docwyklad4-Odkrycie oscylacji
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wyklad4-Odkrycie oscylacji
Odkrycie oscylacji neutrin v Neutrina słoneczne v Neutrina atmosferyczne Fizyka cząstek II D. Kiełczewska wykład 4 Solar neutrinos Solar neutrinos (another mystery of missing other place where!! are neutrinos) missing Fizyka cząstek II D. Kiełczewska wykład 4 „From neutrinos to cosmic sources”, D. Kiełczewska and E. Rondio Standard Solar Model Data are compared with expectations from „SSM” Standard Solar Model: − ρ = 1, 4 cmg 3 ρ 0 ≈ 200 cmg 3 − T0 = 15,6 ⋅ 106 K, TS = 5773 K − composition: H 34%, He 64% − age: 4.5 ⋅ 109 years − 1 au (distance Sun to Earth) 1.5 ⋅1011 m 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) = 10-36 nteractions/atom/sec − R e = 69600 km − luminosity Le =2.4 ⋅1039 − solar constant K e = MeV s Le 4π (1 au ) 2 = 0.849 ⋅1012 Processes producing neutrinos as a function of distance from the Sun center: MeV cm 2 2Ke 2Ke − φν = > = 6.4 × 1010ν / cm 2s 26.73 − 2 Eν 26.73 Fizyka cząstek II D. Kiełczewska wykład 4 Solar Neutrino Spectrum thresholds for different thechniques radiochemical (Gallium & Chlorine): • low threshold • only event rates counte • no time information • no direction Cherenkov detectors Fizyka cząstek II D. Kiełczewska wykład 4 • time and direction • higher threshold Radiochemical experiments First one ever used to detect solar neutrinos Davis-Pontecorvo reaction: ν e + Cl → e + Ar 37 − 37 or ν e + 71Ga → e − + 71Ge Produced isotopes are radioactive with not too long lifetime – they are periodically extracted and counted Ø No information on time of interactions or neutrino directions Ø Fizyka cząstek II D. Kiełczewska wykład 4 Davis experiment at Homestake 615 tons of C2Cl4 run from 1968 for about 30 years Nobel prize for Ray Davis in 2002 Ø 37Ar has half-life time for electron capture of 35 days Ø Argon atoms have to be extracted and counted - about 1 atom per 2 days Fizyka cząstek II D. Kiełczewska wykład 4 Homestake Results: Rate and flux from single extractions Only: ( 34 ± 3) % 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 Gallex/GNO and Sage 71 two detectors ν using + reaction Ga → e − 71 e Ga (ν e , e − )71 Ge + 71Ge 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 Gallex and GNO v Counts as a function of time v Additional test with isotope life time v Background estimate v Calibration of the method with introduction of known number of atoms and counting them v From this measurement – estimate of efficiency of the method Fizyka cząstek II D. Kiełczewska wykład 4 Results after extraction • Expected rate from SSM is: Measured: number of neutrino interactions, From it derived: flux of neutrinos from the Sun reaching the Earth 128+9 SNU −7 45% of neutrinos are missing? Fizyka cząstek II D. Kiełczewska wykład 4 SAGE Water Cherenkov detectors Ø Super-Kamiokande - light water target Ø SNO - heavy water target BOREXINO, KAMLAND(2): Liquid Scintillator v directionality v time of every event Fizyka cząstek II D. Kiełczewska wykład 4 n Super-Kamiokande: Solar peak > 5 MeV signal For E<20 MeV and ν e we have only: background ν + e− → ν + e− Fizyka cząstek II D. Kiełczewska wykład 4 and we know that electron moves forward! Neutrinogram of Sun in SuperKamiokande The electrons of low energy undergo many multiple Coulomb scatterings Low spacial resolution of the the actual size of the Sun – neutrinogram ½ pixel Fizyka cząstek II D. Kiełczewska wykład 4 Solar neutrino flux measured in Super-K Observed: in 1496 days Expected: 48,200 events from SSM 22,400 events (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 Distribution of electron energy in Super-K ν + e− → ν + e− No modulation of the spectrum is observed just the neutrino deficit. 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% Jan.... Jun.. ..Dec with a cut on electron energy>6.5 MeV to avoid radon bkg seasonal fluctuations Fizyka cząstek II D. Kiełczewska wykład 4 95% 99.7% Clues to the mystery of missing solar neutrinos Ø Deficits are observed in all the experiments Ø The fusion reactions in the Sun produce only νe Ø Only electron neutrinos can be measured by radiochemical experiments ν e + 37Cl → e− + 37 Ar ν e + 71Ga → e− + 71Ge Ø Super-K measures only ν + e → ν + e because ν e 16O → e − 16 F It can happen to all neutrino flavors but Eν > 18 MeV cross section is 7 times larger for ν e Ø But SNO measures much more: Fizyka cząstek II D. Kiełczewska wykład 4 Fizyka cząstek II D. Kiełczewska wykład 4 Results from D2O SNO Fizyka cząstek II D. Kiełczewska wykład 4 Detection of neutrons from: ν x d → ν x n p With salt Fizyka cząstek II D. Kiełczewska wykład 4 Results from D2O Fizyka cząstek II D. Kiełczewska wykład 4 Energy distribution was not used for the separation of processes SNO Results Fizyka cząstek II D. Kiełczewska wykład 4 SNO fluxes From event rates to neutrino fluxes: in units: × 106 cm-2s-1 