The MEGA experiment, which searched for the muon- and electron-number violating decay μ-> e + γ, is described. The spectrometer system, the calibrations, the data taking procedures, the data analysis, and the sensitivity of the experiment are discussed. The most stringent upper limit on the branching ratio of μ-> e + γ) < 1.2 x 10^{-11} was obtained.

An experiment has been performed to search for the muon- and electron-number non-conserving decay mu+ to e+_gamma. The upper limit for the branching ratio to be GAMMA(mu+ to e+_gamma)/GAMMA(mu+ to e+_nu_nubar) < 1.2e-11 with 90 confidence.

An experiment has been performed to search for the muon- and electron-number nonconserving decay μ+→e+γ. The upper limit for the branching ratio is found to be Γ(μ+→e+γ)/ Γ(μ+→e+ν¯ν)<1.2×10−11 with 90% confidence.Received 10 May 1999DOI:https://doi.org/10.1103/PhysRevLett.83.1521©1999 American Physical Society

An experiment has been performed to search for the muon- and electron-number nonconserving decay mu(+) --> e(+)gamma. The upper limit for the branching ratio is found to be Gamma(mu(+) --> e(+)gamma)/Gamma(mu(+) --> e(+)nu<(nu)over bar>) < 1.2 X 10(-11) with 90% confidence.

We report on the status of LAMPF experiment E-1240 to measure the Michel rho parameter in direct muon decay. This experiment ran in 1993, and the data are currently being analyzed. The expected precision on the rho parameter is +/-0.0008. This result will provide better constraints on new physics, particularly on the charged vector bosons' mixing angle zeta in the manifestly left-right symmetric extension of the Standard Model.

The trigger for the MEGA detector system is based on signals from single, high-energy photons interacting in one of the three MEGA pair spectrometers. The trigger is divided into a fast and a slow stage. The first stage produces a fast output if a specific pattern of detector hits is observed in the scintillators and high-speed wire chambers of a pair spectrometer. The second, slow-stage interrogates drift chamber hit patterns and provides a veto when the pattern fails a minimal requirement for reconstruction of the hits into a pair of circular orbits. The trigger interacts with the photon detector electronics by gating limited sections of the detector during the read-out of an event. This paper describes the two stage trigger system, the photon detector electronics, and the implementation of the trigger outputs to strobe the data acquisition system. The performance of the trigger is compared to Monte Carlo simulations of the photon detector response.

A new measurement of the Michel parameter ρ in normal muon decay has been performed using the MEGA positron spectrometer. Over 500 million triggers were recorded and the data are currently being analyzed. The previous result has a precision on the value of ρ±0.0026. The present experiment expects to improve the precision to ±0.0008 or better. The improved result will be a precise test of the standard model of electroweak interactions for a purely leptonic process. It also will provide a better constraint on the WR−WL mixing angle in the left‐right symmetric models.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation J. J. Szymanski, J. F. Amann, K. Baker, D. Barlow, K. Black, R. D. Bolton, M. Brooks, S. Carius, Y. Chen, M. D. Cooper, P. S. Cooper, J. Crocker, M. Dzemidzic, R. J. Fisk, J. Flick, W. Foreman, C. A. Gagliardi, D. Haim, A. Hallin, R. Harrison, G. Hart, C. M. Hoffman, G. E. Hogan, E. B. Hughes, E. V. Hungerford, K. Johnston, C. Jui, G. J. Kim, J. E. Knott, D. D. Koetke, M. A. Kroupa, T. Kozlowski, K. Lan, D. Lee, F. Liu, R. Manweiler, R. Marshall, B. W. Mayes, R. E. Mischke, F. J. Naivar, B. M. K. Nefkens, J. Novak, M. A. Oothoudt, J. N. Otis, R. Phelps, L. E. Piilonen, C. Pillai, L. Pinsky, J. Price, M. W. Ritter, S. Schilling, T. D. S. Stanislaus, K. M. Stantz, W. Stephens, J. Sturrock, L. Tang, B. Tippens, R. E. Tribble, X.‐L. Tu, L. A. Van Ausdeln, W. vonWitsch, D. Whitehouse, C. Wilkinson, B. Wright, S. C. Wright, Y. Zhang, W. Zhou, X.‐G. Zhou, K. O. H. Ziock; MEGA: A search for the decay μ→eγ. AIP Conf. Proc. 10 July 1995; 338 (1): 789–792. https://doi.org/10.1063/1.48450 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

Two experiments are currently underway to measure the single‐particle weak mixing matrix element for the 1064 KeV transition in 207Pb. One experiment measures the circular polarization of the 1064 KeV gamma ray emitted from an unpolarized source, while the other experiment measures the forward‐backward asymmetry of gamma rays emitted from a polarized source. Analysis of the first set of polarized source data yields an upper limit of 23 eV for the single‐particle weak mixing matrix element.

Measurements of the helicity dependence of neutron scattering off of heavy nuclei by the TRIPLE collaboration have yielded multiple parity-nonconserving asymmetries. The asymmetries are predominantly positive, in contradiction to the zero average asymmetry predicted by the statistical model of neutron- nucleus scattering. Theoretical calculations that explain the non-zero average asymmetry require single-particle parity- nonconserving matrix elements 10-100 times larger than those predicted by meson exchange models. We are determining the single-particle parity non-conserving mixing in {sup 207}Pb by measuring the circular polarization of the 1.064 MeV {gamma} ray. The experiment uses a transmission polarimeter and a fast data acquisition system. Initial results are presented.