Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS...

36
Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS Experiments Ulrike Schnoor on behalf of the ATLAS and CMS Collaborations [email protected] Physikalisches Institut, Universit¨ at Freiburg May 3, 2017

Transcript of Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS...

Page 1: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Higgs Decays to Bottom and Tau PairsWith the ATLAS and CMS Experiments

Ulrike Schnooron behalf of the ATLAS and CMS Collaborations

[email protected]

Physikalisches Institut, Universitat Freiburg

May 3, 2017

Page 2: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Higgs decays to Bottom and Tau pairs

...directly probe fermion mass generation:

LEWSBf = mf (fLfR + fR fL)︸ ︷︷ ︸

mass term

+gf√

2(fLfR + fR fL)H︸ ︷︷ ︸

Higgs−fermion interaction

Yukawa coupling gf =√

2 mfv

Experimental access to Higgs–fermion coupling:Access Channel Sector Type

Indirect H → γγ quark up/downGGF quark up/down

DirectH → ττ lepton downH → bb quark downttH quark up

[GeV]HM80 100 120 140 160 180 200

Hig

gs B

R +

Tota

l U

ncert

­410

­310

­210

­110

1

LH

C H

IGG

S X

S W

G 2

01

3

bb

ττ

µµ

cc

gg

γγ γZ

WW

ZZ

• H → bb, H → ττ :large branching ratios

• Predictions for GGF,VBF:POWHEG at NLO+ PYTHIA,renormalized toNNLO QCD

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 2/27

Page 3: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Measurements

• Measure cross sections• Express as signal strength µ

µ =σmeasured

prod+decay

(σprod × BR)SM

• Interpretation: coupling modifier κifor production or decay process i :

κ2i = σi/σ

SMi or κ2

i = Γi/ΓSMi

⇒ κi =gi

gSMi

[JHEP 08 (2016) 045]

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 3/27

Page 4: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Measurements of H → ττ and H → bbH → bb- Experimental challenges- ATLAS and CMS MeasurementsH → τ+τ−

- Experimental challenges- ATLAS and CMS MeasurementsInterpretationsSummary

H → bb

• VBF H → bb:ATLAS: 8 TeV, CMS: 8, 13 TeV

• VH H → bb:ATLAS: 8, 13 TeV, CMS: 7, 8 TeV

• VBF+γ H → bb: ATLAS: 13 TeV

• t(t)H: ATLAS: 8, 13 TeV, CMS: 7, 8 , 13 TeV

H → ττ

• GGF, VBF H → ττ :ATLAS: 7, 8 TeV, CMS: 7, 8 TeV

• VH,H → ττ :ATLAS 8 TeV, CMS: 7, 8 TeV

• CP measurement in VBF:ATLAS: 8 TeV

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 4/27

Page 5: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

H → bb

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 5/27

Page 6: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

H → bb... probe Yukawa couplings to (down-type) quarks• Largest BR (∼58 %)• Challenging: large multi-jet and b-jet background

• Profits from good b-tagging• Makes use of leptonic decay of particles produced in association• Uses kinematic properties of the production process

Z(→ ``)H(→ bb) candidate eventRun 2 so far: ATLAS + CMS > 1 M H → bb events

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 6/27

Page 7: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Experimental access to H → bb

GGF overwhelming background, difficult to trigger

VBF large background, trigger on jets, make use ofVBF kinematics

VBF+γ clean signature, small σprod, trigger on photon

VH trigger on decay products of W/Z (e, µ, EmissT )

t(t)H trigger on decay products of top quark(s)

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 7/27

Page 8: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Searches in VBF H → bbATLAS: JHEP 11 (2016) 112 (8 TeV, 20.2 fb−1)CMS: HIG-16-003 (13 TeV, 2.3 fb−1) [JHEP 11 (2016) 112]

• Signal: VBF H (→ bb) + jj, GGF H → bb• Background:

• Resonant: Z (→ bb) + jj• Non-resonant: dominantly multi-jet

(estimated from data in mbb side-band)• Triggers:

