Transcript Standard Model is an Effective Theory
Anticipating New Physics @ the LHC
• Why the Terascale?
• Scenarios for Electroweak Symmetry Breaking and the Gauge Hierarchy – LHC Signatures – Connection to Dark Matter • Summary: Discoveries are only months away!
APS April Meeting, 2007 J. Hewett, Stanford Linear Accelerator Center
Why the Terascale?
• Electroweak Symmetry breaks at energies ~ 1 TeV (Higgs or ???)
• Gauge Hierarchy: Nature is fine-tuned or Higgs mass must be stabilized by New Physics ~ 1 TeV • Dark Matter: Weakly Interacting Massive Particle must have mass ~ 1 TeV to reproduce observed DM density
The LHC is turning on!
The anticipation has fueled many ideas!
A Cellar of New Ideas ’67 The Standard Model ’77 Vin de Technicolor a classic!
aged to perfection better drink now ’70’s Supersymmetry: MSSM mature, balanced, well developed - the Wino’s choice ’90’s-now SUSY Beyond MSSM svinters blend ’90’s CP Violating Higgs all upfront, no finish lacks symmetry ’98 Extra Dimensions bold, peppery, spicy uncertain terrior ’02 Little Higgs complex structure ’03 Fat Higgs ’03 Higgsless ’04 Split Supersymmetry ’05 Twin Higgs young, still tannic needs to develop sleeper of the vintage what a surprise!
finely-tuned double the taste J. Hewett
Discoveries at the LHC will find the vintage nature has bottled.
The Standard Model of Particle Physics
Building Blocks of Matter: Symmetry: SU(3) C x SU(2) L x U(1) Y QCD Electroweak Spontaneously Broken to QED This structure is experimentally confirmed!
The Standard Model Higgs Boson Economy: 1 scalar doublet Higgs Potential: V( ) = 2 2 /2 + 4 /4 Spontaneous Symmetry Breaking Chooses a vacuum v = 0| |0 and shifts the field = - v V( ) = m 2 2 /2 + v 3 + 4 /4 gives 1 physical Higgs scalar with m = 2 v Masses of electroweak gauge bosons proportional to v We need to discover the Higgs and experimentally test this potential and the Higgs properties!
Higgs Mass Upper Bound: Gauge Boson Scattering
Higgs Higgs Bad violation of unitarity ~ E 2 Restores unitarity Expand cross section into partial waves Unitarity bound (Optical theorem!) |Re a 0 | < ½ Gives m H < 1 TeV LHC is designed to explore this entire region!
Present Limits: Direct Searches at LEP: m H > 114.4 GeV Indirect Searches at LEP/SLC: m H < 150-200 GeV @ 95% CL Higgs Z Z Z
Higgs @ the LHC: Production mechanisms & rates Signal determined by final state versus background
Low: M H < 140 GeV Higgs Search Strategies Medium: 130
The Hierarchy Problem
Energy (GeV) 10 19 10 16 Planck GUT Quantum Corrections: Virtual Effects drag Weak Scale to M Pl Future Collider Energies 10 3 Weak All of known physics 10 -18 Solar System Gravity m H 2 ~ ~ M Pl 2
The Hierarchy Problem: Supersymmetry
Energy (GeV) 10 19 10 16 Planck GUT Quantum Corrections: Virtual Effects drag Weak Scale to M Pl boson Future Collider Energies 10 3 Weak m H 2 ~ ~ M Pl 2 fermion All of known physics 10 -18 Solar System Gravity m H 2 ~ ~ - M Pl 2 Large virtual effects cancel order by order in perturbation theory
Supersymmetry
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•Symmetry between fermions and bosons •Predicts that every particle has a superpartner of equal mass gravity ( SUSY is broken: many competing models!) •Suppresses quantum effects •Can make quantum mechanics consistent with (with other ingredients)
Supersymmetry at the LHC
SUSY discovery generally ‘easy’ at LHC Cut: E T miss > 300 GeV
LHC Supersymmetry Discovery Reach
Model where gravity mediates SUSY breaking – 5 free parameters at high energies Squark and Gluino mass reach is 2.5-3.0 TeV @ 300 fb -1
MSSM only viable for m h < 135 GeV Carena, Haber hep-ph/0208209
MSSM: tension with fine-tuning Competing factors: – Mass of lightest higgs m h < M Z at tree-level large quantum corrections from top sector < (130 GeV) 2 If stop mass ~ 1 TeV – Stability of Higgs mass stops cut-off top contribution to quadratic divergence stops can’t be too heavy – Z mass relationship
Resolve Fine-Tuning: Extend the MSSM • NMSSM (Next-to Minimal SSM) – Add a Higgs Singlet - Evade LEP bounds – minimize fine-tuning!
