Dilepton and four-lepton signals at the LHC in the Littlest Higgs model with T-parity violation

Abstract

In the presence of the T-parity violatingWess-Zumino-Witten (WZW) anomaly term, the otherwise stable heavy photon AH in the Littlest Higgs model with T-parity (LHT) decays to either Standard Model (SM) gauge boson pairs, or to SM fermions via loop diagrams. We make a detailed study of the collider signatures where the A_H can be reconstructed from invariant mass peaks in the opposite sign same flavor dilepton or the four-lepton channel. This enables us to obtain information about the fundamental symmetry breaking scale f in the LHT and thereby the low-lying mass spectrum of the theory. In addition, indication of the presence of the WZW term gives us hints of the possible UV completion of the LHT via strong dynamics. The crucial observation is that the sum of all production processes of heavy T-odd quark pairs has a sizeable cross-section at the LHC and these T-odd particles eventually all cascade decay down to the heavy photon A H . We show that for certain regions of the parameter space with either a small f of around 500GeV or relatively light T-odd quarks with a mass of around 400GeV, one can reconstruct the A H even at the early LHC run with √s = 10TeV and a modest integrated luminosity of 200 pb⁻¹. At √s = 14TeV and with an integrated luminosity of 30 fb⁻¹, it is possible to cover a large part of the typical parameter space of the LHT, with the scale f up to 1.5TeV and with T-odd quark masses almost up to 1TeV. In this region of the parameter space, the mass of the reconstructed A H ranges from 66GeV to 230GeV.