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 G3: Nuclear Physics II |
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Chair: Stefan S. Baessler, University of Virginia Room: Monroe Room |
Friday, November 11, 2016 10:45AM - 10:57AM |
G3.00001: An Investigation of Light Ion Production from Coalescence in Nuclear Collisions Wouter de Wet, Lawrence Townsend, Charles Werneth, Ryan Norman, John Norbury, Tony Slaba, William Ford The biological risk posed by the diverse radiation space environment must be carefully considered when assessing crew safety. Detailed knowledge of both the radiation field and the associated doses are necessary to fully understand potential biological consequences. Fragmentation cross-sections are predicted by nuclear collision models and used by radiation transport codes to calculate these quantities. There are significant discrepancies between the magnitudes of light ion production cross sections that are used in various transport codes. These discrepancies stem from differences in light ion production mechanisms, among other factors, in nuclear models. One such production mechanism is the coalescence of abraded nucleons into light ions. In this work, light ion production cross sections, as calculated by the coalescence model implemented in the Relativistic Abrasion-Ablation and De-Excitation Fragmentation code (RAADFRG), are evaluated and compared to experimental data. [Preview Abstract] |
Friday, November 11, 2016 10:57AM - 11:09AM |
G3.00002: Measuring the after pulsing of photomultiplier tubes. Eric Moeller, 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. In high counting rate experiments the after pulsing of PMTs can play an unwanted, important role. As part of the extensive testing of SBS ECAL PMTs carried out at JMU the after pulsing probability was measured. These results will be discussed here. [Preview Abstract] |
Friday, November 11, 2016 11:09AM - 11:21AM |
G3.00003: Measuring the relative quantum efficiency of photomultiplier tubes. William Kemmerer, 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. This presentation focuses on the design and building of a PMT test stand that enables the measurement of PMT (relative) quantum efficiency. Results obtained with this setup will be shown. [Preview Abstract] |
Friday, November 11, 2016 11:21AM - 11:33AM |
G3.00004: A Proton Radius Puzzle? Blaine Norum The proton charge radius $\left (r_p \right)$ as measured using both the muonic atom Lamb shift [0.84087(39) fm] and the atomic hydrogen Lamb shift [new preliminary result 0.83(1) fm] differ significantly from a recent analysis of elastic electron scattering measurements [0.879(8) fm]. This discrepancy has generated a great deal of interest. To examine possible origins of this discrepancy we reanalyzed the published electron scattering data from Saskatchewan (1974), Mainz (1980), and Mainz (2014) using standard statistical methods. We found that these data are actually in very good statistical agreement with the Lamb shift results, thus indicating that no discrepancy exists. In addition, while strictly speaking not germane to the extraction of the charge radius, we found that a simple dipole function with its single parameter fixed to the muonic atom value of the proton radius reproduces $GE_p$ within $\approx 1\%$ up to momentum transfers of $q^2\ =\ 30\ fm^{-2}$. This is far better agreement than is obtained using the ``standard'' dipole function which corresponds to $r_p\ =\ 0.81\ fm$. [Preview Abstract] |
Friday, November 11, 2016 11:33AM - 11:45AM |
G3.00005: Probe of Electroweak Interference Effects in Non-Resonant Inelastic $\vec{e}p$ Scattering James Dowd The $Q_{weak}$ Experiment at Jefferson Lab made the first direct measurement of the proton's weak charge, $Q^p_W$, via a measurement of the parity-violating asymmetry in elastic $\vec{e}p$ scattering with low four-momentum transfer. Energy-dependent radiative corrections must be applied to the asymmetry. The most problematic of these is referred to as the $\gamma Z$ box, where a photon and a Z-boson are simultaneously exchanged. The asymmetry arising from the $\gamma Z$ box depends on the $\gamma Z$ interference structure functions, $F_{1,3}^{\gamma Z}$, for which there is almost no experimental world data. Using the $Q_{weak}$ apparatus, with modifications, a measurement of the parity-violating asymmetry of non-resonant inelastic $\vec{e}p$ scattering was made with 3.35 GeV incident electrons. Inelastically scattered electrons with $Q^2 \approx 0.09$ GeV$^2$ and $W \approx 2.23$ GeV were selected and focused on eight quartz Cerenkov detectors. This asymmetry measurement resides in a kinematic region that will provide additional validation of the theoretical models used to predict the $\gamma Z$ box and can provide insight on hadron structure. Analysis methods and preliminary results will be presented. [Preview Abstract] |
Friday, November 11, 2016 11:45AM - 11:57AM |
G3.00006: Precision measurement of longitudinal and transverse response function of quasielastic electron scattering in the momentum transfer range 0.55 GeV/c $\leq |\vec{q}| \leq$ 1.0 GeV/c Kai Jin To test the Coulomb Sum Rule in nuclei, a precision measurement of inclusive electron scattering cross sections in the quasi-elastic region was performed at Jefferson Lab. Incident electrons with energy ranging from 0.4 GeV to 4 GeV, are scattered from He, C, Fe, and Pb nuclei at four scattering angles(15$^{\circ}$ , 60$^{\circ}$ , 90$^{\circ}$ , 120$^{\circ}$ ), and scattered energies ranging from 0.1 GeV to 4 GeV. The Rosenbluth separation method is used to extract the transverse and longitudinal response functions at three momentum transfers in the range 0.55 GeV/c $\leq |\vec{q}| \leq$ 1.0 GeV/c. The Coulomb Sum is determined in the same $ |\vec{q}|$ range and compared to predictions. We will discuss the impact of our result on short range correlations and possible modification of the nucleon magnetic properties in the nuclear medium. [Preview Abstract] |
Friday, November 11, 2016 11:57AM - 12:09PM |
G3.00007: Neutron Beta Decay Studies in the Nab Experiment Jason Fry The Nab collaboration proposes to measure the electron-neutrino correlation parameter $a$ with a precision of $\delta a / a = 10^{-3}$ and the Fierz interference term $b$ to $\delta b = 3\times10^{-3}$ in unpolarized free neutron $\beta$ decay. These results are expected to lead to a new, precise, independent determination of the ratio $\lambda = G_A / G_V$ that will sensitively test CKM unitarity. A long asymmetric spectrometer guides the decay products to two large area silicon detectors in order to precisely determine the electron energy and proton momentum. The Nab apparatus is under installation on the Fundamental Neutron Physics Beamline at the SNS at ORNL and commissioning will begin in the near future. We present an overview of the Nab experiment and the first tests of the spectrometer. [Preview Abstract] |
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