Ghosts in the UniverseGhosts in the Universe

Jordan A. Goodman

Department of Physics

University of Maryland

Jordan A. Goodman

Department of Physics

University of Maryland

The world we don’t see around us

The world we don’t see around us

PreviewPreview

OutlineOutline

How we see particlesHow we see particles How we know about things we can’t How we know about things we can’t

see (like neutrinos)see (like neutrinos) What is the structure of matterWhat is the structure of matter What makes up most of the UniverseWhat makes up most of the Universe Neutrino massNeutrino mass ““” ” and the Dark side of the forceand the Dark side of the force

How do we see particles?How do we see particles?

Most particles have electric chargeMost particles have electric charge Charged particles knock electrons out Charged particles knock electrons out

of atomsof atoms As other electrons fall in the As other electrons fall in the

atoms emit light atoms emit light

The light from your TV is The light from your TV is from electrons hitting the from electrons hitting the screenscreen

In a sense we are In a sense we are “seeing” electrons“seeing” electrons

The light from your TV is The light from your TV is from electrons hitting the from electrons hitting the screenscreen

In a sense we are In a sense we are “seeing” electrons“seeing” electrons

Cherenkov RadiationCherenkov Radiation

Boat moves throughwater faster than wavespeed.

Bow wave (wake)

Aircraft moves throughair faster than speed ofsound.

Sonic boom

Cherenkov RadiationCherenkov Radiation

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

Cherenkov radiation Cone oflight

The early periodic tableThe early periodic table

The structure of matterThe structure of matter

1869 - Mendeleyev – grouped elements by atomic weights1869 - Mendeleyev – grouped elements by atomic weights

The structure of matter The structure of matter (cont.)(cont.)

This lead eventually to a deeper This lead eventually to a deeper understandingunderstanding

Eventually this led toOur current picture of the atom and nucleus

What are fundamental What are fundamental particles?particles?

We keep finding smaller and We keep finding smaller and smaller thingssmaller things

The search for fundamental The search for fundamental particlesparticles

Proton and electronProton and electron These were known to make up the atomThese were known to make up the atom

The neutron was discoveredThe neutron was discovered Free neutrons were found to decayFree neutrons were found to decay

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

In 1930 Pauli postulated a unseen neutral In 1930 Pauli postulated a unseen neutral particle particle

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

A little history (continued)A little history (continued)

Bethe calculated the neutrino’s Bethe calculated the neutrino’s propertiesproperties He concluded that we might never see He concluded that we might never see

it!it! He was almost right – it took over 20 He was almost right – it took over 20

yearsyears Reines and Cowan first detected the Reines and Cowan first detected the

neutrino in 1956 (at a nuclear neutrino in 1956 (at a nuclear reactor)reactor)

Our current view of Our current view of underlying structure of underlying structure of mattermatter

• P is uud

• N is udd

• is ud

• and so on…

• P is uud

• N is udd

• is ud

• and so on…

The Standard Model

The Standard Model

Facts about neutrinosFacts about neutrinos

Neutrinos are weakly interactingNeutrinos are weakly interacting Interaction length is ~1 light-year of steel Interaction length is ~1 light-year of steel

There are a lot of neutrinos aroundThere are a lot of neutrinos around 40 billion neutrinos continuously hit every cm40 billion neutrinos continuously hit every cm22

on earth from the Sunon earth from the Sun 300 neutrinos in every cm300 neutrinos in every cm33 of the universe are of the universe are

left over from the “Big Bang”left over from the “Big Bang” In 1972 R. Cowsik suggested that if In 1972 R. Cowsik suggested that if

neutrinos have even a small mass they neutrinos have even a small mass they could make up most of the mass in the could make up most of the mass in the UniverseUniverse

Mass in the UniverseMass in the Universe

Could the most mass of the Could the most mass of the Universe be in something we don’t Universe be in something we don’t see?see?

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

Spiral Galaxy M31

Spiral Galaxy M31

Mass in the Universe Mass in the Universe (cont.)(cont.)

