Search for a heavy Higgs boson decaying into a Z boson and another heavy Higgs boson in the ℓℓbb final state in pp collisions at s=13 TeV with the ATLAS detector

Abstract

Search for a heavy Higgs boson decaying into a Z boson and another heavy Higgs boson in the bb final state in p p collisions at √ s = 13 TeV with the ATLAS detectorThe ATLAS Collaboration A search for a heavy neutral Higgs boson, A, decaying into a Z boson and another heavy Higgs boson, H, is performed using a data sample corresponding to an integrated luminosity of 36.1 fb −1 from proton-proton collisions at √ s = 13 TeV recorded in 2015 and 2016 by the ATLAS detector at the Large Hadron Collider. The search considers the Z boson decaying to electrons or muons and the H boson into a pair of b-quarks. No evidence for the production of an A boson is found. Considering each production process separately, the 95% confidencelevel upper limits on the pp → A → Z H production cross-section times the branching ratio H → bb are in the range of 14-830 fb for the gluon-gluon fusion process and 26-570 fb for the b-associated process for the mass ranges 130-700 GeV of the H boson and 230-800 GeV of the A boson. The results are interpreted in the context of two-Higgs-doublet models.Electrons are reconstructed from energy clusters in the electromagnetic calorimeter that are matched to tracks in the inner detector [52]. Electrons are required to have |η| < 2.47 and p T > 7 GeV. To distinguish electrons from jets, isolation and quality requirements are applied [53]. The isolation requirements (the 'LooseTrackOnly' working point) are defined by the p T of tracks within cones around the electron with a size that decreases as a function of the transverse energy. The quality requirements (the 'Loose' working point) refer to both the inner detector track and the calorimeter shower shape. The efficiency for an electron to be reconstructed and meet these criteria is about 85% for electron p T > 7 GeV and increases to about 90% for p T > 27 GeV.Muons are reconstructed by matching tracks reconstructed in the inner detector to tracks or track segments in the muon spectrometer [54]. Muons used for this search must have |η| < 2.5 and p T > 7 GeV, and are required to satisfy 'LooseTrackOnly' isolation requirements, similar to those used for electrons, as well as inner detector and muon spectrometer track 'Loose' quality criteria, corresponding to an efficiency of about 97%.Jets are reconstructed using the anti-k t algorithm [55,56] with radius parameter R = 0.4 from clusters of energy deposits in the calorimeter system [57]. Candidate jets are required to have p T > 20 GeV (p T > 30 GeV) for |η| < 2.5 (2.5 < |η| < 4.5). Low-p T jets from pile-up are rejected by a multivariate algorithm that uses properties of the reconstructed tracks in the event [58].Jets containing b-hadrons are selected using a multivariate tagging algorithm (b-tagging) [59,60]. The energy of the tagged jet (b-jet) is corrected for the average energy loss from semileptonic decays of b-hadrons and out-of-jet-cone tracks with large impact parameters [61]. The b-tagging efficiency for the jet p T range used in this analysis is between 65% and 75%. Applying the b-tagging algor...

Colorful imprints of heavy states in the electroweak effective theory

“…LHC diboson (W W , W Z, ZZ, W h and Zh) production analyses [73][74][75][76][77][78][79][80][81][82][83][84][85][86] confront the search for new physics from a different perspective. Instead of looking for a smooth increase of the signal over the SM background, these studies look for narrow bumps in the diboson invariant mass spectrum.…”

“…The study in this Subsection only refers to the available diboson analyses performed by other groups, which considered a narrow width approximation. In order to extract information on our LECs from those works [73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88], we followed the approximations used therein. These assumptions agree with those in the present work, as we are neglecting one-loop corrections and, in particular, the impact from resonance widths in the intermediate propagators.…”

“…In the range of resonance couplings discussed in [73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88], resonance widths are small enough to safely use the narrow-width approximation. If (much) larger resonance couplings than those depicted in Fig.…”

Natural stabilization of the Higgs boson’s mass and alignment

“…Finally, two searches for a neutral scalar produced in association with bb and decaying to Z plus another scalar which itself decays tobb or τ + τ − has been performed at 13 TeV by CMS and ATLAS [53,54] for models with both scalars' masses below 1 TeV. In order that there is adequate splitting between the scalars in our model, either the common scalar mass of the charged and selected neutral scalar must be greater than ∼ 400 GeV or less than ∼ 350 GeV, implying that the heavier scalar's mass is at least 400 GeV.…”

Complementary bound on the W′ mass from Higgs boson to diphoton decays

“…Direct searches for W have also been performed at the LHC in a plethora of final states [17][18][19][20][21][22][23][24][25] with bounds in the few TeV range. These searches, again, rely on assumptions about the branching ratios (BRs) of W into different channels, which, in turn, depend on the fermionic couplings of the W -boson.…”