Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session BB: Mini-symposium on Low Energy Tests of the SM and Searches for New Physics I |
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Sponsoring Units: DNP JPS Chair: Elie Korkmaz, University of British Columbia Room: Ritz-Carlton Hotel Salon 2 |
Monday, September 19, 2005 7:00PM - 7:30PM |
BB.00001: Nuclei and the Early Universe: Looking Beyond the Standard Model Invited Speaker: Despite the many successes of the Standard Model, we know that it must be the low-energy limit of a more comprehensive theory describing the forces of nature from the earliest moments of the cosmos. Both experimental observation--including neutrino oscillations and the predominance of matter over anti-matter--as well as theoretical considerations, such as the stability of the electroweak scale, point to this more comprehensive theory. In this talk, I discuss a variety of nuclear physics experiments that will provide important clues about the ``new'' Standard Model -- including those that look for tiny deviations from Standard Model predictions as well as experiments sensitive to violations of fundamental symmetries. I emphasize how these studies complement those being carried out at high energy colliders and consider some of the key theoretical issues in their interpretation. [Preview Abstract] |
Monday, September 19, 2005 7:30PM - 7:45PM |
BB.00002: Updates on $\beta$-$\nu$ correlation measurement of optically trapped $^{21}$Na atoms Reina Maruyama, Jamil Abo-Shaeer, Paul Vetter, Stuart Freedman Using magneto-optically trapped sodium-21 neutral atoms produced at the Berkeley 88-inch cyclotron, we are measuring the beta-neutrino correlation coefficient. Optical traps offer a suitable environment for precision measurements, and offer us isotopically pure sodium atoms that are localized, nearly at rest, and relatively free from external perturbations. We can reconstruct the decay kinematics from the time-of-flight of the daughter nuclei from the trap to our detector. Our last measurement yielded a beta-neutrino correlation coefficient, a$_{\beta\nu}$, that disagrees by 3.6$\sigma$ from the Standard Model prediction. I will discuss the status of the experiment, our studies of systematic effects, and possible explanations for this discrepancy. [Preview Abstract] |
Monday, September 19, 2005 7:45PM - 8:00PM |
BB.00003: Beta-neutrino correlations from the beta decay of optically trapped $\rm^{38m}$K atoms A. Gorelov, D. Melconian, M. Trinczek, W.P. Alford, J.A. Behr, P.G. Bricault, M. Dombsky, K.P. Jackson, D. Ashery, F. Gluck The $\beta\!-\!\nu$ correlation parameter, $a$, has been measured in the $0^+\!\rightarrow 0^+$ beta decay of trapped $\rm^{38m}$K (lifetime 0.924s) atoms to place limits on the possible contribution of a scalar interaction to nuclear beta decay [A.Gorelov et al., PRL, {\bf 94}, 142501(2005)]. A magneto-optical trap provides an isomerically selected and backing-free source of atoms, localized in a volume less than 1mm in diameter, so the low-energy recoiling nuclei can freely escape and be detected in coincidence with betas in back-to-back geometry. The $\beta\!-\!\nu$ correlation is measured by observing the positron in a $\Delta E-E$ telescope and the time of flight of the recoiling Ar nucleus in a micro-channel plate (MCP). The application of a uniform electric field along the detection axis toward the MCP allows separation in time of the $\rm Ar^0,Ar^+$ and higher charge states of Ar ions as well as increasing both their collection and detection efficiencies. Analysis of about 160,000 events with the positron energy above $2.5\,$MeV (1/2 the $Q-$value) resulted in the $\beta\!-\!\nu$ correlation parameter $\tilde a=0.9981\pm 0.0030^{+0.0032}_{-0.0037}$, consistent with the Standard Model prediction $\tilde a=1$. Future modifications of the experimental apparatus and data analysis may give us a possibility to reduce systematic errors and extend the search to lower beta energies. [Preview Abstract] |
Monday, September 19, 2005 8:00PM - 8:15PM |
