Y. Kuno

Muon decay and physics beyond the standard model

This article reviews the current theoretical and experimental status of the field of muon decay and its potential to search for new physics beyond the standard model. The importance of rare muon processes with lepton flavor violation is highly stressed, together with precision measurements of normal muon decay. Recent up-to-date motivations of lepton flavor violation based on supersymmetric models, in particular supersymmetric grand unified theories, are described along with other theoretical models. Future prospects of experiments and muon sources of high intensity for further progress in this field are also discussed.

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.

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.

Test of exotic scalar and tensor interactions in K(e3) decay using stopped positive kaons

The form factors of the decay K+ → π0e+νe (Ke3) have been determined from the comparison of the experimental and Monte Carlo Dalitz distributions containing about 105Ke3 events. The following values of the parameters were obtained: λ+=0.0278±0.0017 (stat.)±0.0015 (syst.), |fS/f+(0)|=0.0040±0.0160 (stat.)±0.0067 (syst.), and |fT/f+(0)|=0.019±0.080 (stat.)±0.038 (syst.). Both scalar fS and tensor fT form factors are consistent with the Standard Model predictions of zero values.

Performance of fine mesh photomultiplier tubes designed for an undoped CsI endcap photon detector

Abstract We have developed two types of fine-mesh photomultiplier tubes for an undoped-CsI endcap photon detector installed in a strong axial magnetic field. These photomultiplier tubes have ultraviolet-transmitting glass windows, backed by large-area bialkali photocathodes, in order to efficiently detect scintillation light from undoped-CsI crystals. A gain of more than 2 × 10 5 , in a magnetic field of 1.0 T, was obtained from these tubes with 19-stage fine-mesh dynodes. Gain drops caused by the magnetic field and by high anode currents were investigated. Several performance criteria of the tubes were studied: gain, quantum efficiency, linearity, noise, and transit time spread.

Measurements of the photon detection inefficiency of calorimeters between 185 and 505 MeV

Abstract The detection inefficiencies for photons of total-absorption-type electromagnetic calorimeters, an undoped CsI crystal counter and a lead-scintillator sandwich counter, have been measured at photon energies ( E γ ) between 185 and 505 MeV with the tagged photon beam from the INS-ES. The effect of punch-through is estimated by an EGS calculation. The other source of inefficiency, the photonuclear interaction effect, is examined after the interaction is identified by neutron signals observed with liquid scintillation counters surrounding the sample calorimeter. The inefficiency due to the photonuclear interaction in the case of the CsI calorimeter at 1-MeV threshold is found to be 10 −5 –10 −6 and shows a monotonic decrease with E γ . The detection inefficiency of the sandwich calorimeter is found to be dominated by the sampling effect after photonuclear interactions.

A new limit of T-violating transverse muon polarization in the

A search for T-violating transverse muon polarization (P(T)) in the K+-->pi(0)mu(+)nu decay was performed using kaon decays at rest. A new improved value P(T)=-0.0017+/-0.0023(stat)+/-0.0011(syst) was obtained giving an upper limit |P(T)|<0.0050. The T-violation parameter was determined to be Imxi=-0.0053+/-0.0071(stat)+/-0.0036(syst) giving an upper limit |Imxi|<0.016.

K^{+}\to\pi^{0}\mu^{+} \nu

Future prospects of a search for lepton-flavor-violating rare muon decays, in particular of μ+→e+γ decay, are presented. At first, the use of muon polarization to suppress backgrounds in a search for μ+→e+γ is discussed. Second, current efforts and ideas to improve experimental detections of e+s and photons in μ+→e+γ decay are shown. Finally, a new intense muon source being considered at Japan Hadron Facility (JHF) is briefly mentioned.

decay

A search for the lepton-flavor violating

Lepton flavor violating rare muon decays and future prospects

\mu^{+}\rightarrow e^{+}\gamma