Fully hadronic ttbar cross section measurement with ATLAS detector

TL;DR

This paper measures the top quark pair production cross section in the fully hadronic final state using ATLAS data, addressing background estimation challenges and discussing trigger strategies for future high-luminosity runs.

Contribution

It presents a novel measurement of the ttbar cross section in the fully hadronic channel with data-driven background estimation techniques.

Findings

Observed upper limit of 261 pb at 95% CL

Expected Standard Model cross-section is 165+11-16 pb

Analysis highlights b-jet trigger performance

Abstract

The top quark pair production cross section in the fully hadronic final state is characterized by a six jet topology, two of which could be identified as originating from a b-quark using ATLAS b-tagging algorithms. Compared to other decay channels, this final state presents an advantageous larger branching ratio; on the other hand it suffers from a very large QCD multi-jet background, generally difficult to estimate from Monte Carlo simulation and therefore evaluated using data-driven techniques. The analysis is performed using 36pb-1 of pp collisions produced at the LHC with a center-of-mass energy of 7 TeV. The observed upper limit is set at 261 pb at 95% confidence level, where the expected Standard Model cross-section for the ttbar process is 165+11-16 pb. In the future, when the LHC luminosity increases, it is essential, to efficiently trigger on these fully hadronic ttbar events, to use dedicated triggers. An overview of the analysis for ttbar production cross section measurement in the fully hadronic final state and the state-of-the-art of the b-jet trigger performance estimation are presented in this contribution.