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

On a combination of data and simulation with the

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: misidentified as b jets while for the double-tag channel, a less stringent requirement suffices thereby giving increased per jet tagging efficiency. The D0 single-tag analysis uses a b-tag operating point which gives a typical efficiency of 48% with misidentification rate of 0.5% and an operating point for the double-tag analysis which gives an efficiency of 59% and a misidentification rate of 1.7%. The CDF event selection divides events into three exclusive categories based on which algorithms identify a jet as b tagged. The first category contains events which have two jets tagged by the SECVTX algorithm. The second category contains events not selected into the first category which have one jet identified by the SECVTX algorithm and one by the jet probability algorithm. The third category contains events which are not selected into either of the other two categories and have one jet identified by both the SECVTX and NN algorithms. The sensitivity of the analyses is further improved by using kinematic properties of the events to distinguish signal and background events. The most important variable is the mass of the dijet system corresponding to the Higgs decay. For single-tagged events, the mass is computed using the tagged jet and the highest pT jet remaining, and for the doubletagged events the mass is computed using the two tagged jets. In addition to the mass, other variables can also distinguish signal and background on a statistical basis. To make best use of these, both experiments use a neural network to enhance the separation of signal and background in the final step of the analysis. The CDF neural network has six input variables and the D0 network has seven input variables.4 The variables used by each experiment are listed in Table XXX for comparison. Because of limited statistics in the W þ 3 jet sample, D0 uses the NN only for the W þ 2 jet case and uses the dijet mass for the W þ 3 jet case. Backgrounds to the WH search include W þ jets production [including jets arising from heavy-flavor " (hf) production], tt, single-top, diboson production (WW , WZ, and ZZ) and a small contribution from multijet events in which either the lepton is actually a jet misidentified as a lepton or the lepton arises from heavy-flavor decay and the jet energy is not reconstructed so the lepton appears to be " isolated. Both experiments estimate the tt, single-top, and diboson yields using the product of the theoretical (N)NLO cross section for each process, the luminosity and acceptance times efficiency for each process. Corrections are applied 3 The event selection in recent preliminary results from CDF include additional events in this channel which are selected by ET 6 triggers. 4 Recent preliminary results also used the matrix element method adapted from the top mass measurement and decision trees for the multivariate technique instead of neural networks. mH (GeV=c2 ) 150 160 170 180 ðgg ! H Þ  (VBF) BðH ! WW Þ 54...
View Full Document

This document was uploaded on 09/28/2013.

Ask a homework question - tutors are online