A pulse shape difference between photons and neutrons was observed in the output signals of scintillation light from the un-doped CsI calorimeter of the KOTO experiment for the KL→π0νν̄ decay. We ...developed a discrimination method to reject neutrons and to accept photons in the deposited energy range from 0.1 to 2 GeV. The method rejects 67% of neutron-induced single hadronic clusters and 86% of neutron-induced two-cluster events while keeping more than 90% of photon-induced single electromagnetic clusters and two-photon events.
Search for heavy neutrinos in K + → μ + ν H decays Artamonov, A. V.; Bassalleck, B.; Bhuyan, B. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
03/2015, Letnik:
91, Številka:
5
Journal Article
Odprti dostop
Here, evidence of a heavy neutrino, νH, in the K+→μ+νH decays was sought using the E949 experimental data with an exposure of 1.70 × 1012 stopped kaons. With the major background from the radiative ...K+→μ+νμγ decay understood and suppressed, upper limits (90% C.L.) on the neutrino mixing matrix element between the muon and heavy neutrinos, |UμH|2, were set at the level of 10–7 to 10–9 for the heavy neutrino mass region 175 to 300 MeV/c2.
The Outer-Edge Veto (OEV) counter subsystem for extra-photon detection from the backgrounds for the KL0→π0νν¯ decay is located at the outer edge of the endcap CsI calorimeter of the KOTO experiment ...at J-PARC. The subsystem is composed of 44 counters with different cross-sectional shapes. All counters are made of lead and scintillator plates and read out through wavelength-shifting fibers. In this paper, we discuss the design and performances of the OEV counters under heavy load (~8tons/m2) in vacuum. For 1-MeV energy deposit, the average light yield and time resolution are 20.9 photo-electrons and 1.5ns, respectively. Although no pronounced peak by minimum-ionizing particles is observed in the energy distributions, an energy calibration method with cosmic rays works well in monitoring the gain stability with an accuracy of a few percent.
We have searched for the K{sup +} {yields} {pi}{sup +}{gamma}{gamma} decay in the kinematic region with {pi}{sup +} momentum close to the end point. No events were observed, and the 90% ...confidence-level upper limit on the partial branching ratio was obtained, B(K{sup +} {yields} {pi}{sup +}{gamma}{gamma}, P > 213 MeV/c) < 8.3 x 10{sup -9} under the assumption of chiral perturbation theory including next-to-leading order ''unitarity'' corrections. The same data were used to determine an upper limit on the K{sup +} {yields} {pi}{sup +}{gamma} branching ratio of 2.3 x 10{sup -9} at the 90% confidence level.
A new cylindrical photon-veto detector for the KL→π0νν¯ experiment Murayama, R.; Togawa, M.; Ahn, J. K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2019, Letnik:
953, Številka:
C
Journal Article
Recenzirano
Odprti dostop
The J-PARC KOTO experiment aims to explore new physics beyond the Standard Model through the $K_L$ → $π^0v\bar{v}$ decay. Here we installed a new photon-veto detector, named the Inner Barrel (IB), to ...improve the detection efficiency and the timing resolution for photons in the region transverse to the neutral beam. The IB is a 2.8-m-long cylindrical detector with a 1.5 m inner diameter. The IB is a lead-scintillator sampling shower counter with a 5-radiation-length thickness and with a low mass support structure, and fits inside the 14-radiation-length-thick cylindrical detector. Scintillating light is read out from both ends via wavelength shifting fibers with a short decay time. The design, construction and performance of the IB are presented in this paper.
CsI calorimeter for the J-PARC KOTO experiment Sato, K.; Lee, J. W.; Banno, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2020, Letnik:
982, Številka:
C
Journal Article
Recenzirano
Odprti dostop
An electromagnetic calorimeter made of undoped CsI crystals is used in the J-PARC KOTO experiment to search for new physics beyond the standard model with the KL → π 0 νν¯ decay. The calorimeter is ...designed to operate in vacuum of 0.1 Pa and in a high-rate environment where the counting rate due to KL decays is O(100) kHz. A special method to calibrate the calorimeter during the data taking without using a tracking system for charged particles is reported. The energy, position, and timing resolutions of the calorimeter were evaluated in several beam tests, and the resolutions satisfy the required performance. Finally, the energy resolution with the total energy E is 0.66 ⊕ 1.81/ √ EGeV% in the inner region of the calorimeter.
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