Combination of the Higgs boson main property measurements using the ATLAS detector

Dag Gillberg


2014-07-04 CERN

Combination of the Higgs boson main property measurements

using the ATLAS detector

Dag Gillberg (CERN)

on behalf of the ATLAS Collaboration

ICHEP, Valencia, Spain, July 4, 2014

Outline

Main Higgs boson properties
 studied at ATLAS

I. mass - New! June 2014


main talk by Robert Harrington II. production rate & couplings 


to other particles


main focus of this 
 presentation

III. spin and parity


main talk by Kirill Prokofiev IV. fiducial/differential cross 


sections, kinematic properties;

associated jet activity; BSM …


see talks by S. Laplace, G. Sciolla

2 ^{gg→H VBF} VH ≡ WH or ZH ttH

H H

H H

q W,Z

q

g

g

t

q t q

q q

g

g ^{~87% ~7.2% ~5.0% ~0.6%}

coupling and spin results (II and III) not


yet updated with new calibration/mass

July 4, 2012

It’s been two years!

Happy discovery day Happy discovery day

Higgs boson mass

3

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

Improved calibration of electrons and photons

4

NEW

η|

| 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

MC 1/2 / Edata 1/2E

0.9 0.95 1 1.05

1.1 Z→µµ (trunc. mean)

(MPV) µ

µ Z→ Average

= 20.3 fb-1

t d

∫

=8 TeV, s

ATLAS Preliminary

ID + services Cryostat + Solenoid PS Cables

L1 L2 L3

μ

ID + services

L1 L2 L3

μ

|η|<1.82

|η|>1.82

e e

Unconv γ, E₀<500 MeV

Cryostat

ID end

e

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

NEW

Date (Day/Month) 13/03 23/04 04/06 16/07 27/08 07/10 18/11 30/12

Relative energy scale

0.998 0.9985 0.999 0.9995 1 1.0005

1.001 1.0015

1.002

= 20.3 fb-1

t d

∫

=8 TeV, ATLAS Preliminary s

mee

E/p

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

Improved calibration of electrons and photons

4

NEW

η|

| 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

MC 1/2 / Edata 1/2E

0.9 0.95 1 1.05

1.1 Z→µµ (trunc. mean) (MPV)

µ µ Z→ Average

= 20.3 fb-1

t d

∫

=8 TeV, s

ATLAS Preliminary

ID + services Cryostat + Solenoid PS Cables

L1 L2 L3

μ

ID + services

L1 L2 L3

μ

|η|<1.82

|η|>1.82

e e

Unconv γ, E₀<500 MeV

Cryostat

ID end

e

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

NEW

Date (Day/Month) 13/03 23/04 04/06 16/07 27/08 07/10 18/11 30/12

Relative energy scale

0.998 0.9985 0.999 0.9995 1 1.0005

1.001 1.0015 1.002

= 20.3 fb-1

t d

∫

=8 TeV, ATLAS Preliminary s

mee

E/p

New e/γ calibration (spring 2014)

• Calorimeter layers individually calibrated with µ, e and γ (A)

• Energy response stable within 0.5%

versus time and pileup (B)

• Improved material description of the calorimeters: inactive material

constrained to 2-10%X0

• Precise MVA-based EM cluster

calibration _→ 10% improved H→γγ mγγ resolution

• Data-MC agreement within (small!) uncertainty after calibration (C)

(A) (B)

(C)

[GeV]

mH

123 123.5 124 124.5 125 125.5 126 126.5 127 127.5

Λ-2ln

0 1 2 3 4 5 6 7

1σ 2σ

ATLAS

Ldt = 4.5 fb-1

= 7 TeV ∫

s

Ldt = 20.3 fb-1

= 8 TeV ∫

s

+4l γ Combined γ

γ γ H →

l

→ 4 ZZ*

H →

without systematics

Figure 8: Value of 2 ln⇤as a function ofmHfor the individualH ! andH!ZZ^⇤!4`channels and their combination, where the signal strengthsµ andµ<sub>4</sub>` are allowed to vary independently. The dashed lines show the statistical component of the mass measurements. For the H!ZZ^⇤!4`channel, this is indistinguishable from the solid line that includes the systematic uncertainties.

