ATLAS Sensitivity to Standard Model and SUSY Higgs Bosons

ATLAS Sensitivity to ATLAS Sensitivity to Standard Model and Standard Model and SUSY Higgs Bosons SUSY Higgs Bosons

Stathes Paganis Stathes Paganis University of SheffieldUniversity of SheffieldOn Behalf of the ATLAS On Behalf of the ATLAS

CollaborationCollaboration

SUSY05, 19-July-2005, Durham UKSUSY05, 19-July-2005, Durham UK

19-July-2005 ATLAS Sensitivity to SM and SUSY Higgs

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OutlineOutline

Discovery potential for Standard Model Discovery potential for Standard Model Higgs bosonHiggs boson

Higgs boson propertiesHiggs boson properties

Discovery potential for MSSM Higgs Discovery potential for MSSM Higgs bosonsbosons


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ATLAS @ LHCATLAS @ LHC

Inner Tracker

EM Calorimeter

Hadronic Calorimeter

Muon Detectors


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SM Higgs: SM Higgs: ATLAS Discovery PotentialATLAS Discovery Potential


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SM Higgs xsections and branching SM Higgs xsections and branching ratios ratios

BR

bb

WWZZ

LEP excluded


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SM Higgs Discovery Potential SM Higgs Discovery Potential (Review)(Review)

2004High mass: MH > 180GeVH->ZZ->4lepton Has a narrow peak on top of a low background (pp->ZZ)

Intermediate mass: 115 < MH < 180GeVChallenging for MH < 130GeV


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115GeV Higgs: first year (10fb115GeV Higgs: first year (10fb-1-1))

Total S/ B : ~ 4.2 Systematic errors included

complete detector

H->H-> ttH-ttH->ttbb>ttbb

qqH-qqH->qq>qq

SS 150150 1515 ~10~10

BB 39003900 4545 ~10~10

S/BS/B 0.040.04 0.330.33

S/√BS/√B 2.42.4 2.22.2 ~2.7~2.7

• 3 Channels all around 2, large backgrounds.

• Quite challenging.

Large K-factor~2 not included

L=30fb-1


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115GeV Higgs: Experimental 115GeV Higgs: Experimental ChallengesChallenges

H -> 2photon- EMCalorimeter response uniformity to ~1% is required.

ttH -> WW bb -> blv bjj bb- b-tagging for all 4 b-jets to reduce combinatorics.

qqH -> qq- Forward jet-tagging needed.- Central jet-veto to reduce background.

Common:- Good knowledge of the background 1-10%.- All require low threshold triggers.


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130GeV Higgs: first year (10fb130GeV Higgs: first year (10fb-1-1))

Total S/ B : ~ 6

complete detector

• H->4l small signal but small background• 3/4 channels with less than 3• qqH->qqWW counting channel (no clear

peak); relies on knowledge of background

H->H-> H->4lH->4l qqH->qqH->

qqWWqqWWqqH->qqH->

qqqqSS 120120 55 1818 ~8~8

BB 25002500 <1<1 1515 ~6~6

S/BS/B 0.050.05 ~1~1

S/√BS/√B 2.42.4 2.82.8 3.93.9 2.62.6


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SM Higgs SummarySM Higgs Summary

For MFor MHH>180GeV, discovery should come >180GeV, discovery should come quickly mainly due to the H->4leptonquickly mainly due to the H->4lepton

For MFor MHH<180GeV a few tens of fb-1 will be <180GeV a few tens of fb-1 will be needed (a few years of low luminosity needed (a few years of low luminosity running)running)

The region around the LEP limit (115GeV) is the most challenging

All channels present experimental All channels present experimental challenges:challenges:

Uniformity/Linearity/Calibration of the calorimeters Missing-Et reconstruction b-tagging EM isolation, e/mu efficiencies, tau-ID, ...


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Higgs PropertiesHiggs Properties


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Higgs PropertiesHiggs Properties

Higgs MassHiggs Mass Expect ~0.1% accuracy using H->ZZ->4leptons

300fb-1 and H-> for MH<400GeV (ATLAS+CMS)

Higgs JHiggs JCPCP

Spin from H->ZZ and H->WW. Parity sensitive to angular correlations in H->ZZ-

>4lepton. Needs full luminosity.

