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Ratios of W and Z cross sections at large boson p T as a constraint on PDFs and background to new physics


Malik, Sarah Alam; Watt, Graeme (2014). Ratios of W and Z cross sections at large boson p T as a constraint on PDFs and background to new physics. Journal of High Energy Physics, 2014(2):1-32.

Abstract

We motivate a measurement of various ratios of W and Z cross sections at the Large Hadron Collider (LHC) at large values of the boson transverse momentum ( p T ≳ M W,Z ). We study the dependence of predictions for these cross-section ratios on the multiplicity of associated jets, the boson p T and the LHC centre-of-mass energy. We present the flavour decomposition of the initial-state partons and an evaluation of the theoretical uncertainties. We show that the W + /W - ratio is sensitive to the up-quark to down-quark ratio of parton distribution functions (PDFs), while other theoretical uncertainties are negligible, meaning that a precise measurement of the W + /W - ratio at large boson p T values could constrain the PDFs at larger momentum fractions x than the usual inclusive W charge asymmetry. The W ± /Z ratio is insensitive to PDFs and most other theoretical uncertainties, other than possibly electroweak corrections, and a precise measurement will therefore be useful in validating theoretical predictions needed in data-driven methods, such as using W (→ ℓν) + jets events to estimate the Z(→ ν) + jets background in searches for new physics at the LHC. The differential W and Z cross sections themselves, dσ /d p T , have the potential to constrain the gluon distribution, provided that theoretical uncertainties from higher-order QCD and electroweak corrections are brought under control, such as by inclusion of anticipated next-to-next-to-leading order QCD corrections.

Abstract

We motivate a measurement of various ratios of W and Z cross sections at the Large Hadron Collider (LHC) at large values of the boson transverse momentum ( p T ≳ M W,Z ). We study the dependence of predictions for these cross-section ratios on the multiplicity of associated jets, the boson p T and the LHC centre-of-mass energy. We present the flavour decomposition of the initial-state partons and an evaluation of the theoretical uncertainties. We show that the W + /W - ratio is sensitive to the up-quark to down-quark ratio of parton distribution functions (PDFs), while other theoretical uncertainties are negligible, meaning that a precise measurement of the W + /W - ratio at large boson p T values could constrain the PDFs at larger momentum fractions x than the usual inclusive W charge asymmetry. The W ± /Z ratio is insensitive to PDFs and most other theoretical uncertainties, other than possibly electroweak corrections, and a precise measurement will therefore be useful in validating theoretical predictions needed in data-driven methods, such as using W (→ ℓν) + jets events to estimate the Z(→ ν) + jets background in searches for new physics at the LHC. The differential W and Z cross sections themselves, dσ /d p T , have the potential to constrain the gluon distribution, provided that theoretical uncertainties from higher-order QCD and electroweak corrections are brought under control, such as by inclusion of anticipated next-to-next-to-leading order QCD corrections.

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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
Date:2014
Deposited On:05 Feb 2015 10:06
Last Modified:27 Apr 2017 23:39
Publisher:Springer
ISSN:1029-8479
Publisher DOI:https://doi.org/10.1007/JHEP02(2014)025

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