Y. Fukushima

New upper bound on the electron anti-neutrino mass☆

A new upper bound ofmv < 13 eV at 95% CL has been obtained on the electron anti-neutrino mass. Thus results is based on a more than tenfold improvement in data relative to our previous measurements of the β-spectrum in 3H decay, and its in conflict with the finite mass of 17 <mv< 40 eV reported by an ITEP group

Measurements of the electron drift velocity and positive-ion mobility for gases containing CF4

Abstract Measurements of the electron drift velocity and positive-ion mobility for gases containing CF 4 have been performed. The results are presented for four types of gas mixtures containing CF 4 and hydrocarbons: CF 4 +CH 4 , CF 4 +C 2 H 6 , CF 4 +C 3 H 8 and CF 4 +iso-C 4 H 10 . To make a comparison, also positive-ion mobilities for Ar+C 2 H 6 and Ar+C 3 H 8 gas mixtures have been measured. The drift velocities of electrons in a few mixtures are found to exceed 10 cm/μs, twice that in a conventional drift chamber gas such as Ar(50%)+C 2 H 6 (50%). In particular, the electron drift velocity in CF 4 (10%)+CH 4 (90%) is larger than 10 cm/μs, even at a reduced electric field E / P of more than 1 V/(cm Torr). Results on the measurements of the positive ion mobility are consistent with the interpretation that the hydrocarbon ions are the positive ions eventually drifting toward the cathode in the studied gas mixtures. Their mobilities in CF 4 are found to be smaller than those in Ar.

Test of BaF2 scintillators coupled to a photomultiplier with a CsTe photocathode

Basic properties of BaF2 scintillators coupled to a photomultiplier with a CsTe photocathode have been investigated. The signal from the photomultiplier shows a drastic reduction of the slow component of the BaF2 scintillation light while preserving the good properties associated with the fast component.

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.

An Upper Limit for the Mass of the Electron Anti-neutrino From the Ins Experiment

Abstract The β-spectrum in 3 H decay has measured at INS with an energy resolution of 10–16 eV. The overall response function of the spectrometer system was reliably obtained with a reference 109 Cd source having the same chemical structure as the 3 H source. An upper limit of 32 eV has been obtained for the mass of the electron anti-neutrino with statistical and systematic errors.

Measurements of electron drift velocities and positive ion mobilities for gases containing CF4 II

Measurements of electron drift velocities and positive ion mobilities for gases containing CF4 have been made. Our previous paper described the results on electron drift velocities for gas mixtures containing CF4 and hydrocarbon, and ion mobility results for gas mixtures of CF4 + hydrocarbon, Ar + C2H6 and Ar + C3H8. The present paper is the second and final paper of the series. It describes the results on electron drift velocities for the gas mixtures; Ar + CF4 + hydrocarbon, where hydrocarbon is CH4 or C2H6 or C3H8 or iso-C4H10. The fraction of each gas component was changed systematically for each set of gas mixtures, and the electron drift velocity was measured as a function of the applied drift field between 0.2 and 2.5 kV/cm. Indications were found for relatively large electron drift velocities, even for low electric fields, with better saturation properties than was the case for the gas mixtures of CF4 + hydrocarbon previously measured. Positive ion mobility was measured for several kinds of gas mixtures; Ar + hydrocarbon, CF4 + hydrocarbon and Ar + CF4 + hydrocarbon. Since ion currents and their arrival times were actually measured, the word “positive ion” does not necessarily mean a specific kind of ions but rather a group of ion clusters. The positive ion mobilities were deduced from this measurement under the assumption that Blancs law was valid. A consistent picture was obtained within this approximation.

Precise measurement of Ag KLL Auger-spectrum

Abstract The Ag KLL Auger spectrum has been measured with an energy resolution of 8 eV. The energies and the intensities of all nine lines are precisely determined with 1–2 orders of magnitude better accuracies than those in the previous experiment. The data obtained are found to be in good agreement with the theoretical calculations.

Design and construction of a large cylindrical transition radiation detector for the VENUS experiment

We describe the design considerations and construction techniques of a large cylindrical transition radiation detector (TRD), 296 cm long and 311.4 cm in diameter, for the VENUS experiment at the e+e+ storage ring, TRISTAN. The design is based on measurements by using test chambers with e/π beams and X-ray sources. The test results will be fully described. The TRD contains four modules of radiators, each followed by an X-ray chamber with 8192 (2688) total (sense) wires. The gain calibration of all sense wires has been completed with an accuracy of 5%. The TRD is expected to provide a pion rejection ratio of 15±3 with an electron efficiency of 90% for isolated tracks with momenta above 1 GeV/c.

Initial performance of the VENUS transition radiation detector

The VENUS-TRD is a cylindrical transition radiation detector, extending from 127 cm to 157.7 cm radially and 296 cm axially. It is designed to improve the e/π separation capability of the VENUS detector by a factor of 10 in order to complement the lead glass calorimeter. It covers an angular region of |cos θ| 1 GeV/c in hadronic events due to overlap of the tracks in the chamber cells of the TRD. The VENUS-TRD is the largest TRD to perform in colliding beam experiments.

A Study of charged D* production in e+ e- annihilation at an average center-of-mass energy of 58-GeV

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. ))% .