Neutrino Physics: Advancements, Discoveries, and Future Directions

1. American Physical Society MultiDivisional Neutrino Study DOE-OS Briefing January 7, 2005 Washington DC Stuart Freedman Boris Kayser

2. Part I Why study neutrinos? Super KamiokANDE PMT Matrix

3. A view of the Sun from 1 Km underground

5. Pioneering venture in Neutrino Physics Ray Davis

6. Neutrino Ocillations E2 = m2c2 B. Pontecorvo E1 = m1c2 In the rest frame Boosted to the lab frame

7. Atmospheric Neutrinos

8. The SuperKamiokande Light-Water Cherenkov Detector

9. Solar Neutrino Experiments

10. Neutrino Flavor Composition of 8B Flux SNO

11. LMA: m2 = 5.5x10-5 eV2 sin2 2 = 0.833 Reactor Antineutrino Experiments KamLAND

12. Terrestrial Version of Atmospheric Neutrino Experiment 818 events if no oscillation 56 events observed MINOS (FNAL  Soudan) 2005 If no oscillation: 151  11 Observe: 108

13. KamLAND Is the Neutrino Spectrum Distorted?

14. Is there an oscillation effect

15. Observing the oscillations in the neutrino rest frame

16. LSND at Los Alamos

17. Excerpts from the Charge “…response to the remarkable recent series of discoveries in neutrino physics…” “…build on the 2002 long range plans developed by NSAC and HEPAP.” “…examine the broad sweep of neutrino physics…” “…create a scientific roadmap for neutrino physics.” “…move towards agreement on the next steps…” The Study will lay scientific groundwork for the choices that must be made during the next few years.

18. Neutrino Study Organization • Chairpersons Organizing Committee • Solar and Atmospheric Neutrino Experiments • Reactor Neutrino Experiments • Superbeam Experiments and Development • Neutrino Factory and Beta-Beam Experiments and Development Neutrinoless Double Beta Decay and Direct Searches for Neutrino Mass • What Cosmology/Astrophysics and Neutrino Physics can Teach Each Other Theory Discussion Group Writing Committee

19. APS Neutrino Study: Midcourse Correction April 1-2, 2004 Berkeley Final General Meeting Snowmass June 28-30 www.aps.org/neutrino

20. US scientists participate in neutrino physics worldwide

21. Present US Program in Neutrino Physics NSF NSF DOE NP/HEP DOE NP/HEP DOE NP DOE HEP DOE HEP NASA DOE HEP NSF NP NSF DOE NP DOE HEP

22. Underground Facilities Many of the past experiments and many of the future experiments we feel are particularly important rely on suitable underground facilities. The availability of these facilities will be crucial to future neutrino research.

23. Part II The Story SNO

24. What Have We Learned?What Do We Not Know?

25. From neutrino flavor change (oscillation) experiments, we have learned that — • Neutrinos have nonzero rest masses • Leptons mix • Neutrino masses — There is some spectrum of 3 or more neutrino mass eigenstates i: 4 3 (Mass)2 2 1 Mass (i)  mi

26. We do not know how many different neutrinos there are. Just 3, the partners of the 3 charged leptons?? If the Liquid Scintillator Neutrino Detector (LSND) experiment is confirmed, there are more than 3. If LSND is not confirmed, nature may contain only 3 neutrinos. Then, from the existing neutrino oscillation data, the neutrino spectrum looks like —

27. 3 3 m2atm 2 2 m2sol m2sol } } 1 1 Normal Inverted or (Mass)2 m2atm ~ ~ m2sol = 8 x 10–5 eV2, m2atm = 2.5 x 10–3 eV2

28. A grand goal of elementary particle physics is to unify all the forces of nature into a single force. The Grand Unified Theories, which do this for all the forces of nature save gravity, favor — Grand Unified Theories relate the Leptons to the Quarks. is un-quark-like, and would probably involve a lepton symmetry with no quark analogue.

29. le e, l, l Leptonic mixing — • When W+ l+ + , • the produced neutrino state |> is • |> =  U*i |i> . • Neutrino offlavor Neutrino of definite mass mi Unitary Leptonic Mixing Matrix • Flavor- fraction of i = |< |i>|2 = |Ui|2 . e, , or  i

30. Bounded by reactor exps. with L ~ 1 km From max. atm. mixing, { From (Up) oscillate but (Down) don’t { In LMA–MSW, Psol(e e) = e fraction of 2 From distortion of e(solar) and e(reactor) spectra { From max. atm. mixing, 1+ 2 includes (–)/√2 3 m2atm (Mass)2 2 } m2sol 1 [|Ui|2] [|Ui|2] e [|Uei|2]

31. The Mixing Matrix Solar Atmospheric Cross-Mixing cij cos ijsij sin ij Majorana CP phases 12 ≈ sol ≈ 32°,23 ≈ atm ≈ 36-54°, 13 < 15°  would lead to P() ≠ P().CP But note the crucial role of s13 sin 13. ~

32. Poof! Are Neutrinos the Reason We Exist? The universe contains Matter, but essentially no antimatter. Good thing for us: Matter Antimatter This preponderance ofMatteroverantimattercould not have developed unless the two behave differently. (CP) The observed difference betweenQuarkandantiquarkbehavior, as described by the Standard Model, is inadequate. Could the interactions of Matterandantimatterwith neutrinos provide the crucial difference?