BB.00004: Search for right-handed currents in the \boldmath$\beta^+$ decay of laser-cooled, polarized $^{37}$K D. Melconian, A. Gorelov, J.A. Behr, K.P. Jackson, D. Ashery, O. Aviv, S. Gu, M.R. Pearson, W.P. Alford, S. Fostner We have finished analyzing a measurement of the neutrino asymmetry parameter of the decay of polarized $^{37}$K, which is sensitive to physics outside of the Standard Model. The atom cloud, initially cooled and confined by a magneto-optic trap, was optically pumped to achieve $(96.5\pm0.7)\%$ nuclear polarization. We non-destructively monitored this polarization and the cloud characteristics using a novel photoionization technique. The observed recoil asymmetry, directly related to the neutrino asymmetry, yielded $B_\nu=-0.771\pm0. 020(\mathrm{stat})\pm0.011(\mathrm{syst})$. This initial measurement --- the first in a system other than the neutron --- is in agreement with the Standard Model prediction of $-0. 7692(13)$. In the manifest left-right symmetric model, this limits the mass of a possible right-handed boson to be $\stackrel{>}{\sim}$180$~GeV/c$^2$ (90\%~CL). Though this is not yet competitive with limits from other nuclear, neutron and $\mu$ decay experiments, systematics of this first measurement have been identified and can be reduced. Modest improvements of this method will reach an accuracy of $<0.5\%$, at which point it becomes complementary to other experiments. Supported by NSERC, NRC through {\sc Triumf}, and CIPI. [Preview Abstract] |
Monday, September 19, 2005 8:15PM - 8:30PM |
BB.00005: UCNA: A Measurement of the beta-asymmetry using Ultracold Neutrons (UCN) Henning O. Back, A.T. Holley, R.W. Pattie, A.R. Young, B. Filippone, B. Plaster, J. Yuan, P. Geltenbort, E. Tatar, T. Bowles, R. Hill, G. Hogan, M. Makela, C.L. Morris, A. Saunders, R.R. Mammei, M. Pitt, R.B. Vogelaar, T.M. Ito, A. Garcia, S. Hoedl, D. Melconian, A. Sallaska, S. Sjue, J.W. Martin A measurement of the correlation between the e$^{-}$ momentum and n-spin (the beta-asymmetry) in n (neutron) beta-decay, together with the n lifetime, provides a method for extracting fundamental parameters for the charged-current weak interaction of the nucleon. In particular when combined with $\mu$ decay measurements, one can extract the V$_{ud}$ element of the CKM matrix, a critical element in CKM unitarity tests. By using a new SD$_2$ super thermal source at LANSCE, large fluxes of UCN are expected for the UCNA project. These UCN will be 100\% polarized using a 7T field, and directed into the beta spectrometer. This approach, together with an expected large reduction in backgrounds, will result in an order of magnitude reduction in the critical systematic corrections associated with current n beta-asymmetry measurements. [Preview Abstract] |
Monday, September 19, 2005 8:30PM - 8:45PM |
BB.00006: Measuring the lifetime of the muon to 1 ppm with MuLan at PSI David Hertzog The MuLan collaboration$^{1}$ will measure the positive muon lifetime to 1~ppm. This precision will determine the Fermi coupling constant $G_F$, which sets the strength of the weak interaction, to 0.5~ppm. In addition to its fundamental connection to the structure of the standard model, the $\mu^+$ lifetime is needed as a normalization for muon capture experiments. A $\pm$ 12.5~kV electric kicker is used to impose a pulsed structure on the continuous muon beam at the Paul Scherrer Institute, with a bunch of $\sim 50$ muons arriving within a 5 $\mu$s beam-on time followed by a 22 $\mu$s beam-off measuring period. Muons are stopped in a depolarizing target, either amorphous sulfur or Arnokrone-3, to reduce the effects of spin rotation; an external magnetic field is applied to dephase the muons over the accumulation time. A scintillator hodoscope with 170 tile pairs arranged in a truncated icosohedral (``soccer ball'') geometry provides a high level of segmentation to minimize pulse pileup. Similarly, new waveform digitizers will resolve pulses at separations of 4~ns. A dataset is in hand that should provide an initial result with 7 to 10~ppm precision, a factor of $\sim$ 2 better than the current world average, and major production running is scheduled in 2005 and 2006. MuLan is supported by the National Science Foundation and the Department of Energy $^{1}$ U.C. Berkeley - Boston U. - U. Illinois - Istanbul Tech. U. - James Madison U. - U. Kentucky - KVI - PSI [Preview Abstract] |
