A search for an excited muon decaying to a muon and two jets in pp collisions at √ s = 8 TeV with the ATLAS detector

A new search signature for excited leptons is explored. Excited muons are sought in the channel ${pp} o mu {mu }^{* } o mu mu { m{jet}};{ m{jet}}$, assuming both the production and decay occur via a contact interaction. The analysis is based on 20.3 fb−1 of pp collision data at a centre-of-mass energy of $sqrt{s};=;8;{ m{TeV}}$ taken with the ATLAS detector at the large hadron collider. No evidence of excited muons is found, and limits are set at the 95% confidence level on the cross section times branching ratio as a function of the excited-muon mass ${m}_{{mu }^{* }}$. For ${m}_{{mu }^{* }}$ between 1.3 and 3.0 TeV, the upper limit on $sigma B({mu }^{* } o mu qar{q}$) is between 0.6 and 1 fb. Limits on $sigma B$ are converted to lower bounds on the compositeness scale Λ. In the limiting case ${ m{Lambda }}={m}_{{mu }^{* }}$, excited muons with a mass below 2.8 TeV are excluded. With the same model assumptions, these limits at larger ${mu }^{* }$ masses improve upon previous limits from traditional searches based on the gauge-mediated decay ${mu }^{* } o mu gamma $.