Measurements of the Higgs Boson Coupling Strength in the ATLAS - - PowerPoint PPT Presentation

▶
measurements of the higgs boson coupling strength in the
SMART_READER_LITE
LIVE PREVIEW

Measurements of the Higgs Boson Coupling Strength in the ATLAS - - PowerPoint PPT Presentation

Feb 01, 2024 114 likes •400 views

Measurements of the Higgs Boson Coupling Strength in the ATLAS Experiment Fangzhou Zhang (University of Wisconsin-Madison) DPF Meeting, Ann Arbor, MI August 4, 2015 1 Discovery Property measurement 0 Local p ATLAS 2011 - 2012 Higgs

slide-1
SLIDE 1

DPF Meeting, Ann Arbor, MI August 4, 2015

Measurements of the Higgs Boson Coupling Strength in the ATLAS Experiment

Fangzhou Zhang

(University of Wisconsin-Madison)

1

slide-2
SLIDE 2

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

α tan ⋅ ) SM κ / AVV κ ∼ (
  • 8
  • 6
  • 4
  • 2
2 4 6 8 λ
  • 2 ln
5 10 15 20 25 30 ATLAS Observed signal strength fit to data Expected: Expected: SM l 4 → ZZ* → H
  • 1
= 7 TeV, 4.5 fb s
  • 1
= 8 TeV, 20.3 fb s νµν e → WW* → H
  • 1
= 8 TeV, 20.3 fb s

[GeV]

H

m 110 115 120 125 130 135 140 145 150 Local p

  • 11
10
  • 10
10
  • 9
10
  • 8
10
  • 7
10
  • 6
10
  • 5
10
  • 4
10
  • 3
10
  • 2
10
  • 1
10 1

Obs. Exp. σ 1 ±

  • 1

Ldt = 5.8-5.9 fb

∫

= 8 TeV: s

  • 1

Ldt = 4.6-4.8 fb

∫

= 7 TeV: s

ATLAS 2011 - 2012

σ σ 1 σ 2 σ 3 σ 4 σ 5 σ 6

Discovery → Property measurement

[GeV]

H

m 123 123.5 124 124.5 125 125.5 126 126.5 127 127.5 Λ

  • 2ln

1 2 3 4 5 6 7

σ 1 σ 2

ATLAS

  • 1
Ldt = 4.5 fb

∫

= 7 TeV s
  • 1
Ldt = 20.3 fb

∫

= 8 TeV s l +4 γ γ Combined γ γ → H l 4 → ZZ* → H without systematics

2 − 1 − 1 2 3 (95%CL) λ(Zγ)Z < 3.2 λγZ = 0.90 ± 0.15 (95%CL) λμZ < 2.3 λτZ = 0.99+0.23

−0.19

λbZ = 0.60 ± 0.27 λ ∈ [−1.70, −1.07] ∪[1.03, 1.73] λWZ ∈ [−1.04, −0.81] ∪[0.80, 1.06] λZ = 1.09+0.26

−0.22

κ Z = 1.18 ± 0.16 Parameter value

ATLAS

√s = 7 TeV,4.5 − 4.7 fb−1 √s = 8 TeV,20.3 fb−1 mH = 125.36GeV 68% CL: 95% CL:

2

Mass CP/Parity Coupling

  • Higgs discovery in July 2012 [Phys. Lett. B 716 (2012) 1-29]
  • Now in precision measurement era
  • June 2014: 2-channel combined mass measurements 


[Phys. Rev. D 90, 052004]
 H → γγ / ΖΖ*

  • June 2015: boson channel combined spin/parity

measurements [arXiv:1506.05669]
 H → γγ / ΖΖ* / WW*

  • July 2015: multi-channel combined coupling measurements

[arXiv:1507.04548]
 H → γγ / ΖΖ* / WW* / ττ / bb / Zγ / μμ

slide-3
SLIDE 3

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

Plot Sample: measurement results

3

0.5 1 1.5 2 2.5 3

μttH = 1.81 ± 0.80 μVH = 0.80 ± 0.36 μVBF = 1.23 ± 0.32 μggF = 1.23+0.23

−0.20

Signal strength (μ)

ATLAS

√s = 7 TeV, 4.5 − 4.7 fb−1 √s = 8 TeV, 20.3 fb−1

mH = 125.36 GeV

68% CL: 95% CL:

Measured Value Central Value 1σ error 2σ error

Ref: arXiv:1507.04548

slide-4
SLIDE 4

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

i.,u.

BR )

i.,u.

