J. Goodman – May 2010 Physics Olympics Neutrinos, Dark Matter and the Cosmological Constant The...

Physics Olympics J. Goodman – May 2010

Neutrinos, Dark Matter and the Cosmological Constant

The Dark Side of the Universe


Outline

• The Cosmological Question – the fate of the Universe

• How do we know what the Universe is made of:– From atoms to quarks and leptons

• Why do we think there is Dark Matter• Data on the accelerating Universe

– Type Ia supernova– Cosmic Microwave Background

• Dark Energy• Neutrino Astronomy


The Big Question in Cosmology

• What is the ultimate fate of the Universe?– Will the Universe continue to expand forever?– Or will it collapse back on itself?

• We were told:

– The answer depends on the energy density in the Universe – W0

– W0= Wmass and W0=1 is the critical density.

– If Wmass > 1 then the Universe is closed and it will collapse back

– If Wmass < 1 then the Universe is open and it will expand forever

• Wstars= 0.005 (1/2%)

– Is this the answer?

• Theory says W0=1.0000 W > 1

W < 1


How do we know there really are atoms?

• Brownian Motion - Einstein


Seeing Atoms in the 21st Century


Seeing Atoms - Iron on Copper


Seeing into Atoms

• Atomic Spectra– We see spectral lines– The colors and the spacing of these lines tell us about

the structure of the atoms

E


Hydrogen Spectra


The structure of matter (cont.)

• All of this eventually gave a deeper understanding

Eventually this led toOur current picture of the atom and nucleus


What are fundamental particles?

• We keep finding smaller and smaller things


The search for fundamental particles

• Proton and electron– These were known to make up the atom

• The neutron was discovered• Free neutrons were found to decay

– They decayed into protons and electrons– But it looked like something was missing

• In 1930 Pauli postulated a unseen neutral particle

• In 1933 Fermi named it the “neutrino” (little neutron)


How do we know about things we can’t see?

Three Body Decay

Two Body Particle Decay

neutrino


Our current view of underlying structure of matter

• P is uud• N is udd• p+ is ud• k+ is us• and so

on…The Standard

Model

}Baryons

}Mesons

(nucleons)

J. Goodman – August 2009Teachers as Scholars

Omega Minus Discovery

Particle Symbol Makeup Rest massMeV/c^2 B S Lifetime Decay Modes

Omega sss 1672 +1 -3 0.82x10-10

The omega-minus was produced by a K- p collision which produced the omega-minus and two kaons.


Quark Properties

Quark Symbol Spin Charge BaryonNumber S C B T Mass*

Up U 1/2 +2/3 1/3 0 0 0 0 360 MeV

Down D 1/2 -1/3 1/3 0 0 0 0 360 MeV

Charm C 1/2 +2/3 1/3 0 +1 0 0 1500 MeV

Strange S 1/2 -1/3 1/3 -1 0 0 0 540 MeV

Top T 1/2 +2/3 1/3 0 0 0 +1 174 GeV

Bottom B 1/2 -1/3 1/3 0 0 +1 0 5 GeV


• Baryons


• Baryons Mesons

Table of Baryons

Particle Symbol Makeup Rest massMeV/c^2 Spin B S Lifetime

(seconds> Decay Modes

Proton p uud 938.3 1/2 +1 0 Stable ...

Neutron n ddu 939.6 1/2 +1 0 920

Lambda uds 1115.6 1/2 +1 -1 2.6x10-10

Sigma uus 1189.4 1/2 +1 -1 0.8x10-10

Sigma uds 1192.5 1/2 +1 -1 6x10-20

Sigma dds 1197.3 1/2 +1 -1 1.5x10-10

Delta uuu 1232 3/2 +1 0 0.6x10-23

Delta uud 1232 3/2 +1 0 0.6x10-23

Delta udd 1232 3/2 +1 0 0.6x10-23

Delta ddd 1232 3/2 +1 0 0.6x10-23

XiCascade uss 1315 1/2 +1 -2 2.9x10-10

XiCascade dss 1321 1/2 +1 -2 1.64x10-10

Omega sss 1672 3/2 +1 -3 0.82x10-10

Lmabda udc 2281 1/2 +1 0 2x10-13 ...


Lepton Properties

Particle Symbol Anti-particle

Rest massMeV/c2 L(e) L(muon) L(tau) Lifetime

(seconds)

Electron 0.511 +1 0 0 Stable

Neutrino(Electron) ~0(<7 x 10-6) +1 0 0 Stable

Muon 105.7 0 +1 0 2.20x10-6

Neutrino(Muon) ~0(<0.27) 0 +1 0 Stable

Tau 1777 0 0 +1 2.96x10-13

Neutrino(Tau) ~0(<31) 0 0 +1 Stable


SuperSymmetry

Name Spin Superpartner Spin

Graviton 2 Gravitino 3/2

Photon 1 Photino 1/2

Gluon 1 Gluino 1/2

W+,- 1 Wino+,- 1/2

Z0 1 Zino 1/2

Higgs 0 Higgsino 1/2


Measuring the Universe


Why do we think there is dark matter?

