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Title: Search for right-handed currents by means of muon spin rotation

Abstract

A muon spin rotation (..mu..SR) technique has been used to place limits on right-handed weak currents in ..mu../sup +/ decay. A beam of almost 100% polarized 'surface' muons obtained from the TRIUMF M13 beamline was stopped in essentially non-depolarizing >99.99% pure metal foils. The ..mu../sup +/ spins were precessed by 70-G or 110-G transverse fields. Decay e/sup +/ emitted within 225 mrad of the beam direction and with momenta above 46 MeV/c were momentum-analyzed to 0.2%. Comparison of the ..mu..SR signal amplitude with that expected for (V-A) decay yields an endpoint asymmetry xiP..mu..delta/rho>0.9951 with 90% confidence. In the context of manifest left-right symmetric models with massless neutrinos the results imply the 90% confidence limits M(W/sub 2/)>381 GeV/c/sup 2/ and -0.057

Authors:
Publication Date:
Research Org.:
Lawrence Berkeley Lab., CA (USA)
OSTI Identifier:
5008431
Report Number(s):
LBL-20324
ON: DE86002870
DOE Contract Number:
AC03-76SF00098
Resource Type:
Technical Report
Resource Relation:
Other Information: Thesis
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; CURRENTS; ASYMMETRY; LEPTONIC DECAY; MUONS PLUS; CORRECTIONS; DATA ANALYSIS; EXPERIMENTAL DATA; INTERMEDIATE VECTOR BOSONS; LIFETIME; LINEAR MOMENTUM; NEUTRINOS; POSITRONS; REST MASS; SPIN-SPIN RELAXATION; TRIUMF CYCLOTRON; ACCELERATORS; ANTILEPTONS; ANTIMATTER; ANTIPARTICLES; BASIC INTERACTIONS; BOSONS; CYCLIC ACCELERATORS; CYCLOTRONS; DATA; DECAY; ELEMENTARY PARTICLES; FERMIONS; INFORMATION; INTERACTIONS; INTERMEDIATE BOSONS; ISOCHRONOUS CYCLOTRONS; LEPTONS; MASS; MASSLESS PARTICLES; MUONS; NUMERICAL DATA; PARTICLE DECAY; RELAXATION; WEAK INTERACTIONS; WEAK PARTICLE DECAY; 645102* - High Energy Physics- Particle Interactions & Properties-Experimental- Weak Interactions & Properties

Citation Formats

Stoker, D.P. Search for right-handed currents by means of muon spin rotation. United States: N. p., 1985. Web. doi:10.2172/5008431.
Stoker, D.P. Search for right-handed currents by means of muon spin rotation. United States. doi:10.2172/5008431.
Stoker, D.P. Sun . "Search for right-handed currents by means of muon spin rotation". United States. doi:10.2172/5008431. https://www.osti.gov/servlets/purl/5008431.
@article{osti_5008431,
title = {Search for right-handed currents by means of muon spin rotation},
author = {Stoker, D.P.},
abstractNote = {A muon spin rotation (..mu..SR) technique has been used to place limits on right-handed weak currents in ..mu../sup +/ decay. A beam of almost 100% polarized 'surface' muons obtained from the TRIUMF M13 beamline was stopped in essentially non-depolarizing >99.99% pure metal foils. The ..mu../sup +/ spins were precessed by 70-G or 110-G transverse fields. Decay e/sup +/ emitted within 225 mrad of the beam direction and with momenta above 46 MeV/c were momentum-analyzed to 0.2%. Comparison of the ..mu..SR signal amplitude with that expected for (V-A) decay yields an endpoint asymmetry xiP..mu..delta/rho>0.9951 with 90% confidence. In the context of manifest left-right symmetric models with massless neutrinos the results imply the 90% confidence limits M(W/sub 2/)>381 GeV/c/sup 2/ and -0.057},
doi = {10.2172/5008431},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Sep 01 00:00:00 EDT 1985},
month = {Sun Sep 01 00:00:00 EDT 1985}
}

Technical Report:

