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New NLOPS predictions for $t\overline{t}+b-jet$ production at the LHC


Ježo, Tomáš; Lindert, Jonas M; Moretti, Niccolo; Pozzorini, Stefano (2018). New NLOPS predictions for $t\overline{t}+b-jet$ production at the LHC. European Physical Journal C - Particles and Fields, 78(6):502.

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.

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.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
Dewey Decimal Classification:530 Physics
Uncontrolled Keywords:Physics and Astronomy (miscellaneous), Engineering (miscellaneous)
Language:English
Date:1 June 2018
Deposited On:20 Dec 2018 12:13
Last Modified:24 Sep 2019 23:58
Publisher:Springer
ISSN:1434-6044
OA Status:Gold
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1140/epjc/s10052-018-5956-0

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