Searches for W′ bosons decaying to a top quark and a bottom quark in proton-proton collisions at 13 TeV

Abstract

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...

The experimental status of direct searches for exotic physics beyond the standard model at the Large Hadron Collider

“…2.3. Such models also can result in additional quarks and/or leptons that transform as vectors under the ordinary symmetry of the SM, referred to as "vector-like" quarks (VLQs) or leptons (VLLs) [ [160][161][162], and resonances decaying to VLQs [163]. Overall, the benchmarks used in these searches are RS1 KK gravitons, RS1 KK gluons (for tt resonances), or W bosons (for tb resonances).…”

A generic anti-QCD jet tagger

“…In order to distinguish such jets from the background jets resulting from quarks and gluons, generically denoted as 'QCD jets', several jet substructure analysis techniques have been developed [1][2][3][4][5][6][7][8][9][10][11][12][13]. These are extensively used in searches for W → tb [14,15], tt resonances [16], diboson resonances [17][18][19][20], vector-like quarks [21,22], dark matter produced in association with gauge bosons [23,24] and new light bosons [25].…”

Relaxing LHC constraints on the WR mass

“…while in the M ν R > M W R case, we assume that the contribution comes through the following decay chain: [20]; (top right) The cross section of WR → jj vs WR mass, compared to the ATLAS measurements [25]; (bottom left) The cross section of WR → eejj vs WR mass, for the case Mν R = MW R /2, compared to the CMS data [22]; (bottom right) The cross section of WR → µµjj vs WR mass, for the case where Mν R = MW R /2, compared to [22].…”