Neutrino History ... and some lessons learned

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1 2009 Neutrino Summer School Neutrino History accelerator, atmospheric, reactor and solar experiments... and some lessons learned Karsten M. Heeger University of Wisconsin

2 History of Neutrino Physics - how did we learn what we know today? - from saving energy conservation to discovering physics beyond the Standard Model Historical Lessons - how did we make the discoveries? Text Future Efforts - from discoveries to precision studies, picking the best tools at hand - where will neutrino physics go in the future? - neutrinos in particle/astrophysics?

3 A disclaimer History of neutrino physics in ~1 hr? I will be selective. Apologies to all experiments and results I cannot show. I will draw heavily on my own personal experience (SNO, KamLAND, reactor neutrinos, 0νββ )

4 History of Neutrino Physics

5 Continous Beta-Decay Spectrum 1914 Chadwick N Nʼ + e - some nuclei emit electrons! Bohr: At the present stage of atomic theory, however, we may say that we have no argument, either empirical or theoretical, for upholding the energy principle in the case of β-ray disintegrations.

6 Postulate of the Neutrino 1930 Wolfgang Pauli Pauli proposed that an undetectable particle shared the energy of beta decay with the emitted electron.

7 I have done something very bad today by proposing a particle that cannot be detected; it is something that no theorist should ever do. - Wolfgang Pauli

8 Fermiʼs Theory of Beta Decay 1933 Enrico Fermi Univ. of Chicago Experiment: Fermiʼs Theory of beta decay based on Pauliʼs Letter of Conjecture: M n c 2 = E p + E e + E ν Regrets Consistency requires that E ν is not observable! M n c 2 E p + E e Fermiʼs theory still stands (parity violation added in the 50s).

9 Fermiʼs Idea for Measuring m ν

10 Weak Interactions in the Standard Model The weak gauge bosons W ± act on left-handed doublets (charged-current interaction) β-decay Since m w =80.4 GeV >> m p decay is governed by Fermi coupling G F Fermi coupling G F g 2 = W gauge coupling 2 = g 2 2 8m W 2 Weinberg angle e g 2 = sinθ W = 0.48

11 Crossing Symmetry

12 First Proposal For Direct Detection of Neutrino

13 First Antineutrino Detector Reines and Cowan 1956 ν ν µ ν e + p e + + n

14 Enrico Fermi and the Neutrino Enrico Fermi proposes "neutrino" as the name for Pauli's postulated particle. He formulates a quantitative theory of weak particle interactions in which the neutrino plays an integral part.

15 Reines-Cowan Announcement 1956

16 Observation of the Free Antineutrino 1959 The Savannah River Detector - A new design Second version of Reinesʼ experiment worked! positron annihilation inverse beta decay ν e + p e + + n n capture

17 Reines-Cowan Experiment coincidence event signature event signal electric noise cosmic ray cosmic ray cosmic ray

is not conserved ν e could change into ν µ.

18 Early Neutrino Oscillation Searches New neutrino physics such as oscillations? In 1960 s Pontecorvo contemplates ν - ν oscillation and suggests that if lepton number is not conserved ν e could change into ν µ. Early Reactor ν Experiments Goesgen (3 baselines, 1 detector) Gösgen (baseline 1) (baseline 2) (baseline 3) Phys Rev D 34, 2621 (1986)

Neutrino Oscillation Search with Reactor

19 Neutrino Oscillation Search with Reactor Antineutrinos Oscillation Searches at Chooz + Palo Verde: ν e ν x ν e ν e ν e νe νe ν e ν e + p e + + n Distance: 1km ~3000 events in 335 days 2.7% uncertainty Absolute measurement with 1 detector detector size: several tons

20 Discovery of Muon Neutrino 1962 Lederman, Schwartz, Steinberger spark chamber with Al plates 20 m µ produce nice tracks as they go through the chamber (29 events) e produce showers as they cross Al (0 events) 10 4 ν µ and ν µ

21 Number of Active Neutrinos Precision studies of Z-line shape, determine number of active light neutrinos Each separate (ν ) l i L adds to total Z-width. From LEP, one finds: N ν = ±0.008 which argues strongly for only having 3 generations Before ν τ was detected directly! Big bang nucleosynthesis gives a constraint on the effective number of light neutrinos at T~ 1 MeV: 1.2 < N ν eff < 3.3 [99% CL]

