Charged-lepton flavour-violating (CLFV) processes offer deep probes for new physics with discovery sensitivity to a wide range of new physics models - SUSY, Higgs Doublets, Extra Dimensions, and, particularly, models explaining the neutrino mass hierarchy and the matter- antimatter asymmetry in the Universe via leptogenesis. The most sensitive exploration of CLFV process is provided by experiments that utilize high intensity muon beams to search for CLFV  μ → e transitions:  μ⁺→e⁺γ (experiment MEG at PSI);  μ⁺→e⁺e^-e⁺(experiment Mu3e at PSI), and coherent neutrinoless conversion of a muon into an electron in the field of a nucleus μ⁻N → e⁻N, COMET (COherent Muon to Electron Transition) experiment at J-PARC.

COMET experiment will be implemented in two phases, Phase-I and Phase-II. The experimental sensitivity goal for this process in the Phase-I experiment is 3.1 × 10^-15, or the 90% upper limit of the branching ratio of 7 × 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 µ-e conversion events and for measuring the beam-related background events in view of the Phase-II experiment, respectively.

Scientists from JINR are successfully participating in the preparation stage of the COMET experiment. For the COMET Phase-I experiment, JINR scientists produced and tested in accordance with the requirements the whole set  about 2700 of 9.8-mm straw tubes. For Phase – II JINR scientists will make a full set of 5-mm straw tubes and will also take an active part in the development of the entire straw tracker, electromagnetic calorimeter and Cosmic Ray Veto (CRV) system as well as in assembly and maintanance of detectors and in further data analysis.

Expected results upon completion of the project:

1. Production of all thin-wall straw tubes. Different procedures of the tube tests for pressure, gas leakage and elongation, in accordance with the COMET requirements.

2. R&D for straw tubes with the diameter fo 5 mm and wall thickness of 12μm for the COMET Phase-II. For this purpose, we prepared a new straw line at DLNP.

3. Assembling, testing and installation of the 2nd and 3rd straw tracker stations for Phase-I.

4. Production of a full-scale straw station with a new type of straw tubes for Phase-I.

5. Development and optimization of a crystal calibration method for the calorimeter to be used in COMET Phase‑I and Phase-II.

6. Assembling, testing, installation and operation of the calorimeter.

7. Implementation of a full-scale R&D program to create a cosmic veto system (CRV), providing determination of principles and parameters for the construction of complete CRV system. Manufacturing, assembling, testing of the CRV for Phase-α.

Expected results of the project this year:

1. Participation in the preparation, engineering and physics run of Phase-α.

2. R&D program for production of the straw tubes with the wall thickness of 12 μm and diameter of 5 mmwall. Measurement of all mechanical properties and development of standards for quality control of manufactured brand-new 5 mm diameter straw tubes.

3. Completion of assembly, testing, calibration, installation, cosmic test and maintenance of 2-3 straw detector stations for Phase-I.

4. Production of straw tubes (about 1000) for the full-scale prototype.

5. Production of a full-scale straw station at JINR with new tubes (12 μm, 5 mm).

6. Preparation for mass production and testing of straw tubes for Phase-II.

7. Development and optimization of a crystal calibration method for a COMET calorimeter, with allpwance the features of the experiment: the presence of a magnetic field and high-resolution calorimeter.

8. Participation in the full calorimeter assembling, installation, cosmic test and maintenance.

9. Participation in the assembling and testing of the CRV for Phase-I.

10. Participation in the beam tests of the detector components for Phase-I.

11. Integrated detector system (tracker, calorimeter, etc.) simulation.

12. Participation in the engineering and physics run in Phase-α.