Unformatted text preview: words, hadron collisions at Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1488 the Tevatron and LHC sample events with a larger
average s as comparedﬃﬃﬃto LEP collision energies and
it is exactly those high s events that are most sensitive
to effects of anomalous couplings from new physics at
Because the Tevatron is a pp collider, the production
cross sections for W þ Z and W À Z are equal. The same is
true for W þ and W À production. When produced in a
pp collider such as the LHC, positive and negative net
charge diboson states have different production cross
sections [e.g., ðpp ! W þ ZÞ > ðpp ! W À ZÞ].
2. W The W ﬁnal state observed at hadron colliders provides a
direct test of the WW TGC. Anomalous WW couplings
lead to an enhancement in the production cross section and an
excess of large ET photons. Both CDF and D0 published
measurements of the W cross section using leptonic decays
of the W bosons and Ldt ¼ 0:2 fbÀ1 (Abazov et al.,
2005a; Acosta et al., 2005a). The signature of the W signal
is an isolated high ET lepton, an isolated high ET photon, and
large ET due to the neutrino from the W decay. The dominant
background is from W þ jets where a jet mimics an isolated
photon. A lepton-photon separation requirement in À
space of ÁR ¼ ðÁÞ2 þ ðÁÞ2 > 0:7 is made by both CDF
and D0 to suppress events with ﬁnal-state radiation of the
photon from the outgoing lepton and to avoid collinear
singularities in theoretical calculations. A kinematic requirement on photon ET of ET > 7 (8) GeV is made by CDF (D0)
in the analysis.
ðpp ! W þ X Þ Â BRðW ! lÞ
¼ 18:1 Æ 1:6ðstatÞ Æ 2:4ðsystÞ Æ 1:2ðlumÞ pb
(Acosta et al., 2005b) in agreement with the next-to-leadingorder (NLO) theoretical expectation (ET > 7 GeV) (Baur and
Berger, 1993) of 19:3 Æ 1:4 pb. D0 measures
ðpp ! W þ X Þ Â BRðW ! lÞ
¼ 14:8 Æ 1:6ðstatÞ Æ 1:0ðsystÞ Æ 1:0ðlumÞ pb (Abazov et al., 2005a) also in agreement with the NLO
expectation (ET > 8 GeV) (Baur and Berger, 1993) of
16:0 Æ 0:4 pb. Table VI summarizes the W cross-section
Both CDF and D0 W cross-section measurement are
consistent with the SM expectations at NLO. In a more
recent analysis (Abazov et al., 2008b), D0 uses 4 times
more integrated luminosity as compared to Abazov et al.
(2005a) and adds photons reconstructed in their end cap
calorimeters (1:5 < jdet j < 2:5) to search for anomalous
WW couplings based on the observed photon ET spectrum
(Abazov et al., 2008b) for photons with ET > 9 GeV.
Additionally, the three-body transverse mass of the photon,
lepton, and ET must exceed 120 GeV=c (110 GeV=c) for the
electron (muon) channel in order to suppress ﬁnal-state
radiation. The photon ET spectrum and...
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This document was uploaded on 09/28/2013.
- Fall '13