Single top-quark production at the Tevatron and the LHC

Abstract

This paper provides a review of the experimental studies of processes with a single top quark at the Tevatron proton-antiproton collider and the LHC proton-proton collider. Single top-quark production in the t-channel process has been measured at both colliders. The s-channel process has been observed at the Tevatron, and its rate has been also measured at the center-of-mass energy of 8 TeV at the LHC in spite of the comparatively harsher background contamination. LHC data also brought the observation of the associated production of a single top quark with a W boson as well as with a Z boson. The Cabibbo-Kobayashi-Maskawa matrix element |V tb | is extracted from the single-top-quark production cross sections, and t-channel events are used to measure several properties of the top quark and set constraints on models of physics beyond the Standard Model. Rare final states with a single top quark are searched for, as enhancements in their production rates, if observed, would be clear signs of new physics. * andrea.giammanco@uclouvain.be † schwier@pa.msu.edu arXiv:1710.10699v2 [hep-ex] 27 May 2018 13 4. s-channel 13 B. LHC 15 1. t-channel 15 2. W -associated (tW ) 18 3. tW plus tt in fiducial regions 21 4. s-channel 22 5. Z-associated (tZq) 25 C. Summary of the inclusive cross-section measurements 27 IV. SM parameter extraction and searches for new physics leading to anomalous couplings 29 A. Constraints on |V tb | and other CKM matrix elements 29 B. Cross section ratios as inputs for PDF extraction 32 C. Top-quark mass 33 D. tW b vertex structure 34 E. Searches for Flavor Changing Neutral Currents 37 F. H-associated single top-quark production (tH) 38 V. Conclusions and Outlook 42Acknowledgments 43References 44 1 The symbol x B is used to indicate the quantity "Bjorken x", i.e. the fraction of the incoming proton's total momentum involved in the parton-level scattering. 4insensitive to the b-quark PDF and can therefore act as a control process (Guffanti and Rojo, 2010). Moreover, the integrated or differential charge asymmetry in t-channel production provides a powerful input to constrain PDFs, similar to the case of W -boson production, in a region of x B very relevant for several searches. Examples of new physics that might influence t-channel production include a vector-like fourth generation quark with chromo-magnetic couplings (Nutter et al., 2012), a color triplet (Drueke et al., 2015), and FCNC interactions of the top quark with the gluon and the charm quark (Aguilar-Saavedra, 2009a). The s-channel mode is also sensitive to new resonances decaying to a top quark (Drueke et al., 2015), while the tW mode is sensitive to vector-like quarks (Aguilar-Saavedra, 2009b) and resonances decaying to a top quark and a W boson (Nutter et al., 2012). Experimentally, the study of top quarks proceeds by the reconstruction of its decay products. Almost all top quarks decay into a W boson and a b quark (Aaltonen et al., 2013(Aaltonen et al., , 2014aAbazov et al., 2011a; CMS Collaboration, 2014a). The former promptly decays ei...

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