Discovery of the Higgs boson and most recent measurements at …repodip.fisica.unimi.it/cdip17/talks/1_3_MFanti... · 2018-06-27 · Discovery of the Higgs boson and most recent measurements

Discovery of the Higgs boson

and most recent measurements

at the LHC

Marcello Fanti

(on behalf of the ATLAS-Mi group)

University of Milano and INFN

M. Fanti (Physics Dep., UniMi) title in footer 1 / 35

July 4th, 2012 – the discovery!

“we have a discovery”

ATLAS and CMS observed a “new signal”:

incompatibility with background-only hypothesis was 5σ (CMS) and 6σ (ATLAS)


July 4th, 2012 – the discovery!

“we have a discovery”

What is this? Is it indeed the Higgs boson?. . . and if so, why is it so important?


Symmetries, gauge theories (just a glance. . . )

All interactions (strong, electroweak) are driven by sym-

metry principles:

strong interaction ⇐⇒ “color” symmetry

electroweak interaction ⇐⇒ “isospin” symmetry

⇒ very predictive, only few assumptions

u

d

ν

e

All interactions are reducible to combinations of few elementary processes:

⇒ renormalizable at all perturbative orders, UV-safe, all desirable theory properties . . .


Symmetries, gauge theories (just a glance. . . )

All interactions (strong, electroweak) are driven by sym-

metry principles:

strong interaction ⇐⇒ “color” symmetry

electroweak interaction ⇐⇒ “isospin” symmetry

⇒ very predictive, only few assumptions

u

d

ν

e

All interactions are reducible to combinations of few elementary processes:

⇒ renormalizable at all perturbative orders, UV-safe, all desirable theory properties . . .

BUT: all this works only if all masses are = 0 — masses break gauge symmetries!


The Higgs mechanism and the Higgs boson

A new quantum field φ, with charge = 0 and spin = 0, is postulated, whose

potential U(φ) has a minimum at φ 6= 0

⇒ the vacuum is characterized by a non-vanishing field, interacting with other

particles






particles

Such interactions modify particles’ energies and momenta such to provide a mass (recall: m =√E 2 − p2)

⇒ particles acquire mass dynamically (gauge symmetry is preserved!)

⇒ particles can excite the Higgs field, thus producing an observable quantum: the Higgs particle






particles

Such interactions modify particles’ energies and momenta such to provide a mass (recall: m =√E 2 − p2)

⇒ particles acquire mass dynamically (gauge symmetry is preserved!)

⇒ particles can excite the Higgs field, thus producing an observable quantum: the Higgs particle

The observation of such a particle is the experimental proof of the Higgs mechanism


Observation of the Higgs boson


The LHC

Month in YearJan Apr Jul

Oct

]1

De

live

red

Lu

min

osity [

fb

0

5

10

15

20

25

30

35

40

45

ATLAS Online Luminosity = 7 TeVs2011 pp

= 8 TeVs2012 pp

= 13 TeVs2015 pp

= 13 TeVs2016 pp

= 13 TeVs2017 pp

initia

l 2017 c

alib

ratio

n

Located near Geneva,

27 km long, 100 m underground

Proton beams accelerated to 6.5 TeV

⇒ colliding at 13 TeV

≈ 1014 protons / beam (≈ 1011 protons / bunch)

bunches collide every 25 ns

⇒ 40 millions collisions/s

Peak luminosity ≈ 1034 cm−2s−1


The LHC

Month in YearJan Apr Jul

Oct

]1

De

live

red

Lu

min

osity [

fb

0

5

10

15

20

25

30

35

40

45

ATLAS Online Luminosity = 7 TeVs2011 pp

= 8 TeVs2012 pp

= 13 TeVs2015 pp

= 13 TeVs2016 pp

= 13 TeVs2017 pp

initia

l 2017 c

alib

ratio

n


ATLAS and CMS

ATLASCMS


ATLAS and CMS

ATLASCMS

Characteristics

multi-purpose experiments, made of several nested

detectors

full solid angle coverage, high granularity (millions of

electronics channels)

fast data acquisition (every 25 ns)

high radiation hardness


ATLAS and CMS

ATLASCMS

Characteristics

multi-purpose experiments, made of several nested

detectors

full solid angle coverage, high granularity (millions of

electronics channels)

fast data acquisition (every 25 ns)

high radiation hardness

A little of history

conceived in 1992, approved in 1995

construction started in 1997

tests of prototypes at test beams: 1998 – 2004

assembly and installation: 2003 – 2007

tests with cosmic rays: 2008 – 2009

start of operation at LHC: end 2009


Identifying particles

Only few particles are stable, or “quasi-stable” : e±, γ, π±, p, p, n, n,K 0L , µ

