T. Yamagata

Measurement of the proton-antiproton pair production from two-photon collisions at TRISTAN

Abstract The cross section of the γγ → p p reaction was measured at two-photon center-of-mass energy (Wγγ) between 2.2 and 3.3 GeV, using the two-photon process at an e+e− collider, TRISTAN. The Wγγ dependence of the cross section integrated over a c.m. angular region of | cos θ ∗ | is in good agreement with the previous measurements and the theoreticalv prediction based on diquark model in the high Wγγ region.

Measurement of the Differential Cross-sections of

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

and

e^ + e^ - to tilde gamma tilde gamma

at

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

\sqrt{s}=55

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.

-{GeV}, 56-{GeV}, 56.5-{GeV} and 57-{GeV} and Search for Unstable Photino Pair Production

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.

A study of the charm and bottom quark production in e+e− annihilation at s = 58 GeV using prompt electrons

Abstract We have studied the production of charged D ∗ mesons in e + e − annihilation at an average center-of-mass energy of 58.0 GeV. Charged D ∗ mesons were identified using two independent methods; the mass-difference method and the detection of the low transverse-momentum pion. The forward-backward asymmetry of the charm quark production was measured to be A c = −0.61±0.13(stat.)±0.08(syst.). The cross section of inclusive D ∗ production was found to be σ(e + e − →D ∗ ± +X) = 24.5 ± 5.3 ( stat. )±3.0( syst. ) pb. If we assume the standard model prediction for the charm quark production, we obtain the branching ratio for the charm quark to produce a charged D ∗ meson to be Br (c→D ∗+ + X) = (22±5( stat. )±3( syst. ))% .

Experimental limits on extra

AbstractThe angular distributions of the reactione+e−→μ+μ− ande+e+→τ+τ− have been measured betweenn