S. M. Etesami

Lepton flavor violating interactions are absent in the standard model but are expected in various beyond standard models. In this work, the potential of the future circular electron-positron collider to probe the four fermion lepton flavor couplings via the $e^{+}e^{-}\rightarrow e^{\pm}\tau^{\mp}$ process is revisited by means of an effective field theory approach. We provide constraints at $95\%$ CL on the dimension-six Wilson coefficients including major sources of background processes and considering realistic detector effects at four expected operation energies $\sqrt{s}=157.5$, $162.5$, $240$ and $365$ GeV according to their corresponding integrated luminosities. We demonstrate that statistical combination of the results from four center-of-mass energies improves the sensitivity to the LFV couplings significantly. We compare the results with the prospects from Belle II with $50~ ab^{-1}$ and other studies at electron-positron colliders.

A β–γ coincidence spectrometer consisting of a 2π plastic beta detector and a NaI(Tl) detector, is described. In order to evaluate performance of the spectrometer, Monte Carlo simulation of the plastic and NaI(Tl) scintillators responses has been performed using GEANT4 code. This study reveals the possible efficiency loss of the system and enables us to calculate gamma detection efficiency of the system for different source-detector geometries.