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

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Prezentacja na temat: "Fizyka cząstek II D. Kiełczewska wykład 4 Discovery of neutrino oscillations  Solar neutrinos  Atmospheric neutrinos."— Zapis prezentacji:

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2 Fizyka cząstek II D. Kiełczewska wykład 4 Discovery of neutrino oscillations  Solar neutrinos  Atmospheric neutrinos

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

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

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

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

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

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

9 Fizyka cząstek II D. Kiełczewska wykład 4 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 30 tons of Gallium next upgraded to 57 tons Gallium kept in liquid form (melting point 29.8 o C) Extraction – destillation Callibrated on added 700  g of natural Ge (efficiency 80%)

10 Fizyka cząstek II D. Kiełczewska wykład 4 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

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

12 Fizyka cząstek II D. Kiełczewska wykład 4 Water Cherenkov detectors BOREXINO, KAMLAND(2): Liquid Scintillator  Super-Kamiokande - light water target  SNO - heavy water target  directionality  time of every event

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

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

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

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

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

18 Fizyka cząstek II D. Kiełczewska wykład 4 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:

19 Fizyka cząstek II D. Kiełczewska wykład 4

20 Results from D2O SNO

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

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

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

24 Fizyka cząstek II D. Kiełczewska wykład 4 SNO fluxes 84 external-source neutrons From event rates to neutrino fluxes:  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)

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

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

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

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

29 Results of all the solar experiments

30 Fizyka cząstek II D. Kiełczewska wykład 4 Solar neutrino experiments HomestakeS.Dakota USA Cl( ν e,e - ) 37 Ar1968 stopped SAGE Galex/GNO Baksan, Russia Gran Sasso, Italy Ga ( ν e,e - ) 71 Ge 1990 stopped 1992 stopped KamiokandeKamioka, Japan 2000 νxe- → νxe-νxe- → νxe stopped Super Kamiokande Kamioka, Japan50000 νxe- → νxe-νxe- → νxe SNOSudbury, Canada 8000 ν e d → e - pp ν x d → ν x np ν x e - → ν x e stopped 2001 stopped 1999 stopped BorexinoGran Sasso, Italy 300 νxe- → νxe-νxe- → νxe soon KamLandKamioka, Japan 1000reactor antineutrinos 2001 Name Location Mass Reaction Start

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

32 Fizyka cząstek II D. Kiełczewska wykład 4 Atmospheric Neutrinos Weak decays are sources of neutrinos:  , K mesons decay on the way to Earth  some muons also decay but many reach the surface (m μ =106 MeV; c τ =659 m)

33 Fizyka cząstek II D. Kiełczewska wykład 4 Atmosph

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

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

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

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

38 Fizyka cząstek II D. Kiełczewska wykład 4 Fluxes of  as functions of energies and angles Interactions of  depending on their flavor and energy Momenta and types of the particles produced by  Secondary interactions in nuclei (e.g. 16 O ) 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 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: Monte Carlo samples

39 Fizyka cząstek II D. Kiełczewska wykład 4 Data MC 1ring e-like  -like Sub-GeV (Fully Contained) E vis < 1.33 GeV, P e > 100 MeV, P μ > 200 MeV Data MC 1-ring e-like  -like Multi-GeV Fully Contained (E vis > 1.33 GeV ) Partially Contained (assigned as  -like) Super-Kamiokande results (contained) We take ratios to cancel out errors on absolute neutrino fluxes: Too few muon neutrinos observed!

40 Fizyka cząstek II D. Kiełczewska wykład 4 Super-K I results - upward going muons Up through-going μ, (1678days ) Data: (x cm -2 s -1 sr -1 ) MC: Up stopping μ, (1657days ) Data: (x cm -2 s -1 sr -1 ) MC: Again one observes a muon deficit

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

42 Fizyka cząstek II D. Kiełczewska wykład 4 Atmosph

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

44 Interpretation of the zenith angle distributions Let’s try to find interpretation of the deficit Of ν μ after passing the Earth Looks like   disappearance... What happens to muon neutrinos? Let’s suppose an oscillation : We see that ν e angular distribution is as expected but what is

45 Oscillations of muon neutrinos Looks like   oscillates:.. Remember that we identify neutrinos by the corresponding charged lepton which they produce: But look at the masses: μ 106 MeV τ  eV Does neutrino have enough energy to produce τ 

46   cross sections Total CC cross sections for: compared with  

47 Fizyka cząstek II D. Kiełczewska wykład 4 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.


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