Search for the Lepton Flavour Violating decays $\Upsilon(2S)\rightarrow e^{\pm}\mu^{\mp}$ and $\Upsilon(3S)\rightarrow e^{\pm}\mu^{\mp}$

TL;DR

This paper reports a search for lepton flavor violating decays of the $$Upsilon(2S) and $$Upsilon(3S) mesons into electron-muon pairs, testing physics beyond the standard model using large data samples from the BABAR experiment.

Contribution

First search for $$Upsilon(2S)$ and $$Upsilon(3S)$ decays to $e^{}\mu^{}$ using extensive data sets from BABAR, setting limits on these rare processes.

Findings

No evidence of lepton flavor violation observed.

Set upper limits on branching fractions for the decays.

Constraints on new physics models predicting such decays.

Abstract

Charged lepton flavour violating processes are unobservable in the standard model, but they are predicted to be enhanced in several new physics extensions. We present the results of a search for $\Upsilon (2S)$ and $\Upsilon (3S)$ decays to $e^{\pm}\mu^{\mp}$ decays. The search was conducted using data samples consisting of 99 million $\Upsilon (2S)$ and 122 million $\Upsilon (3S)$ mesons, collected at center-of-mass energies of 10.02 and 10.36 GeV, respectively, by the BABAR detector at the SLAC PEP-II $e^{+}e^{-}$ collider.