Download Phenomenology Beyond the Standard Model

Physics beyond the Standard Model:
Higgs and Supersymmetry –
Why, what, where and how?
Nanyang Technological University
Singapore, January 2012
John Ellis, King’s College London & CERN
Plan of the Lectures
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The Standard Model and issues beyond it
Origin of particle masses: Higgs boson or?
Supersymmetry
Searches for supersymmetry: LHC & dark matter
Summary of the Standard Model
• Particles and SU(3) × SU(2) × U(1) quantum numbers:
• Lagrangian:
gauge interactions
matter fermions
Yukawa interactions
Higgs potential
Gauge Interactions of the Standard Model
• Three separate gauge group factors:
– SU(3) × SU(2) × U(1)
– Strong × electroweak
• Three different gauge couplings:
– g3, g2, g ́
• Mixing between the SU(2) and U(1) factors:
• Experimental value: sin2θW = 0.23120 ± 0.00015
Clue for Grand Unification and supersymmetry
Weak Interactions
• Interactions of lepton doublets:
• Charged-current interactions:
• Neutral-current interactions:
• Mixing between quark flavours:
Status of the Standard Model
• Perfect agreement with all confirmed
accelerator data
• Consistency with precision electroweak data
(LEP et al) only if there is a Higgs boson
• Agreement seems to require a relatively light
Higgs boson weighing < ~ 180 GeV
• Raises many unanswered questions:
mass? flavour? unification?
Precision Tests of the Standard Model
Lepton couplings
Pulls in global fit
Parameters of the Standard Model
• Gauge sector:
– 3 gauge couplings: g3, g2, g ́
– 1 strong CP-violating phase
Unification?
• Yukawa interactions:
– 3 charge-lepton masses
– 6 quark masses
– 4 CKM angles and phase
Flavour?
• Higgs sector:
– 2 parameters: μ, λ
• Total: 19 parameters
Mass?
Open Questions beyond the
Standard Model
• What is the origin of particle masses?
due to a Higgs boson? + other physics?
solution at energy < 1 TeV (1000 GeV)
Susy
• Why so many types of matter particles?
matter-antimatter difference?
• Unification of the fundamental forces?
at very high energy ~ 1016 GeV?
probe directly via neutrino physics, indirectly via masses,
couplings
Susy
• Quantum theory of gravity?
(super)string theory: extra space-time dimensions?
Susy
Why do Things Weigh?
Newton:
Weight proportional to Mass
Einstein:
Energy related to Mass
Neither explained0origin of Mass
Where do the masses
come from?
Are masses due to Higgs boson?
(the physicists’ Holy Grail)
Think of a Snowfield
The LHC looks for
the snowflake:
the Higgs Boson
Skier moves fast:
Like particle without mass
e.g., photon = particle of light
Snowshoer sinks into snow,
moves slower:
Like particle with mass
e.g., electron
Hiker sinks deep,
moves very slowly:
Particle with large mass
The Higgs Boson and Cosmology
• Changed the state of the Universe when it was
about 10-12 seconds old
• May have generated then the matter in the
Universe
• Contributes (too much) to today’s dark energy
• A related inflaton might have expanded the
Universe when it was about 10-35 seconds old
The Higgs Mechanism
• Postulated effective Higgs potential:
• Minimum energy at non-zero value:
• Non-zero masses:
• Components of Higgs field:
• π massless, σ massive:
Masses for Gauge Bosons
• Kinetic terms for SU(2) and U(1) gauge bosons:
where
• Kinetic term for Higgs field:
• Expanding around vacuum:
• Boson masses:
The Seminal Papers
The Englert-Brout-Higgs Mechanism
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Vacuum expectation value of scalar field
Englert & Brout: June 26th 1964
First Higgs paper: July 27th 1964
Pointed out loophole in argument of Gilbert if
gauge theory described in Coulomb gauge
• Accepted by Physics Letters
• Second Higgs paper with explicit example sent on
July 31st 1964 to Physics Letters, rejected!
