Kevin McFarland University of Rochester

1. Neutrinos: Worth the Wait Kevin McFarlandUniversity of Rochester Warwick University Physics Departmental Colloquium30 November 2005

2. Neutrinos: Worth the Waitespecially when snowed in… Kevin McFarlandUniversity of Rochester “snowed in” Warwick University Physics Departmental Colloquium30 November 2005

3. A Typical February View of the George Eastman Theater at the University of Rochester Neutrinos and Slowness… • Neutrino physics has historically been a slowly developing field • due to the properties of the neutrino, as we shall see • But neutrino physics is heating up into a very active field • driven by experimental results • and by new technologies • So first, some history and perspective… K. McFarland, Neutrinos: Worth the Wait

4. The Birth of the Neutrino Wolfgang Pauli K. McFarland, Neutrinos: Worth the Wait

5. Translation, Please? 4th December 1930 Dear Radioactive Ladies and Gentlemen, As the bearer of these lines, to whom I graciously ask you to listen, will explain to you in more detail, how because of the ”wrong” statistics of the N and 6Li nuclei and the continuous beta spectrum, I have hit upon a desperate remedy to save the ”exchange theorem” of statistics and the law of conservation of energy. Namely, the possibility that there could exist in the nuclei electrically neutral particles, that I wish to call neutrons, which have spinand obey the exclusion principle and which further differ from light quanta in that they do not travel with the velocity of light. The mass of the neutrons should be of the same order of magnitude as the electron mass (and in any event not larger than 0.01 proton masses). The continuous beta spectrum would then become understandable by the assumption that in beta decay a neutron is emitted in addition to the electron such that the sum of the energies of the neutron and the electron is constant... From now on, every solution to the issue must be discussed. Thus, dear radioactive people, look and judge. Unfortunately I will not be able to appear in Tübingen personally, because I am indispensable here due to a ball which will take place in Zürich during the night from December 6 to 7…. Your humble servant, W. Pauli 4th December 1930 Dear Radioactive Ladies and Gentlemen, As the bearer of these lines, to whom I graciously ask you to listen, will explain to you in more detail, how because of the ”wrong” statistics of the N and 6Li nuclei and the continuous beta spectrum, I have hit upon a desperate remedy to save the ”exchange theorem” of statistics and the law of conservation of energy. Namely, the possibility that there could exist in the nuclei electrically neutral particles, that I wish to call neutrons, which have spin and obey the exclusion principle and which further differ from light quanta in that they do not travel with the velocity of light. The mass of the neutrons should be of the same order of magnitude as the electron mass (and in any event not larger than 0.01 proton masses). The continuous beta spectrum would then become understandable by the assumption that in beta decay a neutron is emitted in addition to the electron such that the sum of the energies of the neutron and the electron is constant... From now on, every solution to the issue must be discussed. Thus, dear radioactive people, look and judge. Your humble servant, W. Pauli 4th December 1930 Dear Radioactive Ladies and Gentlemen, As the bearer of these lines, to whom I graciously ask you to listen, will explain to you in more detail, how because of the ”wrong” statistics of the N and 6Li nuclei and the continuous beta spectrum, I have hit upon a desperate remedy to save the ”exchange theorem” of statistics and the law of conservation of energy. Namely, the possibility that there could exist in the nuclei electrically neutral particles, that I wish to call neutrons, which have spinand obey the exclusion principle and which further differ from light quanta in that they do not travel with the velocity of light. The mass of the neutrons should be of the same order of magnitude as the electron mass (and in any event not larger than 0.01 proton masses). The continuous beta spectrum would then become understandable by the assumption that in beta decay a neutron is emitted in addition to the electron such that the sum of the energies of the neutron and the electron is constant... From now on, every solution to the issue must be discussed. Thus, dear radioactive people, look and judge. Your humble servant, W. Pauli K. McFarland, Neutrinos: Worth the Wait

6. β-decay The Energy of the “β” Translation, Please? • To save the law of conservation of energy? • If the above picture is complete, conservation of energy says β has one energy, but we observe this instead • Pauli suggests “neutron” takes away energy! • The “exchange theorem of statistics”, by the way, refers to the fact that a spin½ neutron can’t decay to an spin½ proton + spin½ electron • he doesn’t call it the “Pauli exclusion principle”, to his credit… K. McFarland, Neutrinos: Worth the Wait