We can estimate how many stars We can estimate how many stars there are and how much mass they there are and how much mass they havehave We know the mass of our sun from We know the mass of our sun from

the orbit of the planetsthe orbit of the planets

We can look at We can look at thethe rotation curves of rotation curves of other galaxiesother galaxies

They should dropThey should drop off, but they off, but they don’t!don’t!

We can look at We can look at thethe rotation curves of rotation curves of other galaxiesother galaxies

They should dropThey should drop off, but they off, but they don’t!don’t!

Mass in the Universe Mass in the Universe (cont.)(cont.) There must be a large amount of There must be a large amount of

unseen matter in the halo of galaxiesunseen matter in the halo of galaxies Maybe 20 times more than in the stars!Maybe 20 times more than in the stars! Our galaxy looks 30 kpc across but Our galaxy looks 30 kpc across but

recent data shows that it looks like its recent data shows that it looks like its 200 kpc across200 kpc across

What is this ghostly What is this ghostly matter?matter?

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

Proton mass is 938 MeVProton mass is 938 MeV Electron mass is 511 KeVElectron mass is 511 KeV Neutrino mass of 2eV would solve the Neutrino mass of 2eV would solve the

galaxy rotation problemgalaxy rotation problem Theories say it can’t be all neutrinosTheories say it can’t be all neutrinos

They would have messed up star formation They would have messed up star formation in the early universein the early universe

Does the neutrino have Does the neutrino have mass?mass?

Detecting Neutrino MassDetecting Neutrino Mass There are three types of neutrinosThere are three types of neutrinos

Electron (Electron (ee) – Muon () – Muon () – Tau () – Tau ()) Theory tells us that if neutrinos of one type Theory tells us that if neutrinos of one type

transform to another type they must have transform to another type they must have massmass

The rate at which they oscillate will tell us the mass The rate at which they oscillate will tell us the mass difference between the neutrinosdifference between the neutrinos

We built and experiment to look for neutrino We built and experiment to look for neutrino oscillationsoscillations

GeV

kmeVee E

LmLP

222 27.1

ins2sin1;

Neutrino OscillationsNeutrino Oscillations

1 21 2

=Electron =Electron

Electron

Electron

1 21 2

=Muon =Muon

Muon Muon

Super-KamiokandeSuper-Kamiokande

Super-KamiokandeSuper-Kamiokande

Super-K site Super-K site

Super-K siteSuper-K site

MozumiMozumi

How do we see neutrinosHow do we see neutrinos

electrone

e

electronneutrino

muon

-

Detecting neutrinosDetecting neutrinos

Electron or

muon track

Electron or

muon track

Cherenkov ring on the

wall

Cherenkov ring on the

wall

The pattern tells us the energy and type of particle

We can easily tell muons from electrons

The pattern tells us the energy and type of particle

We can easily tell muons from electrons

A muon going through the detectorA muon going through the detector

Stopping MuonStopping Muon

Telling particles apartTelling particles apart

Muon ElectronMuon Electron

How do we look for How do we look for oscillations?oscillations?

about 13,000 km

about 15

km

Neutrinos produced in

the atmosphere

Neutrinos produced in

the atmosphere

Neutrino ProductionNeutrino Production

Ratio predicted to ~ 5%

Absolute Flux Predicted to ~20% :

2

ee

What did we find?What did we find?

We looked at the We looked at the number of electron number of electron and muon and muon neutrinosneutrinos

We saw the We saw the

disappearing disappearing with anglewith angle This is what would This is what would

happen if happen if

andand M2 - M

2=0.0030.003

DM=DM=M2 - M

2=0.003M2 - M

2=0.003

More Evidence of More Evidence of OscillationsOscillations

ResultsResults

Best Fit

Sin22 = 1

M2=3x10-3ev

Best Fit

Sin22 = 1

M2=3x10-3ev

Neutrino Picture of the Neutrino Picture of the SunSun

Neutrinos have massNeutrinos have mass

This tells us that neutrinos have This tells us that neutrinos have massmass

We can estimate that neutrino mass We can estimate that neutrino mass is probably <0.2 eV – (we measure is probably <0.2 eV – (we measure MM22))

Conclusion:Conclusion: Neutrinos can’t make up Neutrinos can’t make up much of the dark matter – but they much of the dark matter – but they can be as massive as all the visible can be as massive as all the visible matter in the Universe!matter in the Universe!

