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Beyond the Terascale with muons

Fermilab Accelerator Physics and Technology Seminar / Low-Emittance Muon Collider Workshop, Fermilab, February 2006. Beyond the Terascale with muons. Peter Skands Theoretical Physics Dept. Fermi National Accelerator Laboratory. Overview. Introduction: the Standard Model What works

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Beyond the Terascale with muons

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  1. Fermilab Accelerator Physics and Technology Seminar / Low-Emittance Muon Collider Workshop, Fermilab, February 2006 Beyond the Terascale with muons Peter Skands Theoretical Physics Dept Fermi National Accelerator Laboratory

  2. Overview • Introduction: the Standard Model • What works • What doesn’t • Beyond the Standard Model • Open-minded model building • Inspirational examples • Collider Physics in the post-LHC era Beyond the Terascale with Muons

  3. Below the Terascale D. B. Leinweber, hep-lat/0004025 Beyond the Terascale with Muons

  4. symmetry • breaking • 1 Higgs boson(scalar) masses The Standard Model (s.m.) What works … • Relativistic Quantum Field Theory w/ Poincare Inv. • 45 matter particles(fermions) • 36 quarks • 9 leptons (incl. neutrinos) • 3 Forces(gauge bosons) • Gauged U(1): electromagnetism • Gauged SU(2): weak force • Gauged SU(3): strong force Beyond the Terascale with Muons

  5. What works data Standard Model . . . etc But is that all? Beyond the Terascale with Muons

  6. What Doesn’t • The Standard Model does face a few problems: • A few experiments … • Some mathematics … • Some cosmetics … •  is the TeV scale inhabited? Beyond the Terascale with Muons

  7. A Few Experiments “I have done a Terrible Thing, I have invented a particle that cannot be detected.” W. Pauli Nobel 2002: Raymond Davis Jr., Masatoshi Koshiba What is giving mass to neutrinos? Beyond the Terascale with Muons

  8. A Few Experiments What’s causing this? (Dark Matter?) Beyond the Terascale with Muons

  9. A Few Experiments • The Supernova Cosmology Project: • Type Ia supernovae = extragalactic ‘standard candles’ • The Supernovae are too dim! • Universe accelerates!  Einstein’s Cosmological constant Λ ≠ 0 What’s causing this? (Dark Energy?) Beyond the Terascale with Muons

  10. + Muons … • Muon spin precession • Ability to control & handle muons to extreme precision may already be informing against the Standard Model: (problematic) Is mu is, or is mu ain’t? muon storage ring (BNL) Beyond the Terascale with Muons

  11. G s F ¾ » 1 6 ¼ + Some Mathematics • WLWL scattering • Pertubative scattering P > 1for s ~ 1 TeV2 • Need something (e.g. Higgs) to unitarize theory. (See also Bogdan’s talk) Beyond the Terascale with Muons

  12. But indirectly we know There must be a spectacular cancellation occurring for this to happen  THE HIERARCHY PROBLEM + Some Mathematics • The Standard model isn’t natural! • The Higgs is special, it’s the only (spin 0) • In QFT, the mass of a scalar gets huge contributions from high-energy quantum fluctuations scalar fluct. to top quark etc… Beyond the Terascale with Muons

  13. + Some Mathematics • Gravity does not fit in the Standard Model! • The graviton is special, it’s the only (spin 2) • General Relativity: metric gμν describes curvature of space-time  a mixture of S=0, S=1, and S=2 fields. • In QFT, S=2 is  no sense! • Also, Gravity appears very weak compared to the other forces  Does that mean anything? tensor non-renormalizable Gravity appears to be fundamentally incompatible with Quantum Field Theory! Beyond the Terascale with Muons

  14. + Some Aesthetics • Why more matter than antimatter? • Why 3 generations of quarks and leptons? • Why 3 forces? • Why 3 spatial dimensions? • Are particles really pointlike? • + your children’s favourite questions … Beyond the Terascale with Muons

  15. There could be new fundamental matter? • Is Dark Matter made of Particles? What are they like? WIMPS? Matter Open-minded model building • So: we ask ourselves. Maybe … • How About Dark Energy? • More than 3 Generations of Fermions? • More Higgs Fields? 2HDM? radion? NMSSM? • New Exotic Particles? With new quantum numbers? (Bogdan) • Instantons? Cosmic Strings? Monopoles? … • ‘Fundamental’ Matter Might Be Composite? • Are Quarks or Leptons Composite? (excited fermions? top?) • Is the Higgs particle a Composite? (Technicolor? Top seesaw?) • Is Matter Made up of Strings? Beyond the Terascale with Muons

