Search for the Lepton-Flavor Violating Decays Upsilon(3S) -> e tau and Upsilon(3S) -> mu tau

TL;DR

This paper reports a search for lepton-flavor violating decays of the Upsilon(3S) meson into electron or muon and tau, setting upper limits on their branching fractions and constraining new physics models.

Contribution

First search for Upsilon(3S) lepton-flavor violating decays, establishing upper limits and implications for beyond-the-Standard Model physics.

Findings

Upper limit on BF(Upsilon(3S) -> e tau) < 5.0e-6

Upper limit on BF(Upsilon(3S) -> mu tau) < 4.1e-6

Constraints on new physics mass scales

Abstract

Charged lepton-flavor violating processes are extremely rare in the Standard Model, but they may occur in several beyond-the-Standard Model theories, including Supersymmetry or models with leptoquarks or compositeness. We present a search for such processes in a sample of 117M Upsilon(3S) decays recorded with the BaBar detector. We place upper limits on the branching fractions BF(Upsilon(3S) -> e tau) < 5.0e-6 and BF(Upilon(3S) -> mu tau) < 4.1e-6 at 90% confidence level. These results are used to place lower limits on the mass scale of beyond-the-Standard Model physics contributing to lepton-flavor violating decays of the Upsilon(3S).