J. Goodman Richtmyer Lecture – Jan. 2002
Richtmyer Lecture
Neutrinos, Dark Matter and the Cosmological Constant
The Dark Side of the Universe
Jordan GoodmanUniversity of Maryland
J. Goodman Richtmyer Lecture – Jan. 2002
Outline
• Matter in the Universe• Why do we care about neutrinos?• Why do we think there is dark matter?• Could some of it be neutrinos?• The search for neutrino mass• Type Ia Supernova and the accelerating
Universe• Dark Energy
J. Goodman Richtmyer Lecture – Jan. 2002
Seeing Big Picture
J. Goodman Richtmyer Lecture – Jan. 2002
The early periodic table
J. Goodman Richtmyer Lecture – Jan. 2002
The structure of matter
1889 - Mendeleyev – grouped elements by atomic weights
J. Goodman Richtmyer Lecture – Jan. 2002
The structure of matter (cont.)
• This lead eventually to a deeper understanding
Eventually this led toOur current picture of the atom and nucleus
J. Goodman Richtmyer Lecture – Jan. 2002
What are fundamental particles?
• We keep finding smaller and smaller things
J. Goodman Richtmyer Lecture – Jan. 2002
Our current view of underlying structure of matter
• P is uud
• N is udd
• is ud
• k is us
• and so on…
The Standard Model
}Baryons
}Mesons
(nucleons)
J. Goodman Richtmyer Lecture – Jan. 2002
Facts about Neutrinos
• Neutrinos are only weakly interacting
• Interaction length is ~1 light-year of steel
• 40 billion neutrinos continuously hit every cm2 on earth from the Sun (24hrs/day)
• 1 out of 100 billion interact going through the Earth
• 1931 – Pauli predicts a neutral particle to explain energy and momentum non-conservation in Beta decay.
• 1934 - Enrico Fermi develops a comprehensive theory of radioactive decays, including Pauli's particle, Fermi calls it the neutrino (Italian: "little neutral one").
• 1959 - Discovery of the neutrino is announced by Clyde Cowan and Fred Reines
J. Goodman Richtmyer Lecture – Jan. 2002
Why do we care about neutrinos?
• Neutrinos – They only interact
weakly– If they have mass at all
– it is very small • They may be small, but there sure are a
lot of them!– 300 million per cubic meter left over from the
Big Bang– with even a small mass they could be most
of the mass in the Universe!
J. Goodman Richtmyer Lecture – Jan. 2002
The Ultimate Fate of the Universe
• measures the total energy density of the Universe– If > 1 Universe is closed– If < 1 Universe is open
• = 1 Universe (Etot=0) - Flat universe • From the mass of the stars we get
• Theorists say • What is the other 99.5% of the Universe?
J. Goodman Richtmyer Lecture – Jan. 2002
Why do we think there is dark matter?
• Isn’t obvious that most of the matter in the Universe is in Stars?
Spiral Galaxy
J. Goodman Richtmyer Lecture – Jan. 2002
Why do we think there is dark matter?
• In a gravitationally bound system out past most of the mass V ~ 1/r1/2
• We can look at the rotation curves of other galaxies– They should drop off
But they don’t!
J. Goodman Richtmyer Lecture – Jan. 2002
Why do we think there is dark matter?
• There must be a large amount of unseen matter in the halo of galaxies– Maybe 20 times more than in the stars!– Our galaxy looks 30 kpc across but recent data
shows that it looks like it’s 200 kpc across
J. Goodman Richtmyer Lecture – Jan. 2002
Measuring the energy in the Universe
• We can measure the mass of clusters of galaxies with gravitational lensing
• These measurements give mass ~0.3
• We also know (from the primordial deuterium abundance) that only a small fraction is nucleons
nucleons < ~0.05 Gravitational
lensing
J. Goodman Richtmyer Lecture – Jan. 2002
What is this ghostly matter?
• Could it be neutrinos?• How much neutrino mass would it take?
