H. Takamure

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.

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 √s=53.3 GeV and 59.5 GeV

Abstract We studied the energy-energy correlation (EEC) and its asymmetry (AEEC) using e + e − hadronic annihilation events obtained at √ s =53.3 GeV and 59.5 GeV with the TOPAZ detector at the TRISTAN collider. We used a Monte Carlo simulation combined with the QCD matrix elements by Gottschalk and Shatz and the Lund string fragmentation model. By comparing the experimental data with simulated events, we determined the strong coupling constant α s at both energies. The results are 0.129±0.007 (stat) ±0.010 (syst) at √ s =53.3 GeV and 0.122±0.008 (stat) ±0.010 (syst) at 59.5 GeV.

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 .

Charge asymmetry measurement in e+e−→μ+μ− and τ+τ− reactions at s=52 GeV and 55 GeV

Abstract The reactions e + e − → μ + μ − and τ + τ − were measured at s =52 GeV and 55 GeV by using the TOPAZ detector at TRISTAN. For the combined data, the observed charge asymmetry is −0.29±0.13 and the total cross section is 27.9±3.0 (stat.)±0.8 (syst.) pb for μ + μ − production, and those for τ + τ − production are −0.20±0.14 and 35.7±4.3 (stat.)±2.4 (syst.)pb, respectively. These values are consistent with predictions by the standard model of electroweak interactions.

Measurement of the Processes

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 .

e^+ e^- \to e^+ e^-

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.

and

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.

e^+ e^- \to \gamma \gamma

Abstract We have measured the cross section for γγ production with the TOPAZ detector in the energy region √ s =50.0–61.4 GeV. The observed cross section for γγ production integrated over |cos θ | ⩽ 0.77 is 50.2±0.8±2.2 pb at 〈√ s 〉=57.6 GeV and the ratio of this value to the QED prediction is 1.01±0.02±0.04. The angular distribution is in good agreement with the QED predictions, thereby setting limits on the compositeness scales, Λ L+R + =168 GeV, Λ L+R − =97 GeV, Λ L,R =141 GeV, Λ L,R − =81 GeV, and Λ L−R ± =68 GeV, at the 95% confidence level. The reaction e + e − → γγγ was also studied and was found consistent with the QED prediction.