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!