26 research outputs found
Precision planar drift chambers and cradle for the TWIST muon decay spectrometer
To measure the muon decay parameters with high accuracy, we require an array
of precision drift detector layers whose relative position is known with very
high accuracy. This article describes the design, construction and performance
of these detectors in the TWIST (TRIUMF Weak Interaction Symmetry Test)
spectrometer.Comment: 44 pages, 16 Postscript figures, LaTeX2e, uses Elsevier class
elsart.cls, package graphicx, submitted to Nuclear Instruments & Methods in
Physics Researc
Longitudinal muon spin relaxation in high purity aluminum and silver
The time dependence of muon spin relaxation has been measured in high purity
aluminum and silver samples in a longitudinal 2 T magnetic field at room
temperature, using time-differential \musr. For times greater than 10 ns, the
shape fits well to a single exponential with relaxation rates of
\lambda_{\textrm{Al}} = 1.3 \pm 0.2\,(\textrm{stat.}) \pm
0.3\,(\textrm{syst.})\,\pms and \lambda_{\textrm{Ag}} = 1.0 \pm
0.2\,(\textrm{stat.}) \pm 0.2\,(\textrm{syst.})\,\pms
A search for two body muon decay signals
Lepton family number violation is tested by searching for
decays among the 5.8 positive muon decay events analyzed by the
TWIST collaboration. Limits are set on the production of both massless and
massive bosons. The large angular acceptance of this experiment allows
limits to be placed on anisotropic decays, which can arise
from interactions violating both lepton flavor and parity conservation.
Branching ratio limits of order are obtained for bosons with masses
of 13 - 80 MeV/c and with different decay asymmetries. For bosons with
masses less than 13 MeV/c the asymmetry dependence is much stronger and
the 90% limit on the branching ratio varies up to . This is
the first study that explicitly evaluates the limits for anisotropic two body
muon decays.Comment: 7 pages, 5 figures, 2 tables, accepted by PR
Measurement of the Muon Decay Parameter delta
The muon decay parameter delta has been measured by the TWIST collaboration.
We find delta = 0.74964 +- 0.00066(stat.) +- 0.00112(syst.), consistent with
the Standard Model value of 3/4. This result implies that the product Pmuxi of
the muon polarization in pion decay, Pmu, and the muon decay parameter xi falls
within the 90% confidence interval 0.9960 < Pmuxi < xi < 1.0040. It also has
implications for left-right-symmetric and other extensions of the Standard
Model.Comment: Extended to 5 pages. Referee's comments answere
Precision muon decay measurements and improved constraints on the weak interaction
The TWIST Collaboration has completed its measurement of the three muon decay
parameters \rho, \delta, and P_\mu\xi. This paper describes our determination
of \rho, which governs the shape of the overall momentum spectrum, and \delta,
which controls the momentum dependence of the parity-violating decay asymmetry.
The results are \rho=0.74977\pm 0.00012(stat.)\pm 0.00023(syst.) and \delta =
0.75049\pm 0.00021(stat.)\pm 0.00027(syst.). These are consistent with the
value of 3/4 given for both parameters in the standard model, and each is over
a factor of 10 more precise than the measurements published prior to TWIST. Our
final results on \rho, \delta, and P_\mu\xi have been incorporated into a new
global analysis of all available muon decay data, resulting in improved
model-independent constraints on the possible weak interactions of right-handed
particles.Comment: 19 pages, 10 figure
Measurement of the Michel Parameter in Muon Decay
The TWIST Collaboration has measured the Michel parameter in normal
muon decay, . In the Standard Model,
= 3/4. Deviations from this value require mixing of left- and
right-handed muon and electron couplings in the muon-decay Lagrangian. We find
= 0.75080 0.00044(stat.) 0.00093(syst.) 0.00023, where
the last uncertainty represents the dependence of on the Michel
parameter . This result sets new limits on the mixing angle in
left-right symmetric models.Comment: 4 pages, 3 figures, submitted to PR
Measurement of P_{mu}xi in Polarized Muon Decay
The quantity P_{mu}^{pi}xi, where xi is one of the muon decay parameters and
is the degree of muon polarization in pion decay, has been
measured. The value P_{mu}^{pi}xi = 1.0003 +- 0.0006 stat. +- 0.0038 syst. was
obtained. This result agrees with previous measurements but is over a factor of
two more precise. It also agrees with the Standard Model prediction for
P_{mu}^{pi}xi and thus leads to restrictions on left-right symmetric models.Comment: 11 pages, 7 figures, Phys. Rev. D 74, 072007 (2006) Final versio
Time projection chambers for the T2K near detectors
The T2K experiment is designed to study neutrino oscillation properties by directing a high intensity neutrino beam produced at J-PARC in Tokai, Japan, towards the large Super-Kamiokande detector located 295 km away, in Kamioka, Japan. The experiment includes a sophisticated near detector complex, 280 m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to better understand neutrino interactions at the energy scale below a few GeV. A key element of the near detectors is the ND280 tracker, consisting of two active scintillator-bar target systems surrounded by three large time projection chambers (TPCs) for charged particle tracking. The data collected with the tracker is used to study charged current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. The tracker is surrounded by the former UA1/Nomad dipole magnet and the TPCs measure the charges, momenta, and particle types of charged particles passing through them. Novel features of the TPC design include its rectangular box layout constructed from composite panels, the use of bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and a photoelectron calibration system. This paper describes the design and construction of the TPCs, the micromegas modules, the readout electronics, the gas handling system, and shows the performance of the TPCs as deduced from measurements with particle beams, cosmic rays, and the calibration system
Precise measurement of parity violation in polarized muon decay
We present a new high precision measurement of parity violation in the weak
interaction, using polarized muon decay. The TWIST collaboration has measured
, where is the polarization of the muon in pion
decay and describes the intrinsic asymmetry in muon decay. We find
, in good
agreement with the standard model prediction of . Our result
is a factor of 7 more precise than the pre-TWIST value, setting new limits in
left-right symmetric electroweak extensions to the standard model.Comment: 18 pages, 12 figures, published in Phys. Rev.