[GeV]

mH

123 123.5 124 124.5 125 125.5 126 126.5 127 127.5 )=125.36 GeV) H(m SMσ/σSignal yield (

0 0.5 1 1.5

2 2.5 3 3.5

4 ATLAS

Ldt = 4.5 fb-1

= 7 TeV ∫

s

Ldt = 20.3 fb-1

= 8 TeV ∫

s

γ+ZZ*

Combined γ γ γ H →

l

→ 4 ZZ*

H → Best fit 68% CL 95% CL

Figure 9: Likelihood contours 2 ln⇤(S,mH) as a function of the normalized signal yieldS = / _SM(mH=125.36 GeV) andmHfor theH! andH!ZZ^⇤!4`channels and their combination, including all systematic uncertainties. For the combined contour, a common normalised signal yieldS is used. The markers indicate the maximum likelihood estimates in the corresponding channels.

22

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

[GeV]

ET

10 20 30 40 50 60 70 80 90 100

Scale∆

-0.02 -0.015 -0.01 -0.005

0 0.005 0.01 0.015

0.02

e-

e+

→ ψ J/

e-

e+

Z →

Calibration uncertainty

|<1.37 Electrons, 0.60<|η

ATLASPreliminary ^{s=8 TeV,}

∫

Improved calibration of electrons and photons

5

NEW

2. 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

NEW

[GeV]

ET

10 20 30 40 50 60

Scale∆

-0.02 -0.015 -0.01 -0.005

0 0.005 0.01 0.015

0.02

Unconverted photons Data

Calibration uncertainty

ATLASPreliminary ^{s = 8 TeV,} ∫Ldt = 20.3 fb^-1

| η

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

Scale∆

-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02

Converted photons Data

Calibration uncertainty

ATLASPreliminary ^{s=8 TeV,} ∫Ldt = 20.3 fb^-1

Entries / 500 MeV

0 50 100 150 200 250 300 350 400 450 500

103

×

= 20.3 fb-1

t d

∫L

=8 TeV, s

ATLAS Preliminary

Calibrated data MC, uncorrected MC

[GeV]

mee

80 82 84 86 88 90 92 94 96 98 100

Ratio to MC

0.9 0.95 1 1.05

1.1 Calibration uncertainty

±0.5%

(C)

Combined Higgs mass: 125.36 ±0.37 (stat) ±0.21 (syst) ZZ-γγ compatibility: 2.0σ

Final ATLAS RunI Higgs mass measurement, 1406.3827

Combined Higgs mass: 125.36 ±0.37 (stat) ±0.21 (syst) ZZ-γγ compatibility: 2.0σ

Final ATLAS RunI Higgs mass measurement, 1406.3827

• Uncertainties:


• µ from H→γγ


• γγ-ZZ compatibility


[GeV] sys stat old 0.6 0.24 new 0.21 0.37

old new

2.5 σ 2.0 σ

old new

1.55±0.30 1.29±0.30

Calorimeter layer intercalibration Stability vs time & pileup Data vs MC & uncertainty

New CMS Combined mass: 125.03 ±0.27 (stat) ±0.15 (syst)

Matter particles

Force carriers (gauge bosons)

The Higgs can interact with (couples to) all massive, fundamental particles

Higgs couplings

•

Search for deviations from the SM Higgs coupling to other particles by

introducing multipliers using a tree-level motivated benchmark model following the LHC Higgs XS WG recommendations: 1209.0040

4

κZ

κW

– 62–

VBF production. The observations by ATLAS and CMS ex- clude a value of ρ_{V BF+V H,ggH+ttH} = 0 at an even greater level of confidence.

