CDF Logo Search for Standard Model Higgs Boson Production in Association with W Bosons at CDF
Public Page
HDG Logo

Contents

  1. Abstract
  2. Authors
  3. Documentation
  4. Event Selection and Search Strategies
  5. Figures
    1. Signal Acceptance and systematic uncertainties
    2. Central Leptons
    3. Plug Electrons
    4. Isolated Tracks
  6. Limits


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 1.9/fb. 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,

σ(ppbar -> WH)*BR(H->bbbar) < 5.26 to 68.9 times the Standard Model expectation 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, Central Lepton Triggered Data 1.9 fb^-1 --- Collected through May 2007 ---
Run II, Missing Transverse Energy + Jets Triggered Data 2.1 fb^-1 --- Collected through August 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 to take 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

Lepton Triggered Events 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


MET+Jet triggered Events
CategoryDouble SECVTX tagOne SECVTX tag
Lepton Isolated track (Pt>20 GeV)
Missing Et>20 GeV
Two Jets > 25 GeV, |η| < 2.0
b-tagging (1st jet)tight SecVtx b-tagtight SecVtx b-tag
b-tagging (2nd jet)tight SecVtx b-tagNo b-tag

The lepton and b-tag categories are selected exclusively.

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 imbalance : 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

NN output shape

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

Figure

Tight Central Lepton Signal acceptance and systematic uncertainties

Central Lepton signal acceptance of single b-tagging category Central Lepton signal acceptance of double b-tagging category Central Lepton systematic uncertainty on the WH acceptance

Search Channels

Central electron and muon
Channel Backgound Summary Kinematics and Limits
Double SECVTX b-tag
Neural Network Inputs
Neural Network Outputs
Other Kineamtic Plots
Limits for This Channel
One SECVTX b-tag + one JetProb b-tag
One SECVTX b-tag w/ NN flavor separator
Plug electron
Channel Backgound Summary Kinematics and Limits
Double SECVTX b-tag
Neural Network Inputs
Neural Network Outputs
Limits for this channel
One SECVTX b-tag + one JetProb b-tag
One SECVTX b-tag w/ NN flavor separator
Isolated Tracks
Channel Backgound Summary Kinematics and Limits
One SECVTX tag Backgrounds
Neural Network Inputs
Neural Network Outputs
Other Kineamtic Plots
Limits for This Channel
Two SECVTX tag Backgrounds

Upper limit calculated from combination of all channels

@ Finally, we combine central and plug result to obtaine best limit
- Below plot shows upper limit normalized by SM expectation

Jason Slaunwhite
Last modified: Mon Jun 2 11:14:10 CDT 2008