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R. E. Mischke

Publications and source records attributed to R. E. Mischke.

At least 19 recordsLinked to original sources
arXiv2024

Measurement of the response function of the PIENU calorimeter

Measurements of the response function of the PIENU NaI(T$\ell$) and CsI crystal calorimeter using a monochromatic 70 MeV/c positron beam at various incidence angles are described. The experimental setup and relevant physical processes involved were simulated using Geant4 to reproduce positron energy spectra. Monte Carlo simulations were compared with experimental data across ten calorimeter-beam angles and showed good agreement. This allowed the validation of simulation parameters that were essential for precise measurements of pion decays.

hep-ex↗
arXiv2021

Search for three body pion decays $π^+{\to}l^+νX$

The three body pion decays $π^+{\rightarrow}l^+νX~(l=e,μ)$, where $X$ is a weakly interacting neutral boson, were searched for using the full data set from the PIENU experiment. An improved limit on $Γ(π^+{\to}e^+νX)/Γ(π^+{\to}μ^+ν_μ)$ in the mass range $0<m_X<120$ MeV/$c^2$ and a first result for $Γ(π^+{\to}μ^+νX)/Γ(π^+{\to}μ^+ν_μ)$ in the region $0<m_X<33.9$ MeV/$c^2$ were obtained. The Majoron-neutrino coupling model was also constrained using the current experimental result of the $π^+{\to}e^+ν_e(γ)$ branching ratio.

hep-ex↗
arXiv2020

Search for the rare decays $π^+ \to μ^+ν_μν\barν$ and $π^+ \to e^+ν_eν\barν$

The rare pion decays $π^+{\rightarrow}μ^+ν_μν\barν$ and $π^+{\rightarrow}e^+ν_{e}ν\barν$ are allowed in the Standard Model but highly suppressed. These decays were searched for using data from the PIENU experiment. A first result for $Γ(π^+{\rightarrow}μ^+ν_μν\barν)/Γ(π^+{\rightarrow}μ^+ν_μ)<8.6{\times}10^{-6}$, and an improved measurement $Γ(π^+{\rightarrow}{e}^+ν_{e}ν\barν)/Γ(π^+{\rightarrow}μ^+ν_μ)<1.6{\times}10^{-7}$ were obtained.

hep-ex↗
arXiv2020

Improved search for two body muon decay $μ^+{\rightarrow}e^+X_H$

Charged lepton flavor violating muon decay $μ^+{\rightarrow}e^+X_H$, where $X_H$ is a massive neutral boson, was sought by searching for extra peaks in the muon decay $μ^+{\rightarrow}e^+ν\barν$ energy spectrum in the $m_{X_H}$ mass region $47.8-95.1$ MeV/$c^2$. No signal was found and 90% confidence level upper limits were set on the branching ratio $Γ(μ^+{\rightarrow}e^+X_H)/Γ(μ^+{\rightarrow}e^+ν\barν)$ at the level of $10^{-5}$ for this region.

hep-ex↗
arXiv2019

Charged particle spectra from $μ^{-}$ capture on Al

Published data on the emission of charged particles following nuclear muon capture are extremely limited. In addition to its interest as a probe of the nuclear response, these data are important for the design of some current searches for lepton flavor violation. This work presents momentum spectra of protons and deuterons following $μ^{-}$ capture in aluminum. It is the first measurement of a muon capture process performed with a tracking spectrometer. A precision of better than 10% over the momentum range of 100--190 MeV/c for protons is obtained; for deuterons of 145--250 MeV/c the precision is better than 20%. The observed partial yield of protons with emission momenta above 80 MeV/c (kinetic energy 3.4 MeV) is $0.0322\pm0.0007(\text{stat})\pm0.0022(\text{syst})$ per capture, and for deuterons above 130 MeV/c (4.5 MeV) it is $0.0122\pm0.0009(\text{stat})\pm0.0006(\text{syst})$. Extrapolating to total yields gives $0.045\pm0.001(\text{stat})\pm0.003(\text{syst}) \pm 0.001(\text{extrapolation})$ per capture for protons and $0.018\pm0.001(\text{stat})\pm0.001(\text{syst})\pm 0.002(\text{extrapolation})$ for deuterons, which are the most precise measurements of these quantities to date.

hep-ex↗
arXiv2019

Search for Heavy Neutrinos in $π\to μν$ Decay

Heavy neutrinos were sought in pion decays $π^+ \rightarrow μ^+ ν$ by examining the observed muon energy spectrum for extra peaks in addition to the expected peak for a massless neutrino. No evidence for heavy neutrinos was observed. Upper limits were set on the neutrino mixing matrix $|U_{μi}|^2$ in the neutrino mass region of 15.7--33.8 MeV/c$^2$, improving on previous results by an order of magnitude.

