Search for lepton flavour violating decays at Belle II

Stage numéro : Doctorat-2124-BE-01
Laboratoire :Centre de Physique des Particules de Marseille Case 902
 163 avenue de Luminy - 13288 Marseille Cedex 9
Directeur :Cristinel Diaconu - 04.91.82.72.01 - diaconu@cppm.in2p3.fr
Correspondant :William Gillard - 04.91.82.72.67 - gillard@cppm.in2p3.fr
Groupe d'accueil :Belle II
Chef de groupe :Justine Serrano - 04.91.82.72.80 - serrano@cppm.in2p3.fr
Directeur de thèse :Justine Serrano - 04 91 82 72 80 - serrano@cppm.in2p3.fr

Thématique : Physique des particules

Being forbidden in the Standard Model (SM) of particle physics, lepton flavour violating decays are among the most powerful probes to search for physics beyond the SM. In view of the recent anomalies seen by LHCb on tests of lepton flavor universality in b → sll and b → clν processes, the interest of tau lepton flavor violating decays has been greatly reinforced. In particular, several new physics models predict branching fractions of τ→ 3 μ and τ→ μγ just below the current experimental limits.

Similarly, b → τX decays provide powerful probes to test the presence of New Physics.

The Belle II experiment located at KEK, Japan, has just started physics data taking, aiming at collecting 50 times more data than its predecessor, Belle, by 2030. Thanks to its clean environment and high τ+ τ cross section, it provides an ideal environment to study tau and b → τ decays. The goal of this thesis is analyse Belle II data to provide the most stringent limit on LFV decays.

Activities:

Data analysis, participation to data taking, participation to Belle II service tasks, activities of outreach and dissemination.

Work context:

This phD will take place at CPPM, Marseille (https://www.cppm.in2p3.fr/web/en/index.html). Travels to KEK for collaboration meetings, and longer stay for participation to the data taking, are foreseen (if allowed by COVID crisis).

The funding of this phD is provided by an ERC grant obtained by Justine serrano.

Références:

https://arxiv.org/abs/1808.10567

https://hflav-eos.web.cern.ch/hflav-eos/tau/spring-2017/lfv-limits-plot.html

https://arxiv.org/abs/1903.11517

https://arxiv.org/pdf/1806.05689.pdf