(BR Λ

  • 2 ln

5 10 15 20 25 30 0.8 − 0.6 − 0.4 − 0.2 − 0.2 0.4 0.6 0.8 ATLAS

SM expected Observed

  • 1

= 7 TeV, 4.5-4.7 fb s

  • 1

= 8 TeV, 20.3 fb s ]

i.,u.

,BR

γ Z

κ ,

g

κ ,

γ

κ [

Plot Sample: 1D likelihood scan

4

Central Value 1σ error 2σ error

Ref: arXiv:1507.04548

slide-5
SLIDE 5

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

V

κ 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3

F

κ 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 ATLAS

  • 1

= 7 TeV, 4.5-4.7 fb s

  • 1

= 8 TeV, 20.3 fb s = 125.36 GeV

H

m Standard Model Best fit 68% CL 95% CL

Plot Sample: 2D likelihood contour

5

Central Value 1σ 2σ

Ref: arXiv:1507.04548

slide-6
SLIDE 6

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

  • Common signal strength: ratio of measured

signal event yields to SM expectation, accounting for all production and decay modes

  • The most precise measurement
  • No straightforward physics model

interpretation, especially for μ > 1

  • Combined result includes 7 decay channels:

  • Compatibility with SM expectation(μ=1) is

18%

Common signal strength (μ)

Contribution from ttH searches assigned to all decay modes except μμ and Zγ

µ = 1.18 ± 0.10(stat) ± 0.07(exp)+0.08

−0.07(theo)

) µ Signal strength (

1 − 1 2 3

ATLAS

  • 1

= 7 TeV, 4.5-4.7 fb s

  • 1

= 8 TeV, 20.3 fb s

= 125.36 GeV

H

m

0.26
  • 0.28
+

= 1.17 µ γ γ → H

0.08
  • 0.12
+ 0.11
  • 0.16
+ 0.23
  • 0.23
+ 0.34
  • 0.40
+

= 1.46 µ ZZ* → H

0.11
  • 0.18
+ 0.13
  • 0.19
+ 0.31
  • 0.35
+ 0.21
  • 0.24
+

= 1.18 µ WW* → H

0.09
  • 0.13
+ 0.14
  • 0.17
+ 0.16
  • 0.16
+ 0.37
  • 0.42
+

= 1.44 µ τ τ → H

0.10
  • 0.16
+ 0.23
  • 0.29
+ 0.29
  • 0.30
+ 0.37
  • 0.39
+

= 0.63 µ b b → H

0.07
  • 0.09
+ 0.23
  • 0.24
+ 0.30
  • 0.31
+ 3.7
  • 3.7
+

= -0.7 µ µ µ → H

0.4
  • 0.4
+ 0.7
  • 0.5
+ 3.6
  • 3.6
+ 4.5
  • 4.6
+

= 2.7 µ γ Z → H

0.3
  • 1.1
+ 1.3
  • 1.7
+ 4.2
  • 4.3
+ 0.14
  • 0.15
+

= 1.18 µ

Combined

0.07
  • 0.08
+ 0.10
  • 0.11
+ 0.10
  • 0.10
+

Total uncertainty µ

  • n

σ 1 ±

(stat.) σ

)

theory sys inc.

(

σ (theory) σ

6

Ref: arXiv:1507.04548

slide-7
SLIDE 7

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

0.5 1 1.5 2 2.5 3

μttH = 1.81 ± 0.80 μVH = 0.80 ± 0.36 μVBF = 1.23 ± 0.32 μggF = 1.23+0.23

−0.20

Signal strength (μ)

ATLAS

√s = 7 TeV, 4.5 − 4.7 fb−1 √s = 8 TeV, 20.3 fb−1

mH = 125.36 GeV

68% CL: 95% CL:

Individual production processes

  • Decouple signal strengths of different Higgs

production modes:

  • Gluon-gluon fusion (ggF, dominant)
  • Vector boson fusion (VBF)
  • Associated production with a vector boson

(WH/ZH)

  • Associated production with a top pair (ttH)
  • Assuming SM Higgs decay branching ratio
  • Results consistent with SM at <2σ

Dominant

ggF

t/b g g H

VBF

W/Z W/Z ¯ q0 q ¯ q0 q H

WH/ZH

W/Z q ¯ q W/Z H

ttH

g g ¯ t/¯ b t/b H

[GeV]

