Transcript ppt

Higgs, more Higgs, less Higgs, or
Higgsless?
John Ellis
King’s College, London
(& CERN)
The ‘Standard Model’ of
Particle Physics
Proposed byAbdus Salam,
Glashow and Weinberg
Tested by experiments
at CERN & elsewhere
Perfect agreement between
theory and experiments
in all laboratories
Open Questions beyond the
Standard Model
• What is the origin of particle masses?
LHC
due to a Higgs boson?
• Why so many flavours of matter particles?LHC
• What is the dark matter in the Universe? LHC
• Unification of fundamental forces?
LHC
• Quantum theory of gravity?
LHC
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)
The Seminal Papers
The Englert-Brout-Higgs Mechanism
Englert & Brout
Guralnik, Hagen & Kibble
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
Mysterious Higgs Potential
Mass2 of Higgs ~ curvature of potential at minimum
Vertical scale ~ 1060 × dark energy
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 Boson placed on the
Experimental Agenda
• Searches at LEP:
(EG, Yellow report 76-18)
• e+e-  Z + H
(EGN 76, Ioffe & Khoze 76,
Lee, Quigg & Thacker 77)
• Z  H + μ+μ(EG 76, Bjorken 1976)
• LEP: MH > 114.4 GeV
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
Latest Higgs Searches @ Tevatron
Experimental
upper limit
Standard Model
prediction
Exclude (100,109); (156,177) GeV
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
There
be New
Physics
viXramust
Blogger’s
Combination
th Data Model
Beyondofthe
Standard
Dec.13
Higgs
potential
collapses
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
Higgs + Higher-Order Operators
Precision EW data suggest they are small: why?
But conspiracies
are possible: mH
could be large,
even if believe
EW data …?
Barbieri, Strumia
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
Cut-off Λ ~ 1 TeV with
Supersymmetry?
New technicolour force?
inconsistent with
precision electroweak data?
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
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
ofwith
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
Theoretical Constraints on Higgs Mass
• Large Mh → large self-coupling → blow up at
low-energy scale Λ due to LHC 95%
exclusion
renormalization
• 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
SUSY vs Data
• Electroweak precision
observables
• Flavour physics
observables
• gμ - 2
• Higgs mass
• Dark matter
• LHC
MasterCode: O.Buchmueller, JE et al.
68% & 95%
CL contours
…..
pre-LHC
___ LHC 1/fb
Higgs mass
χ2 price to pay if Mh = 125 GeV is < 2
Buchmueller, JE et al: arXiv:1112.3564
Favoured values of Mh ~ 119 GeV:
Range consistent with evidence from LHC !
68% & 95%
CL contours
…..
pre-Higgs
___ Higgs @ 125
Buchmueller, JE et al: arXiv:1112.3564
Gluino mass
--- pre-Higgs
___ Higgs @ 125
… H@125, no g-2
Buchmueller, JE et al: arXiv:1112.3564
Favoured values of gluino mass significantly
above pre-LHC, > 2 TeV
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!
Measurements of Higgs Couplings
• Some decays limited by statistics
• Others limited by systematics
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
Higgs Self-coupling @ Hi-Lumi LHC?
Measure triple-Higgs-boson coupling with
accuracy comparable to 0.5 TeV ILC?
Awaits confirmation by detailed experimental simulation
The Fun is just Beginning
• LHC7 may well resolve Higgs issue
• LHC7 (or 8) unlikely to resolve SUSY issue
(or other BSM scenarios)
• Premium on increasing Ecm towards 14 TeV
• Prospects for L factor 500 with Hi-Lumi LHC
• What will follow the LHC?
– Higgs factory? CLIC? High-E LHC?
• A new era about to open: AH (anno Higgsi)
Quo Vadis
gμ - 2?
• Strong discrepancy between
BNL experiment and e+e- data:
– now ~ 3.6 σ
– Better agreement between
e+e- experiments
• Increased discrepancy between
BNL experiment and τ decay
data
– now ~ 2.4 σ
– Convergence between e+eexperiments and τ decay
• More credibility?
MSSM: > 100 parameters
Minimal Flavour Violation: 13 parameters
(+ 6 violating CP)
SU(5) unification: 7 parameters
NUHM2: 6 parameters
NUHM1 = SO(10): 5 parameters
CMSSM: 4 parameters
mSUGRA: 3 parameters
String?
… nevertheless
Supersymmetric Dark Matter in View of 1/fb
of LHC Data
68% & 95%
CL contours
…..
pre-LHC
___ LHC 1/fb
MasterCode: O.Buchmueller, JE et al.
Impact of dropping
gμ-2 constraint
…..
pre-LHC
___ LHC 1/fb
MasterCode: O.Buchmueller, JE et al.
Dropping gμ - 2 allows masses up to dark matter limit
Gluino mass
…..
pre-LHC
___ LHC 1/fb
MasterCode: O.Buchmueller, JE et al.
Favoured values of gluino mass significantly
above pre-LHC, > 1 TeV
+ LHCb
Bs μ+μ-
…..
pre-LHC
___ LHC 1/fb
--- with CDF
MasterCode: O.Buchmueller, JE et al.
Favoured values of BR(Bs μ+μ-) above SM value !
(due to increase in tan β)
Higgs mass
Favoured values of Mh ~ 119 GeV:
Coincides with value consistent with LHC !
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 MT < 2 TeV (mh / 200 GeV)2
MW’ < 6 TeV (mh / 200 GeV)
• Higgs light, other new
MH++ < 10 TeV
physics heavy
Not as complete as susy: more physics >
Searches for
Extra Particles in
Little Higgs
Models
Estimates of mH from different
Measurements
Spread looks natural: no significant disagreemen
Intermediate Models
Effects on Higgs Decays
• Dependences on  of Higgs branching ratios
• Standard Model recovered in limit   0
Grojean, Giudice, Pomarol, Rattazzi
What if no Higgs?
• Higgs must discriminate between different
types of particles:
– Some have masses, some do not
– Masses of different particles are different
• In mathematical jargon, symmetry must be
broken: how?
– Break symmetry in equations?
– Or in solutions to symmetric equations?
• This is the route proposed by Higgs
– Is there another way?
Where to Break the Symmetry?
• Throughout all space?
– Route proposed by Higgs
– Universal Higgs (snow)field breaks symmetry
– If so, what type of field?
• Or at the edge of space?
– Break symmetry at the boundary?
• Not possible in 3-dimensional space
– No boundaries
– Postulate extra dimensions of space
• Different particles behave differently in the extra
dimension(s)
Higgs Hunting @ Tevatron
Exclude (100,109); (156,177) GeV
Comparison between Weakly- and
Strongly-coupled Models
XENON100 & other Experiments
Aprile et al: arXiv:1104.2549
Supersymmetry Searches in ATLAS
Jets + missing energy + 0 lepton
XENON100 Experiment
Aprile et al: arXiv:1104.2549
Early Phenomenological Bounds
• Emission from stars:
MH > 0.7 me (Sato & Sato, 1975)
• Neutron-electron scattering:
MH > 0.7 MeV (Rafelski, Muller, Soff & Greiner;
Watson & Sundaresan; Adler, Dashen & Treiman; 1974)
• Neutron-nucleus scattering:
MH > 13 MeV (Barbieri & Ericson, 1975)
• Nuclear 0+ – 0+ transitions:
MH > 18 MeV (Kohler, Watson & Becker, 1974)
Supersymmetry Searches @ LHC
Jets + missing energy (+ lepton(s))
Applicable to NUHM, CMSSM, VCMSSM, mSUGRA
but need other strategies for other models