Discovery of neutrino oscillations

Prezentacja na temat: "Discovery of neutrino oscillations"— Zapis prezentacji:

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

2 Solar neutrinos other place where are missing
(another mystery of missing neutrinos) Solar neutrinos other place where are missing E. Kearns – May 2002 Fizyka cząstek II D. Kiełczewska wykład 4 „From neutrinos to cosmic sources”, D. Kiełczewska and E. Rondio

3 Fizyka cząstek II D. Kiełczewska wykład 4
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) = nteractions/atom/sec Processes producing neutrinos as a function of distance from the Sun center: Fizyka cząstek II D. Kiełczewska wykład 4

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

8 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 oC) Extraction – destillation Callibrated on added 700 μg of natural Ge (efficiency 80%) Fizyka cząstek II D. Kiełczewska wykład 4

9 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 E. Kearns – May 2002 Fizyka cząstek II D. Kiełczewska wykład 4

10 Fizyka cząstek II D. Kiełczewska wykład 4
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 Water Cherenkov 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 Fizyka cząstek II D. Kiełczewska wykład 4
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 Fizyka cząstek II D. Kiełczewska wykład 4
Results from D2O Fizyka cząstek II D. Kiełczewska wykład 4

22 Fizyka cząstek II D. Kiełczewska wykład 4
SNO Results Energy distribution was not used for the separation of processes External neutrons to neutrony spowodowane przez fotodesyntegracje deuteru przez gammy przychodzace z zewnatrz D2O. Te neutrony sa mierzone z ksztaltu rozkladu w polozeniu Fizyka cząstek II D. Kiełczewska wykład 4

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

26 Fizyka cząstek II D. Kiełczewska wykład 4
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 Homestake S.Dakota USA 615 37Cl(νe,e-)37Ar 1968 stopped SAGE Galex/GNO Baksan, Russia Gran Sasso, Italy 50 30 71Ga (νe,e-)71Ge 1990 stopped 1992 stopped Kamiokande Kamioka, Japan 2000 νxe- → νxe- 1986 stopped Super Kamiokande 50000 1996 SNO Sudbury, Canada 8000 νed→ e- pp νxd → νx np 1999 stopped 2001 stopped Borexino 300 2007 soon KamLand 1000 reactor antineutrinos 2001 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 Fizyka cząstek II D. Kiełczewska wykład 4
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 e/μ identification all assumed to be μ 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/μ identification 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 J.Wentz et al..hep-ph/ 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 1-ring e-like μ-like Data MC 1ring e-like μ-like Partially Contained (assigned as μ-like) 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: (x10-13 cm-2s-1sr-1) MC: Up stopping μ, (1657days) Data: (x10-13cm-2s-1sr-1) MC: Again one observes a muon deficit Fizyka cząstek II D. Kiełczewska wykład 4

40 Double ratios in various experiments
Fig The double ratio R of muon to electron neutrino events, data divided by expectations for various underground atmospheric neutrino detectors. From A. Mann[20] Learned most experiments observed muon deficits Fizyka cząstek II D. Kiełczewska wykład 4

41 Fizyka cząstek II D. Kiełczewska wykład 4
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 going μ 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’s try to find interpretation of the deficit Of νμ after passing the Earth Looks like νμ disappearance... What happens to muon neutrinos? Let’s suppose an oscillation: but what is We see that νe angular distribution is as expected

44 Oscillations of muon neutrinos
Looks like νμ oscillates:.. Remember that we identify neutrinos by the corresponding charged lepton which they produce: But look at the masses: μ MeV τ MeV Does neutrino have enough energy to produce τ ?

45 ντ cross 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