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The elusive neutrino

Fysica 2002 Groningen. The elusive neutrino. Piet M ulders Vrije Universiteit Amsterdam. mulders@nat.vu.nl http://www.nat.vu.nl/~mulders. What is it all about. Neutrinos, quantum mechanics, relativity What are neutrinos? Where do we find neutrinos? How to catch neutrinos?

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The elusive neutrino

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  1. Fysica 2002 Groningen The elusive neutrino PietMulders Vrije Universiteit Amsterdam mulders@nat.vu.nl http://www.nat.vu.nl/~mulders

  2. What is it all about • Neutrinos, quantum mechanics, relativity • What are neutrinos? • Where do we find neutrinos? • How to catch neutrinos? • Neutrino puzzles • How heavy are neutrinos? • Solar neutrinos

  3. What is a neutrino?

  4. Matter

  5. The periodic table

  6. Matter

  7. Matter

  8. Atomic nuclei • Isotopes • Radioactivity alpha beta gamma After 15 min. 1930: W. Pauli 1956: Reines & Cowan

  9. Matter

  10. The buildingblocks of thesubatomicworld

  11. What is special with neutrinos? • No mirror image (only lefthanded) • Barely interacting (crossing the earth without problems)

  12. Origin of neutrinos ?

  13. Origin of neutrinos • Weak decay of atomic nuclei (Sun/reactors): …n…  …p… + e- + ne (righthanded antineutrino)…p…  …n… + e+ + ne (lefthanded neutrino) • Cosmic rays (decay of the pion) p-  m- + nm (rechtshandig antineutrino) p+ m+ + nm (linkshandig neutrino) • Remnants of the big bang just as photons (T = 2.7 K background) one finds about 500 neutrinos per cm3 for all three kinds of neutrinos (ne, nm and nt)

  14. How do we know all of that?

  15. Brokenmirrorsymmetry Wu et al. 1957 (looking at Cobalt nuclei)

  16. From the largest microscope in the world: CERN

  17. Antiparticles

  18. Standard model • 3 families of particles • 4 fundamental forces • Carriers of the forces

  19. Weak interactions Force particles play a role in: • Interactions • Pair creation • Annihilation

  20. Example: neutron decay Neutron beta-decay n  p + e- + ne At the quark level d  u + e- + ne

  21. Three kinds of neutrinos! Z0 decay into: • quark pairs (except top quarks!) • lepton pairs • e+e-, m+m-, t+t- • neutrino pairs lifetime is inverse of decay probability 1/t = G G = S Gi

  22. cross sections GF ~ a/MW2

  23. Collission lengths of neutrinos

  24. Neutrino puzzles

  25. Questions about neutrinos • How heavy are neutrinos? • Where are the solar neutrinos? (compared to the SSM)

  26. How can we detect Neutrinos?

  27. Neutrino detectors Super Kamiokande

  28. Super Kamiokande

  29. Neutrino detection techniques Detection via cherenkov light emitted by particles moving “faster” than light (from antares experiment)

  30. Neutrino oscillations in the atmosphere • Neutrinos from cosmic rays come from decay of pions. These are nm neutrinos • If the nm neutrino is a quantummechanical superposition of neutrinos n1 en n2 one gets oscillations

  31. Vacuum oscillations

  32. Neutrino oscillations in the atmosphere • Superkamiokande found oscillations by looking at the zenith angle dependence • Results are consistent withnmnt oscillations with Dm2 ~ 2 - 3 x 10-3 eV2 and sin2 2q ~ 1 lV ~ 1250 km

  33. My first reaction: Interview in Aik door Wilm Geurts en Joost van Mameren

  34. What are the consequences • For particles with mass both righthanded and lefthanded species exist! • This is only* possible if the neutrino is its own antiparticle (like the photon, but different from the electron) * (I do not discuss sterile neutrinos)

  35. Dirac and Majorana fermions Fermion (general) Dirac neutrino Majorana neutrino

  36. Dirac and Majorana fermions Although it seems as if the Majorana solution restores mirror symmetry, this is NOT true Lefthanded neutrino interacts with lefthanded electron Righthanded neutrino interacts with righthanded positron

  37. CP violation Mixing between mass and weak-interaction eigenstates for quarks AND neutrinos Complex phases (at least requiring 3x3 mixing) leads for both cases to CP violation

  38. Solar neutrinos

  39. Solar neutrinos in SNO(Sudbury Neutrino Observatory) En < 15 MeV All neutrinos (x = e, m, t) • nx + p nx+ p • nx + d nx+ p + n • nx + e- nx+ e- (via Z0-exchange) Electron neutrinos • ne + d e- + p + p • ne + e- ne+ e- (via Z0 and W)

  40. Solar neutrino oscillations • Matter contains protons, neutrons and electrons. • Oscillations arise because ne interacts differently with matter dan nm

  41. Basis states ne and nm

  42. Solar neutrino oscillations • SNO showed that the missing ne appear as different type, most probably nm • le = [2 x 107 m]/(r/rwater) ~ 2 x 105 m (for a density of r/rwater ~ 100) • lV = [2.5 x 103 m](E[GeV]/Dm2[eV2]) • Thus for E ~ 1 MeV and Dm2 ~ 6 x 10-5 eV2 one finds that lV ~ le and thus one can have the situation of a resonance with maximal oscillations!

  43. Why not go the easy way? • Just observa a supernova emitting photons and neutrinos and look which arrive first! • Particles with mass after all move slower than light! • Surprise! Neutrinos from SN 87A arrived first! • Explanation: the velocity of light in matter is smaller than the velocity in vacuum • In spite of a rather low density (in the galaxy about 5/cm3) light is slowed down more than that neutrinos move slower than light in vacuum!

  44. Vlight = 1/n’ ~ 1 – 2p N f(k,q=0)/E2 • Vneutrino = 1 – mn2/2E2 m2 = 10-5 eV2 E = 1 GeV v = 1 – 10-23 Dx = 3 x 10-15 m/yr

  45. Nevertheless high-energy neutrinos might be the messengers that help solving cosmological puzzles!

  46. An underwater laboratory ANTARES (mediterranean Sea) Towards huge volumes of the order of a km3

  47. Event simulation ANTARES

  48. Event simulation AMANDA (South Pole)

  49. Concluding remarks • Neutrinos have mass, but its tiny of the order of 0.05 - 0.001 eV (cf electron with mass of 511,000 eV) • Mass eigenstates are different from weak-interaction states (oscillations) • Explanation of solar neutrino puzzle • No solution for ‘dark matter’ problem • New possibilities in astrophysics

  50. END

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