RevModPhys.84.1477】Tests of the standard electroweak model at the energy frontier

Value for the zz alone is 012 and the combined p

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Unformatted text preview: ed for the observed lepton momenta and ET 6 using leading-order calculations of the differential decay rate for the processes (Campbell and Ellis, 1999). A likelihood ratio discriminant LR is formed which is the signal probability divided by the sum of signal and background probabilities LR ¼ PZZ =ðPZZ þ PWW Þ. The distribution of log10 ð1 À LRÞ for the data compared to the summed signal and background expectation is shown in Fig. 29. The ZZ ! ‘‘‘‘ and ZZ ! ‘‘ results were combined through a likelihood fit which includes the two 4-lepton bins WW tt,Wγ ,W+jets DY ∫ L dt = 1.9 fb-1 Syst. Uncertainty 10 1 10-1 -5 -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 log(1-LR) FIG. 29 (color online). Distribution of the discriminating variable log10 ð1 À LRÞ for the CDF ZZ ! ‘‘ search. From Aaltonen et al., 2008b. Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1498 " TABLE XVI. The integrated luminosity, expected number of signal (Z= Ã Z= Ã ) and background events [tt and Zð Þ þ jets which includes all W=Z= þ jets contributions], and the number of observed candidates in the seven ZZ ! ‘þ ‘À ‘0þ ‘0À subchannels for the D0 ZZ ! ‘‘‘‘ analysis (Abazov et al., 2008d). Uncertainties reflect statistical and systematic contributions added in quadrature. Subchannel 4e2C À1 Zð Þ þ jets " tt Observed events 4e4C 4 22e0C 22e1C 22e2C 1:75 Æ 0:11 0:084 Æ 0:008 1:75 Æ 0:11 0:173 Æ 0:015 1:75 Æ 0:11 0:140 Æ 0:012 1:68 Æ 0:10 0:534 Æ 0:043 1:68 Æ 0:10 þ0 007 0:058À0::006 1:68 Æ 0:10 0:352 Æ 0:040 1:68 Æ 0:10 þ0 045 0:553À0::044 þ0 009 0:030À0::008 0:018þ0::008 À0 007 þ0 002 0:002À0::001 0:0003 Æ 0:0001 þ0 02 0:03À0::01 0:05 Æ 0:01 þ0 004 0:008À0::003 ÁÁÁ 0 Luminosity (fb ) Signal 4e3C ÁÁÁ 0 ÁÁÁ 2 ÁÁÁ 1 þ0 0016 0:0012À0::0009 0 0:005 Æ 0:002 0 0:0007þ0::0009 À0 0005 0 SM yield in the full acceptance and scaling the zero-width Z boson approximation cross section by that fraction. The " measured cross section is ðpp ! ZZÞ ¼ 1:4þ0::7 pb, consisÀ0 6 tent with the SM expectation. This is the first evidence of a ZZ signal with greater than 4 significance in hadron collisions. R The D0 Collaboration uses Ldt ¼ 1:7 fbÀ1 to search for ZZ production in the ZZ ! ‘‘‘‘ channel (Abazov et al., 2008d). This analysis follows up the analysis from Abazov et al. (2008c) using more data and tighter dilepton invariant mass requirements but does not explicitly search for anomalous couplings. Four lepton events are selected using identied muons with jj < 2 and electrons that are either central (j < 1:1) or forward 1:5 < jj < 3:2. It is required that one pair have the same flavor with invariant mass >70 GeV=c2 and another pair have invariant mass >50 GeV=c2 . Table XVI summarizes the expected signal and background contributions to each subchannel, as well as the number of candidate events in data. The total signal a...
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This document was uploaded on 09/28/2013.

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