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
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 Ã and Z=
Ã 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 Ã 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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