That Infamous Boson: from Obscure Curiosity to Holy
That Infamous Boson: from Obscure Curiosity to Holy Grail Higgs Hunting 2011 John Ellis CERN & Kings College London Outline
The context The proposal The baptism
A phenomenological profile The quest for the Holy Grail When is a Higgs not a Higgs? The LHC has shown there is new physics beyond Higgs Life before Higgs Guage theories irrelevant? Early steps towards quantization (Feynman 1963,
deWitt, Faddeev & Popov 1967) But require massless gauge bosons? Spontaneous breaking of global symmetries (Nambu 1960, Goldstone 1961) Later shown renormalizable (Lee, Symanzik 1969) But require massless Goldstone boson? Could two wrongs make a right?
The Curses of the Massless Bosons Counter-example in theory of superconductivity (Anderson 1963) Speculated that the Goldstone and Yang-Mills zero-mass problems could cancel (also Klein & Lee 1964) But this was thought impossible in relativistic theory because no time-like vector (Gilbert 1964)
The Seminal Papers
The Englert-Brout-Higgs Mechanism 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 Guralnik, Hagen & Kibble (Oct. 12th 1964) 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 Nambu, EB, GHK and Higgs Spontaneous breaking of symmetry
Consecration & Baptism Incorporation in electroweak theory (Weinberg 1967, Salam 1968) Renormalizability breakthrough (t Hooft 1970, 1971) Comprehensive & influential review by Ben Lee (Batavia Conference, 1972) Refers repeatedly to Higgs fields, scalars
Ben Lee the Baptist Ben Lee the Baptist 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) A Phenomenological Profile of the Higgs Boson
Neutral currents (1973)
Charm (1974) Heavy lepton (1975) Much 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 on the Experimental Agenda Searches at LEP: (EG, Yellow report 76-18) e+e- Z + H
(EGN 76, Ioffe & Khoze 78, Lee, Quigg & Thacker 77) Z H + +(EG 76, Bjorken 1978) MH > 114.4 GeV Higgs Boson on the LEP Agenda e+e - Z + H
Z H + +- JE & Gaillard, 1976 Higgs Boson on the LEP Agenda _
Higgs Boson on the pp Agenda gg H Georgi, Glashow, Machacek & Nanopoulos, 1978 W/Z0 + H Glashow, Nanopoulos & Yildiz, 1978
Higgs Boson on the SSC Agenda Higgs Boson on the LHC Agenda Higgs Hunting goes Mainstream Estimating the Mass of the Higgs Electroweak radiative corrections are sensitive to massive particles:
Sensitivity to the top quark mass >> sensitivity to Higgs mass: But LEP measurements gave an indication for a light Higgs even before the top discovery JE, Fogli & Lisi, 1990/1 Estimating the Mass of the Higgs
First attempts in 1990, 1991: Very difficult before the discovery of the top JE, Fogli & Lisi, 1990/1 Estimating the Mass of the Higgs After the discovery of the top: Solid indications of a light Higgs
JE, Fogli & Lisi, 1994/5 Precision Tests of the Standard Model Lepton couplings Pulls in global fit The State of the Higgs: Pre-EPS High-energy search: Limit from LEP:
mH > 114.4 GeV High-precision electroweak data: Sensitive to Higgs mass: mH = 96+3024 GeV Combined upper limit: mH < 157 GeV, or 186 GeV including direct limit Exclusion from high-energy search at Tevatron:
mH < 158 GeV or > 173 GeV Higgs Search @ Tevatron Tevatron excludes Higgs between 158 & 173 GeV First Higgs Searches @ LHC No exclusion yet, but significant contribution to global fit
Information from Direct Higgs Searches Gfitter collaboration Combining the Information from Direct Searches and Indirect Data mH = 120+ 12-5 GeV
Gfitter collaboration The Stakes in the Higgs Search
How is particle symmetry broken? Is there an elementary scalar field? What is the fate of the Standard Model? Did mass appear when the Universe was a picosecond old? Did Higgs help create the matter in the Universe? Did a related inflaton make the Universe so big and old? Why is there so little dark energy?
Theoretical Constraints on Higgs Mass Large large self-coupling blow up at low energy scale due to renormalization Small: renormalization due to t quark drives quartic coupling < 0 at some scale
vacuum unstable Bounds on Higgs mass depend on 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 96% CL CL as function of instability scale Espinosa, JE, Giudice, Hoecker, Riotto, arXiv0906.0954
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! Supersymmetry Search at LHC 95% CL region
68% CL region MasterCode collaboration: http://mastercode.web.cern.ch/mastercode/ 2 = 30.2, fit probability = 11.6% Full LHC 2010 data
CMSSM HiggsMass CMSSM O.Buchmueller, JE et al: in preparation Latest Higgs Searches @ Tevatron Exclude (100,109); (156,177) GeV
Nonsense (Bill Murray) Is the much-discussed excess @ (130, 140) large enough to be likely to be a Standard Model Higgs? Watch out for an excess @ ~ 120 GeV! Plots we would like to see? p0CL
fors bkgrd only for signal What would Higgs signal look like? Best fit + bands for /SM p0 expected if
also signal What if the Higgs is not a Higgs? Tree-level Higgs couplings ~ masses Coefficient ~ 1/v Couplings ~ dilaton of scale invariance Broken by Higgs mass term 2, anomalies Cannot remove 2 (Coleman-Weinberg)
Anomalies give couplings to , 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 Possible enhancement of coupling to gg Possible suppression of coupling to Modified self-couplings: effective potential ~ 4 [ln(/V) ] + anomalous dimensions] + anomalous dimensions Pseudo-baryons as dark matter?
There must be New Physics beyond the Higgs Boson Higgs potential collapses Higgs coupling less than in Standard Model
Higgs coupling blows up 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 learn anything! Wouldnt it be better if they found what
you predicted? Supersymmetry? Would unify matter particles and force particles Related particles spinning at different rates 0 - - 1 - 3/2 - 2 Higgs - Electron - Photon - Gravitino Graviton Many phenomenological motivations
Would help fix particle masses Would help unify forces Predicts light Higgs boson Could fix discrepancy in g - 2
Could provide dark matter for the astrophysicists and cosmologists Imagine What liesa Room Beyond? Open
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