measurements of higgs boson production and properties in ...€¦ · introduction v.r.tavolaro...
TRANSCRIPT
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Date and place
Measurements of Higgs boson production and properties in the di-photon decay channel using
the CMS detector
Vittorio Raoul Tavolaro on behalf of the CMS collaboration
38th International Conference on High Energy Physics, 4 August 2016, Chicago IL
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Introduction
V.R.Tavolaro 204.08.2016
• Clean final state with two highly energetic photons
• Final state fully reconstructed with high resolution
• Very small branching fraction (~0.2%)
• Large backgrounds (ɣɣ, ɣj, jj)
• Exclusive categories targeting:gluon-gluon fusion (ggH),vector boson fusion (VBF)and ttH production modes
• Search for a narrow peak on a falling background in mass distribution
• 2016 dataset analysed,12.9/fb collected at 13 TeV (HIG-16-020) [GeV] HM
120 122 124 126 128 130
H+X
) [pb
]
→(p
p σ
1−10
1
10
210 = 13 TeVs
LHC
HIG
GS
XS W
G 2
016
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 + NLO EW)→pp
bbH (NNLO QCD in 5FS, NLO QCD in 4FS)→pp
tH (NLO QCD)→pp
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γ γTransformed BDT0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
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, mγγ→SM H
Analysis strategy
V.R.Tavolaro 304.08.2016
• Photons energy reconstructed and corrected, rejection of fake photons • Events categorised into classes (S/B, mass resolution, additional particles) to improve
the analysis sensitivity • Extraction of signal through fit of di-photon invariant mass spectrum in each category
Di-photoncategorisation
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ents
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σ1 ±σ2 ±
Untagged 0 =0.90µ=125.09 GeV, Hm --
Preliminary CMS TeV) (13-1 12.9 fbγγ→H
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DataS+B fitB component
σ1 ±σ2 ±
Untagged 0 =0.90µ=125.09 GeV, Hm --
Preliminary CMS TeV) (13-1 12.9 fbγγ→H
(GeV)γγm100 110 120 130 140 150 160 170 180
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(GeV)- e+em80 82 84 86 88 90 92 94 96 98 100
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All Categoriesγγ→H
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modelParametric
= 1.88 GeVeffσ
13 TeVCMS Simulation Preliminary
Photon Energy
V.R.Tavolaro 404.08.2016
• Electro-magnetic calorimeter (ECAL) response:
• corrected for change in time
• inter-calibrated to be uniform in η/φ
• adjustment of absolute scale
• Energy and its uncertainty corrected for local and global shower containment:
• regression targeting Etrue/Ereco
• Scale vs time and resolution calibration: Z→ee peak used as reference
• Corrected energies and resolutions used in the analysis
σeff = 1.18GeV in best cat.
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(GeV)T
Z boson p0 20 40 60 80 100 120 140 160 180 200
data
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True vertex efficiency
Average vertex probability
CMS 13 TeV Simulation Preliminary
)-1Data PU scenario (12.9 fb = 125 GeV)
H (mγγ →H
Vertex identification
V.R.Tavolaro 504.08.2016
• Vertex assignment correct within 1 cm → negligible impact on mass resolution
• No ionization in the tracker for photons
• Multi-variate approach for vertex identification
• exploit kinematic correlations and track distribution imbalance
• direction of conversion tracks, when present
• Second MVA estimates probability of correct vertex choice, used for di-photon classification
• Method validated on Z→μμ (ɣ+j for converted ɣ) events, where vertex found after removing muon tracks
εvtx = 80%
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Dat
a/M
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Photon selection
V.R.Tavolaro 604.08.2016
• MVA based photon ID classifier:
• goal: discriminate between prompt and fake photons
• inputs are shower shape variables, particle-flow isolations, kinematic of photon, median energy density (ρ)
• Double-photon trigger selection based on transverse energy, mɣɣ, isolation and electromagnetic shower shapes variables
• Minimal pre-selection, similar to but tighter than trigger selection
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ttH leptonic tagttH tags
• (sub)lead pT/mɣɣ > 1/2(1/4) • at least one lepton (ℓ=e,μ), away
from Z peak • ≥ 2 jets • ≥ 1 b-jet
• (sub)lead pT/mɣɣ > 1/2(1/4) • 0 leptons • ≥ 5 jets • ≥ 1 b-jet
ttH tags
VBF tags
Untagged
ɣɣTagged events
V.R.Tavolaro 704.08.2016
Feynman Diagrams
Andrea Carlo Marini
November 25, 2015