22 Search for tau Neutrino Discovery of τ lepton at SLAC (Martin Pearl, 1975) there should be a corresponding neutrino. In 1989, indirect evidence for the existence of ν τ in measurement of Z-width no one had directly observed the tau neutrino. The tau neutrino interact and form a tau that has an 18% probability of decaying to - a muon and two neutrinos (long event) - an electron and two neutrinos (short event) 86% of all tau decays involve only 1 charged particle (a kink) which is the particle physicists are looking for in DONUT experiment

Discovery of tau Neutrino 2000 An 800 GeV beam of protons from the TeVatron collides with a block of tungsten Experimental Challenges: - Very short lifetime of the τ.

23 Discovery of tau Neutrino 2000 An 800 GeV beam of protons from the TeVatron collides with a block of tungsten Experimental Challenges: - Very short lifetime of the τ. - ν τ is extremely non-interacting (detector must have a very fine resolution). Detecting a τ Neutrino τ decay D s decay into τ and ν τ neutrino D s ν τ + τ τ ν τ + X 6,000,000 candidate events on tape 4 clean tau events

24 A ν τ interacted with a nucleon in a steel layer, producing a τ. Long tau decay because it decays to one charged particle, the electron, and the decay vertex occurs several sheets downstream from the neutrino interaction vertex.

25 Neutral Current Discovery (1973) Gargamelle bubble chamber at CERN showing how an invisible neutrino has jogged an electron Major triumph for the Standard Model

Standard Model Neutrino Physics 1914 Electron Spectrum in β decay is continuous 1930 Pauli postulates that a new particle is emitted 1933 Fermi names the new particle neutrino and introduces

26 Standard Model Neutrino Physics 1914 Electron Spectrum in β decay is continuous 1930 Pauli postulates that a new particle is emitted 1933 Fermi names the new particle neutrino and introduces four-fermion interaction 1956 Reines and Cowan discover the neutrino 1962 At least two neutrinos: ν e ν µ 1973Discovery of neutral currents at CERN 1983 Discovery of the W and Z 1989 Measurement of Z width at CERN N ν = tau neutrino discovered.

27 Neutrinos in the Standard Model Discovery of ν µ and ν τ Accelerator studies of ν The Standard Model 3ν flavors upper limits on m ν from kinematic studies. massless ν (ad hoc assumption in Standard Model)

28 Particle Properties of the Neutrino Interactions weak (and gravitational) only Flavors Charge 3 active flavors Spin s=1/2 Type Dirac ν ν Majorana ν = ν? Mass m νe < 2 ev from tritium β decay m νµ < 170 kev from π decay m ντ < 18 MeV from τ decay

Birth of Neutrino Astrophysics 1938 Bethe & Critchfield p + p 2 H + e + + ν e 1947 Pontecorvo,1949 Alvarez propose neutrino detection through 37Cl + ν e 37 Ar + e - Light Element Fusion Reactions p +

29 Birth of Neutrino Astrophysics 1938 Bethe & Critchfield p + p 2 H + e + + ν e 1947 Pontecorvo,1949 Alvarez propose neutrino detection through 37Cl + ν e 37 Ar + e - Light Element Fusion Reactions p + p 2 H + e + + ν e p + e - + p 2 H + ν e 99.75% 0.25% 2H + p 3 He + γ 85% ~15% ~10-5 % 3He + 3 He 4 He + 2p 3He + p 4 He + e + +ν e 3He + 4 He 7 Be + γ 1960ʼs Ray Davis builds chlorine detector. John Bahcall, generates first solar model calculations and ν flux predictions % 7Be + e - 7 Li + γ +ν e 7Li + p α + α 0.02% 7Be + p 8 B + γ 8B 8 Be* + e + + ν e to see into the interior of a star and thus verify directly the hypothesis of nuclear energy generation in stars... (Bahcall, 1964)

30 Cl-Ar Solar Neutrino Experiment at Homestake ν e + 37 Cl 37 Ar + e SSM Davisʼ experiment only sensitive to ν e

31 What is the Solution? Experimental Errors? But all experiments show similar effect. Astrophysics wrong? Perhaps, but even with all fluxes as free parameters, cannot reproduce the data. P MSM < 1.7% at 95% CL KMH, Robertson PRL 77:3270 (1996) New neutrino physics such as oscillations? In 1968 Pontecorvo suggests that if lepton number is not conserved, ν e could change into ν µ. Since the Cl-Ar detector was sensitive only to ν e, it would appear that the flux was low.

