K. Omata

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.

A beam test of PbWO4 Cherenkov radiators

Abstract PbWO 4 heavily doped with trivalent rare-earth ions like La 3+ , Gd 3+ , Y 3+ , etc. has recently been proposed as an excellent new, heavy and radiation-hard Cherenkov radiator, and the upper limit of the remaining scintillation light yield (LY) was obtained from measurement of radioisotope γ-rays. Since then, we have made a quantitative study of the remaining scintillation LY using a 0.5–1xa0GeV/ c π + /p/d beam. Compared with a standard PbWO 4xa0 :xa0Gd(80xa0atxa0ppm) scintillator, the scintillation LY is quenched to 4.8%, 6.0%, and 11.6% for La 3+ concentration of 8xa0at%, La 3+ of 5xa0at% and Gd 3+ of 3xa0at%, respectively. The scintillation LY remaining in PbWO 4xa0 :xa0La(8xa0at%) was as weak as 15% of the Cherenkov LY for relativistic charged particles.

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.

Performance of fine mesh photomultiplier tubes designed for an undoped CsI endcap photon detector

Abstract We have developed two types of fine-mesh photomultiplier tubes for an undoped-CsI endcap photon detector installed in a strong axial magnetic field. These photomultiplier tubes have ultraviolet-transmitting glass windows, backed by large-area bialkali photocathodes, in order to efficiently detect scintillation light from undoped-CsI crystals. A gain of more than 2 × 10 5 , in a magnetic field of 1.0 T, was obtained from these tubes with 19-stage fine-mesh dynodes. Gain drops caused by the magnetic field and by high anode currents were investigated. Several performance criteria of the tubes were studied: gain, quantum efficiency, linearity, noise, and transit time spread.

Scintillator–Lucite sandwich detector for n/γ separation in the GeV energy region

Abstract A Scintillator–Lucite Sandwich Detector (SLSD) has been developed for n/γ separation in the GeV energy region. An efficient n/γ separation is achieved by measuring a correlation between the scintillation and Cherenkov light yields. The basic performance of the detector has been tested with e, π and p beams with momenta between 0.5 and 2.0 GeV /c ; the results were compared with a Monte-Carlo simulation. The n/γ separation capability of this detector has been studied by simulations in the energy range from 5 MeV to 12 GeV . The SLSD detector was successfully used for a beam survey of the new K L 0 beam line built for a K L 0 → π 0 ν ν experiment at the KEK 12-GeV proton synchrotron.

Search for neutrinoless double beta decay with DCBA

A project called DCBA (Drift Chamber Beta-ray Analyzer) is in progress at KEK in order to search for the events of neutrinoless double beta decay. For investigating technical problems, a test apparatus called DCBA-T has been constructed. The preliminary results of its engineering run are described together with the simulation studies of backgrounds originating from 214Bi and 208Tl.

Silicon strip detector as a real-time, fast, medium-segmented hodoscope

Abstract We have developed a single-sided silicon strip detector with a sensitive area of 64×64xa0mm 2 as a real-time, fast and medium-segmented hodoscope for particle physics experiments in high beam background environment. The signal of each 2xa0mm wide readout strip was integrated in a hybrid preamplifier with a decay constant of 10xa0μs. The output was then amplified 20 times and shaped to a peaking time of ∼50xa0ns in a shaping amplifier. The performance was first examined on a test bench, and then with an intense π − /μ − /e − beam. The Equivalent Noise Charge (ENC, 1 σ ) at the preamplifier input was ∼2000 e (9% of the signal for single minimum ionizing particle ∼22xa0000 e ) at low beam rate, and increased by 10% (or 20%) at a high rate of 150xa0kHz (300xa0kHz) per readout-strip. As the cable length ( L ) from silicon board to preamplifier increased, the ENC increased from 2000 e for L =0.2xa0m to 2600 e for 0.5xa0m, 3500 e for 1xa0m, 3800 e for 1.5xa0m, and 4200 e for 2xa0m.