Searches are presented for heavy gauge bosons decaying into a top and a bottom quark in data collected by the CMS experiment at √ s = 13 TeV that correspond to an integrated luminosity of 2.2 and 2.6 fb −1 in the leptonic and hadronic analyses, respectively. Two final states are analyzed, one containing a single electron, or muon, and missing transverse momentum, and the other containing multiple jets and no electrons or muons. No evidence is found for a right-handed W boson (W R ) and the combined analyses exclude at 95% confidence level W R with masses below 2.4 TeV if M W R M ν R (mass of the right-handed neutrino), and below 2.6 TeV if M W R < M ν R . The results provide the most stringent limits for right-handed W bosons in the top and bottom quark decay channel. The CMS collaboration 23
IntroductionMany theories that extend the standard model (SM) predict additional charged gauge bosons [1][2][3][4][5], often referred to as W bosons. In models where the resonance is sufficiently massive, it is common to postulate that the coupling to third generation quarks might be enhanced relative to the second and first generations [6,7], making a search for the decay W → tb or tb highly appropriate. A particular advantage of this kind of search is that this channel is more easily distinguished from the large continuum of multijet background than -1 -
JHEP08(2017)029searches in the decays to light quarks (W → qq). The search in top and bottom quark (tb) systems complements searches in W → ν (where denotes a charged lepton and ν denotes a neutrino) and W → VV (where V denotes an SM W or Z boson) channels. The tb final state also benefits from the fact that its W mass can be fully determined, whereas in the leptonic mode there is a two-fold ambiguity in its mass. This paper presents the first search performed for a right-handed W (W R ) decaying to a top and a bottom quark at √ s = 13 TeV, using data collected by the CMS experiment corresponding to an integrated luminosity of up to 2.6 fb −1 . In scenarios where a theoretical right-handed neutrino (ν R ) is heavier than the W R , the decay W R → ν R is forbidden and the branching fraction B(W R → tb) is enhanced. This makes the W R → tb decay an important channel in the search for W bosons. Previous searches in the tb channel have been performed at the Fermilab Tevatron [8][9][10] and at the CERN LHC by both the CMS [11, 12] and ATLAS [13, 14] Collaborations. The most stringent limits to date on the production of W bosons with purely right-handed couplings come from the CMS search performed at √ s = 8 TeV [12]. Relative to this 8 TeV search, the expected production cross section of the W R boson at √ s = 13 TeV is enhanced by a factor of approximately 7 (13) for a 2 (3) TeV resonance.We separately analyze events with and without a lepton in the final state (referred to as leptonic and hadronic analyses), and then combine the results. In both analyses, the invariant mass of the tb system (M tb ) is used to conduct searches for the W R boson. The achieved sensi...