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Discovery of neutrino oscillations

Discovery of neutrino oscillations. Solar neutrinos Atmospheric neutrinos. Solar neutrinos other place where  are missing. Solar neutrinos (another mystery of missing neutrinos). „From neutrinos to cosmic sources”, D. Kiełczewska and E. Rondio. Standard Solar Model.

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Discovery of neutrino oscillations

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  1. Discovery of neutrino oscillations • Solar neutrinos • Atmospheric neutrinos Fizyka cząstek II D. Kiełczewska wykład 4

  2. Solar neutrinos other place where are missing Solar neutrinos (another mystery of missing neutrinos) Fizyka cząstek II D. Kiełczewska wykład 4 „From neutrinos to cosmic sources”, D. Kiełczewska and E. Rondio

  3. Standard Solar Model Data are compared with expectations from „SSM” - Standard Solar Model: The model contains also needed cross sections for neutrino interactions with nuclei. Thus eventually its predictions are given in SNUs: 1 SNU (Solar Neutrino Unit) = 10-36nteractions/atom/sec Processes producing neutrinos as a function of distance from the Sun center: Fizyka cząstek II D. Kiełczewska wykład 4

  4. Solar Neutrino Spectrumthresholds for different thechniques • radiochemical • (Gallium & Chlorine): • low threshold • only event rates counted • no time information • no direction • Cherenkov detectors: • time and direction • higher threshold Fizyka cząstek II D. Kiełczewska wykład 4

  5. Radiochemical experiments First one ever used to detect solar neutrinos - Davis-Pontecorvo reaction: or • Produced isotopes are radioactive with not too long lifetime – they are periodically extracted and counted • No information on time of interactions or neutrino directions Fizyka cząstek II D. Kiełczewska wykład 4

  6. Davis experiment at Homestake 615 tons of C2Cl4 run from 1968 for about 30 years Nobel prize for Ray Davis in 2002 • 37Ar has half-life time for electron capture of 35 days • Argon atoms have to be extracted and counted - about 1 atom per 2 days Fizyka cząstek II D. Kiełczewska wykład 4

  7. Homestake Results: Rate and flux from single extractions Rate = 0.48 ± 0.16(stat) ± 0.03(syst) argon atoms/day Flux = 2.56 ± 0.16 ± 0.16 SNU Only: of SSM Fizyka cząstek II D. Kiełczewska wykład 4

  8. Gallex/GNO and Sage two detectors using reaction Threshold at 233 keV, dominant way to study p-p neutrinos SAGE in Caucasus, experiment started with 30tons of Gallium next upgraded to 57 tons Gallium kept in liquid form (melting point 29.8 oC) Extraction – destillation Callibrated on added 700 μg of natural Ge (efficiency 80%) Fizyka cząstek II D. Kiełczewska wykład 4

  9. Gallex and GNO • Counts as a function of time • Additional test with isotope life time • Background estimate • Calibration of the method with introduction of known number of atoms and counting them • From this measurement – estimate of efficiency of the method Fizyka cząstek II D. Kiełczewska wykład 4

  10. Results after extraction Measured: number of neutrino interactions, From it derived: flux of neutrinos from the Sun reaching the Earth Expected rate from SSM is: SAGE 45% of neutrinos are missing? Fizyka cząstek II D. Kiełczewska wykład 4

  11. WaterCherenkov detectors BOREXINO, KAMLAND(2): Liquid Scintillator n • Super-Kamiokande - light water target • SNO - heavy water target • directionality • time of every event Fizyka cząstek II D. Kiełczewska wykład 4

  12. Super-Kamiokande: Solar peak > 5 MeV signal For E<20 MeV and background we have only: and we know that electron moves forward! Fizyka cząstek II D. Kiełczewska wykład 4

  13. Neutrinogram of Sun in Super-Kamiokande The electrons of low energy undergo many multiple Coulomb scatterings Low spacial resolution of the neutrinogram the actual size of the Sun – ½ pixel Fizyka cząstek II D. Kiełczewska wykład 4

  14. Solar neutrino flux measured in Super-K in 1496 days Observed: Expected: 22,400 events 48,200 events from SSM (Standard Solar Model): a) rate of different fusion processes b) neutrino cross sections Hence one obtains: ( in the whole energy range) A half of neutrinos are missing? Fizyka cząstek II D. Kiełczewska wykład 4

  15. Distribution of electron energy in Super-K No modulation of the spectrum is observed just the neutrino deficit. Fizyka cząstek II D. Kiełczewska wykład 4

  16. Seasonal variation of the signal Eccentricity of the Earth orbit measured with the data at SK (lines represent true parameters): 68% 95% Jan.... Jun.. ..Dec 99.7% with a cut on electron energy>6.5 MeV to avoid radon bkg seasonal fluctuations Fizyka cząstek II D. Kiełczewska wykład 4

  17. Clues to the mystery of missing solar neutrinos • Deficits are observed in all the experiments • The fusion reactions in the Sun produce only • Only electron neutrinos can be measured by radiochemical experiments • Super-K measures only because It can happen to all neutrino flavors but cross section is 7 times larger for • But SNO measures much more: Fizyka cząstek II D. Kiełczewska wykład 4

  18. Fizyka cząstek II D. Kiełczewska wykład 4

  19. Results from D2O SNO Fizyka cząstek II D. Kiełczewska wykład 4

  20. Detection of neutrons from: With salt Fizyka cząstek II D. Kiełczewska wykład 4

  21. Results from D2O Fizyka cząstek II D. Kiełczewska wykład 4

  22. SNO Results Energy distribution was not used for the separation of processes Fizyka cząstek II D. Kiełczewska wykład 4

