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A. Hillairet,
R. Bayes,
J. F. Bueno,
Yu. I. Davydov,
P. Depommier,
W. Faszer,
C. A. Gagliardi,
A. Gaponenko,
D. R. Gill,
A. Grossheim, [......],
A. Olin,
R. Openshaw,
J.-M. Poutissou,
R. Poutissou,
V. Selivanov,
G. Sheffer,
B. Shin,
T. D. S. Stanislaus,
R. Tacik,
R. E. Tribble
[show abstract]
[hide abstract]
ABSTRACT: The TWIST Collaboration has completed its measurement of the three muon decay parameters ρ, δ, and Pμξ. This paper describes our determination of ρ, which governs the shape of the overall momentum spectrum, and δ, which controls the momentum dependence of the parity-violating decay asymmetry. The results are ρ=0.749 77±0.000 12(stat)±0.000 23(syst) and δ=0.750 49±0.000 21(stat)±0.000 27(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 ρ, δ, and Pμξ 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.
Phys. Rev. D. 12/2011; 85(9).
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TWIST Collaboration,
J. F. Bueno,
R. Bayes,
Yu. I. Davydov,
P Depommier,
W. Faszer,
C. A. Gagliardi,
A. Gaponenko,
D. R. Gill,
A Grossheim, [......],
A. Olin,
R. Openshaw,
J. -M. Poutissou,
R. Poutissou,
V. Selivanov,
G. Sheffer,
B. Shin,
T. D. S. Stanislaus,
R. Tacik,
R. E. Tribble
[show abstract]
[hide abstract]
ABSTRACT: We present a new high precision measurement of parity violation in the weak
interaction, using polarized muon decay. The TWIST collaboration has measured
$P_\mu^\pi \xi$, where $P_\mu^\pi$ is the polarization of the muon in pion
decay and $\xi$ describes the intrinsic asymmetry in muon decay. We find
$P_\mu^\pi \xi = 1.00084 \pm
0.00029\,(\textrm{stat.})_{-0.00063}^{+0.00165}\,(\textrm{syst.})$, in good
agreement with the standard model prediction of $P_\mu^\pi=\xi=1$. 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.
04/2011;
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J. F. Bueno,
D. J. Arseneau,
R. Bayes,
J. H. Brewer,
W. Faszer, M. D. Hasinoff,
G. M. Marshall,
E. L. Mathie,
R. E. Mischke,
G. D. Morris,
K. Olchanski,
V. Selivanov,
R. Tacik
[show abstract]
[hide abstract]
ABSTRACT: 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 the time-differential muon spin relaxation technique. For times greater than 10 ns, the shape fits well to a single exponential with relaxation rates of λAl=1.3±0.2 (stat.)±0.3 (syst.) ms-1 and λAg=1.0±0.2 (stat.)±0.2 (syst.) ms-1.
Phys. Rev. B. 02/2011; 83(20).
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R Bayes,
J F Bueno,
A Hillairet,
Yu I Davydov,
P Depommier,
W Faszer,
C A Gagliardi,
A Gaponenko,
D R Gill,
A Grossheim, [......],
A Olin,
R Openshaw,
J-M Poutissou,
R Poutissou,
V Selivanov,
G Sheffer,
B Shin,
T D S Stanislaus,
R Tacik,
R E Tribble
[show abstract]
[hide abstract]
ABSTRACT: The TWIST Collaboration has completed a new measurement of the energy-angle spectrum of positrons from the decay of highly polarized muons. A simultaneous measurement of the muon decay parameters ρ, δ, and P(μ)(π)ξ tests the standard model in a purely leptonic process and provides improved limits for relevant extensions to the standard model. Specifically, for the generalized left-right symmetric model |(g(R)/g(L))ζ|<0.020 and (g(L)/g(R))m(2)>578 GeV/c(2), both 90% C.L.
Physical Review Letters 01/2011; 106(4):041804. · 7.37 Impact Factor
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R. Bayes,
J. F. Bueno,
A. Hillairet,
Yu. I. Davydov,
P Depommier,
W. Faszer,
C. A. Gagliardi,
A. Gaponenko,
D. R. Gill,
A Grossheim, [......],
A. Olin,
R. Openshaw,
J. -M. Poutissou,
R. Poutissou,
V. Selivanov,
G. Sheffer,
B. Shin,
T. D. S. Stanislaus,
R. Tacik,
R. E. Tribble
[show abstract]
[hide abstract]
ABSTRACT: The TWIST Collaboration has completed a new measurement of the energy-angle spectrum of positrons from the decay of highly polarized muons. A simultaneous measurement of the muon decay parameters {\rho}, {\delta}, and (P_{\mu}){\xi} tests the Standard Model (SM) in a purely leptonic process and provides improved limits for relevant extensions to the SM. Specifically, these results set significant new limits on the heavy $W$ mass and the mixing angle in a class of left-right symmetric models.
