Sarah Alam Malik, Graeme Watt
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). 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 a detailed study of 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^\pm/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(-> l nu)+jets events to estimate the Z(-> nu \bar{nu})+jets background in searches for new physics at the LHC.
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http://arxiv.org/abs/1304.2424
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