Higgs CouplingsHiggs Couplings Only ratios of couplings (or partial widths) are

measured in a fairly model independent way. Absolute coupling determination requires further

theoretical assumptions. Needs full luminosity.


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Coupling Ratio Coupling Ratio determinationdetermination

A single JCP=0++ Higgs

Assumptions

No extra particles in loops,Only SM particles coupleto Higgs boson

Experimental and theoretical uncertainties for signal and background

Taken into account


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Absolute couplings after Absolute couplings after assumptionsassumptions

Assumptions:

Upper limit for either a coupling or a total width is required. The couplings to W,Z are not stronger than in the SM ( true for any n-Higgs Doublet Model )

Duehrssen et al hep-ph/0407190

Channels considered:

H->ZZ(*)->4lH->H->WW->ll+Et,miss

H->ttH, H->bb


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MSSM Higgs MSSM Higgs


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MSSMMinimal Supersymmetric extension: two Higgs doublets 8 degrees of freedom (5 particles):

CP-even : h,H CP-odd: A Charged: H+,H-

gu gd gV

h cos/sin -sin/cos sin(-)

H sin/sin cos/cos cos(-)

A 1/tan tan 0

Couplings to SM particles modified w.r.t. SM.


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CPConserving Benchmark CPConserving Benchmark ScenariosScenarios

MHMAX scenario maximal mh < 135 GeV (Xt ~ sqrt(6)*MS)

Nomixing scenario small mh < 116 GeV (Xt = 0)

Examples:

At MA>>MZ or MA~Mh,max and tan>>1, the heavy bosons degenerate in mass while the h decouples at Mh~130 GeV (decoupling regime of MSSM)

Maximum Mh depends on stop mixing Xt


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Discovery potential in tanDiscovery potential in tan vs M vs MAA planeplane

LEP tan exclusion: no exclusion for mt larger ~183 GeV !

two expected data volumes

30 fb-1 @ low lumi

300 fb-1 = 30 fb-1@ low lumi.

+ 270fb-1 @high lumi

discovery = 5 sigma excess

using Poissonian statistics

no systematic uncertainties yet

Is at least 1 Higgs boson observable in the entire parameter space?

How many Higgs bosons can be observed?

Can the SM be discriminated from extended Higgs sectors?


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H,h Discovery Potential H,h Discovery Potential 30fb30fb-1-1

almost gurantees

discovery of at least one

h or H with 30 fb-1

studied for MH>110GeVat low lumi running

SM like h with 30 fb-1

ll4


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h Discovery Potential 30fbh Discovery Potential 30fb-1-1

In Maximal Mixing Scenario: VBF hcovers most of the MSSM plane with 30fb-1

The VBF hchannel is also important for other MSSM scenarios

VBF h

Experimental Challenge:

Missing Et Reconstruction


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at least one Higgs boson

observable for all parameters

(true not only for MHMAX)

significant area where only lightest Higgs boson h is observable

can SM be discriminated from

extended Higgs sector by

parameter determination?

similar results in other benchmark scenarios

VBF channels , H/Aonly used with 30fb-1

300 fb-1

Overall Discovery Potential: 300 Overall Discovery Potential: 300 fbfb-1-1


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SM vs MSSM Higgs SM vs MSSM Higgs discriminationdiscrimination

BR(h WW) BR(h )

estimate of sensitivity from rate measurements in VBF channels (30fb-1)

R =

300 fb-1

only statistical errors

assume Mh exactly known needs further study incl. sys. errors

compare expected measurement of R in MSSM with prediction from SM

=|RMSSM-RSM|exp


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The CP violating CPX The CP violating CPX scenarioscenario

maximise effect CPX scenario (Carena et al., Phys.Lett B495 155(2000))

arg(At)=arg(Ab)=arg(Mgluino)=90 degree

scan of Born level parameters: tan and MH+-

CP eigenstates h, A, H mix to mass eigenstates H1, H2, H3

CP conserving at Born level, but CP violation via complex At, Ab Mgl


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CPX PhenomenologyCPX PhenomenologyH1,H2,H3 coupling to W,Z

