Beyond the Terascale with muons

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

• Introduction the Standard Model
• What works
• What doesnt

• Beyond the Standard Model
• Open-minded model building
• Inspirational examples

• Collider Physics in the post-LHC era

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Below the Terascale
D. B. Leinweber, hep-lat/0004025
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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

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What works
data
Standard Model
. . . etc
But is that all?
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What Doesnt

• The Standard Model does face a few problems
• A few experiments
• Some mathematics
• Some cosmetics

• ? is the TeV scale inhabited?

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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?
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A Few Experiments
Whats causing this? (Dark Matter?)
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A Few Experiments

• The Supernova Cosmology Project
• Type Ia supernovae extragalactic standard
  candles
• The Supernovae are too dim!
• Universe accelerates!

? Einsteins Cosmological constant ? ? 0
Whats causing this? (Dark Energy?)
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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 aint?
muon storage ring (BNL)
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Some Mathematics

• WLWL scattering
• Pertubative scattering P gt 1for s 1 TeV2
• Need something (e.g. Higgs) to unitarize theory.

(See also Bogdans talk)
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Some Mathematics

• The Standard model isnt natural!
• The Higgs is special, its 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
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Some Mathematics

• Gravity does not fit in the Standard Model!
• The graviton is special, its the only
  (spin 2)
• General Relativity metric gµ? describes
  curvature of space-time ? a mixture of S0, S1,
  and S2 fields.
• In QFT, S2 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!
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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 childrens favourite questions

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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?

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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
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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
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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 GUTs dont work. SUSY GUTs do
• SUSY is the super in superstrings
• (Gives experimentalists something to look for)

Force
Spacetime
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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
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What can we say beforehand?

• A A complete theory 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
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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 lt 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
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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
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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?

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Collider physics in the post-LHC era

• ILC precision machine. Below 0.5 TeV.
• NB for SUSY WMAP

COBE
WMAP Wilkinson Microwave Anisotropy Probe
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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 ee- , 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)
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A Note on Luminosity

• Goal L1035 cm-2s-1 (acc. units)
• ? L 1000 fb-1 / yr ? 100 evts/yr for s gt 0.1 fb
  
• But lots of physics potential with smaller
  luminosity as well ? s gt a few fb.
• Physics case exists also for L1032,33,34
  cm-2s-1, due to high energy.
• (Large lumi still needed for precision)

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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!