Neutrino Mass How can something so small be so important? Greg Sullivan University of Maryland April 1999

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1 Neutrino Mass How can something so small be so important? Greg Sullivan University of Maryland April 1999 Introduction The The Structure of of Matter Matter Fundamental Particles How How do do we we detect detect particles Atmospheric neutrinos Neutrino Mass Mass & Neutrino Oscillations The Super-Kamiokande Experiment How How it it works works What What we we found found Summary

2 Does the Neutrino Have Mass? ν??? e

3 Early periodic chart of the elements

4 Underlying Structure Mendeleyev - grouped by atomic weights Eventually this led to atomic picture of nucleus

5 More Structure

6 Does the structure continue?

7 Latest Version of Periodic Chart of the Fundamental Particles

8 Properties of the Quarks and Leptons Quarks Leptons

9 Properties of the Quarks and Leptons Our knowledge of the neutrinos is VERY limited!

10 Does the Neutrino Have nmass?

11 Neutrino Facts The earth receives about 40 billion neutrinos per second per cm2 from the sun. About 100 times that amount are passing through us from the big bang. This works out to about 330 neutrinos in every c m 3 of the universe! By comparison there are about protons per cm 3 in the universe. If 100 billion solar neutrinos hit the earth, all but about 1 will come out the other side without hitting anything To shield us from just 2/3 of the neutrinos would take a light year thick piece of steel If neutrinos have even a small mass they could make up most of the mass in the universe! ν ν ν ν ν

12 If Neutrinos have mass they may change from one type to another ν e ν µ

13 Particles of matter can behave as waves. Initial time Later time The neutrino we see is made up of different states traveling together. If the states have different masses, they will travel at different speeds, and the composition of the neutrino will change with time/distance! ν τ ν µ ν τ ν µ

14 Sources of neutrinos Neutrinos are produced in the Weak Interaction Neutrinos from the earth -- natural radioactivity Man-made neutrinos --accelerators, nuclear power plants. Astrophysical neutrinos Solar neutrino Atmospheric neutrinos Relic neutrinos -- those left over from the big bang.

15 Particle Detection Seeing a neutrino requires a very special kind of a detector.

16 Detecting Neutrinos The neutrino is observed by seeing the product of its interaction with matter. ν e neutrino ν µ e Electron µ - Muon We don t see the neutrino coming in, but its products are charged particles.

17 Cherenkov radiation Boat moves through water faster than wave speed. Bow wave Aircraft moves through air faster than speed of sound. Sonic boom Particle moves through transparent media faster than speed of light in that media. Cherenkov radiation Cone of light

18 Super-Kamiokande Super-Kamiokande is a 50,000 ton water Cherenkov detector at a depth of 1000 meters in the Kamioka Mozumi mine in Japan. Super-K detects neutrinos from: The Sun - Solar neutrinos The Atmosphere - Atmospheric Neutrinos

19 The Super-K Site Tokyo Mozumi

20 The Super-K Detector

21 SuperKamiokande Collaboration Institute Institute for for Cosmic Cosmic Ray Ray Research, Research, University University of of Tokyo Tokyo Gifu Gifu University University Institute Institute for for Nuclear Nuclear Study, Study, University University of of Tokyo Tokyo National National Laboratory Laboratory for for High High Energy Energy Physics, Physics, KEK KEK Kobe Kobe University University Miyagi Miyagi Education Education University University Niigata Niigata University University Osaka Osaka University University Tokai Tokai University University Tohoku Tohoku University University Tokyo Tokyo Institute Institute of of Technology Technology Boston Boston University University Brookhaven Brookhaven National National Laboratory Laboratory University University of of California, California, Irvine Irvine California California State State University, University, Dominguez Dominguez Hills Hills Cleveland Cleveland State State University University George George Mason Mason University University University University of of Hawaii Hawaii Los Los Alamos Alamos National National Laboratory Laboratory Louisiana Louisiana State State University University University University of of Maryland Maryland State State University University of of New New York, York, Stony Stony Brook Brook University University of of Warsaw Warsaw University University of of Washington Washington

22 Two Suggestions of Neutrino Transformation Solar Neutrinos (~1-15 Mev n e ) Davis experiment (Cl) saw ~30% of expected flux of n e from 8 B & 7 Be Galium experiments showed less than expected flux of n e from all processes Kamiokande saw ~40% n e from 8 B These results can not be reconciled with the standard solar model Atmospheric Neutrinos (~.1-3 GeV) IMB and Kamiokande saw less than expected ratio of n m / n e One Proposed Explanation was: Neutrino Oscillations Solar neutrinos might be n e Atmos. neutrinos might be n m n m n t

