Measuring the tth coupling from SSDL+2b measurements

TL;DR

This paper assesses the potential of a dedicated SSDL+2b search at the LHC to measure the top Yukawa coupling directly, reducing uncertainties and improving precision over current methods.

Contribution

It introduces a new calculation method for fake leptons and demonstrates how combining measurements across different LHC runs can clarify the top Yukawa coupling.

Findings

Feasibility of measuring tth coupling via SSDL+2b channel

Development of a new fake lepton background calculation method

Combining LHC data improves coupling determination

Abstract

We evaluate the potential of a dedicated search for tth production in the SSDL+2b channel. Such a measurement provides direct access to the top Yukawa coupling, since the sensitivity is not convolved with the loop-level h-gamma-gamma or poorly known hbb coupling, as is the case for present tth searches. Furthermore, susceptibility to uncertainties in the Higgs width can be reduced by considering a ratio of SSDL+2b rates with those of the performed Wh -> WWW* measurement. The SSDL channel can therefore rely primarily on the already well-measured h->WW* decay. This feasibility study required the development of a new calculation method for "fake" leptons, which constitute the dominant background to our search. Combining measurements from LHC7, LHC8 and in the future LHC14 for the Higgs coupling fit would help resolve any remaining ambiguity between the top Yukawa coupling and a BSM contribution to the hgg coupling.