Bulletin of the American Physical Society
2016 Fall Meeting of the APS Division of Nuclear Physics
Volume 61, Number 13
Thursday–Sunday, October 13–16, 2016; Vancouver, BC, Canada
Session FH: Fundamental Symmetries |
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Chair: Kent Paschke, University of Virginia Room: Pavilion Ballroom C |
Friday, October 14, 2016 4:00PM - 4:12PM |
FH.00001: Antihydrogen Electric Charge Neutrality: A New Limit from ALPHA at CERN Andrea Capra, M. Baquero-Ruiz, C. Carruth, A. Charman, L. T. Evans, N. Evetts, J. Fajans, M. C. Fujiwara, D. R. Gill, A. Gutierrez, W. N. Hardy, M. E. Hayden, L. Kurchaninov, J. T. K. McKenna, S. Menary, J. M. Michan, T. Momose, J. J. Munich, K. Olchanski, Arthur Olin, A. Povilus, C. So, R. I. Thompson, J. S. Wurtele, A. I. Zhmoginov The equivalence of the absolute value of the electric charge of the electron and of the proton is experimentally well-established. It also finds strong theoretical motivations within the Standard Model. A similar measurement on positrons and antiprotons provides, in addition, a test of the CPT invariance. The ALPHA collaboration set a new upper limit on the electric charge $Qe$, where $e$ is the elementary charge, of the antihydrogen atom by applying stochastic acceleration to the magnetically confined antiatoms. The limit $|Q|<7.1\times10^{-10}$ (1$\sigma$ confidence level) is a 20-fold improvement on the previously best measurement. The present result places an improved limit on the positron charge anomaly of about 1 ppb. [Preview Abstract] |
Friday, October 14, 2016 4:12PM - 4:24PM |
FH.00002: Search for Dark Photons with the SeaQuest Spectrometer Michelle Mesquita de Medeiros The SeaQuest E906 experiment is a fixed target Drell-Yan experiment which is aimed at studying the anti-quark distributions in the nucleon and nuclei. 120 GeV protons from the Main Injector at Fermilab could also be used to search for massive dark gauge bosons or dark photons in SeaQuest. The interactions of the proton beam with the 5m long iron beam dump can produce dark photons through processes such as proton bremsstrahlung and eta decay. These dark photons can decay into dimuons, and for dark photons with weak coupling to the EM sector, the decay vertex is significantly displaced from the dark photon production point, allowing for a very low background search. By detecting the dimuons with the SeaQuest spectrometer and analyzing its invariant mass distribution, one can search for signatures of these exotic processes. Exclusion limit projections for SeaQuest and preliminary results of the dark photon search will be presented. [Preview Abstract] |
Friday, October 14, 2016 4:24PM - 4:36PM |
FH.00003: Ideogram-based Gaussian Estimator for the Model Uncertainty in the Extraction of Q$_w$(p) from PVES Data Gregory Smith As the Q$_{\rm weak}$ collaboration gets closer to unblinding our final result, a method to account for the model uncertainty in the extraction of Q$_w$(p) from a fit to existing parity-violating electron scattering data has been developed. Choices made in selecting the database used in the fit, the strange dipole mass, the functional form of G$_{\rm E,M}^{\rm s}$, axial constraints, charge-symmetry breaking effects, and in the electromagnetic form factors all contribute to this model uncertainty. An ideogram-inspired Gaussian estimator of this model uncertainty is derived from a fit to a sum of Gaussians, each characterized by the central value and uncertainty of the weak charge obtained from fits using each choice. The width of the resulting summed Gaussian is used to extract the model uncertainty in quadrature from the statistical and systematic errors assumed in the baseline analysis. Finally, this result is compared to the "stand-alone" weak charge determined from the single datum representing the asymmetry expected from the (as yet unblinded) Qweak experiment, using calculated electromagnetic, strange, and axial contributions. [Preview Abstract] |
Friday, October 14, 2016 4:36PM - 4:48PM |
FH.00004: Probing parity nonconservation effects with laser cooled and trapped francium atoms Mukut Kalita, Seth Aubin, John Behr, Robert Collister, Austin DeHart, Alexandre Gorelov, Eduardo Garcia, Gerald Gwinner, Michael Kossin, David Livermore, Luis Orozco, Matt Pearson Measurements of parity nonconservation (PNC) effects in atomic systems test the Standard Model at low energies. We are developing an experiment to probe PNC effect in neutral francium atoms. Francium ions produced at the ISAC radioactive beam facility at TRIUMF are neutralized using a zirconium foil. The foil is momentarily heated and the released atoms are first trapped in a capture magneto optical trap (MOT). Then, the atoms are transported with about 50\% efficiency to another MOT in a science chamber. In this chamber, in one experiment the 7S to 8S atomic transition will be probed using a laser beam, and in another experiment the ground state hyperfine transition will be probed using a microwave beam. In this talk I will report on recent developments towards the measurements. [Preview Abstract] |