• 4 jets incl. 2 b-tagged in HLT• 3 (2) jets incl. 1 (2) forward + 1 b-tagged

jet• Signal efficiency ∼ 6 %

• Selection:4 high-pT jets incl. 2 b-tagged central jets;pT(bb) > 100 GeV

Multivariate analysis: Boosted decision tree (BDT) to discriminate VBFsignal from non-resonant background; fit in mbb in 4 BDT categories

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 8/27

Page 9: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Results for VBF H → bb

ATLAS: JHEP 11 (2016) 112: 8 TeV, 20.2 fb−1

Signal strength: µ = −0.8± 1.3(stat.)+1.8−1.9(syst.) , upper limit µ = 4.4 at 95 %C.L.

CMS: HIG-16-003: 2.3 fb−1(13 TeV)⊕

19.8 fb−1(8 TeV)

• Triggers on 1 forward jet and 1 (2)b-tagged jets (total signal efficiency6.2 %)

• Further selection based on jetkinematics and VBF topology

• Fit in Mbb

• Combined with 8 TeV result:µ = 1.3+1.2

−1.1

• Dominant: statistical uncertainty,QCD background estimate

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 9/27

Page 10: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Searches in VHATLAS-CONF-2016-091: 13 TeV, 13.2 fb−1

CMS: PRD 89 (2014) 012003: 7 TeV (5.1 fb−1), 8 TeV (18.9 fb−1)

[ATLAS-CONF-2016-091]

• Large and complex backgrounds• Trigger on decay products of W/Z• Preselection: ≥ 2 jets, 2 b-tags• Categorization in

0 leptons Z → ννEmiss

T > 150 GeV; 2 or 3 jets1 lepton W → `ν

pT(W ) > 150 GeV;Emiss

T > 30 GeV; 2 or 3 jets2 leptons Z → `+`−

71 < m`` < 121 GeV;pT(Z ) < or > 150 GeV;2 or ≥ 3 jets

• BDT in each category→ simultaneous fit

µ = 0.21+0.36−0.35(stat.)± 0.36(syst.)

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 10/27

Page 11: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Searches in VHATLAS-CONF-2016-091: 13 TeV, 13.2 fb−1

CMS: PRD 89 (2014) 012003: 7 TeV (5.1 fb−1), 8 TeV (18.9 fb−1)

CMS: PRD 89 (2014) 012003: 5.1 fb−1(7 TeV)⊕

18.9 fb−1(8 TeV)

• Channels: W (µν)H, W (eν)H, W (τν)H, Z (µµ)H, Z (ee)H,Z (νν)H

• Single-lepton, tau, EmissT or b-tag triggers

• BDT regression based on b-jet kinematicsand properties of VH system to correct jetenergy

• BDT classification in signal regions⇒ Combined signal strength including gg → ZH

(@NLO) contribution: µ = 0.89± 0.43[PoS ICHEP2016 (2016) 777, Eur. Phys. J. C 75 (2015)212]

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 11/27

Page 12: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Search in VBF+γATLAS-CONF-2016-063: 13 TeV, 12.6 fb−1 [ATLAS-CONF-2016-091]

• Trigger on photon, 4 jets, and maximum dijetmass Mjj > 700 GeV

• Backgrounds: Non-resonant QCD productionof photon and 4 jets, Z (→ bb)+jets

• Event selection:• Suppress non-resonant QCD background:

isolated and high-pT photon• 2 b-jets and 2 jets with high Mjj

• BDT against multi-jet background (jetproperties and kinematics, e.g. photoncentrality)

⇒ Fit to mbb in 3 regions of BDT score:

µ = −3.9+2.8−2.7 and µ < 4.0 at 95 % C.L.