• Revised version (Aug. 31st 1964) accepted by
PRL
The Englert-Brout-Higgs Mechanism
•Englert & Brout
•Guralnik, Hagen & Kibble
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The Higgs Boson
• Higgs pointed out a massive scalar boson
• “… an essential feature of [this] type of theory
… is the prediction of incomplete multiplets of
vector and scalar bosons”
• Englert, Brout, Guralnik, Hagen & Kibble did
not comment on its existence
• Discussed in detail by Higgs in 1966 paper
Nambu, EB, GHK and Higgs
Spontaneous breaking of symmetry
A Phenomenological Profile
of the Higgs Boson
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Neutral currents (1973)
Charm (1974)
Heavy lepton τ (1975)
Attention to search for W±, Z0
For us, the Big Issue: is there a Higgs boson?
Previously ~ 10 papers on Higgs bosons
MH > 18 MeV
First attempt at systematic survey
A Phenomenological Profile
of the Higgs Boson
• Higgs decay modes and searches in 1975:
Higgs Decay Branching Ratios
• Couplings proportional to mass:
– Decays into heavier particles favoured
• But: important couplings through loops:
– gluon + gluon → Higgs → γγ
Constraints on Higgs Mass
• Electroweak observables sensitive via quantum loop
corrections:
• Sensitivity to top, Higgs masses:
• Preferred Higgs mass: mH ~ 80 ± 30 GeV
• Compare with lower limit from direct searches:
mH > 114 GeV
• No conflict!
The State of the Higgs in Mid-2011
• High-energy search:
– Limit from LEP:
mH > 114.4 GeV
• High-precision electroweak data:
– Sensitive to Higgs mass:
mH = 96+30–24 GeV
• Combined upper limit:
mH < 161 GeV, or 190 GeV including direct limit
• Exclusion from high-energy search at Tevatron:
mH < 158 GeV or > 173 GeV
Combining the Information from Previous
Direct Searches and Indirect Data
mH = 125 ± 10 GeV
•Gfitter collaboration
Latest Higgs Searches @ Tevatron
Experimental
upper limit
Standard Model
prediction
Exclude (100,109); (156,177) GeV
A la
recherche du
Higgs perdu
…
Higgs Production at the
LHC
Higgs Hunting @ LHC: Status
th
reported on Dec. 13 , 2011
Exclude 127 to 600 GeV
Exclude 112.7 GeV to 115.5 GeV,
131 GeV to 237 GeV,
251 GeV to 453 GeV
Has the Higgs Boson been
Discovered?
Interesting hints around Mh = 125 GeV ?
CMS sees broad
enhancement
ATLAS prefers
125 GeV
Has the Higgs Boson been
Discovered?
Interesting hints around 125 GeV in both experiments
- but could also be 119 GeV ?
ATLAS
Signals
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γγ: 2.8σ
ZZ: 2.1σ
WW: 1.4σ
Combined: 3.6σ
CMS Signals
Combined: 2.6σ
Has the Higgs Boson been
Discovered?
Unofficial blogger’s combination
NOT ENDORSED BY EXPERIMENTS
but he was right last time !
Combining the Information from Previous
Direct Searches and Indirect Data
Assuming the Standard Model
mH = 125 ± 10 GeV
mH = 124.5 ± 0.8 GeV
Erler: arXiv:1201.0695
The Spin of the Higgs Boson @ LHC
Low mass: if H →γγ,
It cannot have spin 1
Higher mass: angular correlations
in H → ZZ decays
Do we already know the ‘Higgs’
has Spin Zero ?
• Decays into γγ, so cannot have spin 1
• 0 or 2?
• If it decays into ττ or b-bar: spin 0 or 1 or
orbital angular momentum
• Can diagnose spin via angular correlations of
leptons in WW, ZZ decays
Higgs Measurements @ LHC & ILC
For Mh = 120 GeV
•
Higgs
potential
collapses
There
be New
Physics
•viXramust
Blogger’s
Combination
th Data Model
Beyond•ofthe
Standard
Dec.13
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•
Higgs coupling less
than in Standard Model
Precision
Electroweak
data??
Higgs
coupling
blows up!!
Heretical Interpretation of EW Data
What attitude towards LEP, NuTeV?
Do all the data
tell the same story?
e.g., AL vs AH
Chanowitz
What most
of us think
Estimates of mH from different
Measurements
Spread looks natural: no significant disagreement
Higgs + Higher-Order Operators
Precision EW data suggest they are small: why?
Barbieri, Strumia
But conspiracies
are possible: mH
could be large,
even if believe
EW data …?
Do not discard possibility of heavy Higgs
Corridor to
heavy Higgs?
Elementary Higgs or Composite?
