Neutrino Oscillations, Proton Decay and Grand Unified Theories

1. Neutrino Oscillations,Proton Decayand Grand Unified Theories D. CasperUniversity of California, Irvine

2. Outline • A brief history of neutrinos • How neutrinos fit into the “Standard Model” • Grand Unified Theories and proton decay • Recent neutrino oscillation discoveries • Future prospects for neutrino oscillation and proton decay

3. Enrico Fermi Wolfgang Pauli A Desperate Remedy

4. Clyde Cowan Fred Reines Operation Poltergeist

5. Two Kinds of Neutrinos • Reines and Cowan’s neutrinos produced in reaction: • Observed reaction was: • Muon decay was known to involve two neutrinos: • If only one kind of neutrino, the rate for the unobserved process: much too large • Proposal: Conserved “lepton” number and two different types of neutrinos(e and ) • Produce beam with neutrinos from • Neutrinos in beam should not produce electrons!

6. Last, but not least…

7. Three’s Company • Number of light neutrinos can be measured! • Lifetime (and width) of Z0 vector boson depends on number of neutrino species • Measured with high precision at LEP • N = 3.02 ± 0.04 • Probably no more families exist

8. Particles of “The Standard Model” • Three “families” of particles • Families behave identically, but have different masses • Keeping it “in the family”? • Quarks from different families have a small mixing – do the neutrinos also mix? • Each quark comes in three “colors” • The electron and each of its “copies” has a neutrino associated with it • Neutrinos must be massless, or the theory must have something new added to it. Quarks Leptons

9. Forces of The Standard Model  Z  Z  Z  Z • Four known forces hold everything together: • Gravity – the weakest, not included in Standard Model • Electromagnetism – charged particles exchange massless photons • Strong force – holds quarks together, holds protons and neutrons together inside nucleus; particles exchange massless “gluons” • Weak force – responsible for radioactivity; particles exchange W and Z particles W W W gluons

10. u d W+ µ µ Weakly Interacting Neutrinos • Neutrinos interact only via the two weakest forces: • Gravity • Weak nuclear force • W and Z particles extremely massive • W mass ~ Kr atom! • Force extremely short-ranged • This makes the weak force weak • Neutrinos pass through light-years of lead as easily as light passes through a pane of glass!

11. Mysteries of the Standard Model • Why three “families” of quarks and leptons? • Why are do particles have masses? • Why are the masses so different? • m < 10-11  mt • Are neutrinos the only type of matter without mass? • Can quarks turn into leptons? • Are there really three subatomic forces, or just one?

12. X,Y Grand Unified Theories • Maybe quarks and leptons aren’t different after all? • Maybe the three subatomic forces aren’t different either? • Maybe a more complete theory can predict particle masses?

13. 0 Proton Proton Decay e+ e 0 Neutron Neutrino e– Proton Proton Decay • Generic prediction of most Grand Unified Theories • Lifetime > 1033 yr! • Requires comparable number of protons • Colossal Detectors • Proton decay detectors are also excellent neutrino detectors (big!) • Neutrino interactions are a contamination which proved more interesting than the (as yet unobserved) signal

14. IMB • World’s first large, ring-imaging water detector • Total mass 8000 tons • Fiducial mass 3300 tons • 2048 Photomultipliers • Built to search for proton decay • Operated 1983-1990

15. Water Cerenkov Technique Electron Muon • Cheap target material • Surface instrumentation • Vertex from timing • Direction from ring edge • Energy from pulse height, range and opening angle • Particle ID from hit pattern and muon decay

16. The Rise and Fall of SU(5) • SU(5) grand-unified theory predicted proton decay to e+0 with lifetime 4.51029±1.7 years • With only 80 days of data, IMB was able to set a limit > 6.51031 years (90%CL) • SU(5) was ruled out!

17. Nova • February 1987: Neutrino pulse from Large Magellanic Cloud observed in two detectors • Confirmed astrophysical models • Neutrino mass limits comparable to the best laboratory measurements of that time (from 19 events!)

18. Atmospheric Neutrinos • Products of hadronic showers in atmosphere • 2:1 µ:e ratio from naive flavor counting • Flavor ratio (/e) uncertainty ± 5% • Neutrinos produced above detector travel ~15 km • Neutrinos produced below detector travel all the way through the Earth (13000 km)

19. Neutrino Interactions • “Contained” (e ,) • Fully-Contained (FC) • Partially-Contained (PC) • “Upward-Muon” () • Stopping • Through-going • Difficult to detect  • Not enough energy in most atmospheric neutrinos to produce a heavy  particle

20. The Atmospheric Neutrino Problem • Early large water detectors measured significant deficit of  interactions • What happened to these neutrinos? • Smaller detectors did not see the effect • Needed larger and more sensitive experiments, improved checks

