Search for the Neutral MSSM Higgs Bosons

SUSY08, Seoul 19.06.2008

Jana Schaarschmidt(Dresden University of Technology)

On behalf of the ATLAS Collaboration

Search for the Neutral MSSM Higgs Bosons (ATLAS) 1

Outline of the Talk

2Search for the Neutral MSSM Higgs Bosons (ATLAS)

• The ATLAS Experiment

• The MSSM

• Signal Production & Properties

• h/A/H � µµ

• h/A/H � ττ � lep-lep

• Conclusions

Focus on newATLAS results

The ATLAS Experiment

3Search for the Neutral MSSM Higgs Bosons (ATLAS)

Search for the Higgs boson: One benchmark for detector design

|η| < 2.7σ / pT = 2.3 % (pT = 50 GeV)Muon spectrometer

1.5 < |η| < 3.2

3.1 < |η| < 4.9

σ / E = 50 % / √E [GeV] ⊕ 3 %

σ / E = 100 % / √E [GeV] ⊕ 10 %

Hadronic calo: Barrel

Forward

|η| < 2.5σ / E = 10 % /√E [GeV] ⊕ 0.7 %EM calorimetry

|η| < 2.5σ / pT = 0.05 % pT [GeV] ⊕ 1 %Tracking

ηηηη coverageResolutionDetector component

109 Hz � 75 kHz � 100 MB / s storage

Solenoid: 2T

Toroid: 0.5T

Trigger:

• 46 m length, 24 m diameter• 7000 t weight• 3000 km cables

Liquid Argon CalorimeterTile CaloMuon Detectors

Toroid Magnets SCT Pixel TRTSolenoid

Higgs Sector in the MSSM

4Search for the Neutral MSSM Higgs Bosons (ATLAS)

• 2 Higgs doublets � 5 Higgs bosons:h0, H0 (CP = +1), A0 (CP = -1), H±

• Tree level decribed by only two parameters: mA, tanββββ = vu/vd

-tanβcotβA

cos(α−β)cosα/cosβsinα/sinβH

sin(α-β)-sinα/cosβcosα/sinβh

W / Zb / ττττtξξξξ

α = mixing angle between h and H

Couplings: gMSSM = ξξξξ gSM

h/H � ZZ* suppressedA does not couple to W/Z

CP conserved only

h/A/H � ττ enhanced if tanβ large

All parameters except tanββββ, mA fixed in benchmark scenarios:

Additional parameters:

X t Stop mixing parameterMSUSY Energy scale of SUSY breakingM2 Gaugino mass at EW scaleMg Gluino mass at EW scaleµ Strength of SUSY Higgs mixing

~

mhmax: mh < 133 GeV, maximum allowed mass for h

nomixing: mh < 116 GeV, no mixing in stop sector gluphobic: mh < 119 GeV, suppressed gg fusionsmall α: mh < 123 GeV, suppressed ttbar h, h � bb

vu2+vd

2 = v2

• mh < mZ but large loop corrections increase this limit!

Carena, Heinemeyer, Wagner, WeigleinEur. Phys. J. C26 (2003) pp. 601-7

mhmax considered here

Higgs Boson Production & Properties

5Search for the Neutral MSSM Higgs Bosons (ATLAS)

Signal Production

gluon fusion b-quark associated production

Signal Properties

Mass degeneration BR h/A/H � ττ BR h/A/H � µµ

≈ 10 % for low mA

Natural width

Dominantat tanβ<10

σbbH/A ∼ tan2β

103 pb

40 pb

9 pb

95 pb

39 pb

9 pb

150

200

300

σbbAσbbHmA / GeV

Example cross section values:

tanβ=20

Add up cross sections

S. Heynemeyer, W. Hollik, W.B.KilgorePhys. Rev. D 68 (2003) 013001

Irrelevant for h/A/H � ττdue to mass resolution

NLO

mhmax

mA / GeV

≈ 0.03 % for low mA

mA / GeV mA / GeV

mΦ

/ GeV

tanβ

Γ Φ/ G

eV

BR

(Φ�

ττ)

BR

(Φ�

µµ) /

%

S. Dittmaier, M. Kramer, M. SpiraPhys. Rev. D70 (2004) 074010

Analysis of h/A/H � µµ

6Search for the Neutral MSSM Higgs Bosons (ATLAS)

(1/4)

• Much smaller BR than ττ final state

• Very good muon reconstruction efficiency (95 %) and momentum measurement

• Excellent mass resolution:

• Fully reconstructable Higgs boson mass

399.4298.8199.6149.8129.7109.8Rec. mass

15.010.26.294.113.832.59Rec. σ

8.465.613.602.802.482.16Natural width

400300200150130110[GeV] / mA

tanβ=30

ATLASPreliminary

• Overwhelming backgrounds (ie. Z+jets, ttbar)

• Z + udcs reducible with b-tag

• ttbar rejectible by b-veto

• Signal tolopogy: 2 muons and no ET,miss

� ET,missonly due to detector resolution

� good discrimination against ttbar

Good strategy tosplit the analysis

ATLAS Preliminary

ET,miss / GeV

mµµ / GeV

7Search for the Neutral MSSM Higgs Bosons (ATLAS)

(2/4)Analysis of h/A/H � µµ

b-tag requirement

0 b-tags ≥ 1 b-tags • Not possible to separateA from H for mA > 130 GeVA from h for mA < 130 GeV

Preselction: Trigger: One µ with pT > 20 GeVtwo isolated µ, ET,miss< 40 GeV, pT,µ > 20 GeV

Cuts on acoplanarity, 3pTjet

ttbar and Z+jets dominantZ+jets dominating

Final cut: Mass window ∆m = mA ± 2σ

• A and H added due tomass degeneration

tanβ=3030 fb-1

Further Selection:

mµµ / GeV

45619 kall back-grounds

72

≈ 0

384

61

bbH/A

ggH/A

≥ 1 b-tags0 b-tagsProcess

• Number of events after all cuts(mA=200 GeV, tanβ=30, 30 fb-1):

mµµ / GeV

ATLAS Preliminary ATLAS Preliminary

ATLAS Preliminary

8Search for the Neutral MSSM Higgs Bosons (ATLAS)

(3/4)Analysis of h/A/H � µµ

Background estimation from data:• ttbar by selecting eµ final state

Control samples scaled to take in account lower electron recontruction efficiency (εe = 0.84 εµ)

Application in ≥ 1 b-tag mode:

• Z � µµ by using Z � ee

Systematic UncertaintiesMuon efficiency ± 1 %Muon pT scale ± 1 %Muon resolution σ(1/pT) = 0.011/pT r 0.00017Jet energy scale ± 7 % (15 %, |η|>3.2)Jet energy resolutionσ(E) = 0.45 √E (0.63 √E, |η|>3.2)b-tagging efficiency ± 5 %b-tagging fake rate ± 10 %

5 %

27 %

12 %

11 %

Signal

ttbar

Z + b

Z + udsc

UncertaintyProcess

ATLASPreliminary

AT

LAS

Pre

limina

ry

ATLASPreliminary

� Huge uncertainties demand fordata-driven background estimation

Signal cross section uncertainty: 17 %

mRR / GeVmµµ / GeV

30 fb-1

Gentile, Bilokon, Chiarella, NicolettiATLAS-PHYS-PUB-2006-019, July 2006

(dominant)

9Search for the Neutral MSSM Higgs Bosons (ATLAS)

(4/4)Analysis of h/A/H � µµDiscovery Potential of standalone and combined analysis:

Combination of complementary0 b-tag and ≥ 1 btag analysis

ATLASPreliminary

19

17

20

32

tanβ for

exclusion

30

27

32

48

110

150

200

300

tanβ for discovery

mA / GeV

ATLAS Preliminary

ATLASPreliminary

ATLASPreliminary

5 σ Discovery

95% CL ExclusionCombined:

mA / GeV

mA / GeV

mA / GeV

tanβ

for

5σdi

scov

ery

tanβ

for

5σdi

scov

ery

tanβ

for

95%

CL

excl

usio

n

10 fb-1

21 xx

mm

⋅= ll

ττ

10Search for the Neutral MSSM Higgs Bosons (ATLAS)

Conditions:

Alternative to coll. approx: Visible Mass(higher efficiency, worse resolution)

CollinearApproximation:

(1/5)

• Higgs mass large compared to τ mass• Higgs boson has non-zero pT• pT,miss in the detector due to neutrinos only

x = pT,R / pT,τ0 < x < 1

• Higgs boson mass reconstruction

• Mass resolutionin bb h/A/H:

Analysis of h/A/H � τ τ � lep-lep

• Trigger Single or di-lepton trigger

ATLAS preliminary

Higgs bosons carries little pTwhen produced in association with b-quarks

� Mass resolutiondeterioratesfor low pT,Higgs

� High-energy tailin mττ

ATLAS preliminary

σ / GeVmA / GeV

52300

33200

21110

mA = 130 GeV: Mass resolution:

pT,Higgs / GeV

mττ

/ GeV

mττ / GeV

11Search for the Neutral MSSM Higgs Bosons (ATLAS)