±

(i.e. living long enough to cross the full detector)


Identifying particles

Only few particles are stable, or “quasi-stable” : e±, γ, π±, p, p, n, n,K 0L , µ

±

(i.e. living long enough to cross the full detector)

Most heavy particles decay quickly

to lighter ones:

⇒ need to identify decay products

and infer the original particle


Typical “events” at LHC

Proton beams collide every 25 ns:

up to ∼50 proton-proton

interactions

hundreds of particles are

produced

p −→ ←− p





interactions


produced

p −→ ←− p

ZZ → e+e−µ+µ−





interactions


produced

p −→ ←− p

ZZ → e+e−µ+µ− multi-jet event





interactions


produced

p −→ ←− p

ZZ → e+e−µ+µ− multi-jet event

A tiny fraction of such “events” (≈ 1 in 10 billions) is a Higgs boson


How to observe the Higgs boson: decay modes

[GeV]HM80 100 120 140 160 180 200

Hig

gs B

R +

Tota

l U

ncert

[%

]

410

310

210

110

1

LH

C H

IGG

S X

S W

G 2

01

3

bb

ττ

µµ

cc

gg

γγ γZ

WW

ZZ



[GeV]HM80 100 120 140 160 180 200

Hig

gs B

R +

Tota

l U

ncert

[%

]

410

310

210

110

1

LH

C H

IGG

S X

S W

G 2

01

3

bb

ττ

µµ

cc

gg

γγ γZ

WW

ZZ

Most common decay modes ( H → bb, H → τ+τ− ) are

very difficult, due to large hadronic background.



[GeV]HM80 100 120 140 160 180 200

Hig

gs B

R +

Tota

l U

ncert

[%

]

410

310

210

110

1

LH

C H

IGG

S X

S W

G 2

01

3

bb

ττ

µµ

cc

gg

γγ γZ

WW

ZZMost common decay modes ( H → bb, H → τ+τ− ) are

very difficult, due to large hadronic background.

More suitable are:

H → BR pros/cons

γγ 0.002 good mass resolution, S/B ' 0.02

ZZ → 4` 0.0001 good mass resolution, S/B ' 1

WW → `ν`ν 0.009 cannot measure mass


Best discovery channels

H → γγ candidate at CMS H → ZZ ∗ → e+e−µ+µ− candidate at ATLAS

Fully reconstructed final states with good energy resolution


Invariant mass plots

H → γγ decay channel

mγγ =

√(Eγ1 + Eγ2)2 − |~pγ1 + ~pγ2|2

(mγγ peaks at mH if γγ are from Higgs)

[GeV]γγm

110 120 130 140 150 160

data

- fi

tted

bkg

-200

-100

0

100

200

Eve

nts

/ GeV

0

1000

2000

3000

4000

5000

Data

Signal+background

Background

Signal

= 7 TeVs, -1dt = 4.5 fb L∫ = 8 TeVs, -1dt = 20.3 fb L∫

Unweighted sum

ATLAS

H → 4` decay channel

m4` =

√√√√( 4∑`=1

E`

)2

−

∣∣∣∣∣4∑`=1

~p`

∣∣∣∣∣2

(m4` peaks at mH if 4` are from Higgs)

[GeV]4l

m100 150 200 250

Eve

nts

/5 G

eV

0

5

10

15

20

25

30

35

40

1Ldt = 4.6 fb∫ = 7 TeV s1Ldt = 20.7 fb∫ = 8 TeV s

4l→ZZ*→H

Data 2011+ 2012

SM Higgs Boson

=124.3 GeV (fit)H m

Background Z, ZZ*

tBackground Z+jets, t

Syst.Unc.