IV.2.5. Measurement of the coupling properties of H (i) From effective Lagrangians to Higgs observables

All 8 operators of the effective Lagrangian Eq. (13) that were unconstrained before the Higgs data induce, at tree-level, deviations in the Higgs couplings that respect the Lorentz struc- ture of the SM interactions, or generate simple new interactions of the Higgs boson to the W and Z field strengths, or induce some contact interactions of the Higgs boson to photons (and to a photon and a Z boson) and gluons that take the form of the ones that are generated by integrating out the top quark. In other words, the Higgs couplings are described, in the unitary gauge, by the following effective Lagrangian [180,38]

L = κ₃m²_H

2v H³ + κ_Z m²_Z

v Z_µZ^µH + κ_W 2m²_W

v W_µ⁺W^−µH + κ_g α_s

12πvG^a_µνG^aµνH + κ_γ α

2πvA_µνA^µνH + κ_Zγ α

πvA_µνZ^µνH + κ_{V V} α

2πv

!cos² θ_WZ_µνZ^µν + 2 W_µν⁺ W^−µν"

H

−

⎛

⎝κ_t %

f=u,c,t

m_f

v f f + κ_b %

f=d,s,b

m_f

v f f + κ_τ %

f=e,µ,τ

m_f v f f

⎞

⎠H.

(22) The correspondence between the Wilson coefficients of the dimension-6 operators and the κ’s is given in Table 11. In the SM, the Higgs boson does not couple to massless gauge bosons at tree level, hence κ_g = κ_γ = κ_Zγ = 0. Nonetheless, the contact operators are generated radiatively by SM particles loops. In particular, the top quark gives a contribution to the 3 coefficients κ_g, κ_γ, κ_Zγ that does not decouple in the infinite top mass limit. For instance, in that limit κ_γ = κ_g = 1 [19,20,181]

(the contribution of the top quark to κ_Zγ can be found in Ref. [181]).

January 9, 2014 16:22

Effective Lagrangian describing the 
 Higgs couplings in unitarity gauge

Status of Higgs boson physics (PDG), page 62

!

Notreviewed,forinternalcirculationonly

Coupling to Fermions v. Vector Bosons

 V =  W =  Z

 F =  t =  b =  ⌧

I

Normalization profiled in fit.

g g

t,b h

q

q q

q h

q

q W/Z

h W/Z

Production Modes

h

W

h W/Z

W/Z

h b,τ

b,τ h

t,b t,b

Decays

γ γ γ γ

Saxon (UPenn) Combined Higgs Measurements May 5, 2014 8 / 18

Higgs couplings

•

Search for deviations from the SM Higgs coupling to other particles by

introducing multipliers using a tree-level motivated benchmark model following the LHC Higgs XS WG recommendations: 1209.0040

•

Assumptions:

๏

Single, narrow, CP-even scalar resonance


(tensor structure of couplings assumed to be those of the SM)

๏

Narrow width approximation is valid:

!

•

Deviations from SM parametrized using multipliers κ, e.g.


where κ

are effective multipliers since the Higgs boson 
 does not directly couple to these particles, 


but via loops that contains interference:


5

B (i ! H ! f ) =

H

B(gg ! H ! ) = ^{ggF H!}

H

Example:

B (gg ! H ! ) = (

B )

(gg ! H ! ) ⇥ 







= 1.59

0.66



+ 0.07

these relations are modified if non-SM particles enter the loop

Higgs couplings

•

Parameters of interest

• Signal strength µ = σmeasured/σSM 


multiplier for total yield. 


Can also be defined for each production mode, e.g.:


µ

= σ

/ σ

• Multiplier κ for a given coupling


e.g. κ

for the Higgs-top quark coupling, or κ

for general Higgs-fermion coupling

•

Different types of models tested by imposing different relations between kappas

•

In both cases, SM has: µ

Deviations from unity indicate non-SM Higgs couplings

Notreviewed,forinternalcirculationonly

Factorizing

I

Production Modes

I

Fermions v. Bosons

I

Up v. Down

I

Leptons v. Quarks

I

W v. Z : Custodial Sym.

