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 violating Wess-Zumino-Witten (WZW) anomaly term, the otherwise stable heavy photon A_H 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 channels. 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 500 GeV or relatively light T-odd quarks with a mass of around 400 GeV, one can reconstruct the A_H even at the early LHC run with \sqrt{s}=10 TeV and a modest integrated luminosity of 200 pb^{-1}. At \sqrt{s} = 14 TeV 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 1.5 TeV and with T-odd quark masses almost up to 1 TeV. In this region of the parameter space, the mass of the reconstructed A_H ranges from 66 GeV to 230 GeV.

35 pages, 4 figures; v2: additional multiple hard jets included in background simulation using ALPGEN, main conclusions unchanged, references added, version as published in JHEP.

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• Same-sign trileptons at the LHC: a window to lepton-number violating supersymmetry
• Indian Contributions to LHC Theory
• NLO QCD corrections to same-sign $T$-odd quark pair production in the littlest Higgs model with $T$-parity at the LHC
• $T$-odd quark pair production and decay at $\gamma \gamma$ collider in the littlest Higgs model with $T$ parity in next-to-leading order QCD