Ghosts in the Universe Jordan A. Goodman Department of Physics University of Maryland The world we don’t see around us

Preview

Outline How we see particles How we see particles How we know about things we can’t see (like neutrinos) How we know about things we can’t see (like neutrinos) What is the structure of matter What is the structure of matter What makes up most of the Universe What makes up most of the Universe Neutrino mass Neutrino mass “  ” and the Dark side of the force “  ” and the Dark side of the force

How do we see into atoms Atomic Spectra Atomic Spectra We see spectral lines We see spectral lines The colors and the spacing of these lines tell us about the structure of the atoms The colors and the spacing of these lines tell us about the structure of the atoms E

How do we see particles? Most particles have electric charge Most particles have electric charge Charged particles knock electrons out of atoms Charged particles knock electrons out of atoms As other electrons fall in the atoms emit light As other electrons fall in the atoms emit light The light from your TV is from electrons hitting the screen The light from your TV is from electrons hitting the screen In a sense we are “seeing” electrons In a sense we are “seeing” electrons

Detecting light - PMTs

Detecting particles PMT scintillator

Cherenkov Radiation Boat moves through water faster than wave speed. Bow wave (wake) Aircraft moves through air faster than speed of sound. Sonic boom

Cherenkov Radiation When a charged particle moves through transparent media faster than speed of light in that media. Cherenkov radiation Cone of light

The early periodic table

The structure of matter Mendeleyev – grouped elements by atomic weights

The structure of matter (cont.) This lead eventually to a deeper understanding This lead eventually to a deeper understanding Eventually this led to Our current picture of the atom and nucleus

What are fundamental particles? We keep finding smaller and smaller things We keep finding smaller and smaller things

The search for fundamental particles Proton and electron Proton and electron These were known to make up the atom These were known to make up the atom The neutron was discovered The neutron was discovered Free neutrons were found to decay Free neutrons were found to decay They decayed into protons and electrons They decayed into protons and electrons But it looked like something was missing But it looked like something was missing In 1930 Pauli postulated a unseen neutral particle In 1930 Pauli postulated a unseen neutral particle In 1933 Fermi named it the “neutrino” (little neutron) 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

A little history (continued) Bethe calculated the neutrino’s properties Bethe calculated the neutrino’s properties He concluded that we might never see it! He concluded that we might never see it! He was almost right – it took over 20 years He was almost right – it took over 20 years Reines and Cowan first detected the neutrino in 1956 (at a nuclear reactor) Reines and Cowan first detected the neutrino in 1956 (at a nuclear reactor)

Our current view of underlying structure of matter P is uud N is udd   is ud and so on… The Standard Model

Facts about neutrinos Neutrinos are weakly interacting Neutrinos 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 around There are a lot of neutrinos around 40 billion neutrinos continuously hit every cm 2 on earth from the Sun 40 billion neutrinos continuously hit every cm 2 on earth from the Sun 300 neutrinos in every cm 3 of the universe are left over from the “Big Bang” 300 neutrinos in every cm 3 of the universe are left over from the “Big Bang” In 1972 R. Cowsik suggested that if neutrinos have even a small mass they could make up most of the mass in the Universe In 1972 R. Cowsik suggested that if neutrinos have even a small mass they could make up most of the mass in the Universe

Facts about neutrinos (cont.) If 100 billion solar neutrinos hit the earth, all but about 1 will come out the other side without hitting anything! If 100 billion solar neutrinos hit the earth, all but about 1 will come out the other side without hitting anything! In 1972 R. Cowsik suggested that if neutrinos have even a small mass they could make up most of the mass in the Universe In 1972 R. Cowsik suggested that if neutrinos have even a small mass they could make up most of the mass in the Universe

Mass in the Universe Could the most mass of the Universe be in something we don’t see? Could the most mass of the Universe be in something we don’t see? Isn’t obvious that most of the matter in the Universe is in Stars? Isn’t obvious that most of the matter in the Universe is in Stars? Spiral Galaxy M31

Mass in the Universe (cont.) We can estimate how many stars there are and how much mass they have We can estimate how many stars there are and how much mass they have We know the mass of our sun from the orbit of the planets We know the mass of our sun from the orbit of the planets We can look at the We can look at the rotation curves of rotation curves of other galaxies other galaxies They should drop They should drop off, but they don’t! off, but they don’t!

Mass in the Universe (cont.) There must be a large amount of unseen matter in the halo of galaxies There must be a large amount of unseen 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 recent data shows that it looks like its 200 kpc across Our galaxy looks 30 kpc across but recent data shows that it looks like its 200 kpc across

What is this ghostly 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 MeV Proton mass is 938 MeV Electron mass is 511 KeV Electron mass is 511 KeV Neutrino mass of 2eV would solve the galaxy rotation problem Neutrino mass of 2eV would solve the galaxy rotation problem Theories say it can’t be all neutrinos Theories say it can’t be all neutrinos They would have messed up star formation in the early universe They would have messed up star formation in the early universe

Does the neutrino have mass?