I

Photon, Gluon Loops

I

Unobs. or Invisible

g g

t,b h

q

q q

q h

q

q W/Z

h W/Z

Production Modes

h

W

h ^W/Z

W/Z

h b,τ

b,τ h

t,b t,b

Decays

γ γ γ γ

Saxon (UPenn) Combined Higgs Measurements May 5, 2014 6 / 18

gg→H VBF VH ≡ WH or ZH ttH

H H

H H

q W,Z

q

g

g

t

q t q

q q

g g

Note: κ allows for more direct accesses to coupling as µ

contain complex interplay between production and decay

Datasets and analysis strategy

• Combine ATLAS Higgs measurements from 5 different channels

•

Each analysis is further divided into categories that increases sensitivity:


→ different s/b and production mode/decay compositions


→ allows to extract Higgs couplings to different particles

•

Parameter(s) of interest extracted by simultaneous maximal likelihood fit

7

Notreviewed,forinternalcirculationonly

Analysis Categories

Channel Decay Production Tagging

h ! - VBF, `, E/_T, 2-jet VH.

h ! ZZ^⇤ 4` VBF, `

h ! WW ^⇤ `⌫`⌫ 0-jet, 1-jet, 2-jet VBF

V (h ! bb) Z ! ⌫⌫, W ! `⌫, Z ! `` -

h ! ⌧ ⌧ (2012) ⌧_lep⌧_lep, ⌧_lep⌧_had, ⌧_had⌧_had Boosted ggh, VBF

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

One-lepton significance

miss

ET

Low-mass two-jet Tight high-mass two-jet Loose high-mass two-jet

Conv. transition Conv. rest high pTt^Tt

Conv. rest low p^Tt Conv. central high p^Tt Conv. central low p^Tt Unconv. rest high p^Tt Unconv. rest low p^Tt Unconv. central high p^Tt

Unconv. central low p Inclusive

ggF VBF WH ZH ttH

ATLAS Preliminary (simulation) H → γ γ

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

One-lepton significance

miss

ET

Low-mass two-jet Tight high-mass two-jet Loose high-mass two-jet

Conv. transition Conv. rest high pTt^Tt

Conv. rest low p^Tt Conv. central high p^Tt Conv. central low p^Tt Unconv. rest high p^Tt Unconv. rest low p^Tt Unconv. central high p^Tt

Unconv. central low p Inclusive

ggF VBF WH ZH ttH

ATLAS Preliminary (simulation) H → γ γ

Example: Tagged Categories in h → γγ

Saxon (UPenn) Combined Higgs Measurements May 5, 2014 3 / 18

Example:

H→γγ categories

channel decay categories L [fb ¹]

H ! - low/high p_Tt, VBF, `, E_T^miss 4.8+20.3

H ! ZZ^⇤ 4` `, VBF 4.6+20.3

H ! W W⇤ `⌫`⌫ 0, 1, 2 jets, VBF 4.6+20.3

V H ! V b¯b Z ! ⌫⌫, W ! `⌫, Z ! `` - 4.6+20.3

H ! ⌧ ⌧ ``, `-had, had-had boosted, VBF 20.3

γγ, ZZ, WW, 
 bb, τ τ

VBF categories:


large fraction of VBF low-mjj, ETmiss and lepton categories:


large fraction of WH

µ) Signal strength (

-0.5 0 0.5 1 1.5 2

ATLAS Prelim.