ATLAS

(GeV)l4m80 100 120 140 160 180

Eve

nts

/ 3 G

eV0

5

10

15

20

25

30

35 Data

Z+X

,ZZ*γZ

=126 GeVHm

CMS-1 = 8 TeV, L = 19.7 fbs ; -1 = 7 TeV, L = 5.1 fbs


The Higgs mass

[GeV]Hm123 124 125 126 127 128 1290.5−

9

Total Stat. Syst.CMS and ATLAS Run 1LHC Total Stat. Syst.

l+4γγ CMS+ATLAS 0.11) GeV± 0.21 ± 0.24 ( ±125.09

l 4CMS+ATLAS 0.15) GeV± 0.37 ± 0.40 ( ±125.15

γγ CMS+ATLAS 0.14) GeV± 0.25 ± 0.29 ( ±125.07

l4→ZZ→H CMS 0.17) GeV± 0.42 ± 0.45 ( ±125.59

l4→ZZ→H ATLAS 0.04) GeV± 0.52 ± 0.52 ( ±124.51

γγ→H CMS 0.15) GeV± 0.31 ± 0.34 ( ±124.70

γγ→H ATLAS 0.27) GeV± 0.43 ± 0.51 ( ±126.02


The Higgs mass

[GeV]Hm123 124 125 126 127 128 1290.5−

9

Total Stat. Syst.CMS and ATLAS Run 1LHC Total Stat. Syst.

l+4γγ CMS+ATLAS 0.11) GeV± 0.21 ± 0.24 ( ±125.09

l 4CMS+ATLAS 0.15) GeV± 0.37 ± 0.40 ( ±125.15

γγ CMS+ATLAS 0.14) GeV± 0.25 ± 0.29 ( ±125.07

l4→ZZ→H CMS 0.17) GeV± 0.42 ± 0.45 ( ±125.59

l4→ZZ→H ATLAS 0.04) GeV± 0.52 ± 0.52 ( ±124.51

γγ→H CMS 0.15) GeV± 0.31 ± 0.34 ( ±124.70

γγ→H ATLAS 0.27) GeV± 0.43 ± 0.51 ( ±126.02

Once mH is measured, all other

properties can be predicted

⇒ can test the Higgs sector

cross-section decay width branching ratios

[GeV] HM100 200 300 400 500 600 700 800 900 1000

H+

X)

[pb]

→(p

p

σ

110

1

10

210

LH

C H

IGG

S X

S W

G 2

012

=14 TeV

s

H+X at

→

pp

=8 TeV

s

H+X at

→

pp

=7 TeV

s

H+X at

→

pp

[GeV]HM

100 200 300 1000

[G

eV

]H

Γ

210

110

1

10

210

310

LH

C H

IGG

S X

S W

G 2

010

500

[GeV]HM100 200 300 400 500 1000

Hig

gs B

R +

Tota

l U

ncert

310

210

110

1

LH

C H

IGG

S X

S W

G 2

011

bb

ττ

cc

ttgg

γγ γZ

WW

ZZ


Properties of the Higgs boson


Cross-section measurements

Total cross-section vs√s (γγ and 4` combined)

[TeV] s

7 8 9 10 11 12 13

[pb]

H

→p

pσ

0

20

40

60

80

100 ATLAS Preliminary = 125.09 GeVH

m H→pp

σ

QCD scale uncertainty

)s

α PDF+⊕(scale Tot. uncert. γγ→H l4→*ZZ→H

comb. data syst. unc.

