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Contents

  1. Abstract
  2. Authors
  3. Documentation
  4. Event Selection and Search Strategies
  5. Figures and tables
    1. Signal Acceptance and systematic uncertainties
    2. Background estimation
    3. NN input shape
    4. NN output shape
    5. Expected Limit
    6. Observed Limit


Abstract

We present a search for Standard Model Higgs boson production in association with a W boson. This search uses data corresponding to an integrated luminosity of 1.7fb-1. We select double-tagged W + 2 jet events that fall into one of two tag categories: Events with two tight silicon vertex tags or events with one tight silicon vertex tag and one jet probability tag. Discrimination between the Higgs signal and the large backgrounds in the W + 2 jet bin is increased through the use of an artificial neural net. We see no evidence for a Higgs signal, so we set a 95% confidence level upper limit on the WH cross section times the branching ratio of the Higgs to decay to a bbbar pair. Using only the dijet invariant mass to discriminate signal and background, we get &sigma ppbar -> WH)* BR(H->bbbar) < 1.6 to 1.5 pb for Higgs masses from 110 GeV to 150 GeV. Using our neural network discriminant improves the limit by approximately 10%, yielding &sigma (ppbar -> WH)*BR(H->bbbar) < 1.4 to 1.3 pb for Higgs masses from 110 GeV to 150 GeV

Authors:

Tatsuya Masubuchi, Shinhong Kim, Yoshikazu Nagai (University of Tsukuba)
Jay Dittmann, Martin Frank Nils Krumnack (Baylor University)
Richard Hughes, Kevin Lannon, Jason Slaunwhite, Brian Winer (Ohio State University)
Anyes Taffard (UC Irvine)
Pedro Fernandez, Weiming Yao (LBNL)
Jason Nielsen (UC Santa Cruz)

Data: Run II, 1.7 fb^-1 --- Collected through March 2007 ---

Documentation

CDF note 8957 --- Public note

Event selection and Search strategies

Search strategies

We select events with an identified lepton and two jets where the jets are either both tagged by the tight silicon vertex b-tag algorithm (SecVtx) or one is tagged by SecVtx and one is tagged the jet probability b-tag algorithm(JetProb). These types of events are considered separately to take advantage of the different S/N ratios in the two double tag categories. The limits in the two categories are then combined to give the final limit.

Basic event selection

CategoryDouble tight SecVtxOne tight SecVtx + One JetProb
Lepton Central isolated electron or muon (Pt>20 GeV)
Missing Et>20 GeV
Jets>20 GeV, |&eta| < 2.0
b-tagging (1st jet)tight SecVtx b-tag
b-tagging (2nd jet)tight SecVtx b-tagJetProb b-tagging

Figure

Signal acceptance and systematic uncertainties

Signal acceptance of double b-tagging category Systematic uncertainty on the WH acceptance

Background

Double silicon vertex b-tagSummary table
Background for double silicon vertex b-tagging events Background summary table
One silicon vertex b-tag
+ one jet probability b-tagging tag
Summary table
Background for double silicon vertex b-tagging
+ one jet probability b-tagging events
Background summary table

NN input shape

@ Input variables
- Dijet mass
- Pt imbalance defined by Pt(jet1)+Pt(jet2)+Pt(lepton) - Missing Et
- Pt of W+2jets

@ double tight SecVtx events
Dijet massMet imbalancePt of W+2jet
@ one tight SecVtx and one JetProb b-tagging
Dijet massMet imbalancePt of W+2jet

NN output shape

@ NN is trained for each signal mass sample
- For example, we show NN output shape for Higgs mass 120 GeV

NN output shape trained in Higgs mass 120 GeV
(double silicon vertex b-tagging events)
NN output shape trained in Higgs mass 120 GeV
(one silicon vertex b-tagging + jet probability b-tagging events)

Expected limit calculated from each tagging category

The comparison of expected upper 95% limit for each
b-tagging category. These limit means absolute value.
The comparison of expected upper 95% limit for each
b-tagging category. These limit means value normalized by
SM cross section times Branching ratio.

Expected limit

Higgs massExpected limit (pb)Expected limit/SM
110 GeV1.398.6
115 GeV1.3110.0
120 GeV1.2211.9
130 GeV1.0917.4
140 GeV1.0133.0
150 GeV0.9580.6

Upper limit calculated from two double b-tagging category

@ We apply two exclusive double b-tagging categories and combine them to obtain best limit
Absolute value of 95% observed upper limit Upper limit normalized by SM expectation

Observed limit

Higgs massObserved limit (pb)Observed limit/SM
110 GeV1.438.8
115 GeV1.3310.1
120 GeV1.2312.0
130 GeV1.2818.8
140 GeV1.2340.0
150 GeV1.33113.0

Tatsuya Masubuchi
Last modified: Mon Feb 18 13:24:08 CST 2008