H

M 80 100 120 140 160 180 200 H+X) [pb] → (pp σ

  • 2

10

  • 1

10 1 10

2

10 = 8 TeV s

LHC HIGGS XS WG 2012 H (NNLO+NNLL QCD + NLO EW) → pp q q H ( N N L O Q C D + N L O E W ) → p p WH (NNLO QCD + NLO EW) → pp ZH (NNLO QCD +NLO EW) → pp ttH (NLO QCD) → pp

7

Ref: arXiv:1507.04548 Ref: LHC-XS-WG

slide-8
SLIDE 8

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

Boson and fermion-mediated production

  • Categorization of Higgs production processes:
  • Boson mediated (VBF,

VH)

  • Fermion mediated (ggF, ttH)
  • Assume: μfggF = μfttH, μfVBF = μfVH
  • SM expectation within 68% CL contour of

most of the measurements

ggF+ttH f

µ 2 − 1 − 1 2 3 4 5 6 7

VBF+VH f

µ 2 − 1 − 1 2 3 4 5 6 7 ATLAS

  • 1
= 7 TeV, 4.5-4.7 fb s
  • 1
= 8 TeV, 20.3 fb s = 125.36 GeV H m WW* → H ZZ* → H bb → H γ γ → H τ τ → H Standard Model Best fit 68% CL 95% CL
  • Relative production cross section μfggF

+ttH / μfVBF+VH

  • Reduced to production cross section

ratios in individual channels (branching ratio canceled)

µf

ggF+ttH/µf VBF+VH = µggF+ttH/µVBF+VH

8

Ref: arXiv:1507.04548

1 − 0.5 − 0.5 1 1.5 2 2.5 3 3.5

RCombined = 0.96+0.43

−0.31

Rbb = 0.33+1.03

−0.25

Rττ = 0.81+2.19

−0.49

RWW ∗ = 1.47+0.80

−0.54

RZZ ∗ = 0.18+1.20

−0.52

Rγγ = 0.56+0.66

−0.45

R = [σVBF+VH /σggF+ttH]SM

σVBF+VH /σggF+ttH

ATLAS

√ = 7 TeV, 4.5 − 4.7 fb−1 √ = 8 TeV, 20.3 fb

−1

mH = 125.36 GeV

68% CL: 95% CL:
slide-9
SLIDE 9

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

1 − 0.5 − 0.5 1 1.5 2 2.5 3 3.5 4

Γbb/ΓWW ∗ Γττ/ΓWW ∗ ΓZZ ∗/ΓWW ∗ Γγγ/ΓWW ∗ σ H/σ

F

σZH/σ

F

σWH/σ

F

σVBF/σ

F

σ( → H → WW ∗)

Value normalised to SM prediction

ATLAS

√ = 7 TeV, 4.5 − 4.7 fb−1 √ = 8 TeV, 20.3 fb−1

mH = 125.36 GeV

Observed: 68% CL Observed: 95% CL SM prediction

Higgs production and decay modes

  • The ratios of cross sections and branching

ratios can be disentangled without any assumption

  • Only product of production cross section

and decay branching ratios are measured

  • gg→H→WW* is chosen as reference due to

its smallest statistical and overall uncertainties

  • Evidence of non-dominant production modes

(excluding ratio = 0):

  • VBF: 4.3σ (exp. 3.8σ)
  • WH: 2.1σ (exp. 2.0σ)
  • ZH: 0.9σ (exp. 2.1σ)
  • ttH: 2.5σ (exp. 1.5σ)

σi · BRf = σ(gg → H → WW ∗) × ✓ σi σggF ◆ × ✓ Γf ΓW W ∗ ◆

9

Ref: arXiv:1507.04548

slide-10
SLIDE 10

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

Models for coupling measurements

  • Higgs coupling to other particles is proportional to mfermion or mboson2
  • Leading order tree-level motivated framework, with assumptions:
  • Signal in different channels originate from single resonance
  • Narrow-width resonance, which justifies zero-width approximation
  • Lagrangian tensor structure is the same as SM Higgs ( JP=0+ )
  • Coupling strength parametrized via scale factors κi w.r.t SM cross

section or partial decay width

σ · B(i → H → f) = σi · Γf ΓH = σSM

i

· ΓSM

f

ΓSM

H

· κ2

i κ2 f

κ2

H

! κ2

i =

σi σSM

i

κ2

f =

Γf ΓSM

f

κ2

H =

P Γf P ΓSM

f

where

Production Decay Total width

10

slide-11
SLIDE 11

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

V

κ 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3

F

κ 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 ATLAS

  • 1
= 7 TeV, 4.5-4.7 fb s
  • 1
= 8 TeV, 20.3 fb s = 125.36 GeV H m Standard Model Best fit 68% CL 95% CL
  • Higgs couplings to fermions (κF) and

bosons(κV) are essentially different

  • κγ and κg are expressed in terms of tree-

level coupling factors (no BSM contribution)