1 = 7 TeV, 4.5 fbs1 = 8 TeV, 20.3 fbs

*)ZZ (1), 14.8 fbγγ (1 = 13 TeV, 13.3 fbs


Higgs production modes at the LHC

[TeV] s6 7 8 9 10 11 12 13 14 15

H+

X)

[pb

]

→

(pp

σ

2−10

1−10

1

10

210 M(H)= 125 GeV

LH

C H

IGG

S X

S W

G 2

01

6

H (N3LO 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, t-ch + s-ch)

→pp

QCD production EW production

Experimental identification of VBF and VH productions (“tagging”):

τ+

τ−

forwardtag jet

forwardtag jet

pp

µ+

µ−

pp

b-jet

b-jet


Couplings measurements

According to SM, the Higgs couplings are gSMf =

mf

υand gSM

V = 2m2

V

υ

i o

H

i o

κ gi iSM κ go o

SM Couplings are accessible through production (ii → H) and decay (H → oo)

⇒ Several couplings: gµ, gτ , gb, gW , gZ , gt

g

g

Ht, b

H

�

�

H

�

�

W W

H

�

�

t

gluons and photons are massless

⇒ no direct ggH , Hγγ couplings

gg → H through top/bottom virtual loop

⇒ mainly driven by gt , gb

H → γγ through top/bottom and W virtual loops

⇒ mainly driven by gW , gt , gb


Couplings measurements

According to SM, the Higgs couplings are gSMf =

mf

υand gSM

V = 2m2

V

υ

Particle mass [GeV]1−10 1 10 210

vVm

Vκ o

r vF

mFκ

4−10

3−10

2−10

1−10

1W

tZ

b

µ

τ

ATLAS+CMS

SM Higgs boson

] fitε[M,

68% CL

95% CL

Run 1 LHCCMS and ATLAS

decay measure plot

fermions gf gf

bosons gV

√gV2υ

⇒ all scale likem

υas expected,

over > 3 orders of magnitude!

⇒ distinctive signatureof the Higgs mechanism!


Spin

H → γγ: H →WW ∗ → `ν`ν:

Hm

1

m2

Hm

1

m2

W+

W+

W−

W−

l−

l+

l−

l+

ν

ν−

ν−

ν

H → ZZ∗ → 4`:

Spin can be probed

from angular distributions

of decay products


Spin

H → γγ: H →WW ∗ → `ν`ν:

Hm

1

m2

Hm

1

m2

W+

W+

W−

W−

l−

l+

l−

l+

ν

ν−

ν−

ν

H → ZZ∗ → 4`:

Observation of H → γγ decay

excludes spin-1

⇒ test spin-0 against spin-2


Spin

H → γγ: H →WW ∗ → `ν`ν:

Hm

1

m2

Hm

1

m2

W+

W+

W−

W−

l−

l+

l−

l+

ν

ν−

ν−

ν

H → ZZ∗ → 4`:

Use likelihood-ratio test statistic

q ≡ 2 ln

(L(spin-0)

L(spin-2)

)

q~-30 -20 -10 0 10 20 30

Arb

itrar

y no

rmal

isat

ion

-510

-410

-310

-210

-110

1

10

210

310ATLAS l 4→ ZZ* →H

-1 = 7 TeV, 4.5 fbs-1 = 8 TeV, 20.3 fbs

νµνe → WW* →H -1 = 8 TeV, 20.3 fbs

γγ →H -1 = 7 TeV, 4.5 fbs

-1 = 8 TeV, 20.3 fbs

Data SM+0

)gκ=qκ( +2


Spin

H → γγ: H →WW ∗ → `ν`ν:

Hm

1

m2

Hm

1

m2

W+

W+

W−

W−

l−

l+

l−

l+

ν

ν−

ν−

ν

H → ZZ∗ → 4`:

Use likelihood-ratio test statistic

q ≡ 2 ln

(L(spin-0)

L(spin-2)

)

q~-30 -20 -10 0 10 20 30

Arb

itrar

y no

rmal

isat

ion

-510

-410

-310

-210

-110

1

10

210


-1 = 7 TeV, 4.5 fbs-1 = 8 TeV, 20.3 fbs

νµνe → WW* →H -1 = 8 TeV, 20.3 fbs

γγ →H -1 = 7 TeV, 4.5 fbs

-1 = 8 TeV, 20.3 fbs

Data SM+0

)gκ=qκ( +2

⇒ data favour spin-0


Summary


Present measurements

The Higgs boson was discovered, now we are in the middle of the Higgs measurements era.

