Search for tau lepton flavour violating decays at Belle II

Stage numéro : M2-2021-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
Responsable de stage :Justine Serrano - 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.

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 decays. The goal of this internship is to study the τ→ lγ decay while reconstructing the opposite tau in the event into a three prong decay.

The analysis code is based on ROOT and python. Multivariate methods will be studied to optimize the analysis performances.

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