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)
M. Fanti (Physics Dep., UniMi) title in footer 2 / 35
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?
M. Fanti (Physics Dep., UniMi) title in footer 2 / 35
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 . . .
M. Fanti (Physics Dep., UniMi) title in footer 3 / 35
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!
M. Fanti (Physics Dep., UniMi) title in footer 3 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 4 / 35
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
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
M. Fanti (Physics Dep., UniMi) title in footer 4 / 35
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
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
M. Fanti (Physics Dep., UniMi) title in footer 4 / 35
Observation of the Higgs boson
M. Fanti (Physics Dep., UniMi) title in footer 5 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 6 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 6 / 35
ATLAS and CMS
ATLASCMS
M. Fanti (Physics Dep., UniMi) title in footer 7 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 7 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 7 / 35
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)
M. Fanti (Physics Dep., UniMi) title in footer 8 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 8 / 35
Typical “events” at LHC
Proton beams collide every 25 ns:
up to ∼50 proton-proton
interactions
hundreds of particles are
produced
p −→ ←− p
M. Fanti (Physics Dep., UniMi) title in footer 9 / 35
Typical “events” at LHC
Proton beams collide every 25 ns:
up to ∼50 proton-proton
interactions
hundreds of particles are
produced
p −→ ←− p
ZZ → e+e−µ+µ−
M. Fanti (Physics Dep., UniMi) title in footer 9 / 35
Typical “events” at LHC
Proton beams collide every 25 ns:
up to ∼50 proton-proton
interactions
hundreds of particles are
produced
p −→ ←− p
ZZ → e+e−µ+µ− multi-jet event
M. Fanti (Physics Dep., UniMi) title in footer 9 / 35
Typical “events” at LHC
Proton beams collide every 25 ns:
up to ∼50 proton-proton
interactions
hundreds of particles are
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
M. Fanti (Physics Dep., UniMi) title in footer 9 / 35
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
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G 2
01
3
bb
ττ
µµ
cc
gg
γγ γZ
WW
ZZ
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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
Most common decay modes ( H → bb, H → τ+τ− ) are
very difficult, due to large hadronic background.
M. Fanti (Physics Dep., UniMi) title in footer 10 / 35
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
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
M. Fanti (Physics Dep., UniMi) title in footer 10 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 11 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 12 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 13 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 13 / 35
Properties of the Higgs boson
M. Fanti (Physics Dep., UniMi) title in footer 14 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 15 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 16 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 17 / 35
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!
M. Fanti (Physics Dep., UniMi) title in footer 17 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 18 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 18 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 18 / 35
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
⇒ data favour spin-0
M. Fanti (Physics Dep., UniMi) title in footer 18 / 35
Summary
M. Fanti (Physics Dep., UniMi) title in footer 19 / 35
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
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
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
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
⇒ 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
M. Fanti (Physics Dep., UniMi) title in footer 20 / 35
Prospects . . .
Results: ATLAS+CMS, 8 TeV
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
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
M. Fanti (Physics Dep., UniMi) title in footer 22 / 35
Milano’s involvements
Detector
Detector construction
pixel detector (innermost tracking device)
electromagnetic calorimeter
magnets for muon chambers
M. Fanti (Physics Dep., UniMi) title in footer 23 / 35
Milano’s involvements
Detector
Detector construction
pixel detector (innermost tracking device)
electromagnetic calorimeter
magnets for muon chambers
R & D
Electronics: upgrade for high-luminosity phase [talk by
A.Stabile]
Pixel detector: radiation damage studies [poster by
L.Rossini]
M. Fanti (Physics Dep., UniMi) title in footer 23 / 35
Milano’s involvements
Detector
Detector construction
pixel detector (innermost tracking device)
electromagnetic calorimeter
magnets for muon chambers
R & D
Electronics: upgrade for high-luminosity phase [talk by
A.Stabile]
Pixel detector: radiation damage studies [poster by
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]
M. Fanti (Physics Dep., UniMi) title in footer 23 / 35
Milano’s involvements
Detector
Detector construction
pixel detector (innermost tracking device)
electromagnetic calorimeter
magnets for muon chambers
R & D
Electronics: upgrade for high-luminosity phase [talk by
A.Stabile]
Pixel detector: radiation damage studies [poster by
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]
M. Fanti (Physics Dep., UniMi) title in footer 23 / 35
THANKS FOR YOUR
ATTENTION
M. Fanti (Physics Dep., UniMi) title in footer 24 / 35
More Material
M. Fanti (Physics Dep., UniMi) title in footer 25 / 35
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 //
M. Fanti (Physics Dep., UniMi) title in footer 26 / 35
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.
M. Fanti (Physics Dep., UniMi) title in footer 27 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 28 / 35
(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
Run 1 LHCCMS and ATLAS
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)
M. Fanti (Physics Dep., UniMi) title in footer 29 / 35
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
68% CL 95% CL Best fit SM expected
⇒ consider κg , κγ as free and profile others
⇒ again, compatibility with SM (F)
M. Fanti (Physics Dep., UniMi) title in footer 30 / 35
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
M. Fanti (Physics Dep., UniMi) title in footer 32 / 35
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
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
) + 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
M. Fanti (Physics Dep., UniMi) title in footer 33 / 35
Conclusions
Run-I analyses well mature, ATLAS+CMS combined results available for mass and couplings:
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
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
68% CL 95% CL Best fit SM expected
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
(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
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
=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
M. Fanti (Physics Dep., UniMi) title in footer 34 / 35
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
ATLAS Simulation Preliminary
= 14 TeVs
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 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
M. Fanti (Physics Dep., UniMi) title in footer 35 / 35
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