Measurement of properties of the Higgs boson in …...Bruno Lenzi (CERN) Higgs properties from boson in bosonic decay channels in ATLAS - LHCP 02/06/2014 Results from bosonic decays

Measurement of properties of the Higgs boson in bosonic decay channels using the ATLAS detectorBruno Lenzi on behalf of the ATLAS collaboration!!02/06/2014!!LHCP 2014

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Bruno Lenzi (CERN) Higgs properties from boson in bosonic decay channels in ATLAS - LHCP 02/06/2014

Results from bosonic decays of the Higgs in ATLAS

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Limits on H → Zγ PLB 732C (2014), pp. 8-27

Measurement of properties: PLB 726 (2013) • Production and couplings • Spin/CP

NEW mass measurement in H → γγ and H → ZZ* → 4ℓ (paper to be submitted)

Discovery (July 2012) via bosonic decay channels: H → γγ, H → ZZ* → 4ℓ, H → WW* → ℓνℓν

http://www.sciencedirect.com/science/article/pii/S0370269314001713


H → γγ

• Loop decay (W and top), low BR ~ 0.2%

• Simple topology

• Two isolated energetic photons

• ...requiring excellent performance

• Large backgrounds

• Excellent γ ID:75% γγ after cuts

• Signal: narrow peak (good mass resolution)

• S/B ~ 3%

3

z

γ π0

σ X BR ~ 50 fb @ 125.5 GeV


Improved calibration of electrons and photons

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1. Calorimeter non-uniformities and layer inter-calibration corrected using e/γ/μ

• Response stable at ~0.05% vs. time and pileup

• 1-2% precision on E1/2, 5% on EPS

• Constrain inactive material (2-5 X0) to ~2-10% X0

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Improved calibration of electrons and photons

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NEW2. EM cluster energy correction via MVA regression

• 10% better resolution for H → γγ

3. E-scale and resolution extracted with Z → ee

• Good data/MC agreement after corrections

• Linearity and extrapolation to photons checked with Z → ee vs. ET(e-), J/ψ and Z → ℓℓγ

• 0.03-0.05% for 40 GeV ET electrons

• ~0.2-0.5% for photons

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PreliminaryATLAS

H → γγ: mass measurement

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• Selection: isolated photons, PT/mγγ > 0.35, 0.25

• Di-photon vertex from calo segmentation + track information → no impact on mγγ resolution

• Events split according to γ conversions, ηγ and Ptt:

• Mass resolution (1.2-2.4 GeV, 1.65 GeV inclusive)

• E-scale systematics (0.17-0.59%)

• Background modelled by analytical functions

!

!

• Signal strength @ best-fit mass: μ = 1.29 ± 0.30

• Coupling analysis optimised to measure different production modes (to appear soon)

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mH = 125.98 ± 0.42 (stat) ± 0.28 (sys) GeV

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• Previous result: 126.8 ± 0.2 (stat) ± 0.7 (syst) GeV

• Observed / expected change: 0.8 GeV / -0.45 ± 0.35 GeV

• Systematic uncertainties reduced by factor 2.5

• Dominated by photon energy scale

• Stat. error compatible with expectation

• 0.35 (0.45) GeV for μ = 1.3 (1.0), p-value: 16%

• Several cross-checks

• Different event splittings e.g.

• No deviation above 1.5σ

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NEW

γ conversions

Primary vertices

Barrel vs. endcap{

mH = 125.98 ± 0.42 (stat) ± 0.28 (sys) GeV = 125.98 ± 0.50 (GeV)

Bruno Lenzi (CERN) Higgs properties from boson in bosonic decay channels in ATLAS - LHCP 02/06/2014 8

H → ZZ* → 4ℓ

• “Golden channel” but very small rates

• σ X BR ~ 2.9 fb @ 125.5 GeV

• Challenge: e- and μ downto low PT (7, 6 GeV)

• Better e- ID: ~2x less fakes for same eff.

• Narrow peak (1.6-2 GeV) on top of smooth background

• E-p combination for PT(e-) < 30 GeV

• mleading ℓℓ (+ FSR photons)constrained to mZ

• Full event kinematics

• Spin/CP determination using 5 angles and 2 masses → 0+ vs. 0-, 1±, 2+


H → ZZ* → 4ℓ: mass measurement

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NEW• Muon calibration with Z and J/ψ → μμ

• Checked with ϒ → μμ

• Negligible impact on mH uncertainty

!

• 37 events observed (~10.4 bkg + 16.2 signal exp.) within 120 - 130 GeV

• Reducible backgrounds (Z+jets and tt) normalized from control regions

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Figure 6: (a) Distribution of the four-lepton invariant mass for the selected candidates in the m4` range 80–170 GeV for the combinedp

s =7TeV and

ps =8 TeV data samples. Superimposed are the expected distributions of a SM Higgs boson signal for mH=124.5 GeV normalized to

the measured signal strength, as well as the expected ZZ⇤ and reducible backgrounds. (b) Distribution of the BDT response versus the m4` for theselected candidates in the 110–140 GeV m4` range for the combined

ps =7 TeV and

ps =8 TeV data samples. The expected distribution for a SM

Higgs with mH = 124.5 GeV is indicated by the size of the blue boxes, and the total background is indicated by the intensity of the red shading.