Dermisek, Gunion, … - Regions where Higgs discovery is difficult @ LHC • MNMSSM (Minimally Non-minimal MSSM) – Lightest higgs < 145 GeV – Observable @ LHC Panagiotakopoulos, Pilaftis • Gauge Extensions of MSSM – M h < 250 (350) GeV • Split Supersymmetry Batra, Delgado, Kaplan, Tait
Dark Matter in Supersymmetry •A component of Dark Matter could be the Lightest Neutralino of Supersymmetry - stable and neutral with mass ~ 0.1 – 1 TeV •In this case, electroweak strength annihilation gives relic density of Mass of Dark Matter Particle from Supersymmetry (TeV) m 2 Ω CDM h 2 ~ (1 TeV) 2
Determination of Dark Matter Density @ LHC • Measure SUSY properties @ LHC • Benchmark point SPS1a • Dependence on Stau mass determination Baltz, Battaglia, Peskin, Wizansky hep-ph/0602187
The Hierarchy Problem: Extra Dimensions
Energy (GeV) 10 19 10 16 Planck GUT Simplest Model: Large Extra Dimensions Future Collider Energies All of known physics 10 3 10 -18 Weak – Quantum Gravity = Fundamental scale in 4 + dimensions M Pl 2 = (Volume) M D 2+ Gravity propagates in D = 3+1 + dimensions Solar System Gravity Arkani-Hamed, Dimopoulis, Dvali
10 1 10 -1 JLH 10 -2 10 2
Kaluza-Klein Modes in a Detector
Indirect Signature Missing Energy Signature pp g + G n LHC M ee [GeV] Vacavant, Hinchliffe
Graviton Exchange Modified with Running Gravitational Coupling SM D=3+4 M * = 4 TeV t= 1 0.5
Insert Form Factor in coupling to parameterize running M * D-2 [1+q 2 /t 2 M * 2 ] -1 Could reduce signal!
JLH, Rizzo, to appear
Black Hole Production @ LHC: Dimopoulos, Landsberg Giddings, Thomas Black Holes produced when s > M * Classical Approximation: [space curvature << E] E/2 b E/2 b < R s (E) BH forms Geometric Considerations: Naïve = R s 2 (E), details show this holds up to a factor of a few
Production rate is enormous!
Determination of Number of Large Extra Dimensions 1 per sec at LHC!
JLH, Lillie, Rizzo hep-ph/0503178
Black Hole event simulation @ LHC
The Hierarchy Problem: Extra Dimensions
Energy (GeV) 10 19 10 16 Planck GUT Model II: Warped Extra Dimensions strong curvature Future Collider Energies 10 3 Weak wk = M Pl e -kr All of known physics 10 -18 Solar System Gravity Randall, Sundrum
Kaluza-Klein Modes in a Detector: SM on the brane
Number of Events in Drell-Yan For this same model embedded in a string theory: AdS 5 x S Davoudiasl, JLH, Rizzo
Kaluza-Klein Modes in a Detector: SM off the brane
Fermion wavefunctions in the bulk: decreased couplings to light fermions for gauge & graviton KK states gg g n gg G n ZZ Agashe, Davoudiasl, Perez, Soni hep-ph/0701186 Lillie, Randall, Wang, hep-ph/0701164
Issue: Top Collimation g 1 = 2 TeV gg g n tt g 1 = 4 TeV Lillie, Randall, Wang, hep-ph/0701164
The Hierarchy Problem: Little Higgs
Energy (GeV) 10 19 10 16 Planck GUT Little Hierarchies!
Future Collider Energies 10 4 10 3 New Physics!
Weak All of known physics 10 -18 Solar System Gravity Simplest Model: The Littlest Higgs with ~ 10 TeV No UV completion Arkani-Hamed, Cohen, Katz, Nelson
The Hierarchy Problem: Little Higgs
Energy (GeV) Future Collider Energies All of known physics 10 19 10 16 .
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10 6 10 5 10 4 10 3 Planck GUT New Physics!
