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Higgs searches with ATLAS
Joe Price on behalf of the ATLAS experiment
27th Aug 2013Lomonosov Conference
Introduction
ATLAS results from H → γγ, H → ZZ (∗) → llll and H → WW ∗ channels alreadypresented in earlier talk by Richard St. Denis.
Focus on more challenging SM Higgs decays and BR limits on inv. decay of Higgs boson.
[GeV] HM80 100 120 140 160 180 200
H+
X)
[pb]
→(p
p σ
-210
-110
1
10
210= 8 TeVs
LHC
HIG
GS
XS
WG
201
2
H (NNLO+NNLL QCD + NLO EW)
→pp
qqH (NNLO QCD + NLO EW)
→pp
WH (NNLO QCD + NLO EW)
→pp
ZH (NNLO QCD +NLO EW)
→pp
ttH (NLO QCD)
→pp
BR(%) for mH = 125.5 GeVbb WW ττ ZZ γγ Zγ µµ57 22 6.2 2.8 0.23 0.16 0.02
SM x-sec (pb) for mH = 125.5 GeVggF VBF WH ZH ttH
19 1.6 0.7 0.41 0.13
[GeV]HM80 100 120 140 160 180 200
Hig
gs B
R +
Tot
al U
ncer
t [%
]
-410
-310
-210
-110
1
LHC
HIG
GS
XS
WG
201
3
bb
ττ
µµ
cc
gg
γγ γZ
WW
ZZ
Joe Price Lomonosov 2/21
Bibliography used in this talk
ATLAS Higgs results :https://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults
LHC Higgs cross section working group :https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections
Channel ReferenceLuminosity (fb−1)√
s = 7 TeV√
s = 8 TeV
VH → Vbb̄ ATLAS-CONF-2013-079 4.7 20.3
H → ττ ATLAS-CONF-2012-160 4.6 13.0
VH → VWW ∗ ATLAS-CONF-2013-075 4.7 20.7
H → Zγ ATLAS-CONF-2013-009 4.6 20.7
tt̄H → tt̄γγ ATLAS-CONF-2013-080 - 20.3
H → µµ̄ ATLAS-CONF-2013-010 - 20.7
ZH → l l̄ + inv ATLAS-CONF-2013-011 4.7 13.0
Joe Price Lomonosov 3/21
VH → Vbb̄
Associated (W /Z )H production, with W → lν, Z → ll and Z → νν,and with H → bb.
Each channel is further divided up into 2/3 jets ⊗ 5pW /Z
Tbins
(pW /Z
T ) = [< 90], [90 − 120], [120 − 160], [160 − 200], [> 200] GeV.
Flavour composition of main backgrounds is determined from data.
50 100 150 200 250
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nts
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W+bbW+ccW+clZ+bbZ+blZ+ccZ+clUncertaintyPre-fit background
=1.0)µVH(bb) (
ATLAS Preliminary -1Ldt = 4.7 fb∫ = 7 TeV s
-1Ldt = 20.3 fb∫ = 8 TeV s
>200 GeVV
T0 lep., 2 jets, 2 tags, p
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t, s+t chanWtW+bbW+blW+ccW+clW+lUncertaintyPre-fit background
=1.0)µVH(bb) (
ATLAS Preliminary -1Ldt = 4.7 fb∫ = 7 TeV s
-1Ldt = 20.3 fb∫ = 8 TeV s
>200 GeVV
T1 lep., 2 jets, 2 tags, p
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=1.0)µVH(bb) (
ATLAS Preliminary -1Ldt = 4.7 fb∫ = 7 TeV s
-1Ldt = 20.3 fb∫ = 8 TeV s
>200 GeVV
T2 lep., 2 jets, 2 tags, p
[GeV]bbm50 100 150 200 250
Dat
a/M
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1.5
Joe Price Lomonosov 4/21
2 lepton (ZH → llbb)1 lepton (WH → lνbb)0 lepton (ZH → ννbb)
VH → Vbb̄ Results
[GeV]bbm
50 100 150 200 250
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ghte
d ev
ents
afte
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btra
ctio
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1DataVH(bb) (best fit)VZUncertainty
=1.0)µVH(bb) (
ATLAS Preliminary -1Ldt = 4.7 fb∫ = 7 TeV s
-1Ldt = 20.3 fb∫ = 8 TeV s
0+1+2 lep., 2+3 jets, 2 tagsWeighted by Higgs S/B
Background subtracted mbb distribution,combining all regions with S/B weighting
] µSignal strength [-4 -2 0 2 4
ATLAS Prelim.