The expanding UniverseThe expanding Universe

The Universe is The Universe is expanding expanding

Everything is moving Everything is moving away from away from everythingeverything

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

Energy in the UniverseEnergy in the Universe

measures the total energy measures the total energy density of the Universedensity of the Universe If If > 1 the Universe is closed > 1 the Universe is closed If If < 1 the Universe is open < 1 the Universe is open

may be made up of 2 parts may be made up of 2 parts – mass and “dark energy” – mass and “dark energy” ((Cosmological ConstantCosmological Constant) )

massmassenergyenergy

Theory tells us thatTheory tells us that

The newest data tells us The newest data tells us

Measuring the energy in the Measuring the energy in the UniverseUniverse

Dark Matter gives Dark Matter gives mass ~0.3 (<5% mass ~0.3 (<5% nucleons from Deut. nucleons from Deut. abundance)abundance)

Studying the Cosmic Studying the Cosmic Microwave radiation looks Microwave radiation looks back at the radiation from back at the radiation from the “Big Bang”. This gives the “Big Bang”. This gives total total ~1~1

Gravitational lensing

Gravitational lensing

Supernova Cosmology Supernova Cosmology ProjectProject

Set out to measure Set out to measure the deceleration of the deceleration of the Universe the Universe

Look at distance vs Look at distance vs brightness of a brightness of a standard candle standard candle (type Ia Supernova)(type Ia Supernova)

The Universe seems The Universe seems to be accelerating!to be accelerating!

Doesn’t fit Hubble Doesn’t fit Hubble Law (at 99% prob)Law (at 99% prob)

brig

hte

rb

righ

ter

distancedistance

Results of SN Cosmology Results of SN Cosmology ProjectProject

The data require a The data require a positive value of positive value of whichwhichis called the is called the “Cosmological “Cosmological Constant”Constant”

This acts like a This acts like a negative pressurenegative pressure Einstein invented it to Einstein invented it to

keep the Universe statickeep the Universe static He later rejected it!He later rejected it! He called it his “biggest He called it his “biggest

blunder”blunder”

What does all the data What does all the data say?say?

Three pieces of data Three pieces of data come together to in one come together to in one region region ~ 0.72 ~ 0.72 mm~ ~ 0.28 (uncertainty 0.28 (uncertainty ~0.1)~0.1)

Universe is expanding & Universe is expanding & won’t collapsewon’t collapse

A previously unknown A previously unknown and unseen “dark and unseen “dark energy” pervades all of energy” pervades all of space and is causing it to space and is causing it to expandexpand

Best Fit

Best Fit

Newest ResultsNewest Results

Best Fit

Best Fit

2000 Boomerang Results 2000 Boomerang Results

What’s NextWhat’s Next

SNAPSNAP Look at 1000’s Look at 1000’s

of Ia of Ia SupernovaeSupernovae

Look back Look back further in time – further in time – Z~1.6Z~1.6

2m Mirror with 2m Mirror with a Gigapixel CCDa Gigapixel CCD

ConclusionConclusion

Conclusion the Conclusion the Universe is : Universe is : 1% Stars + 1% Stars + 1% Neutrinos + 1% Neutrinos + 26% Dark Matter + 26% Dark Matter +

72% Dark Energy72% Dark Energy

We can see 1%We can see 1% We can measure We can measure

1%1% We can see the We can see the

effect of 26%effect of 26% And we are pretty And we are pretty

much clueless much clueless about the other about the other 72% of the 72% of the UniverseUniverse

Ghosts in the UniverseGhosts in the Universe

We really don’t see 99% of the Universe around

us!

We really don’t see 99% of the Universe around

us!