32 The Sudbury Neutrino Observatory

33 The Solar Neutrino Problem and Its Resolution Too few ν e observed from the Sun. ν e ν e ν e ν e Even with all solar neutrino fluxes as free parameters, cannot reproduce the data. P MSM < 1.7% at 95% CL KMH, Robertson PRL 77:3270 (1996) Neutral Current (NC) Elastic Scattering (ES) Charged Current (CC) CC Neutral-Current shape Elastic Scattering Results from Charged-Current SNO, 2002 constrained Neutrino Signal (SSM/BP00) SSM 5.3 σ 0.0 CC shape unconstrained ν e + ν µ +ν τ ν e (ν µ +ν τ ) 2/3 of initial Total solar Neutrino ν e are observed flux Electron at SNO Neutrino to be ν flux µ,τ Model-independent evidence for solar neutrino flavor change ν e

34 Neutrino Oscillation Neutrino States First Mass States Mass states Second First Weak States Weak states Second First Second First Second ν 1 ν 2 ν e ν µ Time Evolution ν 2 ν µ sinθ cosθ ν ν e e ν a = cos θ ν 1 sin θ ν 2 ν e ν b = sin θ ν 1 θ + cos θ ν 2 θ ν 1 Pure ν µ µ cosθ sinθ ν ( = ) =( )( ν 1 1 ν ) cosθ 2 ν e cosθ sinθ ν µ 2sinθ cosθ ν µ 2sinθ ν 2 Pure ν µ µ Pure ν µ ν 2 2 ν 1 Pontecorvo, Time, t Time, t L P i i = sin 2 2θ sin Δm 2 E oscillation energy and baseline- dependent effect

35 Borexino 2009 vacuum-matter transition in solar neutrino oscillation

36 Reactor Antineutrinos in Japan Japanese Reactors Reactor Antineutrinos Kashiwazaki Takahama Ohi 235 U: 238 U: 239 Pu: 241 Pu = 0.570: 0.078: : reactors ~ 200 MeV per fission ~ 6 ν e per fission Japan Kamioka ~ 2 x ν e /GW th -sec reactor ν flux ~ 6 x 10 6 /cm 2 /sec

37 KamLAND Antineutrino Detector ν e + p e + + n n light from the e gives a measu E p + E n MeV, E νe through inverse β-decay liquid scintillator target: - proton rich > protons - good light yield

KamLAND 2003: First Direct Evidence for Reactor ν e Disappearance Reactor Neutrino Physics 1956-2003 PRL 90:021802 (2003) Observed ν e 54 events No-Oscillation 86.8 ± 5.

38 KamLAND 2003: First Direct Evidence for Reactor ν e Disappearance Reactor Neutrino Physics PRL 90: (2003) Observed ν e 54 events No-Oscillation 86.8 ± 5.6 events Background 1 ± 1 events Livetime: ton-yr reactor antineutrino experiment suggested by solar neutrino experiments Japan Thermal Power Flux (µw/cm 2 ) mean, flux-weighted reactor Many distance reactors, ~ 180kmfar away Distance (km) Survival Evis >2.6 MeV

39 KamLAND 2008: Precision Measurement of Oscillation Prompt event energy spectrum for νe number of events expected: 2179 ± 89 (syst) observed: 1609 bkgd: 276 ± 23.5 Spectral Distortions: A unique signature of neutrino oscillation! significance of distortion: > 5σ best-fit χ 2 /ndf=21/16 (18% C.L.) significance of disappearance (with 2.6 MeV threshold): 8.5σ no-osc χ 2 /ndf=63.9/17

40 KamLAND 2008: Precision Measurement of Oscillation L/E Dependence Survival Probability Data - BG - Geo & e Expectation based on osci. parameters determined by KamLAND L0=180km L 0 /E &e (km/mev) Solar neutrino problem solved! L/E figure demonstrates ν oscillation first identified by Ray Davis (missing solar νe) SNO observes neutrino flavor change, finds evidence for neutrino mass KamLAND demonstrates ν oscillation, precision measurement of Δm 2

Neutrino Physics at Reactors Next - Discovery and precision measurement of θ 13 Daya Bay Double Chooz Reno 2008 - Precision measurement of Δm12 2.