Ldt = 4.6-4.8 fb-1

∫

= 7 TeV s

Ldt = 20.3 fb-1

∫

= 8 TeV s

= 125.5 GeV mH

0.28 -

0.33

= 1.57+

µ γ γ H →

0.12 - 0.17 +

0.18 -

0.24 +

0.22 -

0.23 +

0.35 -

0.40

= 1.44+

µ

→ 4l ZZ*

H →

0.10 -

0.17 +

0.13 -

0.20 +

0.32 -

0.35 +

-0.29 0.32

= 1.00+

µ lν lν WW* → H →

0.08 -

0.16 +

0.19 -

0.24 +

0.21 - 0.21 +

0.20 - +0.21

= 1.35 µ

, ZZ*, WW*

γ γ H→

Combined

0.11 -

0.13 +

0.14 -

0.16 +

0.14 -

0.14 +

-0.6 0.7

= 0.2+

µ b

→ b W,Z H

<0.1

±0.4

±0.5

0.4 -

0.5

= 1.4+

µ

(8 TeV data only)

τ τ H →

0.1 -

0.2 +

0.3 - + 0.4

0.3 - + 0.3

0.32 -

0.36

= 1.09+

τ µ , τ b

→b H

Combined

0.04 -

0.08 +

0.21 -

0.27 +

0.24 -

0.24 +

-0.17 0.18

= 1.30+

µ

Combined

0.08 -

0.10 +

0.11 -

0.14 +

0.12 -

0.12 +

Total uncertainty on µ

1σ

±

(stat.) σ

theory )

sys inc.

(

σ

(theory) σ

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

Section 2. In the H ! ⌧⌧ channel, the ratio µ_VBF+VH/µ_ggF+ttH has an infinite 1 upper bound, because the 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 µ_VBF/µ_ggF+ttH. In order not to influence the VBF measurement through the VH categories, the parameter µ_VH/µ_ggF+ttH is treated independently and profiled. A value of

µ_VBF/µ_ggF+ttH = 1.4⁺⁰_0.4^.5 (stat)⁺⁰_0.3^.4 (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

Combined signal strength

8

iv.b Combining Coupling measurements Combined signal strength results for µ and µ

/µ

:

µ) Signal strength (

-0.5 0 0.5 1 1.5 2

ATLAS Prelim.

Ldt = 4.6-4.8 fb-1

∫

= 7 TeV s

Ldt = 20.3 fb-1

∫

= 8 TeV s

= 125.5 GeV mH

0.28 - +0.33

= 1.57 µ

γ γ H →

0.12 -

0.17 +

0.18 -

0.24 +

0.22 -

0.23 +

0.35 -

0.40

= 1.44+

µ

→ 4l ZZ*

H →

0.10 -

0.17 +

0.13 -

0.20 +

0.32 -

0.35 +

0.29 -

0.32

= 1.00+

µ lν lν WW* → H →

0.08 -

0.16 +

0.19 -

0.24 +

0.21 -

0.21 +

0.20 -

0.21

= 1.35+

µ

, ZZ*, WW*

γ γ H→

Combined

0.11 -

0.13 +

0.14 -

0.16 +

0.14 -

0.14 +

-0.6 +0.7

= 0.2 µ

b

→ b W,Z H

<0.1

±0.4

±0.5

0.4 - +0.5

= 1.4 µ

(8 TeV data only)

τ τ H →

0.1 -

0.2 +

0.3 -

0.4 + - 0.3

0.3 +

0.32 -

0.36

= 1.09+

τ µ , τ b

→b H

Combined

0.04 -

0.08 +

0.21 -

0.27 +

0.24 -

0.24 +

0.17 -

0.18

= 1.30+

µ

Combined

0.08 -

0.10 +

0.11 -

0.14 +

0.12 -

0.12 +

Total uncertainty on µ

1σ

±

(stat.) σ

theory )

sys inc.

(

σ

(theory) σ

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

Section 2. In the H channel, the ratio µ_VBF+VH/µ_ggF+ttH has an infinite 1 upper bound, because the 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 µ_VBF/µ_ggF+ttH. In order not to influence the VBF measurement through the VH categories, the parameter µ_VH/µ_ggF+ttH is treated independently and profiled. A value of

µ_VBF/µ_ggF+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

ggF+ttH

/ µ

VBF+VH

µ

0 1 2 3 4 5

ATLAS Prelim.

