Dark-photon searches via ZH production at e+e− colliders

Abstract

We study the ZH associated production followed by the Higgs H → γγ decay into a photon plus an invisible and massless dark photon, at future high-energy e + e − facilities. Large H → γγ decay rates (with branching ratios up to a few percent) are allowed, thanks to possible nondecoupling properties of the Higgs boson under specific conditions, and unsuppressed darkphoton couplings in the dark sector. Such large decay rates can be obtained in the framework of recent flavor models that aim to naturally explain the observed spread in the fermion mass spectrum. We analyze the experimental prospects for observing the e + e − → ZH process followed by the semi-invisible Higgs decay into a photon plus a massless invisible system. Search strategies for both the leptonic and the hadronic final states (arising from Z → µ + µ − and Z → qq, respectively) are outlined. We find that a 5σ sensitivity to a branching fraction BR γγ ∼ 3 × 10 −4 can be achieved by combining the two channels with an integrated luminosity of 10 ab −1 at a c.m. energy of 240 GeV. This is considerably better than the corresponding sensitivity in alternative channels previously studied at lepton colliders. The analysis is model independent, and its results can be straightforwardly applied to the search of any Higgs twobody decay into a photon plus an undetected light particle.

Neutrino-electron scattering: general constraints on Z′ and dark photon models

“…They are supposed to be much lighter than 90 GeV, the mass of the Z boson. Such particles have also been subject of intense searches at low energy colliders and accelerators [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. We emphasize that when we refer to the Z mass in our work, we mean the gauge boson mass in a general way, because the Z can take the form of a dark photon-like boson.…”

Dark origin of the quark flavor hierarchy and mixing

“…To conclude, we briefly discuss the main phenomenological aspects of the proposed model. Although the signatures of this scenario at collider and low energy experiments match those of the original proposal [9,10,11,12,13,15,16,17], the presence of novel dark flavon interactions strongly modifies its possible cosmological implications. In particular, imposing the flavor symmetry in the messenger sector for both the up and down sectors, the scenario predicts a dark fermion mass spectrum that matches the SM fermion one upon an almost constant rescaling.…”

“…In this construction, the messengers and the dark fermions are charged under a dark U (1) D gauge symmetry, accompanied by the corresponding massless gauge photon: the dark-photon. Phenomenological implications of this scenario have been analyzed in the context of dark photon searches [9,10,11,12] and Z boson physics [13].…”

Searching for massless Dark Photons at the LHC via Higgs boson production

“…While the predicted massless dark photonγ has in general suppressed interactions with the ordinary matter, for typical values of the charges and mixing parameters of the model the Higgs boson can enter in a nondecoupling regime. Then, the one-loop interaction with the dark photon (mediated by the messengers) is not suppressed by a large energy scale but by just the Higgs-boson field vacuum expectation value v [5,6]. This regime gives rise to new peculiar signatures in the Higgs decays that could be observed in Higgs production at high-energy collisions.…”