10/2010;
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A. Hillairet,
R. Bayes,
J. F. Bueno,
Y. I. Davydov,
P Depommier,
W. Faszer,
M C Fujiwara,
C. A. Gagliardi,
A. Gaponenko,
A Grossheim, [......],
A. Olin,
R. Openshaw,
J. -M. Poutissou,
R. Poutissou,
V. Selivanov,
G. Sheffer,
B. Shin,
T. D. S. Stanislaus,
R. Tacik,
R. E. Tribble
[show abstract]
[hide abstract]
ABSTRACT: The TRIUMF Weak Interaction Symmetry Test (TWIST) experiment was designed to test the standard model at high precision in the purely leptonic decay of polarized muons. A general four-fermion interaction model is used to describe the muon decay. TWIST measures three of the four muon decay parameters of this model, $\rho$, $\delta$ and $P_{\mu}^{\pi} \xi$, from the shape of the momentum-angle spectrum. The results of this model independent approach are compared to the standard model predictions and used to constrain new physics. Our collaboration has finalized the blind analysis of the final experimental data taken in 2006 and 2007. This analysis mostly reached our goal of a precision of an order of magnitude improvement over the pre-TWIST measurements. Comment: 6 pages, 3 figures, proceedings for the Lake Louise Winter Institute 2010
06/2010;
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A Grossheim,
R. Bayes,
J. F. Bueno,
P Depommier,
W. Faszer,
M C Fujiwara,
C. A. Gagliardi,
D. R. Gill,
P. Gumplinger, M. D. Hasinoff, [......],
A. Olin,
R. Openshaw,
J. -M. Poutissou,
R. Poutissou,
V. Selivanov,
G. Sheffer,
B. Shin,
T. D. S. Stanislaus,
R. Tacik,
R. E. Tribble
[show abstract]
[hide abstract]
ABSTRACT: We present the first measurement of the energy spectrum up to 70 MeV of electrons from the decay of negative muons after they become bound in $^{27}$Al atoms. The data were taken with the TWIST apparatus at TRIUMF. We find a muon lifetime of (864.6 $\pm$ 1.2) ns, in agreement with earlier measurements. The asymmetry of the decay spectrum is consistent with zero, indicating that the atomic capture has completely depolarised the muons. The measured momentum spectrum is in reasonable agreement with theoretical predictions at the higher energies, but differences around the peak of the spectrum indicate the need for \oalpha radiative corrections to the calculations. The present measurement is the most precise measurement of the decay spectrum of muons bound to any nucleus.
08/2009;
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[show abstract]
[hide abstract]
ABSTRACT: We report measurements of the pi;{-}p-->pi;{0}n differential cross sections at six momenta (104-143 MeV/c) and four angles (0 degrees -40 degrees ) by detection of gamma-ray pairs from pi;{0}-->gammagamma decays using a photon-pair spectrometer at TRIUMF. This kinematic region exhibits a vanishing zero-degree cross section from destructive interference between s and p waves, thus yielding special sensitivity to pion-nucleon dynamics. Our data and previous data do not agree, with important implications for earlier claims of large isospin-violating effects.
Physical Review Letters 09/2008; 101(10):102301. · 7.37 Impact Factor
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TWIST Collaboration: R. P. MacDonald,
R. Bayes,
J. Bueno,
Yu. I. Davydov,
P Depommier,
W. Faszer,
M C Fujiwara,
C. A. Gagliardi,
A. Gaponenko,
D. R. Gill, [......],
R. Openshaw,
J. -M. Poutissou,
R. Poutissou,
M. A. Quraan,
V. Selivanov,
G. Sheffer,
B. Shin,
T. D. S. Stanislaus,
R. Tacik,
R. E. Tribble
[show abstract]
[hide abstract]
ABSTRACT: The TWIST collaboration has performed new measurements of two of the parameters that describe muon decay: $\rho$, which governs the shape of the overall momentum spectrum, and $\delta$, which governs the momentum dependence of the parity-violating decay asymmetry. This analysis gives the results $\rho=0.75014\pm 0.00017(\text{stat})\pm 0.00044(\text{syst})\pm 0.00011(\eta)$, where the last uncertainty arises from the correlation between $\rho$ and the decay parameter $\eta$, and $\delta = 0.75067\pm 0.00030(\text{stat})\pm 0.00067(\text{syst})$. These are consistent with the value of 3/4 given for both parameters in the Standard Model of particle physics, and are a factor of two more precise than the measurements previously published by TWIST. A new global analysis of all available muon decay data incorporating these results is presented. Improved lower and upper limits on the decay parameter $P_\mu^\pi\xi$ of $0.99524 < P_\mu^\pi\xi \leq \xi < 1.00091$ at 90% confidence are determined, where $P_\mu^\pi$ is the polarization of the muon when it is created during pion decay, and $\xi$ governs the muon decay asymmetry. These results set new model-independent constraints on the possible weak interactions of right-handed particles. Specific implications for left-right symmetric models are discussed.