23 The Neutrino Image of the Sun 500 Days of Data

24 Atmospheric Neutrinos p Primary Cosmic-ray interaction in the atmosphere. Cascade of secondaries π,κ Decay of secondaries µ µ ν µ Neutrinos formed from decay of other particles ν µ ν µ ν µ ν e ν e

25 Properties of neutrino oscillations The mathematics of neutrino oscillations gives us: Neutrino energy Oscillation distance ~ E DM 2 If M 2 = 0 No Oscillations This means small DM 2 distance. (m 12 -m 22 ) long oscillation Can search for oscillations by doing experiments at different distances from the source. Source ν µ ν? Exp. 1 Exp. 2

26 Cherenkov Event Reconstruction Pattern of Hits Where the event occurred ID of particle (e or m) Amount of Light Energy of particle

27 Through-Going Muon Event

28 Stopping Muon

29 Electron from decay of stopping muon

30 Muon - Electron Identification

31 Study ν µ and ν e as a function of distance traveled about 15 km about 13,000 km Neutrinos produced in the atmosphere at ~15 km altitude... travel through the earth and interact in the detector.

32 L/E Distribution of Atmospheric Neutrinos The dashed lines show the expected shape for ν µ ν τ at m 2 =2.2 x 10-3 ev 2 and sin 2 2θ = 1.

33 Zenith Angle Dependence

34 Atmospheric Results

35 East-West Effect

Also observed in larger scale e.g. galactic clusters.

36 Dark Matter Expect velocity to decrease with increasing distance from core. Observe flat rotational velocity Galaxy M51 Unseen mass surrounding galaxy halo Also observed in larger scale e.g. galactic clusters. NGC3198 As much as 90% of the matter making up the universe may be objects or particles that cannot be seen!

37 How much mass does the neutrino have? Super-K (and all other oscillation exp.) are only sensitive to Dm 2 We find Dm 2 ~ 6 x 10-3 ev If we assume that one neutrino is light then we have m heavy ~ 0.1eV How much mass is 0.1eV? (E=mc 2 ) P 938,000,000 ev 1800 M = 511,000 ev e ~10 Billion M >~ 0.1 ev. n 5 Million

38 Summary Atmospheric Neutrinos Super-K sees ν µ s disappearing with distance Electron neutrino s don t change with distance This is strong evidence for n m -> n t ( or n s ) This implies massive neutrinos Dm 2 ~ 6 x 10-3 ev 2 Sin 2 (2q) >0.8 Requires physics beyond the Standard Model This mass at minimum implies: Neutrinos may have as much mass as all the visible material in the universe Neutrinos are unlikely to be the only dark matter

40 Summary The The Solar Neutrino Problem Rate Rate of ofnn e from e from Sun Sun is is Low Low Astrophysical Solutions improbable Neutrino Oscillation Explanation? nn e Y e Ynn m oscillation m Requires neutrino mass mass New New Physics Implications for for Cosmology Dark Dark Matter Matter Closed Closedvs. vs. Open Open Universe SuperKamiokande is is Now Running New New generation of of Detector ~100 ~100 times times the the event event rate rate of of previous generation of of detector Started taking taking Data Data April April 1, 1, After 30 30yrs May May be be Close to to the the Answer

41 Neutrino Oscillations If Neutrinos Have Mass they can Mix Consider 2 neutrinos ( n m & n e ) Sin 2q Mechanical Analogy for Neutrino Oscillations Spring = Sin 2 q In the Vacuum Length = Mass n e Resonance n m In the Sun When length (i.e. effective mass) are equal the coupling is enhanced. As a n e travels from the core of the sun and exits its effective mass decreases. When the mass crosses the n m mass the mixing is enhanced by a resonance coupling between the two states.

42 Neutrino Oscillations If n mass is not 0 and flavor is not absolutely conserved then mixing may occur between different type of neutrinos. Weak eigenstates of the neutrino are mixtures of the neutrinos with definite mass. For two neutrino species ν e and ν µ we have: ν e = ν 1 cos θ + ν sin ν = ν sinθ + ν cosθ µ 1 where ν 1 and ν 2 are the mass eigenstates. 2 2 In a weak decay one produces a definite weak eigenstate ν ( t ) = 0 = ν. e. At a later time the probability of the final state will be: θ ν ie1t ie2t ( t) = ν e cosθ + ν e sinθ 1 2 The survival probability is: m ( ) ( ) ev Lkm P ν = e ν e; L 1 sin 2θ sin EGeV.