– Proton mass is 938 MeV– Electron mass is 511 KeV
• A neutrino mass of only 2eV would solve the galaxy rotation problem – 6 eV would close the Universe
J. Goodman Richtmyer Lecture – Jan. 2002
Does the neutrino have mass?
J. Goodman Richtmyer Lecture – Jan. 2002
Detecting Neutrino Mass
• If neutrinos of one type transform to another type they must have mass:
• The rate at which they oscillate will tell us the mass difference between the neutrinos and their mixing
GeV
kmeVxe E
LmLP2
22 27.1ins2sin;
J. Goodman Richtmyer Lecture – Jan. 2002
Neutrino Oscillations
1 2
=Electron
Electron
1 2
=Muon
Muon
J. Goodman Richtmyer Lecture – Jan. 2002
Super-Kamiokande
J. Goodman Richtmyer Lecture – Jan. 2002
Super-Kamiokande
J. Goodman Richtmyer Lecture – Jan. 2002
Super-Kamiokande
J. Goodman Richtmyer Lecture – Jan. 2002
How do we see neutrinos?
muon
electronee-
J. Goodman Richtmyer Lecture – Jan. 2002
Cherenkov Radiation
Boat moves throughwater faster than wavespeed.
Bow wave (wake)
J. Goodman Richtmyer Lecture – Jan. 2002
Cherenkov Radiation
Aircraft moves throughair faster than speed ofsound.
Sonic boom
J. Goodman Richtmyer Lecture – Jan. 2002
Cherenkov Radiation
When a charged particle moves throughtransparent media fasterthan speed of light in thatmedia.
Cherenkov radiation
Cone oflight
J. Goodman Richtmyer Lecture – Jan. 2002
Detecting neutrinos
Electron or
muon track
Cherenkov ring on the
wall
The pattern tells us the energy and type of particleWe can easily tell muons from electrons
J. Goodman Richtmyer Lecture – Jan. 2002
A muon going through the detector
J. Goodman Richtmyer Lecture – Jan. 2002
A muon going through the detector
J. Goodman Richtmyer Lecture – Jan. 2002
A muon going through the detector
J. Goodman Richtmyer Lecture – Jan. 2002
A muon going through the detector
J. Goodman Richtmyer Lecture – Jan. 2002
A muon going through the detector
J. Goodman Richtmyer Lecture – Jan. 2002
A muon going through the detector
J. Goodman Richtmyer Lecture – Jan. 2002
Stopping Muon
J. Goodman Richtmyer Lecture – Jan. 2002
Stopping Muon – Decay Electron
J. Goodman Richtmyer Lecture – Jan. 2002
Atmospheric Oscillations
about 13,000 km
about 15
km
Neutrinos produced in
the atmosphere
We look for transformations by looking at s with different distances from production
SK
J. Goodman Richtmyer Lecture – Jan. 2002
Telling particles apart
MuonElectron
J. Goodman Richtmyer Lecture – Jan. 2002
Multi-GeV Sample
Oscillations (1.0, 2.4x10-3eV2)
No Oscillations
to neutrino oscillations
UP going Down UP Down
J. Goodman Richtmyer Lecture – Jan. 2002
Summary of Atmospheric Results
Best Fit for to
Sin22 =1.0,
M2=2.4 x 10-3eV2
2min=132.4/137 d.o.f.
No Oscillations
2min=316/135 d.o.f.
99% C.L.
90% C.L.
68% C.L.
Best Fit
Compelling evidence for to atmospheric neutrino oscillations
J. Goodman Richtmyer Lecture – Jan. 2002
Solar Neutrinos in Super-K
• Super-K measures:– The flux of 8B solar neutrinos (electron type)– Energy, Angles, Day / Night rates, Seasonal
variations• Super-K Results:
– We see the image of the sunfrom 1.6 km underground
– We observe a lower than predictedflux of solar neutrinos (45%)
J. Goodman Richtmyer Lecture – Jan. 2002
Solar Neutrinos
)s cm 10x (syst)0.03(stat) (2.32
ssm) (syst) %0.5%(stat) (45.1%1-2-608.0
0.07
1.61.4 -
e
From SunToward Sun
J. Goodman Richtmyer Lecture – Jan. 2002
Combined Results e to
SK+Gallium+Cholrine exp’s- flux only allowed 95% C.L.
