Spin and model identification ofZ′bosons at the LHC

Abstract

Heavy resonances appearing in the clean Drell-Yan channel may be the first new physics to be observed at the proton-proton CERN LHC. If a new resonance is discovered at the LHC as a peak in the dilepton invariant mass distribution, the characterization of its spin and couplings will proceed via measuring production rates and angular distributions of the decay products. We discuss the discrimination of the spin-1 of ${Z}^{\ensuremath{'}}$ representative models (${Z}_{\mathrm{SSM}}^{\ensuremath{'}}$, ${Z}_{\ensuremath{\psi}}^{\ensuremath{'}}$, ${Z}_{\ensuremath{\eta}}^{\ensuremath{'}}$, ${Z}_{\ensuremath{\chi}}^{\ensuremath{'}}$, ${Z}_{\mathrm{LR}}^{\ensuremath{'}}$, and ${Z}_{\mathrm{ALR}}^{\ensuremath{'}}$) against the Randall-Sundrum graviton resonance (spin-2) and a spin-0 resonance (sneutrino) with the same mass and producing the same number of events under the observed peak. To assess the range of the ${Z}^{\ensuremath{'}}$ mass where the spin determination can be performed to a given confidence level, we focus on the angular distributions of the Drell-Yan leptons, in particular, we use as a basic observable an angular-integrated center-edge asymmetry, ${A}_{\mathrm{CE}}$. The spin of a heavy ${Z}^{\ensuremath{'}}$ gauge boson can be established with ${A}_{\mathrm{CE}}$ up to ${M}_{{Z}^{\ensuremath{'}}}\ensuremath{\simeq}3.0\text{ }\text{ }\mathrm{TeV}$, for an integrated luminosity of $100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, or minimal number of events around 110. We also examine the distinguishability of the considered ${Z}^{\ensuremath{'}}$ models from one another, once the spin-1 has been established, using the total dilepton production cross section. With some assumption, one might be able to distinguish among these ${Z}^{\ensuremath{'}}$ models at 95% C.L. up to ${M}_{{Z}^{\ensuremath{'}}}\ensuremath{\simeq}2.1\text{ }\text{ }\mathrm{TeV}$.