RevModPhys.84.1477】Tests of the standard electroweak model at the energy frontier

Production provides a sensitive probe of new physics

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Unformatted text preview: es a sensitive probe of new physics, including anomalous trilinear gauge couplings, new resonances such as the Higgs boson, and large extra dimensions (Kober, Koch, and Bleicher, 2007). Recent results on diboson production from the Tevatron are discussed in Sec. III.E. A. Heavy gauge boson production In high-energy proton-antiproton collisions at the Fermilab Tevatron, heavy vector bosons (V  W; Z) are produced at " tree level via quark-antiquark annihilation (qq ! V ) as shown in Fig. 1. At high transverse momentum,1 the " leading-order QCD subprocesses are qq ! Vg and qg ! Vq. The production properties of heavy gauge bosons provide tests of perturbative QCD and, under certain circumstances, information about quark and gluon momentum distributions within the proton and antiproton. " The heavy vector boson production cross section in a pp collision is given by Z "" ðV Þ ¼ 0;V fðxq Þfðxq Þdxq dxq " in which 0;V is the cross section for production of a vector boson by a quark, antiquark pair with Feynman x values of xq "" and xq , respectively, and fðxq Þ and fðxq Þ are the parton " distribution functions for the proton and antiproton. As defined here, contributions from pure à and Z= à interference terms are not included but are accounted for in comparisons with theory in the measurements we describe. The remainder of this section includes a summary of current W and Z cross section measurements that the Tevatron and their comparisons with theory. As mentioned, these measurements of W and Z boson production cross sections primarily test QCD rather than electroweak theory. We include them here since detailed study of heavy gauge boson states are central to tests of electroweak theory and, therefore, it is important to consider how well their produc" tion in pp collisions is understood. The cross section times branching fraction of W and Z bosons is measured in the fully leptonic decay channels W ! ‘ and Z ! ‘‘, where ‘  e, , . While the final states involving  leptons are important for many reasons, we restrict ourselves to the e and  final states for the cross section discussion since these give the highest precision measurements. The fully leptonic decay channels are chosen 1 Throughout this paper, ‘‘transverse’’ is taken to be in a plane perpendicular to the beam directions, and unless otherwise noted, quantities with a ‘‘T ’’ subscript, e.g., ET , are values projected onto this plane. Also, charge conjugation is assumed throughout. Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 FIG. 1. Leading-order (a) W and (b) Z boson production via quark-antiquark annihilation. The production is dominated by q ¼ u, d valence quarks. The à contribution interferes with the Z diagram but is not shown. over hadronic channels for these measurements, since the latter suffer from large backgrounds to due to the hadronic decay of jets produced by QCD processes. 1. W a...
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This document was uploaded on 09/28/2013.

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