  • κF-κV relative sign: ambiguity reduced by

interference from W- and t-loop in H→γγ, negative disfavored at ~ 4.0σ

  • Assume no BSM contribution to κH (total

width)

  • Compatibility with SM prediction: 41%

Fermion vs. boson coupling (1)

κ2

H ≈ 0.25κ2 V + 0.75κ2 F

κ2

γ ≈ 0.07κ2 F (t) + 1.59κ2 V (W ) − 0.66κF κV

V

κ 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

F

κ 4 − 3 − 2 − 1 − 1 2 3 4 ATLAS

  • 1

= 7 TeV, 4.5-4.7 fb s

  • 1

= 8 TeV, 20.3 fb s = 125.36 GeV

H

m γ γ → H ZZ* → H WW* → H τ τ → H bb → H Combined SM 68% CL Best fit 95% CL

κV = 1.09 ± 0.07 κF = 1.11 ± 0.16

11

Ref: arXiv:1507.04548

slide-12
SLIDE 12

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

0.5 1 1.5 2 2.5

ΓSM

H

ΓH = 1.07+0.27 −0.21

(95%CL) BRi.,u. < 0.13 κF = 1.05 ± 0.16 (95%CL) κV > 0.93 Parameter value

ATLAS

√s = 7 TeV, 4.5 − 4.7 fb

−1

√s = 8 TeV, 20.3 fb

−1

mH = 125.36 GeV 68% CL: 95% CL: κV < 1

ΓSM H ΓH = 1.38+1.35 −0.31

(95%CL) BR i.,u. < 0.52 κF = 1.17+0.25

−0.16

κV = 1.13+0.23

−0.07

κon = κoff

ΓSM H ΓH = 1.23+0.30 −0.26

κF = 1.11 ± 0.16 κV = 1.09 ± 0.07

BRi.,u. = 0

Fermion vs. boson coupling (II)

  • Add BRi.,u. as a free parameter to the

κV-κF model: allow variation in SM coupling and the total width, with additional (weaker) constraints:
 


  • κV < 1, OR
  • κon-shell = κoff-shell (coupling strength of
  • ff-shell Higgs from H → WW*/ZZ*

above 2mW/2mZ)

  • Weaker constraints on Higgs width

from off-shell (95% C.L on BRi.,u.):

  • κV < 1: BRi.,u. < 0.13
  • off-shell: BRi.,u. < 0.52

Compatibility with SM prediction:

  • κV < 1: 99%
  • off-shell: 29%

κ2

H =

κ2

H,SM(κV , κF )

(1 − BRi.,u.)

12

Ref: arXiv:1507.04548

slide-13
SLIDE 13

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

Fermion vs. boson coupling (III)

VV

κ 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

FV

λ 0.6 0.8 1 1.2 1.4 1.6 1.8 ATLAS

  • 1

= 7 TeV, 4.5-4.7 fb s

  • 1

= 8 TeV, 20.3 fb s = 125.36 GeV

H

m Standard Model Best fit 68% CL 95% CL

λF V = 1.02+0.15

−0.13

κV V = 1.07+0.14

−0.13

  • Remove the assumption on κH, which provides strong constraint on the

fermion coupling

  • Compatibility with SM prediction: 41% 


λF V = κF /κV , κV V = κ2

V /κH

κ2

H ≈ 0.25κ2 V + 0.75κ2 F

FV

λ )

FV

λ ( Λ

  • 2 ln

5 10 15 20 25 30 2.5 − 2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 2.5 ATLAS

SM expected Observed

  • 1

= 7 TeV, 4.5-4.7 fb s

  • 1

= 8 TeV, 20.3 fb s ]

FV

λ ,

VV

κ [

13

Ref: arXiv:1507.04548

slide-14
SLIDE 14

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

lq

λ )

lq

λ ( Λ

  • 2 ln

5 10 15 20 25 30 2.5 − 2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 2.5 ATLAS

SM expected Observed
  • 1
= 7 TeV, 4.5-4.7 fb s
  • 1
= 8 TeV, 20.3 fb s ] lq λ , Vq λ , qq κ [

λlq ∈ [−1.34, −0.94] ∪ [0.94, 1.34]

  • Up-down-type fermion symmetry: test

extension of Standard Model (certain Two-Higgs-Doublet Models)

