Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session FD: Electroweak Experiment and Theory |
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Chair: Dinko Pocanic, University of Virginia Room: Hilton Kohala 3 |
Friday, October 26, 2018 9:00AM - 9:15AM |
FD.00001: Measurement of systematic effects in the UCNτ experiment Eric Michael Fries There have been various measurements of the free neutron lifetime (τn) using either cold neutron beams, or ultracold neutrons (UCN) stored in a trap. There is a ∼4σ discrepancy in measured lifetimes between the two methods. The UCNτ experiment at Los Alamos Neutron Science Center uses an asymmetric magneto-gravitational trap to store UCN, and counts the UCN remaining in the trap after various holding times to measure τn. Analysis of our 2016-2017 data established a current limit for our systematic uncertainty of +0.4/-0.2 s. Some systematic effects that can change the measured τn are depolarization and microphonic heating of trapped UCN, insufficient cleaning of UCN with energies above the trapping potential, and phase space evolution of UCN during storage. The effect of depolarization is measured by changing the strength of the magnetic holding field, the effects of heating and insufficient cleaning are measured by detecting high-energy UCN, and the effect of phase space evolution is measured by comparing the time distributions of UCN after different holding times. We will present details of how these systematic uncertainties are measured and projections of how they will be better constrained. |
Friday, October 26, 2018 9:15AM - 9:30AM |
FD.00002: Limiting Tensor Currents in the Electron-Antineutrino Correlation of Lithium-8 Beta Decay Mary Burkey, Guy Savard, Nicholas David Scielzo, Aaron Gallant, Jason A Clark, Tsviki Hirsh, Ralph Segel, Rodney Orford, Barbara Wang, Elizabeth K Heckmaier, Daniel P Burdette, Jacob Pierce, Louis Varriano, Jeffrey Klimes, Graeme Morgan, Scott T Marley, Kay Kolos, Stephen Padgett, Kumar Sharma High-precision measurements of the beta-neutrino correlation coefficient (a) have long been used as a probe for New Physics due to the constant’s sensitivity to scalar and tensor currents, both predicted to be 0 by the Standard Model’s electroweak interaction. With a high Q-value, the delayed alpha emission from the daughter nucleus, and an essentially pure Gamow-Teller structure, the beta decay of Lithium-8 is a highly suitable reaction for measuring a. Utilizing stopped Lithium-8 ions in a Paul Trap surrounded by silicon strip detectors backed with plastic scintillators, the full kinematics of each decay product can be reconstructed. Upon completing the analysis of a high-statistics dataset of 2 million full Lithium-8 decays obtained in 2016, we are well positioned to constrain tensor currents in the weak interaction to approximately 0.2 percent, the most stringent limit yet achieved in the low energy regime. |
Friday, October 26, 2018 9:30AM - 9:45AM |
FD.00003: Measurements of Transverse Spin Asymmetries in eC and eAl Elastic Scattering at the Qweak Experiment. Wouter Deconinck Previous measurements of the beam-normal single-spin asymmetry An on light nuclei with atomic masses up to carbon agree with the AQ/Z scaling predicted by two-photon exchange calculations. However, the agreement breaks down for the heavy nucleus of lead which has a measured An consistent with zero (at 95% C.L.). Measurements at atomic masses between carbon and lead may explain the reasons for the disagreement. The Qweak experiment at Jefferson Lab has made the first precise determination of the weak charge of the proton in elastic scattering of longitudinally polarized electrons from unpolarized protons in a liquid hydrogen target. To correct for the contributions from background processes, we conducted several additional parity-violating and parity-conserving asymmetry measurements at different kinematics, with longitudinal and transverse beam polarization, and on several nuclear targets. I will present new preliminary measurements of the beam-normal single-spin asymmetry in elastic electron scattering from carbon and aluminum nuclei. The aluminum measurement will provide the first data with an atomic mass between the existing data on carbon and lead. |
(Author Not Attending)
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FD.00004: The P2 Experiment: A future high-precision measurement of the electroweak mixing angle at low momentum transfer Michael T Gericke We provide a brief overview of the future P2 experiment at the upcoming MESA accelerator in Mainz, Germany. The MESA facility is optimized for the detection of order ppb level parity-violating cross-section asymmetries in electron scattering. The experiment aims for a determination of the weak mixing angle to a precision of 0.14%, at a four-momentum transfer of 0.0045 GeV2. The proposed accuracy is comparable to existing measurements at the Z pole. This requires a measurement of the parity-violating cross-section asymmetry in elastic electron-proton scattering, with a total accuracy of 0.56 ppb (1.4%) in a 10000 hour long run using a 155 MeV, 150 μA beam of polarized electrons, impinging on a 60 cm LH2 target. At this low momentum transfer, the relation between the measured asymmetry, the weak charge of the proton, and the weak mixing angle is precisely predicted and therefore comprises a sensitive test of the standard model up to a mass scale of 50 TeV. We will briefly describe the measurement methodology, the experimental setup, and the physics. |
Friday, October 26, 2018 10:00AM - 10:15AM |
FD.00005: Electron Beam Polarimetry using Atomic Hydrogen Møller Polarimeter for P2 experiment Rakitha S Beminiwattha P2 experiment at the upcoming MESA accelerator in Mainz aims for a high precision determination of the weak mixing angle sin2θW to a precision of 0.13% at a four-momentum transfer of Q2 = 4.5 × 10−3 GeV2 to provide a sensitive test of the standard model up to a mass scale of 50 TeV, extendable to 70 TeV. The experiment will be conducted at 155 MeV due to small γZ-box contributions. The size of the asymmetry at the proposed at 155 MeV electron beam energy will be the smallest asymmetry ever measured in electron scattering requiring high precision electron beam polarimetry. An atomic Hydrogen trap polarimeter, “Hydro-Møller” utilizing Møller scattering will provide online beam polarization measurements for the P2 experiment. The “Hydro-Møller” polarimeter will replace conventional ferromagnetic target with a trapped polarized hydrogen atomic target located inside an 8 T solenoid with a magnetic field pointing along the beam direction. The target will generate high purity electronic spin ensemble that will give the main advantage with respect to existing Møller polarimeters. The current status and future plans for Hydro-Møller polarimeter development will be provided. |