7. Fundamental Forces • Of the four fundamental forces, three are important for the structure of matter around us Strong force • holds nucleus together • so strong that quarks are confined Gravity • holds planets,galaxies, etc.together Electromagnetism • holds atoms together • keeps matter from collapsing under the force of gravity K. McFarland, Neutrinos: Worth the Wait

8. Enrico Fermi Neutron Beta Decay Neutrino-Neutron“Quasi Elastic” Scattering Theories of Forces • Modern force description isquantum field theory… • often illustrated w/ its lowest orderperturbative expansion… • First theory of weak interactions(Fermi theory of beta decay, 1933) • also names the “neutrino” to distinguish from Chadwick’s neutron K. McFarland, Neutrinos: Worth the Wait

9. How to Hunt a Neutrino • How do we see any fundamental particle? • Electromagneticinteractions kickelectrons awayfrom atoms • But neutrinos don’t haveelectric charge. They only interact weakly • so we only see by-products of their weak interactions K. McFarland, Neutrinos: Worth the Wait

10. How Weak is Weak? • Weak is, in fact, weak. • A 3 MeV neutrino producedin fusion from the sun will travelthrough water, on average, before interacting. • The 3 MeV positron (anti-matter electron) produced in the same fusion process will travel 3 cm, on average. • Moral: to find neutrinos, you need a lot of neutrinos and a lot of detector! 53 light-years K. McFarland, Neutrinos: Worth the Wait

11. Discovery of the Neutrino • Reines and Cowan (1955) • Nobel Prize 1995 • 1 ton detector • Neutrinos from a nuclearreactor Reines and Cowan at Savannah River K. McFarland, Neutrinos: Worth the Wait

12. Solar Neutrino Hunting Ray Davis • Radiochemical DetectorRay Davis (Nobel prize, 2002) • ν+np+e- (stimulated β-decay) • Use this to produce an unstableisotope, ν+37Cl37Ar+e- , whichhas 35 day half-life • Put 615 tons ofPerchloroethylenein a mine • expect one 37Ar atomevery 17 hours. K. McFarland, Neutrinos: Worth the Wait

13. Solar Neutrino Hunting • Ran from 1969-1998 • Confirmed that sun shines from fusion • But found 1/3 of ν ! K. McFarland, Neutrinos: Worth the Wait

14. Modern Solar Neutrino Hunting • Kamiokande andSuper-Kamiokande(Masatoshi Koshiba, Rochester PhD 1955, Nobel Laureate 2002) K. McFarland, Neutrinos: Worth the Wait

15. Modern Neutrino Hunting • The Sun, imaged in neutrinos, bySuper-Kamiokande sadly, not the same angular scale Existence of the sun confirmed by neutrinos! The Sun, optical image K. McFarland, Neutrinos: Worth the Wait

16. Our Timescale So Far… 1930 • Pauli and Fermi (theory) • to Reines and Cowan (discovery) • to Davis (solar neutrinos) • to Koshiba (supernova and oscillations) • progress continues to accelerate into theexciting neutrino programs of today… 1950 1970 1990 K. McFarland, Neutrinos: Worth the Wait

17. n n Next Steps: The Broadest Goals • Understand mixing of neutrinos • a non-mixing? CP violation? • Understand neutrino mass • absolute scale and hierarchy • Understand n interactions • new physics? new properties? • Use neutrinos as probes • nucleon, earth,sun, supernovae K. McFarland, Neutrinos: Worth the Wait

18. Qualitative Questions • The questions facing us now are fundamental, and not simply a matter of “measuring oscillations better” • Examples: • Are there more than three neutrinos? • What is the hierarchy of masses? • Can neutrinos contribute significantly to the mass of the universe? • Is there CP violation in neutrino mixings? K. McFarland, Neutrinos: Worth the Wait

19. n n The Broadest Goals • Understand mixing of neutrinos • a non-mixing? CP violation? • Understand neutrino mass • absolute scale and hierarchy • Understand n interactions • new physics? new properties? • Use neutrinos as probes • nucleon, earth, etc. K. McFarland, Neutrinos: Worth the Wait

20. What We Hope to Learn From Neutrino Oscillations • Near future • validation of three generation picture • confirm or disprove LSND oscillations (>3 neutrinos) • precision tests of “atmospheric” mixing at accelerators • Farther Future • neutrino mass hierarchy, CP violation? • Precision at reactors • sub  multi MegaWatt sources • 10  100  1000 kTon detectors K. McFarland, Neutrinos: Worth the Wait

