Abstract
We consider the possibility of new physics giving rise to effective interactions of the form e+e−Hff¯, where f represents a charged lepton ℓ or a (light) quark q, and H the recently discovered Higgs boson. Such vertices would give contributions beyond the standard model to the Higgs production processes e+e−→Hℓ+ℓ− and e+e−→Hqq¯ at a future e+e− collider. We write the most general form for these vertices allowed by Lorentz symmetry. Assuming that such interactions contribute in addition to the standard model production processes, where the final-state fermion pair comes from the decay of the Z boson, we obtain the differential cross section for the processes e+e−→Hℓ+ℓ− and e+e−→Hqq¯ to linear order in the effective interactions. We propose several observables with differing CP and T properties which, if measured, can be used to constrain the couplings occurring in interaction vertices. We derive possible limits on these couplings that may be obtained at a collider with centre-of-mass energy of 500 GeV and an integrated luminosity of 500 fb−1. We also carry out the analysis assuming that both the electron and positron beams can be longitudinally polarized, and find that the sensitivity to the couplings can be improved by a factor of 2–4 by a specific choice of the signs of the polarizations of both the electron and positron beams for the same integrated luminosity.
Highlights
While the present data from the LHC indicate that the particle of mass around 125 GeV discovered recently may be the standard model (SM) Higgs boson, the accuracy of the present experiments is not sufficient to nail the issue
We restrict ourselves to the case when the Higgs boson is accompanied by a fermion pair. Such a final state can arise in the SM or its extensions through the HiggsStrahlung (HS) process e+e− → H Z, an important mechanism for the production of the Higgs boson, with the final Z decaying into a fermion pair
We have considered in the foregoing a model-independent way of characterizing the production of a Higgs mass eigenstate H in a possible extension of SM at an e+e− collider
Summary
While the present data from the LHC indicate that the particle of mass around 125 GeV discovered recently may be the standard model (SM) Higgs boson, the accuracy of the present experiments is not sufficient to nail the issue. The CP violation could come either from the mixing of the Higgs fields with different CP properties, or from a combination of interaction vertices, some of which violate CP, and contribute to make up the form factors. We investigate here how these interaction form factors can be determined, or constrained, at a linear collider, with or without longitudinally polarized beams. We shall calculate the differential cross section including the SM amplitudes and the amplitude coming from the effective interaction for the generic process (1), without distinguishing the various final states, it being understood that the VBF contribution will be absent when the final state does not have f ≡ e, and SM couplings and the form factors coming from (2) will be appropriately chosen, depending on the final state
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