hep-ex↗
arXiv2018

Improved Search for Heavy Neutrinos in the Decay $π\rightarrow eν$

A search for massive neutrinos has been made in the decay $π\rightarrow e^+ ν$. No evidence was found for extra peaks in the positron energy spectrum indicative of pion decays involving massive neutrinos ($π\rightarrow e^+ ν_h$). Upper limits (90 \% C.L.) on the neutrino mixing matrix element $|U_{ei}|^2$ in the neutrino mass region 60--135 MeV/$c^2$ were set, which are %representing an order of magnitude improvement over previous results.

hep-ex↗
arXiv2015

Status of the TRIUMF PIENU Experiment

The PIENU experiment at TRIUMF aims to measure the pion decay branching ratio $R=Γ(π^+{\rightarrow}e^+ν_e(γ))/Γ(π^+{\rightarrow}μ^+ν_μ(γ))$ with precision $<0.1$% to provide a sensitive test of electron-muon universality in weak interactions. The current status of the PIENU experiment is presented.

physics.ins-det↗
arXiv2015

Improved measurement of the $π\rightarrow \mbox{e} ν$ branching ratio

A new measurement of the branching ratio, $R_{e/μ} =Γ(π^+ \rightarrow \mbox{e}^+ ν+ π^+ \rightarrow \mbox{e}^+ νγ)/ Γ(π^+ \rightarrow μ^+ ν+ π^+ \rightarrow μ^+ νγ)$, resulted in $R_{e/μ}^{exp} = (1.2344 \pm 0.0023 (stat) \pm 0.0019 (syst)) \times 10^{-4}$. This is in agreement with the standard model prediction and improves the test of electron-muon universality to the level of 0.1 %.

hep-ex↗
arXiv2015

Detector for measuring the $π^+\to e^+ν_e$ branching fraction

The PIENU experiment at TRIUMF is aimed at a measurement of the branching ratio $R^{e/μ}$ = ${Γ\big((π^{+} \rightarrow e^{+} ν_{e}) + (π^{+} \rightarrow e^{+} ν_{e}γ)\big)}/{Γ\big((π^{+} \rightarrow μ^{+} ν_μ)+(π^{+} \rightarrow μ^{+} ν_μγ)\big)}$ with precision $<$0.1\%. Incident pions, delivered at the rate of 60 kHz with momentum 75 MeV/c, were degraded and stopped in a plastic scintillator target. Pions and their decay product positrons were detected with plastic scintillators and tracked with multiwire proportional chambers and silicon strip detectors. The energies of the positrons were measured in a spectrometer consisting of a large NaI(T$\ell$) crystal surrounded by an array of pure CsI crystals. This paper provides a description of the PIENU experimental apparatus and its performance in pursuit of $R^{e/μ}$.

physics.ins-det↗
arXiv2015

A search for two body muon decay signals

Lepton family number violation is tested by searching for $μ^+\to e^+X^0$ decays among the 5.8$\times 10^8$ positive muon decay events analyzed by the TWIST collaboration. Limits are set on the production of both massless and massive $X^0$ bosons. The large angular acceptance of this experiment allows limits to be placed on anisotropic $μ^+\to e^+X^0$ decays, which can arise from interactions violating both lepton flavor and parity conservation. Branching ratio limits of order $10^{-5}$ are obtained for bosons with masses of 13 - 80 MeV/c$^2$ and with different decay asymmetries. For bosons with masses less than 13 MeV/c$^{2}$ the asymmetry dependence is much stronger and the 90% limit on the branching ratio varies up to $5.8 \times 10^{-5}$. This is the first study that explicitly evaluates the limits for anisotropic two body muon decays.

hep-ex↗
arXiv2012

Precision muon decay measurements and improved constraints on the weak interaction

The TWIST Collaboration has completed its measurement of the three muon decay parameters ρ, δ, and P_μξ. 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=0.74977\pm 0.00012(stat.)\pm 0.00023(syst.) and δ= 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 ρ, δ, and P_μξhave 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.

hep-ex↗
arXiv2011

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 $P_μ^πξ$, where $P_μ^π$ is the polarization of the muon in pion decay and $ξ$ describes the intrinsic asymmetry in muon decay. We find $P_μ^πξ= 1.00084 \pm 0.00029\,(\textrm{stat.})_{-0.00063}^{+0.00165}\,(\textrm{syst.})$, in good agreement with the standard model prediction of $P_μ^π=ξ=1$. 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.

hep-ex↗
arXiv2011

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 $λ_{\textrm{Al}} = 1.3 \pm 0.2\,(\textrm{stat.}) \pm 0.3\,(\textrm{syst.})\,\pms$ and $λ_{\textrm{Ag}} = 1.0 \pm 0.2\,(\textrm{stat.}) \pm 0.2\,(\textrm{syst.})\,\pms$.

cond-mat.mtrl-sci↗
arXiv2010

New Experimental Constraints for the Standard Model from Muon Decay

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)ξ tests the Standard Model (SM) in a purely leptonic process and provides improved limits for relevant extensions to the SM. 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.

hep-ex↗
arXiv2010

Blind analysis results of the TWIST experiment

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, $ρ$, $δ$ and $P_μ^π ξ$, 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.

hep-ex↗
arXiv2009

Decay of negative muons bound in $^{27}$Al

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.

hep-ex↗