What Particle Physicists Want to Know

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What Particle PhysicistsWant to Know

• Hitoshi Murayama
• Letters Science Forum
• December 2, 2002

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We are interested inthings we dont see
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Energy budget of Universe

• Stars and galaxies are only 0.5
• Neutrinos are 0.310
• Rest of ordinary matter (electrons and protons)
  are 5
• Dark Matter 30
• Dark Energy 65
• Anti-Matter 0
• Higgs condensate 1062??

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The Cosmic Questions

• What is Dark Matter?
• What is Dark Energy?
• How much is Neutrino component?
• Is Higgs Boson really there?
• Where did Anti-Matter go?

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Einsteins Dream

• Is there an underlying simplicity behind vast
  phenomena in Nature?
• Einstein dreamed to come up with a unified
  description
• But he failed to unify electromagnetism and
  gravity (GR)

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History of Unification
electric
magnetic
planets
atoms
apple
electromagnetiesm
Quantum mechanics
gravity
mechanics
g-decay
b-decay
a-decay
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We are just about to achieveanother layer of
unification

• HERA ep collider

• Unification of electromagnetic and weak forces
• ? electroweak theory
• Long-term goal since 60s
• We are getting there!
• The main missing link
• Higgs boson

EM
weak
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What are they?
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Wimpy and AbundantNeutrinos are Everywhere

• They come from the Big Bang
• When the Universe was hot, neutrinos were created
  equally with any other particles
• They are still left over 300 neutrinos per cm3
• They come from the Sun
• Trillions of neutrinos going through your body
  every second
• They are shy
• If you want to stop them, you need to stack up
  lead shield up to three light-years

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Neutrinosfrom backstage to center stage

• Pauli postulated neutrinos in order to save the
  energy conservation in nuclear b-decay in 1930
• Finally discovered by Cowan and Reines using a
  nuclear reactor in 1958
• Massless Neutrinos in the Standard Model (60s)
• Evidence for neutrino mass from SuperK (1998) and
  SNO (2002)

• First evidence that the minimal Standard Model of
  particle physics is incomplete!
• 2002 Nobel to pioneers Davis and Koshiba

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Neutrinos Have Mass
SuperKamiokande
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Raised More Questions

• Why do neutrinos have mass at all?
• Why so small?
• At least million times smaller than the lightest
  particle electron
• We have seen mass differences. What are the
  masses? Wnmn/15eV
• Are neutrinos and anti-neutrinos the same?

• How do we extend the Standard Model to
  incorporate massive neutrinos?

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Evidence for Dark Matter

• Galaxy and cluster of galaxies are held together
  by mass far bigger than all stars combined

• Crucial ingredient in the standard cosmology
  and structure formation
• It is not dim small stars (e.g., MACHOs)
• WIMPs (Weakly Interacting Massive Particle)
  strongly favored
• Stable heavy particle produced in early Universe,
  left-over from near-complete annihilation
• TeV1012eV (or T1016 degrees) the correct
  energy scale to produce them

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Type-IA Supernovae

• Type-IA Supernovae standard candles
• Brightness not quite standard, but correlated
  with the duration of the brightness curve
• Apparent brightness
• ? how far (time)
• Know redshift
• ? expansion since then
• Expansion of Universe is accelerating

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Accelerating Universe

• Einsteins equation
• If the energy dilutes as Universe expands, it
  must slow down
• Need something that gains in energy as Universe
  stretches
• i.e, negative pressure
• The cosmological constant L has the equation of
  state wp/r1
• Generically called Dark Energy

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Embarrassment with Dark Energy

• A naïve estimate of the cosmological constant in
  Theory
• rLMPl4GN210120 times observation
• The worst prediction in theoretical physics!
• People had argued that there must be some
  mechanism to set it zero
• But now it seems finite???

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Cosmic Coincidence Problem

• Why do we see matter and cosmological constant
  almost equal in amount?
• Why Now problem
• Actually a triple coincidence problem including
  the radiation
• If there is a deep reason for rL GN2(TeV)8,
  coincidence natural

Arkani-Hamed, Hall, Kolda, HM
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What is the Dark Energy?

• We have to measure w
• For example with a dedicated satellite experiment

SNAP
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Mystery of the weak force

• Gravity pulls two massive bodies (long-ranged)
• Electric force repels two like charges
  (long-ranged)
• Weak force pulls protons and electrons
  (short-ranged) acts only over 1016 cm need
  it for the Sun to burn!

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Something is in the Universe

• There is something filling our Universe
• It doesnt disturb gravity or electric force
• It does disturb weak force and make it
  short-ranged
• No longer go with speed of light, acquire a mass
• Mother of mass of all elementary particles
• Electron, quarks, muon,
• What is it??

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Cosmology and Particle Physicsmeet at TeV scale

• Dark Matter
• mWIMPTeV
• Fermi (Higgs) scale
• v1/4 TeV
• Dark Energy
• rL(2meV)4 vs GN1/2(TeV)20.5meV
• Neutrino
• (Dm2LMA)1/27meV vs GN1/2(TeV)20.5meV
• TeV-scale physics likely to be rich

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LHC

• Large Hadron Collider
• 14 TeV pp
• CERN (Geneva)
• Under construction
• LHC would discover Standard Model Higgs boson of
  any mass within 3 years!
• Measure mass, some ratio of couplings

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LC

• Linear ee Collider
• 0.51.5 TeV
• International Project
• Planning stage
• Tests if Higgs Boson is the Mother of Mass

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Dark MatterThe Missing Link?

• Dark Matter likely to be TeV-scale electrically
  neutral weakly interacting particle (e.g., LSP,
  Lightest KK)
• Then accessible at accelerators (LHC LC)
• Precision measurement at LC of its mass,
  couplings in order to calculate its cosmic
  abundance
• If it agrees with cosmological observations, we
  understand Universe back to 1010 sec after the
  Big Bang

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Where Did Anti-Matter Go?
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Matter and Anti-MatterEarly Universe
10,000,000,001
10,000,000,000
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Matter and Anti-MatterCurrent Universe
us
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The Great Annihilation
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Baryogenesis

• What created this tiny excess matter?
• Necessary conditions for baryogenesis (Sakharov)
• matter number non-conservation
• CP violation
• (subtle difference between matter and
  anti-matter)
• Non-equilibrium
• ? G(DBgt0) gt G(DBlt0)
• Possible new consequences in
• Matter instability
• CP violation

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Do We Exist Thanks to Neutrino Mass?

• Plans to shoot neutrino beams over thousands of
  kilometers to see this

• CP-violation may be observed in neutrino
  oscillation

Its of course completely safe!
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Conclusion

• What is Universe made of?
• Einsteins Dream towards unified description
• Physics at TeV scale likely to be rich
• LHC LC major assault on physics at TeV-scale
• Many cosmic questions accessible experimentally
• Dark Matter, Dark Energy, Higgs Condensate,
  Anti-Matter