• Higgs field:
<0|H|0> ≠ 0
• Quantum loop problems
• Fermion-antifermion
condensate
• Just like QCD, BCS
superconductivity
•Cutoff
•Λ = 10 TeV • Top-antitop condensate?
needed mt > 200 GeV
• New technicolour force?
heavy scalar resonance?
• Cut-off Λ ~ 1 TeV with • inconsistent with
•
Supersymmetry?
precision electroweak data?
Comparison between Weakly- and
Strongly-coupled Models
Interpolating Models
• Combination of Higgs boson and vector ρ
• Two main parameters: mρ and coupling gρ
• Equivalently ratio weak/strong scale:
g ρ / mρ
Grojean, Giudice, Pomarol, Rattazzi
Generic Little
Higgs Models
(Higgs as pseudo-Goldstone
boson of larger symmetry)
Loop cancellation mechanism
Little Higgs
Supersymmetry
Little Higgs Models
• Embed SM in larger gauge group
• Higgs as pseudo-Goldstone boson
• Cancel top loop
with new heavy T quark
new gauge bosons, Higgses
• Higgs light, other new
physics heavy
MT < 2 TeV (mh / 200 GeV)2
MW’ < 6 TeV (mh / 200 GeV)2
MH++ < 10 TeV
Not as complete as susy: more physics > 10 TeV
What if the Higgs is not quite a Higgs?
• Tree-level Higgs couplings ~ masses
– Coefficient ~ 1/v
• Couplings ~ dilaton of scale invariance
• Broken by Higgs mass term –μ2, anomalies
– Cannot remove μ2 (Coleman-Weinberg)
– Anomalies give couplings to γγ, gg
• Generalize to pseudo-dilaton of new (nearly)
conformal strongly-interacting sector
• Couplings ~ m/V (V > v?), additions to anomalies
A Phenomenological Profile of a
Pseudo-Dilaton
• New strongly-interacting sector at scale ~ V
• Pseudo-dilaton only particle with mass << V
• Universal suppression of couplings to Standard
Model particles ~ v/V
•Compilation
•Updated
•of
•with
constraints
Dec. 11
• Γ(gg) may be enhanced
•constraints
• Γ(γγ) may be suppressed
• Modified self-couplings
• Pseudo-baryons
as dark matter?
1000
900
800
V (GeV)
700
600
500
400
precision data
300
N =3
g
200
100
•Campbell, JE, Olive: arXiv:1111.4495
200
300
400
m (GeV)
500
600
700
Higgsless Models?
• Four-dimensional versions:
Strong WW scattering @ TeV, incompatible with
precision data?
• Break EW symmetry by boundary conditions in extra
dimension:
delay strong WW scattering to ~ 10 TeV?
Kaluza-Klein modes: mKK > 300 GeV?
compatibility with precision data?
• Warped extra dimension + brane kinetic terms?
Lightest KK mode @ few 00 GeV, strong WW @ 6-7 TeV
Theorists getting Cold Feet
• Composite Higgs model?
conflicts with precision electroweak data
• Interpretation of EW data?
consistency of measurements? Discard some?
• Higgs + higher-dimensional operators?
corridors to higher Higgs masses?
• Little Higgs models?
extra `Top’, gauge bosons, `Higgses’
• Higgsless models?
strong WW scattering, extra D?
Particle Spectrum in Simplest
Model with Extra Dimensions
Lowest-lying states have flat wave functions (n = 0)
Excitations (Kaluza-Klein) have nodes (n > 0):
Mass ~ n/R (R = radius of circle)
‘Fold’ Circle: Orbifold
• Identify two halves of circle: up to a minus sign
• ‘Even’ particles include massless: odd ones all massive
• A way to give masses to particles that are asymmetric
Mechanism to break Gauge Symmetry
• Identify two halves up to a group transformation U
• Unbroken part of gauge group commutes with U
• Masses for asymmetric particles:
– e.g., SU(2) × U(1)  U(1)
Search for Vector Resonance in
Higgsless Model
Vector resonance structure in WZ
scattering
Simulation of resonance
structure in mWZ @ LHC
Theoretical Constraints on Higgs Mass
• Large Mh → large self-coupling → blow up at
low-energy scale Λ due to •LHC 95%
renormalization
•exclusion
• Small: renormalization
due to t quark drives
quartic coupling < 0
at some scale Λ
→ vacuum unstable
• Vacuum could be stabilized by supersymmetry
•Espinosa, JE, Giudice, Hoecker, Riotto, arXiv0906.0954
Vacuum Stability vs Metastability
• Dependence on scale up to which Standard Model remains
– Stable
– Metastable at non-zero temperature
– Metastable at zero temperature
What is the probable fate of the SM?
