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

25 10 04 10 02 28 06 13 03 004 001 02

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: program. Both D0 (Abazov et al. (2007e) and CDF (Aaltonen et al., 2008f) published results in this final state. The D0 publication uses a R data sample corresponding to R dt ¼ 0:45 fbÀ1 . The CDF L published results correspond to Ldt ¼ 1:0 fbÀ1 . The initial selections for both experiments require events with two leptons whose invariant mass is consistent with a Z boson and two additional jets. The backgrounds in this " channel arise from Z þ jets, tt events, diboson production, and from jets misidentified as leptons or a lepton þ jet system being misidentified as an isolated lepton. They are determined using a combination of simulated events and data control samples in essentially the same manner as for the WH channel. One difference with respect to the WH Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 calculation is that sidebands of the ‘‘ invariant mass distribution are used by D0 to determine the misidentification and false isolation background. Both experiments identify b jets using secondary vertex algorithms.5 The CDF result splits the final tagged sample into single- and double-tagged samples as in the WH analysis, but the D0 result does not. The D0 result is derived using the dijet mass distribution only, while the CDF result is based on the binned likelihood of a NN output. The sources of systematic uncertainties for these channels are the same as for the WH result. Table XXXIII shows the yields for the single- and double-tag analyses from CDF, and Table XXXIV shows the yields for the dijet and doubletagged samples for D0, respectively. Figure 54 (Fig. 55) shows the dijet invariant mass (neural network output) distribution from the D0 (CDF) analysis. This distribution is used as the input to the limit setting program. Systematic uncertainties are included for trigger and lepton identification efficiencies, parton density functions, background cross sections, b-tagging efficiencies, jet energy reconstruction, and the methods used to estimate instrumental backgrounds. The CDF result also includes a systematic from the top mass uncertainty. The systematic uncertainties for the D0 measurement range between 2% and 20% expressed as a fraction of the total background. The systematic uncertainties for the CDF measurement range between 1% and roughly 25% of the total background. The largest contribution for both experiments is from the background cross sections. 5 For D0 this differs from the WH case because the published ZH results predate the availability of the NN tagger. More recent D0 preliminary results use the same NN tagger described in the WH analysis. Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1517 10 2 σ(95% CL) (pb) Expected Limit Observed Limit 10 1 10 -1 100 FIG. 54 (color online). Dijet mass distribution for the D0 1:0 fbÀ1 ZH ! ‘‘bb analysis. The final limits, derived using the same methods as the WH results, are shown for CDF in Fig. 56 and for D0 in Fig. 57. As...
View Full Document

This document was uploaded on 09/28/2013.

Ask a homework question - tutors are online