FINAL REPORT For Japan-Korea Joint Research Project

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1 (Form4-2) FINAL REPORT For Japan-Korea Joint Research Project AREA 1. Mathematics & Physics 2. Chemistry & Material Science 3. Biology 4. Informatics & Mechatronics 5. Geo-Science & Space Science 6. Medical Science 7. Humanities & Social Sciences 1. Research Title: Experimental study of the rare decay of the neutral K meson at J-PARC 2. Term of Research: From July 1 st, 2010 To June 30 th, Total Budget a. Financial Support by JSPS: Total amount: 2,400 thousand yen 1 st Year 800 thousand yen 2 nd Year 1,200 thousand yen 3 rd Year 400 thousand yen b. Other Financial Support : Total amount: 0 thousand yen 4. Project Organization a. Japanese Principal Researcher Komatsubara Takeshi Name Institution / Department Position High Energy Accelerator Research Organization () / Institute of Particle and Nuclear Studies (IPNS) Professor b. Korean Principal Researcher Name Ahn JungKeun Institution / Department Position Pusan National University / Department of Physics Professor 1

2 c. List of Japanese-side Participants (Except for Principal Researcher) Name Institution/Department Position Takao Inagaki Takahiro Sato GeiYoub Lim Tadashi Nomura Hiroaki Watanabe Noboru Sasao Hajime Nanjo Naoki Kawasaki Takahiko Masuda Daichi Naito Yosuke Maeda Shigeto Seki Taku Yamanaka Manabu Togawa Koji Shiomi Eito Iwai Kazufumi Sato Jong-won Lee Rie Murayama Yasuyuki Sugiyama Shintaro Banno Shiro Suzuki Tetsushi Shimogawa Hiroshi Yoshida Yasuhisa Tajima Naohiro Hobara Takao Shinkawa Toru Matsumura Hisashi Yokota Okayama Univ./ Research Core of Extreme Quantum World Saga Univ./Dept. of Physics Saga Univ./Dept. of Physics Yamagata Univ./Institute of Arts and Sciences Yamagata Univ./Institute of Arts and Sciences Yamagata Univ./Dept. of Physics emeritus emeritus Assistant Assistant postdoc. fellow research fellow research fellow Assistant 2

3 d. List of Korean-side Participants (Except for Principal Researcher) Name Institution/Department Position KwangYun Baek Sangyong Kim Jaeki Lee Eun-Joo Kim Myungshin Chung Yong Joo Kim Jong-Kwan Woo JeWou Ko Silin Na Hyosang Lee Chonbuk Nat. Univ./Dept. of Physics Hanyang Univ./Dept. of Physics Seoul Nat. Univ./Dept. of Physics Assistant Assistant Assistant postdoc. fellow 5. Number of Exchanges during the Final Fiscal Year* a. from Japan to Korea *Japanese fiscal year begins April 1. Name Home Institution Duration Host Institution Total: 0 persons Total: 0 man-days Numbers of Exchanges during the Past Fiscal Years FY2010: Total 0 persons FY2011: Total 2 persons b. from Korea to Japan Name Home Institution Duration Host Institution Eun-Joo Kim Sangyong Kim Jaeki Lee JeWou Ko JungKeun Ahn Chonbuk Nat.Univ. Jeju Nat. Univ. May 10 th to 13 th May 10 th to 15 th May 10 th to 16 th May 11 th to 13 th June 5 th, J-PARC, J-PARC Total: 5 persons Numbers of Exchanges during the Past Fiscal Years FY2010: Total 7 persons FY2011: Total 11 persons Total: 21 man-days 3

4 6. Objective of Research K L π 0 νν, which is a decay of the neutral K meson (kaon) into a neutral πmeson (pion) plus two neutrinos, is an extremely-rare physics phenomenon predicted in the Standard Model of particle physics to occur once in a few ten-billion times. In the measurement of this decay the CP-violating process, which governs the particle-antiparticle asymmetry in the Universe, can be determined with kaons containing the strange quark. Since theoretical uncertainties in the decay are small, a signature of new physics beyond the Standard Model can be observed through it. On the other hand, both of the initial and final states of the decay consist of neutral particles, and only the two photons from the subsequent neutral-pion decay are observable in the detector. Thus the measurement is extremely difficult. Our research group has performed the first experiment dedicated to the decay, E391a, at the proton synchrotron of, Tsukuba, Japan, in E391a s final results, of the world s record, were published in Based on the experience, we proceed to the precise measurement in our new experiment, KOTO, at J-PARC: Japan Proton Accelerator Research Complex, Tokai, Japan. For the KOTO experiment, Japanese and Korean teams had played a major role in the construction and survey of the new neutral beam line and in the beam tests of a prototype detector. The objective of this Japan-Korean Joint Research Project in was to continue the collaboration between two research teams, and enable us to move on to the construction of the KOTO detector. We also pursued R&D s for detector upgrades. The Korean collaborators were in the main force of the KOTO group and, with this research project, the contribution of the Korean team to the experiment was enhanced; in particular, we performed the construction, engineering run, and recovery works of the CsI calorimeter. 4

5 7. Methodology Neutral kaons are produced with the 30GeV proton beam from the J-PARC accelerator to the Experimental Hall. The neutral beam line for the KOTO experiment extracts only the neutral particles, directed at 16 degrees, to the experimental area located downstream. In Japanese fiscal year (JFY) 2009 we constructed the beam line and performed a survey of the beam quality and yield. In parallel, we designed and developed the detector subsystems to be used in the KOTO experiment. The main parts of the KOTO detector for K L π 0 νν are 1) the calorimeter with undoped CsI crystals to measure the neutral pion, 2) hermetic extra-photon counters around the decay region, and 3) the in-beam photon and charged-particle counters. One major upgrade from E391a to KOTO was to replace the 7cm x 7cm x 30cm CsI crystals in E391a by the 2.5cm x 2.5cm x 50cm and 5.0cm x 5.0cm x 50cm CsI crystals, 2716 in total, used in the past in the KTeV experiment at Fermilab, USA. We built the calorimeter in JFY 2010, and performed the engineering runs of the calorimeter three times: October 2010, February and June For the large extra-photon counter in the barrel region of the KOTO detector, we at first reuse the shower-counter modules in E391a,whose thickness is 14 radiation-lengths (X 0 s). Then we add new modules with 5 X 0 thick inside the barrel counter. We plan to start the installation of the new modules in the summer of To read out the signals from in-beam counters in high rate environment, we will use the 500MHz waveform digitizers. A candidate for them is 500MHz flash-adc boards being developed by Korean collaborators. Tests of the basic performance of the flash-adc boards were made with beam counters in the KOTO experimental area. 5

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