Angular distributions intt¯H(H→bb¯)reconstructed events at the LHC

S P Amor Dos Santos,A Onofre,J P Araque,A Reigoto,N F Castro,J Silva,H Peixoto,R Cantrill,R Santos,R Martins,M C N Fiolhais,R Frederix,R Gonçalo

doi:10.1103/physrevd.92.034021

Abstract

The associated production of a Higgs boson and a top-quark pair, $t{\bar t} H$, in proton-proton collisions is addressed in this paper for a center of mass energy of 13TeV at the LHC. Dileptonic final states of $t{\bar t}H$ events with two oppositely charged leptons and four jets from the decays $t\rightarrow bW^+ \rightarrow b \ell^+\nu_\ell$, $\bar{t}\rightarrow \bar{b}W^- \rightarrow \bar{b} \ell^-\bar{\nu}_\ell$ and $h\rightarrow b\bar{b}$, are used. Signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed by applying a kinematic fit. New angular distributions of the decay products as well as angular asymmetries are explored in order to improve discrimination of $t{\bar t} H$ signal events over the dominant irreducible background contribution, $t{\bar t}b{\bar b}$. Even after the full kinematic fit reconstruction of the events, the proposed angular distributions and asymmetries are still quite different in the $t\bar{t}H$ signal and the dominant background ($t\bar{t}b\bar{b}$).

Highlights

On July 4, 2012 the ATLAS [1] and CMS [2] collaborations announced the discovery of a scalar particle at CERN’s Large Hadron Collider (LHC)
We argue the full kinematical reconstruction of the undetected neutrinos in such events, even if difficult, still preserves the angular distributions that could help in discriminating signal from irreducible backgrounds
We explore the advantages of fully reconstructing the ttH system in the dileptonic topology, by applying a kinematic fit to the events using mass constraints and energy-momentum conservation

Summary

INTRODUCTION

On July 4, 2012 the ATLAS [1] and CMS [2] collaborations announced the discovery of a scalar particle at CERN’s Large Hadron Collider (LHC). The production of the Higgs boson in association with a top quark-antiquark pair, pp → ttH [5], constitutes the only way (together with single top plus Higgs which has an even smaller cross section) to directly probe the top-quark Yukawa couplings. It is contaminated by a huge background coming mainly from pp → tt þ jets. One should note that ttH production can be studied at future linear colliders such as the ILC, which will lead to a tremendous improvement in the precision of measurements of the Yukawa couplings [14]

SIGNAL AND BACKGROUND GENERATION AT THE LHC

RECONSTRUCTION OF DILEPTON ttH EVENTS AFTER DETECTOR SIMULATION

ANGULAR DISTRIBUTIONS

FORWARD-BACKWARD ASYMMETRIES

CONCLUSIONS