Higgs searches with ATLAS - msu.runuclphys.sinp.msu.ru/conf/epp10/Price.pdf · Introduction ATLAS...

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


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

Eve

nts

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20

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80 DataVH(bb) (best fit)VZtt

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

[GeV]bbm50 100 150 200 250

Dat

a/M

C

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1.5 50 100 150 200 250

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DataVH(bb) (best fit)VZMultijettt

t, s+t chanWtW+bbW+blW+ccW+clW+lUncertaintyPre-fit background

=1.0)µVH(bb) (


-1Ldt = 20.3 fb∫ = 8 TeV s

>200 GeVV


[GeV]bbm50 100 150 200 250

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18 DataVH(bb) (best fit)VZZ+bbZ+blZ+ccZ+clUncertaintyPre-fit background

=1.0)µVH(bb) (


-1Ldt = 20.3 fb∫ = 8 TeV s

>200 GeVV


[GeV]bbm50 100 150 200 250

Dat

a/M

C0.5

1

1.5


2 lepton (ZH → llbb)1 lepton (WH → lνbb)0 lepton (ZH → ννbb)

VH → Vbb̄ Results

[GeV]bbm

50 100 150 200 250

Wei

ghte

d ev

ents

afte

r su

btra

ctio

n

0

0.2

0.4

0.6

0.8

1DataVH(bb) (best fit)VZUncertainty

=1.0)µVH(bb) (


-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


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.


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]∆

0 20 40 60 80 100 120 140 160 180 200 220

Eve

nts/

4 G

eV

0

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400

600

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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]∆

0 20 40 60 80 100 120 140 160 180 200 220

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-1Ldt = 20.7 fb∫γZ+

Z+jets

+ WZttbkg uncertainty

= 8 TeV Datas

ATLAS Preliminary

µµ →, Z γ Z→H


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]∆

25 30 35 40 45 50 55 60

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nts/

1 G

eV

0

50

100

150

200

250

300Data 2012

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

0

5

10

15

20

25

30

35

40

45ObservedExpected

σ 1±σ 2±

= 7 TeVs, -1 Ldt = 4.6 fb∫ = 8 TeVs , -1 Ldt = 20.7 fb∫

ATLAS Preliminary


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.


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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

[GeV]γγm100 110 120 130 140 150 160

1000

2000 Control region -1Ldt = 20.3 fb∫ = 8 TeV s

[GeV]Hm

120 122 124 126 128 130

Htt SM

σ/Htt σ

95%

CL

limit

on

0

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40 limitsCLObserved limitsCLExpected

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.


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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L dt = 13.0 fb∫Data

ZMultijet

WTop

WW

WZZZ

(*) WW→, H

(*) ZZ→SM H

= 125 GeV)H

Signal (SM ZH, m

ATLAS = 8 TeVsPreliminary

ll+invisible→ZH

[GeV]missTE

0 50 100 150 200 250 300Dat

a / M

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11.21.4

[GeV]missTE

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ATLAS =8 TeVsPreliminary -1

L = 13.0 fb∫Data

ZTop

WZWW

ZZ Other BG

=125 GeV)H

Signal (SM ZH, m


�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

L

-210

-110

1 Observed

Expected

PreliminaryATLAS

ll(inv)→ZH-1 Ldt=4.7fb∫=7TeV, s-1 Ldt=13.0fb∫=8TeV, s

[GeV]Hm

120 140 160 180 200 220 240 260 280 300

ll in

v) [f

b]→

BR

(ZH

×Z

Hσ

95%

CL

limit:

10

20

30

40

50

60

70 ll inv)→BR(ZH×ZH,SMσ

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.


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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Dataττ→(125)H2 x

ττ→Zµµ,ee→Z

+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

[GeV]ττmMMC mass 50 100 150 200

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ττ→(125)H5 x (OS-SS)ττ→Z

Others (OS-SS)Same Sign DataBkg. uncert.

ATLAS Preliminary

= 8 TeVs

-1 L dt = 13.0 fb∫

Boostedhadτe + hadτµ

τhadτhad

VBF, Boosted

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ATLAS Preliminary

= 8 TeVs

-1 L dt = 13.0 fb∫

+2-jets VBFH hadτhadτ


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

100 110 120 130 140 150

SM

σ/σ 9

5% C

L Li

mit

on

0

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8ττ →H

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

SM

B/B

× V

BF

+V

Hµ

-3

-2

-1

0

1

2

3

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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


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

20

30

40

50

60ATLAS

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

20

30

40

50

60

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


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.


Leptonic tt̄H → tt̄γγ candidate event


Backups

backups...


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 ∗


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 ∗


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


Higgs searches with ATLAS - msu.runuclphys.sinp.msu.ru/conf/epp10/Price.pdf · Introduction ATLAS...

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