Search for excited electrons and muons in sqrt(s)=8 TeV proton-proton collisions with the ATLAS detector

TL;DR

This paper reports a search for excited electrons and muons at the LHC using ATLAS data, setting new limits on their masses and the compositeness scale, with no evidence of their existence found.

Contribution

The study provides the first limits on excited lepton masses and the compositeness scale at 8 TeV proton-proton collisions, extending previous searches.

Findings

No evidence for excited leptons was observed.

Masses below 2.2 TeV are excluded for certain model assumptions.

Upper limits on production cross sections were established.

Abstract

The ATLAS detector at the LHC is used to search for excited electrons and excited muons in the channel pp -> ll* -> llgamma, assuming that excited leptons are produced via contact interactions. The analysis is based on 13 fb-1 of pp collisions at a centre-of-mass energy of 8 TeV. No evidence for excited leptons is found, and a limit is set at the 95% credibility level on the cross section times branching ratio as a function of the excited-lepton mass m_l*. For m_l* > 0.8 TeV, the respective upper limits on sigma*B(l* -> lgamma) are 0.75 fb and 0.90 fb for the e* and mu* searches. Limits on sigma*B are converted into lower bounds on the compositeness scale Lambda. In the special case where Lambda = m_l*, excited-electron and excited-muon masses below 2.2 TeV are excluded.