Table 3: The number of expected signal events for the mH=125 GeV hypothesis, the number of ZZ⇤ and reducible background events, togetherwith the numbers of observed events, in a window of 120 < m4` < 130 GeV for 4.5 fb�1 at

ps = 7 TeV and 20.3 fb�1 at

ps = 8 TeV as well as

for the combined sample. For reference, the number of expected signal events is also given for the full mass range.

total signal signal ZZ(⇤) Z + jets, tt̄ s/b expected observedfull mass range p

s = 7 TeV4µ 1.00 ± 0.10 0.91 ± 0.09 0.46 ± 0.02 0.10 ± 0.04 1.7 1.47 ± 0.10 2

2e2µ 0.67 ± 0.06 0.58 ± 0.06 0.32 ± 0.02 0.09 ± 0.03 1.5 0.99 ± 0.07 22µ2e 0.51 ± 0.05 0.44 ± 0.04 0.21 ± 0.01 0.36 ± 0.08 0.8 1.01 ± 0.09 1

4e 0.47 ± 0.05 0.39 ± 0.04 0.19 ± 0.01 0.40 ± 0.09 0.7 0.98 ± 0.10 1total 2.65 ± 0.31 2.32 ± 0.23 1.17 ± 0.06 0.96 ± 0.18 1.1 4.45 ± 0.30 6p

s = 8 TeV4µ 5.80 ± 0.57 5.28 ± 0.52 2.36 ± 0.12 0.68 ± 0.11 1.7 8.33 ± 0.6 12

2e2µ 3.92 ± 0.39 3.46 ± 0.34 1.67 ± 0.08 0.59 ± 0.10 1.5 5.73 ± 0.37 72µ2e 3.07 ± 0.32 2.71 ± 0.28 1.17 ± 0.08 0.36 ± 0.09 1.8 4.23 ± 0.30 5

4e 2.79 ± 0.29 2.38 ± 0.25 1.03 ± 0.07 0.35 ± 0.08 1.7 3.77 ± 0.27 7total 15.6 ± 1.5 13.8 ± 1.4 6.24 ± 0.35 1.98 ± 0.26 1.7 22.0 ± 1.5 31p

s = 7 TeV andp

s = 8 TeV4µ 6.80 ± 0.67 6.19 ± 0.61 2.82 ± 0.14 0.78 ± 0.12 1.7 9.80 ± 0.64 14

2e2µ 4.59 ± 0.45 4.05 ± 0.40 1.99 ± 0.10 0.68 ± 0.10 1.5 6.72 ± 0.43 92µ2e 3.58 ± 0.37 3.15 ± 0.32 1.38 ± 0.09 0.72 ± 0.12 1.5 5.24 ± 0.35 6

4e 3.26 ± 0.34 2.77 ± 0.29 1.22 ± 0.09 0.75 ± 0.11 1.4 4.75 ± 0.32 8total 18.2 ± 1.7 16.2 ± 1.6 7.41 ± 0.41 2.94 ± 0.32 1.6 26.5 ± 1.7 37

The measured Higgs boson mass in the H ! ZZ⇤ ! 4` decay channel obtained with the baseline 2D method is:655

mH = 124.51 ± 0.52 (stat) ± 0.04 (sys) GeV = 124.51 ± 0.52 GeV (4)

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s = 7 TeV4µ 1.00 ± 0.10 0.91 ± 0.09 0.46 ± 0.02 0.10 ± 0.04 1.7 1.47 ± 0.10 2

2e2µ 0.67 ± 0.06 0.58 ± 0.06 0.32 ± 0.02 0.09 ± 0.03 1.5 0.99 ± 0.07 22µ2e 0.51 ± 0.05 0.44 ± 0.04 0.21 ± 0.01 0.36 ± 0.08 0.8 1.01 ± 0.09 1

4e 0.47 ± 0.05 0.39 ± 0.04 0.19 ± 0.01 0.40 ± 0.09 0.7 0.98 ± 0.10 1total 2.65 ± 0.31 2.32 ± 0.23 1.17 ± 0.06 0.96 ± 0.18 1.1 4.45 ± 0.30 6p

s = 8 TeV4µ 5.80 ± 0.57 5.28 ± 0.52 2.36 ± 0.12 0.68 ± 0.11 1.7 8.33 ± 0.6 12

2e2µ 3.92 ± 0.39 3.46 ± 0.34 1.67 ± 0.08 0.59 ± 0.10 1.5 5.73 ± 0.37 72µ2e 3.07 ± 0.32 2.71 ± 0.28 1.17 ± 0.08 0.36 ± 0.09 1.8 4.23 ± 0.30 5

4e 2.79 ± 0.29 2.38 ± 0.25 1.03 ± 0.07 0.35 ± 0.08 1.7 3.77 ± 0.27 7total 15.6 ± 1.5 13.8 ± 1.4 6.24 ± 0.35 1.98 ± 0.26 1.7 22.0 ± 1.5 31p

s = 7 TeV andp

s = 8 TeV4µ 6.80 ± 0.67 6.19 ± 0.61 2.82 ± 0.14 0.78 ± 0.12 1.7 9.80 ± 0.64 14

2e2µ 4.59 ± 0.45 4.05 ± 0.40 1.99 ± 0.10 0.68 ± 0.10 1.5 6.72 ± 0.43 92µ2e 3.58 ± 0.37 3.15 ± 0.32 1.38 ± 0.09 0.72 ± 0.12 1.5 5.24 ± 0.35 6

4e 3.26 ± 0.34 2.77 ± 0.29 1.22 ± 0.09 0.75 ± 0.11 1.4 4.75 ± 0.32 8total 18.2 ± 1.7 16.2 ± 1.6 7.41 ± 0.41 2.94 ± 0.32 1.6 26.5 ± 1.7 37



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s = 7 TeV4µ 1.00 ± 0.10 0.91 ± 0.09 0.46 ± 0.02 0.10 ± 0.04 1.7 1.47 ± 0.10 2

