Make No Little Plans: A Bright Future for Neutrinos at Accelerators

1. Make No Little Plans: A Bright Future for Neutrinos at Accelerators Kevin McFarlandUniversity of RochesterDepartment of Physics and Astronomy Colloquium20 January 2010

2. My Kind of Town? "Make no little plans. They have no magic to stir men's blood and probably will not themselves be realized.“Daniel Burnham • Burnham is most well known as one of two lead architects of the 1893 Chicago Columbian Exposition • Famously envisaged Chicago asthe “Paris of the Prairie” • Louis Sullivan accused Burnham of “setting American architecture back 40 years” with his neo-classicist style of the Exposition K. McFarland, Neutrinos at Accelerators

3. Lessons for neutrino physicists… • Dreaming big can be a good thing. At least when the goals are worthwhile • now, we believe we have such goals and the means to realize them • When you get a chance to engage in urban planning before pouring concrete, synergy of effort may follow • a collection of buildings, after all, is not a city • You will never make all the critics happy K. McFarland, Neutrinos at Accelerators

4. A Disjointed Drama in Three Acts… • What we hope to learn from Neutrino Oscillations (a lengthy exposition…) • current status of knowledge and future goals • Future Experiments (detailed plot development) • how can we make these measurements • what difficulties will we encounter? • Neutrino interactions (not the denouement, but rather one of the many plot threads…) • needs and experiments. And MINERvA… K. McFarland, Neutrinos at Accelerators

5. The Birth of the Neutrino Wolfgang Pauli K. McFarland, Neutrinos at Accelerators

6. 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… I agree that my remedy could seem incredible because one should have seen those particles very earlier if they really exist. But only the one who dare can win and the difficult situation, due to the continuous structure of the beta spectrum, is lighted by a remark of my honored predecessor, Mr. Debye, who told me recently in Bruxelles: "Oh, It's well better not to think to this at all, like new taxes". 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… I agree that my remedy could seem incredible because one should have seen those particles very earlier if they really exist. But only the one who dare can win and the difficult situation, due to the continuous structure of the beta spectrum, is lighted by a remark of my honored predecessor, Mr. Debye, who told me recently in Bruxelles: "Oh, It's well better not to think to this at all, like new taxes". 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… I agree that my remedy could seem incredible because one should have seen those particles very earlier if they really exist.But only the one who dare can win and the difficult situation, due to the continuous structure of the beta spectrum, is lighted by a remark of my honored predecessor, Mr. Debye, who told me recently in Bruxelles: "Oh, It's well better not to think to this at all, like new taxes". 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 at Accelerators

7. 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 at Accelerators

8. 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 at Accelerators

9. Enrico Fermi Neutron Beta Decay Neutrino-Neutron“Quasi Elastic” Scattering Theories of the Weak Force • First theory of weak interactions(Fermi theory of beta decay, 1933) • also names the “neutrino” to distinguish from Chadwick’s neutron • the weak force is weak because the Force Carrier (W boson) is heavy and off mass-shell K. McFarland, Neutrinos at Accelerators

10. 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 at Accelerators

11. 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. • A 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 at Accelerators

12. 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 at Accelerators

13. 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 at Accelerators

14. Solar Neutrino Hunting • Ran from 1969-1998 • Confirmed that sun shines from fusion • But found 1/3 of ν ! K. McFarland, Neutrinos at Accelerators

15. Modern Solar Neutrino Hunting • Kamiokande andSuper-Kamiokande(Masatoshi Koshiba, Rochester PhD 1955, Nobel Laureate 2002) K. McFarland, Neutrinos at Accelerators

16. 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 at Accelerators

17. Our Timescale So Far… 1930 • Pauli and Fermi (theory) • to Reines and Cowan (discovery) • to Davis (solar neutrinos) • to Koshiba(supernova and oscillations) • Apparently, patience is a virtue 1950 1970 1990 K. McFarland, Neutrinos at Accelerators

18. Isn’t there some shortcut? • Why, yes! Leave it to Star Trek to point the way! • According to several episodes, Lt. JordyLaForge’s VISOR can actually detect “neutrino fieldemissions” • and what do we do in science exceptemulate Star Trek? • Sarcasm aside, nature has made studying neutrino physics just plain hard. • Now we’ll see what the payoff may be. K. McFarland, Neutrinos at Accelerators

19. n n Neutrinos: The Broadest Goals • Understand mixing of neutrinos • 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 at Accelerators

20. Neutrino Flavors • Remember that neutrinos were discovered by • the final state positron is no accident! • we’ve seen neutrinosproduce all threecharged leptons • And the Z bosondecays into three neutrino states K. McFarland, Neutrinos at Accelerators

21. Neutrino Flavor Mixing • Are these neutrinos “of definite flavor”the “real neutrinos” • i.e., is a neutrino flavor eigenstate inan eigenstate of the neutrino mass matrix • Or are we looking at neutrino puree? • And of course, so what if it is puree? K. McFarland, Neutrinos at Accelerators

22. Neutrino Flavor Mixing (cont’d) • If neutrinos mass states mixto form flavors • and the masses are different… • flavors of neutrinos can change in flight • This would explain the disappearing solar ns! • since only electron flavor neutrinos make the detection reaction, ν+n→p+e-, occur K. McFarland, Neutrinos at Accelerators