  16. ³ ´ + 4 2 n 4 p ¹ d R ¡ ¡ g x 2 b R R R R R + + ¹ º ¹ º ¾ ½ a c ¹ º ¹ º ¾ ½ • What is gravity, at the fundamental level? • Deviations from Einstein Gravity? • What is The Quantum Description Of Gravity? • String Theory? G Open-minded model building • So: we ask ourselves. Maybe … • There could be new fundamental interaction(s)? • New Short-range Gauge Forces? (Z’ / W’ ? Technicolor?) • Could there be Lepton or Baryon Number Violation? Matter (Bogdan) • Known forces might not be fundamental? • Grand Unification One Single Primeval Force? [SU(5), SO(10), Supersymmetric Grand Unification, … ] • ‘Stepwise unification’ ?  Left-Right symmetry, flipped SU(5), … Force Beyond the Terascale with Muons

  17. SUSY generators anticommute: They relate particles of different spin: Every SM state must have one (or more) spin-partners! scalar quarks and leptons, gluino, gauginos, higgsinos Open-minded model building • So: we ask ourselves. Maybe … • There could be new symmetries of space-time? • Is There a Supersymmetry (SUSY) in Nature? (Probably most well-studied BSM possibility) Matter Force Spacetime Beyond the Terascale with Muons

  18. Open-minded model building • So: we ask ourselves. Maybe … • There could be new symmetries of space-time? • Is There a Supersymmetry (SUSY) in Nature? (Probably most well-studied BSM possibility) Matter • Why should Nature have this weird symmetry? • SUSY is largest possible symmetry of space-time • Stabilises the Higgs mass  no hierarchy problem • Good dark-matter candidate: lightest neutralino • SM GUT’s don’t work. SUSY GUT’s do • SUSY is the “super” in superstrings • (Gives experimentalists something to look for) Force Spacetime Beyond the Terascale with Muons

  19. Open-minded model building • So: we ask ourselves. Maybe … • There could be new symmetries of space-time? • Is There a Supersymmetry (SUSY) in Nature? (Probably most well-studied BSM possibility Matter • Known symmetries might break down? • Is Lorentz Symmetry Violated to some Small Extent? Force • There could be extra dimensions? • How Many are There? • What Do They Look Like? (Flat / Curved? Big / Small?) • What Lives in Them? (All Matter / Gravity / Exotics /Branes?) (Randall, last week) Spacetime Beyond the Terascale with Muons

  20. What can we say beforehand? • A] A completetheory should: • explain the origin of mass • explain dark matter and dark energy • explain neutrino masses • unitarize WW scattering • agree with all measurements so far • address the hierarchy problem • incorporate quantum gravity • B] A complete theory could: • involve grand unification (we have hints of it) • involve a deviation from the SM (g-2)mu • be aesthetic and natural • be simple Matter Force Spacetime Beyond the Terascale with Muons

  21. What can we say beforehand? • On one hand, we may roughly say • Simplest explanation for neutrino masses involves no new observable physics  • Quantum Gravity extremely difficult to probe experimentally, due to smallness of hG  • Dark Energy: no great ideas at the moment  Matter Force • But! • Best Dark Matter candidate is a weakly-interacting particle with <~ TeV-scale mass  • WW scattering must be unitarised below the TeV scale, probably by Higgs or similar  • If Higgs is there, then hierarchy problem means something new likely at TeV scale  Spacetime Beyond the Terascale with Muons

  22. Collider physics in the post-LHC era • We believe TeV scale to be inhabited • LHC: powerful machine, good discovery potential. Large backgrounds. Composite initial state. Strong-interaction debris, QCD radiation, beam remnants. Difficult to reach high precision. Real life is more complicated Textbook Beyond the Terascale with Muons

  23. High Precision is *important*! • (apologies) ILC propaganda (but also works for MC!): • High precision allows us to extrapolate to fundamental scales GUT? Superheavy intermediate physics? Beyond the Terascale with Muons

  24. Collider physics in the post-LHC era • ILC:precision machine. Below ~ 0.5 TeV. • NB for SUSY: WMAP COBE WMAP Wilkinson Microwave Anisotropy Probe Beyond the Terascale with Muons

  25. ? 1 TeV Collider physics in the post-LHC era • ILC:precision machine. Below ~ 0.5 TeV. • WMAP killed the bulk  • CLIC: technically challenging, but serious alternative. • Both are e+e- , muons are different. • (E.g. intermediate SUSY Higgs factory at 500GeV?) • Neutrino Factory • Probe new physics differently (talk by D. Cline) (talk by B. Dobrescu) Beyond the Terascale with Muons

  26. A Note on Luminosity • Goal: L=1035 cm-2s-1 (acc. units) •  L ~ 1000 fb-1 / yr  100 evts/yr for σ > 0.1 fb • But lots of physics potential with smaller luminosity as well  σ > “a few” fb. • Physics case exists also for L=1032,33,34cm-2s-1, due to high energy. • (Large lumi still needed for precision) Beyond the Terascale with Muons

  27. Outlook for the TeV scale and the muon collider • We believe the TeV scale to be inhabited • The LHC is a powerful machine, but difficult to get high precision • And high precision is important! • If built, ILC will add immensely to our knowledge no matter what, but need higher energy if LHC indicates new physics is heavy • Even if new physics is within ILC reach, it is likely only the top of an iceberg. Higher energies will still be needed to probe the full spectrum! Beyond the Terascale with Muons

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