Search for the lepton flavor violating decay $Z \rightarrow e \mu$ in pp collisions at $\sqrt{s}$ = 8 TeV with the ATLAS detector

TL;DR

This paper reports a search for lepton flavor violation in Z boson decays to electron-muon pairs using ATLAS data, setting a new upper limit on the decay's branching fraction.

Contribution

First search for $Z ightarrow e $ decay at 8 TeV with ATLAS, establishing the most stringent upper limit to date.

Findings

No evidence of $Z ightarrow e $ decay was found.

Set an upper limit on the branching fraction: < 7.5 x 10^{-7}.

Method reduces systematic uncertainties using similar topology events.

Abstract

The ATLAS detector at the Large Hadron Collider is used to search for the lepton flavor violating process $Z \rightarrow e \mu$ in pp collisions using 20.3 $fb^{-1}$ of data collected at $\sqrt{s}$ = 8 TeV. An enhancement in the $e \mu$ invariant mass spectrum is searched for at the Z boson mass. The number of Z bosons produced in the data sample is estimated using events of similar topology, $Z \rightarrow ee$ and $\mu \mu$, significantly reducing the systematic uncertainty in the measurement. There is no evidence of an enhancement at the Z boson mass, resulting in an upper limit on the branching fraction, $B(Z \rightarrow e \mu)$ < 7.5 x 10$^{-7}$ at the 95% confidence level.