1 Higgs
ggŸH
g
g
p
p
H
qq̄ŸH
q̄
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ttH leptonic tagttH tags
• (sub)lead pT/mɣɣ > 1/2(1/4) • at least one lepton (ℓ=e,μ), away
from Z peak • ≥ 2 jets • ≥ 1 b-jet
• (sub)lead pT/mɣɣ > 1/2(1/4) • 0 leptons • ≥ 5 jets • ≥ 1 b-jet
VBF tags
ttH tags
VBF tags
Untagged
ɣɣTagged events
V.R.Tavolaro 804.08.2016
• Identify events with 2 jets through a MVA • inputs: pT/mɣɣ of both photons, pT of both jets, mjj, Δηjj,
Zeppenfeld variable, Δφɣɣjj
• 2 jets with pT1 > 30GeV, pT2 >20 GeV, |η| < 4.7, mjj >250 GeV
• VBF Classification BDT combines di-jet and diphoton BDT: 2 data categories (VBF tag 0-1)
Feynman Diagrams
Andrea Carlo Marini
November 25, 2015
1 Higgs
ggŸH
g
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p
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q̄
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g
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1
Feynman Diagrams
Andrea Carlo Marini
November 25, 2015
1 Higgs
ggŸH
g
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qq̄ŸH
q̄
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HZ/W
qq̄ŸVH
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“Untagged” events
V.R.Tavolaro 904.08.2016
• Multivariate discriminator is used to separate diphoton pairs with signal-like kinematics, high photon ID scores and good mass resolution from background
• Input variables: pT of the two photons rescaled by pair mass, η, cos(Δφ), photon ID scores, relative mass resolutions under correct/incorrect vertex selection hypotheses, vertex probability estimate
• 4 event categories (“Untagged” events)
• Categorise events into classes (S/B, resolution) to improve the analysis sensitivity ttH tags
VBF tags
Untagged
ɣɣ
Unta
gged
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Unta
gged
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Signal and background models
V.R.Tavolaro 1004.08.2016
• Fully parametric signal model from simulation
• physical nuisances allowed to float
• corrections and data/MC efficiency scale factors applied
• Background model data driven:
• background functional form treated as discrete nuisance parameter
• for each category, use different functional forms(sums of exponentials, sums of power law terms, Laurent series and polynomials)
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TTH Hadronic Tag =0.95µ=126.0 GeV, Hm --
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V.R.Tavolaro 1104.08.2016
ttH leptonic
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Preliminary CMS TeV) (13-1 12.9 fbγγ→H
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(GeV)γγm100 110 120 130 140 150 160 170 180150−
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Mass spectra, untagged events
V.R.Tavolaro 1204.08.2016
Untagged 0Untagged 1
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Mass spectra, all categories
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(GeV)Hm116 118 120 122 124 126 128 130 132 134
Loca
l p-v
alue
10−10
9−10
8−10
7−10
6−10
5−10
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1σ1 σ2
σ3
σ4
σ5
σ6
Observed
Expected
= 125.09 GeVHmExpected
Preliminary CMSγγ→H
(13TeV)-112.9 fb
Results
V.R.Tavolaro 1404.08.2016
• Significance at 125.09 GeV: 5.6σ observed (6.2σ expected)
• Maximum observed significance is 6.1σ at 126.0 GeV
• Best-fit signal strength
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µ2− 0 2 4 6 8
-1.2+1.5 1.91
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-0.8+0.9 1.61
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-0.23+0.25 0.77
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0.18−0.21+ = 0.95
combinedµ
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SMµ=µ
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γγ→H
TeV) (13-1 12.9 fb
= 1VHµ
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3
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4Best Fit
SM
σ1
σ2
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TeV) (13-112.9 fb
ProfiledHm
• Signal strength measured is measured in bosonic and fermionic components
Results
V.R.Tavolaro 1504.08.2016
• Production mechanism signal strengths measurements compatible with SM
• More details on mass: see Ulascan Sarica’s talk“Combined results of the 125 GeV Higgs boson on the mass, tensor structure, and couplings measured by the CMS detector”, today@1:10pm
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decorr|γγ/mmσ
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
Even
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310×
Data
(MC)-e+ e→Z
MC syst. uncert.
