H. Hayashii

Measurement of the inclusive cross section of jets in γγ interactions at TRISTAN

Abstract We have investigated the properties of jet production in almost real γγ collisions at √s=58 GeV with the TOPAZ detector at the TRISTAN e+e− collider. The data were analyzed with a jet-clustering method based on a cone algorithm. The jet rate shows evidence for a hard scattering effect of the hadronic constituents of a photon (resolved photon processes). We have also observed a substantial energy flow in the small-angle region, which is additional evidence for resolved photon processes. We present the transverse momentum dependence of the inclusive jet and two-jet cross sections and compare them with different model predictions.

Search for SUSY Particles in e+ e- Annihilation at Tristan

Abstract The TOPAZ detector has accumulated about 11 pb−1 of data in the energy range s =52−57 GeV . Charged supersymmetric particles have been searched for. Assuming the photino to be massless, we place limits on the chargino of m χ GeV , on the scalar muon, tau, and quark of m μ GeV , m τ GeV , and m q GeV . The scalar electron can be excluded up to a mass of ∼ 28 GeV. Other cases are examined.

Measurement of the photon structure function F2γ and jet production at TRISTAN

Abstract We have measured the photon structure function F2γ in the reaction e+e− → e+e− hadrons for average Q2 values from 5.1 to 338 GeV2 by using data collected by the TOPAZ detector at TRISTAN. The data have been corrected for detector effects and are compared with theoretical expectations based on QCD. The structure function F2γ increases as ln Q2, as expected. A sample of events with one or two distinct jets has been identified in the final state. Although two-jet events can be explained solely by the point-like perturbative part, one-jet events require a significant hadron-like part in addition.

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.

Measurements of αs in e+e- annihilation at /TRISTAN

Abstract The strong coupling constant α s was determined from analyses of the thrust, heavy jet mass and, differential 2-jet rate, using e + e - hadronic events at s = 58 GeV with the TOPAZ detector at TRISTAN. The NLLjet Monte Carlo simulation (NLLjet) and analytic formulae based on resummation up to the next-to-leading logarithms combined with O ( α 2 s ) calculations were used to evaluate α s . The average α s values at Q 2 = (58 GeV) 2 from the analyses are α s = 0.125 ± 0.009 for NLLjet and α s = 0.132 ± 0.008 for the resummed analytic formulae.

Cross sections and charge asymmetries for e+e−→μ+μ− and e+e−→τ+τ−reactions at s=52−61.4 GeV

The process e+e−→μ+μ−and e+e− have been studied in the energy range s=52−61.4 GeV, using the TOPAZ detector at TRISTAN. From an integrated luminosity of L = 74.0 pb−1, lowest-order cross sections and forward-backward asymmetries are measured to be n〈σμμ〈 = 25.4±0.9±1.2 pb, 〈Aμμ〉 = (−32.2±3.1±1.1)%, 〈σττ〉 = 27.1±1.1±1.2 pb, 〈Aττ〉 = (−33.9±4.9±1.0)% n, at an average energy of s〉=57.87 GeV. From the measured assymetry we derive axial vector couplings of acaμ=0.96±0.09±0.01,and acaτ=1.01±0.14±0.01±. These results are consistent with standard model expectations. Lower limits in the range 2–5 TeV (95%CL)are placed on compositeness scale parameters for leptons.

Measurements of b-quark forward-backward charge asymmetry and axial-vector coupling using inclusive muons in e+e− annihilation at s=52−61.4 GeV

We have collected 122 multi-hadronic inclusive muon events with the TOPAZ detector at 〈s〉 = 58.27 GeV with ∫Ldt=40.61 pb−1. From this event sample we derived the differential cross section for B-hadron productions and determined B-hadron forward-backward asymmetry (Abb) to be Abb = −0.71 ± 0.34 (stat)+0.07−0.08(syst). A fit to the differential cross section, after correcting for the effect of B0B0 mixing, yielded the axial-vector coupling constant of the b-quark (ab):ab = −1.79+0.34−0.32(stat)+0.15−0.14(syst). We also set a 90% confidence level limit of χ<0.37 on the B0B0 mixing parameter.

Measurement of the processes e+e−→e+e− and e+e−→γγ at s=52 GeV

Abstract Differential cross sections for the processes e + e − → e + e − (Bhabha scattering) and e + e − → γγ have been measured with the TOPAZ detector at s =52 GeV . The results agree with the predictions of quantum electrodynamics (QED). The lower limits for the QED cut-off parameters have been obtained to be Λ + ⩾115 GeV and Λ − ⩾236 GeV for Bhabha scattering, and Λ + ⩾94 GeV and Λ − ⩾59 GeV for the reaction e + e − → γγ .

k0 (K̄0) production in two-photon processes at TRISTAN

Abstract We have carried out an inclusive measurement of K 0 ( K 0 ) production in two-photon processes at TRISTAN. The mean s was 58 GeV and the integrated luminosity was 199 pb−1. High-statistics Ks samples were obtained under such conditions as no-, anti-electron, and remnant-jet tags. The remnant-jet tag, in particular, allowed us, for the first time, to measure the cross sections separately for the resolved-photon and direct processes.

An experimental study of muon pair production in tagged two-photon interactions

Abstract The process e + e − →e + e − μ + μ − has been studied in single-tag and double-tag configurations using the TOPAZ detector at TRISTAN. The data correspond to the integrated luminosity of 45.3pb − at center-of-mass energies ranging from 52 to 61.4 GeV. The observed events in both configurations have shown a good agreement with QED predictions in order α 4 . Although the AMY group reported an excess of e + e − →e + e − μ + μ − events in double-tag mode at low muon invariant mass region less than 1.0 GeV/c 2 , we did not observed such excess in our data.