New NLOPS predictions for tt¯+btt¯+b -jet production at the LHC

Ježo, Tomáš; Lindert, Jonas M.; Moretti, Niccolo; Pozzorini, Stefano

Abstract

Measurements of tt¯H production in the H→bb¯ channel depend in a critical way on the theoretical uncertainty associated with the irreducible tt¯+b -jet background. In this paper, analysing the various topologies that account for b-jet production in association with a tt¯ pair, we demonstrate that the process at hand is largely driven by final-state g→bb¯ splittings. We also show that in five-flavour simulations based on tt¯+ multi-jet merging, b-jet production is mostly driven by the parton shower, while matrix elements play only a marginal role in the description of g→bb¯ splittings. Based on these observations we advocate the use of NLOPS simulations of pp→tt¯bb¯ in the four-flavour scheme, and we present a new Powheg generator of this kind. Predictions and uncertainties for tt¯+b -jet observables at the 13 TeV LHC are presented both for the case of stable top quarks and with spin-correlated top decays. Besides QCD scale variations we consider also theoretical uncertainties related to the Powheg matching method and to the parton shower modelling, with emphasis on g→bb¯ splittings. In general, matching and shower uncertainties turn out to be remarkably small. This is confirmed also by a consistent comparison against Sherpa+OpenLoops.

Citation

Ježo, T., Lindert, J. M., Moretti, N., & Pozzorini, S. (2018). New NLOPS predictions for tt¯+btt¯+b -jet production at the LHC. The European Physical Journal C, 78(6), Article 502. https://doi.org/10.1140/epjc/s10052-018-5956-0

• Journal Article Type: Article
• Acceptance Date: May 31, 2018
• Online Publication Date: Jun 18, 2018
• Publication Date: Jun 18, 2018
• Deposit Date: Jun 28, 2018
• Publicly Available Date: Jun 28, 2018
• Journal: European Physical Journal C: Particles and Fields
• Print ISSN: 1434-6044
• Electronic ISSN: 1434-6052
• Publisher: SpringerOpen
• Peer Reviewed: Peer Reviewed
• Volume: 78
• Issue: 6
• Article Number: 502
• DOI: https://doi.org/10.1140/epjc/s10052-018-5956-0
• Public URL: https://durham-repository.worktribe.com/output/1356069