A search for an excited muon decaying to a muon and two jets in pp collisions at $\sqrt{s}\;=\;8\;{\rm{TeV}}$ with the ATLAS detector

• Published in: New journal of physics 2016-07, Vol.18 (7), p.73021
• Main Authors: Aad, G, Abbott, B, Abdallah, J, Abdinov, O, Abeloos, B, Aben, R, Abolins, M, AbouZeid, O S, Abramowicz, H, Abreu, H, Abreu, R, Abulaiti, Y, Acharya, B S, Adamczyk, L, Adams, D L, Adelman, J, Adomeit, S, Adye, T, Affolder, A A, Agatonovic-Jovin, T, Agricola, J, Aguilar-Saavedra, J A, Ahlen, S P, Ahmadov, F, Aielli, G, Akerstedt, H, Åkesson, T P A, Akimov, A V, Alberghi, G L, Albert, J, Albrand, S, Alconada Verzini, M J, Aleksa, M, Aleksandrov, I N, Alexa, C, Alexander, G, Alexopoulos, T, Alhroob, M, Alimonti, G, Alio, L, Alison, J, Alkire, S P, Allbrooke, B M M, Allen, B W, Allport, P P, Aloisio, A, Alonso, A, Alonso, F, Alpigiani, C, Alvarez Gonzalez, B, Álvarez Piqueras, D, Alviggi, M G, Amadio, B T, Amako, K, Amaral Coutinho, Y, Amelung, C, Amidei, D, Amor Dos Santos, S P, Amorim, A, Amoroso, S, Amram, N, Amundsen, G, Anastopoulos, C, Ancu, L S, Andari, N, Andeen, T, Anders, C F, Anders, G, Anders, J K, Anderson, K J, Andreazza, A, Andrei, V, Angelidakis, S, Angelozzi, I, Anger, P, Angerami, A, Anghinolfi, F, Anisenkov, A V, Anjos, N, Annovi, A, Antonelli, M, Antonov, A, Antos, J, Anulli, F, Aoki, M, Aperio Bella, L, Arabidze, G, Arai, Y, Araque, J P, Arce, A T H, Arduh, F A, Arguin, J-F, Argyropoulos, S, Arik, M, Armbruster, A J, Arnaez, O, Arnold, H, Arratia, M, Arslan, O, Artamonov, A
• Format: Article
• Language: English
• Subjects: excited leptons; lepton compositeness; leptoquarks; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
• ISSN: 1367-2630; 1367-2630
• DOI: 10.1088/1367-2630/18/7/073021

In this study, a new search signature for excited leptons is explored. Excited muons are sought in the channel ${pp}\to \mu {\mu }^{* }\to \mu \mu \ {\rm{jet}}\;{\rm{jet}}$, 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 $\sqrt{s}\;=\;8\;{\rm{TeV}}$ 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 $\sigma B({\mu }^{* }\to \mu q\bar{q}$) 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 ${\rm{\Lambda }}={m}_{{\mu }^{* }}$, 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 }^{* }\to \mu \gamma $.