Friday, October 26, 2018 10:15AM - 10:30AM |
FD.00006: Precise Half-Life Measurement of 30S V.E. Iacob, J.C. Hardy, L. Chen, V. Horvat, M. Bencomo, N. Nica, H.I. Park, B.T. Roeder, A. Saastamoinen As part of our program to test the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix via 0+→0+ superallowed β decays, we measured the half-life of 30S. The radioactive beam was produced by the 1H(31P, 2n)30S reaction, in which a 30A MeV primary 31P beam bombarded a hydrogen target held at liquid nitrogen temperature and a pressure of 2.0 atm. With the MARS spectrograph we selected a high-purity 30S beam from the recoils. The beam was then extracted in air, passed through a 0.3-mm-thick BC-404 plastic scintillator and a set of Al degraders, adjusted to stop the 30S nuclei in the center of the 76-μm-thick aluminized-mylar tape of our fast tape-transport system. We collected 30S nuclei for 2.4 s; then the beam was switched off and the activity was moved in less than 0.2 s to the center of a 4π proportional counter. The observed decays were then multi-scaled over 24 s. Such collect-move-detect cycles were repeated until a total of 1.4×108 decays were recorded. We split the experiment into 33 runs, each differing from the others in its discriminator threshold, detector bias or dominant dead-time. No systematic effects were identified in these parameters. We found the half-life of 30S to be 1.17992(34) s, a result that is 5 times more precise than any previous measurement. |
Friday, October 26, 2018 10:30AM - 10:45AM |
FD.00007: Consistent Methods for Extracting the Proton’s Weak Charge Gregory Smith The final results of the Qweak collaboration were published this year (Androic, et al., Nature 557, 207 (2018)). That work describes how the proton’s weak charge was extracted from the parity-violating asymmetry measured in ep scattering at Q2=0.0248 (GeV/c)2. Hadronic corrections were accounted for by including other parity-violating experiments in a global fit which was extrapolated to Q2=0 to obtain the proton’s weak charge. Here we describe a new fitting technique which has the advantage that the extrapolation is linear in Q2. It also relies on measured parity-violating asymmetries, but uses calculated instead of fitted axial and strange form factors. The weak charge obtained in this new procedure is consistent with that obtained in the recent publication. |
Friday, October 26, 2018 10:45AM - 11:00AM |
FD.00008: Relativistic Treatment of Frequency Shifts for Spin 1/2 Particles in Electromagnetic Fields. Lakshya Malhotra, Robert Golub, Eva Krägeloh, Nima Nouri, Bradley Plaster
We present a relativistic generalization to the problem of calculating frequency shifts for spin-1/2 particles undergoing Larmor precession in electromagnetic fields. Such effects are important in the interpretation of the results from experiments employing Larmor precession techniques. For the case in which these particles are moving in a highly-uniform magnetic field with small non-uniformities and a non-zero electric field, magnetic fields oriented in the transverse direction relative to the primary magnetic field direction can induce frequency shifts in the particles' Larmor spin precession frequencies. In a situation which employs both electric and magnetic fields, there are, in general, two possible sources of transverse magnetic fields in the particle rest frame: gradients in the magnetic field, leading to off-primary-axis transverse field components, and relativistic transformations of electric fields. Considerations of such are then of paramount importance to the interpretation of results from a precision measurement of a Larmor spin precession frequency. |
Friday, October 26, 2018 11:00AM - 11:15AM |
FD.00009: Parity-Violating Asymmetry in the N-> ∆ Transition Anna Lee The primary focus of the Qweak experiment at Jefferson Lab is the recently published determination of the proton’s weak charge. To properly make corrections to the measured asymmetry, dedicated measurements were made of the parity-violating asymmetry at low Q2 in inelastic e-p scattering at the N-> ∆ transition for two different beam energies. The asymmetries are used to extract an additional physics result, the low energy constant d∆ , which is responsible for the Siegert term that causes the asymmetry to be non-zero even at the photon point (Q2 =0). The d∆ term is a measure of the hadronic parity violation in this transition. It has been shown [S.L. Zhu, et al. Phys. Rev. Lett. 87, 201802 (2001)] to be related to some puzzles in radiative hyperon decays. These theoretical analyses suggest potential values of d∆ much larger than its natural scale. The measurements described here were done at beam energies of 877 MeV (Q2 = 0.011 GeV2 ) and 1165 MeV (Q2 = 0.021 GeV2 ) using the Qweak apparatus. An overview of the motivations for the measurement, the experimental approach, and the status of the analysis will be presented. |
Friday, October 26, 2018 11:15AM - 11:30AM |
FD.00010: Neutrinos, Leptons, Quarks -- Geometrical Isospin Daniel Galehouse Fermi particles are described in an eight dimensional space corresponding to the direction manifold of an arbitrary spinor. The inter-conversion of particles, such as an electron to a neutrino is possible depending on extended motion. The Dirac equation appears but does not exhaust the complex structure of the geometrical space. The extra dimensions of this spinor space can be related to the internal properties of particles as they are observed. This formalism is new and suggests approaches and assessments for some of the current problems in nuclear and particle physics. |
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