21. Minimal Oscillation Formalism • If neutrino mass eigenstates: n1, n2, n3, etc. • … are not flavor eigenstates: ne, nm, nt • … then one has, e.g., take only two generations for now! different masses alter time evolution time K. McFarland, Neutrinos: Worth the Wait

22. e- density Oscillation Formalism (cont’d) • So, still for two generations… • Oscillations require mass differences • Oscillation parameters are mass-squared differences, dm2, and mixing angles, q. • One correction to this is matter… changes q, L dep. appropriate units give the usual numerical factor1.27 GeV/km-eV2 Wolfenstein, PRD (1978) K. McFarland, Neutrinos: Worth the Wait

23. SAGE - The Russian-AmericanGallium Experiment Solar Neutrinos • There is a glorious historyof solar neutrino physics • original goals: demonstratefusion in the sun • first evidence of oscillations K. McFarland, Neutrinos: Worth the Wait

24. Culmination: SNO • D2O target uniquely observes: • charged-current • neutral-current • The former is onlyobserved for ne(lepton mass) • The latter for all types • Solar flux is consistentwith models • but not all ne at earth K. McFarland, Neutrinos: Worth the Wait

25. KAMLAND • Sources areJapanesereactors • 150-200 kmfor most offlux. Rate uncertainty ~6% • 1 kTon scint. detector inold Kamiokande cavern • overwhelming confirmationthat neutrinos change flavorin the sun via mattereffects K. McFarland, Neutrinos: Worth the Wait

26. Solar Observations vs. KAMLAND • Solar neutrino observations are best measurement of the mixing angle • KAMLAND does better on dm212 + KAMLAND = K. McFarland, Neutrinos: Worth the Wait

27. Atmospheric Neutrinos • Neutrino energy: few 100 MeV – few GeV • Flavor ratio robustly predicted • Distance in flight: ~20km (down) to 12700 km (up) K. McFarland, Neutrinos: Worth the Wait

28. Super-Kamiokande • Super-Kdetector hasexcellent e/mseparation • Up / down difference! 2004 Super-K analysis old, but good data! K. McFarland, Neutrinos: Worth the Wait

29. Neutrino Beam from KEK to Super-K K2K figures courtesy T. Nakaya • Experiment has completeddata-taking • confirms atmosphericneutrino oscillation parameters with controlled beam • constraint on dm223 (limited statistics) K. McFarland, Neutrinos: Worth the Wait

30. Enough For Three Generations figures courtesy B. Kayser • Oscillations have told us the splittings in m2, but nothing about the hierarchy • The electron neutrino potential (matter effects) can resolve this in oscillations, however. dmsol2 dm122≈8x10-5eV2dmatm2 dm232≈2.5x10-3eV2 K. McFarland, Neutrinos: Worth the Wait

31. Three Generation Mixing slide courtesy D. Harris • Note the new mixing in middle, and the phase, d K. McFarland, Neutrinos: Worth the Wait

32. But CHOOZ… • Like KAMLAND, CHOOZ and Palo Verde expt’s looked at anti-ne from areactor • compare expected to observed rate, s~4% • If electron neutrinos don’t disappear, they don’t transform to muon neutrinos • limits nm->ne flavor transitions at and therefore |Ue3| is “small” dm223 K. McFarland, Neutrinos: Worth the Wait

33. Optimism has been Rewarded • By which he meant…had not Eatm n/Rearth < dmatm2 <Eatm n/hatmand had not solar density profileand dmsol2 beenwell-matched… • We might not be discussingn oscillations! “We live in the best of all possible worlds” – Alvaro deRujula, Neutrino 2000 K. McFarland, Neutrinos: Worth the Wait

34. Are Two Paths Open to Us? • If “CHOOZ” mixing, q13, is small, but not too small, there is an interesting possibility • At atmospheric L/E, dm232, q13 ne nm dm122, q12 LARGE SMALL LARGE SMALL K. McFarland, Neutrinos: Worth the Wait

35. Implication of two paths • Two amplitudes • If both small,but not too small,both can contribute ~ equally • Relative phase, d, between them can lead toCP violation (neutrinos and anti-neutrinos differ) in oscillations! dm232, q13 ne nm dm122, q12 K. McFarland, Neutrinos: Worth the Wait

36. Leptonic CP Violation in Oscillations • CP violation and matter effects lead to a complex mix… • CP violation gives ellipsebut matter effects shiftthe ellipse in along-baseline acceleratorexperiment… • Stakes are high: • CP violation in leptons could, in fact, haveseeded Universe’smatter-antimatter asymmetry Minakata & Nunokawa JHEP 2001 K. McFarland, Neutrinos: Worth the Wait

