S. Higashi

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.

Production of direct e+e− pairs in proton-nucleus collisions at 13 GeV/c

Abstract A measurement of direct production of electron pairs of masses below 1.3 GeV in proton-nucleus collisions at 13 GeV/ c has been performed using a two-arm spectrometer. An enhanced low mass dielectron continuum below the ϱ mass is observed and is discussed in terms of the mechanism of soft annihilation of partons.

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^-

We have measured the total e+e− hadronic annihilation cross section at the center of mass energies between 50.0 GeV and 61.4 GeV with the TOPAZ detector at TRISTAN. The full electroweak radiative corrections (up to O(α3)) were applied to the data which were analysed together with the published data from PEP and PETRA. We then determined the standard model parameters, Mz (the mass of the Z), sinw2θ (the Weinberg angle) and ΛMS (the QCD scale parameter) by comparing the experimental data with the prediction of the standard model. The best fit values are Mz = 89.2−1.8+2.1 GeV/c2, sin2θw = 0.233 −0.025+0.035 and ΛMS = 0.327−0.206+0.275 GeV. A constraint is obtained on the heavy top quark mass through the radiative corrections if we take the SLC value of Mz (91.1 GeV/c2).

and

Abstract A search for fourth-generation charge - 1 3 ( b ′) quarks using inclusive muon events in e + e - annihilations at s =56.5-60.8 GeV is presented, considering its decays through loop-induced flavor-changing neutral-current as well as its charged current decays. Production of b′ (and top) was excluded as the cause of slightly high R -values observed at ∈ s =⩾56.0 GeV, if they decay dominantly through a charged-current (68%). One large aplanarity event ( A =0.17 with an isolated muon, observed at s =60.8 GeV, is also presented.

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

Abstract Direct production of single electrons in proton-nucleus collisions at 13 GeV/c has been measured. A rising e π ratio with decreasing pT above the 10−4 level is observed for low pT single electrons. The source of the rising e π ratio at low e π ratio at low pT is discussed in connection with the low mass dielectron continuum below the ϱ mass region.

at

Excited leptons, e∗, μ∗ and τ∗, have been searched for with the TOPAZ detector at TRISTAN e+e− collider in the energy region s=52−60.8 GeV. e∗ and μ∗ have been searched for in the single production process, e+e−→ι+ι−γ, and the pair production process, e+e−→ι+ι−γ, where ι stands for e or μ.e∗ has also been searched for in the processes e+e−→eγ(e) (quasi-real Compton scattering) and e+e−→γγ.τ∗ has been searched for in the τ∗-pair production process, e+e−→τ +τ−γγ. No evidence for the production of excited leptons has been found, and new limits on e∗, μ∗ and τ∗ production are set.

\sqrt{s}=52

Excited leptons, e∗, μ∗ and τ∗, have been searched for with the TOPAZ detector at TRISTAN e+e− collider in the energy region s=52−60.8 GeV. e∗ and μ∗ have been searched for in the single production process, e+e−→ι+ι−γ, and the pair production process, e+e−→ι+ι−γ, where ι stands for e or μ.e∗ has also been searched for in the processes e+e−→eγ(e) (quasi-real Compton scattering) and e+e−→γγ.τ∗ has been searched for in the τ∗-pair production process, e+e−→τ +τ−γγ. No evidence for the production of excited leptons has been found, and new limits on e∗, μ∗ and τ∗ production are set.