2010/02/24「フレーバー物理の新展開」研究会
筑波大学 金 信弘、佐藤 構二、須藤 裕司

Search for Higgs Bosonin H  WW  lνjj

1

SM Higgs decays mainly into WWfor MH > 135 GeV.

Main production modes ofstandard model Higgs
are gg  H, WH and ZH.

H → WWHiggs Boson Production Cross section
and Branching Ratio

2 Backgrounds
W+jets , dibosons, single top, tt, non-W Addition of this mode will enhance CDF sensitivity• gg  H  WW  lνjj

 Backgrounds
dibosons (WW, WZ, ZZ) , Z/γ*, tt, Wγ, W+jets

 Dominant search mode
 Analysis considers WH, ZH, VBF modes.

• gg  H  WW  lνlνHigh Mass Search

W Decay Modelν ~ 10 %cs, ud ~ 30 %Wq(U)W-Hq(D)W+
νW+l+• WW  lνjj has a branching ratio 6 times larger thanWW  lνlν, though it will have a huge QCD W + 2jbackground.
• We can take advantage of the decay kinematics ofthe Higgs ( spin=0), by tagging charm jets.
• Finally compose Likelihood discriminant for S/Bseparation.
- Angular distribution between lepton and down type jet.
- Dijet mass, reconstructed higgs mass, .......

Motivation and Analysis Idia
H  WW  lνjj

4• Signal topology: H  WW  lνjj
• Standard set of cuts for l + MET + exact 2 jets
- One Lepton ( CEM/CMUP/CMX )- ET > 20 GeV, |η| < 1.1- MET > 20 GeV- Exact 2 jets
- ET > 20 GeV, |η| < 2.0

Base Cuts

5

Why tag charm?

H →WW (mH=170)

cosθ*CharmElwk WWW+cs(HEPG level)• We of course use NoTag sample for search as well.
• Half of signal is H → WW→ lνcs :• Tag charm jets with JetProb<0.05 to obtain pure search sample,
finally combine tagged and no-tag samples.
– C-tagging will enable use of unique kinematics of Higgs decay,
because Higgs has a spin=0.

cosθ*Lepton

DeltaPhi(lepton-UP)

deltaPhi (lepton – jet)Up-type quark jet
Down-type quark jet• For events that are not tagged, we assume the jet that has
smaller |DeltaPhi(lepton,jet)| as down-type for no-tag events.

Up/Down-type distinction

• Fit MET distribution to obtain non-W normalization.

– Deltaφ(MET,Jet1) > 1.9-MET/20– Deltaφ(MET,Jet2) > 1.8-MET/25• We follow Method II prescription.
• Instead of recent QCD veto, we adopt an angular cuts:

Background Estimation

1.1 fb-1

1.1 fb-1

MET• After angular cuts, we require:– MET>20– 60<Mt(lepton,MET)<100

Mt(lepton,MET)

Efficiency:
H→WW(170): 79.3 %Bkgd: 36.2 %Search Sample

|Deltaφ(Wlep,Whad)|Pt(D)Pt(lep)Signal (170)
Backgroundfor tag

DeltaR(lep,D)|DeltaR(U,D)|• W+c+1P MC sample is used to model background.
• Using 9 kinematic variables.

Likelihood Composition

Pt(U)|Deltaφ(lep,Whad)|

Dijet Mass

Higgs Mass

|Deltaφ(Wlep,Whad)|
Signal (170)
Backgroundfor no-tag

Pt(D)Pt(lep)DeltaR(lep,D)• W+c+1P MC sample is used to model background.
• Using 9 kinematic variables.

Likelihood Composition

Pt(U)|Deltaφ(lep,Whad)||DeltaR(U,D)|

Dijet Mass

Higgs Mass

|DeltaR(U,D)|

Pt(U)Higgs MassPt(D)|Deltaφ(Wlep,Whad)|

Broad red:
HWW(170)

Dijet MassPt(lep)|Deltaφ(lep,Whad)|

DeltaR(lep,D)

Tag Likelihood Inputs

|DeltaR(U,D)|

Pt(U)Higgs MassPt(D)|Deltaφ(Wlep,Whad)|

Broad red:
HWW(170)

Dijet Mass

Pt(lep)|Deltaφ(lep,Whad)|

DeltaR(lep,D)No-tag Likelihood Inputs

Notag channel

Tag channel

W+jetsInclusive analysis (pretag)
W+jets

We performed the sensitivity study withhistograms scaled to 3.4 fb-1.

Higgs mass 170 GeV.
Analyzed data correspond to 1.1 fb-1.

Likelihood Discriminant• Combining 2 channels is performed by defining
the likelihood as product of two Poissonfunctions.

∫– P(n,m) : Poisson dist. with center value m.
σ max– N=P ( S + B , A L σ )d σ0– A = acceptance to signal.
– L = luminosity.

– L(s,S,B) = P(S+B, ALσ+B) / N• For now, no Pseudo-Exp, simply Poisson stat.
• Given S and B estimated number of signal andbkgd events, the likelihood for higgs production
cross section s is:

Sensitivity Estimation

#Ev above Likelihood cut

Likelihood discriminantHσ (pb)Upper limit on σ at 95% C.L.:
2.73 pb

95%

B=5832, S=21.8, A=1.79%

Estimation of Expected
Limit
m = 170 GeV, inclusive analysis:

L(σ,S,B) = P(S+B, ALσ+Β) / ΝTag channel

Notag channel

Likelihood discriminantHσ (pb)Upper limit on σ at 95% C.L.:
2.61 pb95%

B=269, S=2.61, A=0.21%

B=4238, S=16.7, A=1.37%

Estimation of Expected
Limit
m = 170 GeV, tag+notag analysis:

L(σ,S,BS,B)

mH=170 GeV

For each higgs mass assumption, we scan the cut on likelihood
discriminant, and look for optimum cut that gives the lowest limit on
cross section.

Tag+Notag
Inclusive

Statistical only, doesn’t include systematic uncertainties.
Estimated 95% C.L. limit for 3.4 fb-1.

Estimated Sensitivity

limit / SM cross section

0140

2468

101214150

160

170

180 190 200 210
higgs mass (GeV)

incl. ana
tag+notag ana
dilepton ana

0140

1

2

3

4

56

Statistical only, doesn’t include systematic uncertainties.
Estimated 95% C.L. upper limit for 4.8 fb-1.
Dilepton number is from 4.8 fb-1 analysis.

150160170

Expected sensitivity

limit / Dilepton limit

180 190 200 210
higgs mass (GeV)

incl. ana
tag+no-tag ana

• We are starting a search for SM Higgs boson
decaying to H → WW → lνjj.
• We compose a likelihood discriminant with 9
kinematic variables as input.
• We estimate our upper limit on cross section
will be x4.2 of the dilepton analysis at mH=170
GeV, with the number going down with highermass.

Summary

Backup21

H  WW group, Roman Lysák, CDF collaboration meeting Oct. 23 2009

Recent Result 4.8 fb-1

H  WW  lνlν22