-1Ldt = 4.7 fb∫ = 7 TeV s-1Ldt = 20.3 fb∫ = 8 TeV s
= 125 GeVHm
1.4
1.4+ = -2.1µ), 7 TeVbVH(b
0.2±0.9±1.1±
1.9
2.2+ = -2.7µVH, 0 lepton 1.8±
1.9
2.0+ = -2.5µVH, 1 lepton 1.6±
3.6
4.0+ = 0.6µVH, 2 leptons 3.1±
0.7
0.7+ = 0.6µ), 8 TeVbVH(b
<0.10.4±0.5±
0.9
1.0+ = 0.9µVH, 0 lepton 0.8±
1.1
1.1+ = 0.7µVH, 1 lepton 0.8±
1.3
1.5+ = -0.3µVH, 2 leptons 1.2±
0.6
0.7+ = 0.2µ)bComb. VH(b
<0.10.4±0.5±
0.9
0.9+ = 0.5µVH, 0 lepton 0.8±
1.0
1.0+ = 0.1µVH, 1 lepton 0.8±
1.4
1.5+ = -0.4µVH, 2 leptons 1.2±
Total uncertaintyµ on σ 1±
(stat)σ(sys)σ(theo)σ
Joe Price Lomonosov 5/21
µ = 0.2+0.7−0.6 for mH = 125 GeV
VH → VWW∗, H → WW
∗ → lνlν
Complementary to the H → WW ∗ channel with ggF and VBFproduction.
Search only for leptonic decays of W and Z bosons.
Two separate channels: WH → WWW ∗ → lνlνlν andZH → ZWW ∗ → lllνlν.
4σ (3.8σ exp.) excess when combined with H → WW ∗ analysis.
Joe Price Lomonosov 6/21
7.2 (3.2 expected) × SM predictionfor mH = 125 GeV at 95% CL
H → Zγ, Z → l l̄
H → Zγ proceeds via electro-weak loops.
Much smaller BR than H → γγ but canconstrain BSM physics independently.
At least 2 isolated high pT electrons ormuons.
At least 1 high pT isolated photon.
∆R(γ, l) > 0.3.
mllγ > (mZ − 10) GeV.
Use ∆m = mllγ − mll as thediscriminating variable.
m [GeV]∆
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-1Ldt = 20.7 fb∫γZ+
Z+jets
+ WZttbkg uncertainty
= 8 TeV Datas
ATLAS Preliminary
ee→, Z γ Z→H
m [GeV]∆
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4 G
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-1Ldt = 20.7 fb∫γZ+
Z+jets
+ WZttbkg uncertainty
= 8 TeV Datas
ATLAS Preliminary
µµ →, Z γ Z→H
Joe Price Lomonosov 7/21
EVENT SELECTION
H
W
Z
γH
f
f
f
Z
γ
H
W
W
W
Z
γ
H → Zγ, Z → l l̄
Background determined fromdata driven method.
More statistics required beforethis channel becomes sensitive toSM Higgs boson.
m [GeV]∆
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20)×SMσ=125 GeV, H
(mγZ→H
ee→, Z-1Ldt = 20.7 fb∫ = 8 TeV, s
7195 events
ATLAS Preliminary
[GeV]Hm120 125 130 135 140 145 150
)γZ
→(H
SM
σ)/γ
Z→
(Hσ95
% C
L lim
it on
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45ObservedExpected
σ 1±σ 2±
= 7 TeVs, -1 Ldt = 4.6 fb∫ = 8 TeVs , -1 Ldt = 20.7 fb∫
ATLAS Preliminary
Joe Price Lomonosov 8/21
18.2 (13.5 expected) × SMprediction formH = 125 GeV at 95% CL
tt̄H → tt̄γγ
Search includes di-lepton, single lepton and fully hadronic tt̄ decays.
2 isolated photons, 1 with pT > 40 GeV, the other with pT > 30 GeV.
Leptonic:
At least one electron or muon.At least one b-tagged jet.Emiss
T > 20 GeV.
Hadronic:
6 jets, at least 2 b-tagged.Lepton veto.
Joe Price Lomonosov 9/21
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10 preliminaryATLAS
Hadronic channelSignal region
DataSR+CR background fit
= 126.8 GeV)H
SM signal (mSR-only background fit
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Leptonic channelSignal region
DataSR+CR background fit
= 126.8 GeV)H
SM signal (mSR-only background fit
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[GeV]Hm
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Htt SM
σ/Htt σ
95%
CL
limit
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σ 1±σ 2±
ATLAS preliminary
γγ →H H channels comb.tt
= 8 TeV sData 2012 -1Ldt = 20.3 fb∫ 5.3 (6.4 expected) × SM prediction
at mH = 126.8 GeV at 95% CL
H → µµ
Only channel where coupling to second generation can be measured.
Large dataset required.
