Difference: FJPPLMuonPhysics (8 vs. 9)

Summary :
New particles and interactions beyond the Standard Model (SM) of particle physics are required to explain neutrino masses and mixing angles. The search for traces of this new physics (NP) is pursued on many fronts. One possibility is to look directly for the new particles implicated in neutrino mass generation, for instance at the LHC. A complementary approach seeks indirectly new interactions among rare processes, such as charged lepton flavour violation (CLFV). CLFV transitions can be induced by the observed massive neutrinos in the SM, at unobservable rates suppressed by 10 e-48. A detectable rate would point to the existence of new heavy particles, as may arise in models that generate neutrino masses, or that address other puzzles of the SM such as the hierarchy problem. Observations of CLFV are therefore crucial to identifying the NP of the lepton sector, providing information complementary to direct searches. The experimental sensitivity to a wide variety of CLFV processes is systematically improving. Current bounds on branching ratios of the muon to electron flavour changing processes are currently of order of 10 e-13. Future experimental sensitivities should improve by several orders of magnitude, in particular, the COMET and Mu2e experiments which aim to reach a sensitivity to μ-e conversion on nuclei of ∼ 10 e-16. Given such rapid experimental progress in the future, our main area of research is to study in details physics opportunities for the CLFV processes, and explore new opportunities, by the joint collaboration of theorists and experimentalists between Japan and France. We have already made the first research achievement, on the study of spin-depended muon to electron conversion, which has been published in a scientific journal of Physics Letters in 2017 [1]. This physics case has never previously been considered. We will explore further unique physics cases in our research collaboration. To achieve this goal, we are planning to organize informal meetings and workshops between French and Japanese.

French members :
A. M. Teixeira, S. Davidson, C. Hati, J. Kriewald, T. Salgues

Japanese members :
J. Sato, Y. Kuno, M. Yamanaka, Y. Uesaka, H. Kakizawa, K. Sugawara

References :
[1] V. Cirigliano, S. Davidson and Y. Kuno, “Spin-dependent μ→e conversion“, Phys. Lett. B771 (2017) 242-246
[2] S. Davidson, Y. Kuno, A. Saporta, “Spin-dependent μ→e conversion on light nuclei”, Eur.Phys.J. C78 (2018) 109