Search for charged Higgs bosons in e+e- collisions at energies up to s=209 GeV

29/11/2001 Search for charged Higgs bosons 1

Search for charged Higgs bosons in e+e- Search for charged Higgs bosons in e+e- collisions at energies up to collisions at energies up to s=209 GeV s=209 GeV Search for charged Higgs bosons in e+e- Search for charged Higgs bosons in e+e- collisions at energies up to collisions at energies up to s=209 GeV s=209 GeV

History of the History of the analysisanalysis

Data selectionData selection

channelchannel

cscs channel channel

cscs channelcscs channel

resultsresults

P. Colas, B. Fabbro, M-C. Lemaire, E. Locci, B. Tuchming


IntroductionIntroduction IntroductionIntroduction

• General considerationsGeneral considerations– Charged HiggsesCharged Higgses are predicted in almost any extension of the are predicted in almost any extension of the

Standard Model (In the MSSM, MStandard Model (In the MSSM, MH+H+>M>MWW, except if CP violation)., except if CP violation).

– In case of one HIn case of one H++ and one H and one H--, the couplings to Z, , the couplings to Z, are fixed, are fixed,

thus thus the cross section depends only on the massthe cross section depends only on the mass..

– Decays considered here are Decays considered here are and and cscs, assumed to saturate the , assumed to saturate the

width. The c and s flavours are not explicitly used in the analysis.width. The c and s flavours are not explicitly used in the analysis.

• Experimental signatures:Experimental signatures: – : 2 acoplanar jets: 2 acoplanar jets– cscs : 2 hadronic jets M : 2 hadronic jets Meffeff~M~MH+H+, one tau and missing energy, one tau and missing energy– cscs : 4 jets; 2dijets of equal masses cscs : 4 jets; 2dijets of equal masses

• Then the 3 channels are combined as a function of BR(Then the 3 channels are combined as a function of BR())


HistoryHistory HistoryHistory

• Papers already publishedPapers already published– 130-172 GeV : PLB 418 (1998) 419130-172 GeV : PLB 418 (1998) 419

– 181-184 GeV : PLB 450 (1999) 467181-184 GeV : PLB 450 (1999) 467

– 189 GeV : PLB 487 (2000) 419189 GeV : PLB 487 (2000) 419

• Proposal : this draftProposal : this draft – 189 -209 GeV 189 -209 GeV – New analyses for each channel, all with LDANew analyses for each channel, all with LDA– cscs and and use the charge asymmetry in WW to use the charge asymmetry in WW to

reject backgroundreject background– cscs re-optimized (with fewer variables)cscs re-optimized (with fewer variables)


Data Data selectionselection

Data Data selectionselection • Common to the 3 analysesCommon to the 3 analyses

• 618 pb618 pb-1-1 from 189 GeV to 209 GeV from 189 GeV to 209 GeV– Use the WW selectionUse the WW selection

– 189 GeV data re-analysed with the new analyses189 GeV data re-analysed with the new analyses

Data Data analysisanalysis

Data Data analysisanalysis • Similar to other Higgs analysesSimilar to other Higgs analyses

– pre-select events with cutspre-select events with cuts

– use a multivariate analysis (LDA) to select use a multivariate analysis (LDA) to select

optimally the candidatesoptimally the candidates

– calculate CLcalculate CLss with clfft with a discriminant variable with clfft with a discriminant variable

(mass or LDA)(mass or LDA)


against If two leptons )ore(both must have: sE 1.0

WWZZ,),( elll

well within acceptance 9601 .|cos| 9602 .|cos|

against

165 170missing

missing GeVPT 10missing GeVE 80

GeVm 70

against CMSvis Em 0750.

012 )( E

44 -like

Number of positive charged tracks1Number of negative charged tracks1

Force in 2 jets )/( 23 cGeVm jet

CLASS 11 2( )6Number of charged tracks

In each jet: number of charged tracks 0

selectionselection selectionselection

Selects 45 evts(exp. 40.63)


selection efficiencyselection efficiency selection efficiencyselection efficiency Background Background

compositioncomposition Background Background

compositioncomposition

W+W- 80%

-> l+l- 6.4%

ZZ 6%

+- 5.3%

We, Zee,… 2.3%

Then corrected for E12=0 cut (8%in ‘ 98, 6.5% in ‘ 99, 7% in 2000)

M H+


• Multivariate analysisMultivariate analysis– Linearly combine the Linearly combine the

variables of the variables of the

preselection, plus the preselection, plus the

charge-tagged charge-tagged polar polar

angleangle

H

1

2

H

W

W

2

1


• LDA OptimizationLDA Optimization– 4 variables are 4 variables are

sufficient:sufficient:

1/2 (Q1/2 (Q11coscos11+ Q+ Q22coscos22))

angle angle between taus between taus

event missing Pevent missing PTT

yy2323


Angle between jets


Use this optimal linear combination as a discriminant in CL calculation.


