While we compare with the already-available centrality dependence data on charged particle dN/d$\eta $ at mid-pseudorapidity in Pb$+$Pb collisions at 5.02 TeV [3], we make predictions [2] on identified particle dN/dy, p$_{\mathrm{T}}$ spectra, anisotropic flows v$_{\mathrm{n}}$, and factorization ratios r$_{\mathrm{n}}(\eta^{\mathrm{a}}$,$\eta ^{\mathrm{b}})$ for longitudinal correlations. [1] Z.W. Lin, C.M. Ko, B.A. Li, B. Zhang, and S. Pal, Phys. Rev. C 72, 064901 (2005); source codes available at http://myweb.ecu.edu/linz/ampt/ [2] G.L. Ma and Z.W. Lin, Phys. Rev. C 93, 054911 (2016). [3] J. Adam et al. [ALICE Collaboration], Phys. Rev. Lett. 116, 222302 (2016). [Preview Abstract] |
Thursday, November 10, 2016 11:33AM - 11:45AM |
B3.00005: Background studies for neutron beta decay experiments Noah Birge Neutron $\beta$-decay experiments provide access to important parameters of the Standard Model and are sensitive to new physics Beyond the Standard Model. Modern neutron decay experiments aim to measure decay correlation parameters with a high sensitivity and therefore require very precise particle detection in either energy, time-of-flight, or both. The Nab ($a$ and $b$ parameters) and UCNB ($B$ parameter) experimental apparatuses use thick, large-area, and highly segmented (127 pixels) silicon detectors with a 100 nm thick dead layer. Characterization of this detector and electronics has been conducted at the Los Alamos National Laboratory on a measurement of the $^{45}$Ca $\beta$ spectrum. Results of detector studies as well as the status of data analysis will be presented. [Preview Abstract] |
Thursday, November 10, 2016 11:45AM - 11:57AM |
B3.00006: Calculation of coalescence parameters in Monte Carlo models Tony Perez, Natasha Sharma, Andy Castro, Christine Nattrass, Paul Stankus High energy collisions between heavy nuclei release sufficiently high energies to result in the deconfinement of the constituent quarks and gluons of the colliding hadrons, producing a strongly interacting quark-gluon-plasma (QGP). The production of light nuclei in relativistic heavy ion collisions has been described using recombination of nucleons in the hadronic phase of the collision. The production of deuterons is quantified using the coalescence parameter $B_{\mathrm{2}}$, the spectrum of deuterons divided by the spectrum of protons squared. A similar coalescence parameter, $B_{\mathrm{3}}$, the $^{\mathrm{3}}$He or triton spectrum divided by the proton spectrum cubed, is used to quantify the production of tritons and $^{\mathrm{3}}$He. The increase of $B_{\mathrm{2}}$ with momentum observed in Pb-Pb collisions has been hypothesized to be due to an increase in correlated nucleons with momentum due to either flow or jet production. These hypotheses are difficult to test in Monte Carlo models because most Monte Carlo models do not include coalescence, and some, such as PYTHIA, do not include deuteron production by default. We developed an afterburner to implement coalescence in Monte Carlo models and apply it to several Monte Carlo models in order to test whether the coalescence parameters observed in the data are consistent with flow or jets. We further explore the use of high-pT hadron-deuteron correlations as a means to distinguish deuteron production in jets from production in the bulk. [Preview Abstract] |
Thursday, November 10, 2016 11:57AM - 12:09PM |
B3.00007: Photomultiplier gain versus high voltage measurements for the SuperBigBite spectrometer electronic calorimeter. William Shaver, Gabriel Niculescu A number of crucial experiments exploring the intricate tomography of protons and neutrons will be carried out in Hall A at Jefferson Lab using the SuperBigBite Spectrometer (SBS), a large acceptance magnetic spectrometer sporting 0.5{\%} momentum and 0.5 mr angular resolution. As part of the standard SBS detector package the electromagnetic calorimeter ECAL will detect electrons and photons in the 5 GeV energy range. ECAL's readout will be carried out by \textasciitilde 3,000 28 mm FEU84 photomultiplier (PMT) tubes. In order to characterize these tubes the PMT gain and relative quantum efficiency were measured as a function of high voltage in the 1100-1500 V range, as was the afterpulsing probability. A test stand and a set of complex computer algorithms that almost completely automate the testing procedure and (Root/C$++$-based) data analysis were developed. The custom-built GUI that governs the whole testing procedure as well as the gain dependence on the high voltage will be presented. [Preview Abstract] |
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