Top jets at the LHC

by Gilad Perez (Weizmann Institute)

Friday 10 Oct 2008, 14:00 → 15:00 Europe/Zurich

TH Theory Conference Room (CERN)

We focus on high $p_T$ hadronically-decaying top quarks, due to high degree of collimation the efficacy of conventional reconstruction methods tends to be very low. We look at the extreme case where the decay products of the top quark are reconstructed as a single jet, a ``top-jet". We first consider ``top-tag" method based on jet mass. We analyze both theoretical and experimental aspects of the large irreducible QCD jet background. We derive a simple approximation for the shape of the QCD jet mass spectrum via QCD factorization. A good agreement between our analytic predictions and the Monte Carlo results is obtained. We consider Standard Model, top pair production as an example. Our theoretical QCD jet mass functions allow us to efficiently characterize the background via a side band analysis; we find a discovery reach of up to $p_T\sim 1.5$ TeV, with 100 $fb^{-1}$, without relying on $b$ tagging. To further improve the significance we consider jet shapes (0807.0234 [hep-ph]), which resolve substructure of energy flow within the cone. The main virtues of our approach are: (i) it does not rely blindly on results from Monte Carlo but rather on first principle calculations; (ii) it Applies to high $p_T$ objects and is less susceptible to finite-detector resolution effects.

Slides topjets_CERN.pdf