Confidence Levels (CL)
without/with Tevatron exclusion
Confidence Levels (CL) for different fates
Blow-up excluded
at 99.2% CL
CL as
function of
instability
scale 
Espinosa, JE, Giudice, Hoecker, Riotto
The LHC will Tell the Fate of the SM
Examples with LHC measurement of mH = 120 or 115 GeV
Espinosa, JE, Giudice, Hoecker, Riotto
How to Stabilize a Light Higgs Boson?
• Top quark destabilizes potential: introduce
introduce stop-like scalar:
• Can delay collapse of potential:
• But new coupling must be
fine-tuned to avoid blow-up:
• Stabilize with new fermions:
– just like Higgsinos
• Very like Supersymmetry!
•Higgs mass
•χ2 price to pay if Mh = 125 GeV is < 2
•Favoured values of Mh ~ 119 GeV:
•Range consistent with evidence from LHC
•Buchmueller, JE et al: arXiv:1112.3564
The Stakes in the Higgs Search
• How is gauge symmetry broken?
• Is there any elementary scalar field?
• Would have caused phase transition in the Universe when
it was about 10-12 seconds old
• May have generated then the matter in the Universe:
electroweak baryogenesis
• A related inflaton might have expanded the Universe
when it was about 10-35 seconds old
• Contributes to today’s dark energy: 1060 too much!
Intermediate Models
Effects on Higgs Decays
• Dependences on  of Higgs branching ratios
• Standard Model recovered in limit   0
•Grojean, Giudice, Pomarol, Rattazzi
At what Energy is the New Physics?
Origin of mass
Dark matter
A lot accessible
to the LHC
Some accessible only indirectly:
Astrophysics & cosmology?
Summer 2008
Indications on the Higgs Mass
Sample observable:
W mass @ LEP & Tevatron
Combined information
on Higgs mass
The State of the Higgs: November 2009
• Direct search limit from LEP:
mH > 114.4 GeV
• Electroweak fit sensitive to mt
(Now mt = 173.1 ± 1.3 GeV)
• Best-fit value for Higgs mass:
mH = 89+35–26 GeV
• 95% confidence-level upper limit:
mH < 157 GeV, or 186 GeV including direct limit
• Tevatron exclusion:
mH < 162 GeV or > 166 GeV
Higgs Search @ Tevatron
Tevatron excludes Higgs between 162 & 166 GeV
Higgs Search @ Tevatron
Tevatron excludes Higgs between 162 & 166 GeV
Combining the Higgs Information
mH = 116.4+ 15.6-1.3 GeV
Progress of
Tevatron
Higgs Search
Past improvements
Possibility of
future evidence
Theoretical Constraints on Higgs Mass
• Large → large self-coupling → blow up at low
energy scale Λ due to
renormalization
• Small: renormalization
due to t quark drives
quartic coupling < 0
at some scale Λ
→ vacuum unstable
• Bounds on Higgs mass depend on Λ
The Large Hadron Collider (LHC)
Proton- Proton Collider
7 TeV + 7 TeV
1,000,000,000 collisions/second
Primary targets:
•Origin of mass
•Nature of Dark Matter
•Primordial Plasma
•Matter vs Antimatter
Huge Statistics thanks to High Energy and Luminosity
Event rates in ATLAS or CMS at L = 1033 cm-2 s-1
Process
Events/s
Events per year
W e
15
108
Z ee
1.5
107
107 LEP
tt
1
107
104 Tevatron
bb
106
1012 – 1013
H m=130 GeV
0.02
105
?