Ldt = 4.6-4.8 fb-1

∫

= 7 TeV s

Ldt = 20.3 fb-1

∫

= 8 TeV s

= 125.5 GeV mH

-0.6 +0.8

= 1.2

ggF+ttH

µ^VBF+VH µ

γ γ H →

1 σ 2 σ

- 0.2 + 0.2 0.2 -

0.4 +

0.5 -

0.7 +

-0.9 2.4

= 0.6+

ggF+ttH

µ^VBF+VH µ

→ 4l ZZ*

H →

1 σ - 0.2

+ 0.3 0.2 -

0.6 + - 0.9

2.3 +

1.0 -

1.9

= 1.8+

ggF+ttH

µ^VBF+VH µ

lν lν WW* → H →

1 σ 0.2

- + 0.5

0.4 -

1.3 + - 0.9 + 1.4

-1.2 +∞

= 1.7

ggF+ttH

µ^VBF+VH µ

τ τ H →

0.3 - +∞

0.6 - +∞

1.0 -

5.3 +

0.5 - +0.7

= 1.4

ggF+ttH

µ^VBF+VH µ

Combined

1 σ 2 σ

0.1 -

0.2 +

0.2 -

0.4 + - 0.4

0.5 +

Total uncertainty 1σ

± ± 2σ

(stat.) σ

theory )

sys inc.

(

σ

(theory) σ

Figure 3: Measurements of the µ_VBF+VH/µ_ggF+ttH ratios for the individual final states and their combi- nation, for a Higgs boson mass m_H =125.5 GeV. The best-fit values are represented by the solid vertical lines, with the total ±1 and ±2 uncertainties indicated by the green and yellow shaded bands, re- spectively, and the statistical uncertainties by the superimposed horizontal error bars. The numbers in the second column specify the contributions of the statistical uncertainty (top), the total (experimental and theoretical) systematic uncertainty (middle), and the theoretical uncertainty (bottom) on the signal cross section (from QCD scale, PDF, and branching ratios) alone. For a more complete illustration, the likelihood curves from which the total uncertainties are extracted are overlaid. The measurements are based on Refs. [3, 6], with the changes mentioned in the text.

means in particular that the observed state is assumed to be a CP-even scalar as in the SM (this assumption was tested by both the ATLAS [15] and CMS [16] Collaborations).

The LO-motivated coupling scale factors j are defined in such a way that the cross section j and the partial decay width _j associated with the SM particle j scale with the factor ²_j when compared to the corresponding SM prediction. Details can be found in Refs. [14, 17].

In some of the fits the effective scale factors and _g for the processes H and gg H, which are loop-induced in the SM, are treated as a function of the more fundamental coupling scale factors t,

b, W, and similarly for all other particles that contribute to these SM loop processes. In these cases the scaled fundamental couplings are propagated through the loop calculations, including all interference effects, using the functional form derived from the SM. Similarly the scaling of the VBF cross section

8

Overall signal production strength: µ = 1.30

Evidence for VBF+VH: µ

/µ

= 1.4

10 / 21

µ

/µ

= 1.4

Combined µ = 1.30

3.7σ 4.1σ

ATLAS-CONF-2014-009

Evidence for VBF Higgs production

9

iv.c Combining Coupling measurements

Projection in µ

-µ

plane:

τ τ ,ZZ*,WW*, γ

γ

ggF+ttH

µ

-2 -1 0 1 2 3 4 5 6

ττ,ZZ*,WW*,γγ VBF+VHµ

-2 0 2 4 6 8

10 Standard Model

Best fit 68% CL 95% CL

γ γ H →

→ 4l ZZ*

H →

lν lν WW* → H →

τ τ H →

Preliminary ATLAS

Ldt = 4.6-4.8 fb-1

∫

= 7 TeV s

Ldt = 20.3 fb-1

∫

= 8 TeV s

= 125.5 GeV mH

Figure 2: Likelihood contours in the (µ_ggF^f _+ttH, µ_VBF^f _+VH) plane for the channels f=H , H ZZ 4 , H WW , H and a Higgs boson mass m_H = 125.5 GeV. The sharp lower edge of the H ZZ 4 contours is due to the small number of events in this channel and the require- ment of a positive pdf. The best-fit values to the data ( ) and the 68% (full) and 95% (dashed) CL contours are indicated, as well as the SM expectations (+).

