Modelisation of light transmission through surfaces with optical coating in Geant4

• Laurie Cappellugola

Surfaces with optical coating may be used to improve light transmission between a scintillating crystal and a photodetector. For the ClearMind project, we develop a detection module made of a PbWO4 crystal and a photocathode directly deposited on thin passivation film coating the crystal face. Scintillation photons will then be transmitted through this thin film that has a thickness of the order of scintillation light wavelength. Interference phenomena and frustrated transmission beyond the limit angle have then to be considered. We present the modelisation of light transmission through surfaces with optical coating in Geant4, which is achieved by defining a new method that provides a transmission probability for optical tracking of scintillation photons.

Search for the lepton flavour violating τ→lФ decay at Belle II

• Leonard Polat (Aix Marseille Univ, CNRS/IN2P3, CPPM, Marseille, France)

Being forbidden in the Standard Model (SM) of particle physics, lepton flavour violating (LFV) 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 in τ LFV decays has been greatly reinforced: in particular, several new physics models predict branching fractions just below the current experimental limits. The Belle II experiment located at KEK, Japan, started to take data in 2019. Thanks to its clean environment and high τ+τ− cross section, it provides an ideal environment to study the τ→lФ decay, a very promising channel with regard to leptoquark searches. Such an analysis relies heavily on an effective background suppression strategy that we present here, with a first look at data and simulation comparison using control channels.