Yorikiyo Nagashima

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 .

A limit on massive neutrino dark matter from Kamiokande

Abstract We have searched for possible high-energy neutrino signals expected from massive neutrino dark matter captured by the earth and the sun, by making use of upward-going muon samples collected in the seven years of operation of the Kamiokande detector. No excess of events was found from the earth or the sun, thus giving an excluded mass range of Dirac-(Majorana-) type neutrinos, 6 (24) ⩽ m ν ⩽ several hundred GeV, as the dark matter which consitutes the halo of the galaxy. The upper bounds extend to a mass range never before analyzed in previous indirect searches.

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.

Vertex detector for the KEK B-factory

Abstract We are designing a silicon vertex detector to be installed in a detector for the KEK Asymmetric B-factory project. In order to fulfill the accuracy required for the vertex resolution from the physics motivation we made several studies about the various aspects of the construction technology as well as the studies, is presented. The validity and performance of the design are also discussed through which was derived from the above studies, is presented. The validity and performance of the design are also discussed through results of a study of the detector simulation which incorporated a capacitive network model for the distribution of collected charge.

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.

A study of nonflammable gas mixtures for limited streamer tubes in the VENUS detector at TRISTAN

Abstract Performances of limited streamer tubes operated with nonflammable gas mixtures composed of argon (Ar), carbon-dioxide (CO 2 ) and isobutane (i-C 4 H 10 ) with ratios of 1:1.5:0.15, 1:2:0.2, 1:3:0.3, 1:4:0.4 and 1:6:0.6 were studied. It was found that these mixtures were very suitable for the VENUS detector. The charge spectra exhibited very sharp distributions and indicated the possibility for the limited streamer tubes to be applied to calorimetry use. A mixture of 1:2:0.2 was chosen for the VENUS streamer tubes because of its moderate gain and long efficiency plateau.

Self-supporting cylindrical multiwire proportional chambers with two dimensional read-out

Abstract Cylindrical MWPCs have been constructed with anode diameters of 240–430 mm and a length of 750 mm. Cathode strips run helically with 38°–61° to the anode wires, and the induced charges were read out by ADC. Both the anode and the cathode efficiency were well above 99%. The resolution (σ) for the longitudinal position of the avalanche was 0.6 mm by the centre of gravity method, if the cathode was read out per 12 mm width by summing two adjacent cathode strips.

Photoproduction of Positive Pions from Carbon Nuclei

Positive pions with energies ranging from 30 MeV to 150 MeV were produced on a carbon target by the bremsstrahlung beam from the 750-MeV electron-synchrotron and detected by means of a π-µ decay counter telescope at an angle of 90° in the laboratory. The counts were corrected for the electronic efficiency of the pion counting system and for the loss of pions in the detection system by decay in flight, nuclear absorption, nuclear scattering and multiple Coulomb scattering. Absolute cross sections of the pion production are given as a function of the peak bremsstrahlung energies extending from 180 MeV to 550 MeV. Applying the photon difference method to the cross section per equivalent quantum, the differential cross sections, (\(d^{2}\sigma/d\varOmega dT_\pi\)) and (\(d\sigma/d\varOmega\)), are obtained, and compared with theoretical values, which are calculated on the bases of the impulse and closure approximation, the nuclear momentum distribution of a Gaussian type of the average kinetic energy of 19 Me...

Search for susy partners of charged leptons in e+e- collisions with s up to 60.8 GeV

Abstract Supersymmetric partners of charged leptons, scalar leptons were searched for in e + e − collisions at TRISTAN with center-of-mass energies up to 60.8 GeV. The pair production of unstable scalar leptons were searched for among identified lepton-pair events, and stable ones among collinear two-track events. No evidence was found for them. Mass limits are presented for both large-splitting and degenerate cases.

Precise determination of

Measurements of the semileptonic weak neutral-current reactions ..nu../sub ..mu../p..--> nu../sub ..mu../p and nu-bar/sub ..mu../p..-->..nu-bar/sub ..mu../p which yield the absolute differential cross sections dsigma(..nu../sub ..mu../p)/dQ/sup 2/ and dsigma(nu-bar/sub ..mu../p)/dQ/sup 2/ described. The weak-neutral-current parameter, sin/sup 2/theta/sub W/, is determined to be sin/sup 2/theta/sub W/ = 0.220 +- 0.016 (stat)/sub -0.031//sup +0.023/(syst).