FINAL REPORT For Japan-Korea Joint Research Project

Transcription

1 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, 2008 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 (KEK) / Institute of Particle and Nuclear Studies (IPNS) Associate 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 Koji Shiomi Naoki Kawasaki Takahiko Masuda Daichi Naito Yosuke Maeda Goh Takahashi Taku Yamanaka Manabu Togawa Yongdok Ri Eito Iwai Kazufumi Sato Jong-won Lee Shiro Suzuki Tetsushi Shimogawa Hiroshi Yoshida Yasuhisa Tajima Tomoaki Kamibayashi 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 postdoc. fellow d. List of Korean-side Participants (Except for Principal Researcher) Name Institution/Department Position HyoSang Lee KwangYun Baek Eun-Joo Kim Eun-San Kim In-Kyu Park Pusan Nat. Univ./Dept. of Physics Pusan Nat. Univ./Dept. of Physics Chonbuk Nat. Univ./Dept. of Physics Kyungpook Nat. Univ./Dept.of Physcs postdoc. fellow 2

3 Myungshin Chung SeoKon Kang MinKyu Choi Yong Joo Kim Jong-Kwan Woo JeWou Ko research 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 GeiYoub Lim KEK April 20 th to 25th Daejeon Convention Center (Korean Physical Society meeting) Total: 1 persons Total: 5 man-days Numbers of Exchanges during the past fiscal years FY2008: Total 15 persons FY2009: Total 2 persons b. from Korea to Japan Name Home Institution Duration Host Institution Myungshin Chung Univ. of Seoul May 27 th to 30th KEK Total: 1 persons Total: 4 man-days Numbers of Exchanges during the past fiscal years FY2008: Total 4 persons FY2009: Total 8 persons 3

4 6. Objective of Research K L π 0 νν, which is a decay of the neutral K meson (kaon) into a neutral π meson 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. Measurement of this decay is precious because the CP-violating process, which governs the particle-antiparticle asymmetry in the Universe, can be determined with kaons containing the strange quark. Further merit is, 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 π-meson decay are observable in the detector. Thus the measurement is extremely difficult. Our research group has performed the first experiment dedicated to the decay mode, E391a, at the proton synchrotron of High Energy Accelerator Research Organization (KEK), Japan, in E391a s final results, published in April 2010, were of the world s record. Based on the experience, we proceed to the precise measurement in our new experiment (E14, KOTO) at J-PARC: Japan Proton Accelerator Research Complex at Tokai, Ibaraki, Japan. The experiment was officially approved by KEK/J-PARC in August The objective of this Japan-Korean Joint Research Project was to design and develop the detector system for the new J-PARC experiment through closely cooperative works with the physicists in the Korean team participating in both the E391a and KOTO experiments. Expanding the collaboration with them was of crucial importance to perform the measurement of K L π 0 νν. Through the project, Japanese and Korean teams played a major role in the construction and survey of the new neutral beam line ( ) and in a beam test of a prototype detector ( ). 7. Methodology The 30GeV proton beam was successfully extracted from the J-PARC accelerator to the Experimental Hall in January The construction of a neutral beam line 4

5 for the KOTO experiment and the measurement of the neutral kaons produced by the proton beam in the experimental area located downstream, called beam survey, are the first step toward the experiment. In 2008, our research group finalized the design of the new beam line and prepared the equipment. We also developed and built the detectors to measure the neutral kaons, neutrons and photons in the beam. In 2009, we constructed the beam line at the Experimental Hall from April to September and performed a survey of the beam quality from October to February. In 2010, we analyzed the data of the beam survey to determine the yields and momentum spectra of kaons, neutrons and photons. At the same time, we designed and developed the detector subsystems to be used in the KOTO experiment. In 2008, based on the data analysis of the E391a experiment and the computer simulations, we studied the main parts of the KOTO detector: the calorimeter with undoped CsI crystals and the large extra-photon counter in the barrel region. 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 used in the KTeV experiment at Fermilab, USA. In 2009, we constructed a proto-type CsI calorimeter. We performed the beam test twice (January and April 2010) by using the electron beam facility of Research Center for Electron Photon Science, Tohoku University at Sendai, Miyagi, Japan. In 2010, we analyzed the data from the beam test and evaluated the performance of the CsI calorimeter. We also studied the procedures to build up the KOTO detector. 5