Development of the Diamond based Proton Beam Monitor for COMET Experiment

Yuki Fujii

Research output: Chapter in Book/Report/Conference proceedingConference PaperResearch


The COMET experiment searches for the muon-to-electron(µ-e) conversion with a sensitivity below 10 16 which is 10,000 times better than the present upper limit. This process is strictly forbidden in the standard model because of the lepton flavor conservation law. In contrast, its branching ratio can be sizable around 10 15 in many models of physics beyond the standard model (BSM). Therefore the discovery of the µ-e conversion should be unambiguous evidence of BSM. Since sufficient amount of muons can be collected owing to the world most powerful pulsed proton beam at J-PARC, the background suppression is the most important to achieve the target sensitivity. In COMET, the measurement will be done between 500–1000 ns after coming the beam bunch to highly suppress the beam related prompt background. Even in this case, signals can be detected because of muon’s long life time (τµ ∼ 800 ns) in a muonic-atom in case of using aluminum. In this scheme, the “extinction factor”, (≡(#of residual protons between two bunches)/(#of protons in a bunch)), must be less than 10 9. To ensure such an extremely low extinction factor during the data taking, an innovative diamond detector will be adopted since it has high radiation tolerance to an intensive proton beam, and a fast time response to identify a single proton after the prompt beam. Recently, a prototype detector was developed based on a single-crystal diamond with a metal-insulator-metal type structure to perform the direct proton measurement inside the abort beam-line of J-PARC main ring. The installation was completed in this Spring and the direct beam measurement was conducted with the high intensity pulsed proton beam and the low intensity continuous beam. In this paper, results of above measurements are reported together with prospects.

Original languageEnglish
Title of host publicationProceedings of Science
Subtitle of host publicationThe European Physical Society Conference on High Energy Physics
PublisherSissa Medialab, SRL
Number of pages4
Publication statusPublished - 1 Jan 2017
Externally publishedYes
EventEuropean Physical Society Conference on High Energy Physics 2017 - Palazzo del Cinema and Palazzo del Casinò, Venice, Italy
Duration: 5 Jul 201712 Jul 2017

Publication series

NameProceedings of Science
PublisherSissa Medialab, SRL
ISSN (Print)1824-8039


ConferenceEuropean Physical Society Conference on High Energy Physics 2017
Abbreviated titleEPS-HEP 2017
OtherThe European Physical Society Conference on High Energy Physics (EPS-HEP) is one of the major international conferences that review the field. It takes place every other year since 1971. It is organized by the High Energy and Particle Physics Division of the European Physical Society. The latest conferences in this series were held in Vienna, Stockholm, Grenoble, Krakow, Manchester, Lisbon and Aachen.
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