Speaker
Dr
Paolo Crivelli
(ETH Zurich, Institute for Particle Physics)
Description
In the Standard Model (SM) there are several canonical examples of purely leptonic processes involving the muon, the electron and the corresponding neutrinos which are connected by the crossing
symmetry: i) the decay of muon, ii) the inverse muon decay and iii) the annihilation of a muon and an electron into two neutrinos.
Although the first two reactions have been observed and measured since long ago, the third process, resulting in the invisible final state, has never been experimentally tested.
It may go either directly, or, at low energies, via the annihilation of a muon and an electron from an atomic bound state, called muonium (Mu).
The Mu annihilation into two neutrinos is expected to be a very rare process, with the branching fraction predicted to be 6.6 x 10^-12 with respect to the ordinary muon decay rate.
In this talk, we will present our proposal for an experiment (MUTON) dedicated to the sensitive search for this process with a primary goal to observe it for the first time.
A feasibility study of the experimental setup shows that the sensitivity of the search in branching fraction at the level of 10^-12 could be achieved.
The Mu annihilation rate could be enhanced by non-SM contributions, e.g. due the muonium transition into a hidden sector.
This may occur in the mirror matter model due to muonium-mirror muonium conversion. The current indirect limit < 5.7 x 10^-6 (90\%C.L.) is quite modest, still leaving a big gap of about 6 orders of magnitude between this bound and the predictions.
The experiment is also sensitive to an exotic decay mode muon->invisible. This leptonic charge-non conserving process may hold in four-dimensional world in models with infinite extra dimensions, thus making its search complementary to colliders experiments probing new physics.
Primary author
Dr
Paolo Crivelli
(ETH Zurich, Institute for Particle Physics)