New Physics!
New Physics!
Weak Stacks of Little Hierarchies Simplest Model: The Littlest Higgs with 1 ~ 10 TeV 2 3 …..
~ 100 TeV ~ 1000 TeV 10 -18 Solar System Gravity
Little Higgs: The Basics • The Higgs becomes a component of a larger multiplet of scalars, • transforms non-linearly under a new global symmetry • New global symmetry undergoes SSB leaves Higgs as goldstone • Part of global symmetry is gauged Higgs is pseudo-goldstone • Careful gauging removes Higgs 1-loop divergences m h 2 2 ~ , (16 2 ) 2 > 10 TeV, @ 2-loops!
3-Scale Model > 10 TeV: New Strong Dynamics f ~ /4 v ~ f/4 Global Symmetry ~ TeV: Symmetires Broken Pseudo-Goldstone Scalars New Gauge Fields New Fermions ~ 100 GeV: Light Higgs SM vector bosons & fermions Sample Spectrum
Little Higgs Gauge Production WZ W H WZ 2j + 3l + Azuelos etal, hep-ph/0402037 Birkedal, Matchev, Perelstein, hep-ph/0412278
The Hierarchy Problem: Higgsless
Energy (GeV) 10 19 10 16 Planck GUT Warped Extra Dimensions strong curvature Future Collider Energies 10 3 Weak wk = M Pl e -kr With NO Higgs boson!
All of known physics 10 -18 Solar System Gravity Csaki, Grojean,Murayama, Pilo, Terning
Framework: EW Symmetry Broken by Boundary Conditions SU(2) L x SU(2) R x U(1) B-L Planck brane in 5-d Warped bulk TeV-brane BC’s restricted by variation of the action at boundary SU(2) R x U(1) B-L W R , Z R get U(1) Y Planck scale masses SU(2) L x SU(2) R SU(2) D SU(2) Custodial Symmetry is preserved!
W , Z get TeV scale masses left massless!
Unitarity in Gauge Boson Scattering: What do we do without a Higgs?
Exchange gauge KK towers: Conditions on KK masses & couplings: (g 1111 ) 2 4(g 1111 ) 2 = k M 1 2 (g 11k ) 2 = k (g 11k ) 2 M k 2 Csaki etal, hep-ph/0305237 Necessary, but not sufficient, to guarantee perturbative unitarity!
Production of Gauge KK States @ LHC gg, qq g 1 dijets Davoudiasl, JLH, Lilllie, Rizzo Balyaev, Christensen
The Hierarchy Problem: Who Cares!!
Planck Scale Gauge Hierarchy Problem Weak Scale Cosmological Constant Problem Cosmological Scale We have much bigger Problems!
Energy (GeV)
Split Supersymmetry
: Arkani-Hamed, Dimopoulis hep-ph/0405159 Giudice, Romanino hep-ph/0406088 M GUT ~ 10 16 GeV M S : SUSY broken at high scale ~ 10 9-13 Scalars receive mass @ high scale GeV M weak 1 light Higgs + Fermions protected by chiral symmetry
Collider Phenomenology: Gluinos • Pair produced via strong interactions as usual • Gluinos are long-lived • No MET signature • Form R-hadrons Gluino pair + jet cross section ~ q ~ g 100 fb -1 q 1 0 q Rate ~ 0, due to heavy squark masses!
JLH, Lillie, Masip, Rizzo hep-ph/0408248
Density of Stopped Gluinos in ATLAS Arvanitaki, etal hep-ph/0506242 See also ATLAS study, Kraan etal hep-ph/0511014
This is a Special Time in Particle Physics
• Urgent Questions Provocative discoveries lead to urgent questions • Connections Questions seem to be related in fundamental, yet mysterious, ways • Tools We have the experimental tools, technologies, and strategies to tackle these questions
We are witnessing a Scientific Revolution in the Making!
The LHC is Turning On!!!!!!!!
And we are ready!
Higgs Coupling Determinations @ LHC Observed Channels: Duhrssen, Heinemeyer, Logan, Rainwater, Weiglein, Zeppenfeld – gg H – qqH ZZ, WW, qqZZ, qqWW, qq , qq – WH WWW, W ; ZH – ttH, with H WW, , bb Z Employ Narrow Width Approx: (H) B(H xx) = (H) SM p p SM x tot Theoretical Assumption: V V SM , V=W,Z