37. But LSND… figures courtesy S. Brice • LSND anti-ne excess • 87.9±22.4±6.0 events • statistically overwhelming;however… LSND dm2 ~ 0.1-1.0 eV2 Atmos. dm2 ≈ 2.5x10-3 eV2 Solar dm2 ≈ 8.0x10-5 eV2 cannot be accommodated with only three neutrinos K. McFarland, Neutrinos: Worth the Wait

38. SignalMis-IDBeam MiniBooNE figures courtesy S. Brice • A very challenging experiment! • Have ~0.6E21protons on tape • First neappearanceresults inearly 2006 (?) K. McFarland, Neutrinos: Worth the Wait

39. Next Steps(Brazenly Assuming Three Neutrinos) • MINOS and CNGS • Reactors • T2K and NOvA • Mating Megatons and Superbeams • Beta (ne) beams andneutrino factories (mne and nm) graphical witcourtesy A. deRujula K. McFarland, Neutrinos: Worth the Wait

40. Isn’t all of this overkill? • Disentangling the physics from the measurements is complicated • Different measurements have different sensitivity to matter effects, CP violation • Matter effects amplified for long L, large En • CP violation cannot be seen in disappearance (reactor) measurement nene Huber, Lindner, Rolinec,Schwetz, Winter K. McFarland, Neutrinos: Worth the Wait assumes sin22q13 = 0.1

41. NuMI-Based Long Baseline Experiments • 0.25 MWatt  0.4 MWatt proton source • Two generations: • MINOS (running) • NOvA (future)15mrad Off Axis K. McFarland, Neutrinos: Worth the Wait

42. MINOS Goal: precise nmdisappearance measurement Gives dm223 735km baseline 5.4kton Far Det. 1 kton Near Det. Running since early 2005 K. McFarland, Neutrinos: Worth the Wait

43. t n 1 mm Pb Emulsion layers 1.8kTon fiugres courtesy A. Bueno figures courtesy D. Autiero CNGS • Goal: ntappearance • 0.15 MWatt source • high energy nmbeam • 732 km baseline • handfuls of events/yr e-, 9.5 GeV, pT=0.47 GeV/c  interaction, E=19 GeV 3kton K. McFarland, Neutrinos: Worth the Wait

44. Back to Reactors • Recall thatKAMLANDsaw anti-nedisappearanceat solar L/E • Have not seendisappearance atatmospheric L/E K. McFarland, Neutrinos: Worth the Wait

45. Why Reactors? • CHOOZ (reactor) has left us without evidence of anti-ne disappearance indicating |Ue3|>0 • reactors are still the most sensitive probe! • CHOOZ used a single detector • therefore, dead-reckoning used to estimate neutrino flux from the reactor • could improve with a near/far technique • KAMLAND has improved knowledge of how to reject backgrounds significantly(remember, their reactors are ~200 km away!) K. McFarland, Neutrinos: Worth the Wait

46. not an engineering drawing How Reactors? • To get from ~4% uncertainties to ~1% uncertainties, need a near detector to monitor neutrino flux • For example, Double-CHOOZ proposes to add a secondnear detector and compare rates • new detectors with 10 ton mass • total error budget on rate ~2% • low statistics 10t limit spectraldistortion, 1 km baseline likelyshorter than optimum • Optimization beyond Double-CHOOZ… • ~100 ton detector mass • optimize baseline for dm223 • background reduction with active or passive shielding K. McFarland, Neutrinos: Worth the Wait

47. Where Reactors? • A series of proposals with different technical choices • All challenging experiments to limit systematics K. McFarland, Neutrinos: Worth the Wait

48. Megawatt Class Beams • J-PARC • initially 0.7 MWatts  4 MWatts • FNAL Main Injector • current goal 0.25 MWatts  0.4 MWatts • future proton driver upgrades? • Others? K. McFarland, Neutrinos: Worth the Wait

49. J-PARC Facility K. McFarland, Neutrinos: Worth the Wait

50. A Digression: Off-axis • First Suggested by Brookhaven (BNL 889) • Take advantage of Lorentz Boost and 2-body kinematics • Concentrate nm fluxat one energy • Backgrounds lower: • NC or other feed-downfrom highlow energy • ne (3-body decays) figure courtesy D. Harris K. McFarland, Neutrinos: Worth the Wait