Odkrycie oscylacji neutrin

Wielkość: px

Rozpocząć pokaz od strony:

Download "Odkrycie oscylacji neutrin"

Grzegorz Sokołowski
7 lat temu
Przeglądów:

1 Odkrycie oscylacji neutrin v Neutrina słoneczne v Neutrina atmosferyczne

2 Solar neutrinos Solar neutrinos (another other place mystery where of missing are neutrinos) missing From neutrinos to cosmic sources, D. Kiełczewska and E. Rondio

3 Data are compared with expectations from SSM - Standard Solar Model: ρ = 1, 4 ρ T0 T S = 15,6 10 K, = 5773 K composition: H 34%, He 64% age: years 9 1 au (distance Sun to Earth) m R = km e luminosity L = solar g cm e g cm 39 MeV s Le constant Ke = = π 1 au ( ) Standard Solar Model MeV 2 2 cm 2Ke 2Ke 10 2 φν = > = ν / cm s E ν 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:

threshold only event rates counte no time information

4 Solar Neutrino Spectrum thresholds for different thechniques radiochemical (Gallium & Chlorine): low threshold only event rates counte no time information no direction Cherenkov detectors time and direction higher threshold

5 Radiochemical experiments First one ever used to detect solar neutrinos - Davis-Pontecorvo reaction: ν e + Cl e + Ar or ν e + Ga e + Ge Ø 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

6 Davis experiment at Homestake 615 tons of C 2 Cl 4 run from 1968 for about 30 years Ø 37 Ar 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 Nobel prize for Ray Davis in 2002

7 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

8 Gallex/GNO and Sage ν e + Ga e + Ge two detectors using reaction 71 Ga (ν e, e ) 71 Ge 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 µg of natural Ge (efficiency 80%)

9 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

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: SNU SAGE 45% of neutrinos are missing?

11 Water Cherenkov detectors Ø Super-Kamiokande - light water target Ø SNO - heavy water target v directionality v time of every event BOREXINO, KAMLAND(2): Liquid Scintillator n

12 Super-Kamiokande: Solar peak > 5 MeV signal background For E<20 MeV and ν e we have only: ν + e ν + e and we know that electron moves forward!

13 Neutrinogram of Sun in Super- Kamiokande The electrons of low energy undergo many multiple Coulomb scatterings the actual size of the Sun ½ pixel Low spacial resolution of the neutrinogram

14 Solar neutrino flux measured in Super-K Observed: 22,400 events in 1496 days Expected: 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?

15 Distribution of electron energy in Super-K ν + e ν + e No modulation of the spectrum is observed just the neutrino deficit.

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

17 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 Ø Only electron neutrinos can be measured by radiochemical experiments ν e ν + Cl e + Ar e ν + Ga e + Ge e Ø Super-K measures only because It can happen to all neutrino flavors but cross section is 7 times larger for Ø But SNO measures much more: ν + e ν + e ν e ν e O e F > 18 MeV E ν

19 Results from D2O SNO

20 Detection of neutrons from: ν x d ν x n p With salt

21 Results from D2O

22 SNO Results Energy distribution was not used for the separation of processes

SNO fluxes From event rates to neutrino fluxes: in units: 6-2 -1 10 cm s 84 external-source neutrons v Results with salt consistent with those from

23 SNO fluxes From event rates to neutrino fluxes: in units: cm s 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 (Standard Solar Model)

24 Determination of neutrino fluxes from SNO measurements Number of interactions of a neutrino of flavor x: N x = const ϕ ( x E ) ν σ ( x E ν )de ν E 0 mass x time-of-exposure flux cross section Assuming the spectrum of 8 B neutrinos: ϕ x (E ν ) = Φ x f B ( E ν ) f B (E ν ) : f B (E ν ) de ν =1 0 and knowing cross sections one can find: Φ x

SNO Results phase 1+2 ϕ CC = ϕ e ϕ ES = ϕ e + 0.