2e2µ 0.67 ± 0.06 0.58 ± 0.06 0.32 ± 0.02 0.09 ± 0.03 1.5 0.99 ± 0.07 22µ2e 0.51 ± 0.05 0.44 ± 0.04 0.21 ± 0.01 0.36 ± 0.08 0.8 1.01 ± 0.09 1

4e 0.47 ± 0.05 0.39 ± 0.04 0.19 ± 0.01 0.40 ± 0.09 0.7 0.98 ± 0.10 1total 2.65 ± 0.31 2.32 ± 0.23 1.17 ± 0.06 0.96 ± 0.18 1.1 4.45 ± 0.30 6p

s = 8 TeV4µ 5.80 ± 0.57 5.28 ± 0.52 2.36 ± 0.12 0.68 ± 0.11 1.7 8.33 ± 0.6 12

2e2µ 3.92 ± 0.39 3.46 ± 0.34 1.67 ± 0.08 0.59 ± 0.10 1.5 5.73 ± 0.37 72µ2e 3.07 ± 0.32 2.71 ± 0.28 1.17 ± 0.08 0.36 ± 0.09 1.8 4.23 ± 0.30 5

4e 2.79 ± 0.29 2.38 ± 0.25 1.03 ± 0.07 0.35 ± 0.08 1.7 3.77 ± 0.27 7total 15.6 ± 1.5 13.8 ± 1.4 6.24 ± 0.35 1.98 ± 0.26 1.7 22.0 ± 1.5 31p

s = 7 TeV andp

s = 8 TeV4µ 6.80 ± 0.67 6.19 ± 0.61 2.82 ± 0.14 0.78 ± 0.12 1.7 9.80 ± 0.64 14

2e2µ 4.59 ± 0.45 4.05 ± 0.40 1.99 ± 0.10 0.68 ± 0.10 1.5 6.72 ± 0.43 92µ2e 3.58 ± 0.37 3.15 ± 0.32 1.38 ± 0.09 0.72 ± 0.12 1.5 5.24 ± 0.35 6

4e 3.26 ± 0.34 2.77 ± 0.29 1.22 ± 0.09 0.75 ± 0.11 1.4 4.75 ± 0.32 8total 18.2 ± 1.7 16.2 ± 1.6 7.41 ± 0.41 2.94 ± 0.32 1.6 26.5 ± 1.7 37



19

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|<2.5ηCB muons |

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µµ → ψJ/


H → ZZ* → 4ℓ: mass measurement

10

NEW• Signal strength @ best-fit mass:

• Mass measurement with 2D fit to m4l and BDT discriminant against ZZ*

• 8% improvement over simple m4l fit

mH = 124.51 ± 0.52 (stat) ± 0.04 (sys) → compatible between all final states (20%)

(previous result: )

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µ = 1.66+0.45�0.38

NEW

with separate statistical and systematic uncertainties. The measured signal strength for this inclusive selection is µ =656

1.66+0.45�0.38, consistent with the SM expectation of one. The most precise results for µ from this data are based on an anal-657

ysis optimized to measure the signal strength [18]. With the improved uncertainties of the electron and muon energy658

scales, the mass uncertainty given above is predominantly statistical with a nearly negligible contribution from system-659

atic uncertainties. The mass measurement performed with the 1D model is mH = 124.63±0.54 (stat) ±0.04 (sys) GeV.660

These measurements can be compared to the previously reported result [15] of 124.3+0.6�0.5 (stat) +0.5

�0.3 (sys) GeV, which661

was obtained using the 1D model. A significant improvement in the systematic uncertainty can be seen. The di↵er-662

ence in the measured value arises primarily from the changes to the channels with electrons - the new calibration and663

resolution model, the introduction of the E-p combination, and the improved identification, as well as the recovery of664

non-collinear FSR photons, which a↵ects all channels. In the 120-130 GeV mass window, there are four new events665

and one missing event as compared to Ref [15]. Monte Carlo pseudo-experiments have been used to estimate the666

expected compatibility between the 1D and 2D methods. The di↵erence has an expected RMS of 250 MeV, which667

is consistent with the 120 MeV di↵erence seen between the two results. Finally as a third cross-check, the measured668

mass obtained with the per-event-error method is within 60 MeV of the value found with the 2D method.669

Figure 7 shows the scan of the profile likelihood, �2 ln⇤(mH), for the 2D model as a function of the mass of670

the Higgs boson for the four final states, as well as for all of the channels combined. The signal strength and all671

the nuisance parameters are profiled (allowed to float to the values which maximize the likelihood) in the scan. The672

compatibility among the mass measurements from the four final states is estimated to be about 20% using a �2 test.673

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Figure 7: The profile likelihood as a function of mH for the combination of all H ! ZZ⇤ ! 4` channels and for the individual channels for thecombined

ps =7 TeV and

ps =8 TeV data samples.

