Towards constraining dark matter at the LHC: higher order QCD predictions for tt¯+ Z(Z → ν`ν¯`)

Bevilacqua, G.; Hartanto, H.B.; Kraus, M.; Weber, T.; Worek, M.

Abstract

Triggered by ongoing dark matter searches in the top quark sector at the Large Hadron Collider we report on the calculation of the next-to-leading order QCD corrections to the Standard Model process pp → t t¯ + Z (Z → νℓ v¯¯¯ ℓ). This calculation is based on matrix elements for e+νeμ−ν¯¯¯μbb¯¯ντν¯¯¯τ production and includes all non-resonant diagrams, interferences, and off-shell effects of the top quarks. Non-resonant and off-shell effects due to the finite W -boson width are also consistently taken into account. As it is common for such studies, we present results for both integrated and differential cross sections for a few renormalisation and factorisation scale choices and three different parton distribution functions. Already with the fairly inclusive cut selection and independently of the scale choice and the parton distribution function non-flat differential K -factors are obtained for pmissT , ∆????ℓℓ, ∆????ℓℓ, cos θℓℓ, HT, H′T observables that are relevant for new physics searches. Good theoretical control over the Standard Model background is a fundamental prerequisite for a correct interpretation of possible signals of new physics that may arise in this channel. Thus, these observables need to be carefully reexamined in the presence of more exclusive cuts before any realistic strategies for the detection of new physics signal can be further developed. Since from the experimental point of view both t t¯ and t t¯ + Z (Z → νℓ v¯¯¯ ℓ) comprise the same final states, we additionally study the impact of the enlarged missing transverse momentum on various differential cross section distributions. To this end normalised differential distributions for pp → e+νeμ−ν¯¯¯μbb¯¯ντν¯¯¯τ and pp → e+νeμ−ν¯¯¯μbb¯¯ are compared.

Citation

Bevilacqua, G., Hartanto, H., Kraus, M., Weber, T., & Worek, M. (2019). Towards constraining dark matter at the LHC: higher order QCD predictions for tt¯+ Z(Z → ν`ν¯`). Journal of High Energy Physics, 2019(11), https://doi.org/10.1007/jhep11%282019%29001

• Journal Article Type: Article
• Acceptance Date: Oct 22, 2019
• Online Publication Date: Nov 4, 2019
• Publication Date: Nov 4, 2019
• Deposit Date: Nov 13, 2019
• Publicly Available Date: Nov 14, 2019
• Journal: Journal of High Energy Physics
• Print ISSN: 1126-6708
• Electronic ISSN: 1029-8479
• Publisher: Scuola Internazionale Superiore di Studi Avanzati (SISSA)
• Peer Reviewed: Peer Reviewed
• Volume: 2019
• Issue: 11
• DOI: https://doi.org/10.1007/jhep11%282019%29001
• Public URL: https://durham-repository.worktribe.com/output/1277598