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 experimentsat CERN & elsewhere
Perfect agreement betweentheory and experiments
in all laboratories
Open Questions beyond the Standard Model
• What is the origin of particle masses?
due to a Higgs boson?
• Why so many flavours of matter particles?
• What is the dark matter in the Universe?
• Unification of fundamental forces?
• Quantum theory of gravity?
LHC
LHC
LHC
LHC
LHC
Why do Things Weigh?
0
Where do the masses come from?
Newton:Weight proportional to Mass
Einstein:Energy related to Mass
Neither explained origin of Mass
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
• 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
• Higgs decay modes and searches in 1975:
A Phenomenological Profile of the Higgs Boson
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
Exclude (100,109); (156,177) GeV
Standard Model
prediction
Experimental
upper limit
Higgs Hunting @ LHC: Status reported on Dec. 13th, 2011
Exclude 112.7 GeV to 115.5 GeV,
131 GeV to 237 GeV,
251 GeV to 453 GeV
Exclude 127 to 600 GeV
Has the Higgs Boson been Discovered?
Interesting hints around Mh = 125 GeV ?
CMS sees broadenhancement
ATLAS prefers125 GeV
Has the Higgs Boson been Discovered?
Interesting hints around 125 GeV in both experiments- but could also be 119 GeV ?
ATLASSignals
• 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 combinationNOT ENDORSED BY EXPERIMENTS
but he was right last time !
Combining the Information from Previous Direct Searches and Indirect Data
mH = 125 ± 10 GeVErler: arXiv:1201.0695
mH = 124.5 ± 0.8 GeV
Assuming the Standard Model
Precision
Electroweakdata??Higgs
couplingblows up!!
Higgspotentialcollapses
Higgs coupling lessthan in Standard Model
viXra Blogger’s Combination of Dec.13th Data
There must be New PhysicsBeyond the Standard Model
Heretical Interpretation of EW Data
Do all the data tell the same story?e.g., AL vs AH
What attitude towards LEP, NuTeV?
What mostof us think
Chanowitz
Higgs + Higher-Order Operators
Precision EW data suggest they are small: why?
But conspiraciesare possible: mH
could be large, even if believeEW data …?
Do not discard possibility of heavy Higgs
Corridor toheavy Higgs?
Barbieri, Strumia
Elementary Higgs or Composite?
• Higgs field:
<0|H|0> ≠ 0• Quantum loop problems
• Fermion-antifermion condensate
• Just like QCD, BCS superconductivity
• Top-antitop condensate? needed mt > 200 GeV
New technicolour force? inconsistent with precision electroweak data? Cut-off Λ ~ 1 TeV with
Supersymmetry?
Cutoff Λ = 10 TeV
Interpolating Models
• Combination of Higgs boson and vector ρ
• Two main parameters: mρ and coupling gρ
• Equivalently ratio weak/strong scale:
gρ / 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• Γ(gg) may be enhanced• Γ(γγ) may be suppressed• Modified self-couplings• Pseudo-baryons
as dark matter?
Compilationof constraints
Campbell, JE, Olive: arXiv:1111.4495
Updatedwith Dec. 11constraints
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 renormalization
• Small: renormalization due to t quark drives quartic coupling < 0at some scale Λ→ vacuum unstable
• Vacuum could be stabilized by supersymmetryEspinosa, JE, Giudice, Hoecker, Riotto, arXiv0906.0954
LHC 95%exclusion
SUSY vs Data
• Electroweak precision observables
• Flavour physics observables
• gμ - 2
• Higgs mass
• Dark matter
• LHCMasterCode: O.Buchmueller, JE et al.
68% & 95% CL contours
….. pre-LHC___ LHC 1/fb
Favoured values of Mh ~ 119 GeV:Range consistent with evidence from LHC !
Higgs mass
χ2 price to pay if Mh = 125 GeV is < 2
Buchmueller, JE et al: arXiv:1112.3564
….. pre-Higgs___ Higgs @ 125
68% & 95% CL contours
Buchmueller, JE et al: arXiv:1112.3564
Favoured values of gluino mass significantlyabove pre-LHC, > 2 TeV
Gluino mass
--- pre-Higgs___ Higgs @ 125… H@125, no g-2
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!
Measurements of Higgs Couplings
• Some decays limited by statistics
• Others limited by systematics
The Spin of the Higgs Boson @ LHC
Higher mass: angular correlations in H → ZZ decays
Low mass: if H →γγ,It cannot have spin 1
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 Vadisgμ - 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+e-
experiments and τ decay
• More credibility?
MSSM: > 100 parametersMinimal Flavour Violation: 13 parameters
(+ 6 violating CP)
SU(5) unification: 7 parameters
NUHM2: 6 parameters
NUHM1 = SO(10): 5 parameters
CMSSM: 4 parametersmSUGRA: 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.
Dropping gμ - 2 allows masses up to dark matter limit
….. pre-LHC___ LHC 1/fb
Impact of droppinggμ-2 constraint
MasterCode: O.Buchmueller, JE et al.
Favoured values of gluino mass significantlyabove pre-LHC, > 1 TeV
….. pre-LHC___ LHC 1/fb
Gluino mass
MasterCode: O.Buchmueller, JE et al.
Favoured values of BR(Bs μ+μ-) above SM value !(due to increase in tan β)
+ LHCbBs μ+μ-
….. pre-LHC___ LHC 1/fb--- with CDF
MasterCode: O.Buchmueller, JE et al.
Favoured values of Mh ~ 119 GeV:Coincides with value consistent with LHC !
Higgs mass
Generic LittleHiggs Models
Loop cancellation mechanism
SupersymmetryLittle Higgs
(Higgs as pseudo-Goldstone
boson of larger symmetry)
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 heavyNot as complete as susy: more physics > 10 TeV
MT < 2 TeV (mh / 200 GeV)2
MW’ < 6 TeV (mh / 200 GeV)2
MH++ < 10 TeV
Searches for Extra Particles in
Little Higgs Models
Spread looks natural: no significant disagreement
Estimates of mH from different Measurements
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