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Register a new userImproving quark flavor separation with forward W and Z production at LHCb
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Juan Rojo
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We quantify the constraints on the flavour separation between the quarks and antiquarks in the proton provided by the recent forward weak gauge boson production data from the LHCb experiment at $sqrt{s}=7$ and 8 TeV. Performed in the framework of the NNPDF3.1 global analysis, this study highlights the key role that the LHCb W and Z data have in achieving a robust quark flavour separation in the large-x region, including the strange and charm quarks. We demonstrate how the LHCb measurements lead to improved determinations of the the up and down quark PDFs in the region $xge 0.1$, with an uncertainty reduction that can be as large as a factor 2. We also show how the LHCb forward measurements severely restrict the size of the fitted charm PDF at large x, imposing stringent constraints on non-perturbative models for the charm content of the nucleon.
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We report on the first computation of the next-to-next-to-leading order (NNLO) QCD corrections to $W^{pm}Z$ production in proton collisions. We consider both the inclusive production of on-shell $W^{pm}Z$ pairs at LHC energies and the total $W^{pm}Z$ rates including off-shell effects of the $W$ and $Z$ bosons. In the off-shell computation, the invariant mass of the lepton pairs from the $Z$ boson decay is required to be in a given mass window, and the results are compared with the corresponding measurements obtained by the ATLAS and CMS collaborations. The NNLO corrections range from 8% at $sqrt{s}$=7 TeV to 11% at $sqrt{s}$=14 TeV and significantly improve the agreement with the LHC data at $sqrt{s}$=7 and 8 TeV.
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Inclusive c and b-jet tagging algorithms have been developed to utilize the excellent secondary vertex reconstruction and resolution capabilities of the LHCb detector. The validation and performance of these tagging algorithms are reported using the full run 1 LHCb dataset at 7 and 8 TeV. Jet-tagging has been applied to muon+jet final states to measure both the W+c,b-jet charge asymmetries and the ratios of W+c,b-jet to W+jet and W+jet to Z+jet production. The forward top production cross-section is also measured using the muon+b-jet final. All results are found to be consistent with standard model predictions.
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