95% excluded by SK flux-independent zenith angle energy spectrum
95% C.L allowed. - SK flux constrained w/ zenith angle energy spectrum
J. Goodman Richtmyer Lecture – Jan. 2002
SNO Results - Summer 2001
• SNO measures just e
• SK measures mostly e but also other flavors (~1/6 strength)
• From the difference we see oscillations!
}This is from
&
neutral current
J. Goodman Richtmyer Lecture – Jan. 2002
Neutrinos have mass
• Oscillations imply neutrinos have mass!• We can estimate that neutrino mass is
probably <0.2 eV – (we measure M2)• Neutrinos can’t make up much of the
dark matter – • But they can be as massive as all the
visible matter in the Universe!• ~ ½% of the closure density
J. Goodman Richtmyer Lecture – Jan. 2002
Supernova Cosmology Project
• Set out to directly measure the deceleration of the Universe
• Measure distance vs brightness of a standard candle (type Ia Supernova)
•The Universe seems to be accelerating!•Doesn’t fit Hubble Law (at 99% c.l.)
J. Goodman Richtmyer Lecture – Jan. 2002
Energy Density in the Universe
may be made up of 2 parts a mass term and a “dark energy” term (Cosmological Constant)
massenergy
• Einstein invented to keep the Universe static
• He later rejected it when he found out about Hubble expansion
• He called it his “biggest blunder”
m
J. Goodman Richtmyer Lecture – Jan. 2002
What is the “Shape” of Space?
• Open Universe <1– Circumference (C) of a
circle of radius R is C > 2R
• Flat Universe =1– C = 2R– Euclidean space
• Closed Universe >1– C < 2R
J. Goodman Richtmyer Lecture – Jan. 2002
Results of SN Cosmology Project
• The Universe is accelerating
• The data require a positive value of “Cosmological Constant”
• If =1 then they find
~ 0.7 ± 0.1
J. Goodman Richtmyer Lecture – Jan. 2002
Accelerating Universe
J. Goodman Richtmyer Lecture – Jan. 2002
Accelerating Universe
J. Goodman Richtmyer Lecture – Jan. 2002
Measuring the energy in the Universe
• Studying the Cosmic Microwave radiation looks back at the radiation from the “Big Bang”.
• This gives a measure of 0
J. Goodman Richtmyer Lecture – Jan. 2002
Latest Results - May 2001
2001 Boomerang Results
0=1 nucleon
mass from clusters
J. Goodman Richtmyer Lecture – Jan. 2002
What does all the data say?
• Three pieces of data come together in one region
~ 0.7 m~ 0.3
(uncertainty ~0.1)• Universe is expanding &
won’t collapse• Only ~1/6 of the dark matter
is ordinary matter (baryons) • A previously unknown and
unseen “dark energy” pervades all of space and is causing it to expand
J. Goodman Richtmyer Lecture – Jan. 2002
What do we know about “Dark Energy”
• It emits no light• It acts like a large negative pressure
Px ~ - x
• It is approximately homogenous– At least it doesn’t cluster like matter
• Calculations of this pressure from first principles fail miserably – assuming it’s vacuum energy you predict a value of ~ 10120
• Bottom line – we know very little!
J. Goodman Richtmyer Lecture – Jan. 2002
Conclusion
• total = 1 ± 0.04– The Universe is flat!
• The Universe is : ~1/2% Stars
~1/2% Neutrinos ~33% Dark Matter
(only 5% is ordinary matter) ~66% Dark Energy
• We can see ~1/2%• We can measure ~1/2%• We can see the effect of
~33% (but don’t know what most of it is)
• And we are pretty much clueless about the other 2/3 of the Universe
There is still a lot of Physics to learn!