Pair production of doubly charged scalars: neutrino mass constraints and signals at the CERN LHC

Abstract

We study the pair production of doubly charged Higgs bosons at the CERN Large Hadron Collider (LHC), assuming the doubly charged Higgs to be part of an SU(2)L triplet which generates Majorana masses for left-handed neutrinos. Such pair production has the advantage that it is not constrained by the triplet vacuum expectation value, which tends to make the single production rate rather small. We point out that, in addition to the Drell-Yan production mechanism, two-photon processes also contribute to H⁺⁺H⁻⁻ production at a level comparable to the QCD corrections to the Drell-Yan channel. Decays of the doubly charged Higgs into both the ℓ⁺ℓ⁺ and W⁺W⁺ modes are studied in detail to optimize the signal observation over the backgrounds. Doubly charged scalars should be observable at the LHC with 300  fb⁻¹ integrated luminosity in the ℓ^±ℓ^± channel up to the mass range of 1 TeV even with a branching fraction of about 60%, and in the W^±W^± channel up to a mass of 700 GeV. Such a doubly charged Higgs, if it is a member of a triplet that generates neutrino masses, cannot be long-lived on the scale of collider detectors although it might lead to a displaced secondary vertex during its decay if it is lighter than about 250 GeV.