T. Nakamura

Determination of the QCD scale parameter ΛMS with QCD cascade on the basis of the next-to-leading logarithmic approximation

Abstract The relative production ratio of 3-jet events to the total number of hadronic events was studied in e+e− annihilations at centre-of-mass energies between 54 and 61.4 GeV. The QCD scale parameter has been determined to be Λ MS =254 −47 +55 ±56 MeV on the basis of a QCD cascade with the next-to-leading logarithmic approximation.

Measurement of R and search for new quark flavors decaying into multi-jet final states in e+e− collisions between 54.0 and 61.4 GeV CM energies

Abstract We accumulated e+e− annihilations into multi-hadrons at CM energies between 54.0 and 61.4 GeV with the VENUS detector at TRISTAN. Measured R-ratios are consistent with the standard model using the Z-boson mass; 91.1 GeV/c2. Using two new observables, we searched for a planar four-jet and other multi-jet events resulting from the decay of a charge — 1 3 e b quark. Having observed no positive signals, we excluded b masses between 19.4 and 28.2 GeV/c2 with a 95% confidence level, regardless of branching into charged current and loop-induced flavor-changing neutral current decay, including a possible Higgs decay process. The charge + 2 3 e top quark was excluded below f30.2 GeV/c2.

Measurement of the differential cross sections ofe+e−→γγ ande+e−→γγγ at\(\sqrt s = 55,56,56.5\) and 57 GeV and search for unstable photino pair production

AbstractDifferential cross sections fore+e−→γγ have been measured at center-of-mass energies of 55, 56, 56.5 and 57 GeV. The results are in good agreement with those predicted by QED. Possible deviations from QED are studied in terms of contact interactions, and the limits on compositeness scales are obtained. Using events with a gramma pair in the final state, a search is made for the pair production of unstable photons,n

A study on single photon production at √s=54.0-61.4 GeV

e^ + e^ - to tilde gamma tilde gamma

Charge asymmetry of hadron jets and limits on the compositeness scales in the e+e-→qq̄ reaction at 〈√s〉 = 57.6 GeV

n. No candidate events were found and a new limit on the photino mass is obtained.

A search for excited electrons in the e+e− reactions up to the √s of 56 GeV

Abstract We have studied c (charm) and b (bottom) quark production at the TRISTAN energy region by tagging prompt electrons from the semileptonic decays. Electrons were identified over a wide momentum range between 1 and 29 GeV/c by a transition-radiation-detector in addition to a lead-glass calorimeter. The production cross sections of c and b quarks and the mean values of the fragmentation functions for c and b quarks were obtained as σc = 55.9±8.8(stat.)±7.9(syst.) pb, σb = 13.1±2.9(stat.)±1.0(syst.) pb, 〈xc〉 = 0.44±0.08(stat.)±0.04(syst.) and 〈xb〉 = 0.72±0.12(stat.)±0.08(syst.), respectively. The forward-backward asymmetries of the c and b quarks were also measured to be −0.57±0.16(stat.)±0.06(syst.) and −0.64±0.26(stat.)± 0.07(syst.), respectively. Both the cross sections and the forward-backward asymmetries of the c and b quarks are consistent with the standard model.

A study of single photon production in e+e− annihilation at √s=58 GeV

Abstract A study of single photon events, produced in association with light neutrinos or other weakly interacting neutral particlaes in e + e − collisions, has been performed at √ s =54.0–61.4 GeV with the VENUS detector at TRISTAN. No anomalous signal has been observed in a data sample corresponding to an integrated luminosity of 28.2 pb −1 . This result indicates that the upper limit on the number of light neutrinos, N ν , is 11 (15) at a 90 (95)% confidence level. Combining this with published results from other e + e − experiments, the number of light neutrinos is limited to N ν

Search for heavy neutral spinless particles using e+e− → e+e− and e+e− → γγ reactions in the CM energy range between 54 and 64 GeV

Abstract We have tested extra Z models in the reactions e+e−→μ+μ−, τ+τ− and hadrons in the energy range 50 s GeV using the VENUS detector at the TRISTAN e+e− storage ring. Our data are in good agreement with the standard model prediction ( χ 2 N Df = 2.9 31 ) ). We have obtained 90% confidence-level lower limits of 105, 125 and 231 GeV for the masses of ZΨ, Zη and Zχ bosons which are expected from the E6 grand unified theory. We also place a 90% confidence-level lower limit of 426 GeV for the mass of an extra-Z boson whose couplings to quarks and leptons are assumed to be the same as those for the standard Z boson. Our results exceed the previous experimental limits from the p p collider experiments, although there have been some combined analyses reporting the limits better than those obtained in the present analysis.