Abstract
A search is performed for a new resonance decaying into a lighter resonance and a Z boson. Two channels are studied, targeting the decay of the lighter resonance into either a pair of oppositely charged tau leptons or a b b-bar pair. The Z boson is identified via its decays to electrons or muons. The search exploits data collected by the CMS experiment at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.8 inverse femtobarns. No significant deviations are observed from the standard model expectation and limits are set on production cross sections and parameters of two-Higgs-doublet models.
Highlights
The observation of a new particle with a mass of approximately 125 GeV was reported by the ATLAS and CMS experiments at the CERN LHC in the WW, ZZ and γ γ final states [1,2,3]
The expected signal corresponding to mH = 350 GeV and mA = 90 GeV, whose cross section times branching fraction is normalised to the NNLO SusHi prediction, is superimposed for tan β = 1.5 and cos(β − α) = 0.01 in the 2HDM type-II scenario
The feature observed in the exclusion limit for the region around = (75–100, 200–300) GeV is the result of an interplay between the larger Z + jets background yields expected in this region and the quickly evolving signal cross section
Summary
The observation of a new particle with a mass of approximately 125 GeV was reported by the ATLAS and CMS experiments at the CERN LHC in the WW, ZZ and γ γ final states [1,2,3]. A recent theoretical study [10] has shown that, in this limit, a large mass splitting (>100 GeV) between the A and H bosons would favour the electroweak phase transition that would be at the origin of baryogenesis in the early universe, satisfying thereby the currently observed matter–antimatter asymmetry In this context, the most frequent decay mode of the pseudoscalar A boson would be A → ZH. The CMS Collaboration / Physics Letters B 759 (2016) 369–394 onance, the results can be interpreted in the reversed topology H → ZA, where the expected 2HDM mass hierarchy is inverted and the mass of A is expected to be light [17] For both topologies, the lighter scalar resonance (A or H) is not identified with the SM-like Higgs boson. Given its sensitivity to the 2HDM parameter space region where cos(β − α) ≈ 0, the search presented in this paper is complementary to other related searches performed in the same final state by the ATLAS and CMS collaborations [19,20]
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