33. There is a natural way in which they could. The most popular theory of why neutrinos are so light is the — See-Saw Mechanism { Familiar light neutrino  } Very heavy neutrino N The heavy neutrinos N would have been made in the hot Big Bang.

34. In time, they would have decayed into lighter particles. If Matter and antimatter interact differently with these heavy neutrinos N, then we can have — Probability [ Ne- + … ] ≠ Probability [ Ne+ + … ] Matterantimatter in the early universe. This phenomenon (leptogenesis) would have led to a universe containing unequal amounts of Matter and antimatter.

35. We cannot repeat the early universe. But we can lend credibility to the hypothesis of leptogenesis by showing that Matter and antimatter interact differently with the light neutrinos . A neutrino flavor change involving Matter: - e-  Source Detector A neutrino flavor change involving antimatter: + e+  Source Detector If these two flavor changes have different probabilities, then quite likely so do — Ne- + … andNe+ + …

36. If N decays led to the present preponderance of Matter over antimatter, then we are all descendants of heavy neutrinos.

37. In Pursuit of 13 If sin2213 < 0.01, a neutrino factory will be needed to study both of these issues. Both CP violation and our ability to tell whether the spectrum is normal or inverted depend on 13. How may 13 be measured?

38. sin213 3 m2atm (Mass)2 2 } m2sol 1 sin213 is the small e piece of 3. 3 is at one end of m2atm. We need an experiment sensitive to m2atm, and involving e.

39. Complementary Approaches Reactore disappearance while traveling L ~ 1.5 km. L/E ~ 500 km/GeV. This process depends on 13 alone. Accelerator  e while traveling L > Several hundred km. L/E ~ 400 km/GeV. This process depends on 13 and other neutrino properties, including whether the spectrum is normal or inverted.

40. How To Determine If The Spectrum Is Normal Or Inverted In the experiments we will do with earth-born neutrinos, the neutrinos will travel through earth matter. Exploit the fact that, in matter, e – e interactions raise the effective mass of e.

41. sin213 sin213 2 3 } m2sol 1 m2atm vs. (Mass)2 m2atm 2 } m2sol 3 1   e If m2atm shrinks (grows) in matter, 13 grows (shrinks).

42. The effect of matter increases as the neutrino distance of travel within it, L, does. Using larger L to determine whether the spectrum is normal or inverted could be a unique contribution of the U.S. program.

43. Are Neutrinos Their Own Antiparticles? Does — • i = i (Majorana neutrinos) • or • i ≠ i (Dirac neutrinos) ? • e+ ≠ e– since Charge(e+) = – Charge(e–). • But neutrinos may not carry any conserved charge-like quantum number. • A conserved Lepton Number L defined by—L() = L(l–) = –L() = –L(l+) = 1 may not exist. • If it does not, then i=iand we can have —

44. i Neutrinoless Double Beta Decay (0) e– e– i W– W– Nuclear Process Nucl’ Nucl • Observation would establish that — • Lepton number L is not conserved • Neutrinos are Majorana particles (  =  ) • The origin of neutrino mass is not the same as the origin of the masses of charged leptons, quarks, nucleons, humans, the earth, galaxies Then neutrinos and their masses are very distinctive.

45. The Quest for the Origin of Mass Neutrino experiments and the search for the Higgs boson both probe the origin of mass. The see-saw mechanism suggests that the physics behind neutrino mass resides at 1015 GeV, the extremely high energy where Grand Unified Theories say all the forces of nature, save gravity, become one.

46. The Open Questions

47. Neutrinos and the New Paradigm • What are the masses of the neutrinos? • What is the pattern of mixing among the different types of neutrinos? • Are neutrinos their own antiparticles? • Do neutrinos violate the symmetry CP?

48. Neutrinos and the Unexpected • Are there “sterile” neutrinos? • Do neutrinos have unexpected or exotic properties? • What can neutrinos tell us about the models of new physics beyond the Standard Model?

49. Neutrinos and the Cosmos • What is the role of neutrinos in shaping the universe? • Is CP violation by neutrinos the key to understanding the matter – antimatter asymmetry of the universe? • What can neutrinos reveal about the deep interior of the earth and sun, and about supernovae and other ultra high energy astrophysical phenomena?

50. Part III Recommendations for future experiments KamLAND