CDF Logo Search for Standard Model Higgs Boson Production in Association with W Bosons at CDF
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Contents

  1. Abstract
  2. Authors
  3. Documentation
  4. Event Selection and Search Strategies
  5. Figures
    1. Signal Acceptance and systematic uncertainties
    2. Background estimation
    3. NN input shape
    4. NN output shape
    5. 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 1.9fb-1.
We select double b-tagged W + 2 jets events and one b-tagged W+ 2jets events. NN flavor separation is applied to one b-tagged events to increase purity of signal events. Three b-tagging categories (double silicon vertex b-tagged events, one silicon vertex b-tagged + Jet Probability b-tagged and one silicon vertex b-tagged w/ NN flavor separator) which have different purity are analized separately.
The discrimination between the Higgs signal and the large backgrounds in the W + 2 jets bin is increased through the use of an artificial neural net. We see no evidence for a Higgs signal in NN output distribution, therefore 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 our neural network discriminant gives best results,

&sigma(ppbar -> WH)*BR(H->bbbar) < 1.4 to 0.9 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)
Weiming Yao (LBNL)
Pedro Fernandez (FNAL)
Jason Nielsen (UC Santa Cruz)
Thomas Peiffer, Jeannine Wagner-Kuhr, Thomas Muller, Wolfgang Wagner (Universitat Karlsruhe)
Andreas Warburton, Adrian Buzatua (McGill University)

Data: Run II, 1.9 fb^-1 --- Collected through May 2007 ---

Docementation

CDF note 9219 --- Public note

Event selection and Search strategies

Search strategies

Double silicon vertex (SECVTX) b-tag events (ST+ST), one SECVTX b-tag + one jet probability (JetProb) b-tag events (ST+JP) and one SECVTX b-tag with NN flavor separator evens are estimated separately due to taking advantage of the S/N ratio in two double tag categories and one single tag category. The best result is given by combined likelihood of two double b-tagging events and one b-tagging events.

Basic event selection

CategoryDouble SECVTXOne SECVTX + One JetProbOne SECVTX w/ NN
Lepton Central isolated electron or muon and Plug isolated electron (Pt>20 GeV)
Missing Et>20 GeV(Central), >25 GeV(Plug)
Two Jets>20 GeV, |&eta| < 2.0
b-tagging (1st jet)tight SecVtx b-tagtight SecVtx b-tag w/ NNtag
b-tagging (2nd jet)tight SecVtx b-tagJetProb b-tagNo b-tag
QCD vetoPlug electron only
# These three categories are selected exclusively.

Figure

Signal acceptance and systematic uncertainties

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

Background

Central electron and muon
Double SECVTX b-tagSummary table

One SECVTX b-tag + one JetProb b-tagSummary table

One SECVTX b-tag w/ NN flavor separatorSummary table

Plug electron
Summary table (Double SECVTX b-tag)

Summary table (One SECVTX b-tag + one JetProb b-tag)

Summary table (One SECVTX b-tag w/ NN flavor separator)

NN input shape

@ Input variables
- Dijete mass+ : Invariant mass of the two jets plus an extra loose jet if within &Delta R < 0.9 of one of the tight jets
- Pt imvalance : defined by Pt(jet1)+Pt(jet2)+Pt(lepton) - Missing Et
- Pt of W+2jets : Pt of the lepton, MET and jets system
- Min Invariant mass : Maximum of invariant mass of lepton, MET and leading jet or next leading jet (Z component of neutrino momenta is alculated as 0)
- &Delta R between lepton and neutrino : $Delta R of lepton and neutrino, where the z component of neutrino momenta is chosen to be the maximum Pz solution to the W mass constraint
- Scalar sum of loose jet Et : Scalar sum of all loose jet (Et > 12, |&eta| < 2.4) Et

Central electron and muon
@ double SECVTX events
Dijet mass+Pt imbalancePt of W+2jet
Min invariant mass (lep+Met+jet)Delta R (Met-Lepton)Scalar sum of loose jet Et

@ one SECVTX and one JetProb b-tagging
Dijet mass+Pt imbalancePt of W+2jet
Min invariant mass (lep+Met+jet)Delta R (Met-Lepton)Scalar sum of loose jet Et

@ one SECVTX w/ NN fravor separator
Dijet mass+Pt imbalancePt of W+2jet
Min invariant mass (lep+Met+jet)Delta R (Met-Lepton)Scalar sum of loose jet Et

Plug electron
@ double SECVTX events
Dijet mass+Pt imbalancePt of W+2jet
Min invariant mass (lep+Met+jet)Delta R (Met-Lepton)Scalar sum of loose jet Et

@ one SECVTX and one JetProb b-tagging
Dijet mass+Pt imbalancePt of W+2jet
Min invariant mass (lep+Met+jet)Delta R (Met-Lepton)Scalar sum of loose jet Et

@ one SECVTX w/ NN fravor separator
Dijet mass+Pt imbalancePt of W+2jet
Min invariant mass (lep+Met+jet)Delta R (Met-Lepton)Scalar sum of loose jet Et

NN output shape

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

Central electron and muon
double SECVTX b-tag eventsone SECVTX b-tag + one JetProb b-tagone SECVTX b-tag w/ NN flavor separator

Plug electron
double SECVTX b-tag eventsone SECVTX b-tag + one JetProb b-tagone SECVTX b-tag w/ NN flavor separator

Single-top like plug electron analysis
As a cross check, a neural network analysis based on the single-top like selection is performed. For these analysis only two tagging categories (single and double tag) are obtained.
double SECVTX b-tag eventsone SECVTX b-tag events

Upper limit calculated from three b-tagging category (Central electron and muon)

@ We apply three exclusive single and double b-tagging categories and combine them to obtaine best limit
- Left plots means absolute value of upper limit and right plots shows upper limit normalized by SM expectation
Higgs massObserved(Expected) limit (pb)Observed(Expected) limit/SM
110 GeV1.38 (1.23)8.5 (7.6)
115 GeV1.28 (1.18)9.7 (8.9)
120 GeV1.08 (1.03)10.5 (10.0)
130 GeV1.08 (0.88)17.2 (14.0)
140 GeV0.98 (0.78)31.9 (25.3)
150 GeV0.93 (0.73)78.9 (61.8)

Upper limit calculated from three b-tagging category (Plug electron)

@ We apply three exclusive single and double b-tagging categories and combine them to obtaine best limit.
- Below plot shows upper limit normalized by SM expectation. The table shows also the expected and observed limits for the single-top like analysis.
Higgs massObserved(Expected) limit/SMObserved(Expected) limit/SM for single-top like analysis
110 GeV22.8 (31.6)27.8 (33.0)
115 GeV25.8 (35.7)27.8 (34.8)
120 GeV47.2 (43.7)28.2 (43.0)
130 GeV75.2 (68.9)69.8 (64.7)
140 GeV250.2 (127.3)
150 GeV282.8 (254.6)

Upper limit calculated from three b-tagging category (Combined)

@ Finally, we combine central and plug result to obtaine best limit
- Below plot shows upper limit normalized by SM expectation
Higgs massObserved(Expected) limit/SM
110 GeV6.8 (6.5)
115 GeV8.2 (7.3)
120 GeV9.8 (8.9)
130 GeV15.8 (12.6)
140 GeV37.8 (23.4)
150 GeV85.2 (57.6)

Other kinematic plots

Link
Tatsuya Masubuchi
Last modified: Sat Mar 1 10:48:50 CST 2008