Search for an exotic decay of the Higgs boson to a pair of light pseudoscalars in the final state of two muons and two τ leptons in proton-proton collisions at $$ \sqrt{s}=13 $$ TeV

Abstract

Search for an exotic decay of the Higgs boson to a pair of light pseudoscalars in the final state of two muons and two τ leptons in proton-proton collisions at √ s = 13 TeVThe CMS Collaboration * Abstract A search for exotic Higgs boson decays to light pseudoscalars in the final state of two muons and two τ leptons is performed using proton-proton collision data recorded by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV in 2016, corresponding to an integrated luminosity of 35.9 fb −1 . Masses of the pseudoscalar boson between 15.0 and 62.5 GeV are probed, and no significant excess of data is observed above the prediction of the standard model. Upper limits are set on the branching fraction of the Higgs boson to two light pseudoscalar bosons in different types of two-Higgs-doublet models extended with a complex scalar singlet.Signal processes, for both h → aa → 2µ2τ and h → aa → 4τ, are generated using the MADGRAPH5 aMC@NLO 2.2.2 generator [23] with its implementation of the 2HDM and the NMSSM, in gluon fusion and vector boson fusion production. They are simulated at leading order (LO) in perturbative quantum chromodynamics (QCD) with the MLM jet matching and merging scheme [24]. The generator is interfaced with PYTHIA 8.212[25] to model the parton showering and fragmentation as well as the decay of the τ leptons. The CUETP8M1 tune [26] is chosen for the PYTHIA parameters controlling the description of the underlying event. The ZZ background from quark-antiquark annihilation is generated at next-to-LO (NLO) in perturbative QCD with POWHEG v2.0 [27][28][29], while the gg → ZZ process is generated at LO with MCFM 7.0 [30]. The set of parton distribution functions is NLO NNPDF3.0 for NLO samples, and LO NNPDF3.0 for LO samples [31]. The fully differential cross section for the qq → ZZ process has been computed at next-to-NLO (NNLO) [32], and the NNLO/NLO K-factor is applied to the POWHEG sample as a function of the invariant mass of the Z boson pair. Rare processes, such as triboson, ttZ, or SM Higgs boson production, have a negligible contribution to the signal region because they typically have a larger invariant mass of the four leptons in the final state.Simulated samples include additional pp interactions per bunch crossing (pileup), and are reweighted so as to match the pileup distribution observed in data. Generated events are processed through a simulation of the CMS detector based on GEANT4 [33].The reconstruction of events relies on the particle-flow (PF) algorithm [34], which combines the information from the CMS subdetectors to identify and reconstruct the particles emerging from pp collisions: charged and neutral hadrons, photons, muons, and electrons. Combinations of these PF objects are used to reconstruct higher-level objects such as jets or τ h candidates. The reconstructed vertex with the largest value of summed physics-object p 2 T is taken to be the primary pp interaction vertex, where p T denotes the transverse momentum. The physics

Two-real-scalar-singlet extension of the SM: LHC phenomenology and benchmark scenarios

“…Figure 4 (left) illustrates that experimental searches in this channel are beginning to directly constrain the TRSM for resonance masses between around 380 GeV and 550 GeV. In contrast, LHC searches [67][68][69][70][71][72][73] for the inverted signature of single-production of h 125 which then decays into a pair of light h a (a ∈ {1, 2}) are not yet sensitive, as the indirect constraints from Higgs signal rates on the possible new decay modes, BR(h 125 → NP) ≤ 7.3% (see Fig. 2), are much stronger than the direct limits from these searches.…”

“…In general, decays directly to SM particle final states as well as to two lighter scalar states ("Higgs-to-Higgs decays") are possible. While some of the former decays are already searched for by the LHC experiments, current searches for Higgs-to-Higgs decays focus almost exclusively on the signatures h S → h 125 h 125 (where h S denotes the new Higgs state with mass above 250 GeV) [55][56][57][58][59][60][61][62][63][64][65][66], or h 125 → h S h S (with the h S mass below 62.5 GeV) [67][68][69][70][71][72][73]. The model, however, features also Higgs decays to unidentical scalar bosons ("asymmetric decays"), Higgs decays involving only non-SMlike Higgs bosons, as well as the possibility of successive Higgs-to-Higgs cascade decays.…”

Searches for additional Higgs bosons decaying to tau leptons at the LHC

“…→ µµττ) where the h → aa → 4τ process is considered as a part of the signal, and is scaled with respect to the h → aa → µµττ signal. [20,21] This translates to limits on (σ(h)/σ SM )×B(h → aa) in the different 2HDM+S scenarios. As explained at the beginning of Section 4.2, the different scenarios are related to how the leptons, up-quark, and down-quark interact with the two doublets introduced.…”

“…The analysis here presented are based on pp collisions collected in 2016 by the CMS experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 f b −1 . Decay chains considered are aa → bbττ [20] and aa → µµττ [21]. Masses of the pseudoscalar boson between 15.0 and 62.5 GeV are probed.…”

Searching for a light Higgs boson via the Yukawa process at lepton colliders

“…The associated production can explore the Type-X 2HDM parameter space at high luminosity LHC where the mass of H ± or H (m H ± , m H ) is around 200 GeV and m A is close to 40 GeV [21]. On the other hand, the present upper limit on the branching ratio (BR) of the SM Higgs decaying to an AA pair is BR(h → A A) < 3 − 4% [23]. However, in general the mass of the new scalars (m H ± , m H ) can be larger than 200 GeV, also the hAA coupling is independent of the parameters involving (g − 2) µ and it is possible that the BR(h → AA) can be much smaller than the limit possible to obtain at the LHC [20], rendering the pseudoscalar virtually untraceable at the LHC.…”