• Isn’t obvious that most of the matter in the Universe is in Stars?

Spiral Galaxy


Measuring the Matter in Galaxies

• 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

This is evidence for invisible matter or “Dark Matter”


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

College Park


Lensing


Gravitational Lensing


Clusters produce distinctive tangential patterns


Measuring the energy in the Universe

• We can measure the mass of clusters of galaxies with gravitational lensing

• These measurements give Wmass ~0.3

• We also know (from the primordial deuterium abundance) that only a small fraction is nucleons

Wnucleons < ~0.04 Gravitational

lensing


Dark Matter


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!


Facts about Neutrinos

• Neutrinos are only weakly interacting

• 40 billion neutrinos continuously hit every cm2 on earth from the Sun (24hrs/day)

• Interaction length is ~1 light-year of steel

• 1 out of 100 billion interact going through the Earth


What about neutrino mass?

• Could it be neutrinos?• How much neutrino mass would it take?

– Proton mass is 938 MeV– Electron mass is 511 KeV– Neutrino mass of 2eV would solve the galaxy

rotation problem – 20eV would close the Universe• Theories say it can’t be all neutrinos

– They have difficulty forming the kinds of structure observed. The structures they create are too large and form too late in the history of the universe


Does the neutrino have mass?

n


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; nn


Neutrino Oscillations

n1 n2

=Electron n

Electron n

n1 n2

=Muon n

Muon n


Super-Kamiokande


How do we see neutrinos?

muonnm

m-

electronnee-


Cherenkov Radiation

Boat moves throughwater faster than wavespeed.

Bow wave (wake)


Cherenkov Radiation

Aircraft moves throughair faster than speed ofsound.

Sonic boom

J. Goodman – Univ. of Maryland

Cherenkov Radiation


Cherenkov Radiation

When a charged particle moves throughtransparent media fasterthan speed of light in thatmedia.

Cherenkov radiation

Cone oflight


Cherenkov Radiation


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


A muon going through the detector


Stopping Muon


Stopping Muon – Decay Electron


Atmospheric Oscillations

about 13,000 km

about 15

km

Neutrinos produced in

the atmosphere

We look for n transformations by looking at ns with different distances from production

SK


Telling particles apart

MuonElectron


Moderate Energy Sample


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


Hubble Law


The expanding Universe


The expanding Universe

• The Universe is expanding

• Everything is moving away from everything

• Hubble’s law says the faster things are moving away the further they are away


Supernova


Actually Ia’s are “standardizable” candles


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.)


The Cosmological Constant


Energy Density in the Universe

W0 may be made up of 2 parts a mass term and a “dark energy” L term (Cosmological Constant)

W0= Wmass + Wenergy

• Einstein invented L to keep the Universe static

• He later rejected it when he found out about Hubble expansion

• He called it his “biggest blunder”

L

mW0=1


Results of SN Cosmology Project

• The Universe is accelerating

• The data require a positive value of L “Cosmological Constant”

• If W0 =1 then they find

WL ~ 0.7 ± 0.1


Accelerating Universe


Cosmic Microwave Background


Measuring the energy in the Universe

• Studying the Cosmic Microwave radiation looks back at the radiation from 400,000 years after the “Big Bang”.

• This gives a measure of W0


2002 Results

W0=1 Wnucleon


WMAP -2003


WMAP Results


WMAP - 2009


Density Fluctuations to Galaxies


Concordance model, aka LCDM

Physics Olympics

Combining the Data 2010

J. Goodman – May 2010


Combining All Results

• Universe is 13.7 billion years old with a margin of error of close to 1%

• Expansion rate (Hubble constant) value: Ho= 71 km/sec/Mpc (with a margin of error of about 2%)

• Neutrinos only contribute as much matter as stars

• Content of the Universe: 4% Atoms, 23% Cold Dark Matter, 72% Dark energy.


What About Dark Matter?

• ~85% of the matter in the Universe is Dark Matter– At most a few % of the matter is baryons – Most people believe that the lightest SUSY particle is a

stable neutralino and is probably the dark matter– These are weakly interacting and heavy– LHC should be the answer…

IceCube

Physics Olympics

IceCube

J. Goodman – May 2010


χ

atm n

cosmic-ray μ’s

nm nm

χ

Sun

cosmic-ray


Conclusion

• Wtotal = 1.005 ± 0.006– The Universe is flat!

• The Universe is : ~1/2% Stars

~1/2% Neutrinos ~27% Dark Matter

(only 4% is ordinary baryonic matter)

~72% Dark Energy

• We can see ~1/2%• We can measure ~1/2%• We can see the effect of

~27% (but don’t know what most of it is)

• And we are pretty much clueless about the other 3/4 of the Universe

There is still a lot of Physics to learn!

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