Using the per-event-error method a direct limit on the total width of the Higgs boson of �H < 2.6 GeV at 95% CL674

is obtained. This has to be compared with an expected limit of �H < 6.2 GeV at 95% CL for a signal at the SM rate675

and �H < 3.5 GeV at 95% CL for the observed signal rate. The di↵erence between the observed and expected result676

arises from the higher signal strength observed in the data, as well as from the measured m4`, BDTZZ⇤ and resolution677

values of the selected candidate events. The limit on the total width has been cross-checked with a 2D fit using signal678

templates parametrized as a function of the particle width and found to be in agreement.679

6. Statistical procedure and systematic uncertainties treatment680

The statistical treatment of the data is described in Refs. [41–45]. Confidence intervals are based on the profile681

likelihood ratio ⇤(↵) [46]. The latter depends on one or more parameters of interest ↵, such as the Higgs boson mass682

20


H → WW* → ℓνℓν

11

• Signature: opposite-sign leptons (e,μ) and large missing transverse energy

• Moderate S/B, limited mass resolution

• Large backgrounds: WW, W+jets, top, Z/γ*, di-bosons (mostly data-driven)

σ X BR ~ 200 fb @ 125.5 GeV


H → WW* → ℓνℓν

12

• Signature: opposite-sign leptons (e,μ) and large missing transverse energy

• Moderate S/B, limited mass resolution

• Large backgrounds: WW, W+jets, top, Z/γ*, di-bosons (mostly data-driven)

• Observed significance: 3.8σ,

• Good handle on VBF production (forward jets)

No

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Draft version 00-06-01

ATLAS NOTEATLAS-CONF-2013-XYZ

February 26, 2013

Evidence for the Higgs boson candidate in the WW(∗)→ ℓνℓν decay1

channel using 21 fb−1 of√

s= 8 TeV and 4.6 fb−1 of√

s= 7 TeV data2

collected with the ATLAS detector at the LHC3

The ATLAS Collaboration4

Abstract5

Evidence for the Higgs boson candidate in the H→WW (∗)→ ℓνℓν channel is presented6

using the complete 2012 and 2011 data samples collected by the ATLAS detector at the7

LHC. The data correspond to an integrated luminosity of 21 fb−1 at a centre-of-mass8

energy of 8 TeV and 4.6 fb−1 at 7 TeV, respectively. The analysis focuses on such a boson9

in the Standard Model with a mass of mH = 125 GeV, where an excess over the expected10

number of background events is observed at that mass. This excess corresponds to 3.811

standard deviations while the expected significance is 3.7. The ratio of the observed12

and expected number of events is consistent with unity, µ= 1.0± 0.3. The case where13

the signal is accompanied by two or more jets is optimised for the vector boson fusion14

production, and this process is observed with a significance of 2.4 standard deviations,15

while the expected value is 1.6.16

c⃝ Copyright 2013 CERN for the benefit of the ATLAS Collaboration.Reproduction of this article or parts of it is allowed as specified in the CC-BY-3.0 license.

H!WW Results from ATLAS - John Alison - Aspen 2013 “Higgs Quo Vadis”

March 9, 2013 – 22 : 12 DRAFT 40

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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

Eve

nts

/ 0

.15 r

ad

0

50

100

150

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WW γ WZ/ZZ/W

t t Single Top

Z+jets W+jets

H [125 GeV]



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[GeV]llm

10 20 30 40 50 60 70 80 90

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nts

/ 1

0 G

eV

0

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300

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500


WW γ WZ/ZZ/W

t t Single Top

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H [125 GeV]



WW→H

[GeV]Tm

50 100 150 200 250 300

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nts

/ 1

0 G

eV

0

50

100

150

200

250


WW γ WZ/ZZ/W

t t Single Top

Z+jets W+jets

H [125 GeV]



WW→H

Figure 21: Kinematic distributions in the Njet = 0 channel after the full selection: pℓℓT

(top left), |∆φℓℓ |(top right), mℓℓ (bottom left), and mT (bottom right). The eµ and µe channels are combined. The signal

is added on top of the background. The WW and top backgrounds are scaled to use the normalisation

derived from the corresponding control regions described in the text. The shaded area represents the

uncertainty on the signal and background yields from statistical, experimental, and theoretical sources.

[GeV]T,lead lep

p

20 40 60 80 100 120 140

Eve

nts

/ 5

GeV

0

100

200

300

400


WW γ WZ/ZZ/W

t t Single Top

Z+jets W+jets

H [125 GeV]



WW→H

[GeV]T,sublead lep

p

10 20 30 40 50 60 70 80 90 100E

vents

/ 5

GeV

0

100

200

300

400

500

600


WW γ WZ/ZZ/W

t t Single Top

Z+jets W+jets

H [125 GeV]



WW→H

Figure 22: Kinematic distributions in the Njet = 0 channel after the full selection: leading lepton pT

(left) and sub-leading lepton pT (right). The eµ and µe channels are combined. The signal is added on

top of the background. The WW and top backgrounds are scaled to use the normalisation derived from

the corresponding control regions described in the text. The shaded area represents the uncertainty on

the signal and background yields from statistical, experimental, and theoretical sources.

SM "=1.0

March 9, 2013 – 22 : 12 DRAFT 40

[GeV]llTP

0 20 40 60 80 100 120 140 160

Eve

nts

/ 5

GeV

0

50

100

150

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250

300


WW γ WZ/ZZ/W

t t Single Top

Z+jets W+jets

H [125 GeV]



WW→H

[rad]ll

φ∆

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

Eve

nts

/ 0

.15 r

ad

0

50

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150

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WW γ WZ/ZZ/W

t t Single Top

Z+jets W+jets

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WW→H

[GeV]llm

10 20 30 40 50 60 70 80 90

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nts

/ 1

0 G

eV

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300

400

500


WW γ WZ/ZZ/W

t t Single Top

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WW→H

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Eve

nts

/ 1

0 G

eV

0

50

100

150

200

250


WW γ WZ/ZZ/W

t t Single Top

Z+jets W+jets

H [125 GeV]



WW→H

Figure 21: Kinematic distributions in the Njet = 0 channel after the full selection: pℓℓT

(top left), |∆φℓℓ |(top right), mℓℓ (bottom left), and mT (bottom right). The eµ and µe channels are combined. The signal

is added on top of the background. The WW and top backgrounds are scaled to use the normalisation

derived from the corresponding control regions described in the text. The shaded area represents the

uncertainty on the signal and background yields from statistical, experimental, and theoretical sources.