For each s,Signal LDA shape parametrisedby sum of 2 gaussians

and interpolated as a function of Higgs mass

Background :sum of 3 gaussians

LDA LDA

LDA LDA


Confidence levels calculated with CLFFT

MH+

CL(s+b) / Cb 1-Cb

MH+


Signal 85 GeV


cscs cscs

• Select one Select one + 2 jets + missing + 2 jets + missing

energyenergy– if several if several minijets, take the one with minijets, take the one with

min min 22 of the 2C fit (E,p conservation and of the 2C fit (E,p conservation and

equality of the jet-jet and equality of the jet-jet and masses) masses)

– define a first discriminant Ddefine a first discriminant D11 combining : combining :

• the event missing pthe event missing pTT, ,

• the isolation angle the isolation angle isoiso (cone around the (cone around the

containing 5% of the energy)containing 5% of the energy)

• the the 22 of the 2C fit of the 2C fit

• the decay angle of the leptonic Higgs the decay angle of the leptonic Higgs

candidate, multiplied by the candidate, multiplied by the charge charge

• Require DRequire D11>-0.1>-0.1


cscs cscs

• define a second discriminant Ddefine a second discriminant D22

combining :combining :• the decay angle of the leptonic Higgs the decay angle of the leptonic Higgs

candidate, multiplied by the candidate, multiplied by the charge charge

• a a polarisation estimator polarisation estimator

• Require DRequire D22>-0.3>-0.3

– efficiency from 49.1% for MH=60 GeV efficiency from 49.1% for MH=60 GeV

to 38.8% for MH=80 GeVto 38.8% for MH=80 GeV

• Background compositionBackground composition

– 93% WW93% WW– rest is Werest is We, ZZ and qq, ZZ and qq

Selects 279 evts(289.3 expected)

Year 2000 data


cscs cscs


cscscscs cscscscs

•4 jet preselection (>9 charged tracks, Ech>0.1 s, anti-ISR cuts, y34>0.003, T<0.9)

•5C fit with ABCFIT (as in WW) -> pairing with min 2

•calculate m with rescaled jet energies ( fixed) and require m<30 GeV

•Perform a LDA (optimized on a cocktail of higgs masses 80 to 88 GeV) with:

•Production angle

• m

• 25C/Ndof

•E jet min * jet-jet min

•log10 (QCD matrix element)

Cut D3>1.3

Selects 2762 evts

(2892 expected)

BG: 78%WW

10% qq


cscscscs cscscscs


cscscscs cscscscs


cscscscs cscscscs W mass set to 80.45 GeV


cscscscs cscscscs Confidence levels calculated with CLFFT

MH+ MH+

1-CbCL(s+b) / Cb


Systematic effectsSystematic effects Systematic effectsSystematic effects

Systematic effects on signal and BG normalisation are taken into account by smearing (s+b)/b

signal normalisation : •cross-section +-1% (rad. corr.)•calorimeter calibration : vary had/em scale by 2%/0.7%:

+-0.5% for cs and +-0.3% for cscs•for cscs: shift all variables by 1 of their mean:0.5%

background normalisation :•WW cross-section taken from RACOON: lower KORALW by 2.5%•WW cross-section uncertainty 2%• ->leptons cross-section uncertainty 5% for • qq cross-section uncertainty 5%•for cscs: shift all variables by 1 of their mean:0.5%•calorimeter calibration : vary had/em scale by 2%/0.7%


SystematicsSystematics SystematicsSystematics

%

cs%

cscs%

Signal .MC statothers

2.72.41.

3.22.91.4

1.81.31.2

BG norm.MC statothers

2.11.21.7

4.32.53.5

3.00.52.9

norm


FINAL FINAL RESULTSRESULTSFINAL FINAL RESULTSRESULTS

95 % C.L. limits in GeV

including systematics

BR(H->)=0 80.4 (exp. 78.2)

BR(H->)=1. 87.7 (exp. 89.2)

Any BR 79.2 (exp. 77.1)


COMPARISON WITH OTHER EXPERIMENTSCOMPARISON WITH OTHER EXPERIMENTSCOMPARISON WITH OTHER EXPERIMENTSCOMPARISON WITH OTHER EXPERIMENTS

ALEPH DELPHI L3 OPAL

BR=0 80.4(78.2)

77.4(77.0)

77.2(77.1)

76.2(77.1)

BR=1 87.7(89.2)

85.4(89.3)

84.9(83.0)

84.5(86.5)

ANY BR 79.2(77.1)

73.8(75.4)

67.1(75.0)

72.2(74.5)

(*) summer 2001

***

Obs

(exp)

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Search for charged Higgs bosons in e+e- collisions at energies up to s=209 GeV

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