This preview shows page 1. Sign up to view the full content.
Unformatted text preview: rs invoked in the effective Lagrangian approach are
unnecessary in an effectiveﬁeldtheory approach.
In the presence of new physics, neutral TGCs (those
involving only and Z bosons) can contribute to Z and
ZZ production. As described, neutral TGCs are anomalous by
their very nature since these couplings are absent in the SM.
For each of the diboson ﬁnal states Z and ZZ, one can
follow an analogous procedure to the anomalous charged
TGCs (those involving a W boson) by writing down the
most general effective Lagrangian that respects Lorentz
invariance and electromagnetic gauge invariance (Baur and
Berger, 1993; Baur and Rainwater, 2000). Using prescriptions detailed by Baur and Berger (1993) and Baur and
Rainwater (2000), the effective Lagrangians introduce
anomalous coupling parameters hV ðV ¼ ; Z and i ¼ 3; 4Þ
i0
V
and fj0 ðV ¼ ; Z and j ¼ 4; 5Þ, respectively, which can be
constrained through an analysis of Z and ZZ production in
highenergy collider data. It is important to note that, under
the assumption of onshell Z bosons, the Z
Z couplings
contributing to Z production and ZZ couplings contributing to ZZ production are completely independent (Baur and
Rainwater, 2000).
In general, the effects on observables from turning on
anomalous TGCs are correlated. When we refer to ‘‘1D
limits,’’ we refer to the limits derived on one parameter
when the others are set to their SM values.
There are a few important differences regarding the study
of diboson physics in particle collisions at LEP, Tevatron, and
the LHC that are worth pointing out at this stage:
At LEP, eþ eÀ collisions occur at a welldeﬁned energy
that is set by the accelerator. Therefore, the centerofmass energy is known with good precision and there are
no form factors in anomalous coupling analyses.
In eþ eÀ collisions, the initial state has zero electric
charge. Therefore, exclusive states with net charge,
such as WZ and W
, cannot be produced at LEP. The
WW and ZZ states can and have been produced and
studied at LEP. A measurement of the WW cross section
over a scan in beam energy dramatically illustrates the
existence of the WWZ coupling in electroweak theory
(Quigg, 2009).
pﬃﬃﬃ
At hadron colliders, s is ﬁxed for long periods of time
(deﬁning different periods of the accelerator operation
pﬃﬃﬃ
^
that change very infrequently), but s varies collision
byﬃ collision. Any anomalous couplings are likely to be
pﬃﬃ
^
s dependent. The form factor ansatz used ﬃﬃﬃ cut off the
p to
^
anomalous coupling parameters at large s to preserve
Smatrix unitary of the amplitude reﬂects this dependence. For this reason, it is reasonable to expect that,
once a sufﬁcient amount of integrated luminosity has
been acquired, the higherenergy reach afforded by
highenergy hadron collisions will lead to better sensitivity to anomalous couplings as compared to the limits
from LEP, despite larger backgrounds in a typical hadron collision event. In other...
View
Full
Document
This document was uploaded on 09/28/2013.
 Fall '13
 Energy

Click to edit the document details