• Statistically limitedUlrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 12/27

Page 13: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Searches in association with single top quarksCMS: CMS-PAS-HIG-16-019 (2.3 fb−1, 13 TeV)

tH production

Interference betweenproduction with HWW and Httvertices→ sensitive tomagnitude and sign of κt

• Several kinematic categories according to top and Higgs kinematics• BDT for jet-quark assignment• BDT for discrimination from

single top, t t , t tH

• For SM: upper limit 113.7× σSM

• Limits on Higgs boson coupling to topquarks (κt ): −→(κV = κb = 1)

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 13/27

Page 14: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Searches in association with top quark pairsATLAS: ATLAS-CONF-2016-080 (13.2 fb−1, 13 TeV);CMS: CMS-PAS-HIG-16-038 (12.9 fb−1, 13 TeV)

ttH production

• One or both top quarks decayingleptonically

• Backgrounds: t t+light jets,t t + bb, t t + b and t t + cc

• Combine:• BDT based on object

kinematics, event shape,b-tagger⇒ discriminationagainst inclusive t t

• Matrix-Element Method (MEM):M(t tH)

M(t t+bb)⇒ discrimination

against t t + bb• MEM = final discriminant µ = −0.19+0.45

−0.44(stat.)+0.66−0.68(syst.)

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 14/27

Page 15: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Searches in association with top quark pairsATLAS: ATLAS-CONF-2016-080 (13.2 fb−1, 13 TeV);CMS: CMS: CMS-PAS-HIG-16-038 (12.9 fb−1, 13 TeV)

ttH production

• One or both top quarks decaying leptonically• Backgrounds: t t+light jets, t t+ ≥ 1b and

t t+ ≥ 1c

• Categories defined according to numberof leptons, jets, b-tags

• Two step multivariate analysis:• Jet assignment• Signal/background classification

• Fit to the discriminants in each category

→ combined µ = 2.1+1.0−0.9

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 15/27

Page 16: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

H → ττ

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 16/27

Page 17: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

H → τ+τ−

... probe Yukawa coupling to down-type leptons• large BR (∼6.3 %)• multi-jets or Z+jets background• profits from good hadronic τ trigger and identification⇒ trigger on Higgs decay products

Accessible production channels

GGF boosted topology

VBF VBF topology

VH associated gauge bosonUlrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 17/27

Page 18: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

VBF and GGFATLAS: JHEP 1504 (2015) 117: 7 TeV (4.5 fb−1), 8 TeV (20.3 fb−1);CMS: JHEP 1405 (2014) 104: 7 TeV (4.9 fb−1), 8 TeV (19.7 fb−1)

[JHEP 1504 (2015) 117]

• Signal: H → ττ• Channels:

• τ`τ`, τ`τhad , τhadτhad• leptonic decays: isolated leptons• hadronic decays: tau identification through MVA→ different background composition

• Main background Z → τ+τ−: estimatedwith data-driven “embedding” technique

• Reconstruction of di-tau mass:Missing Mass Calculator (MMC) based onlikelihood scan

• 2 preselection regions:• Boosted topology (GGF dominated)• VBF topology (VBF dominated)

• Maximum likelihood fit to BoostedDecision Tree outputs

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 18/27

Page 19: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

VBF and GGFATLAS: JHEP 1504 (2015) 117: 7 TeV (4.5 fb−1), 8 TeV (20.3 fb−1);CMS: JHEP 1405 (2014) 104: 7 TeV (4.9 fb−1), 8 TeV (19.7 fb−1)

• Mass reconstruction using likelihood-based algorithm (mττ )• Several BDTs to suppress backgrounds• Including also VH channel

[JHEP 1405 (2014)104]

• QCD background from same-chargecontrol region

• Z → τ+τ− background from Z → µµdata with simulated τs embedded

• Extract signal from binnedmaximum-likelihood fit to mττ

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 19/27

Page 20: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

VBF and GGFATLAS: JHEP 1504 (2015) 117:

7 TeV (4.5 fb−1), 8 TeV (20.3 fb−1)

CMS: JHEP 1405 (2014) 104:

7 TeV (4.9 fb−1), 8 TeV (19.7 fb−1)

Combination of all channels,regions, center-of-massenergies, ATLAS and CMS:

