Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session B9: Electroweak Interactions |
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Sponsoring Units: DNP Chair: Gordon Cates, University of Virginia Room: 250A |
Saturday, April 16, 2016 10:45AM - 10:57AM |
B9.00001: Overview of the parity violation measurement of $n+^{3}$He$\rightarrow p+t$ Christopher Coppola The hadronic weak interaction remains the least well-understood of the weak interactions. There are multiple models with effective degrees of freedom characterizing its spin and isospin dependence. Measuring the strength of this interaction is difficult due to the much larger strong interaction between nucleons. However, parity violation in few-body reactions allows isolation of weak contributions on the order of $10^{-7}$ from the strong background. The size of parity violating asymmetry in the reaction $n+^{3}$He is expected to be of this order. The experiment has fininshed taking data from a $^{3}$He target in a polarized pulsed neutron beam at the Spallation Neutron Source at Oak Ridge National Laboratory. The expected precision of the asymmetry calculations is on the order of $10^{-8}$, and we are now in the analysis phase. [Preview Abstract] |
Saturday, April 16, 2016 10:57AM - 11:09AM |
B9.00002: A measurement of the parity conserving asymmetry in the neutron capture on $^3He$ at SNS. Latiful Kabir The $n^3He$ experiment at the Spallation Neutron Source is motivated to measure the parity violating asymmetry of the recoil proton momentum $k_p$ with respect to the neutron spin $\sigma_n$ in the reaction n+ $^3$He $\to$ p +T+765 KeV. This is sensitive to isospin $\Delta I$ = 0 and 1 components of the Hadronic Weak Interaction (HWI), and is expected to be extremely small (~$10^{-7}$). There is an additional parity even nuclear asymmetry proportional to $\vec{k}_p \cdot \vec{\sigma}_n \times \vec{k}_n$ predicted by R-matrix analysis to be $1\times10^{-6}$ at 5 meV [1]. We measured this asymmetry for the first time for verification of nuclear theory in this new observable and for confirmation of the sensitivity of our experiment to the parity violating asymmetry. I will present the measurement of the PC asymmetry and discuss on data analysis. [1] G. Hale, Hadronic Parity Violation Workshop, Madison, WI, 2007. [Preview Abstract] |
Saturday, April 16, 2016 11:09AM - 11:21AM |
B9.00003: Parity-Violating and Parity-Conserving Asymmetries in \boldmath$\vec{e}p$ and \boldmath$\vec{e}N$ Scattering in the Qweak Experiment Wouter Deconinck The Qweak experiment at Jefferson Lab has made the first determination of the weak charge of the proton in elastic scattering of longitudinally polarized electrons from unpolarized protons at a momentum transfer $Q^2$ of 0.025 (GeV/c)$^2$. To achieve the required precision to measure the small parity-violating asymmetry of -279 parts per billion, we directed a 180 $\mu$A 85\%-polarized electron beam on a 35 cm long liquid hydrogen target and integrated scattered events in eight azimuthally symmetric fused silica Cerenkov detectors. Based on 4\% of the total data collected by the experiment, we find a value for the weak charge of proton in agreement with predictions of the Standard Model. To correct for the contributions from background processes, we conducted several additional parity-violating and parity-conserving asymmetry measurements with different kinematics (elastic and $N \to \Delta$), electron polarization (longitudinal and transverse), and targets (protons, electrons, aluminum, and carbon). In many cases, these ancillary results are first or high-precision measurements as well. I will discuss the analysis and anticipated results of the main experiment with a focus on several of the ancillary results. [Preview Abstract] |
Saturday, April 16, 2016 11:21AM - 11:33AM |
B9.00004: $A_y^0$ Measurement from Quasi-Elastic $^3\mbox{He}^\uparrow(e,e'n)$ Scattering at Jefferson Lab Elena Long Due to the lack of free neutron targets, studies of the structure of the neutron are typically made by scattering electrons from either $^2$H or $^3$He targets. In order to extract useful neutron information from a $^3$He target, one must first understand how the neutron in a $^3$He system differs from a free neutron by taking into account nuclear effects such as final state interactions and meson exchange currents. The target single spin asymmetry $A_y^0$ is an ideal probe of such effects, as any deviation from zero indicates effects beyond plane wave impulse approximation. When nuclear effects within the $^3$He wave function are taken into account, calculations show that this asymmetry can become large ($>50\%$). New measurements of the target single spin asymmetry $A_y^0$ were made at Jefferson Lab using the quasi-elastic $^3\mathrm{He}^{\uparrow}(e,e'n)$ reaction. The measured asymmetry decreases by over two orders of magnitude, from $>70\%$ at $Q^2=0.1$ (GeV/$c)^2$ to nearly zero at $Q^2=1$ (GeV$/c)^2$, providing evidence of the dominance and fall-off of nuclear effects when studying neutron structure by electron scattering from $^3$He. Details of the measurement will be presented. [Preview Abstract] |
