Abstract
Abstract The Technical Design for the COMET Phase-I experiment is presented in this paper. COMET is an experiment at J-PARC, Japan, which will search for neutrinoless conversion of muons into electrons in the field of an aluminum nucleus ($\mu$–$e$ conversion, $\mu^{-}N \rightarrow e^{-}N$); a lepton flavor-violating process. The experimental sensitivity goal for this process in the Phase-I experiment is $3.1\times10^{-15}$, or 90% upper limit of a branching ratio of $7\times 10^{-15}$, which is a factor of 100 improvement over the existing limit. The expected number of background events is 0.032. To achieve the target sensitivity and background level, the 3.2 kW 8 GeV proton beam from J-PARC will be used. Two types of detectors, CyDet and StrECAL, will be used for detecting the $\mu$–$e$ conversion events, and for measuring the beam-related background events in view of the Phase-II experiment, respectively. Results from simulation on signal and background estimations are also described.
Highlights
Despite successfully predicting and allowing understanding of phenomena in particle physics such as, most notably, the prediction and discovery of the Higgs boson, the Standard Model (SM) cannot provide the ultimate description of nature: it lacks a viable dark matter candidate, offers no explanation for the observed matter–antimatter asymmetry of the Universe, and does not account for neutrino oscillation phenomena
The COMET Phase-I experiment is a search for μ–e conversion, but at the same time it is an intermediate stage before the Phase-II experiment
Two special experimental runs will be carried out during the Phase-I experiment, beam measurement and background assessment, which will be dedicated measurements aiming for the preparation of the Phase-II experiment, and for a better understanding of the μ–e conversion data from the Phase-I experiment Both run programs will use the StrECAL detector with augmented configurations
Summary
Despite successfully predicting and allowing understanding of phenomena in particle physics such as, most notably, the prediction and discovery of the Higgs boson, the Standard Model (SM) cannot provide the ultimate description of nature: it lacks a viable dark matter candidate, offers no explanation for the observed matter–antimatter asymmetry of the Universe, and does not account for neutrino oscillation phenomena. The observation of neutrino oscillations implies that neutrinos are massive, and that individual lepton flavors are not conserved This contradicts the original SM formulation, in which neutrinos are massless by construction, and (accidental) symmetry leads to the conservation of total and individual lepton numbers. Such a departure from the SM paradigm indicates that numerous other processes that are forbidden in the SM might occur in nature. In the presence of new physics, one of the most interesting CLFV processes that can occur is the transition of a muon to an electron in the presence of a nucleus μ−N → e−N. A third phase, PRISM (Phase-Rotated Intense Slow Muons) [4,5], is being investigated and could potentially provide a further factor of 100 improvement
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