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

2. 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. 4 Matter

5. 5 The periodic table

6. 6 Matter

7. 7

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

9. 9 Matter

10. 10 The building blocks of the subatomic world

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

12. Origin of neutrinos ?

13. 13 Origin of neutrinos Weak decay of atomic nuclei (Sun/reactors): …n…  …p… + e  + e (righthanded antineutrino) …p…  …n… + e  + e (lefthanded neutrino) Cosmic rays (decay of the pion)      +  (rechtshandig antineutrino)      +  (linkshandig neutrino) Remnants of the big bang just as photons (T = 2.7 K background) one finds about 500 neutrinos per cm 3 for all three kinds of neutrinos ( e,  and  )

14. How do we know all of that?

15. Broken mirror symmetry Wu et al. 1957 (looking at Cobalt nuclei)

16. 16 From the largest microscope in the world: CERN

17. 17 Antiparticles

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

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

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

21. 21 Three kinds of neutrinos! Z 0 decay into: quark pairs (except top quarks!) lepton pairs  e  e ,    ,      neutrino pairs lifetime is inverse of decay probability     i

22. 22 cross sections G F ~  /M W 2

23. 23 Collission lengths of neutrinos

24. Neutrino puzzles

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

26. How can we detect Neutrinos?

27. 27 Neutrino detectors Super Kamiokande

28. 28 Super Kamiokande

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

30. 30 Neutrino oscillations in the atmosphere Neutrinos from cosmic rays come from decay of pions. These are  neutrinos If the  neutrino is a quantummechanical superposition of neutrinos  en  one gets oscillations

31. 31 Vacuum oscillations

32. 32 Neutrino oscillations in the atmosphere Superkamiokande found oscillations by looking at the zenith angle dependence Results are consistent with    oscillations with  m 2 ~ 2 - 3 x 10 -3 eV 2 and sin 2 2  ~ 1 V ~ 1250 km

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

34. 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. 35 Dirac and Majorana fermions Fermion (general) Dirac neutrino Majorana neutrino

36. 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. 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. 39 Solar neutrinos in SNO (Sudbury Neutrino Observatory) All neutrinos (x = e,  )  x + p  x  + p  x + d  x  + p + n  x + e-  x + e- (via Z 0 -exchange) Electron neutrinos  e + d  e- + p + p  e + e-  e  + e- (via Z 0 and W) E < 15 MeV

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

41. Basis states e and 

42. 42 Solar neutrino oscillations SNO showed that the missing e appear as different type, most probably  e = [2 x 10 7 m]/(  /  water ) ~ 2 x 10 5 m (for a density of  /  water ~ 100) V = [2.5 x 10 3 m](E[GeV]/  m 2 [eV 2 ]) Thus for E ~ 1 MeV and  m 2 ~ 6 x 10 -5 eV 2 one finds that V ~ e and thus one can have the situation of a resonance with maximal oscillations!

43. 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/cm 3 ) light is slowed down more than that neutrinos move slower than light in vacuum!

44.  V light = 1/n’ ~ 1 – 2  N f(k,  =0)/E 2  V neutrino = 1 – m 2 /2E 2 m 2 = 10 -5 eV 2 E = 1 GeV v = 1 – 10 -23  x = 3 x 10 -15 m/yr

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

46. 46 An underwater laboratory Towards huge volumes of the order of a km 3 ANTARES (mediterranean Sea)

47. 47 Event simulation ANTARES

48. 48 Event simulation AMANDA (South Pole)

49. 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