320 research outputs found
Effects of radiation damage caused by proton irradiation on Multi-Pixel Photon Counters (MPPCs)
We have investigated the effects caused by proton-induced radiation damage on
Multi-Pixel Photon Counter (MPPC), a pixelized photon detector developed by
Hamamatsu Photonics. The leakage current of irradiated MPPC samples linearly
increases with total irradiated doses due to radiation damage, which is not
completely recovered even after a year from the irradiation. No significant
change has been observed in the gains at least up to 8.0 Gy (
n/mm in 1 MeV neutron equivalent fluence, ). The device has
completely lost its photon-counting capability due to baseline fluctuations and
noise pile-up after 21 Gy irradiation ( n/mm in ), which might be problematic for some applications, such as ring-imaging
Cherenkov detectors. We have found that the pulse-height resolution has been
slightly deteriorated after 42 Gy irradiation ( n/mm in
), where the measured sample has been illuminated with a few
hundred photons. This effect should be considered in the case of
energy-measurement applications.Comment: 18 pages, 10 figure
Long-lived neutral-kaon flux measurement for the KOTO experiment
The KOTO ( at Tokai) experiment aims to observe the CP-violating rare
decay by using a long-lived neutral-kaon
beam produced by the 30 GeV proton beam at the Japan Proton Accelerator
Research Complex. The flux is an essential parameter for the measurement
of the branching fraction. Three neutral decay modes, , , and were used to
measure the flux in the beam line in the 2013 KOTO engineering run. A
Monte Carlo simulation was used to estimate the detector acceptance for these
decays. Agreement was found between the simulation model and the experimental
data, and the remaining systematic uncertainty was estimated at the 1.4\%
level. The flux was measured as per protons on a
66-mm-long Au target.Comment: 27 pages, 16 figures. To be appeared in Progress of Theoretical and
Experimental Physic
Search for the decay
We performed a search for the decay with the
E391a detector at KEK. In the data accumulated in 2005, no event was observed
in the signal region. Based on the assumption of
proceeding via parity-violation, we obtained the single event sensitivity to be
, and set an upper limit on the branching ratio to
be at the 90% confidence level. This is a factor of 3.2
improvement compared to the previous results. The results of proceeding via parity-conservation were also presented in this paper
Improved measurement of the K+->pi+nu(nu)over-bar branching ratio
An additional event near the upper kinematic limit for K+-->pi(+)nu(nu) over bar has been observed by experiment E949 at Brookhaven National Laboratory. Combining previously reported and new data, the branching ratio is B(K+-->pi(+)nu(nu) over bar)=(1.47(-0.89)(+1.30))x10(-10) based on three events observed in the pion momentum region 211<P<229 MeV/c. At the measured central value of the branching ratio, the additional event had a signal-to-background ratio of 0.9
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