[TeV] s

7 8 9 10 11 12 13

[pb]

H

→pp

σ

0

20

40

60

80


m H→pp

σ


)s



1 = 7 TeV, 4.5 fbs1 = 8 TeV, 20.3 fbs

*)ZZ (1), 14.8 fbγγ (1 = 13 TeV, 13.3 fbs


vVm

Vκ o

r vF

mFκ

4−10

3−10

2−10

1−10

1W

tZ

b

µ

τ

ATLAS+CMS

SM Higgs boson

] fitε[M,

68% CL

95% CL


q~-30 -20 -10 0 10 20 30

Arb

itrar

y no

rmal

isat

ion

-510

-410

-310

-210

-110

1

10

210


-1 = 7 TeV, 4.5 fbs-1 = 8 TeV, 20.3 fbs

νµνe → WW* →H -1 = 8 TeV, 20.3 fbs

γγ →H -1 = 7 TeV, 4.5 fbs

-1 = 8 TeV, 20.3 fbs

Data SM+0

)gκ=qκ( +2

⇒ We are still compatible with Standard Model prediction . . . but uncertainties are still large.

Meanwhile, huge effort from theorists to improve their uncertainties [see talk by G.Ferrera].Important to pursue precision measurements in the Higgs sector, to investigate possible deviations from SM


Prospects . . .

Results: ATLAS+CMS, 8 TeV


vVm

Vκ o

r vF

mFκ

4−10

3−10

2−10

1−10

1W

tZ

b

µ

τ

ATLAS+CMS

SM Higgs boson

] fitε[M,

68% CL

95% CL


Expected: 13 TeV, 300 fb−1 and 3000 fb−1(ATLAS only)

iy

310

210

110

1Z

W

t

b

τ

µ

ATLAS Simulation Preliminary

= 14 TeVs

νlνl→WW*→4l, h→ZZ*→, hγγ→h

γZ→, hµµ→bb, h→, hττ→h

]µκ, τκ, bκ, tκ, Wκ, Zκ[

=0i,uBR

1dt = 300 fbL∫1dt = 3000 fbL∫

[GeV]i

m

110 1 10 210

Ratio to S

M

0.8

0.9

1

1.1

1.2

Some “educated guesses” — With 300 fb−1at 13 TeV:

Precise measurements of H → τ+τ−, observation of H → bb, evidence of ttH production

Evidence of H → µ+µ−, precision measurements of all individual κ’s to . 10% accuracyM. Fanti (Physics Dep., UniMi) title in footer 21 / 35

Milano’s involvement


Milano’s involvements

Detector

Detector construction

pixel detector (innermost tracking device)

electromagnetic calorimeter

magnets for muon chambers



Detector





R & D

Electronics: upgrade for high-luminosity phase [talk by

A.Stabile]

Pixel detector: radiation damage studies [poster by

L.Rossini]



Detector





R & D


A.Stabile]


L.Rossini]

In Higgs analyses

H → γγ:

photon energy calibration

photon identification and background treatment

mH and couplings measurement

spin measurement

H → τ+τ−:

measurement of the missing transverse momentum

(recall, τ decays to ντ (invisible!) + other particles)

τ reconstruction

CP measurement [poster by A.Murrone]



Detector





R & D


A.Stabile]


L.Rossini]

In Higgs analyses

H → γγ:

photon energy calibration

photon identification and background treatment

mH and couplings measurement

spin measurement

H → τ+τ−:

measurement of the missing transverse momentum

(recall, τ decays to ντ (invisible!) + other particles)

τ reconstruction

CP measurement [poster by A.Murrone]

More analyses in ATLAS where Milano is involved:

searches for SUSY [poster by S.Carra]

other exotic searches, including Dark Matter [talk by D.D’Angelo]


THANKS FOR YOUR

ATTENTION


More Material


Decay modes of the Higgs boson

All hadronic decay modes (H → bb and H → ZZ ,W +W− → qqqq) are dominant, but overwhelmed by the QCD

backgrounds! ⇒ final states with isolated leptons, photons, missing transverse energy are the only viable

[GeV]HM80 100 120 140 160 180 200

Hig

gs B

R +

Tota

l U

ncert

[%

]

410

310

210

110

1

LH

C H

IGG

S X

S W

G 2

013

bb

ττ

µµ

cc

gg

γγ γZ

WW

ZZ

[GeV]H

M

100 150 200 250

BR

[pb]