  • Compatibility with SM prediction: 51%
  • Evidence of Higgs coupling to down-

type: 4.5σ

Fermion coupling sector

du

λ )

du

λ ( Λ

  • 2 ln

5 10 15 20 25 30 2.5 − 2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 2.5 ATLAS

SM expected Observed
  • 1
= 7 TeV, 4.5-4.7 fb s
  • 1
= 8 TeV, 20.3 fb s ] du λ , Vu λ , uu κ [

λdu ∈ [−1.08, −0.81] ∪ [0.75, 1.04]

λdu = κd/κu

λlq = κl/κq

  • Quark-lepton symmetry
  • Compatibility with SM prediction: 53%
  • Evidence of Higgs coupling to lepton:

4.4σ

14

Ref: arXiv:1507.04548

slide-15
SLIDE 15

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

0.5 1 1.5 2 2.5 3 (95%CL) κZγ < 3.3 κ = 1.12 ± 0.12 κγ = 1.00 ± 0.12 Parameter value

ATLAS

√s = 7 TeV, 4.5 − 4.7 fb−1 √s = 8 TeV, 20.3 fb

−1

mH = 125.36 GeV 68% CL: 95% CL: BRi.,u. = 0

BSM contribution to loop processes

  • Higgs loop-induced processes are very

sensitive to heavy unknown particles: promising probes for potential BSM contribution

  • Effective coupling to gluon(κg), γ(κγ) and

Zγ(κΖγ)

  • Assume no BSM contribution to all other

couplings (scale factors fixed to 1) and decay width

  • Compatibility with SM prediction: 69%
γ

κ 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4

g

κ 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 ATLAS

  • 1
= 7 TeV, 4.5-4.7 fb s
  • 1
= 8 TeV, 20.3 fb s = 125.36 GeV H m Standard Model Best fit 68% CL 95% CL

κg κγ,κΖγ

t/b g g H

t/b ¯ t/¯ b t/b H γ γ/Z

W ± W − W + H γ γ/Z W ± W ± H γ γ/Z

15

Ref: arXiv:1507.04548

slide-16
SLIDE 16

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

0.5 1 1.5 2 2.5 3

ΓSM H ΓH = 1.03+0.13 −0.03

(95%CL) BRi.,u. < 0.27 (95%CL) κZγ < 3.3 κ = 1.12+0.14

−0.11

κγ = 1.00 ± 0.12 Parameter value

ATLAS

√s = 7 TeV, 4.5 − 4.7 fb−1 √s = 8 TeV, 20.3 fb−1 mH = 125.36 GeV 68% CL: 95% CL:

BSM Contribution to total width and loop processes (I)

  • Add BRi.,u. as a free parameter to allow

variation of total width
 


  • Effective coupling to gluon(κg), γ(κγ) and

Zγ(κΖγ)

  • Assume no BSM contribution to all other

couplings (scale factors fixed to 1)

  • Constraint on Higgs width mostly by

VBF and VH production: BRi.,u. < 0.27 (95% CL)

  • Compatibility with SM prediction: 74%

κ2

H =

κ2

H,SM(1, κg, κγ, κZγ)

(1 − BRi.,u.)

i.,u.

BR )

i.,u.

(BR Λ

  • 2 ln

5 10 15 20 25 30 0.8 − 0.6 − 0.4 − 0.2 − 0.2 0.4 0.6 0.8 ATLAS

SM expected Observed
  • 1
= 7 TeV, 4.5-4.7 fb s
  • 1
= 8 TeV, 20.3 fb s ] i.,u. ,BR γ Z κ , g κ , γ κ [

16

Ref: arXiv:1507.04548

slide-17
SLIDE 17

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

0.5 1 1.5 2 2.5 3 3.5

ΓSM

H

ΓH = 1.05+0.34 −0.25

(95%CL) BRi.,u. < 0.27 (95%CL) κZγ < 3.3 κ = 1.13+0.21

−0.18

κγ = 1.00 ± 0.13 κF = 1.01 ± 0.19 (95%CL) κV > 0.85 Parameter value

ATLAS

√s = 7 TeV, 4.5 − 4.7 fb−1 √s = 8 TeV, 20.3 fb

−1

mH = 125.36 GeV 68% CL: 95% CL: κV < 1

ΓS M H ΓH = 1.23+1.45 −0.34

(95%CL) BRi.,u. < 0.54 (95%CL) κZγ < 4.3 κ = 1.18+0.31

−0.16

κγ = 1.05+0.29

−0.15

κF = 1.08+0.29

−0.20

κV = 1.08+0.25

−0.11

κon = κoff

BSM Contribution to total width and loop processes (II)

