M. Sakuda

Measurement of R and search for new heavy quarks in e+e- annihilation at 50 and 52 GeV centre-of-mass energies

Abstract The total cross section for the process of the e+e- annihilation into hadrons has been measured at the centre-of-mass energies of 50 GeV and 52 GeV and a search has been made for new heavy quarks. The ratios R = σ(e+e- → hadrons)/σpoint(e+e- → μ+μ-) obtained are 4.4±0.5 at 50 GeV and 4.7±0.3 at 52 GeV, respectively. An additional systematic uncertainty is 10%. From the event shape analysis we found no evidence for a new quark with charge 2 3 e .

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.

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

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 on single photon production at √s=54.0-61.4 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 the Top Quark in e+e- Annihilation at \(\sqrt{s}=50\) GeV: The First Result from the VENUS Detector at TRISTAN

A result of the search for the top quark in e + e - annihilation into hadrons at (sqrt{s}=50) GeV is presented. The experiment has been perforrnxed using the VENUS detector at TRISTAN. No evidence has been found for the production of the top quark. From the study using the event shape of the multihadron events, the upper limit of the production cross section is found to be 16 pb at thcc 95% confidence level.

Experimental limits on extra-Z bosons from e+e− annihilation data with the VENUS detector at s=50–64 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.

Experimental limits on extra

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.

Z

A search has been made for a light scalar top squark ([ital [tilde t]][sub 1]), which has remained unexcluded by previous [ital e][sup +][ital e][sup [minus]] experiments up to the [ital Z][sup 0] pole. By assuming the decay [ital [tilde t]][sub 1][r arrow][ital c]+[ital [tilde Z]][sub 1] (lightest neutralino), [ital e][sup +][ital e][sup [minus]] annihilation data at [ital E][sub c.m.]=58 GeV have been analyzed. The number of events comprising large-acoplanarity particle groups is consistent with that expected from known processes. We excluded [ital [tilde t]][sub 1] in the mass range 7.6--28.0 GeV/[ital c][sup 2] and [ital [tilde Z]][sub 1] with a mass very close to the kinematical limit at the 95% C.L.

bosons from

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