× σ

-410

-310

-210

-110

1

10

LH

C H

IGG

S X

S W

G 2

012

= 8TeVs

µl = e,

τν,µν,eν = νq = udscb

bbν± l→WH

bb-l+ l→ZH

b ttb→ttH

-τ+τ →VBF H

-τ+τ

γγ

qqν± l→WW

ν-lν

+ l→WW

qq-l+ l→ZZ

νν-l+ l→ZZ

-l

+l

-l

+ l→ZZ

H → BR σ · BR (fb) events produced mass mH background(@ mH = 125 GeV) with 25 fb−1 resolution range

γγ 2.28 · 10−3 50 1250 ,, . 150 GeV /ZZ ∗ → 4` 1.25 · 10−4 2.7 67 ,, & 130 GeV ,WW ∗ → `ν`ν 1.06 · 10−2 230 5700 /// anywhere /τ+τ− (VBF) 6.32 · 10−2 100 2500 / . 150 GeV //bb (VH, Z → `+`− + W → `ν) 5.77 · 10−1 106 2600 / . 150 GeV //


Cross-section by CMS

Fiducial cross-section vs√s

H → 4`

(TeV) s7 8 9 10 11 12 13 14

[fb]

fidσ

0

1

2

3

4

5

sys. unc.)⊕Data (stat.

Systematic uncertainty

Model dependence

H)→LO gg3 = 125 GeV, NH

Standard model (m

(13 TeV) -1 (8 TeV), 12.9 fb-1 (7 TeV), 19.7 fb-15.1 fb

CMS Preliminary

4l) + X→ (H →pp

H → γγ

(TeV)s7 8 9 10 11 12 13 14

(fb

)fid

.σ

20

30

40

50

60

70

80

90

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.


Couplings: the κ-framework

Reminder: in SM Higgs couplings are gSMf =

mf

υand gSM

V = 2m2

V

υ

i o

H

i o

κ gi iSM κ go o

SM

Couplings are accessible through production (ii → H) and decay (H → oo)

Define “couplings modifiers” κx =gxgSMx

(compatibility with SM ⇐⇒ κ ≈ 1)

⇒ Several couplings: κµ, κτ , κb, κW , κZ , κt and two effective couplings: κg , κγ

g

g

Ht, b

H

�

�

H

�

�

W W

H

�

�

t

gg → H (mainly) through top/bottom virtual loop

⇒ κg depends on κt, κb

H → γγ through top/bottom and W virtual loops

⇒ κγ depends on κt, κb, κW


(Universal) couplings to fermions and weak bosons

Assume weak gauge boson universality: κW , κZ = κV and fermion universality: κt, κb, κτ , κµ = κf

fVκ

0 0.5 1 1.5 2

f Fκ

0

0.5

1

1.5

2

2.5

3

Combinedγγ→H

ZZ→HWW→Hττ→H

bb→H

68% CL 95% CL Best fit SM expected


Exploit final state topologies (e.g.

VBF, VH)

⇒ measure κV , κf for each decay

channel

⇒ then combine decay channels

⇒ all measurements compatible

with SM prediction (F)

(κV = 1, κf = 1)


Testing the ggH and Hγγ interactions

g

g

H

H

�

�

H

�

�

H

�

�

ggH and Hγγ interactions in SM are mediated by loops

⇒ particularly sensitive to new particles in the loops

γκ0.6 0.8 1 1.2 1.4 1.6

gκ

0.6

0.8

1

1.2

1.4

1.6Run 1 LHC

CMS and ATLAS ATLAS+CMS

ATLAS

CMS


⇒ consider κg , κγ as free and profile others

⇒ again, compatibility with SM (F)


Couplings: the κ-framework

Reminder: in SM Higgs couplings are gSMf =

mf

υand gSM

V = 2m2

V

υand σSMii→H→oo ∝

ΓiiΓoo

ΓH

i o

H

i o

κ gi iSM κ go o

SM

Couplings are accessible through production (ii → H) and decay (H → oo)

