J. Imazato

Flavor physics of leptons and dipole moments

This chapter of the report of the “Flavor in the era of the LHC” Workshop discusses the theoretical, phenomenological and experimental issues related to flavor phenomena in the charged lepton sector and in flavor conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavor structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the standard model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments.

Muon spin resonance by strong pulsed r.f. field with pulsed muons

Muon spin resonance experiments have been performed for the μ+ in H2O and for some other cases, and the first observation has been made of the time-differential pattern of muon spin resonance, namely, spin precession around the r.f. field vector under various resonance conditions. In the present experiment, a high-power pulsed r.f. field was effectively applied to the pulsed muon beam in our laboratory of the KEK-Booster Meson Facility (BOOM). Potential uses of muon spin resonance, particularly for research in the border regions of solid state and nuclear physics, are discussed in comparison with the conventional spin rotation method.

Scintillation ring hodoscope with WLS fiber readout

Abstract A simple tracking system for measuring the K+ decay vertex along the beam axis in the T-Violation Experiment (E246) at KEK is described. It consists of 32 grooved BC408 plastic scintillator rings with embedded Y11 wavelength-shifting (WLS) optical fibers. Both ends of each multi-clad WLS fiber are directly viewed by a green-extended photomultiplier. Light yield of 46 photoelectrons per minimum ionizing particle in the 5 mm thick ring has been achieved. This configuration gives 1.7 mm position resolution determined purely by the 6 mm width of each ring. Time resolution of 1.0 ns and detection efficiency of 98.4% were obtained.

Apparatus for a search for T-violating muon polarization in stopped-kaon decays

Abstract The detector built at KEK to search for T-violating transverse muon polarization in K + → π 0 μ + ν μ ( K μ 3 ) decay of stopped kaons is described. Sensitivity to the transverse polarization component is obtained from reconstruction of the decay plane by tracking the μ+ through a toroidal spectrometer and detecting the π0 in a segmented CsI(Tl) photon calorimeter. The muon polarization was obtained from the decay positron asymmetry of muons stopped in a polarimeter. The detector included features which minimized systematic errors while maintaining high acceptance.

μ+ diffusion in copper studied by zero field μSR

Diffusion of muons in high purity Cu was studied by the zero-fieldμSR method at temperatures from 134 K down to 0.09 K. The experimental data show clear evidence that the muons still diffuse below 15 K; the measured diffusion rate has a minimum at around 15 K and seems to become independent of temperature below about 0.5 K.

Precise measurement of low temperature diffusion of positive muons in Cu: Evidence for the effect of muon-electron interaction in metals

Abstract The diffusion rate of positive muons in high purity Cu was measured by means of the zero field muon spin relaxation method for temperatures from 69 mK to 135 K. We found that with decreasing temperature the rate reaches a minimum at around 20 K and increases down to 0.5 K, where it clearly levels off. The origin of the observed temperature dependence is discussed in the light of recently developed theories taking into account the μ + -conduction electron interaction in metals, where the basic coupling constant K is determined to be 0.32.

Non-secular part of nuclear dipolar broadening detected by zero-field spin relaxation of positive muon

Abstract The zero-field spin relaxation function of μ+ observed in ZrH2 has revealed that the second moment of the nuclear dipolar broadening is five times larger than the high-field value. This experiment clearly demonstrates the recovery of the non-secular part of dipolar interaction between unlike spins. A general expression of zero-field relaxation function is presented to account for a slow modulation of random fields on μ+ found at room temperature.

Measurement of Γ(Kμ3)/Γ(Ke3) ratio using stopped positive kaons

Abstract The ratio of the K + → π 0 μ + ν ( K μ 3 + ) and K + → π 0 e + ν ( K e 3 + ) decay widths, Γ ( K μ 3 )/ Γ ( K e 3 ), has been measured with stopped positive kaons. K μ 3 + and K e 3 + samples containing 2.4×10 4 and 4.0×10 4 events, respectively, were analyzed. The Γ ( K μ 3 )/ Γ ( K e 3 ) ratio was obtained to be 0.671±0.007(stat.)±0.008(syst.) calculating the detector acceptance by a Monte Carlo simulation. The coefficient of the q 2 dependent term of the f 0 form factor was also determined to be λ 0 =0.019±0.005(stat.)±0.004(syst.) with the assumption of μ – e universality in K l 3 + decay. The agreement of our result with the λ 0 value obtained from K μ 3 + Dalitz plot analyses supports the validity of the μ – e universality.

Long-lived muonium in water revealed by pulsed muons

Abstract The relaxation rate of muonium in pure water has been found to be smaller than 0.05 × 10 6 s −1 . With the aid of pulsed muong. μSR and MuSR measurements have been carried out over a longer time range than ever achieved. The results indicate a stability of thermal muonium in water from 3 to 29°C.

Development of 500 MHz muon spin resonance spectrometer

The 500 MHz muon resonance was newly developed. The system was constructed with 500MHz resonance cavity, pulsed high power RF-source and the superconducting helmholz coil. This system provide the oppotunity to achieve the diamagnetic muon spectroscopy at 37KG and 500MHz. Also muonic radical resonance and muonium resonance at magnetic field corresponding to the 500MHz resonance frequency. Some preliminary but important result was also reported.