Preliminary CMS (13TeV)-112.9 fb
) < 1.442η, 1ηmax(
(TeV)s7 8 9 10 11 12 13 14
(fb)
fid.
σ
20
30
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60
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100Preliminary CMS
(13 TeV)-1 (8 TeV) + 12.9 fb-119.7 fb
γγ→H)Hbest-fit mData (
syst. uncertainty)=125.09 GeVHmSM (
- norm. LHC Higgs XSWG YR4MC@NLOA- acc.
Fiducial cross section
V.R.Tavolaro 1604.08.2016
• Fiducial cross section measured profiling mH:
• Theoretical prediction for mH=125.09 GeV
• Different event categorisation: 3 mass resolution categories
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Summary
V.R.Tavolaro 1704.08.2016
• CMS H→ɣɣ results using 12.9/fb of 13 TeV collision data collected in 2016 have been presented
• Observation (6.1σ peak significance) of the Higgs boson in the di-photon channel
• Best fit signal strength is
• Bosonic and fermionic components of signal strength are observed
• Fiducial cross-section is measured to be
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V.R.Tavolaro 1804.08.2016
BACKUP
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Event yields per category
V.R.Tavolaro 1904.08.2016
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Event yields per category
V.R.Tavolaro 2004.08.2016
Vκ0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
fκ
1−
0.5−
0
0.5
1
1.5
2
2.5
3 ) fκ, Vκq(
0
2
4
6
8
10
Best Fitσ1σ2
SM
Preliminary CMS TeV) (13-112.9 fb
γγ→H ProfiledHm
γκ0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
gκ
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2 ) gκ, γκq(
0
2
4
6
8
10
Best Fitσ1σ2
SM
Preliminary CMS TeV) (13-112.9 fb
γγ→H ProfiledHm
• Measurement of coupling modifiers to vector bosons and fermions (kV, kf) and to photons and gluons (kɣ,kg)
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Analysis flowchart
V.R.Tavolaro 2104.08.2016
Energy regression
Vtx ID BDT
Vtx prob BDT
Pho ID BDT
DiPho BDT
DiJet BDT
VBF BDT
Untagged cats.
VBF cats.
Scale and res. corr.
E σE/E
ttH cats.
ttH req.
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• Vertex ID BDT:
• if conversions are present
• Vertex probability BDT
Vertex BDTs inputs
V.R.Tavolaro 2204.08.2016
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Preselection details
V.R.Tavolaro 2304.08.2016
• pT>30 (20) GeV, pT/mɣɣ > 1/3 (1/4) for (sub)leading-pT photon
• |η|<2.5, removing 1.44<|η|<1.57, electron veto
• either R9>0.8, or charged hadron isolation < 20 GeV, or charged hadron isolation relative to pT <0.3
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BDTɣ ID inputs
V.R.Tavolaro 2404.08.2016
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BDTɣ ID
V.R.Tavolaro 2504.08.2016
• BDTɣ ID of the lowest-scoring photon for data and simulation, after preselection
BDT score of the photon ID1− 0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8 1
Even
ts
210
310
410
510
610
710
810DataSimulation:
4 = 125 GeV)x10H
(mγγ→Htotal background+stat.uncert.γ-γ
-jetγjet-jet
DataSimulation:
4 = 125 GeV)x10H
(mγγ→Htotal background+stat.uncert.γ-γ
-jetγjet-jet
DataSimulation:
4 = 125 GeV)x10H
(mγγ→Htotal background+stat.uncert.γ-γ
-jetγjet-jet
DataSimulation:
4 = 125 GeV)x10H
(mγγ→Htotal background+stat.uncert.γ-γ
-jetγjet-jet
DataSimulation:
4 = 125 GeV)x10H
(mγγ→Htotal background+stat.uncert.γ-γ
-jetγjet-jet
DataSimulation:
4 = 125 GeV)x10H
(mγγ→Htotal background+stat.uncert.γ-γ
-jetγjet-jet
(13 TeV)-112.9 fbCMS Preliminary
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BDTɣɣ inputs
V.R.Tavolaro 2604.08.2016
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BDTɣɣ systematic uncertainties
V.R.Tavolaro 2704.08.2016
γ γTransformed BDT0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Even
ts/0
.04
0
20
40
60
80
100
120
310×
Data
(MC)-e+ e→Z
MC syst. uncert.
