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Unformatted text preview: κγ 1.5 2 FIG. 13. The (a) photon ET distribution for the D0 W analysis.
From Abazov et al., 2008b. The photon ET distribution of events is
used to constrain anomalous coupling parameters shown in (b). probability for compatibility between the data and the SM
expectation, demonstrating a reasonable level of agreement.
To speciﬁcally investigate the dip region around Q‘ Â Áy ¼
À1=3 indicative of the RAZ effect, a simple test statistic R is
constructed which is the ratio of the number events observed
in a bin including the dip region to the number of events
observed in a bin with more negative Q‘ Â Áy where a
maximum is expected, based on Monte Carlo simulation,
from the SM including the total D0 acceptance in this analysis. A value of R ¼ 0:64 is observed in the data and it is
determined that 28% of SM pseudoexperiments give a value
as large or larger than 0.64.
A particular anomalous coupling hypothesis corresponding
to ¼ 0, ¼ À1 is chosen to test against as a null
hypothesis since it is a speciﬁc model which leads to a
Q‘ Â Áy distribution without a dip as shown in the inset of
Fig. 14(b). Only the shape is tested such that the null
‘‘nodip’’ distribution is normalized to the yield expected
from the SM. The R distribution for the SM and nodip
hypotheses are shown in Fig. 14(b) along with the value
(0.64) observed in the data. From this analysis, the nodip
hypothesis is excluded at 2:6 Gaussian signiﬁcance.
3. Z As mentioned in Sec. III.E.1, photons do not directly
couple to Z bosons at tree level in the SM. Therefore,
observation of such a coupling constitutes evidence for new
phenomena. The Z ﬁnal state at hadron colliders involves a
Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 0
0.5 0 0.5 1 1.5 2 2.5 3 3.5 R value
FIG. 14. (a) The backgroundsubtracted chargesigned rapidity
difference of events is shown along with the SM expectation from
Abazov et al. (2008b). Consideration of the full covariance matrix
gives a 15% 2 probability for compatibility between the data and
the SM expectation. (b) Distributions of the Rtest statistic for the
SM (solid line) and ‘‘nodip’’ (dashed line) hypothesis pseudoexperiments from Abazov et al. (2008b). The data result is 0.64 shown
by the vertical line where only 45 out of 104 nodip pseudoexperiments had a value smaller as small or smaller than 0.64. The Rtest
statistic is deﬁned as the ratio of events in the ‘‘Dip Bin’’ to the
‘‘Small Max Bin,’’ as shown in the inset where the solid line is the
SM expectation and the dashed line is for the nodip hypothesis. combination of ZZ and Z couplings. Both CDF and D0
made measurements of the Z cross section in leptonic decay
channels of the Z boson. The signature of the Z signal is two
isolated high ET charged leptons having the same ﬂavor and
opposite charge with invariant mass consistent with decay of
a Z boson, and an isolated high ET photon. The dominant
background is from Z þ je...
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This document was uploaded on 09/28/2013.
 Fall '13
 Energy

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