Search for New Particles
Decaying into bb and Produced in Association with W Boson

Contents
(1)  Aughors
(2)  Documentation
(3)  Abstract
(4)  Introduction
(5)  Dataset
(6)  Event Selections
(7)  Optimization of Jet Et Selections
(8)  >= 1 Tag Analysis
  (8-1) Background Estimation
  (8-2) Dijet Mass Distributions
  (8-3) Signal Acceptance with Systematic Uncertainty
  (8-4) 95% C.L. Upper Limit
(9)  Double Tags Analysis
  (9-1) Background Estimation
  (9-2) Dijet Mass Distribution
  (9-3) Signal Acceptance with Systematic Uncertainty
  (9-4) 95% C.L. Upper Limit
(10) Conclusion
(11) Figures
(1) Authors

Yoshio Ishizawa (University of Tsukuba)
Jason Nielsen (Lawrence Berkeley National Laboratory)
Weiming Yao (Lawrence Berkeley National Laboratory)
(2) Documentation

CDF Public Note
PS
(3) Abstract

 We present a search for new particles decaying into bbbar
and produced inassociation with W^{\pm} bosons in ppbar collisions
at sqrt{s}=1.96 TeV. The search uses the approximately 318.5 pb^{-1}
for CEM and CMUP, and 305.2 pb^{-1} for CMX of the dataset accumulated
by the CDF collaboration at the Fermilab Tevatron. Events with an electron
or muon, missing E_{T}, and two jets, one of them b-tagged, are selected.
The number of tagged events and the dijet mass distribution are consistent
with Standard Model expectations, and we set a 95% confidence level upper
limit on the production cross section times branching ratio as a function of
the new particle mass.


(4) Introduction

We search for WX to lvbb.
(a) pp -> WH -> lvbb (Standard Model Higgs Boson)
(b) pp -> rho_{T} -> Wpi^{0}_{T} -> lvbb (Technicolor Particle)

Figure 1 shows the Feynman diagrams of the process (a) and (b).
In this analysis, we focus on the Standard Model Higgs boson search.
Figure 2 and Figure 3 show the production cross section at Tevatron and the branchind ratio.
(5) Dataset

We use data up to Aug./2004 shutdown.
The integrated luminosity is about 319 pb^{-1}.
(6) Event Selections

We applied the following selection ctireria:
Tight central isolated electron or muon (Et > 20 GeV),
Dilepton Veto,
Z^{0} Veto,
Extra Isolated Track Veto,
Conversion Veto for electron,
Cosmic Veto for muon,
Missing Et > 20 GeV,
Jet Et > 15 GeV,
Jet |Eta| < 2,
Extra Jet Veto,
Jet Multiplicity = 2,
At least one tag (SECVTX)
(7) Optimization of Jet Et Selections

We tried to optimize 1st and 2nd leading jet Et selection criteria.
Jet Et cut values are optimized using significance for WH MC sample and background (Data and MC).
Figure 4 shows the significances as a function of 1st and 2nd leading jet Et selection criteria
for at least one tag.
The 1st leading jet Et is not sensitive to the significance
So we use the following jet Et selection criteria:

    1st leading jet Et > 15 GeV,
    2nd leading jet Et > 15 GeV.
(8) >= 1 Tag Analysis
(8-1) Background Estimation

We consider the following backgrounds:
(i)   Mistags           ... based on negative tag rates in jet data sample,
(ii)  W+HF              ... based on data and MC,
(iii) non-W             ... scale non-W number from ttbar cross section group,
(iv)  Other backgrounds ... based on MC

The following table shows the estimated number of events (jpeg, eps):
                                                                                CDF Run II Preliminary (L = 319 pb^{-1})
Background
 W + 1 jet
 W + 2 jets
 W + 3 jets
 W + >=4 jets
Events before Tagging
 26218
 3910
 602
 160
Mistags
 98.0 +- 7.9
 39.3 +- 3.1
 12.1 +- 1.2
 5.9 +- 0.8
W+bb
 99.3 +- 34.2
 54.0 +- 18.4
 10.5 +- 3.5
 1.6 +- 0.7
W+cc
 37.6 +- 13.0
 19.5 +- 6.6
 4.2 +- 1.4
 0.7 +- 0.3
W+c
 83.2 +- 20.9
 16.8 +- 4.3
 2.2 +- 0.6
 0.3 +- 0.1
Diboson/Z->tautau
 3.7 +- 0.9
 5.0 +- 1.1
 1.5 +- 0.5
 0.3 +- 0.1
non-W
 34.3 +- 6.3
 16.5 +- 3.2
 4.8 +- 1.0
 1.9 +- 0.4
tt
 1.2 +- 0.2
 14.1 +- 2.5
 34.3 +- 6.0
 54.2 +- 9.5
single top
 3.4 +- 0.7
 9.6 +- 2.0
 2.0 +- 0.5
 0.4 +- 0.1
Total Backgrounds
 360.6 +- 52.7
 174.7 +- 26.3
 71.6 +- 8.7
 65.3 +- 9.9
Observed positive tags
 362
 187
 75
 62

Figure 5 shows the jet multiplicity distribution.


(8-2) Dijet Mass Distributions

Figure 6 and Figure 7 shows the dijet mass distributions before and after b-tagging.
The predicted dijet mass distributions are consistent with the measured distributions.


