Lepton family number violation is tested by searching for $mu^+to e^+X^0$ 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 $mu^+to e^+X^0$ 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.
The design, construction and testing of neutrino detector prototypes at CERN are ongoing activities. This document reports on the design of solid state baby MIND and TASD detector prototypes and outlines requirements for a test beam at CERN to test t
hese, tentatively planned on the H8 beamline in the North Area, which is equipped with a large aperture magnet. The current proposal is submitted to be considered in light of the recently approved projects related to neutrino activities with the SPS in the North Area in the medium term 2015-2020.
A neutrino factory has unparalleled physics reach for the discovery and measurement of CP violation in the neutrino sector. A far detector for a neutrino factory must have good charge identification with excellent background rejection and a large mas
s. An elegant solution is to construct a magnetized iron neutrino detector (MIND) along the lines of MINOS, where iron plates provide a toroidal magnetic field and scintillator planes provide 3D space points. In this report, the current status of a simulation of a toroidal MIND for a neutrino factory is discussed in light of the recent measurements of large $theta_{13}$. The response and performance using the 10 GeV neutrino factory configuration are presented. It is shown that this setup has equivalent $delta_{CP}$ reach to a MIND with a dipole field and is sensitive to the discovery of CP violation over 85% of the values of $delta_{CP}$.
This paper describes the performance and sensitivity to neutrino mixing parameters of a Magnetised Iron Neutrino Detector (MIND) at a Neutrino Factory with a neutrino beam created from the decay of 10 GeV muons. Specifically, it is concerned with the
ability of such a detector to detect muons of the opposite sign to those stored (wrong-sign muons) while suppressing contamination of the signal from the interactions of other neutrino species in the beam. A new more realistic simulation and analysis, which improves the efficiency of this detector at low energies, has been developed using the GENIE neutrino event generator and the GEANT4 simulation toolkit. Low energy neutrino events down to 1 GeV were selected, while reducing backgrounds to the $10^{-4}$ level. Signal efficiency plateaus of ~60% for $ u_mu$ and ~70% for $bar{ u}_mu$ events were achieved starting at ~5 GeV. Contamination from the $ u_murightarrow u_tau$ oscillation channel was studied for the first time and was found to be at the level between 1% and 4%. Full response matrices are supplied for all the signal and background channels from 1 GeV to 10 GeV. The sensitivity of an experiment involving a MIND detector of 100 ktonnes at 2000 km from the Neutrino Factory is calculated for the case of $sin^2 2theta_{13}sim 10^{-1}$. For this value of $theta_{13}$, the accuracy in the measurement of the CP violating phase is estimated to be $Delta delta_{CP}sim 3^circ - 5^circ$, depending on the value of $delta_{CP}$, the CP coverage at $5sigma$ is 85% and the mass hierarchy would be determined with better than $5sigma$ level for all values of $delta_{CP}$.
The TWIST Collaboration has completed its measurement of the three muon decay parameters rho, delta, and P_muxi. This paper describes our determination of rho, which governs the shape of the overall momentum spectrum, and delta, which controls the mo
mentum dependence of the parity-violating decay asymmetry. The results are rho=0.74977pm 0.00012(stat.)pm 0.00023(syst.) and delta = 0.75049pm 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_muxi 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.
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 t
he 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.
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 si
ngle exponential with relaxation rates of $lambda_{textrm{Al}} = 1.3 pm 0.2,(textrm{stat.}) pm 0.3,(textrm{syst.}),pms$ and $lambda_{textrm{Ag}} = 1.0 pm 0.2,(textrm{stat.}) pm 0.2,(textrm{syst.}),pms$.
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 Mo
del (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){zeta}|<0.020 and (g_L/g_R)m_2> 578 GeV/c^2, both 90% C.L.
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.
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.