Reines at UC Irvine KamLAND 1980s & 1990s - Reactor neutrino flux measurements in U.S.

41 Neutrino Physics at Reactors Next - Discovery and precision measurement of θ 13 Daya Bay Double Chooz Reno Precision measurement of Δm12 2. Evidence for oscillation Evidence for spectral distortion First observation of reactor antineutrino disappearance Nobel Prize to Fred Reines at UC Irvine KamLAND 1980s & 1990s - Reactor neutrino flux measurements in U.S. and Europe First observation of (anti)neutrinos Chooz Chooz Past Reactor Experiments Hanford Savannah River ILL, France Bugey, France Rovno, Russia Goesgen, Switzerland Krasnoyark, Russia Palo Verde Chooz, France Savannah River

42 Atmospheric Neutrino Studies

43 Super-Kamiokande Atmospheric Neutrino Studies

44 Atmospheric Neutrino Flavor Change 1998 Super-K evidence for νμ disappearance: zenith-angle dependence Δm 2 = 2.5x10-3 ev 2 0 at least 1 mν 0 Mixing angle is quite large (θ ~ 45 )

45 Precision Science with Accelerator ν Minos

46 Precision Science with Accelerator ν

A Decade of Discovery: 1998-2008 Atmospheric

47 A Decade of Discovery: Atmospheric (Super-K) Accelerator (K2K) Solar (SNO) Reactor (KamLAND) Super-K: atmospheric νμ neutrino oscillation ν e ν µ,τ ν µ ν τ K2K: accelerator νμ oscillation SNO: solar νe flavor transformation KamLAND: reactor νe disappearance and oscillation

48 Experimental Indications for Neutrino Oscillations LSND Experiment L = 30m E = ~40 MeV Atmospheric Neutrinos L = 15-15,000 km E = MeV Solar Neutrinos L = 10 8 km E = 0.3 to 3 MeV Δm 2 = ~ ev 2 Prob OSC = ~100% Δm 2 = 0.3 to 3 ev 2 Prob OSC = 0.3 % Δm 2 = ~ ev 2 Prob OSC = ~100%

49 LSND Experiment Oscillations? LSND took data from ,000 Coulombs of protons - L = 30m and 20 < E ν < 53 MeV Saw an excess of: 87.9 ± 22.4 ± 6.0 events. With an oscillation probability of (0.264 ± ± 0.045)%. 3.8 σ evidence for oscillation.

50 Other oscillations? Sterile Neutrinos? ν µ ν e? ν µ ν τ LSND Cannot be explained by 3 active neutrinos! ν e ν µ,τ

51 MiniBoone - 1 GeV neutrinos (Booster) ton oil Cerenkov - operating since νµ > νe appearance null hypothesis: 93% CL νµ > νe appearance only analysis is a limit on oscillation

52 Historical Lessons - how did we make the discoveries? #1 persistence #2 data anomalies, the unforeseen #3 theorists arenʼt (always) right #4 unique, model-independent measurements #5 big steps vs incremental improvements #6 and a little bit of luck... in detecting a supernova

53 #1 persistence SSM Davisʼ experiment only sensitive to ν e

54 #2 anomalies Solar Neutrino Problem Atmospheric Neutrino Anomaly Low-Energy Excess in MiniBoone?

55 #3 theorists arenʼt (always) right... quark mixing pre 2002 neutrino mixing

56 #3 theorists arenʼt (always) right... Oscillation mixing angles must be small like the quark mixing angles Wrong Atmospheric neutrino anomaly must be other physics or experimental problem because it needs such a large mixing angle Natural scale for Δm 2 ~ ev 2 since needed to explain dark matter Wrong Wrong LSND result doesnʼt fit in so must not be an oscillation signal???

eliminate model-dependent assumptions and interpretation physics result

57 #4 unique, model-independent measurements a pure ν e source a ν x detector Charged-Current (CC) ν e +d e - +p+p Neutral-Current (NC) ν x +d ν x +n+p eliminate model-dependent assumptions and interpretation physics result independent of Monte Carlo any result from SNO would have been interesting: win-win situation!