[GeV]T,lead lep

p

20 40 60 80 100 120 140

Eve

nts

/ 5

GeV

0

100

200

300

400


WW γ WZ/ZZ/W

t t Single Top

Z+jets W+jets

H [125 GeV]



WW→H

[GeV]T,sublead lep

p

10 20 30 40 50 60 70 80 90 100

Eve

nts

/ 5

GeV

0

100

200

300

400

500

600


WW γ WZ/ZZ/W

t t Single Top

Z+jets W+jets

H [125 GeV]



WW→H

Figure 22: Kinematic distributions in the Njet = 0 channel after the full selection: leading lepton pT

(left) and sub-leading lepton pT (right). The eµ and µe channels are combined. The signal is added on

top of the background. The WW and top backgrounds are scaled to use the normalisation derived from

the corresponding control regions described in the text. The shaded area represents the uncertainty on

the signal and background yields from statistical, experimental, and theoretical sources.

SR1 SR2

SM "=1.0

Signal ExtractionFinal Fit to Transverse Mass

Split Improves Sensitivity - Different Signal/Bkg ratios - Different mix of backgrounds

12

Critical to understand WW / W+jet / W# backgrounds

m2T =

✓qm2

ll + |�pTll |2 + Emiss

T

◆2

�⇣�pTll + �Emiss

T

⌘2

Exploit Mass Information

Split 0-jet e" signal region

SR Region Split New for this Analysis

Even

ts /

10 G

eV

100

200

300

400

500

600

700

800 Data 2011+2012 Total sig.+bkg. SM Higgs boson

= 125 GeVH m

WW

t t Other VV Single Top W+jets

*a Z/

ATLAS-1 Ldt = 4.6 fb0 = 7 TeV s

-1 Ldt = 20.7 fb0 = 8 TeV s

+ 0/1 jetsililAWW*AH

[GeV]Tm60 80 100 120 140 160 180 200 220 240 260

Data

- Bk

g.

-200

20406080

100 Bkg. subtracted data = 125 GeV

H SM Higgs boson m

[GeV]Tm50 100 150 200 250 300

Even

ts /

20 G

eV

0

2

4

6

8

10

12 Data 2011+2012 Total sig.+bkg.

= 125 GeVH VBF m = 125 GeV

H ggF m

t t WW

*a Z/

Other VV Single Top

W+jets

ATLAS-1 Ldt = 4.6 fb0 = 7 TeV s

-1 Ldt = 20.7 fb0 = 8 TeV s 2 j* + iµieAWW*AH

2 or more jets0 or 1 jet

No

trev

iew

ed

,fo

rin

tern

al

circu

la

tio

no

nly

Global Signal Strength

Common signal strength scale factors (μ) account for all productions and decay modes •  Evaluated at mH =125.5 GeV •  Using H��, H�ZZ�4l and H�WW�lvlv

and H-> (4.1� signal significance) H->bb (no significant excess over background) •  Combination of H�bb and H�

•  3.7 � evidence for direct coupling to fermions.

•  Combining all the channels:

•  Theory uncertainty (QCD scale and PDF+�s) comparable to experimental and statistical uncertainties.

02/06/14 L. Aperio Bella (PLHC 2014) 7

Compatibility of ~7% with SM (=1)

) µSignal strength (-0.5 0 0.5 1 1.5 2

ATLAS Prelim.

-1Ldt = 4.6-4.8 fb∫ = 7 TeV s

-1Ldt = 20.3 fb∫ = 8 TeV s

= 125.5 GeVHm

0.28-0.33+ = 1.57µ

γγ →H

0.12- 0.17+ 0.18- 0.24+ 0.22- 0.23+

0.35-0.40+ = 1.44µ

4l→ ZZ* →H

0.10- 0.17+ 0.13- 0.20+ 0.32- 0.35+

0.29-0.32+ = 1.00µ

νlν l→ WW* →H

0.08- 0.16+ 0.19- 0.24+ 0.21- 0.21+

0.20-0.21+ = 1.35µ

, ZZ*, WW*γγ→HCombined

0.11- 0.13+ 0.14- 0.16+ 0.14- 0.14+

0.6-0.7+ = 0.2µ

b b→W,Z H <0.1

0.4±

0.5±

0.4-0.5+ = 1.4µ

(8 TeV data only) ττ →H

0.1- 0.2+ 0.3- 0.4+ 0.3- 0.3+

0.32-0.36+ = 1.09µ

ττ, bb→HCombined

0.04- 0.08+ 0.21- 0.27+ 0.24- 0.24+

0.17-0.18+ = 1.30µ

Combined 0.08- 0.10+ 0.11- 0.14+ 0.12- 0.12+

Total uncertaintyµ on σ 1±

(stat.)σ

)theorysys inc.(σ

(theory)σ

Figure 1: The measured signal strengths for a Higgs boson of mass mH =125.5 GeV, normalised to theSM expectations, for the individual final states and various combinations. The best-fit values are shownby the solid vertical lines. The total ±1� uncertainties are indicated by green shaded bands, with theindividual contributions from the statistical uncertainty (top), the total (experimental and theoretical)systematic uncertainty (middle), and the theory uncertainty (bottom) on the signal strength (from QCDscale, PDF, and branching ratios) shown as superimposed error bars. The measurements are based onRefs. [3, 5, 6], with the changes mentioned in the text.

