Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session X12: Invited Session: Precision Tests of New Physics Using Neutrons and Nuclei |
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Sponsoring Units: DNP Chair: Fred Wietfeldt, Tulane University Room: Grand Hall East A/B |
Tuesday, April 3, 2012 1:30PM - 2:06PM |
X12.00001: Nuclear Matrix Elements from Lattice QCD Invited Speaker: Joseph Wasem Lattice QCD (LQCD) is the only known method for performing fully non-perturbative calculations of nuclear observables directly from the underlying theory of QCD. With the recent emergence of LQCD from a decades-long R{\&}D period, LQCD is now beginning to make precise statements about nuclear processes which, up to now, have been poorly constrained empirically. Such LQCD calculations offer the nuclear physics community information on precision electroweak quantities (such as the QCD correction to the muon g-2), well-known nuclear quantities (such as the nucleon axial charge), as well as first glimpses of poorly understood quantities (such as the parity violating nucleon-pion coupling). I will briefly review the Lattice QCD efforts for calculations of these (and other) nuclear matrix elements, discussing both the promise and the problems that must be overcome. The lattice calculation of the parity violating nucleon-pion coupling will then be examined in more detail, with a discussion of possible future directions. [Preview Abstract] |
Tuesday, April 3, 2012 2:06PM - 2:42PM |
X12.00002: Isospin-symmetry-breaking effects in nuclear $\beta$ decay Invited Speaker: Dan Melconian Precisely measured $ft$ values of $J^\pi=0^+\!\!\rightarrow 0^+${} $\beta$ decays of isospin $T=1$ nuclei are used to set stringent limits on scalar and right-handed interactions, verify the conserved vector current hypothesis at the $\sim10^{-4}$ level, and provide the most precise measurement of $V_{ud}$, the up-down element of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix. In order to utilize the measured $ft$ values for these purposes, one must first apply theoretical corrections for isospin-symmetry-breaking and radiative effects. In recent years, the nuclear-structure-dependent isospin-symmetry-breaking calculations have been placed under intense scrutiny; concurrently, experimental work has measured these corrections in cases where they are relatively large. This talk will review the effects of isospin-symmetry breaking in superallowed transitions and discuss recent results aimed at testing the validity of the corrections that are applied. [Preview Abstract] |
Tuesday, April 3, 2012 2:42PM - 3:18PM |
X12.00003: Precision Measurements of the Neutron Decay Asymmetry A Invited Speaker: Bastian Maerkisch Neutron beta decay is the simplest semi-leptonic weak process, and precision measurements of angular correlations coefficients provide unique information about the weak interaction and contribute significantly to precision tests of the Standard Model of particle physics. In particular, measuring the beta asymmetry correlation coefficient $A$ in polarized neutron decay is the most precise way to directly determine the ratio of axialvector and vector coupling constants $\lambda = G_{\mathrm{A}} / G_{\mathrm{V}}$. This ratio is for example required for predicting the abundance of light elements from primordial nucleosynthesis, the solar neutrino flux and the spin content of nucleons. Measurements of $\lambda$ and the neutron lifetime $\tau_{\mathrm{n}}$ are used to determine the element $V_{\mathrm{ud}}$ of the CKM-matrix from neutron decay data only. Recent experiments by \textsc{Perkeo~II}, UCNA and \textsc{Perkeo~III} have successfully reduced total corrections to the raw data to the percent level. The \textsc{Perkeo~III} instrument used a pulsed polarized cold neutron beam to effectively eliminate major sources of systematic error, such as beam related background and edge effects. All systematic uncertainties of this measurement are smaller than $10^{-3}$ on $A$ and the total error is thus reduced to a level of $\Delta \lambda/\lambda \approx 5 \cdot 10^{-4}$. In the talk I will give an overview of recent precision measurements of the beta asymmetry $A$ correlation coefficient and present the recent results of \textsc{Perkeo~II} and \textsc{Perkeo~III}. [Preview Abstract] |
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