Define “couplings modifiers” κx =gxgSMx

and κ2H

def=

ΓH

ΓSMH

⇒ σii→H→oo = σSMii→H→oo ×κ2i κ

2o

κ2H

If no decays beyond Standard Model (BSM), ΓH =∑

o∈{SM}

ΓH→oo =∑

o∈{SM}

κ2oΓSM

H→oo ⇒ κ2H =

∑o∈{SM}

κ2oBR

SMH→oo

⇒ Several couplings: κµ, κτ , κb, κW , κZ , κt and two effective couplings: κg , κγ

Assume weak gauge boson universality: κW , κZ = κV and fermion universality: κt, κb, κτ , κµ = κf

g

g

Ht, b

H

�

�

H

�

�

W W

H

�

�

t

If loop-mediated interactions occur as in SM:

gg → H (mainly) through top/bottom virtual loop

⇒ κg = κt,b = κf

H → γγ through top and W virtual loops

⇒ κ2γ = (1.26κW − 0.26κt)

2 = (1.26κV − 0.26κf )2

. . . and κ2H = 0.75κ2

f + 0.25κ2V — computed using BRSM

H→oo @ mH = 125 GeVM. Fanti (Physics Dep., UniMi) title in footer 31 / 35

Spin

H → γγ: flat | cos θ∗| for spin-0, sensitive to spin-2

spin 2

*|θ|cos

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.02

0.04

0.06

0.08

0.1

0.12

kq = kg

kq = 0

kq = 2 kg

H →WW ∗ → `ν`ν: W +/W− spin correlation

spin 0

Hm

1

m2

Hm

1

m2

W+

W+

W−

W−

l−

l+

l−

l+

ν

ν−

ν−

ν

(ll)φ∆

0 1 2 3

Arb

itra

ry N

orm

alis

ation

0

0.1

0.2

0.3 PreliminaryATLAS

= 8 TeVsSimulation,

e + 0 jetsµ/µ e→(*)

WW→H

[125]+

H 0

[125]+

H 2

[GeV]llm

20 40 60 80

Arb

itra

ry N

orm

alis

ation

0

0.1

0.2

PreliminaryATLAS

= 8 TeVsSimulation,

e + 0 jetsµ/µ e→(*)

WW→H

[125]+

H 0

[125]+

H 2

sensitive to spin and parity

H → ZZ∗ → 4`:

5 angular observables + m12, m34

can probe polarization of both H and Zs

sensitive to spin and parity


Spin-2 tests

effective lagrangian

[HiggsCharacterization]

[ below, q ≡ −2 ln(LJP

L0+

)]

effective transition amplitude [JHU]

q~-30 -20 -10 0 10 20 30

Arb

itrar

y no

rmal

isat

ion

-510

-410

-310

-210

-110

1

10

210


-1 = 7 TeV, 4.5 fbs-1 = 8 TeV, 20.3 fbs

νµνe → WW* →H -1 = 8 TeV, 20.3 fbs

γγ →H -1 = 7 TeV, 4.5 fbs

-1 = 8 TeV, 20.3 fbs

Data SM+0

)gκ=qκ( +2

) + 0 /

LP J

ln(L

×-2

-60

-40

-20

0

20

40

60

80

100

120CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb ZZ + WW→X

Observed Expectedσ 1± +0 σ 1± PJσ 2± +0 σ 2± PJσ 3± +0 σ 3± PJ

- 1 + 1 m+ 2 h2+ 2 h3+ 2 h+ 2 b+ 2 h6+ 2 h7+ 2 h- 2 h9- 2 h10

- 2 m+ 2 h2+ 2 h3+ 2 h+ 2 b+ 2 h6+ 2 h7+ 2 h- 2 h9- 2 h10

- 2

qq gg production productionqq

⇒ data favour spin-0


Conclusions

Run-I analyses well mature, ATLAS+CMS combined results available for mass and couplings:


