Search for Charged Lepton Flavor Violation in Narrow Upsilon Decays

TL;DR

This paper reports a search for charged lepton flavor violation in narrow Upsilon decays, setting upper limits on branching fractions and constraining new physics models beyond the standard model.

Contribution

First search for charged lepton flavor violation in Upsilon decays using large BABAR data, establishing upper limits and bounds on new physics scales.

Findings

Upper limits on BF(Y(2S) -> e tau) and BF(Y(2S) -> mu tau) at 10^(-6)

Upper limits on BF(Y(3S) -> e tau) and BF(Y(3S) -> mu tau) at 10^(-6)

Lower limits of about 1 TeV on charged lepton flavor violating operators

Abstract

Charged lepton flavor violating processes are unobservable in the standard model, but they are predicted to be enhanced in several extensions to the standard model, including supersymmetry and models with leptoquarks or compositeness. We present a search for such processes in a sample of 99M Y(2S) decays and 117M Y(3S) decays collected with the BABAR detector. We place upper limits on the branching fractions BF(Y(nS) -> e tau) and BF(Y(nS) -> mu tau) (n = 2, 3) at the 10^(-6) level and use these results to place lower limits of order 1 TeV on the mass scale of charged lepton flavor violating effective operators.