Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session 2WA: Workshop on Electroweak and Precision Physics II |
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Chair: Doug Higenbotham, Jefferson Lab Room: Newport News Marriott at City Center Pearl Salon I |
Wednesday, October 10, 2007 2:00PM - 2:35PM |
2WA.00001: Scalar and right-handed current searches using trapped atoms Invited Speaker: Neutral atom traps coupled to a radioactive ion beam facility can be used to provide an ideal source of $\beta$ decaying atoms: the atoms are cold, compact, and the daughter particles escape the source with negligible distortions to their momenta. By measuring the $\beta-\nu$ correlation parameter in the $0^+\rightarrow0^+$ decay of $^{\mathrm{38m}}$K, the TRINAT collaboration has improved the limits on possible scalar currents (Gorelov, \emph{et al.}, Phys.\ Rev.\ Letts.\ {\bf 94} (2005) 142501). We have recently demonstrated the ability to highly polarize laser-cooled atoms and to search for right-handed currents by measuring the neutrino asymmetry parameter in the $I^\pi=\frac{3}{2}^+$ decay of $^{\mathrm{37}}$K (Melconian \emph{et al.}, Phys.\ Lett.\ B {\bf 649} (2007) 370). A summary of these experiments and the planned improvements will be presented. [Preview Abstract] |
Wednesday, October 10, 2007 2:35PM - 3:10PM |
2WA.00002: The Search for the Neutron Electric Dipole Moment Invited Speaker: A non-zero neutron Electric Dipole Moment (EDM) would indicate a violation of Time Reversal Symmetry and, via the CPT Theorem, also a violation of Charge Conjugation/Parity (CP) symmetry. New experiments are underway to increase the sensitivity to a neutron EDM to $\sim $ 1 x 10$^{-28}$ e-cm, representing an improvement over the existing limits of about two orders-of-magnitude. A positive result from these experiments would imply that new sources, beyond our present Standard Model, of CP violation must exist. I will discuss the progress and plans for a new neutron EDM experiment to be carried out at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source. [Preview Abstract] |
Wednesday, October 10, 2007 3:10PM - 3:30PM |
2WA.00003: COFFEE BREAK
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Wednesday, October 10, 2007 3:30PM - 4:05PM |
2WA.00004: aCORN: A Precision Measurement of the Neutron Decay a-Coefficient Invited Speaker: The experimental parameters of neutron beta decay can be used to measure the weak coupling constants $g_A$ and $g_V$, determine the CKM matrix element $V_{ud}$, and search for hints of non- Standard Model physics. The aCORN experiment will make a precision ($<1$\%) measurement of the electron-antineutrino angular correlation ($a$-coefficient). It uses a new method in which the $a$-coefficient is proportional to an asymmetry in beta-proton coincidence count rates. Precision spectroscopy of recoil protons, which has systematically limited previous experiments at the 5\% level, is not necessary in aCORN. The apparatus is currently under construction. It will be integrated and tested at the new LENS facility at Indiana University and then moved to the NIST Center for Neutron Research in 2008 for the initial physics run. [Preview Abstract] |
Wednesday, October 10, 2007 4:05PM - 4:40PM |
2WA.00005: An Experiment to Measure the Proton's Weak Charge Invited Speaker: Precision measurements of Standard Model-suppressed, weak-scale observables provide a window on potential new physics at the TeV scale. An attractive observable is the proton neutral weak charge, $Q_{Weak}^p$, which measures the coupling of the Standard Model Z boson to the proton and is proportional to the relatively small quantitity $1 - 4\sin^2\theta_W$. The proton weak charge can now be calculated to very high precision in the Standard Model but has never been directly measured. Its value could be significantly shifted by new, parity-violating electron-quark interactions such as those found in leptquark models or RPV SUSY models. The existence of new $Z'$s could also shift the observed value. By measuring the parity-violating asymmetry in elastic $e+p$ scattering at low momentum transfer, the proton weak charge can be determined with hadronic ambiguities which are significantly smaller than our projected error bar. After overviewing the physics and our plans for a 4/% measurement, the status of the construction effort will be summarized. [Preview Abstract] |
Wednesday, October 10, 2007 4:40PM - 5:15PM |
2WA.00006: Probing the TeV Scale with Parity-Violating Electron Scattering: New Opportunities with the 12 GeV Upgrade Invited Speaker: The technique of parity-violating electron scattering, involving measurements of the asymmetry in the scattering of longitudinally polarized electrons off fixed targets, has become increasingly precise and broad in its scope over the past two decades. Such asymmetries are sensitive to weak neutral current interactions between electrons and target particles, mediated by the $Z^0$ boson, and are being used to investigate the strangeness content of the nucleon, the neutron distribution in heavy nuclei and to probe for the limits of the validity of the electroweak theory in a manner complementary to direct searches for new physics at high energy scales at colliders. At Jefferson Laboratory, experimental techniques have now been developed, that allow for asymmetries to be measured with statistical and systematic errors approaching 1 part per billion. With the completion of the 12 GeV upgrade, further precise measurements become feasible, in parity-violating deep inelastic scattering and in electron-electron (M\o ller) scattering. In particular, the latter measurement could potentially lead to the best measurement of the electroweak mixing angle $\sin^2\theta_W$ at low energy, with precision equal to or better than the two best collider measurements. In deep inelastic scattering, apart from testing the electroweak theory, the measurements would provide new precision probes of the high-$x$ structure of the nucleon by testing for the onset of charge symmetry violation and allowing a clean and accurate measurement of $d(x)/u(x)$ as $x\rightarrow 1$. In this talk, we will first give an introduction to the experimental technique and report on recent developments. We will then elaborate on the physics motivation for the abovementioned program of new measurements in detail. [Preview Abstract] |
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