58 #5 taking big steps baseline: 1 km 180 km size: 5 ton 1000 ton Survival Probability Data - BG - Geo & e Expectation based on osci. parameters determined by KamLAND L 0 /E &e (km/mev)

59 #6 and a little bit of luck...in detecting a SN Supernova 1987A Nobel Prize for the Detection of Cosmic Neutrinos Kamiokande was ready to seize the opportunity

60 Future Efforts - from discoveries to precision studies, picking the best tools at hand - what are the future directions of neutrino physics? - neutrinos in particle/astrophysics

61 1! What we know... Neutrino Mass Splitting KamLAND 2008 ) 2 (ev KamLAND 95% C.L. 99% C.L % C.L. best fit $m 2 21 Solar 95% C.L. 99% C.L % C.L. best fit tan 2 " 12 normal inverted KamLAND provides most precise value of Δm12 2 (~2.8%)

62 What we know... Neutrino Mixing Angles ) 2 2 Δm 2 " m (ev! SNO solar Δm 2 SK atmospheric U e1 U e2 U e U e 3 U = U µ1 U µ2 U µ 3 = U τ1 U τ 2 U τ % CL 95% CL 99.73% CL U MNSP Matrix Maki, Nakagawa, Sakata, Pontecorvo ! tan 2 θ cosθ 13 0 e iδ CP sinθ 13 cosθ 12 sinθ = 0 cosθ 23 sinθ sinθ 12 cosθ sinθ 23 cosθ 23 e iδ CP sinθ 13 0 cosθ 0 e iα / 2 0 iα / 2+iβ e atmospheric, K2K reactor and accelerator SNO, solar SK, KamLAND 0νββ θ 23 = ~ 45 θ 13 =? maximal? θ 12 ~ 32 large, but not maximal!

Open Questions P(ν µ ν e ) P(ν µ ν e ) = 16s 12 c 12 s 13 c 2 13 s 23 c 23 sinδ sin Δm 2 12 4E L sin Δm 2 13 4E L sin Δm 2 23 4E L?

63 Open Questions P(ν µ ν e ) P(ν µ ν e ) = 16s 12 c 12 s 13 c 2 13 s 23 c 23 sinδ sin Δm E L sin Δm E L sin Δm E L? Questions Is there µ τ symmetry in neutrino mixing? Is there leptonic CPV? What is mass hierarchy? Do neutrinos have Majorana mass? What is the absolute mass scale? What is the role of neutrinos in the Universe?

64 Open Questions The Tools reactor & accelerator experiments search for 0νββ β-decay experiments astrophysics & cosmology Questions Is there µ τ symmetry in neutrino mixing? Is there leptonic CPV? What is mass hierarchy? Do neutrinos have Majorana mass? What is the absolute mass scale? What is the role of neutrinos in the Universe?

5 proton per cm 3 Supernova Neutrinos Atmospheric

65 Neutrino Sources Neutrinos from the Big Bang ~330 neutrinos per cm proton per cm 3 Supernova Neutrinos Atmospheric Neutrinos High Energy Cosmic Neutrinos Geo Neutrinos Accelerator&Reactor Neutrinos Solar Neutrinos

66 Neutrino Energies Big-Bang neutrinos ~ ev Neutrinos from the Sun < 20 MeV depending of their origin. Antineutrinos from nuclear reactors < 10.0 MeV Atmospheric neutrinos ~ GeV Neutrinos from accelerators up to GeV (10 9 ev)

67 A World of Neutrino Detectors

68 Reactor and Accelerator Experiments reactor (ν e disappearance) P ee 1 sin 2 2θ 13 sin 2 Δm 31 2 L 4E ν Δm cos 4 θ 13 sin 2 2θ 12 sin E ν 2 L - Clean measurement of θ 13 - No matter effects accelerator (ν e appearance) mass hierarchy CP violation matter - sin 2 2θ 13 is missing key parameter for any measurement of δ CP

Precision Measurement of Mixing with Reactor ν Search for θ 13 in new oscillation experiment with multiple detectors Δm 2 P ee 1 sin 2 2θ 13 sin 2 31 L Δm cos 4 θ 13 sin 2 2θ 12 sin 2 21 4E ν 4E ν 2

69 Precision Measurement of Mixing with Reactor ν Search for θ 13 in new oscillation experiment with multiple detectors Δm 2 P ee 1 sin 2 2θ 13 sin 2 31 L Δm cos 4 θ 13 sin 2 2θ 12 sin E ν 4E ν 2 L Small-amplitude oscillation due to θ 13 integrated over E 1.1 Large-amplitude oscillation due to θ θ 13 ~1-1.8 km > 0.1 km νe N osc /N no_osc Δm 2 13 Δm 2 23 detector 1 detector Baseline (km)

