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Richtmyer Lecture

This lecture discusses the role of neutrinos and dark matter in the universe, including their potential connection and impact on the cosmological constant. It also explores the search for neutrino mass, type Ia supernova, and dark energy.

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Richtmyer Lecture

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  1. Richtmyer Lecture Neutrinos, Dark Matter and the Cosmological Constant The Dark Side of the Universe Jordan Goodman University of Maryland

  2. 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

  3. Seeing Big Picture

  4. The early periodic table

  5. The structure of matter 1889 - Mendeleyev – grouped elements by atomic weights

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

  7. What are fundamental particles? • We keep finding smaller and smaller things

  8. Our current view of underlying structure of matter • P is uud • N is udd • p+ is ud • k+ is us • and so on… }Baryons (nucleons) }Mesons The Standard Model

  9. 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 Facts about Neutrinos

  10. Neutrinos They only interact weakly If they have mass at all – it is very small Why do we care about neutrinos? • 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!

  11. The Ultimate Fate of the Universe • W0 measures the total energy density of the Universe • If W0 > 1 Universe is closed • If W0 < 1 Universe is open • W0 = 1 Universe (Etot=0) - Flat universe • From the mass of the stars we get W0~0.005 (1/2%) • Theorists say W0=1.000 • What is the other 99.5% of the Universe?

  12. Spiral Galaxy Why do we think there is dark matter? • Isn’t obvious that most of the matter in the Universe is in Stars?

  13. 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!

  14. 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

  15. 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 < ~0.05 Measuring the energy in theUniverse Gravitational lensing

  16. 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

  17. n Does the neutrino have mass?

  18. 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

  19. =Electron n =Muon n n1n2 n1n2 Muonn Electronn Neutrino Oscillations

  20. Super-Kamiokande

  21. Super-Kamiokande

  22. Super-Kamiokande

  23. m- e- electron ne muon nm How do we see neutrinos?

  24. Boat moves through water faster than wave speed. Bow wave (wake) Cherenkov Radiation

  25. Cherenkov Radiation Aircraft moves through air faster than speed of sound. Sonic boom

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

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

  28. A muon going through the detector

  29. A muon going through the detector

  30. A muon going through the detector

  31. A muon going through the detector

  32. A muon going through the detector

  33. A muon going through the detector

  34. Stopping Muon

  35. Stopping Muon – Decay Electron

  36. about 15 km about 13,000 km Atmospheric Oscillations We look for n transformations by looking at ns with different distances from production SK Neutrinos produced in the atmosphere

  37. Telling particles apart Muon Electron

  38. Multi-GeV Sample nmtont neutrino oscillations No Oscillations Oscillations (1.0, 2.4x10-3eV2) Down UP Down UP going

  39. Summary of Atmospheric Results Compelling evidence for nm to nt atmospheric neutrino oscillations Best Fit for nmto nt Sin22q =1.0, DM2=2.4 x 10-3eV2 c2min=132.4/137 d.o.f. No Oscillations c2min=316/135 d.o.f. 99% C.L. 90% C.L. 68% C.L. Best Fit

  40. 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 sun from 1.6 km underground • We observe a lower than predicted flux of solar neutrinos (45%)

  41. Solar Neutrinos Toward Sun From Sun

  42. Combined Results netonm,t 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

  43. SNO measures just ne SK measures mostly ne but also other flavors (~1/6 strength) From the difference we see oscillations! This is from nm & nt neutral current } SNO Results - Summer 2001

  44. Neutrinos have mass • Oscillations imply neutrinos have mass! • We can estimate that neutrino mass is probably <0.2 eV – (we measure DM2) • 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

  45. Set out to directly measure the deceleration of the Universe Measure distance vs brightness of a standard candle (type Ia Supernova) Supernova Cosmology Project • The Universe seems to be accelerating! • Doesn’t fit Hubble Law (at 99% c.l.)

  46. W0may 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 m Energy Density in the Universe W0=1

  47. What is the “Shape” of Space? • Open Universe W0<1 • Circumference (C) of a circle of radius R is C > 2pR • Flat Universe W0=1 • C = 2pR • Euclidean space • Closed Universe W0>1 • C < 2pR

  48. 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 Results of SN Cosmology Project

  49. Accelerating Universe

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