Monday, September 19, 2005 8:45PM - 9:00PM |
BB.00007: Precise Measurement of Muon Capture on the Proton Frederick Gray The $\mu$Cap experiment is measuring the rate of muon capture on the proton in hydrogen. Muons are stopped in a time projection chamber (TPC) filled with isotopically pure protium gas that contains of order $10^{-6}$ deuterium and $10^{-8}$ higher-$Z$ impurity contamination. This active target allows the muon to be tracked to its stopping point so that only those stopping within the chamber, well away from the walls, are included in the data set. The effective lifetime of the negative muon is measured in this environment from the time spectrum of decay electrons. It is compared with the positive muon lifetime to determine the capture rate, which in turn gives $g_p$, the induced weak pseudoscalar form factor of the proton. Precise theoretical predictions of $g_p$ have been made using heavy baryon chiral perturbation theory, with uncertainties at the level of $3\%$. The current experimental situation is controversial and inconsistent, with significant ambiguity introduced by the formation of $p \mu p$ molecular states in the liquid hydrogen targets that were used in these experiments, a difficulty that is avoided with the present gas target of 100 times lower density. A precise measurement to compare with theory will provide a sensitive test of the chiral symmetry of QCD. A ``blind'' analysis of the data collected in fall 2004 (a $\sim 15\%$ measurement of $g_p$) is in progress. Data collection will continue in 2005 and 2006, with an eventual precision goal of $1\%$ in the capture rate corresponding to $7\%$ in $g_p$. The support of DOE and NSF is gratefully acknowledged. [Preview Abstract] |
Monday, September 19, 2005 9:00PM - 9:15PM |
BB.00008: Towards Higher Precision Measurements of the Muon Decay Parameters by TWIST Richard Mischke The TWIST experiment has just published its first results for the Muon Decay Parameters $\rho = 0.75080 \pm 0.00032(stat.) \pm 0.00097(syst.) \pm 0.00023(\eta)$ and $\delta = 0.74964 \pm 0.00066(stat.) \pm 0.00112(syst.)$. These results limit any possible deviations from the Standard Model predictions for these parameters by a precision 2 to 3 times better than the previous results. This talk will discuss the next phase of the experiment, which will include higher statistical precision and reduced systematic uncertainties. [Preview Abstract] |
Monday, September 19, 2005 9:15PM - 9:30PM |
BB.00009: First Direct Measurement of P$_{\mu}\xi$ by TWIST Michael Hasinoff The TWIST experiment is completing its first direct measurement of the Muon Decay Parameter P$_{\mu}\xi$. Together with the other Michel parameters describing normal muon decay, $\xi$ provides sensitive tests of the Standard Model of electroweak interactions. This talk will discuss the measurement and the assessment of systematic uncertainties, which dominate the precision of the result. The physics implications will be presented. [Preview Abstract] |
Monday, September 19, 2005 9:30PM - 9:45PM |
BB.00010: New results from the PIBETA experiment Dinko Pocanic The PIBETA project has undertaken a to make precise measurements of the branching ratios of the rare pion decays: $\pi^+ \to \pi^0 e^+ \nu$ (beta), and $\pi^+ \to e^+ \nu \gamma$ (radiative), as well as the muon radiative decay $\mu^+ \to e^+ \nu \bar{\nu}\gamma$. We report updated results for the integral and differential branching ratio for these processes, as well as derived physical quantities: $V_{ud}$, the Cabibbo-Kobayashi-Maskawa quark mixing matrix element, $F_A$ and $F_V$, the pion axial and vector form factors, respectively, a new limit on $F_T$, the pion tensor form factor, as well as a new value of the muon decay parameter $\bar{\eta}$. The project will next turn its attention to a new measurement of the $\pi^+ \to e^+ \nu$ decay rate. [Preview Abstract] |