5 Coupling fits

In the previous section signal strength scale factors µ_i^f for given Higgs boson production or decay modes are discussed. However, for a measurement of Higgs boson couplings, production and decay modes cannot be treated independently. Scenarios with a consistent treatment of Higgs boson couplings in production and decay modes are studied in this section. All uncertainties on the best-fit values shown in this Section take into account both experimental and theoretical systematic values.

5.1 Framework for coupling scale factor measurements

Following the leading order (LO) tree level motivated framework and benchmarks recommended in Ref. [14], measurements of coupling scale factors are implemented for the combination of all analyses and channels summarised in Table 1. This framework is based on the following assumptions:

• The signals observed in the different search channels originate from a single narrow resonance with a mass near 125.5 GeV. The case of several, possibly overlapping, resonances in this mass region is not considered.

• The width of the assumed Higgs boson near 125.5 GeV is neglected, i.e. the zero-width approxi- mation is used. Hence the product BR(i H f) can be decomposed in the following way for all channels:

BR(i H f) = ⁱ · ^f

H ,

where _i is the production cross section through the initial state i, _f the partial decay width into the final state f and _H the total width of the Higgs boson.

• Only modifications of couplings strengths, i.e. of absolute values of couplings, are taken into account, while the tensor structure of the couplings is assumed to be the same as in the SM. This

7

ggF+ttH

µ

VBF / µ

-0.5 0 0.5 1 1.5 2 2.5 3 3.5

Λ-2 ln

0 2 4 6 8 10 12 14 16 18 20 22 24

combined SM expected

Preliminary ATLAS

Ldt = 4.6-4.8 fb-1

∫

= 7 TeV s

Ldt = 20.3 fb-1

∫

= 8 TeV s

= 125.5 GeV mH

Figure 4: Likelihood curve for the ratio µ

/µ

for the combination of the H , H ZZ 4 , H WW and H channels and a Higgs boson mass m

= 125 . 5 GeV. The parameter µ

/µ

is profiled in the fit. The dashed curve shows the SM expectation. The horizontal dashed lines indicate the 68% and 95% CL.

and the total width scale factor

are expressed as functions of the more fundamental coupling scale factors in some fits. To a very good approximation, the relevant expressions for m

= 125 . 5 GeV are:

2

1 . 59 ·

0 . 66 ·

+ 0 . 07 ·

(2)

2g

1 . 06 ·

0 . 07 ·

+ 0 . 01 ·

(3)

2VBF

0 . 74 ·

+ 0 . 26 ·

(4)

2H

0 . 57 ·

+ 0 . 22 ·

+ 0 . 09 ·

+ 0 . 06 ·

+ 0 . 03 ·

+ 0 . 03 ·

. (5) For details and the exact expressions used, see Appendix A and Ref. [14].

The assumptions made for the various measurements are summarised in Table 2 and discussed in the next sections together with the results. The functional dependence of the signal strengths on the e ff ective scale factors

is explicated for each benchmark model considered and for the most important Higgs boson production and decay modes in Appendix A.

5.2 Fermion versus vector (gauge) couplings

This benchmark is an extension of the fit to the single parameter µ , where di ff erent strengths for the fermion and vector couplings are probed. It assumes that only SM particles contribute to the H and gg H vertex loops, and modifications of the coupling strength factors for fermions and vector bosons are propagated through the loop calculations. The fit is performed in two variants, with and without the assumption that the total width of the Higgs boson is given by the sum of the known SM Higgs boson decay modes (modified in strength by the appropriate fermion and vector coupling scale factors).