70 Reactor and Accelerator Experiments reactor (ν e disappearance) P ee 1 sin 2 2θ 13 sin 2 Δm 31 2 L 4E ν Δm cos 4 θ 13 sin 2 2θ 12 sin E ν 2 L - Clean measurement of θ 13 - No matter effects accelerator (ν e appearance) mass hierarchy CP violation matter - sin 2 2θ 13 is missing key parameter for any measurement of δ CP

71 Accelerator Experiments (NOvA, T2K etc) Long Baseline Accelerator Experiments - νe appearance - long baselines, off-axis - matter effects

Future Neutrino Oscillation Experiments Large

- astrophysics - atm ν, geo ν R&D in US,

72 Future Neutrino Oscillation Experiments Large Detectors and Long Baselines - search for CP violation with neutrino beam - ν mass hierachy - proton decay (10 34 yrs yrs) - astrophysics - atm ν, geo ν R&D in US, Europe, and Japan Ultimate oscillation experiment by 2020?

Mass: 50 kton Size : 48 m (x) 16m (y) 12 m

73 India Neutrino Observatory (INO) A Next-Generation Atmospheric Neutrino Experiment magnetized iron calorimeter Magnetic field ~ 1 Tesla along y-direction Mass: 50 kton Size : 48 m (x) 16m (y) 12 m (z) 140 layers of 6 cm thick iron with 2.5 cm gap for active elements

2ν mode: conventional 2 nd order process in nuclear physics 0ν mode: hypothetical

74 Search for 0νββ The Next Frontier in Neutrino Physics search for 0νββ is the only feasible method we know to establish the Majorana nature of neutrinos! 2ν mode: conventional 2 nd order process in nuclear physics 0ν mode: hypothetical process only if M ν 0 AND ν = ν Γ 2ν = G 2ν M 2ν 2 Γ 0ν = G 0ν M 0ν 2 m ββ 2 G are phase space factors G 0ν ~ Q5

75 Neutrinos in the Universe neutrinos are the most abundant particles in the Universe besides photons

76 Neutrinos and the Universe very early universe big bang nucleosynthesis CMB late time structure formation WMAP large-scale structure matter-antimatter ratio CMB large-scale structure

Future Cosmological Constraints on Σm ν Cosmology probes important

of state Partial degeneracy between m ν, ω (neutrino mass states and

measurements Ref: astr-ph/0603019 Planck + LSST-like lensing survey

77 Future Cosmological Constraints on Σm ν Cosmology probes important aspects of particle physics: - Neutrino mass - Dark energy equation of state Partial degeneracy between m ν, ω (neutrino mass states and dark energy equation) cross-correlate CMB and LSS, weak lensing, BAO measurements Ref: astr-ph/ Planck + LSST-like lensing survey survey σ(σm ν ) 0.05 ev probes difference between normal and inverted hierarchy

78 Neutrinos and Supernovae SN 1987A without neutrinos dying stars would not explode no oscillations oscillations in SN envelope Earth effects included Ref: G. Raffelt

79 Neutrinos and Supernovae neutrino oscillation effects on supernova light-element synthesis c neutrinos helped cook the light elements in the Universe Astrophys.J.649: ,2006

80 Interdependencies/Redundancies of Experiments Need all types of experiments & observations absolute mass scale Majorana Nature Hierarchy θ13 δcp αʼs β-decay 0νββ -decay reactor accelerator atmospheric ( ) astrophysics /cosmology ( ) ( )

81 Some Concluding Thoughts - Last 10 years have been the decade of discovery in neutrino physics. Neutrino physics has demonstrated physics beyond the Standard Model. - Neutrino physics is transitioning from a discovery to a precision science. Reactor and accelerator experiments will play a critical role in precision studies (solar and atmospheric may help). - A rich program of neutrino experiments is underway to understand neutrino properties. - Neutrinos are important in many astrophysical processes, and astrophysics/cosmology may help us understand the particle nature of neutrinos

Recent Discoveries in Neutrino Physics

Recent Discoveries in Neutrino Physics Experiments with Reactor Antineutrinos Karsten Heeger http://neutrino.physics.wisc.edu/ Karsten Heeger, Univ. of Wisconsin NUSS, July 13, 2009 Standard Model and