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Proceedings of the XXIX PHYSICS IN COLLISION
Paolo Mastrandrea *,
* Fermilab, Batavia, IL 60510-5011, USA
t On behalf of CDF and DO collaborations
The studies of the diboson production in pp collisions
at 1.96 TeV performed by CDF and DO collaborations
at the Tevatron collider are reported in this paper. The
diboson events are identified by means of both leptonic
and semi-leptonic final states. The presented results use
different statistical samples collected by the Tevatron up
to 4.8 fb-1. Measured production cross sections are in
good agreement with Standard Model predictions and
the limits on the anomalous triple gauge boson couplings
are competitive with those measured by experiments at
the Large Electron-Positron collider (LEP).
Measurements of the associated production of two vec-
tor bosons (-y, W, Z) are important tests of the elec-
troweak sector of the Standard Model (SM). The pro-
duction of a diboson final state (Fig. 1.) can occur by
particle-antiparticle annihilation (t-channel) or by boson
self-interaction (s-channel). This kind of final state rep-
resents a unique probe for the triple gauge boson coupling
(TGC). Vector boson self-couplings are fundamental pre-
dictions of the SM resulting from the non-Abelian nature
of the SU(2)L x U(1)y gauge symmetry theory, which
was firstly demonstrated by precision measurement of
W+W- and ZZ pair production at LEP II . Ob-
serving TGCs not permitted in the SM or with different
intensity with respect to the SM predictions, would be a
sign of new physics. A summary of the different TGC's
is reported in Table 1.
The VWW vertices are completely described by 14 in-
dependent couplings, 7 each for ZWW and -WW pro-
cesses. Assuming C and P conservation and electro-
magnetic gauge invariance, the number of independent
parameters can be reduced to 5. A common adopted set
is (K'y, nz, Ay, Az, gf), where 'my i z g = 1 and
Ay Az 0, in the SM at tree level. Using constraints
due to gauge invariance, Kz and Az can be expressed as
a function of the other parameters and the weak mixing
angle OW as: Kz g1 (Ky -1) tan2(Ow) and Az Ay.
A common formulation to report the independent
parameters describing the TGC in VWW vertices is
(AKy, Agf, Ay), where AK2 Ky-1 and Agz = 1.
Deviations from the SM prediction for the Z-* and
Z-yZ* couplings may be described in terms of 4 param-
Table 1. Summary of the triple gauge boson couplings.
Coupling Final state
WI--> W Not present at LEP
VWW (V=Z, y) y->VWW
Z -WW LEP and Tevatron
Zyy* and ZyZ* *>
Z* - Zy Absent in SM
ZZy* and ZZZ* y* ZZ
0, Z WP
Fig. 1. Diboson production via particle-antiparticle annihila-
tion (t-channel) on the left, and via boson self-interaction
(s-channel) on the right.
eters each, h> (i 1, .., 4), respectively for V y
and V Z. All these anomalous contributions to the
cross section increase rapidly with the center-of-mass
energy. In order to ensure unitarity, these parameters
are usually described by a form-factor representation,
hv(s) h oe/(1 + s/A2)n, where A is the energy scale
for the manifestation of a new phenomenon and n is a
sufficiently large power. Usual values adopted for A in
the presented results are 1.5 TeV and 2 TeV.
Deviations from the SM prediction for the ZZy* and
ZZZ* couplings may be described in terms of 2 param-
eters each, f7 (i 4, 5), respectively for V =y and
All the couplings h> and f7v are zero at tree level in
All the presented analysis have been performed uti-
lizing the data collected by the CDF and DO detectors
installed at the Fermilab's Tevatron, an accelerator capa-
ble to collide proton with antiproton at a center-of-mass
energy x 1.96 TeV and an instantaneous luminosity
3 - 1032 cm-2 s-1. Both CDF and DO are gen-
eral purpose detectors, cylindrically symmetric around
the beam axis which is oriented as the z direction. The
polar angle 0 is measured from the origin of the coordi-
nate system at the center of the detector with respect to
the z axis. The pseudorapidity, transverse energy and
transverse momentum are defined as -ln tan(O/2),
ET E sin(0) and PT p sin(0), respectively. Detailed
descriptions of the features of the two detectors can be
found in  and .
Several combinations of the Wi and Z bosons decay
channels are utilized to reconstruct the diboson events.
High-PT electrons and muons are widely used in the re-
construction of the vector bosons candidates because of
the clear signatures provided in an hadronic environ-
ment. Neutrinos are identified evaluating the missing
transverse energy (VT) in the event. The missing ET is
defined by gT VT 1, T F Efi, where fi; is
a unit vector perpendicular to the beam axis and point-
ing at the ith calorimeter tower. The index i runs over
all the calorimeter towers with an energy deposit over a
An anomalous TGC can affect both the production
cross section and kinematics observables of the diboson
final states. The PT or ET distributions of fully recon-
structed candidate bosons or of the charged leptons from
@2009 by Universal Academy Press, Inc.
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Mastrandrea, Paolo. Multi-boson production, article, September 1, 2010; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc1012956/m1/1/: accessed October 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.