Monday, September 19, 2005 9:45PM - 10:00PM |
BB.00011: aCORN: A Precision Measurement of the Neutron Decay $a$-coefficient F.E. Wietfeldt, R. Badici, B.M. Fisher, C. Trull, M. Leuschner, B. Collett, G.L. Jones, A. Komives, R. Wilson, B.G. Yerozolimsky, M.S. Dewey, J.S. Nico, Yu. Mostovoy, J. Byrne The aCORN experiment will make a precision ($<1$\%) measurement of the electron-antineutrino angular correlation ($a$- coefficient) in neutron beta decay. It uses a novel collimation geometry in which the $a$-coefficient is proportional to an asymmetry in beta-proton coincidence count rates, so that precision spectroscopy of the particles is not necessary. The apparatus is now being constructed; it will be integrated and tested at the new LENS facility at Indiana University in 2007 and then moved to the NIST Center for Neutron Research for a precision physics measurement in 2008. The current status of design and construction will be presented. Work supported by NSF grants PHY-0420851, PHY-0420361, PHY-0420716, PHY-0420563, and NIST (U.S. Dept. of Commerce). [Preview Abstract] |
Monday, September 19, 2005 10:00PM - 10:15PM |
BB.00012: Measuring the Proton's Weak Charge David Mack Precision measurements of Standard Model-suppressed, weak-scale observables provide a window on potential new physics at the TeV scale. The proton neutral weak charge, $Q_{Weak}^p$, is just such a suppressed quantity being proportional to $1 - 4\sin^2\theta_W \approx 0.05$. In particular, $Q_{Weak}^p$ can be shifted from its Standard Model value by any new physics which modifies electron-quark interactions such as leptoquarks, substructure, $Z'$s, or R-parity violating SUSY. Our experiment, currently under construction, will measure the proton's neutral weak charge with a projected total error of 4\%. The interference between $\gamma$ and $Z$ exchange in elastic $e+p$ scattering produces a parity-violating asymmetry which at low momentum transfers is dominated by $Q_{Weak}^p$. The measurement is highly interpretable and complementary to other measurements of the weak charge of the electron and atomic nuclei. Achieving the necessary statistical error on the -300 ppb parity-violating asymmetry will require JLab's high intensity and high polarization electron beam as well as the world's highest power liquid Hydrogen target (2.5 KWatts). Elastically scattered electrons will be focused by a resistive, toroidal spectrometer onto one of eight 2 meter long bars of radiation-hard fused silica. Cerenkov light will be converted to current by PMTs and digitized by 18-bit, fast sampling ADC's. The beam polarization will be reversed at nearly 300 Hz. After overviewing the physics and the experiment, the status of the construction effort will be summarized. [Preview Abstract] |
Monday, September 19, 2005 10:15PM - 10:30PM |
BB.00013: PRISM and Search for Charged Lepton Mixing Yoshitaka Kuno Search for charged lepton mixing attracts much interest after neutrino mixing has been discovered. The search is known to be sensitive to new physics beyond the Standard Model (SM) and beyond neutrino oscillation phenomena. One of various extension to the SM is supersymmetric grand unification theories or supersymmetric seesaw models.The predictions by these models are just a few orders magnitudes lower than the present experimental limits, indicating large discovery potentials. One of the best system to search for charged lepton mixing is the muon. In Japan, we are developing a new muon source with high intensity, high purity and high luminosity. It is based on solenoid pion capture, phase rotation by FFAG (fixed field alternating gradient accelerator). The purpose is to carry out an experiment to search for the muon-to-electron conversion processes at a sensitivity of 10$^{-18}$. At Osaka university, the FFAG ring accelerator is being constructed. The status and future plan of the PRISM project will be presented. [Preview Abstract] |
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