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  • A muon spin rotation (..mu..SR) technique has been used to place limits on right-handed weak currents in ..mu../sup +/ decay. A beam of almost 100% polarized surface muons obtained from the TRIUMF M13 beamline was stopped in essentially non-depolarizing >99.99% pure metal foils. The ..mu../sup +/ spins were precessed by 70-G or 110-G transverse fields. Decay e/sup +/ emitted within 225 mrad of the beam direction and with momenta above 46 MeV/c were momentum-analyzed to 0.2%. Comparison of the ..mu..SR signal amplitude with that expected for (V-A) decay yields an endpoint asymmetry XiP/sub ..mu../delta/rho > 0.9951 with 90% confidence. Inmore » the context of manifest left-right symmetric models with massless neutrinos the results imply the 90% confidence limits M(W/sub 2/) > 381 GeV/c/sup 2/ and -0.057 < zeta < 0.044, where W/sub 2/ is a predominantly right-handed gauge boson and zeta is the left-right mixing angle. Limits on M(W/sub 2/) for M(nu/sub ..mu..R/) does not equal 0 are also presented. The endpoint asymmetry is used to deduce limits on the nu/sub ..mu..L/ mass and helicity in ..pi../sup +/ decay, non-(V-A) couplings in helicity projection form, and the mass scale of composite leptons.« less
  • A muon-spin-rotation technique has been used to place limits on right-handed currents in ..mu../sup +/ decay. The spins of polarized ..mu../sup +/ stopped in metal targets were precessed by 70-G of 110-G transverse fields. The muon-spin-rotation signal amplitude produced by high-momentum decay e/sup +/ emitted near the beam direction implies xiP/sub ..mu../delta/rho>0.9955 and M(W/sub 2/)>370 GeV (90% confidence), where W/sub 2/ is predominantly right-handed gauge boson. The present result combined with our previous spin-held analysis yields xiP/sub ..mu../delta/rho>0.9966 and M(W/sub 2/)>400 GeV.
  • Limits are reported on right-handed currents, based on precise measurement of the e/sup +/ spetrum end point in ..mu../sup +/ decay. Highly polarized muons from the TRIUMF surface beam were stopped in metal foils within a 1.1 T spin-holding longitudinal field or a 70 G spin-precessing field. For the spin-held data, the V-A rate vanishes in the beam direction at the end point. Measurement of this sets the 90% confidence limits xi P/sub mu/delta/rho > 0.9959 and M(W/sub R/) > 380 GeV, where W/sub R/ is the possible right-handed gauge boson. The ..mu.. SR signal amplitude of the spin-precessed datamore » independently sets the limits xi P/sub ..mu../delta/rho > 0.9918 and M(W/sub R/) > 320 GeV. Limits on non-(V-A) currents, familons, and composite leptons are also presented. 27 references.« less
  • We report preliminary results of an experiment designed to measure the mass of the right-handed intermediate vector boson. The presence of such a particle in electroweak interactions is predicted by left-right symmetric gauge theories. The experiment measures the momentum spectrum of the positrons from the decay at rest of (1) longitudinally polarized muons produced in the decay at rest of ..pi../sup +/ ..-->.. ..mu../sup +/nu (polarization P/sub ..mu../) and (2) unpolarized muons. The endpoints of these two spectra are used to determine the quantity xi P/sub ..mu../ where xi is a Michel parameter. This product is related to the ratiomore » of the mass of left and right handed W and to the phase between the two helicity states. We measure, at the 90% CL, 1 - delta/rho < 0.0041 and infer the mass M(W/sub R/) > 380 GeV/c/sup 2/.« less
  • Limits are reported on charged right-handed currents, based on precise measurement of the endpoint e/sup +/ spectrum in ..mu../sup +/ decay. Highly polarized ..mu../sup +/ from the TRIUMF ''surface'' muon beam were stopped in high purity metal foils and liquid He targets selected to minimize depolarization effects. Decay e/sup +/ emitted within 160 mrad of the beam direction were momentum-analyzed to 0.15%. Muons were stopped within either a spin-processing transverse field (70-G or 110-G) or a spin-holding longitudinal field (0.3-T or 1.1-T). Data collected with the spin-precessing field were used for the momentum calibration of the spectrometer. The spin-held datamore » were used to measure the relative e/sup +/ rate at the endpoint. An extrapolation was made to extract the endpoint rate opposite to the ..mu../sup +/ spin. In terms of the standard muon decay parameters this rate is given by (1-xi P/sub ..mu../delta/rho) where P/sub ..mu../ is muon polarization. The result for xi P/sub ..mu../delta was consistent with the V-A prediction of 1. It is quoted as a 90% confidence lower limit xi P/sub ..mu../delta/rho > 0.9975 since we are unable to correct for all possible sources of muon depolarization. For the model with manifest left-right symmetry and massless neutrinos the result implies 90% confidence limits m(W/sub 2/) > 432 GeV/c/sup 2/ and -0.050 < xi < 0.035, where W/sub 2/ is the predominantly right-handed boson and xi is the left-right mixing angle. With the assumption of no left-right mixing an equivalent 90% confidence upper limit of 0.025 is obtained on the absolute value of the ratio of a possible V+A amplitude to the dominant V-A amplitude in muon and pion decays. Limits are also deduced on the nu/sub ..mu..L/ mass and helicity in ..pi../sup +/ decay, non-(V-A) couplings in helicity projection form, the mass scale of composite leptons, and the branching ratio for ..-->.. e+f where f (familon) is the neutral massless Nambu-Goldstone boson associated with flavor symmetry breaking. 39 refs., 12 figs.« less