Kasuke Takahashi

Atmospheric Neutrino Background and Pion Nuclear Effect for KAMIOKA Nucleon Decay Experiment

The main source of background for nucleon decay experiments is the interaction of atmospheric neutrinos in the detector. To estimate this background a Monte Carlo program was developed, which simulates the neutrino interactions and the nuclear effects of secondary pions. The program reproduced existing neutrino data as well as global features of the contained events in the KAMIOKA nucleon decay experiment. Neutrino induced background for nucleon decay was then calculated.

Search for Nucleon Decay Into Charged Lepton + Mesons

With a 3000 ton water Cerenkov detector operated 2700 m.w.e. underground, 103 fully contained events were observed during a live time of 343 days. Most of the events are well interpreted as due to ν interactions. Four multi-ring events survive after applying criteria for nucleon decay. The lower limits on τ/ B obtained from these data exceed 10 31 yr (90% C.L.) for most of the possible decay modes.

Search for Nucleon Decays Catalyzed by Magnetic Monopoles

Search for nucleon decays induced by magnetic monopoles has been carried out with a 3000 ton water Cherenkov detector by two independent methods. Search for multiple nucleon decays in the detector gives the cross section and velocity dependent limits on the monopole flux, F M <2.5×10 -15 cm -2 s - sr -1 for 5×10 -5 <β M <10 -3 and for σ=100 mb at 90% C.L. Search for low energy neutrinos (30< E ν <52 MeV) from the Sun gives a limit, F M (σ 0 /1 mb)<1.6×10 -21 (β M /10 -3 ) 2 cm -2 s -1 sr -1 at 90% C.L.

Search for Nucleon Decays Into Anti-neutrino + Mesons

With a 3000 ton water Cherenkov detector, the nucleon decays into an antineutrino+mesons are searched for. No evidence for nucleon decay has been found during 474 days of detector live time. The lower limits on partial nucleon life time, τ/ B , are 0.5-4.2×10 31 yr at 90% C.L. depending on the nucleon decay modes.

Time resolution of a large area planar spark counter

Abstract A planar spark counter of size 1.0 m × 0.1 m has been developed and tested. The constituent elements are a semiconductive glass anode and a window float-cast glass cathode coated by vacuum-deposited copper. The distance between electrodes is 200 μm. A single counter time resolution of 61 ps was achieved with cosmic rays.

The DCBA experiment for studying neutrinoless double beta-decay

In order to search for neutrinoless double beta-decay, the DCBA (Drift Chamber Beta-ray Analyzer) experiment uses a momentum analyzer, which mainly consists of drift chamber and a uniform magnetic field. A beta ray from a source plate make helical trajectory in the drift chamber owing to the magnetic field. Momentum of each beta ray is obtained by three-dimensional track reconstruction. A test prototype called DCBA-T2 has been constructed and operated at KEK. Another prototype DCBA-T3 is also under construction to improve the energy resolution. The results of DCBA-T2 engineering run are described together with the status of DCBA-T3.

A Test of Lead Glass Shower Counters

In order to design an electromagnetic shower calorimeter for the TRISTAN experiment, lead glass shower counters made of SF6 were tested with positron beams in Beam Line 19 at SLAC. The beam energy ranged over 2–17.5 GeV, and the energy resolution and beam position dependence of the pulse height were studied for lead glass blocks of various length. The effect of the light guide on the pulse height was clearly observed when the shower leaked into the glass light guide. The effect of the absorber, the wedge-shaped lead glass and a mesh-type photomultiplier were also tested.

An automatic film scanner (KAMA) utilizing a new type CRT with double deflection scheme

Abstract A newly developed high precision CRT with a double deflection scheme is utilized for a flying spot generator in the KAMA system, an automatic film measuring apparatus at KEK, National Laboratory for High Energy Physics. A concept of man-machine communication is introduced by using an optical and a graphical display. The spot size of the CRT presently used is about 25 μm equally over the area of about 80 × 80 mm 2 on the screen of the 9″ tube. The spot is reduced to about 12.5 μm on the film plane by the demagnification by a factor 2. The reproducibility of a point digitization is within less than 1 μm, and the track reconstruction residuals peak at 4.5 μm on the film for 4.5 GeV/ c π − tracks. Event measurements have been carried out under the vertex guidance method. The failure rate of the KAMA automatic measurements in TVGP-processing is less than 10% for the 4-pronged events from the 4.5 GeV/ c π − p SLAC-LBL 82″ hydrogen bubble chamber film. The general lay-out and performance of the KAMA, an easy-handling high-precision CRT film scanner are described.

On the Nuclear Effects in Nucleon Decays

Various nuclear effects upon nucleon decays, which occur in a nucleus, are extensively studied with an emphasis on a huge water Cerenkov detector. The Monte Carlo calculation is carried out for the typical decay process nucleon– positron+pion. The virtual meson exchange process is also taken into consideration. Results show that apart from the Fermi motion effect about 50% of nucleon decay signals are completely free from nuclear effects in the case of 13 O nucleus. The advantage of using material made from light nuclei is discussed.

Inclusive Non-Strange Meson Production and Particle Ratios in π-p Interactions at 6 GaV/c

Inclusive production of ρ°(770), ω(783) and f(1270) has been studied in π - p interactions at 6 GeV/c. The inclusive cross sections for ρ° and f are; 2.9 ±0.3 mb and 0.47 ±0.07 mb. The semi-inclusive cross section for ω is 0.20 ±0.03 mb. These cross sections and ratios of ρ°/ π, f/ ρ° and K *+ / ρ° are compared with higher energy data. The differential cross sections for ρ°, ω and f are presented as a function of Feynman scaling variable x and squared transverse momentum P T 2 . The x distributions for ρ° and ω show them to be produced primarily in the forward direction. Inclusive ρ°, ω and f resonance production in 6 GeV/c π - p interactions seems to have not yet reached the high energy limiting behavior.