K. Takahashi

High sensitivity search for a 17 keV neutrino. Negative indication with an upper limit of 0.095

Abstract We have performed a search for a 17 keV neutrino by looking for a kink in the 63 Ni β-spectrum near the expected energy threshold. Using a large number of events (2.4 × 10 9 ) accumulated in a narrow energy region with the INS iron-free π √2 β -spectrometer, we obtain a mixing strength of [1.8±3.3(stat.)±3.3(syst.)]×10 −4 , and no indication of the presence of a 17 keV neutrino with the order of 1% mixing. We set an upper limit of 0.095% for the admixture of a neutrino with a mass of 17 keV and of 0.1% with a mass range of 10–24 keV, at the 95% confidence level.

A limit on massive neutrino dark matter from Kamiokande

Abstract We have searched for possible high-energy neutrino signals expected from massive neutrino dark matter captured by the earth and the sun, by making use of upward-going muon samples collected in the seven years of operation of the Kamiokande detector. No excess of events was found from the earth or the sun, thus giving an excluded mass range of Dirac-(Majorana-) type neutrinos, 6 (24) ⩽ m ν ⩽ several hundred GeV, as the dark matter which consitutes the halo of the galaxy. The upper bounds extend to a mass range never before analyzed in previous indirect searches.

Experimental study of b-quark jets in e+e− annihilation at TRISTAN

Abstract An experimental study of b-quark jets using high-pT electrons was carried out at √s=58 GeV with the TOPAZ detector at the e+e− collider TRISTAN at KEK. The forward-backward charge asymmetry of the b-quark was obtained to be A b b =−0.55±0.27( stat. )±0.07( syst. ) , consistent with the standard model prediction. Also, such jet properties of the b-quark as the average charged multiplicity and the rapidity of charged particles were analyzed. In order to purify the b-quark event samples in this analysis, only events with backward-going electrons or forward-going positrons were used. The energy dependence of these jet properties was studied by making comparisons with the results of the DELCO experiment at the PEP collider (√s=29 GeV) at SLAC.

Charge asymmetry of hadronic events in e+e− annihilation at √s=57.9 GeV

Abstract The charge asymmetry of quark jets produced in e + e − annihilations at 〈√ s 〉=57.9 GeV was measured with the TOPAZ detector at TRISTAN. The observed charge asymmetry is +0.091±0.014(stat.)±0.016(sys.). From the measured differential cross section, the axial vector coupling constant averaged over all quark flavors was determined to be 1.09 −0.21 +0.27 . These values are consistent with the standard model predictions. Possible deviations from the standard model were examined in terms of contact interactions, and the lower limits on the compositeness scale parameters were obtained to be 1.2–7.1 TeV at the 95% confidence level.

InclusiveK*'s and∑*'s production in 360 GeV/cpp interactions using the European hybrid spectrometer

We have studied the inclusive production of strange meson and baryon resonances in 360 GeV/cpp interactions. Cross sections forK*+(892) andK*−(892) are estimated to be 4.42±0.62 mb and 2.54±0.47 mb respectively and those for∑+(1385) and∑−(1385) are 0.67±0.11 mb and 0.26±0.07 mb respectively. Longitudinal and transverse momentum distributions forK*(892) and Σ(1385) are presented, as well as for their decay productsK0 and Λ. An estimation is given on theK*(1430) and∑*(1915) productions.

A study of pion pair production in the two-photon process

Abstract We studied the e+e−→e+e−π+π− interaction with the untagged two-photon sample obtained by the TOPAZ detector at the TRISTAN e+e− collider. The sample was taken in the energy region s =55.0−60.8 GeV . One of the QED backgrounds, e+e−→e+e−, was clearly removed by the measurement of dE/dx by the TOPAZ-TPC. The π+π− invariant mass spectrum is well reproduced by the f2(1270) resonance, the Born term and their interference. We determined the radiative width of the f2(1270) to be 2.27±0.47(stat.)±0.11(syst.) keV.

A search for charged Higgs bosons at tristan

Abstract We searched for pair production of charged Higgs bosons via e+e− annihilation, using data (23.3 pb−) collected by the TOPAZ detector in the energy range s = 52.0 – 61.4 GeV. We observed no evidence for charged Higgs pair production and extended the excluded region in the MH±BR (hadron) plane. The 95% CL lower mass limit is the most stringent for BR (hadron) = 0.6, giving mH±

Search for pair production of heavy stable particles at TRISTAN

We searched for signatures of new stable particles in e+ e− annihilation using the TOPAZ detector at TRISTAN between √s = 52 and 60 GeV. The search made use of the particle identification by the Time Projection Chamber (TPC). We set new limits on the pair production of new stable charged particles with spins 0 and 12, and charges between 23 and 43. The limits on the production cross section were translated to the lower mass limits of hypothetical new particles, SUSY particles, free quarks and heavy leptons.

Study of 360 GeV/c proton-nucleus interactions using CERN holographic bubble chamber

SummaryThe study of high-energy proton-nucleus collisions is done with a holographic film from the exposure of CERN heavy liquid bubble chamber (HOBC) to a 360 Ge V/c proton beam. The multiplicity, the pseudorapidity distributions of its secondary charged particles and their correlations are analysed and compared with those of some Monte Carlo event generators. Results suggest that the multichain model including the concept of formation zone is suitable to reproduce our experimental data. It is found that the intranuclear cascade process is important in order to describe the production mechanism, especially in the backward hemisphere, of high-energy proton-nucleus collisions.