25 SNO Results phase 1+2 ϕ CC = ϕ e ϕ ES = ϕ e ϕ µτ ϕ NC = ϕ e + ϕ µτ to compare with: Φ = 5.05 SSM ν e ν µ τ Hime, Nu06 /

26 SNO final phase

27 Neutron counters in SNO 3 He( n, p)t Counters 2-3 m long. 36 strings on 1x1 m grid

28 Results of all the solar experiments

29 Solar neutrino experiments Name Location Mass Reaction Start Homestake S.Dakota USA Cl(ν e,e - ) 37 Ar 1968 stopped SAGE Galex/GNO Baksan, Russia Gran Sasso, Italy Ga (ν e,e - ) 71 Ge 71 Ga (ν e,e - ) 71 Ge 1990 stopped 1992 stopped Kamiokande Kamioka, Japan 2000 ν x e - ν x e stopped Super Kamiokande Kamioka, Japan ν x e - ν x e SNO Sudbury, Canada 8000 ν e d e - pp ν x d ν x np ν x e - ν x e - Borexino Gran Sasso, Italy 300 ν x e - ν x e stopped 2001 stopped 1999 stopped KamLand Kamioka, Japan Fizyka cząstek 1000 II D. Kiełczewska reactor antineutrinos 2001

30 Odkrycie oscylacji neutrin atmosferycznych w Super- Kamiokande

31 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 (m μ =106 MeV; cτ=659 m) Fizyka cząstek II D. Kiełczewska

32 Atmosph

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 Upward

33 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 Upward stopping µ e/µ identification all assumed to be µ l different energy scale l different analysis technique l different systematics ν µ interactions in rocks below the detector

34 Neutrino energy spectra Fully contained FC Partially contained PC e/μ identification Upµ thru µ all assumed to be µ Upµ stop Interactions in rocks ν µ

35 Particle Identification T i Hit times are corrected for Cherenkov photon time of flight. e-like: electrons gammas mostly ν e + N1 e+ N2 µ ν ν T Fizyka cząstek II D. i Kiełczewska µ-like: e e µ 0 π mostly 2γ ν + N µ + N µ muons charged pions protons 1 2

36 Super-K: particle identification points: DATA histogram: MC simulation the variable PID describes how diffuse a ring is

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. 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 samples

38 Super-Kamiokande results (contained) Sub-GeV (Fully Contained) E vis < 1.33 GeV, P e > 100 MeV, P µ > 200 MeV Data MC 1-ring e-like µ-like Multi-GeV Fully Contained (E vis > 1.33 GeV) Data MC 1ring e-like µ-like R Sub ( µ / e) data = = ± ± ( µ / e) MC Partially Contained (assigned as µ-like) We take ratios to cancel out errors on absolute neutrino fluxes: R Multi ( µ / e) data = = ± ( µ / e) MC Too few muon neutrinos observed!

39 Super-K I results - upward going muons Up through-going µ, (1678days) Up stopping µ, (1657days) Data: (x10-13 cm -2 s -1 sr -1 ) MC: Data: (x10-13 cm -2 s -1 sr -1 ) MC: Again one observes a muon deficit

40 Double ratios in various experiments most experiments observed muon deficits

41 Atmosph

42 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 Missing are the muon neutrinos passing through the Earth!

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

44 Oscillations of muon neutrinos Looks like ν µ oscillates:.. ν ν µ τ Remember that we identify neutrinos by the corresponding charged lepton which they produce: ν µ τ + N µ + ν + N τ + X X But look at the masses: µ 106 MeV τ 1777 MeV Does neutrino have enough energy to produce τ?

45 ν τ cross sections Total CC cross sections for: ν + N τ + X τ + ν + N τ + X compared with ν µ τ

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.

Podobne dokumenty

Eksperymenty reaktorowe drugiej generacji wyznaczenie ϑ 13

Eksperymenty reaktorowe drugiej generacji wyznaczenie ϑ 13 v Przypomnienie wyniku eksperymentu KamLAND - weryfikującego oscylacje neutrin słonecznych v Formuły na prawdopodobieństwo disappearance antyneutrin