2 oppositely charged muons, one with pT > 25 GeVanother with pT > 15 GeV.
Divided into 2 categories, |η(µ1, µ2)| < 1 and1 < |η(µ1, µ2)| < 2.5 to take advantage of narrowersignal width in central region.
Background modelled by sum of Breit-Wigner and exp.
Joe Price Lomonosov 10/21
9.8 (8.2 expected) × SM predictionfor mH = 125 GeV at 95% CL
ZH → ll + inv
SM Higgs decay to invisible particles via H → ZZ (∗) → νν̄ν′
ν̄′
is very small.Search for enhancements in the inv. decay fraction due to BSM physics from SM Higgscandidate at mH = 125 GeV and for additional Higgs decaying invisibly.Assume SM production rate and 100% BR to invisible particles for additional Higgs.
2 OS leptons (pT > 20 GeV) with|mZ − mll | < 15 GeV.
Third lepton veto (pT > 7 GeV).
EmissT
> 90 GeV.
∆φ(l , l) < 1.7.
∆φ(Z ,EmissT
) > 2.6.
|EmissT
− pZT|/pZ
T< 0.2.
∆φ(EmissT
, pmissT
< 0.2).
Jet veto (jets with pT > 20 GeV and|η| < 2.5).
EmissT
distribution after all cuts is used asfinal discriminator.
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(*) WW→, H
(*) ZZ→SM H
= 125 GeV)H
Signal (SM ZH, m
ATLAS = 8 TeVsPreliminary
ll+invisible→ZH
[GeV]missTE
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ZTop
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=125 GeV)H
Signal (SM ZH, m
Joe Price Lomonosov 11/21
�Z
Z
h
q
q̄
ℓ+
ℓ−
χ
χ
ZH → ll + inv
No excess in search for additionalHiggs bosons.
Set limits on σ × BR in range115 < mH < 300 GeV.
inv) → BR(H
0 0.2 0.4 0.6 0.8 1
1-C
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Expected
PreliminaryATLAS
ll(inv)→ZH-1 Ldt=4.7fb∫=7TeV, s-1 Ldt=13.0fb∫=8TeV, s
[GeV]Hm
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ll in
v) [f
b]→
BR
(ZH
×Z
Hσ
95%
CL
limit:
10
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Observed
Expected
σ1±
σ2±
PreliminaryATLAS
ll(inv)→ZH-1 Ldt=4.7fb∫=7TeV, s-1 Ldt=13.0fb∫=8TeV, s
Limit on invisible BR of SMHiggs candidate atmH = 125 GeV.
Red lines indicate 68% and 95%CL.
Joe Price Lomonosov 12/21
BR(H → inv) <65% (84% expected) formH = 125 GeV at 95% CL
H → ττ
Analysis yet to be updated to full 2012 statistics.
Search includes di-lepton (τlepτlep), single lepton (τlepτhad) and fullyhadronic (τhadτhad) channels.
τlepτlep
2-jet VBF, Boosted,2-jet VH, 1-jet and0-jet
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+single-topttWW/WZ/ZZFake leptonsBkg. uncert.
ATLAS Preliminary
= 8 TeVs
-1 L dt = 13.0 fb∫
+2-jet VBFH µµ + µe + ee
τlepτhad
VBF, Boosted, 1-jetand 0-jet
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= 8 TeVs
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Boostedhadτe + hadτµ
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= 8 TeVs
-1 L dt = 13.0 fb∫
+2-jets VBFH hadτhadτ
Joe Price Lomonosov 13/21
H → ττ
Combined 2011 + 2012 data has 1.1σ excess above SM backgroundonly expectation.
The observed upper limit on σ × BR at 95% CL on the H → ττdecay is 1.9 × SM prediction, 1.2 expected.