Section 2. In the H ! ⌧⌧ channel, the ratio µVBF+VH/µggF+ttH has an infinite 1� upper bound, becausethe signal is almost only observed in the VBF mode, hence the ggF denominator can be arbitrarily small.

To test the sensitivity to VBF production alone, the data are also fitted with the ratio µVBF/µggF+ttH .In order not to influence the VBF measurement through the VH categories, the parameter µVH/µggF+ttHis treated independently and profiled. A value of

µVBF/µggF+ttH = 1.4+0.5�0.4 (stat) +0.4

�0.3 (sys)

is obtained from the combination of the four channels (Fig. 4). This result provides evidence at the 4.1�level that a fraction of Higgs boson production occurs through VBF.

6

parameters ✓,

⇤(↵) =L�↵ , ˆ̂✓(↵)

�

L(↵̂, ✓̂). (1)

The likelihood functions in the numerator and denominator of the above equation are built using sumsof signal and background probability density functions (pdfs) in the discriminating variables. Thesevariables are the ��, 4` and 2b-jet masses for H! ��, H!ZZ⇤! 4` and H ! bb̄, respectively, thetransverse mass mT (defined in Ref. [3]) for the H!WW⇤! `⌫`⌫ channel and a multivariate discriminantoutput distribution for H ! ⌧⌧. The pdfs are derived from MC simulation for the signal and from bothdata and simulation for the background. Likelihood fits to the observed data are done for the parametersof interest. The single circumflex in Eq. 1 denotes the unconditional maximum likelihood estimate ofa parameter and the double circumflex denotes the conditional maximum likelihood estimate for givenfixed values of the parameters of interest ↵.

Systematic uncertainties and their correlations [8] are modelled by introducing nuisance parameters ✓described by likelihood functions associated with the estimate of the corresponding e↵ect. The choice ofthe parameters of interest depends on the test under consideration, with the remaining parameters being“profiled”, i.e., similarly to nuisance parameters they are set to the values that maximise the likelihoodfunction for the given fixed values of the parameters of interest.

Asymptotically, a test statistic �2 ln⇤(↵) of several parameters of interest ↵ is distributed as a �2

distribution with n degrees of freedom, where n is the dimensionality of the vector ↵. In particular,the 100(1 � �)% confidence level (CL) contours are defined by �2 ln⇤(↵) < k�, where k� satisfiesP(�2

n > k�) = �. For two degrees of freedom the 68% and 95% CL contours are given by �2 ln⇤(↵) = 2.3and 6.0, respectively. All results presented in the following sections are based on likelihood evaluationsand therefore give only approximate CL intervals.1

For the measurements in the following sections the compatibility with the Standard Model, pSM, isquantified using the p-value obtained from the profile likelihood ratio ⇤(↵ = ↵S M), where ↵ is the set ofparameters of interest and ↵S M are their Standard Model values. For a given coupling benchmark model,↵ is the set of ki and li j parameters of that model, where the indices i, j refer to the parameters of interestof the model. All other parameters are treated as independent nuisance parameters.

4 Signal Strength in Production and Decay Modes

This section focuses on the measurement of the global signal strength parameter µ and the individualsignal strength parameters µ f

i which depend upon the Higgs boson production mode i and the decaychannel f , for a fixed mass hypothesis corresponding to the measured value mH = 125.5 GeV [3]. Theparameters µ and µ f

i are determined from a fit to the data using the profile likelihood ratio ⇤(µ) (seeEq. 1).

The results are shown in Fig. 1, where the signal strengths measured in the five individual channelsare presented2. The signal strength normalised to the SM expectation, obtained by combining the threediboson channels, was published in Ref. [3] as µ��,ZZ⇤,WW⇤ = 1.33 ± 0.14 (stat) ± 0.15 (sys). With thechanges described in Section 2, this value is updated to µ��,ZZ⇤,WW⇤ = 1.35 ± 0.14 (stat) +0.16

�0.14 (sys). Thecombination of the two fermion channels H ! bb̄ and H ! ⌧⌧ yields a signal strength

µbb,⌧⌧ = 1.09 ± 0.24 (stat) +0.27�0.21 (sys),

1Whenever probabilities are translated into the number of Gaussian standard deviations the two-sided convention is chosen.2The results for H! ��, H!ZZ⇤! 4` and H ! bb̄ are taken from the individual analyses, while the results for

H!WW⇤! `⌫`⌫ and H ! ⌧⌧ are taken from the combination of these two channels with independent signal strengths forthe two final states in order to take the signal cross contamination into account (see Section 2).

4

corresponding to 3.7� evidence for the direct decay of the Higgs boson into fermions.Finally, the signal strength, obtained by combining all five channels, is:

µ = 1.30 ± 0.12 (stat) +0.14�0.11 (sys).

A significant component of the systematic uncertainty is associated to the theoretical values of the crosssections and branching ratios. The uncertainty on the cross section amounts to ±7%, dominated byuncertainties on the QCD renormalisation and factorisation scales and the parton distribution function(PDF) for the gluon-gluon fusion process (ggF). The uncertainty on the mass measurement of ±0.6 GeVreported in Ref. [3] leads to a ±3% uncertainty on µ.

The compatibility between this measurement and the SM Higgs boson expectation (µ = 1) is about7%; the use of a flat likelihood for the ggF QCD scale systematic uncertainty in the quoted ±1� intervalyields a similar level of compatibility (8%) with the µ = 1 hypothesis. The overall compatibility betweenthe signal strengths measured in the five final states and the SM predictions is about 11%. Both the centralvalue of µ and the SM compatibility have changed little with respect to the diboson measurements ofRef. [3]. The contribution of the diboson channels still dominates the measurement, and the combinationof the H ! bb̄ and H ! ⌧⌧ modes has a compatible measured value of µ .

