Transcript Supersymmetry - University of California, Berkeley

Supersymmetry
The Coming Revolutions in Particle Physics
Hitoshi Murayama (UC Berkeley)
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Introduction
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20th Century Physics
• Two great discoveries of 20th cent. physics:
– Quantum Mechanics
– Einstein’s Special Relativity
(Electromagnetism)
• Marriage between the two
 Existence of Anti-matter
doubled #particles
– Positron (anti-particle of electron) 1932
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– Anti-proton 1955 (Bevatron, Berkeley)
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21st Century Physics
• Marriage of Quantum Mechanics and
Gravity (Einstein’s General Relativity)
 Existence of Super-matter
Double #particles again
• Photino (superpartner of photon) 2004?
• Selectron (superpartner of electron) 2010?
 Supersymmetry
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Outline
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Introduction
Anti-Matter
Weak Force and God Particle
God Particle’s Problem
Supersymmetry
Conclusion
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Anti-Matter
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Matter & Anti-Matter Annihilate!
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Why was Anti-Matter Needed?
• At the end of 19th century: a “crisis” about
electron
– Like charges repel: hard to keep electric charge
in a small pack
– Electron is point-like
– At least smaller than 10-17 cm
• Need a lot of energy to keep it small!
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E=mc
• Need more than 109 eV of
energy to pack electric
charge tightly inside the
electron
• But the observed energy of
the electron is only 5 105 eV
• Electron cannot be smaller
than 10–13 cm??
• Breakdown of theory of
electromagnetismAAAS 2001 San Francisco
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Uncertainty Principle
• Energy-Time Uncertainty
Principle:
You can violate energy
conservation if it is only for a
short time
• Vacuum is full of
quantum bubbles!
Werner Heisenberg
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Anti-Matter Helps
• Electron creates a
force to repel itself
• Vacuum bubble of
matter anti-matter
creation/annihilation
• Electron annihilates
the positron in the
bubble
 only 10% of mass
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Anti-Matter Helps
• “Anti-matter attraction” cancels “Likecharge repulsion”
• It does not cost too much energy to tightly
pack the electric charge inside the electron
• Needed anti-matter: double #particles
• Theory of electromagnetism now works at
very short distances (12 digits accuracy!)
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Weak Force and God Particle
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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 10–16 cm
[need it for the Sun to burn!]
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Something is in the Universe
• There is something filling our Universe
• It doesn’t disturb gravity or electric force
• It does disturb weak force and make it shortranged
• What is it??
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The God Particle
• “Higgs Boson” fills
our Universe
• It disturbs the weak
force so that it cannot
act very far
• We are sure it exists.
But nobody has seen it
yet
• Mother of all masses
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But soon?
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Fermi’s dream era
• Fermi formulated the
first theory of weak
force (1933)
• Knew the required
energy to study the
problem: 1012 eV
• We are finally
getting there!
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God Particle’s Problem
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Higgs repels itself, too
• Just like electron
repeling itself because
of its charge, Higgs
boson also repels itself
• Requires a lot of
energy to contain itself
in its point-like size!
• Breakdown of theory
of weak force
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But there is gravity
• Gravity and quantum mechanics unify at an
extremely short distance 10–33 cm
• Higgs boson must be this small, too, to have
a sensible unified theory of gravity and
quantum mechanics
• But current theory of weak force breaks
down already at 10–17 cm
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Supersymmetry
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History repeats itself?
• Double #particles again 
superpartners
• “Vacuum bubbles” of
superpartners cancels the energy
required to contain Higgs boson
in itself
• Theory of weak force made
consistent with unification of
gravity and quantum mechanics
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Einstein’s dream
• Forces with very different
strengths:
electromagnetism, strong,
weak forces
• Strengths change at
different distance scales
• They become equal:
share the same origin
 “Grand Unification”
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Where are the superpartners?
• They need to cancel self-repelling energy of
the Higgs boson
• Cannot be too heavy to do this job
• Have to be below 1012 eV or “Fermi
energy”
• We are getting there this decade
– Tevatron (Fermilab, Illinois)
– LHC (CERN, Switzerland)
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2001–
2006–
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Superpartners everywhere?
• There are unknown
“Dark Matter” in our
galaxy and outside
• It amounts for about
30% of the Universe
• Lightest superpartner
one of the best
candidates
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Superpartners as probe
• Most exciting thing
about superpartners
beyond existence:
They carry
information of smalldistance physics to
something we can
measure
e.g., “Is Grand
Unification true?”AAAS 2001 San Francisco
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Conclusions
– We are finally reaching “Fermi’s dream era”
– We will know what is disturbing the weak
force, and generating all masses soon
– To make Higgs boson contain itself without
needing too much energy, we need
supersymmetry
– Superpartners are within the reach this decade
– They bring more information about ultimate
short-distance physics
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