  23. SNO fluxes From event rates to neutrino fluxes: 84 external-source neutrons • Results with salt consistent with those from pure heavy water • Fluxes deduced from different reactions are inconsistent • Only the NC flux agrees with expectations from SSM (Standard Solar Model) Fizyka cząstek II D. Kiełczewska wykład 4

  24. Determination of neutrino fluxesfrom SNO measurements Number of interactions of a neutrino of flavor x: cross section mass x time-of-exposure flux Assuming the spectrum of 8B neutrinos: and knowing cross sections one can find: Fizyka cząstek II D. Kiełczewska wykład 4

  25. SNO Results phase 1+2 to compare with: Fizyka cząstek II D. Kiełczewska wykład 4 Hime, Nu06

  26. SNO – final phase Fizyka cząstek II D. Kiełczewska wykład 4

  27. Neutron counters in SNO Counters 2-3 m long. 36 strings on 1x1 m grid Fizyka cząstek II D. Kiełczewska wykład 4

  28. Results of all the solar experiments Fizyka cząstek II D. Kiełczewska wykład 4

  29. Solar neutrino experiments Name Location Mass Reaction Start Fizyka cząstek II D. Kiełczewska wykład 4

  30. Odkrycie oscylacji neutrin atmosferycznych w Super-Kamiokande Fizyka cząstek II D. Kiełczewska wykład 4

  31. Atmospheric Neutrinos • Weak decays are sources of • neutrinos: • π, K mesons decay on the way to Earth • some muons also decay but many reach the surface (mμ=106 MeV; cτ=659 m) Fizyka cząstek II D. Kiełczewska wykład 4

  32. Atmosph Fizyka cząstek II D. Kiełczewska wykład 4

  33. Neutrino events in Super-K All have to be separated from „cosmic” muons (3Hz) Contained events: Fully contained FC Partially contained PC Upward through-going muons μ Upward stopping μ all assumed to be μ e/μidentification interactions in rocks below the detector • different energy scale • different analysis technique • different systematics Fizyka cząstek II D. Kiełczewska wykład 4

  34. Neutrino energy spectra Fully contained FC Partially contained PC μ e/μidentification all assumed to be μ Upμ thru Upμ stop Fizyka cząstek II D. Kiełczewska wykład 4 Interactions in rocks

  35. Particle Identification Hit times are corrected for Cherenkov photon time of flight. e-like: mostly electrons gammas mostly μ-like: muons charged pions protons Fizyka cząstek II D. Kiełczewska wykład 4

  36. Super-K: particle identification points: DATA histogram: MC simulation the variable „PID” describes how diffuse a ring is Fizyka cząstek II D. Kiełczewska wykład 4

  37. Monte Carlo simulations The purpose of Monte Carlo simulations is to prepare sample of events which resemble real data events as much as possible. MC code considers: • Fluxes of ν as functions of energies and angles • Interactions of ν depending on their flavor and energy • Momenta and types of the particles produced by ν • Secondary interactions in nuclei (e.g. 16O ) • Interactions of particles passing through e.g water • Simulation of the detector e.g. • radiation of Cherenkov photons • photon absorption, scattering, reflections • probability to produce photoelectrons • Reconstruction of simulated events using the same software as for real data Monte Carlo samples Fizyka cząstek II D. Kiełczewska wykład 4

  38. Super-Kamiokande results (contained) Sub-GeV(Fully Contained) Multi-GeV Evis < 1.33 GeV, Pe > 100 MeV, Pμ > 200 MeV Fully Contained (Evis > 1.33 GeV) Data MC 1ring e-like 772 707.8 μ-like 664 968.2 Data MC 1-ring e-like 32663081.0 μ-like 3181 4703.9 Partially Contained (assigned as μ-like) 913 1230.0 We take ratios to cancel out errors on absolute neutrino fluxes: Too few muon neutrinos observed! Fizyka cząstek II D. Kiełczewska wykład 4

  39. Super-K I results - upward going muons Up through-going μ, (1678days) Data: 1.7 +- 0.04 +- 0.02 (x10-13cm-2s-1sr-1) MC: 1.97+-0.44 Up stopping μ, (1657days) Data: 0.41+-0.02+-0.02(x10-13cm-2s-1sr-1) MC:0.73+-0.16 Again one observes a muon deficit Fizyka cząstek II D. Kiełczewska wykład 4

  40. Double ratios in various experiments most experiments observed muon deficits Fizyka cząstek II D. Kiełczewska wykład 4

  41. Atmosph Fizyka cząstek II D. Kiełczewska wykład 4

  42. Zenith angle distributions e-like 1 ring μ-like 1 ring μ-like multi- ring upward goingμ Sub-GeV Multi-GeV Red: MC expectations Black points: Data Green: next lectures Missing are the muon neutrinos passing through the Earth! up down Fizyka cząstek II D. Kiełczewska wykład 4

  43. Interpretation of the zenith angle distributions Let’stry to findinterpretation of the deficit Of νμafterpassing the Earth ...... Lookslikeνμdisappearance... What happens to muon neutrinos? Let’s suppose an oscillation: but what is We seethatνeangulardistributionis as expected

  44. Oscillations of muon neutrinos Lookslikeνμoscillates:.. Remember that we identify neutrinos by the corresponding charged lepton which they produce: But lookat the masses: μ106 MeV τ1777 MeV Does neutrino haveenough energy to produceτ?

  45. ντcross sections Total CC cross sections for: compared with νμ

  46. Atmospheric neutrino experiments The largest statistics of atmospheric neutrino events were collected in Super-Kamiokande. The results showed: a deficit of muon neutrinos passing long distances through the Earth. first evidence of neutrino oscillatons Atmospheric neutrinos were also measured in MACRO and SOUDAN detectors. The results were consistent with neutrino oscillations. Fizyka cząstek II D. Kiełczewska wykład 4

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