  • Add BRi.,u. as a free parameter to the

κV-κF model: allow variation in SM coupling and the total width, with additional constraints:

  • κV < 1, OR
  • κon-shell = κoff-shell
  • Simultaneously probe BSM contribution

to loop induced processes via effective coupling κγ, κg and κZγ

  • Weaker constraints on Higgs width

from off-shell (95% C.L on BRi.,u.):

  • κV < 1: BRi.,u. < 0.27
  • off-shell: BRi.,u. < 0.54

Compatibility with SM prediction:

  • κV < 1: 96%
  • off-shell: 64%

17

Ref: arXiv:1507.04548

slide-18
SLIDE 18

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 (95%CL) |κμ| < 2.28 κτ ∈ [−1.22, −0.80] ∪[0.80, 1.22] κb ∈ [−0.90, −0.33] ∪[0.28, 0.96] κ = 0.94 ± 0.21 κZ ∈ [−1.06, −0.82] ∪[0.84, 1.12] κW = 0.91 ± 0.14 Parameter value

ATLAS

√s = 7 TeV,4.5 − 4.7 fb−1 √s = 8 TeV,20.3 fb−1 mH = 125.36 GeV 68% CL: 95% CL: BRi.,u. = 0

Generic model I: SM loops and total width

  • Generic model of tree-level coupling

factors, with 2 assumptions:

  • No BSM contribution to loop-induced

processes

  • No BSM contribution to total width
  • Compatibility with SM prediction: 57%

Particle mass [GeV]

  • 1

10 1 10

2

10 v

V

m

V

κ

  • r

v

F

m

F

κ

  • 3

10

  • 2

10

  • 1

10 1 Z W t b τ µ ATLAS

  • 1

= 7 TeV, 4.5-4.7 fb s

  • 1

= 8 TeV, 20.3 fb s Observed SM Expected

  • Reduced coupling strength scale factor:

linear ~ mi
 


  • ν: vacuum expectation value of Higgs

field

yV,i = √κV,i mV,i ν yF,i = κF,i mF,i ν

18

κW assumed positive by convention Ref: arXiv:1507.04548

slide-19
SLIDE 19

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

Generic model II: variation in loop and total width

  • Generic model of tree-level and

effective loop coupling factors, allowing variation in loop processes and total width

  • Additional constraints when total width

variation is allowed:

  • κV < 1, OR
  • κon-shell = κoff-shell
  • Compatibility with SM prediction:
  • BRi.u. = 0: 73%
  • κV < 1: 80%
  • κon-shell = κoff-shell: 57%

2 − 1 − 1 2 3

ΓSM

H

ΓH

BRi.,u. κZγ κ κγ κμ κτ κb κ κZ κW Parameter value

ATLAS

√s = 7 TeV, 4.5 − 4.7 fb

−1

√s = 8 TeV, 20.3 fb

−1

mH = 125.36 GeV 68% CL: 95% CL: κV < 1 BRi.,u. = 0 κon = κoff

19

Parameter boundaries Ref: arXiv:1507.04548

slide-20
SLIDE 20

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

t

κ )

t

κ ( Λ

  • 2 ln

2 4 6 8 10 12 14 16 18 20 2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 ATLAS

  • Obs. tH
  • Exp. tH
ggZH κ
  • Obs. tH,
γ Z κ , γ κ , g κ , ggZH κ
  • Exp. tH,
g κ , ggZH κ
  • Obs. tH,
γ Z κ , γ κ , g κ , ggZH κ
  • Obs. tH,
  • 1

= 7 TeV, 4.5-4.7 fb s

  • 1

= 8 TeV, 20.3 fb s

Coupling sign sensitivity: κt

ggZH

t/b g g Z H t/b Z g g Z H

tH: tHjb

g q ¯ b q0 t H g q ¯ b q0 t H
  • Sign sensitivity of κt: negative solution

strongly disfavored at 3.1σ (exp. 2.9σ)

  • + resolve ggZH: little information on κt
  • + resolve ggF: more precise κt, but reduce

sign sensitivity

  • + resolve γ and Ζγ loop: greatly improve

sign sensitivity but little contribution to the precision of |κt|

tH:WtH

b g W H t b g t H W

20

Ref: arXiv:1507.04548

slide-21
SLIDE 21

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

2 − 1 − 1 2 3 (95%CL) λ(Zγ)Z < 3.2 λγZ = 0.90 ± 0.15 (95%CL) λμZ < 2.3 λτZ = 0.99+0.23