08/2008;
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[show abstract]
[hide abstract]
ABSTRACT: We report measurements of the $\pi^- p \to \pi^o n$ differential cross sections at six momenta (104-143 MeV/c) and four angles (0-40 deg) by detection of $\gamma$-ray pairs from $\pi^o \to \gamma \gamma$ decays using the TRIUMF RMC spectrometer. This region exhibits a vanishing zero-degree cross section from destructive interference between s-- and p--waves, thus yielding special sensitivity to pion-nucleon dynamics and isospin symmetry breaking. Our data and previous data do not agree, with important implications for earlier claims of large isospin violating effects in low energy pion-nucleon interactions.
05/2008;
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[show abstract]
[hide abstract]
ABSTRACT: We report measurements of double radiative capture in pionic hydrogen and pionic deuterium. The measurements were performed with the RMC spectrometer at the TRIUMF cyclotron by recording photon pairs from pion stops in liquid hydrogen and deuterium targets. We obtained absolute branching ratios of $(3.02 \pm 0.27 (stat.) \pm 0.31 (syst.)) \times 10^{-5}$ for hydrogen and $(1.42 \pm ^{0.09}_{0.12} (stat.) \pm 0.11 (syst.)) \times 10^{-5}$ for deuterium, and relative branching ratios of double radiative capture to single radiative capture of $(7.68 \pm 0.69(stat.) \pm 0.79(syst.)) \times 10^{-5}$ for hydrogen and $(5.44 \pm^{0.34}_{0.46}(stat.) \pm 0.42(syst.)) \times 10^{-5}$ for deuterium. For hydrogen, the measured branching ratio and photon energy-angle distributions are in fair agreement with a reaction mechanism involving the annihilation of the incident $\pi^-$ on the $\pi^+$ cloud of the target proton. For deuterium, the measured branching ratio and energy-angle distributions are qualitatively consistent with simple arguments for the expected role of the spectator neutron. A comparison between our hydrogen and deuterium data and earlier beryllium and carbon data reveals substantial changes in the relative branching ratios and the energy-angle distributions and is in agreement with the expected evolution of the reaction dynamics from an annihilation process in S-state capture to a bremsstrahlung process in P-state capture. Lastly, we comment on the relevance of the double radiative process to the investigation of the charged pion polarizability and the in-medium pion field.
02/2007;
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TWIST Collaboration,
B. Jamieson,
R. Bayes,
Yu. I. Davydov,
P Depommier,
J. Doornbos,
W. Faszer,
M C Fujiwara,
C. A. Gagliardi,
A. Gaponenko, [......],
M. A. Quraan,
N L Rodning,
V. Selivanov,
G. Sheffer,
B. Shin,
T. D. S. Stanislaus,
R. Tacik,
V. D. Torokhov,
R. E. Tribble,
M. A. Vasiliev
[show abstract]
[hide abstract]
ABSTRACT: The quantity P_{mu}^{pi}xi, where xi is one of the muon decay parameters and $P_{\mu}^{\pi}$ 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 version
05/2006;
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[show abstract]
[hide abstract]
ABSTRACT: We report a measurement of the ortho-para transition rate in the p mu p molecule. The experiment was conducted at TRIUMF via the measurement of the time dependence of the 5.2 MeV neutrons from muon capture in liquid hydrogen. The measurement yielded an ortho-para rate Lambda op = (11.1 +/- 1.7 +/-(0.9)(0.6)) x 10(4) s(-1), which is substantially larger than the earlier result of Bardin et al. The result has striking implications for the proton's induced pseudoscalar coupling g(p), changing the value of g(p) obtained from the most precise ordinary muon capture measurement from 10.6 +/- 2.7 to 0.8 +/- 2.8, and from the sole radiative muon capture measurement from 12.2 +/- 1.1 to 10.6 +/- 1.2, bringing the latter result closer to theoretical predictions.