[GeV]Hm
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σ/σ 9
5% C
L Li
mit
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sCLObserved
sCLExpected
σ 2±σ 1±
ATLAS Preliminary = 7 TeVs, -1 L dt = 4.6 fb∫ = 8 TeVs, -1 L dt = 13.0 fb∫
SM B/B× ggF
µ-2 0 2 4 6 8
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B/B
× V
BF
+V
Hµ
-3
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-1
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5 ATLAS Preliminary
= 7 TeVs, -1
L = 4.6 fb∫ = 8 TeVs,
-1 L = 13.0 fb∫
= 125 GeVHm
best fit>0)µbest fit (
95% Contour
68% ContourSM prediction
Background only
Joe Price Lomonosov 14/21
best fit µ = 0.7 ± 0.7 usingmH = 125 GeV
Reminder of BSM Higgs analyses
2011 analyses on BSM Higgs searches using 4.7 fb−1 at 7 TeV.MSSM:
H → ττ and H → µµ - JHEP02 2013 095Charged Higgs:
H+ → τν - JHEP 2013 076H+ → cs̄ - Eur.Phys.J C 73 (2013) 2465
Doubly charged Higgs:H → l±l± - Eur.Phys.J. C72 (2012) 2244
MSSM H → ττ
[GeV]Am100 150 200 250 300 350 400 450 500
βta
n
10
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MSSM combination, 95% CL limit
-1 Ldt = 4.7 - 4.8 fb∫ = 7 TeVs
>0µ, maxhm
Observed CLsExpected CLs
σ 1±σ 2±
LEP
H+ → τν
[GeV]+Hm90 100 110 120 130 140 150 160
βta
n
0
10
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Median expected exclusion
Observed exclusion 95% CL
theoryσObserved +1
theoryσObserved -1
-1Ldt = 4.6 fb∫Data 2011
=7 TeVs maxhm
ATLAS
H → l±l±
) [GeV]±±m(H
100 200 300 400 500 600
) [fb
]± l’± l
→ ±± B
R(H
×)−− H
++
H→
(pp
σ
1
10 ±e±Observed limit: e±e±Expected limit: e±µ±µObserved limit: ±µ±µExpected limit: ±µ±Observed limit: e±µ±Expected limit: e
)=1±l’± l→ ±±), BR(H−−
L H++
L H→(pp σ
)=1±l’± l→ ±±), BR(H−−
R H++
R H→(pp σ
ATLAS
∫ -1Ldt = 4.7 fb
= 7 TeVs
Joe Price Lomonosov 15/21
Conclusions and Outlook
Searches for SM Higgs in ATLAS in low-rate final states has beenpresented.
VH → Vbb and H → ττ starting to become sensitive to SM Higgs.
Still compatible with both background only and signal plus backgroundexpectations.
VH → VWW ∗ channel gives additional sensitivity to H → WW ∗
analysis.
H → Z + γ, tt̄H and H → µµ̄ not yet sensitive to SM Higgs signal.
ZH → ll + inv sets limit on possible BSM physics in the Higgs sector.
No excess seen in final EmissT distribution.
Direct(indirect) limit of BR(H → inv) at < 0.65(0.6) at 95%CL.
H → ττ and ZH → l l̄ + inv still to be updated with full 2012 dataset.
Joe Price Lomonosov 16/21
Leptonic tt̄H → tt̄γγ candidate event
Joe Price Lomonosov 17/21
Backups
backups...
Joe Price Lomonosov 18/21
WH → WWW∗ → lνlνlν
Exactly 3 isolated leptons, with pT > 15 GeV and total charge ±1
One lepton must have pT > 25 GeV
Split into Z -enriched (one SFOS lepton pair) and Z -depleted (no such pair)
Cut Z-enriched Z-depleted
Jet multiplicity Njet ≤ 1b-veto Nb−tag = 0
EmissT ,Rel
EmissT ,Rel
> 40 GeV EmissT ,Rel
> 25 GeV
Dilepton mass cut |mll − mZ | < 25 GeV and mll > 12 GeV mll > 12 GeVAngular cut ∆φl0l1 < 2.0overlap Remove events selected by H → WW ∗
Joe Price Lomonosov 19/21
ZH → ZWW∗ → l l̄ lνlν
Cut
EmissT
EmissT
> 30 GeV
plT
highest pT lepton: pT > 25 GeVsecond highest pT lepton: pT > 20 GeVthird highest pT lepton: pT > 15 GeVfourth highest pT lepton: pT > 10 GeV
Jet multiplicity Njet ≤ 1b-veto Nb−tag = 0
Mass cuts|ml2l3 − mZ | < 10 GeV10 < |ml0 l1 | < 65 GeV
Angular cut ∆φ01 < 2.5Channel separation 2SFOS 1SFOSpT4l pT4l > 30 GeV -m4l m4l > 130 GeV -overlap Remove events selected by H → WW ∗
Joe Price Lomonosov 20/21
VH → Vbb selection
Object 0-lepton 1-lepton 2-leptonLeptons 0 loose lept 1 tight + 0 loose lept 1 med. + 1 loose lept
Jets
2 b − tagged jets
pjet1T
> 45 GeV
pjet2T
> 20 GeV2 b − tagged jets≤ 1 extra jets
EmissT
EmissT
> 120 GeV
EmissT
> 25 GeV EmissT
< 60 GeVpmiss
T> 30 GeV
∆φ(EmissT
, pmissT
) < π/2min[∆φ(Emiss
T, jet)] > 1.5
∆φ(EmissT
, bb) > 2.8
Vector boson - mWT
< 120 GeV 83 < mll < 99 GeV
Joe Price Lomonosov 21/21