43 Neutrino Oscillations ν µ > ν e sin 2 (2θ)=

44 Radon Level Rn Rn -> -> Bi Bi -> -> b (E<3.26 Mev) Serious Background problem Kamiokande was was ~0.5 ~0.5Bq/m 3 3 Now Now reaching Bq/m 3 3 level level Event Event Rate Rate correlated with withrn Rnlevel

45 Water Transparency Measured by through going muons 30m April 1 ===> 60m June

46 Linac

47 Atmospheric Neutrinos ν + ν µ µ ν e + ν e 2 Ratio predicted to ~ 5% Absolute Flux Predicted to ~20% : primary CR spectrum geomagnetic cutoff hadron production modeled from accelerator data

48 Atmospheric Neutrino Interactions Charged Current n m m - W + Reaction Threshold n p electron: 1.5 MeV Muon: 110 MeV Tau: 3500 MeV n e e - W + n p Neutral Current ν µ,ν e, ν τ p,n Z 0 p,n p 0 g g

49 Data Sample Fully Contained events (FC) The muon stops in the detector (pattern) ν µ Detector m Partially Contained Events (PC) The muon exits the detector (pattern) ν µ Detector m

50 Particle Identification

51 Sub-Gev (535 days) E vis < 1.33 GeV P e > 100 MeV/c P µ > 200 MeV/c Data MC 1 Ring e-like m -like Multi-ring ( µ / e) ( µ / e) Data MC = 0.63 ±.026( stat) ±.05( syst)

52 Multi-Gev (535 days) E vis > 1.33 GeV Fully Contained Data MC 1 Ring e-like m-like Multi-ring Partially Contained Data MC Total = m-like ( µ / e) ( µ / e) Data MC = 0.65 ±.05 ( stat ) ±.08 ( syst )

53 If the muon n s oscillate, what it look like? Depletion of n m relative to n e double ratio R R = ( µ / e) ( µ / e) data MC < 1 L dependence of n m flux Zenith angle dependence

54 Zenith Angle Dependence Survival Probability vs. Distance (1GeV,.003 ev^2) Probability Distance (km) P km ( ν ν ; L) = 1 sin 2θ sin µ µ EGeV m 2 L

55 Zenith Angle Dependence

56 L/E Distribution

57 Worldwide Results on R

58 Atmospheric Results

59 The Sun We see only the outside The energy source is deep inside The energy from the core takes a very long time to get out Nuclear fusion reactions power the sun These reactions are fairly well understood It is important to test our models Only neutrinos can escape the core of the sun Experiments started in the 1960 s look for neutrinos from the sun

60 Neutrino production from Nuclear Reactions in the Sun Basic Energy Source of of the the Sun Sun 4p 4p 4 4 He He + 2e 2e ν 2ν e e

61 Solar Neutrino Experiments Homestake --Radiochemical Huge Huge tank tank of of Cleaning Fluid Fluid n n e Cl Cl e Ar Ar Mostly Mostly 8 8 B neutrinos + some some 7 7 Be Be years years at at <0.5 <0.5ev/day 1/3 1/3 SSM SSM Sage/Gallex --Radiochemical All All neutrinos n n e Ga Ga e Ge Ge 4 years years at at ~0.75 ~0.75ev ev /day /day ~2/3 ~2/3 SSM SSM Kamiokande-II and and -III -III 8 8 B neutrinos only only n n e Elastic Elastic Scattering years years at at ev ev /day /day ~1/2 ~1/2 SSM SSM

62 Solar Neutrino Spectrum

63 Summary of Results Before Super-K Four experiments measured versus predicted from solar model Experiment SSM(BP92) DATA DATA/SSM GALLEX (Ga) SAGE (Ga) Homestake (Cl) Kamioka (H 2 O)

64 The three taken together Kamiokande Result Measure of the 8 B neutrinos only SSM Homestake experiment measures 8 B & 7 Be only subtract 8 B measurement to get 7 Be SSM Galium measures all neutrinos Subtract 7 Be & 8 B to get pp flux ~0.9 SSM

65 The Solar Neutrino Problem All Experiments show a deficit wrt SSM 8 B is 1/3-1/2 SSM PP neutrinos are also low 2/3 SSM Changing the T sun won t fix it! Any change to fix 8 B will not touch PP The SSM is well constrained The data are inconsistent with a simple change in SSM Even normalizing the flux won t make the data consistent Looking at Kam III and Homestake does not leave room for 7 Be Neutrino Ocsillations can resolve the problem MSW mechanism gives consistent solutions Large Angle Non-adiabatic This implies neutrino mass! Better measurements are needed

66 BP95 FROM Langacker -Allowed regions at 95% CL from individual experiments and from the global fit. The Earth effect is included for both timeaveraged and day/night asymmetry data, full astrophysical and nuclear physics uncertainties and their correlations are accounted for, and a joint statistical analysis is carried out. The region excluded by the Kamiokande absence of the day/night effect is also indicated.