~g
~ m= 1 TeV
g
0.001
104
---
Black holes
m > 3 TeV
0.0001
103
Total statistics collected
at previous machines by 2007
104 LEP / 107 Tevatron
109 Belle/BaBar ?
---
(MD=3 TeV, n=4)
LHC is a factory for anything: top, W/Z, Higgs, SUSY, etc….
mass reach for discovery of new particles up to m ~ 5 TeV
The LHC Physics Haystack(s)
Interesting cross sections
Susy
Higgs
• Cross sections for heavy particles
~ 1 /(1 TeV)2
• Most have small couplings ~ α2
• Compare with total cross section
~ 1/(100 MeV)2
• Fraction ~ 1/1,000,000,000,000
• Need ~ 1,000 events for signal
• Compare needle
~ 1/100,000,000 m3
• Haystack ~ 100 m3
• Must look in ~ 100,000 haystacks
The LHC’s Most Anticipated
Discovery
a Higgs boson
a Higgs boson
1
…
fb-1
The LHC Roulette Wheel
Standard Model
Higgs boson
A Simulated Higgs Event in CMS
A la recherche du
Higgs perdu …
Higgs Production at the
LHC
… not far away?
Combining direct,
Indirect information
A la recherche
du
Higgs perdu …
Some Sample Higgs Signals
γγ
ZZ* -> 4 leptons
ττ
Some Sample Higgs Signals
γγ
ZZ* -> llll
ttH
bbH
Measuring Higgs Self-Coupling
Light Higgs @ low-energy LC
Heavier Higgs possible @ SLHC
When will ATLAS discover the Higgs boson?
Duehrssen, La Thuile 2010
When will the LHC discover the Higgs boson?
1 ‘year’ @ 1033
‘month’ @ 1033
‘month’ @ 1032
Blaising, JE et al: 2006
The Stakes in the Higgs Search
• How is gauge symmetry broken?
• Is there any elementary scalar field?
• Would have caused phase transition in the Universe when
it was about 10-12 seconds old
• May have generated then the matter in the Universe:
electroweak baryogenesis
• A related inflaton might have expanded the Universe
when it was about 10-35 seconds old
• Contributes to today’s dark energy: 1060 too much!
International Linear Collider
• e+e- collisions
up to Ecm = 1 TeV
• Option for next
collider
• Now subject of
Global Design Effort
• Hope for decision
by 2012?
• To be constructed by
2020?
Tasks for the TeV ILC
•
•
Measure mt to <  100 MeV
If there is a light Higgs of any
kind, pin it down:
Does it have standard model
couplings?
What is its precise mass?
•
If there are extra light particles:
Measure mass and properties
•
If LHC sees nothing new below
~ 500 GeV:
Look for indirect signatures
Measuring Properties of Light Higgs
LC capabilities
bb, ττ, gg, cc, WW, γγ
Other studies …
Measuring top-Higgs
couplings
Higgs Measurements @ ILC & LHC
For Mh = 140 GeV
For Mh = 120 GeV
Sensitivity to Strong WW scattering
@ LHC
@ 800 GeV LC
Measuring a WW Resonance
Form factor measurements
@ 500 GeV LC
Resonance parameters
@ LHC
Resonance parameters @ 500 GeV LC
After LHC @ CERN - CLIC?
Electron-Positron
collisions up to 3 TeV
CLI C
The CLIC main parameters
Center of mass Energy (TeV)
Luminosity (1034 cm-1s-1)
Mean energy loss (%)
Photons / electron
Coherent pairs per X
Rep. Rate (Hz)
109 e± / bunch
Bunches / pulse
Bunch spacing (cm)
H/V en (10-8 rad.m)
Beam size (H/V) (nm)
Bunch length (mm)
Accelerating gradient (MV/m)
Overall length (km)
Power / section (MW)
RF to beam efficciency (%)
AC to beam efficiency (%)
Total AC power for RF (MW)
Total site AC power (MW)
J.P.Delahaye: Scientific Policy Committee (SPC) 16-03-04
0.5 TeV
2.1
4.4
0.75
700
200
4
154
20
200/1
202/1.2
35
150
10.2
230
23.1
9.3
105
175
3 TeV
8.0
21
1.5
6.8 108
100
4
154
20
68/1
60/0.7
35
150
33.2
230
23.1
9.3
319
410
Large Cross Section
@ CLIC
Can measure rare decay modes …
H  bb
Δg/g = 4%
mH = 120 GeV
Δg/g = 2%
mH = 180 GeV
If the Higgs boson is heavier …
Can establish its existence
beyond any doubt if < 1 TeV:
ee  H ee
Find resonance in strong
WW scattering if > 1 TeV:
ee  H νν
Measuring Effective Higgs
Potential @ Higher-Energy LC
Large cross section
for HH pair production
Accuracy in measurement of HHH coupling
MH = 240 GeV
180 GeV 11%
140 GeV
120 GeV 9%