(8-3) Signal Acceptance with Systematic Uncertainty

Figure 8 shows the signal acceptance with the systematic uncertainty as a function of the Higgs boson mass.
The following table shows the systematic uncertainties.
source
 Uncertainty (%)
Lepton ID
 5
Trigger
 < 0.1
Parton Distribution Function
 1
Initial State Radiation
 3
Final State Radiation
 7
Energy Scale
 3
Secondary Vertex Tag
 5
Jet Energy Smearing
 1
Soft Jet Modeling
 1
Total
 11


(8-4) 95% C.L. Upper Limit

Since there is no significant mass peak in the dijet mass distribution from the Higgs boson,
we set the 95% C.L. upper limit.
Figure 9 shows the upper limits as a function of the Higgs boson mass.
The measured upper limits are 3 to 10 pb.
Figure 10 shows the expected upper limits using pseudo experiments.
The red line shows the measured upper limit.

mH (GeV/c^2)
 95% C.L. Upper Limit (pb)
  Expected  Upper Limit (pb)
110
 10.0
 5.8
115
 8.6
 5.4
120
 7.2
 5.0
130
 4.9
 4.5
140
 3.5
 4.1
150
 2.8
 3.9


(9) Double Tag Analysis
(9-1) Background Estimation

The following table shows the estimated number of events (jpeg, eps):
                                                                                CDF Run II Preliminary (L = 319 pb^{-1})
Background
 W + 2 jets
 W + 3 jets
 W + >=4 jets
Mistags
 1.03 +- 0.11
 0.41 +- 0.06
 0.21 +- 0.03
W+bb
 8.04 +- 2.96
 1.32 +- 0.47
 0.25 +- 0.12
W+cc
 0.41 +- 0.15
 0.08 +- 0.03
 0.02 +- 0.01
Diboson/Z->tautau
 0.34 +- 0.06
 0.10 +- 0.03
 0.02 +- 0.00
non-W
 0.38 +- 0.13
 0.31 +- 0.11
 0.12 +- 0.04
tt
 3.12 +- 0.54
 8.31 +- 1.45
 15.98 +- 2.78
single top
 1.30 +- 0.30
 0.43 +- 0.12
 0.09 +- 0.4
Total Backgrounds
 14.62 +- 3.25
 10.96 +- 1.68
 16.69 +- 2.84
Observed positive tags
 14
 12
 19

Figure 11 shows the jet multiplicity distributions.


(9-2) Dijet Mass Distribution

Figure 12 shows the dijet mass distribution.
The predicted dijet mass distributions are consistent with the measured distributions.


(9-3) Signal Acceptance with Systematic Uncertainty

Figure 13 shows the signal acceptance with the systematic uncertainty as a function of the Higgs boson mass.


(9-4) 95% C.L. Upper Limit

Figure 14 shows the 95% C.L. upper limit.
The measured upper limits are 7 to 10 pb.
mH (GeV/c^2)
 95% C.L. Upper Limit (pb)
  Expected Upper Limit (pb)
110
 9.7
 9.9
115
 8.8
 8.3
120
 8.3
 8.0
130
 7.1
 7.2
140
 6.7
 6.8
150
 6.6
 6.5


(10) Conclusion

We search for WX to lvbb using 319 pb^{-1},
where X is the Standard Model Higgs boson.
Since there is no significant mass peak from the Higgs boson,
we set the upper limit as a function of the Higgs boson mass.

    (1) >= 1 tag   :  sigma(ppbar->WX) * Br(H->bbbar) = 3 to 10 pb for mH=110 to 150 GeV/c^{2}
    (2) double tags:  sigma(ppbar->WX) * Br(H->bbbar) = 7 to 10 pb for mH=110 to 150 GeV/c^{2}

The sensitivity of the present search is limited by statistics
to a cross section approximately one order of magnitude higher
than the predicted cross section for the Standard Model Higgs production.
(11) Figures

Description
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 eps
Figure1
 The Feynman diagrams of Standard Model Higgs boson and Technicolor particles
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Figure2
 Production cross section of Standard Model Higgs
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Figure3
 Branching ratio of Standard Model Higgs boson
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Figure4
 Significance as a function of 1st and 2nd leading jet Et
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Figure5
 Jet Multiplicity for >= 1 tag
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Figure6
 Dijet mass distribution before b-tagging with Higgs mass distribution (mH=115 GeV/c^{2}) for >= 1 tag
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Figure7
 Dijet mass distribution after b-tagging with Higgs mass distribution (mH=115 GeV/c^{2}) for >= 1 tag
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jepg2
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Figure8
 Signal acceptance with systematic uncertainty for >= 1 tag
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Figure9
 95% C.L. upper limit for >= 1 tag
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Figure10
 Expected upper limit using pseudo experiment for >= 1 tag
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Figure11
 Jet Multiplicity for double tags
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Figure12
 Dijet mass distribution after b-tagging with Higgs mass distribution (mH=115 GeV/c^{2}) for double tags
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Figure13
 Signal acceptance with systematic uncertainty for double tags
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Figure14
 95% C.L. upper limit for double tags
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Note: Please uncheck "Antialias" in gv option for Figure 5, Figure 7 (1,2), Figure 9, Figure 11 and Figure 14 eps files. Then you can see the error region.