−0.19

λbZ = 0.60 ± 0.27 λ ∈ [−1.70, −1.07] ∪[1.03, 1.73] λWZ ∈ [−1.04, −0.81] ∪[0.80, 1.06] λZ = 1.09+0.26

−0.22

κ Z = 1.18 ± 0.16 Parameter value

ATLAS

√s = 7 TeV,4.5 − 4.7 fb−1 √s = 8 TeV,20.3 fb−1 mH = 125.36GeV 68% CL: 95% CL:

Generic Model III: coupling ratios

  • Most generic model (coupling ratios) with no

assumption on loop processes or total width

  • Probe custodial symmetry: W and Z bosons

have related couplings to the Higgs boson


  • Sign sensitivity from tH and ggZH

production modes: negative solution disfavored at 0.5σ (exp. 0.3σ)

  • Compatibility with SM prediction: 73%

gHVV ∼ m2

V/VEV

λij = κi/κj, κii = κ2

i /κH

21

Ref: arXiv:1507.04548 Parameter boundaries

slide-22
SLIDE 22

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

Conclusion

  • Higgs physics is in the precise measurement phase
  • ATLAS combined mass measurement:

  • Evidence of production processes:

VBF(4.3σ), WH(2.1σ), ZH(0.9σ), ttH(2.5σ)

  • Coupling measurements are consistent with SM expectation at

the level of 2σ or better for all models considered

  • The combined coupling measurement of both ATLAS and CMS

experiment is ongoing.

  • More precise measurement will be achieved with data from the
  • ngoing Run II

mγγ+4l

H

= 125.36 ± 0.37(stat) ± 0.18(sys) GeV mγγ+4l

H

= 125.36 ± 0.37(stat) ± 0.18(sys) GeV mγγ+4l

H

= 125.36 ± 0.37(stat) ± 0.18(sys) GeV

22

slide-23
SLIDE 23

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

Backup

23

slide-24
SLIDE 24

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

Bibliography

  • All results discussed in this presentation can be found at

Measurement of the Higgs boson mass from the H → γγ and H → ZZ* → 4l channels with the ATLAS detector at the LHC


  • Phys. Rev. D. 90, 052004 (2014)

and Measurements of the Higgs boson production and decay rates and couplings using pp collision data at sqrt(s) = 7 and 8 TeV in the ATLAS experiment
 arXiv:1507.04548 (submitted to EPJC)

24

slide-25
SLIDE 25

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

[GeV]

l 4

m 80 90 100 110 120 130 140 150 160 170 Events / 2.5 GeV 5 10 15 20 25 30 35

Data = 1.50) µ = 125.4 GeV H Signal (m Background ZZ* t Background Z+jets, t Systematic uncertainty

l 4 → ZZ* → H

  • 1
Ldt = 4.5 fb

∫

= 7 TeV: s
  • 1
Ldt = 20.3 fb

∫

= 8 TeV: s

ATLAS

m4l

H = 124.51 ± 0.52(stat) ± 0.06(sys) GeV

[GeV]

H

m 123 123.5 124 124.5 125 125.5 126 126.5 127 127.5 Λ

  • 2ln

1 2 3 4 5 6 7

σ 1 σ 2

ATLAS

  • 1

Ldt = 4.5 fb

∫

= 7 TeV s

  • 1

Ldt = 20.3 fb

∫

= 8 TeV s

l +4 γ γ Combined γ γ → H l 4 → ZZ* → H without systematics

Prerequisite: combined mass measurement

[GeV] γ γ m 110 120 130 140 150 160 weights - fitted bkg ∑
  • 8
  • 6
  • 4
  • 2
2 4 6 8 weights / GeV ∑ 20 40 60 80 100 120 140 160 180 200 Data Combined fit: Signal+background Background Signal = 7 TeV s
  • 1
Ldt = 4.5 fb ∫ = 8 TeV s
  • 1
Ldt = 20.3 fb ∫ s/b weighted sum Mass measurement categories ATLAS

mγγ

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

  • Precise mass measurement: a prerequisite of coupling

measurements

  • Higgs mass: last unconstrained parameter in Standard

Model


  • Improvements:
  • Energy calibration → better mass resolution
  • Analyses dedicated to mass measurement

mγγ+4l

H

= 125.36 ± 0.37(stat) ± 0.18(sys) GeV mγγ+4l

H

= 125.36 ± 0.37(stat) ± 0.18(sys) GeV mγγ+4l

H

= 125.36 ± 0.37(stat) ± 0.18(sys) GeV

25

Ref: Phys. Rev. D. 90, 052004 (2014)

slide-26
SLIDE 26

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

Coupling model parametrization

Production Loops Interference Expression in fundamental coupling-strength scale factors σ(ggF) X b–t κ2

g ⇠

1.06 · κ2

t + 0.01 · κ2 b 0.07 · κtκb

σ(VBF)

