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TRANSCRIPT
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!