Saturday, April 16, 2016 11:33AM - 11:45AM |
B9.00005: Search for New Physics with Experiment E36 at J-PARC Dongwi Dongwi The E36 experiment conducted at J-PARC in Japan will provide a precision test of lepton universality in the $K_{e2}/K_{\mu2}$ ratio to search for new physics beyond the Standard Model (SM). The SM prediction for the ratio of leptonic $K^{+}$ decays is very precise with an uncertainty of $\bigtriangleup R_{K}/R_{K}=4\cdot10^{-4}$. Any observed deviation from the SM prediction would break the universality of the lepton couplings and provide clear indication of New Physics beyond the SM. The detector apparatus allows sensitivity to search for light $U(1)$ gauge bosons and sterile neutrinos below $300 MeV/c^2$, which could be associated with dark matter or explain established muon-related anomalies such as the muon $g-2$ value, and perhaps the proton radius puzzle. The experiment was set up at the J-PARC K1.1BR kaon beamline in the fall of 2014, fully commissioned in the spring of 2015 and completed production data accumulation in Dec 2015. A scintillating fiber target was used to stop a beam of up to 1.2 Million $K^+$ per spill. The $K^+$ products were detected with a large-acceptance toroidal spectrometer capable of tracking charged particles with high resolution, combined with a CsI(TI) photon detector and particle ID systems. The status of the data analysis will be presented. [Preview Abstract] |
Saturday, April 16, 2016 11:45AM - 11:57AM |
B9.00006: Branching ratio for the superallowed beta-decay of $^{10}$C Tommi Eronen, M. Bencomo, L. Chen, J.C. Hardy, V. Horvat, V. Iacob, N. Nica, H.I. Park, B. Roeder, A. Saastamoinen Superallowed $\beta$ decays play a key role in testing the Standard Model of Particle Physics. These decays occur between nuclear analog states having spin-parity of $0^+$ and isospin $T=1$. Currently, and in the foreseeable future, they offer the most accurate value for the $V_{ud}$ matrix element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. Each superallowed transition is characterized with an ${\mathcal F}t$ value combining both experimental and theoretical quantities. We have just made a preliminary new measurement of the $^{10}$C branching ratio, which currently is the least precisely known quantity for any of the ``traditional nine'' superallowed transitions. Furthermore, $^{10}$C is the only case that appears to have its corrected ${\mathcal F}t$ value outside the world average value, which could be explained with the existence of a scalar current. We performed the branching-ratio measurement with a $\beta$-$\gamma$ coincidence setup using a scintillator for $\beta$ and an HPGe with $\pm$0.15\% calibrated relative efficiency for $\gamma$ detection. Since the branching ratio is obtained from the ratio of intensities of 718 keV and 1022 keV $\gamma$ lines, most systematic uncertainties cancel out. I will show an overview of the experiment and preliminary results. [Preview Abstract] |
Saturday, April 16, 2016 11:57AM - 12:09PM |
B9.00007: Improving the Precision of the Half Life of $^{\mathrm{34}}$Ar V.E. Iacob, J.C. Hardy, M. Bencomo, L. Chen, V. Horvat, N. Nica, H.I. Park Currently, precise \textit{ft}-values measured for superallowed $0^{+}\to 0^{+}\beta $ transitions provide the most accurate value for $V_{\mathrm{ud}}$, the up-down quark mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. This enables the most demanding test of CKM unitarity, one of the pillars of the Standard Model. Further improvements in precision are possible if the \textit{ft} values for pairs of mirror $0^{+}\to 0^{+}$transitions can be measured with 0.1{\%} precision or better. The decays of $^{\mathrm{34}}$Ar and $^{\mathrm{34}}$Cl are members of such a mirror pair, but so far the former is not known with sufficient precision. Since our 2006 publication of the half-life of $^{\mathrm{34}}$Ar [1], we have improved significantly our acquisition and analysis techniques, adding refinements that have led to increased accuracy. The $^{\mathrm{34}}$Cl half-life is about twice that of $^{\mathrm{34}}$Ar. This obscures the $^{\mathrm{34}}$Ar contribution to the decay in measurements such as ours, which detected the decay positrons and was thus unable to differentiate between the parent and daughter decays. We report here two experiments aiming to improve the half-life of $^{\mathrm{34}}$Ar: The first detected positrons as in [1] but with improved controls; the second measured $\gamma $ rays in coincidence with positrons, thus achieving a clear separation of $^{\mathrm{34}}$Ar decay from $^{\mathrm{34}}$Cl. [1] V. Iacob \textit{et al.} Phys. Rev. C \textbf{74}, 055502 (2006) [Preview Abstract] |
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