The measurements of the signal strengths described above do not give direct information on the rel-ative contributions of the di↵erent production mechanisms. Furthermore, fixing the ratios of the produc-tion cross sections for the various processes to the values predicted by the Standard Model may concealdi↵erences between data and theoretical predictions. Therefore, in addition to the signal strengths ofdi↵erent decay channels, the signal strengths of di↵erent production processes contributing to the samedecay channel3 are determined, exploiting the sensitivity o↵ered by the use of event categories in theanalyses of all the channels.

The data are fitted separating the VBF and VH processes, which involve the Higgs boson couplingto vector bosons, from the ggF and ttH processes, which involve the Higgs boson coupling to fermions(mainly the top-quark).4 Two signal strength parameters, µ f

ggF+ttH = µfggF = µ

fttH and µ f

VBF+VH = µfVBF =

µ fVH , which scale the SM-predicted rates to those observed, are introduced for the channels H! ��,

H!ZZ⇤! 4`, H!WW⇤! `⌫`⌫ and H ! ⌧⌧ indexed by the parameter f . The H ! bb̄ final state isnot included, as the current analysis is only sensitive to the VH production mode, and not to the VBF orggF production modes. The results are shown in Fig. 2. The 95% CL contours of the measurements areconsistent with the SM expectation.

A combination of all four channels provides a higher-sensitivity test of the theory. This can be done ina model-independent way (i.e. without assumptions on the Higgs boson branching ratios) by measuringthe ratios µVBF+VH/µggF+ttH for the individual final states and their combination. The result of the fit tothe data with the likelihood ⇤(µVBF+VH/µggF+ttH) is

µVBF+VH/µggF+ttH = 1.4+0.5�0.4 (stat) +0.4

�0.2 (sys).

The results for individual channels and their combination are shown in Fig. 3. Good agreement withthe SM expectation is observed. The main components of the systematic uncertainty 5 come from thetheoretical predictions for the ggF contributions to the various categories and jet multiplicities.

The changes in the results of the H!WW⇤! `⌫`⌫ and H ! ⌧⌧ channels, respectively from Ref. [3]and Ref. [6], are mainly due to the separation of their VBF signal regions by the cut on m⌧⌧ described in

3Such an approach avoids model assumptions needed for a consistent parameterisation of production and decay channelsin terms of Higgs boson couplings.

4Such a separation is possible under the assumption that the kinematic properties of these production modes agree with theSM predictions within uncertainties.

5A component of the statistical uncertainty in the results for µVBF+VH/µggF+ttH in Ref. [3] was incorrectly counted as sys-tematic error there. It is corrected here.

5

µ =� ⇥BR

(� ⇥BR)SM

ATLAS-CONF-2014-009

σ X BR ~ 200 fb @ 125.5 GeV


Properties: couplings, spin, differential distributions

13

Signal strength0 1 2 3 4 5 6

ATLAS2011-2012

= 126.8 GeVHm

-1Ldt = 4.8 fb0 = 7 TeV s

-1Ldt = 20.7 fb0 = 8 TeV s

Total

Stat.

Syst.

µ

ggH+ttHµ

VBFµ

VHµ

signal composition (%)0 10 20 30 40 50 60 70 80 90 100

One-lepton significancemiss

TE

Low-mass two-jet

Tight high-mass two-jet

Loose high-mass two-jet

Conv. transitionTt

Conv. rest high pTt

Conv. rest low pTt

Conv. central high pTt

Conv. central low pTt

Unconv. rest high pTt

Unconv. rest low pTt

Unconv. central high pTt

Unconv. central low pInclusive

ggF VBF WH ZH ttHATLAS Simulation aaAH

Differential distributions unfolded to particle level

Not updated!

}}

Spin/CP •Spin 1 and 2 excluded(combining the channels)•Parity+ favored @ >97% CL

q-15 -10 -5 0 5 10 15

Nor

mal

ised

to u

nity

0

0.05

0.1

0.15

0.2

0.25 Data+ = 0PJ- = 0PJ

ATLAS 4l→ ZZ* →H

-1Ldt = 4.6 fb∫ = 7 TeV s-1Ldt = 20.7 fb∫ = 8 TeV s

No significant deviation from

SM Higgs


H → Zγ → ℓℓγ

• Selection:

• Opposite charged leptons (mℓℓ > mZ - 10 GeV)

• Isolated photon (ET > 15 GeV), ΔR(ℓγ) > 0.3

• Main backgrounds:

• Z+γ (82%) and Z+jet (17%)

• Modelled by analytical functions

• Categories:

• 7/8 TeV and ee/μμ

• Δη(Zγ) and Ptt → 30% better sensitivity

• 95% CL limit at 125.5 GeV:

• 11 x SM (9 expected)

14

σ X BR ~ 2.3 fb @ 125.5 GeV

[GeV]Hm120 125 130 135 140 145 150

)γZ→

(HSMσ)/γZ

→(Hσ

95%

CL

limit

on

0

5

10

15

20

25

30ObservedExpected

σ 1±σ 2±

= 7 TeVs, -1 Ldt = 4.5 fb∫ = 8 TeVs , -1 Ldt = 20.3 fb∫

ATLAS

[GeV]γllm120 130 140 150 160 170

Even

ts/G

eV

0

100

200

300

400

500

600

Data50)×SMσ=125 GeV,

H (mγZ→H

=7 TeVs, -1Ldt = 4.5 fb∫=8 TeVs, -1Ldt = 20.3 fb∫

ATLAS


Conclusions

• A particle discovered via its decays to bosons!