H3

H2

H1

H2,H3 H1H1, ZH1,WW, ZZ decays

sum rule:

i gi (ZZHi)

= gSM

no absolute limit on mass of H1 from LEP

strong dependence of excluded region

on value for mtop

on calculation used FeynHiggs vs CPH

2

2


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CPX scenario: overall discovery CPX scenario: overall discovery potentialpotential

MH1: < 70 GeVMH2: 105 to 120 GeV

MH3: 140 to 180 GeV

small masses below 70 GeVnot yet studied in ATLAS

FeynHiggs with Mt=175 GeV

OPAL exclusion for Mt=174.3GeV

small uncovered area at low MH+-

FeynHiggs and CPSUPERH calculations

300 fb-1


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Not just science fiction ...Not just science fiction ...

First Cosmic rays observed by theATLAS Tile calorimeter in the underground cavern in mid-June

Huge effort from ATLAS physicists to understand the detector (calibration, alignment, etc)


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SummarySummary SM Higgs should be discovered with a few SM Higgs should be discovered with a few

tens of fbtens of fb-1-1 over the full mass range. over the full mass range.

Higgs coupling measurement will require Higgs coupling measurement will require full luminosity. Accuracies of 15-50% are full luminosity. Accuracies of 15-50% are expected depending on the channel.expected depending on the channel.

At least one of the MSSM h or H should be At least one of the MSSM h or H should be discovered with a few tens of fbdiscovered with a few tens of fb-1-1

Studies of the CPX scenario have started.Studies of the CPX scenario have started.


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Backup SlidesBackup Slides


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Absolute couplings after Absolute couplings after assumptionsassumptions

SM-like Higgs assumptions:

Couplings to W and Z as in the SM.No new particles enter the loop for decay.


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4 CPConserving Benchmark 4 CPConserving Benchmark ScenariosScenarios Carena et al. , Eur.Phys.J.C26,601(2003)

Gluophobic scenario small gh,gluon mh < 119 GeV

Small scenario small ghbb and gh mh <123 GeV

MHMAX scenario maximal mh < 133 GeV

Nomixing scenario small mh < 116 GeV

Affects gluon fusion channels:gg h, h and hZZ4 l

Affects:VBF, h tth, hbb


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MSSM experimental inputsMSSM experimental inputschannelchannel lumi lumi Mass rangeMass range PublicationPublicationVBF, HVBF, HWWWW lowlow M>110 GeVM>110 GeV SN-ATLAS-2003-024SN-ATLAS-2003-024

ttH, HttH, Hbbbb low+higlow+highh

M>70GeVM>70GeV ATL-PHYS-2003-003ATL-PHYS-2003-003

bbH/AbbH/A low+higlow+highh

70<M<135GeV70<M<135GeV

M> 120 GeVM> 120 GeV

ATL-PHYS-2002-021ATL-PHYS-2002-021

ATL-PHYS-2000-005ATL-PHYS-2000-005

bbH/AbbH/Alep.had,lep.had,had.Hhad.Hadad

lowlow

lowlowM>120GeVM>120GeV

M > 450 GeVM > 450 GeV

ATL-PHYS-2000-001 ATL-PHYS-2000-001 ATL-PHYS-2003-008ATL-PHYS-2003-008

gbgbtH+-, HtH+-, H,tb,tb low+higlow+highh

M >180 GeVM >180 GeV SN-ATLAS-2002-017SN-ATLAS-2002-017

ttttbW bH+-, H+-bW bH+-, H+- lowlow M < 170 GeVM < 170 GeV ATL-PHYS-2003-58ATL-PHYS-2003-58

H/AH/A low+higlow+highh

M > 350 GeVM > 350 GeV TDRTDR

AAZhZhllbb, llbb, HHhhhhbbbb

low+higlow+highh

60 <ML<130 60 <ML<130 100<MH<360100<MH<360

TDR TDRTDR TDR

HH low+higlow+highh


ZZZZ4l 4l low+higlow+highh


WWWWllll low+higlow+highh

140<M 140<M <120GEV<120GEV

TDRTDR

WHWHllbbbb lowlow 70<M<130GeV70<M<130GeV TDRTDR

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ATLAS Sensitivity to Standard Model and SUSY Higgs Bosons

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