Preliminary CMS (13TeV)-112.9 fb
• Impact on BDTɣɣ of systematic uncertainties associated to:
• relative energy resolution (±5% relative shift)
• photon ID BDT (± 0.03 shift plus linearly increasing term)
• Z→ee events with electrons reconstructed as photons
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ttH leptonic tag details
V.R.Tavolaro 2804.08.2016
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ttH hadronic tag details
V.R.Tavolaro 2904.08.2016
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Systematic uncertainties
V.R.Tavolaro 3004.08.2016
• Theory uncertainties (PDFs, αS, QCD scale, underlying event and parton shower, H→ɣɣ branching fraction)
• ggH contamination in VBF and ttH tagged categories
• Trigger efficiency, integrated luminosity, vertex efficiency, preselection
• Non-unformity of light collection, non-linearity, detector simulation, modeling of the material budget, shower shape corrections
• Photon energy scale and resolution
• BDTɣ ID and per-photon energy resolution
• Jet energy scale and smearings
• b-tagging efficiency, gluon-splitting fraction, parton shower, ID efficiency for e and μ
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µ2− 0 2 4 6 8-1.4+2.0TTH Leptonic Tag 1.15
-1.2+1.6TTH Hadronic Tag 2.10
-0.8+1.2VBF Tag 1 0.04
-0.6+0.8VBF Tag 0 1.58
-0.6+0.9Untagged 3 1.33
-0.31+0.32Untagged 2 0.44
-0.29+0.33Untagged 1 1.04
-0.5+0.6Untagged 0 0.95
0.18−0.21+ = 0.95
combinedµ
ProfiledHm
σ 1±Combined
σ 1±Per category
SMµ=µ
Preliminary CMS
γγ→H
TeV) (13-1 12.9 fb
Per category signal strength
V.R.Tavolaro 3104.08.2016
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Fiducial cross section: mass spectra
V.R.Tavolaro 3204.08.2016
Even
ts /
GeV
0
100
200
300
400
500
600
700
800
DataS+B fitB component
σ1 ±σ2 ±
category 0 decorr
/M |Mσ=126.0 GeVHm --
Preliminary CMS TeV) (13-1 12.9 fbγγ→H
(GeV)γγm100 110 120 130 140 150 160 170 180
60−
40−
20−
0204060 B component subtracted
Even
ts /
GeV
0
200
400
600
800
1000
1200
1400
1600
DataS+B fitB component
σ1 ±σ2 ±
category 1 decorr
/M |Mσ=126.0 GeVHm --
Preliminary CMS TeV) (13-1 12.9 fbγγ→H
(GeV)γγm100 110 120 130 140 150 160 170 180
80−60−40−20−0
20406080 B component subtracted
Even
ts /
GeV
0
500
1000
1500
2000
2500
3000
3500
4000
4500
DataS+B fitB component
σ1 ±σ2 ±
category 2 decorr
/M |Mσ=126.0 GeVHm --
Preliminary CMS TeV) (13-1 12.9 fbγγ→H
(GeV)γγm100 110 120 130 140 150 160 170 180
150−100−
50−0
50100150200 B component subtracted