Search for heavy Majorana neutrinos in e±e±+ jets and e±µ±+ jets events in proton-proton collisions at √s = 8 TeV

Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Asilar, E. and Filipovic, Nicolas and Bencze, György and Hajdú, Csaba and Hidas, Pál and Horváth, Dezső and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Zsigmond, Anna Júlia and Molnár, József and Bartók, Márton and Makovec, Alajos and Trócsányi, Zoltán and Ujvári, Balázs and Veres, Gábor (2016) Search for heavy Majorana neutrinos in e±e±+ jets and e±µ±+ jets events in proton-proton collisions at √s = 8 TeV. JOURNAL OF HIGH ENERGY PHYSICS (4). ISSN 1126-6708

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Abstract

A search is performed for heavy Majorana neutrinos (N) decaying into a Wboson and a lepton using the CMS detector at the Large Hadron Collider. A signature of two jets and either two same sign electrons or a same sign electron-muon pair is searched for using 19.7 fb−1 of data collected during 2012 in proton-proton collisions at a centre-of- mass energy of 8 TeV. The data are found to be consistent with the expected standard model (SM) background and, in the context of a Type-1 seesaw mechanism, upper limits are set on the cross section times branching fraction for production of heavy Majorana neutrinos in the mass range between 40 and 500 GeV. The results are ad- ditionally interpreted as limits on the mixing between the heavy Majorana neutrinos and the SM neutrinos. In the mass range considered, the upper limits range between 0.00015-0.72 for |VeN|2 and 6.6 × 10−5-0.47 for |VeNV∗ μN|2/(|VeN|2 + |VμN|2), where V`N is the mixing element describing the mixing of the heavy neutrino with the SM neu- trino of flavour `. These limits are the most restrictive direct limits for heavy Majorana neutrino masses above 200 GeV.

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