Detecting Neutrino Mass There are three types of neutrinos There are three types of neutrinos Electron ( e ) – Muon (  ) – Tau (  ) Electron ( e ) – Muon (  ) – Tau (  ) Theory tells us that if neutrinos of one type transform to another type they must have mass Theory tells us that 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 The rate at which they oscillate will tell us the mass difference between the neutrinos We built and experiment to look for neutrino oscillations We built and experiment to look for neutrino oscillations

Neutrino Oscillations 1 2 =Electron Electron 1 2 =Muon Muon

Super-Kamiokande

Super-Kamiokande

Super-K Huge tank of water shielded by a mountain in western Japan Huge tank of water shielded by a mountain in western Japan 50,000 tons of ultra clean water 50,000 tons of ultra clean water 11,200 20in diameter PMTs 11,200 20in diameter PMTs Under 1km of rock to reduce downward cosmic rays Under 1km of rock to reduce downward cosmic rays 100 scientists from US and Japan 100 scientists from US and Japan

Super-K site

Mozumi

How do we see neutrinos electron e ee neutrino muon  --

Detecting neutrinos Electron or muon track Cherenkov ring on the wall The pattern tells us the energy and type of particle We can easily tell muons from electrons

A muon going through the detector

Stopping Muon

Telling particles apart MuonElectron

How do we look for oscillations? about 13,000 km about 15 km Neutrinos produced in the atmosphere

Neutrino Production Ratio predicted to ~ 5% Absolute Flux Predicted to ~20% :

What did we find? We looked at the number of electron and muon neutrinos We looked at the number of electron and muon neutrinos We saw the  disappearing with angle We saw the  disappearing with angle This is what would happen if    and This is what would happen if    and M  2 - M  2 = DM= M  2 - M  2 =0.003

More Evidence of Oscillations

Results Best Fit Sin 2 2  = 1  M 2 =3x10 -3 ev

Neutrino Picture of the Sun

Neutrinos have mass This tells us that neutrinos have mass This tells us that neutrinos have mass We can estimate that neutrino mass is probably <0.2 eV – (we measure  M 2 ) We can estimate that neutrino mass is probably <0.2 eV – (we measure  M 2 ) Conclusion: Neutrinos can’t make up much of the dark matter – but they can be as massive as all the visible matter in the Universe! Conclusion: Neutrinos can’t make up much of the dark matter – but they can be as massive as all the visible matter in the Universe!

The expanding Universe The Universe is expanding The Universe is expanding Everything is moving away from everything Everything is moving away from everything Hubble’s law says the faster things are moving away the further they are away Hubble’s law says the faster things are moving away the further they are away

Energy in the Universe  measures the total energy density of the Universe  measures the total energy density of the Universe If  > 1 the Universe is closed If  > 1 the Universe is closed If  < 1 the Universe is open If  < 1 the Universe is open  may be made up of 2 parts – mass and “dark energy” (Cosmological Constant)  mass  energy  may be made up of 2 parts – mass and “dark energy” (Cosmological Constant)  mass  energy Theory tells us that   Theory tells us that   The newest data tells us   The newest data tells us  

Measuring the energy in the Universe Dark Matter gives  mass ~0.3 (<5% nucleons from Deut. abundance) Dark Matter gives  mass ~0.3 (<5% nucleons from Deut. abundance) Studying the Cosmic Microwave radiation looks back at the radiation from the “Big Bang”. This gives  total ~1 Gravitational lensing

Supernova Cosmology Project Set out to measure the deceleration of the Universe Set out to measure the deceleration of the Universe Look at distance vs brightness of a standard candle (type Ia Supernova) Look at distance vs brightness of a standard candle (type Ia Supernova) The Universe seems to be accelerating! The Universe seems to be accelerating! Doesn’t fit Hubble Law (at 99% prob) Doesn’t fit Hubble Law (at 99% prob) brighter distance

Results of SN Cosmology Project The data require a positive value of  which is called the “Cosmological Constant” The data require a positive value of  which is called the “Cosmological Constant” This acts like a negative pressure This acts like a negative pressure Einstein invented it to keep the Universe static Einstein invented it to keep the Universe static He later rejected it! He later rejected it! He called it his “biggest blunder” He called it his “biggest blunder”

What does all the data say? Three pieces of data come together to in one region   ~ 0.72  m ~ 0.28 (uncertainty  ~0.1) Three pieces of data come together to in one region   ~ 0.72  m ~ 0.28 (uncertainty  ~0.1) Universe is expanding & won’t collapse Universe is expanding & won’t collapse A previously unknown and unseen “dark energy” pervades all of space and is causing it to expand A previously unknown and unseen “dark energy” pervades all of space and is causing it to expand Best Fit

Newest Results Best Fit 2000 Boomerang Results

What’s Next SNAP SNAP Look at 1000’s of Ia Supernovae Look at 1000’s of Ia Supernovae Look back further in time – Z~1.6 Look back further in time – Z~1.6 2m Mirror with a Gigapixel CCD 2m Mirror with a Gigapixel CCD

Conclusion Conclusion the Universe is : 1% Stars + 1% Neutrinos + 26% Dark Matter + Conclusion the Universe is : 1% Stars + 1% Neutrinos + 26% Dark Matter + 72% Dark Energy 72% Dark Energy We can see 1% We can measure 1% We can see the effect of 26% And we are pretty much clueless about the other 72% of the Universe

Ghosts in the Universe We really don’t see 99% of the Universe around us!

Upward Going Through Muons

Neutral Current Enriched

Oscillations to  or 

Solar Neutrinos

Day / Night.

Energy Spectrum

Orbital Eccentricity