Different Scales for Higgs Physics
From an obscure term in an equation to
a headline discovery – and beyond
John Ellis
King’s College London
(& CERN)
The (G)AEBHGHKMP’tH Mechanism
The only one
who mentioned a
massive scalar boson
Why a Higgs Boson is Needed
• Trouble with WW scattering: M ~ E2
 uncontrollable infinities in loop diagrams
•
can be cancelled by
•
scalar exchange
with HWW couplings
• Need new physics @ TeV scale
2011: Combining Information from
Previous Direct Searches and Indirect Data
mH = 125 ± 10 GeV
Gfitter collaboration
Higgs Mass Measurements
• CMS γγ and ZZ* measurements consistent
Higgs Mass Measurements
• Tension in ATLAS γγ and ZZ* measurements
Comparison with Electroweak Fit
Quite consistent: Δχ2 ~ 1.5
Theoretical Constraints on Higgs Mass
• Large Mh → large self-coupling → blow up at
low-energy scale Λ due to
Instability @
renormalization
10 – 1013 GeV
10
• Small: renormalization
due to t quark drives
quartic coupling < 0
at some scale Λ
→ vacuum unstable
• Vacuum could be stabilized by Supersymmetry
Degrassi, Di Vita, Elias-Miro, Giudice, Isodori & Strumia, arXiv:1205.6497
Vacuum Instability in the Standard Model
• Very sensitive to mt as well as MH
• Present vacuum probably metastable with
lifetime >> age of the Universe
Degrassi, Di Vita, Elias-Miro, Giudice, Isodori & Strumia, arXiv:1205.6497
Some Questions
• What is it?
–Higgs or …?
• What else is there?
–Supersymmetry …?
• What next?
–A Higgs factory or …?
Supersymmetric
model fits
Elementary Higgs or Composite?
• Higgs field:
<0|H|0> ≠ 0
• Quantum loop problems
• Fermion-antifermion
condensate
• Just like QCD, BCS
superconductivity
e.g., cutoff
Λ = 10 TeV • Top-antitop condensate?
needed mt > 200 GeV
Cut-off Λ ~ 1 TeV with
Supersymmetry?
New technicolour force?
- Heavy scalar resonance?
- Inconsistent with
precision electroweak data?
Higgs as a
Pseudo-Goldstone
Boson
‘Little Higgs’ models
(breakdown of larger symmetry)
Loop cancellation mechanism
Little Higgs
Supersymmetry
Phenomenological Framework
• Assume custodial symmetry:
• Parameterize gauge bosons by 2 × 2 matrix Σ:
• Coefficients a = c = 1 in Standard Model
Global Analysis of Higgs-like Models
• Rescale couplings: to bosons by a, to fermions by c
Global
bW
Z
τbbar
γW
τγZ
• Standard Model: a = c = 1
No evidence for
deviation from SM
JE & Tevong You, arXiv:1303.3879
It Walks and Quacks like a Higgs
• Do couplings scale ~ mass? With scale = v?
Global
fit
JE & Tevong You, arXiv:1303.3879
• Red line = SM, dashed line = best fit
Loop Corrections ?
• ATLAS sees excess in γγ, CMS sees deficit
JE & Tevong You, arXiv:1303.3879
• Loop diagrams ~ Standard Model?
What else is there?
• Higher-dimensional operators as relics of higherenergy physics?
• Operators constrained by SU(2) × U(1) symmetry:
Corbett, Eboli & Gonzalez2
• Constrain using LHC +
Tevatron Higgs
measurements
What else is there?
Combine Higgs
coupling
measurements
with constraints
on anomalous
triple-gauge boson
couplings
Corbett, Eboli & Gonzalez2
What else is there?
Constraints from energy dependence of
Higgs production cross section on
Λ > ~ 250 GeV
JE, Sanz & You, arXiv:1303.0208
What else is there?
Supersymmetry
• Successful prediction for Higgs mass
– Should be < 130 GeV in simple models
• Successful predictions for Higgs couplings
– Should be within few % of SM values
• Could explain the dark matter
• Naturalness, GUTs, string, … (???)
MSSM Higgs Masses & Couplings
Lightest Higgs mass
up to ~ 130 GeV
Heavy Higgs masses
quite close
Consistent
With LHC
Searches with
~ 5/fb8 @
TeV
8 TeV
Data
“Classic” missing-energy search
Multiple searches including b, leptons
2
5
Scan of CMSSM
Impacts of searches
with full 2012 data
Update of Buchmueller et al: arXiv:1207.3715
p-value of simple models < 10%
1
Gluino mass
5
CMSSM
Update of Buchmueller, JE et al: arXiv:1207.3715
Favoured values of gluino mass significantly
above pre-LHC, > 1.5 TeV
2
-40
10
-41
10
-42
10
-43
10
-44
10
-45
10
-46
10
-47
10
-48
Spin-independent
Dark matter scattering
Excluded by
XENON100
5 .9 9
0
1
10
2
m χ˜ 01 [GeV]
5 .9 9 0
5 .9 9 0
10
Excluded
by LHC
2.
30
2.3 00
5 .9 9 0
σpSI [cm 2 ]
--- 1/fb
___ 5/fb
10
5
0
10
3
Buchmueller, JE et al: arXiv:1207.3715
Favoured values of dark matter scattering
cross section significantly below XENON100
What Next: A Higgs Factory?
To study the ‘Higgs’ in detail:
•The LHC
– Rethink LHC upgrades in this perspective?
•A linear collider?
– ILC up to 500 GeV
– CLIC up to 3 TeV
(Larger cross section at higher energies)
•A circular e+e- collider: LEP3, TLEP
– A photon-photon collider: SAPPHiRE
•A muon collider
What Higgs Factory?
New large tunnel
could also be used
for pp collisions
ECM up to 100 TeV
TLEP Steering Group, arXiv:1208.0504, 1305.6498, 1306.5981
Possible Layouts for TLEP
Comparison of Possible Higgs
Factory Measurements
Impact of Higgs Factory?
• Predictions of current best fits
in simple SUSY models
• Current uncertainties in SM
calculations [LHC Higgs WG]
• Comparisons with
–
–
–
–
LHC
HL-LHC
ILC
TLEP
• Don’t decide before LHC 13/4
Supersymmetric
model fits
Part of a Vision for the Future
• A large circular tunnel
– Circumference ~ 80 to 100 km
• Could accommodate TLEP and VHE-LHC
– ECM up to 100 TeV with 15 Tesla magnets
• Could be sited around Geneva
– Interest in China, US
• TLEP Study Group under way
• Timely to study VHE-LHC
Conversation with Mrs Thatcher: 1982
What do you do?
Think of things for the
experiments to look
for, and hope they find
something different
Then we would not
know how to progress!
Wouldn’t it be
better if they
found what
you predicted?