Friday, October 14, 2016 4:48PM - 5:00PM |
FH.00005: The MOLLER Experiment Juliette Mammei The Measurement of a Lepton Lepton Exclusive Reaction, or MOLLER, experiment is a search for physics beyond the Standard Model that will run at Jefferson Lab. Due to the ultra-precise nature of this measurement, the uncertainty on the value of the weak mixing angle will be on par with that from the two most precise collider measurements at the Z pole. MOLLER is sensitive to potential new physics with contact interaction scales well over 10 TeV. In order to achieve this extreme precision, the contributions to the systematic uncertainty need to be well understood and controlled. This talk will give an overview of the experiment and discuss the ongoing pre-R{\&}D work that will allow the experiment to make a sub-ppb measurement of the parity-violating asymmetry, APV. [Preview Abstract] |
Friday, October 14, 2016 5:00PM - 5:12PM |
FH.00006: Detector Simulations and Background Studies for the MOLLER Experiment Sakib Rahman The MOLLER experiment proposes to measure the parity-violating asymmetry $A_{PV}$ in electron-electron (M{\o}ller) scattering. $A_{PV}=\frac{\sigma_+-\sigma_-}{\sigma_++\sigma_-}$ where $\sigma_+$ and $\sigma_-$ are the cross-sections for scattered electrons with positive and negative helicity respectively. In the experiment, an 11 GeV beam of longitudinally polarized electrons is incident on a liquid hydrogen target. The yields in each helicity state are measured by an array of 224 integrating quartz detectors 28 meters downstream from the target position. A spectrometer consisting of two resistive toroidal magnets and a system of collimators provides kinematic separation and shielding from backgrounds. The yields need to be corrected for helicity-correlated beam properties and background asymmetries to achieve high precision. The goal of this work is to optimize the signal-to-background contributions at the detector plane, including both the dilution and asymmetry from different backgrounds by minimizing and understanding their sources and the relative responses of the detectors. In this presentation, I will discuss the status of background studies performed with the Geant 4 simulation toolkit and the development of a parametrized detector geometry in the simulation. [Preview Abstract] |
Friday, October 14, 2016 5:12PM - 5:24PM |
FH.00007: Electrophobic Scalar Boson and Muonic Puzzles Yu-Sheng Liu, David McKeen, Gerald A. Miller A new scalar boson which couples to the muon and proton can simultaneously solve the proton radius puzzle and the muon anomalous magnetic moment discrepancy. Using a variety of measurements, we constrain the mass of this scalar and its couplings to the electron, muon, neutron, and proton. Making no assumptions about the underlying model, these constraints and the requirement that it solve both problems limit the mass of the scalar to between about 100 keV and 100 MeV. We identify two unexplored regions in the coupling constant-mass plane. Potential future experiments and their implications for theories with mass-weighted lepton couplings are discussed. [Preview Abstract] |
Friday, October 14, 2016 5:24PM - 5:36PM |
FH.00008: Interpretation of the 17 MeV anomaly in $^8$Be$^*$ decay as light, weakly coupled new physics Susan Gardner, Jonathan Feng, Bartosz Fornal, Iftah Galon, Jordan Smolinsky, Tim Tait, Philip Tanedo Recently a 6.8$\sigma$ anomaly has been reported in the opening angle and invariant mass distributions of $e^+ e^-$ pairs produced in $^8$Be nuclear transitions (Krasznahorkay et al., PRL 116 (2016) 042501). We find that the data can be explained by a 17 MeV vector gauge boson $X$ that is produced in the decay ${}^8{\rm Be}^* \to {}^8{\rm Be}\, X$, with $X$ decaying through $X \to e^+ e^-$. The $X$ boson mediates a new force with a characteristic range of 12 fm, and it has milli-charged couplings to up and down quarks and electrons, yielding a proton coupling that is suppressed relative to neutrons. We show that such a "protophobic" $X$ boson is compatible with all other experimental constraints in this mass range and discuss how such an object can emerge from fundamental physics. The $X$ boson may also alleviate the current 3.6$\sigma$ discrepancy between the predicted and measured values of the muon's anomalous magnetic moment. [Preview Abstract] |
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