vVm

Vκ o

r vF

mFκ

4−10

3−10

2−10

1−10

1W

tZ

b

µ

τ

ATLAS+CMS

SM Higgs boson

] fitε[M,

68% CL

95% CL


γκ0.6 0.8 1 1.2 1.4 1.6

gκ

0.6

0.8

1

1.2

1.4

1.6Run 1 LHC

CMS and ATLAS ATLAS+CMS

ATLAS

CMS


q~-30 -20 -10 0 10 20 30

Arb

itrar

y no

rmal

isat

ion

-510

-410

-310

-210

-110

1

10

210


-1 = 7 TeV, 4.5 fbs-1 = 8 TeV, 20.3 fbs

νµνe → WW* →H -1 = 8 TeV, 20.3 fbs

γγ →H -1 = 7 TeV, 4.5 fbs

-1 = 8 TeV, 20.3 fbs

Data SM+0

)gκ=qκ( +2

(MeV)HΓ0 10 20 30 40 50 60

lnL

∆-2

0

2

4

6

8

10

95% CL

68% CL

ZZ→H

CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb

observedl4

expectedl4

observedon-shell

l + 4ν2l2

expectedon-shell

l + 4ν2l2

Combined ZZ observed

Combined ZZ expected

Run-II: efficient data-taking, analyses progressing fast, (cross-section)×(luminosity) already beated Run-I

[TeV] s

7 8 9 10 11 12 13

[pb]

H

→pp

σ

0

20

40

60

80


m H→pp

σ


)s



1 = 7 TeV, 4.5 fbs1 = 8 TeV, 20.3 fbs

*)ZZ (1), 14.8 fbγγ (1 = 13 TeV, 13.3 fbs

=125 GeVH for mHtt

µbest fit 0 2 4 6 8 10

H combinationtt

H combinationtt

)bb→H(Htt

/ZZ)ττWW/→H(Htt

)γγ→H(Htt

0.8−+0.81.7 , 0.5−

+0.5 0.6−+0.7 ( )

0.7−+0.71.8 , 0.4−

+0.4 0.5−+0.6 ( )

0.9−+1.02.1 , 0.5−

+0.5 0.7−+0.9 ( )

1.1−+1.32.5 , 0.7−

+0.7 0.9−+1.1 ( )

1.0−+1.2-0.3 , 1.0−

+1.2 0.2−+0.2 ( )

( tot. ) ( stat. , syst. )total stat.

)-1(13 TeV 13.3 fb

)-1(13 TeV 13.2 fb

)-1(13 TeV 13.2 fb

(13 TeV)

)-1( 7-8TeV, 4.5-20.3 fb

ATLAS Preliminary -1=13 TeV, 13.2-13.3 fbs

Vκ0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

fκ1−

0.5−

0

0.5

1

1.5

2

2.5

3 ) fκ,Vκ

q(

0

2

4

6

8

10

Best Fit

σ1

σ2

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 Fit

σ1

σ2

SM

Preliminary CMS TeV) (13-112.9 fb

γγ→H ProfiledHm

⇒ We are still compatible with Standard Model prediction . . . but uncertainties are still large.

Theory uncertainties improved a lot. Important to pursue precision measurements in the Higgs sector, in Run-II andbeyond, to investigate possible deviations from SM


Prospects . . .

Vκ

0.9 0.95 1 1.05 1.1

Fκ

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

1.25 , w/ theory1300 fb , w/ theory13000 fb

, w/o theory1300 fb , w/o theory13000 fb

Standard Model


= 14 TeVs

iy

310

210

110

1Z

W

t

b

τ

µ


= 14 TeVs

νlνl→WW*→4l, h→ZZ*→, hγγ→h

γZ→, hµµ→bb, h→, hττ→h

]µκ, τκ, bκ, tκ, Wκ, Zκ[

=0i,uBR

1dt = 300 fbL∫1dt = 3000 fbL∫

[GeV]i

m

110 1 10 210R

atio to S

M

0.8

0.9

1

1.1

1.2

Some “educated guesses” — With 300 fb−1at 13 TeV:

Precise measurements of H → τ+τ−, observation of H → bb, evidence of ttH production

Evidence of H → µ+µ−, precision measurements of all individual κ’s to . 10% accuracy


Documents

Discovery of the Higgs boson and most recent measurements at …repodip.fisica.unimi.it/cdip17/talks/1_3_MFanti... · 2018-06-27 · Discovery of the Higgs boson and most recent measurements