67 ν e - Electron Scattering ν e W - e - - e ν e Charged Current (electron ν s only) ν x ν x Z 0 e - e - Neutral Current (all ν flavors)

68 SuperKamiokande Solar Neutrinos Neutrino-Electron Elastic Scattering (+) (+) Points Points to to sun sun Cos(q)=(1+M e /E e /E )/(1+2 )/(1+2 M n n e e /T)1/2 /T)1/2 Dq Dq ~28 ~28 o o at at MeV MeV (-) (-) Poor Poor neutrino energy energy determination Energy 16%/(E) 1/2 1/2 at at MeV MeV Event Rate ~100x Kamiokande ~ // day day above above MeV MeV ~ // day day above above 5 MeV MeV Two Two Possible Smoking Guns Electron Energy Spectrum Day/Night Effect Effect

69 Data Taking Current data data set set of of days taken taken from from June, June, October, Data Rates Raw Raw rate rate of of ~11Hz ~11Hz -> -> 1 million million events/day Solar Solar neutrino rate rate ~ events/day Reduction Fiducial cuts cuts kton kton volume Low Low Energy Background Radon Radon Background Gammas from from radioactivity at at walls walls High High Energy background --Nuclear Spallation m m O m m + X X: X: 12 N b b ( (0.01 sec) sec) MeV B b b ( (0.02 sec) sec) MeV 8 8 B b b ( (0.77 sec) sec) MeV 8 8 Li Li b b ( (0.84 sec) sec) MeV N b b ( (7.13 sec) sec) MeV MeV :: removed by by using using DL DL (spatial correlation) and and Dt Dt (time (time correlation) between muon muon track track and and electron vertex. vertex.

70 Spallation Background Radon Background Gammas from radioactivity at at walls Nuclear Spallation m m O m m + X X: X: N b b ( (0.01 sec) sec) MeV B b b ( (0.02 sec) sec) MeV 8 8 B b b ( (0.77 sec) sec) MeV 8 8 Li Li b b ( (0.84 sec) sec) MeV N b b ( (7.13 sec) sec) MeV :: removed by by using using DL DL (spatial correlation) and anddt Dt (time (time correlation) between muon muon track track and and electron vertex vertex as as a function of of Q (muon (muonenergy deposition).

71 Energy Calibration Convert from N hit to hit ton eff eff Compensate for for light light attenuation in in water water geometric effects effects Monitor for forstabilty with withni NiSource Uniformity across across detector Stability with with time time Absolute scale set set with with LINAC calibrate electron energy energy with with Germanium Crystal Fit Fit LINAC LINAC data data for for Energy vs vs N eff eff

72 Solar Neutrinos 374 Days, 22.5 kton MeV

73 Solar Neutrino Flux s cm syst stat Flux / / 10 ) ( ) ( = + + ) ) ( ) ( ( events syst stat + + ) ( ) ( syst stat SSM Data BP + + =

74 Solar Neutrino Flux (New 708 Day Data )

75 Day-Night Results D D + N N = ± 0.020( stat) ± 0.014( syst)

76 Day Night Results

77 Energy Spectrum

78 Solar Neutrino Exclusion Plot

79 Summary of Results Atmospheric Neutrinos Evidence for neutrino oscillations Dm 2 = 6 x 10-3 ev 2 fi m >.1 ev Ω ν Ω star if masses are degenerate and in the few ev range they can comprise the bulk of the dark matter! Solar neutrino oscillations implies even greater effect since the two masses are nearly equal mass in this case also. Need W n ~.3 (with W ~.7) L Ω ν = 40 m ν ev m ν 3 4 ev

ν?? Solar & Atmospheric Oscillation Experiments Greg Sullivan University of Maryland Aspen Winter Conference January 21, 1999 )Past )Present )Future

ν?? Solar & Atmospheric Oscillation Experiments Greg Sullivan University of Maryland Aspen Winter Conference January 21, 1999 )Past )Present )Future Solar & Atmospheric Oscillation Experiments Greg Sullivan of Maryland Aspen Winter Conference January 21, 1999 ν?? e )Past z Neutrino Mass Mass & Oscillations )Present z Atmospheric neutrinos z Solar Solar