23. Neutrino Flavor Oscillation So each neutrino wavefunctionhas a time-varying phase in its rest frame, Now, imagine you produce a neutrino of definite momentum but is a mixture of two masses, m1, m2 so pick up a phase difference in lab frame K. McFarland, Neutrinos at Accelerators

24. Neutrino Oscillation (cont’d) ν2 νμ ν3 • Phase difference leads to interference effect, just like with sound waves of two frequencies • frequency difference sets period of “beats” K. McFarland, Neutrinos at Accelerators

25. Neutrino Oscillation (cont’d) only two generations for now! • Phase difference • Analog of “volume disappearing” in beats is original neutrino flavor disappearing • and appearance of a new flavor • more generally, mixing need not be maximal K. McFarland, Neutrinos at Accelerators

26. e- density Neutrino Oscillation (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 at Accelerators

27. 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 at Accelerators

28. 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 at Accelerators

29. 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 at Accelerators

30. Solar Observations vs. KAMLAND • Solar neutrino observations are best measurement of the mixing angle • KAMLAND does better on dm212 + KAMLAND = K. McFarland, Neutrinos at Accelerators

31. 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 at Accelerators

32. Super-Kamiokande • Super-Kdetector hasexcellent e/mseparation • Up / down difference! 2004 Super-K analysis old, but good data! K. McFarland, Neutrinos at Accelerators

33. 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 at Accelerators

34. MINOS 735km baseline 5.4kton Far Det. 1 kton Near Det. Running since early 2005 Precise measurement of nmdisappearance energy gives dm223 K. McFarland, Neutrinos at Accelerators

35. 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 at Accelerators

36. Qualitative Questions • The questions facing us now are fundamental, and not simply a matter of “measuring oscillations better” • Examples: • 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 at Accelerators

37. n n Of The Broadest Goals… • Understand mixing of neutrinos • 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 at Accelerators

38. What We Hope to Learn From Neutrino Oscillations • Near future • validation of three generation picture • 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 at Accelerators

39. 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 at Accelerators

40. Three Generation Mixing slide courtesy D. Harris • Note the new mixing in middle, and the phase, d K. McFarland, Neutrinos at Accelerators

41. But CHOOZ… • Like KAMLAND, CHOOZ and Palo Verde expt’s looked at anti-ne from a reactor • 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 at Accelerators

42. Optimism has been Rewarded • By which he meant…had notEatm 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 at Accelerators

43. LARGE SMALL LARGE SMALL 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 K. McFarland, Neutrinos at Accelerators

44. 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 at Accelerators

45. Observable Effects due to this Interference • “CP violation” (interference term) and matter effects lead to a complicated mix… • Simplest case:first oscillationmaximum, neutrinos andanti-neutrinos • CP violation gives ellipsebut matter effects shiftthe ellipse in along-baseline acceleratorexperiment… Minakata & Nunokawa JHEP 2001 K. McFarland, Neutrinos at Accelerators

46. Beyond the oscillation maximum… • See different mixture of solar/interference “CP” term,matter effects at different oscillation maxima • This shows E. Recall argument of vacuum oscillation term is ~L/E FNAL-DUSEL L~1300km K. McFarland, Neutrinos at Accelerators

47. Why Care about CP Violation? • θ13 and δ are of some interest for models attempting to unify quark and lepton sectors • if zero or near-zero, is there a symmetry (or barely broken symmetry) that suppresses them? • Must more interesting… matter asymmetry in Universe • Baryon excess, YB=nB/s≈8x10-11 is observed • Recently, Petcov and collaboratorshave shown how to generatethis from δ phase • Requires large(ish) θ13, non-degenerate neutrino mass spectrum,and Majorana neutrinos with heavy right handed partners • Discovery of CP violation in neutrinooscillations could hint at a source of large YB! Pascoli, Petcov, Riotto,hep-ph/0611338 K. McFarland, Neutrinos at Accelerators

48. Next Steps • Reactors (in progress) • cannot be sensitive to CP violation but do directly measure size of the “small” mixing (like CHOOZ did) • “Superbeam” experiments (in progress) • T2K and NOvA • Why so many next steps? • Combining experiments separates masses, mixings Huber, Lindner, Rolinec, Schwetz, Winter K. McFarland, Neutrinos at Accelerators

49. E Parameters for a “Super-Beam” • All experiments will want to see first oscillation maximum, L/E ~ 400 km/GeV • Then one has a choice… Broad Band Beam Covering Multiple Oscillation Peaks Narrow Band Beam at First Oscillation Peak • Because there are many parameters, need neutrino and anti-neutrino measurements (minimally) • Perhaps multiple baselines • In principle, can measure everything with one experiment! • However require much larger L/E and L • Also need good energy resolution at low neutrino energies K. McFarland, Neutrinos at Accelerators

50. Narrow Band Beam:Off-axis Techinque • First Suggested by BNL-889 proposal • 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) • Generally optimal if onlyaccessing “first maximum” figure courtesy D. Harris K. McFarland, Neutrinos at Accelerators