84 external-source neutrons v Results with salt consistent with those from pure heavy water v Fluxes deduced from different reactions are inconsistent v Only the NC flux agrees with expectations from SSM Fizyka cząstek II D. Kiełczewska (Standard Solar Model) wykład 4 Determination of neutrino fluxes from SNO measurements Number of interactions of a neutrino of flavor x: ∞ N x = const × ∫ ϕ ( E ) σ ( E ) dE x ν x ν ν E0 mass x time-of-exposure flux cross section ∞ Assuming the spectrum of 8B neutrinos: f B (Eν ) : ∫f B (Eν ) dEν =1 0 ( ) ϕ x (Eν ) = Φ x f B Eν and knowing cross sections one can find: Fizyka cząstek II D. Kiełczewska wykład 4 Φx SNO Results phase 1+2 ϕ CC = ϕ e ϕ ES = ϕ e + 0.154 ⋅ ϕ µτ ϕ NC = ϕ e + ϕ µτ to compare Φ SSM = 5.05+−1.0 0.8 with: Fizyka cząstek II D. Kiełczewska wykład 4 ν e → ν µ /τ Hime, Nu06 SNO – final phase Fizyka cząstek II D. Kiełczewska wykład 4 Neutron counters in SNO 3 He ( n, p ) t Counters 2-3 m long. 36 strings on 1x1 m grid Fizyka cząstek II D. Kiełczewska wykład 4 Results of all the solar experiments Fizyka cząstek II D. Kiełczewska wykład 4 Solar neutrino experiments Name Location Mass 615 Reaction Homestake S.Dakota USA -)37Ar 1968 stopped SAGE Galex/GNO Baksan, Russia Gran Sasso, Italy 71Ga (νe,e-)71Ge 71Ga (ν ,e-)71Ge e 1990 stopped 1992 stopped Kamiokande Kamioka, Japan 2000 ν x e- → ν x e- 1986 stopped Super Kamiokande Kamioka, Japan 50000 ν x e- → ν x e- 1996 SNO Sudbury, Canada 8000 νed→ e- pp νxd → νx np ν x e- → ν x e- 1999 stopped 2001 stopped 1999 stopped Borexino Gran Sasso, Italy 300 ν x e- → ν x e- 2007 KamLand Kamioka, Japan 1000 reactor Fizyka cząstek II D. Kiełczewska wykład 4 antineutrinos 50 30 37Cl(ν e,e Start 2001 Odkrycie oscylacji neutrin atmosferycznych w SuperKamiokande Fizyka cząstek II D. Kiełczewska wykład 4 Atmospheric Neutrinos Weak decays are sources of neutrinos: Ø π, K mesons decay on the way to Earth Ø some muons also decay but many reach the surface (mμ=106 MeV; cτ=659 m) Fizyka cząstek II D. Kiełczewska wykład 4 Atmosph Fizyka cząstek II D. Kiełczewska wykład 4 Neutrino events in Super-K Contained events: Fully contained FC Partially contained PC All have to be separated from „cosmic” muons (3Hz) Upward through-going muons µ e/µ identification all assumed to be µ l different energy scale l different analysis technique l different systematics Fizyka cząstek II D. Kiełczewska wykład 4 Upward stopping µ νµ interactions in rocks below the detector Neutrino energy spectra Fully contained FC Partially contained PC µ e/μ identification Upµ thru all assumed to be µ Upµ stop Fizyka cząstek II D. Kiełczewskain Interactions wykład 4 rocks νµ Particle Identification Hit times are corrected for Cherenkov photon time of flight. e-like: Ti electrons gammas µ-like: µ → eν eν µ Ti Fizyka cząstek II D. Kiełczewska wykład 4 mostly ν e + N1 → e + N 2 π 0 → mostly 2γ ν µ + N1 → µ + N2 muons charged pions protons 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 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 Super-Kamiokande results (contained) Sub-GeV (Fully Contained) Evis < 1.33 GeV, Pe > 100 MeV, Pµ > 200 MeV Data 1-ring e-like µ-like 3266 3181 Multi-GeV Fully Contained (Evis > 1.33 GeV) MC 3081.0 4703.9 1ring e-like µ-like Data 772 664 MC 707.8 968.2 Partially Contained (assigned as µ-like) 913 1230.0 We take ratios to cancel out errors on absolute neutrino fluxes: RSub ( µ / e) data ( µ / e) data = = 0.638 ± 0.016 ± 0.050 RMulti = = 0.658+−0.030 0.028 ± 0.078 ( µ / e) MC ( µ / e) MC Too few muon neutrinos observed! Fizyka cząstek II D. Kiełczewska wykład 4 Super-K I results - upward going muons Up through-going µ, (1678days) Data: 1.7 +- 0.04 +- 0.02 (x10-13 cm-2s-1sr-1) 1.97+-0.44 MC: Up stopping µ, (1657days) Data: MC: 0.41+-0.02+-0.02 (x10-13cm-2s-1sr-1) 0.73+-0.16 Again one observes a muon deficit Fizyka cząstek II D. Kiełczewska wykład 4 Double ratios in various experiments most experiments observed muon deficits Fizyka cząstek II D. Kiełczewska wykład 4 Atmosph Fizyka cząstek II D. Kiełczewska wykład 4 Zenith angle distributions e-like 1 ring µ-like 1 ring µ-like multi- ring upward going µ Sub-GeV Multi-GeV up down Red: MC expectations Black points: Data Green: next lectures Fizyka cząstek II D. Kiełczewska wykład 4 Missing are the muon neutrinos passing through the Earth! 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: ν µ →ν x but what is νx We see that νe angular distribution is as expected ν x ≠νe Oscillations of muon neutrinos Looks like νµ oscillates:.. ν µ → ντ Remember that we identify neutrinos by the corresponding charged lepton which they produce: νµ + N → µ + X − ντ + N → τ − + X But look at the masses: µ 106 MeV τ 1777 MeV Does neutrino have enough energy to produce τ ? ντ cross sections Total CC cross sections for: ντ + N → τ − + X ντ + N → τ + + X compared with νµ 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