µ = 1.11+0.24−0.22

[JHEP 08 (2016) 045]• Dominated by statistics• Normalization of Z , W ,

multijets backgrounds

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 20/27

Page 21: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Searches in VHATLAS: Phys. Rev. D 93, 092005 (2016): 8 TeV (20.3 fb−1),CMS: CMS-PAS-HIG-12-053: 7 TeV (5.0 fb−1) + 8 TeV (19.5 fb−1)

Signal:Selection: multiple objects defining the final stateBackground: W+jets, Z+jets,t t with 1 prompt and 1 fake lepton

• WH channels: `±`±τh and `τhτh

• ZH channels: ``LL with LL = eµ,eτh, µτh, τhτh

• Background in hadronic channels dominated by fake τh CMS-PAS-HIG-12-053

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 21/27

Page 22: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Searches in VH[Phys. Rev. D 93, 092005 (2016)]

Selection:• Isolation and quality of leptons• Only same-charge same-flavor lepton pairs• b-veto• Requirement on scalar pT sum of leptons and

taus

Exclusionlimits:

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 22/27

Page 23: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Properties (CP nature)ATLAS: Eur. Phys. J. C76 (2016) 658 (8 TeV, 20.2 fb−1)

[Eur. Phys. J. C76 (2016) 658]

• Measurement based on 8 TeV H → ττ couplings analysis• Use Optimal Observable (OO) as CP-odd observable:

if 〈OO〉 6= 0⇒ CP violation• Matrix element for OO calculation and event reweighting extracted fromHAWK [Denner, Dittmaier, Kallweit, Muck, Comput. Phys. Commun. 195 (2015)]

• OO =2<(M∗SMMCP−odd)

|MSM |2

• Set limits on CP-mixing couplingd (EFT parameter):Leff = LSM + d e

2mW sin θwHW +

µνW−µν

• No signal strength information• Only shape information• Fit to full OO distribution to

extract exclusion limits on d

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 23/27

Page 24: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Exclusion limits on CP odd contribution

Expected 68 % confidence interval: [-0.08,0.08] for µ = 1.55

Observed confidence interval at 68 % C.L.:[-0.11,0.05]

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 24/27

Page 25: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Up-type vs. Down-type fermions

JHEP 08 (2016) 045

λdu = κd/κu

λVu = κV/κu

κuu = κu · κu/κH

• Coupling modifiers

κ =g

gSM

⇒ σi × BFf =σi (~κ)× Γf (~κ)

ΓH

• Many BSM extensions (e.g.2HDMs) predict λdu 6= 1

• No sensitivity on sign of λdu

• Precision: |λdu| ∈ [0.80,1.04]

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 25/27

Page 26: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Leptons vs. Quarks

• Many BSM extensions (e.g.2HDMs) predict λ`q 6= 1

• Quark couplings mainly probed byGGF, H → γγ, H → bb

• Lepton couplings probed byH → ττ

• Precision: |λ`q | = 1.06+0.15−0.18 JHEP 08 (2016) 045

λ`q = κ`/κq

λVq = κV/κq

κqq = κq · κq/κHUlrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 26/27

Page 27: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Summary

• Evidence for H → bb still not reached (measured significance in Run-1combination 2.6σ [exp. 3.7σ])

→ Quite challenging; search over many production modes• Evidence for H → ττ established at 7, 8 TeV (measured significance in

Run-1 combination 5.5σ [exp. 5.0σ], coupling precision ∼ 14 %)→ Rediscovery at 13 TeV ongoing• Challenging decay channels with state-of-the art techniques• Results interpreted in terms of coupling modifiers for up-type vs.

down-type fermions as well as leptons vs. quarks: in good agreementwith SM predictions

• Results being updated with full 2015+16 datasets

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 27/27

Page 28: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Discussion points

• Mostly still statistics dominated (also via background estimates), but:Theory uncertainties (QCD scale, jet bin migration) start to play a role

• Measuring “Higgs properties” in a model-independent way: limitations ofκ-framework, limited validity of EFT, Templified Cross Sections, ...

