No 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.

We correct a factor in the Lagrangian, a sign of a coupling constant and 3-body decay rate. The factor of the second term in the interaction Lagrangian, (2), should be multiplied by 2,

The experimental sensitivity to µ → e conversion on nuclei is set to improve by four orders of magnitude in coming years. However, various operator coefficients add coherently in the amplitude for µ → e conversion, weighted by nucleus-dependent functions, and therefore in the event of a detection, identifying the relevant new physics scenarios could be difficult. Using a representation of the nuclear targets as vectors in coefficient space, whose components are the weighting functions, we quantify the expectation that different nuclear targets could give different constraints. We show that all but two combinations of the 10 Spin-Independent (SI) coefficients could be constrained by future measurements, but discriminating among the axial, tensor and pseudoscalar operators that contribute to the Spin-Dependent (SD) process would require dedicated nuclear calculations. We anticipate that µ → e conversion could constrain 10 to 14 combinations of coefficients; if µ → eγ and µ → eēe constrain eight more, that leaves 60 to 64 "flat directions" in the basis of QED×QCD-invariant operators which describe µ → e flavour change below § Another interesting observable at these experiments is the µ − e − → e − e − in a muonic atom. This process could have not only photonic dipole but also contact interactions, and the atomic number dependence of its reaction rate makes possible to discriminate the type of relevant CLFV interactions [7,8,9]. * * Since the current MEG bound on the dipole coefficients constrains them to be below the sensitivity of the current µ → e conversion bounds, the dipole overlap integral was set to zero in obtaining this Figure.