5.2.1 Only SM contributions to the total width

The fit parameters are the coupling scale factors

for all fermions and

for all vector couplings:

V

=

=

F

=

=

= =

.

As only SM particles are assumed to contribute to the gg H vertex loop in this benchmark, the gluon fusion process depends directly on the fermion scale factor

. The relevant scaling formulae can be found in Appendix A.1.1.

9

Coupling ratio for VBF production only: µ

/µ

= 1.4

! Evidence at 4.1 for VBF production!

11 / 21

iv.c Combining Coupling measurements

Projection in µVBF+VH-µggF+ttH plane:

τ τ ,ZZ*,WW*, γ

γ ggF+ttH

µ

-2 -1 0 1 2 3 4 5 6

ττ,ZZ*,WW*,γγ VBF+VHµ

-2 0 2 4 6 8

10 Standard Model

Best fit 68% CL 95% CL

γ γ

→ H

→ 4l ZZ*

→ H

ν νl

→ l WW*

→ H

τ τ

→ H

Preliminary ATLAS

Ldt = 4.6-4.8 fb-1

∫

= 7 TeV s

Ldt = 20.3 fb-1

∫

= 8 TeV s

= 125.5 GeV mH

Figure 2: Likelihood contours in the (µ_ggF+ttH^f , µ_VBF+VH^f ) plane for the channels f=H , H ZZ 4 , H WW , H and a Higgs boson mass m_H = 125.5 GeV. The sharp lower edge of the H ZZ 4 contours is due to the small number of events in this channel and the require- ment of a positive pdf. The best-fit values to the data ( ) and the 68% (full) and 95% (dashed) CL contours are indicated, as well as the SM expectations (+).

5 Coupling fits

In the previous section signal strength scale factors µ_i^f for given Higgs boson production or decay modes are discussed. However, for a measurement of Higgs boson couplings, production and decay modes cannot be treated independently. Scenarios with a consistent treatment of Higgs boson couplings in production and decay modes are studied in this section. All uncertainties on the best-fit values shown in this Section take into account both experimental and theoretical systematic values.

5.1 Framework for coupling scale factor measurements

Following the leading order (LO) tree level motivated framework and benchmarks recommended in Ref. [14], measurements of coupling scale factors are implemented for the combination of all analyses and channels summarised in Table 1. This framework is based on the following assumptions:

• The signals observed in the different search channels originate from a single narrow resonance with a mass near 125.5 GeV. The case of several, possibly overlapping, resonances in this mass region is not considered.

• The width of the assumed Higgs boson near 125.5 GeV is neglected, i.e. the zero-width approxi- mation is used. Hence the product BR(i H f) can be decomposed in the following way for all channels:

BR(i H f) = ⁱ · ^f

H ,

where i is the production cross section through the initial state i, f the partial decay width into the final state f and _H the total width of the Higgs boson.

• Only modifications of couplings strengths, i.e. of absolute values of couplings, are taken into account, while the tensor structure of the couplings is assumed to be the same as in the SM. This

7

ggF+ttH

µ

VBF / µ

-0.5 0 0.5 1 1.5 2 2.5 3 3.5

Λ-2 ln

0 2 4 6 8 10 12 14 16 18 20 22 24

combined SM expected

Preliminary ATLAS

Ldt = 4.6-4.8 fb-1

∫

= 7 TeV s

Ldt = 20.3 fb-1

∫

= 8 TeV s

= 125.5 GeV mH

Figure 4: Likelihood curve for the ratio µ_VBF/µ_ggF+ttH for the combination of the H , H ZZ 4 , H WW and H channels and a Higgs boson mass m_H = 125.5 GeV. The parameter µ_VH/µ_ggF+ttH is profiled in the fit. The dashed curve shows the SM expectation. The horizontal dashed lines indicate the 68% and 95% CL.

and the total width scale factor ²_H are expressed as functions of the more fundamental coupling scale factors in some fits. To a very good approximation, the relevant expressions for m_H = 125.5 GeV are:

2 1.59 ·