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.

The transport properties of a quasi-three-dimensional, 200 layer quantum well structure are investigated at integer filling in the quantum Hall state. We find that the transverse magnetoresistance R xx , the Hall resistance R xy , and the vertical resistance R zz all follow a similar behavior with both temperature and in-plane magnetic field. A general feature of the influence of increasing in-plane field B in is that the Hall conductance quantization first improves, but above a characteristic value B C in , the quantization is systematically removed. We consider the interplay of the chid edge state transport and the bulk (quantum Hall) transport properties. This mechanism may arise from the competition of the cyclotron energy with the superlattice band structure energies. A comparison of the resuIts with existing theories of the chiral edge state transport with in-plane field is also discussed.

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

The MEGA experiment, which is a search for the decay murarregamma with a branching ratio sensitivity of about 10-13, employs highly modular, fast detectors, state-of-the-art electronics, and a staged trigger with on-line filters. The detectors are contained in a 1.5-T solenoidal field produced by a superconducting magnet. Positrons are confined to the central region and are measured by a set of thin MWPCs. Photons are measured by one of four layers of pair spectrometers in the outer region. Most aspects of the design have been validated in engineering runs; data taking will begin in 1990 with much of the electron arm and one pair spectrometer layer installed.

New experimental upper limits for the branching ratios of the lepton‐family‐number nonconserving decays μ+ → e+γ and μ+ → e+γγ are presented. A new determination of γ, the ratio of pion axial‐vector to vector form factors, from radiative pion decay is also reported. These results are from data taken with the Crystal Box detector at LAMPF.

An array of 49 NaI(Tl) modules each 20 inch in depth and 2.5 inch × 2.5 inch in cross section has been constructed and its properties, especially energy resolution, explored for positrons in the range 20 MeV – 18 GeV. A subsequent much larger detector, the Crystal Box, has also been constructed from 396 modules of the same cross section, but mostly 12 inch in depth, and operated as a γ-ray and positron detector in a search for rare muon decays. The calibration procedure used for the Crystal Box and its characteristic resolutions in energy, impact point and time are described.

A discussion is given of the mechanisms by which a light scalar or pseudoscalar boson, such as a familon, may be emitted in the radiative decay of a muon. The results of a new experimental search for the decay ${\ensuremath{\mu}}^{+}$\ensuremath{\rightarrow}${e}^{+}$\ensuremath{\gamma}f, where f is such a boson, are presented. The resulting bounds on the coupling strength are comparable to, but of wider validity than, those from ${\ensuremath{\mu}}^{+}$\ensuremath{\rightarrow}${e}^{+}$f. .AE