• Signal strength compatible with SM prediction

• Consistent with JP = 0+

!

• New mass measurements:

• Total uncertainty reduced by ~40% (syst. by ~factor 3)

• Compatibility between channels (2.5σ previously): 2.0σ (4.8%), 1.6σ with μ = 1

15

A Higgs boson (related to EWSB)

As an additional cross-check some of the systematic uncertainties related to the photon energy scale, namely749

the one related to the knowledge of the inner detector material and the one related to the modeling of the photon750

lateral leakage, have been implemented with a “box-like” PDF using a double-Fermi-Dirac function. This choice751

is compatible with the fact that for these uncertainties there is no preferred value suggested by the data within the752

systematic error range. In this case the compatibility between the two masses increases to 7.5%, equivalent to 1.78�.753

The compatibility between the two measurements increases to 11% (1.61�) if the two signal strengths are set to the754

SM value of one, instead of being treated as free parameters.755

With respect to the value published in Ref [15], the compatibility between the measurements from the individual756

channels has changed from 2.5 to 2.0�.757

The contribution of the main sources of the systematic uncertainty to the measurements of the combined mass and758

mass di↵erence are shown in Table 4.759

In the mass measurement fit, the post-fit values of the most relevant nuisance parameters, which are related to the760

photon energy scale, do not show significant deviations from their pre-fit input values.761

8. Conclusions762

An updated measurement of the mass of the Higgs boson has been derived from a combined fit to the invariant763

mass spectra of the decay channels H ! �� and H!ZZ⇤! 4`. These measurements are based on the collision data764

sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at center-of-mass energies ofp

s=7765

TeV andp

s=8 TeV, corresponding to an integrated luminosity of 25 fb�1. As shown in Table 5, the measured value766

of the Higgs boson mass is mH = 125.36±0.37 (stat)±0.18 (sys) GeV. The compatibility between the mass measured767

from the two individual channels is at the level of 2.0� corresponding to a probability of 4.8%. This result is based768

on improved calibrations for photons, electrons and muons and on improved analysis techniques with respect to the769

one reported in Ref. [15], and therefore supersedes the previous result.770

Table 5: Summary of Higgs boson mass measurements.

Channel Mass measurement (GeV)

H ! �� 125.98 ± 0.42 (stat) ± 0.28 (sys) = 125.98 ± 0.50

H!ZZ⇤! 4` 124.51 ± 0.52 (stat) ± 0.04 (sys) = 124.51 ± 0.52

Combined 125.36 ± 0.37 (stat) ± 0.18 (sys) = 125.36 ± 0.41

Upper limits on the total width of the Higgs boson are derived from fits to the mass spectra of the H ! �� and771

H!ZZ⇤! 4` decay channels, under the assumption that there is no interference with background processes. From772

the first channel a 95% CL limit of 4.4 (5.4) GeV is observed (expected). From the second one a 95% CL limit of 2.6773

(6.2) GeV is observed (expected).774

9. Acknowledgements775

We thank CERN for the very successful operation of the LHC, as well as the support sta↵ from our institutions776

without whom ATLAS could not be operated e�ciently.777

We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF and FWF, Aus-778

tria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CON-779

ICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR,780

Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; EPLANET, ERC and NSRF, European Union;781

IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany;782

GSRT and NSRF, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS,783

Japan; CNRST, Morocco; FOM and NWO, Netherlands; BRF and RCN, Norway; MNiSW, Poland; GRICES and784

FCT, Portugal; MERYS (MECTS), Romania; MES of Russia and ROSATOM, Russian Federation; JINR; MSTD,785

24

Previous result: 125.5 ± 0.2 (stat)+0.5-0.6 (syst)


Mass vs. σ or signal strength

16

[GeV]Hm123 123.5 124 124.5 125 125.5 126 126.5 127 127.5

=125

.36

GeV

)H

(mSMσ/

σ

0

0.5

1

1.5

2

2.5

3

3.5

4 PreliminaryATLAS-1Ldt = 4.5 fb∫ = 7 TeV s

-1Ldt = 20.3 fb∫ = 8 TeV s

+ZZ*γγCombined γγ →H

l 4→ ZZ* →H

Best fit68% CL95% CL

[GeV]Hm123 123.5 124 124.5 125 125.5 126 126.5 127 127.5

)µ

Sign

al s

treng

th (

0

0.5

1

1.5

2

2.5

3

3.5

4 PreliminaryATLAS-1Ldt = 4.5 fb∫ = 7 TeV s

-1Ldt = 20.3 fb∫ = 8 TeV s

+ZZ*γγCombined γγ →H

l 4→ ZZ* →H

Best fit68% CL95% CL


Systematic uncertainties on mass measurement

17

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

(layer 1)LAr cell non-linearity

(barrel)Presampler energy scale

ee calibration→Z

)Tt

(unconv rest low p background modelγγ→H

Lateral shower shape (unconv)

Lateral shower shape (conv)

| < 1.1)ηID material model (|

LAr layer calibration (barrel)

before presampler (barrel)LAr syst on material

(layer 2)LAr cell non-linearity

-20 -10 0 10 20 [%])H

(mtotσ)σ1±=θ(Hm∆

θσ)/0θ-θ(

PreliminaryATLAS-1Ldt = 4.5 fb∫ = 7 TeV s

-1Ldt = 20.3 fb∫ = 8 TeV s

Documents

Measurement of properties of the Higgs boson in …...Bruno Lenzi (CERN) Higgs properties from boson in bosonic decay channels in ATLAS - LHCP 02/06/2014 Results from bosonic decays