• Multivariate Analyses: Matrix-Element/Optimal Observable Methods vs.Machine Learning

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 28/27

Page 29: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

BACKUP

Backup

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 29/27

Page 30: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

Coupling modifiers

Fermionic Higgs coupling:

• From SM Lagrangian: Mass term ∼ mFv f f for fermion-Higgs coupling

• From definition of coupling modifiers: κ2F =

ΓmeasiΓSM

i∼ g2

v (meas)g2

v (SM)⇒ κF =

gmeasFgSM

F

• Thus, the quantity that is proportional to the particle’s mass in the SM is

κFmF

v(SM)∼ gF ∼ mF

→ probes the proportionality of the coupling to the mass

Bosonic Higgs coupling:• From SM Lagrangian: Mass term ∼ m2

V VµVµ

• Thus, in the SM, this is proportional to the particle’s mass:

√κv

mV

v(SM)=

mV

v∼ mV

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 30/27

Page 31: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

B-Tagging in ATLAS

• possible offline and in HLT• generally: exploiting relatively long lifetime and large mass of b-hadrons• require presence of tracks with large impact parameter w.r.t. primary

vertex, plus secondary decay vertices• this information is combined into a single neural-network discriminant• several working-points in terms of efficiency/purity and mis-tag rates are

provided• Reference: JINST 11 (2016) P04008, arXiv:1512.01094 [hep-ex].

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 31/27

Page 32: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

VBF H → bb+ jj

ATLAS AnalysisOffline selection:• events with exactly 4 jets with pT > 50 GeV, |η| < 4.5• jets ordered in eta: η1 < η2 < η3 < η4

• jets with smallest and largest etas are the tagging jets: J1, J4• the other two jets (J2, J3) are associated with Higgs decay, required to be

b-tagged and |η| < 2.5• trigger matching• pT(bb) > 100GeV (due to the 50 GeV cut on the jet pT, the Mbb

distribution of non-resonant backgrounds is shaped in such a way that itgets a peak around 130GeV. This is removed by requiring the pT of thebb system to be pT(bb) > 100GeV )

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 32/27

Page 33: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

VBF H → bb+ jjATLAS AnalysisMVA analysis: BDT• trained to discriminate between VBF H → bb signal and non-resonant

backgrounds using data in the side-band regions (Mbb: 70..90 GeV and150..190GeV)

• chose input variables which exploit the difference in topologies betweensignal and bg while keeping them as uncorrelated as possible with Mbb.Most important discriminating variables:

• jet width (for jets with |η| < 2.1) to distinguish between quark and gluonjets

• scalar sum of pT of additional jets with pT > 20 GeV in the region|η| < 2.5 (central jet activity)

• Mjj, |∆η(jj)|• max( |η1|, |η2| )• separation between tagging jets’ average |η| and that of the Higgs jets• polar angle of the cross product of the tagging jets momenta (∆φ(jj))

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 33/27

Page 34: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

H → ττ

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 34/27

Page 35: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

CP-odd observables

CP-odd observables have non-zero mean in presence of CP violation (modelindependent→ EFT used for quantification)

Signed azimuthal difference of jets Sgnd∆φ(jj)

• Sgnd∆φ(jj) = φ(jη>0)− φ(jη<0)

• non-signed ∆φ(jj) is CP-even

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 35/27

Page 36: Higgs Decays to Bottom and Tau Pairs With the ATLAS and CMS …cds.cern.ch/record/2262647/files/ATL-PHYS-SLIDE-2017-215.pdf · Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and

Introduction H → bb H → τ+τ− Interpretations Summary

CP-odd observables

Optimal Observable OO

OO =2<(M∗SMMCP−odd)

|MSM |2

• defined with the reconstructed four-momenta of particles in the events(tagging jets, Higgs reconstructed with MMC)

• Why optimal?→ combines the information on the entire phase space in one scalarvariable (for small d)[D. Atwood, A. Soni; Phys. Rev. D45 (1992)] , [M. Davier et al.; Phys. Lett. B306 (1993)] ,[M. Diehl, O. Nachtmann; Z. Phys. C62 (1994)]

Ulrike Schnoor (Freiburg) Higgs Decays to Bottom and Tau Pairs 36/27