T. Ohama

A separation method of 0ν- and 2ν-events in double beta decay experiments with DCBA

Abstract A detector called Drift Chamber Beta-ray Analyzer (DCBA) will provide momentum information of each β-ray in double beta decay. The DCBA is expected to have good capabilities for particle identification, detection efficiency, background elimination and decay-source integration. Under the assumption of mass mechanism dominance in neutrinoless double beta decay, a simulation study shows that a combination method using both sum and single-energy distributions of double beta decay events can separate 0 ν - and 2 ν -events down to 0.05 eV of the effective neutrino mass with the help of a calculated nuclear matrix element, even though the DCBA has relatively poor energy resolution.

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.

A proposed detector DCBA for double beta decay experiments

Abstract A magnetic tracking detector called DCBA (Drift Chamber Beta-ray Analyzer) is proposed for double beta decay experiments. The DCBA project is divided into two stages: DCBA-I and -II. DCBA-I will be able to measure the half life of the two-neutrino double beta decay of 150 Nd, though natural Nd is used as the decay source material. DCBA-II will make it possible to investigate the effective mass of the Majorana neutrino down to 0.5-0.1 eV, since it is expected to have the ability to measure the half-life limit up to 4 × 10 24 yr using enriched 150 Nd. A fundamental strategy of the DCBA project and some details of DCBA-I are described.

A 100 MHz FADC system based on CompactPCI for DCBA

Abstract A flash analog to digital converter (FADC) board of low cost and power saving has been developed based on Compact Peripheral Component Interface (CompactPCI) for Drift Chamber Beta-ray Analyzer (DCBA), which is an experiment to study double-beta decay. This board has been designed and constructed with 8 channels, each of which has an 8-bit 100 MHz FADC chip and a double-buffered memory. The design philosophy using recent semiconductor technology is described together with the performance of the FADC board.

A vertex drift chamber for the VENUS detector at TRISTAN

Abstract A high-precision drift chamber has been constructed in order to add vertex information to the VENUS detector at the TRISTAN e + e − collider. It is a jet-type drift chamber comprising 12 tilted drift sectors filled with pressurized slow gas. The structure and initial performance are described.

Measurement of the reactionse+e−→μ+μ− ande+e−→τ+τ− between\(\sqrt s = 50\) and 60.8 GeV

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

The DCBA experiment for studying neutrinoless double beta-decay

sqrt s = 50

ELECTRICAL MEASUREMENT OF WIRE TENSION IN A MULTI-WIRE DRIFT CHAMBER

n and 60.8 GeV with the VENUS detector at TRISTAN. The average total cross section and the forward-backward charge asymmetry for μ-pair production are observed to be 28.3±1.4±0.8 pb and (−29.0−4.8+5.0±0.5)%, and those for τ-pair production are 27.6±1.7±1.0 pb and (−32.8−6.2+6.4±1.5)% atn