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DARK MATTER
Jonathan FengUniversity of California, Irvine
University of Colorado, Boulder21 June 2011
Credit: John K
orm
endy
21 June 11 Feng 2
PHYSICS: TRADITIONAL VIEW
small largeParticlePhysics
NuclearPhysics
AtomicPhysics
CondensedMatter Physics
Biophysics
Astrophysics
Cosmology
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Particle Physics
CondensedMatter Physics
Biophysics
Astrophysics
Cosmology
Nuclear Physics
Atomic Physics
PHYSICS: UPDATED VIEW
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21 June 11 Feng 5
THE LARGE FRONTIER
clusters ofgalaxies
1012
meters
solar system galaxy
1017
meters1023
meters> 1026
meters
universe
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EVIDENCE FOR DARK MATTER:CLUSTERS OF GALAXIES
In the 1930’s Fritz Zwicky observed the Coma cluster and found that the galaxies were moving too fast to be
contained by the visible matter
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EVIDENCE FOR DARK MATTER:INDIVIDUAL GALAXIES
In the 1970’s Vera Rubin and collaborators and Albert Bosma found that stars in galaxies were rotating too fast
to be contained by the visible matter
THE STANDARD MODEL OF COSMOLOGY
• Atoms make up only 4% of the Universe
• The rest of the matter is dark matter, which does not shine or reflect light– Not atoms– Cold– Stable
• Also, 73% of the Universe isn’t even matter
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THE SMALL FRONTIER
electron
1010 meters(thickness of human
hair ~ 10-5 m)
up quarkdown quark
atom
nucleus protonneutron
1014
meters1015
meters< 108
meters
• Strong
• Weak
4 FORCES OF NATURE
• Gravity
• Electromagnetism
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STANDARD MODEL OF PARTICLE PHYSICS
Atoms
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Known DM properties
WHICH PARTICLE IS DARK MATTER?
• Not atoms
The extraordinarily successful standard models of cosmology and particle physics are inconsistent
• Cold
• Stable
• In 1821 Alexis Bouvard found anomalies in the path of Uranus and suggested they could be caused by unseen matter
• In 1845-46 Urbain Le Verrier determined where this matter should be. With this guidance, Johann Galle discovered the unseen matter at the Berlin Observatory in 1846
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• Le Verrier wanted to call it Le Verrier, but this matter is now known as Neptune, the farthest known planet (1846-1930, 1979-1999, 2006-present)
WHAT SHOULD WE DO?
• Strong
• Weak
WHICH FORCES DOES DARK MATTER FEEL?
• Gravity
• Electromagnetism
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?
OPTION 1: WIMPS
• Dark matter feels the weak force
• DM = WIMPs: weakly-interacting massive particles
• Why WIMPs? Looking under the lamp post
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THE WIMP MIRACLE
• But there’s more to it than that
• Many theories predict WIMPs that are around 100 times heavier than the proton
Feng 16
DM DM
q q
time
• Such particles are present just after the Big Bang, but then annihilate in pairs. Assuming they annihilate through the weak force, calculations show that they should be ~ 10% of the Universe now. This is what is required to be dark matter!
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WIMP DETECTION
• If WIMPs annihilated in the early Universe, they should also be doing that now
• We can look for rare forms of matter and anti-matter created in these collisions
Feng 17
DM DM
q qtim
e21 June 11
ICECUBE IN ANTARCTICA
Looking for neutrinos produced by WIMP annihilation in the Sun
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ALPHA MAGNETIC SPECTROMETER
Carried by Space Shuttle to the International Space Station
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Feng 20
WIMP PRODUCTION
• If WIMPs annihilated in the early Universe, we should also be able to run time backwards
• We can collide two normal particles at high velocities to create dark matter, which we detect as missing energy
Feng 20
DM DM
q qtim
e21 June 11
Feng 21
LARGE HADRON COLLIDER
Colliding protons at 99.999999% the speed of light
Feng 2121 June 11
Feng 22
Billion collisions per second; dark matter is a needle in the haystack
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CMS
WIMP RECOILS• If WIMPs annihilated in the early Universe, we should also be
able to run time sideways
• We can watch for normal matter recoiling from a WIMP collision. At any given time, there is roughly 1 WIMP per coffee cup, but their interactions are weak and recoils are rare
Feng 23
DM DM
q q
time21 June 11
CRYOGENIC DARK MATTER SEARCH
Colliding protons at 99.999999% the speed of lightOperating at milli-Kelvin temperatures in a mine in Minnesota
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Collision rate should change as the Earth goes around the Sun: annual modulation (1986)
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DAMA/LIBRA signal with period ≈ 1 year, maximum ≈ June 2
DAMA/LIBRA IN ITALYD
AM
A/L
IBR
A (2
01
0)
OPTION 2: SUPERWIMPS
• Dark matter does not feel the weak force
• DM = SuperWIMPs: superweakly-interacting massive particles
• Seemingly a lost cause
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GRAVITINOS
Feng 27
• An example: gravitinos proposed by Pagels and Primack in 1982
• Gravitinos feel only gravity
• But they may be created by decaying particles that have dramatic implications for the LHC
Long-lived progenitor(charge and mass)
q(charge)
SuperWIMP(mass)
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GRAVITINOS AT THE LHC
D. A
kerib
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SUMMARY
• We now have two extraordinarily successful theories of the large and small, but they don’t match
• A quarter of the Universe is dark matter, but we don’t know what it is
• We have some ideas, though, and many interesting search experiments underway
Feng 2921 June 11