21. Neutrino Oscillation • Quantum mechanical interference effect: • Start with one type of neutrino and end up with another! • Requires: • Neutrinos have different masses (m20) • Neutrino states of definite flavor are mixtures of several masses (and vice-versa) (mixing 0, like quarks mix) • Simplest expression (2-flavor): • Oscillation probability = sin2(2) sin2(m2L/E)

22. Checking the Result • A number of incorrect “discoveries” of neutrino oscillation made over the years • Atmospheric neutrino problem was treated with (appropriate) skepticism • Less exotic explanations were explored: • Incorrect calculation of expected flux? • Many comparisons of calculations failed to find any mistake • Systematic problem with particle ID? • Beam tests of water detector particle ID performed at KEK lab in Japan – proved that water detectors can discriminate e and  • Conclusive confirmation required with higher statistics, improved sensitivity

23. Super-Kamiokande • Total Mass: 50 kt • Fiducial Mass: 22.5 kt • Active Volume: • 33.8 m diameter • 36.2 m height • Veto Region: > 2.5m • 11,146  50 cm PMTs • 1,885  20 cm PMTs

24. SuperK Preliminary1289 days best fit:sin22=1.0m2 = 2.5  10-3 eV22 = 142/152 DoF no oscillation: 2 = 344/154 DoF Evidence for Oscillation • SuperK also sees deficit of  interactions • Also clear angular (L) and energy (E) effects • Finally a smoking gun! • All data fits  oscillation perfectly • Surprise: • Maximal mixing between neutrino flavors

25. Checking the Result (Again) • Look for expected East/West modulation of atmospheric flux • Due to earth’s B field • Independent of oscillation • Fit the data to a function of sin2(LEn) • Best fit at ~-1 (L/E)

26. Ray Davis The Solar Neutrino Problem • Homestake experiment first to measure neutrinos from Sun, finds huge deficit (factor of 3!) • Anomaly confirmed by SAGE, GALLEX, Kamiokande experiments

27. SuperK Solar Neutrinos • Real-time measurement allows many tests for signs of oscillation: • Day/Night variation • Spectral distortions • Seasonal variation • Allowed oscillation parameter space is shrinking • SMA is disfavored by SK data

28. SNO • Water detector with a difference: • Heavy water • Able to measure charged current (e) and neutral current (x) • Can determine (finally!) whether solar neutrinos are oscillating or not

29. Resolving the Solar Neutrino Problem • In July, 2000 SNO published their first results • Measured the rate of D charged-current scattering (only e) • Compare with SuperK precision measurement of e scattering (x) • Significant difference between flux of e and x implies non-zero  +  flux from the Sun: oscillation! • Combined flux of all neutrinos agrees well with solar model

30. SuperK pe+0 • Require 2-3 showering rings, 0 e • 0 mass cut if 3 rings • Overall Detection Efficiency: 43% • No candidates (0.2 background expected) • / > 5.7 × 1033 yrs (90% CL)

31. 236 MeV/c+ Prompt6.3 MeV K+(~12 ns)   16O15N*+ K+, K+ + No candidates 16O p Present limit for K+:/>21033 years

32. Status of Proton Decay

33. The K2K Experiment

34. K2K Results • 56 events observed at Super-K, vs. 80±6 expected • Energy spectrum of observed events consistent with oscillation • Appears completely consistent with SuperK • More data next year

35. 2nd Generation LongBaseline (MINOS,CNGS) • 730 km baselines • MINOS: • Factor ~500 more events than K2K (at 3 distance) • Disappearance and appearance (e, ) experiments • CNGS • Higher-energy beam from CERN to look for  appearance at Gran Sasso • Only a handful of signal events expected

36. JHF/SuperK Experiment • Approved: • 50 GeV PS • 0.77 MW • (K2K is 0.005 MW) • Proposed: • Neutrino beamline to Kamioka • Upgrade to 4 MW • Outlook: • Completion of PS in 2006

37. Neutrino Factory • The Ultimate Neutrino Beam: • Produce an intense beam of high-energy muons • Allow to decay in a storage ring pointed at a distant detector • Perfectly known beam • Technically very challenging!

38. UNO (and Hyper-Kamiokande) • Fiducial Mass: 450 kton • 20  Super-Kamiokande • Sensitive to proton decay up to 1035 yr lifetime • Able to study leptonic CP violation (with neutrino beam) • Hyper-Kamiokande • 1 Mton Japanese version

39. A World-Wide Neutrino Web? • Enormous interest in future long-baseline oscillation experiments world-wide! • Some theoretical indications that proton decay may be within reach

40. Solving the Mysteries • Why three “families” of quarks and leptons? • Quark and lepton family mixing seems very different • Only beginning to measure lepton mixings in detail • Why are do particles have masses? • Why are the masses so different? • m < 10-11  mt • Are neutrinos the only type of matter without mass? • It now seems clear that neutrinos have (very tiny) masses • Can quarks turn into leptons? • Are there really three subatomic forces, or just one? • Mixing between families, and the small neutrino masses may tell us a lot about a Grand Unified Theory • Observation of proton decay would be direct evidence for it!