  • ⇠

0.74 · κ2

W + 0.26 · κ2 Z

σ(WH)

  • ⇠

κ2

W

σ(q¯ q ! ZH)

  • ⇠

κ2

Z

σ(gg ! ZH) X Z–t κ2

ggZH ⇠

2.27 · κ2

Z + 0.37 · κ2 t 1.64 · κZκt

σ(bbH)

  • ⇠

κ2

b

σ(ttH)

  • ⇠

κ2

t

σ(gb ! WtH)

  • W–t

⇠ 1.84 · κ2

t + 1.57 · κ2 W 2.41 · κtκW

σ(qb ! tHq0)

  • W–t

⇠ 3.4 · κ2

t + 3.56 · κ2 W 5.96 · κtκW

Partial decay width Γb¯

b

  • ⇠

κ2

b

ΓWW

  • ⇠

κ2

W

ΓZZ

  • ⇠

κ2

Z

Γττ

  • ⇠

κ2

τ

Γµµ

  • ⇠

κ2

µ

Γγγ X W–t κ2

γ ⇠

1.59 · κ2

W + 0.07 · κ2 t 0.66 · κWκt

ΓZγ X W–t κ2

Zγ ⇠

1.12 · κ2

W + 0.00035 · κ2 t 0.12 · κWκt

Total decay width ΓH X W t b t κ2

H ⇠

0.57 · κ2

b + 0.22 · κ2 W + 0.09 · κ2 g+

0.06 · κ2

τ + 0.03 · κ2 Z + 0.03 · κ2 c+

0.0023 · κ2

γ + 0.0016 · κ2 Zγ + 0.00022 · κ2 µ

26

slide-27
SLIDE 27

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

  • Likelihood function constructed for each individual channel

  • Combination by taking product of the likelihood of individual

channels and correlating systematics, if necessary


  • Hypothesis testing based on the profile likelihood ratio

Statistical Procedure

conditional minimum for a given μ unconditional(global) minimum

Λ(µ) = L(µ, ˆ ˆ θ(µ)) L(ˆ µ, ˆ θ)

not simple product of gp,c individual likelihood excluding constraint

L(D|ν, θ) = Y

c

˜ Lc(Dc|νc, θc) Y

p

gp(ap|θp)

expected evt # systematics: nuisance parameter (NP) constraint on NPs

  • bserved evt #
  • bservable

estimated central value of θp,c

Lc(Dc|νc, θc) = Pois(nc|νc)

nc

Y

ec=1

fc(xec|θc) · Y

p

gp,c(ap,c|θp,c)

μ: parameter of interest, e.g

  • signal strength (μi)
  • mass (mH) and mass difference (ΔmH)
  • coupling scale factors λi, κi

27

slide-28
SLIDE 28

Fangzhou Zhang (UW Madison) 2015 DPF Meeting, Ann Arbor

Formulae for Various Measurements

  • Likelihood for combined mass measurement:
  • Likelihood for consistency check of mass measurements:
  • SM loop-induced processes:
  • SM total Higgs decay width:
  • Expected event yield:

Λ(mH) = L(mH, ˆ ˆ µγγ(mH), ˆ ˆ µ4l(mH), ˆ ˆ θ(mH)) L( ˆ mH, ˆ µγγ, ˆ µ4l, ˆ θ) Λ(∆mH) = L(∆mH, ˆ ˆ µγγ(∆mH), ˆ ˆ µ4l(∆mH), ˆ ˆ mH(∆mH), ˆ ˆ θ(∆mH)) L( ˆ ∆mH, ˆ µγγ, ˆ µ4l, ˆ mH, ˆ θ)

κ2

γ(g) =

P

i,j κiκjΓij γγ(gg)

P

i,j Γij γγ(gg)

i, j ∈ ( {t, b} for κg {t, b, l, W} for κγ

κ2

H =

X

x

κ2

x · BRSM(H → xx)

nk

signal =

X

i

µi⇥i,SM × Ak

if × k if

! × µf × Bf,SM × L → µ = µi · µf

28