Physical Review Letters 03/2006; 96(7):073401. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We report a measurement of the ortho-para transition rate in the p$\mu$p molecule. The experiment was conducted at TRIUMF via the measurement of the time dependence of the 5.2 MeV neutrons from muon capture in liquid hydrogen. The measurement yielded an ortho-para rate $\Lambda_{op} = (11.1 \pm 1.7 \pm^{0.9}_{0.6}) \times 10^4$ s$^{-1}$ that is substantially larger than the earlier result of Bardin {\it et al.} We discuss the striking implications for the proton's induced pseudoscalar coupling $g_p$. Comment: 4 pages, 3 figures, submitted to Phys. Rev. Lett
09/2005;
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J R Musser,
R Bayes,
Yu I Davydov,
P Depommier,
J Doornbos,
W Faszer,
C A Gagliardi,
A Gaponenko,
D R Gill,
P Green, [......],
V Selivanov,
G Sheffer,
B Shin,
F Sobratee,
T D S Stanislaus,
R Tacik,
V D Torokhov,
R E Tribble,
M A Vasiliev,
D H Wright
[show abstract]
[hide abstract]
ABSTRACT: The TWIST Collaboration has measured the Michel parameter rho in normal muon decay, mu(+)--> e(+)nu(e)nu (mu). In the standard model, rho = 3/4. Deviations from this value imply mixing of left- and right-handed muon and electron couplings. We find rho=0.750 80+/-0.000 32(stat) +/- 0.000 97(syst) +/- 0.000 23, where the last uncertainty represents the dependence of rho on the Michel parameter eta. This result sets new limits on the W(L)-W(R) mixing angle in left-right symmetric models.
Physical Review Letters 03/2005; 94(10):101805. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We report a search for low-lying exotic baryons via double radiative capture on pionic hydrogen. The data were collected at the TRIUMF cyclotron using the RMC spectrometer by detecting gamma-ray pairs from pion stops in liquid hydrogen. No evidence was found to support an earlier claim for exotic baryons of masses 1004 and 1044 MeV/$c^2$. We obtain upper limits on the branching ratios for double radiative capture via these exotic states of $< 3 \times 10^{-6}$ and $< 4 \times 10^{-6}$ respectively. Comment: 13 pages, 4 figures
03/2004;
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[show abstract]
[hide abstract]
ABSTRACT: We report measurements of γ-ray spectra from muon capture on 35Cl. For the allowed Gamow-Teller transitions to the 35S(2939,3/2+) state and the 35S(3421,5/2+) state we obtained their capture rates, hyperfine dependences, and γ–ν correlation coefficients. The capture rates and hyperfine dependences were compared to shell model calculations using the complete 1s–0d space and the universal SD interaction. With gp/ga=6.7 and ga=-1.00 (or ga=-1.26) we found agreement of the model and the data at the 1–2 σ level. However, we caution that the transitions are sensitive to l=2 forbidden matrix elements.
Phys. Rev. C. 12/2002; 66(6).
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[show abstract]
[hide abstract]
ABSTRACT: We report the first observation of double radiative capture on pionic hydrogen. The experiment was conducted at the TRIUMF cyclotron using the RMC spectrometer and detected gamma-ray coincidences following pi(-) stops in liquid hydrogen. We found the branching ratio for double radiative capture to be [3.05+/-0.27(stat)+/-0.31(syst)]x10(-5). The measured branching ratio and angle-energy distributions support the theoretical prediction of a dominant contribution from the pipi-->gammagamma annihilation mechanism.
Physical Review Letters 12/2002; 89(25):252501. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We report a search for d^* dibaryon production by double-radiative capture on pionic deuterium. The experiment was conducted at the TRIUMF cyclotron using the RMC cylindrical pair spectrometer, and detected gamma-ray coincidences following pion stops in liquid deuterium. We found no evidence for narrow dibaryons, and obtained a branching ratio upper limit, BR < 6.7 times 10^{-6} (90% C.L.), for narrow d^* production in the mass range from 1920 to 1980 MeV. Replaced with Physics Letter B accepted version and corrected normalization. Comment: 9 pages, 4 figures
07/2002;
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[show abstract]
[hide abstract]
ABSTRACT: We report measurements of $\gamma$--ray spectra from muon capture on $^{35}$Cl. For the allowed Gamow--Teller transitions to the $^{35}$S$(2939, 3/2^+)$ state and the $^{35}$S$(3421, 5/2^+)$ state we obtained their capture rates, hyperfine dependences and $\gamma$--$\nu$ correlation coefficients. The capture rates and hyperfine dependences were compared to shell model calculations using the complete 1s--0d space and the universal SD interaction. With $g_p / g_a = 6.7$ and $g_a = -1.00$ (or $g_a = -1.26$) we found agreement of the model and the data at the 1--2 $\sigma$ level. However, we caution that the transitions are sensitive to $\ell = 2$ forbidden matrix elements. Comment: 29 pages, 9 figures, submitted to Phys. Rev. C
04/2002;
