Search for anomalous t t-bar production in the highly-boosted all-hadronic final state

TL;DR

This paper searches for heavy Z' particles decaying into top-antitop pairs in highly-boosted all-hadronic final states, using advanced jet substructure techniques to suppress background and set limits on new physics models at 7 TeV collision energy.

Contribution

It introduces new jet substructure analysis methods to identify boosted top quarks and sets experimental limits on Z' and Kaluza-Klein gluon production cross sections.

Findings

Set upper limits of about 1 pb on Z' production cross section.

Constrained possible enhancements in t t-bar production above Standard Model expectations.

Analyzed data from 7 TeV collisions with 5 fb^{-1} luminosity.

Abstract

A search is presented for a massive particle, generically referred to as a Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z' modeled for several widths, as well as for a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any enhancement in t t-bar production beyond expectations of the standard model for t t-bar invariant masses larger than 1 TeV.