(2/5)Analysis of h/A/H � τ τ � lep-lep

≥≥≥≥ 1 b-tagsNo b-tag applied (inclusive)

Visible mass, mA=130 GeV,tanβ=30:

• gluon fusion and b-associated production• aims at early datawhen b-tag is not fully understood

• Event Selection:

mA = 130 GeV mA = 200 GeV

• Trigger• no jets (against ttbar)• eµ final state (against Z � ee/µµ)• kinematic cuts (eg. pT,Higgs)

• exclusively b-associated production

• all lep-lep final states

• mA independent preselection: Trigger, ≥1 b-tag, lepton selection,coll. approximation, < 3 jets

• mA dependent optimized kinematic cutseg. various pT cuts, x1•x2

• Asymmetric mass window cut

S / B = 33 / 25 S / B = 2051 / 8398 S / B = 379 / 1709

tanβ=20

30 fb-11 fb-1

mττ / GeV mττ / GeVATLAS Preliminary ATLAS Preliminarymvis / GeV

ATLASPreliminary

20 60 100 140 180

Eve

nts

/ 10

GeV

0

10

20

12Search for the Neutral MSSM Higgs Bosons (ATLAS)

(3/5)Analysis of h/A/H � τ τ � lep-lep

Estimation of irreducible Z ���� ττττττττ background from data

• Selection of Z ���� µµµµµµµµ events from data (sideband)

• Manipulation of µ energies and momenta according toZ ���� ττττττττ reference histograms (MC, signal region)

• Data-driven calculation ofnormalization of Z � ττ shape

ATLASPreliminary

Application in ≥≥≥≥ 1 b-tag analysis:

ATLAS Preliminary

(tanβ=20, 30 fb-1, mA =110 GeV)

Shape comparisons:

ATLASPreliminary

ATLASPreliminary

|cos

ξ|

Eµ(cosξ>0) Eµ(cosξ<0)

13Search for the Neutral MSSM Higgs Bosons (ATLAS)

(4/5)Analysis of h/A/H � τ τ � lep-lep

Systematic Uncertainties in ≥≥≥≥ 1 b-tags analysis

� Systematics fully included in final significance

Electron efficiency ± 0.2 %Electron E scale ± 0.2 %Electron resolution σ(ET) = 0.0073 ETMuon efficiency ± 1 %Muon pT scale ± 1 %Muon resolution σ(1/pT) = 0.001/pT r 0.00017

Jet energy scale ± 7 % (15 %, |η|>3.2)Jet energy resolutionσ(E) = 0.45 √E (0.63 √E, |η|>3.2)

b-tagging efficiency ± 5 %b-tagging fake rate ± 10 %

Overall ttbar uncertainty:

10 % - 23 %

ATLAS Preliminary

(Higgs mass dependent)

Impact of systematics evaluated onlyfor remaining background (ttbar)

Higgs mass dependent signal cross section uncertainty:

10 %

200

13.5 %

160

15.5 %

130

18 %∆σbb h/H/A

110mA / GeV

(dominant)

14Search for the Neutral MSSM Higgs Bosons (ATLAS)

(5/5)Analysis of h/A/H � τ τ � lep-lep

Results in the inclusive analysis (early data):

ATLAS Preliminary

Results in the ≥≥≥≥ 1 b-tags analysis (30 fb-1):

ATLASPreliminary

mA=130 GeVmA=200 GeV

tanβ

Sig

nific

ance

tanβ

tanβ

Luminosity (fb-1)

ATLASPreliminary

mA=130 GeV1 fb-1

ATLASPreliminary

ATLASPreliminary

10 20 30 40 50

1

10

0.1

0.01 1 2 3 4 5

Luminosity (fb-1)2 3 4 51

10

20

30

40

tanβ

10

20

30

40

Conclusions & Outlook

15Search for the Neutral MSSM Higgs Bosons (ATLAS)

Acknowledgments:

Michael Kobel, Wolfgang Mader, Markus Warsinsky, Sandra Horvat,Dimitris Fassouliotis, Ohad Silbert, Eilam Gross and others

• Investigation of ATLAS discovery potential on neutral MSSM Higgs bosonsin h/A/H � µµ and h/A/H � ττ � lep-lep

• h/A/H � ττ � lep-lep very powerful discovery channel

• h/A/H � µµ suitable for discovery and Higgs mass measurement

• Results will be published soon

Outlook:

• Update of h/A/H � ττ � lep-had mode and combination with lep-lep

� Data-taking is approaching...

� Looking forward to LHC start-up!