Discovery of neutrino oscillations

Fizyka cząstek II D. Kiełczewska wykład 4

Discovery of neutrino oscillations

Solar neutrinos

Atmospheric neutrinos


Solar neutrinos other place where are missing

„From neutrinos to cosmic sources”, D. Kiełczewska and E. Rondio

Solar neutrinos(another mystery of missing neutrinos)


Standard Solar ModelData are compared with expectations from „SSM” - Standard Solar Model:

3 30

60

9

11

39 MeVs

1,4 200

15,6 10 K, 5773 K composition: 34%, 64%

age: 4.5 10 years

1 au (distance Sun to Earth) 1.5 10 m R 69600 km

luminosity =2.4 10

solar

g gcm cm

ST TH He

L

2

12 MeV2 cm

10 2

constant 0.849 104 1 au

2 2 6.4 10 / cm s

26.73 2 26.73

LK

K KE

1 SNU (Solar Neutrino Unit) = 10-36 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:


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


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:

37 37e Cl e Ar

71 71e Ga e Ge

or


Davis experiment at Homestake

615 tons of C2Cl4

run from 1968for 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


Homestake Results:

Rate = 0.48 ± 0.16(stat) ± 0.03(syst) argon atoms/dayFlux = 2.56 ± 0.16 ± 0.16 SNU

Rate and flux from single extractions

Only:

of SSM


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%)

71 71e Ga e Ge


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


•

Results after extraction

SAGE

Measured: number of neutrino interactions, From it derived: flux of neutrinos from the Sun reaching the Earth

Expected ratefrom SSM is:

45% of neutrinos are missing?


WaterCherenkov detectors BOREXINO,

KAMLAND(2):Liquid Scintillator Super-Kamiokande

- light water target SNO - heavy water target

directionality time of every event


Super-Kamiokande: Solar peak > 5 MeV

For E<20 MeVand ewe have only:e e

and we know thatelectron moves forward!

signal

background


Neutrinogram of Sun in Super-Kamiokande

the actual size of the Sun –½ pixel

The electrons of low energyundergo many multiple Coulombscatterings

Low spacial resolution of the neutrinogram


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 energyrange)

A half of neutrinos are missing?


Distribution of electron energy in Super-K

No modulation of the spectrum is observedjust the neutrino deficit.

e e


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.. ..Decwith a cut on electron energy>6.5 MeV to avoid radon bkg seasonal fluctuations


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 byradiochemical 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:

37 37

71 71

e

e

Cl e Ar

Ga e Ge

e e 16 16

18 MeVe O e FE

e

e


Results from D2OSNO


Detection of neutrons from: x xd n p

With salt


Results from D2O


SNO ResultsEnergy distribution was not used for the separation of processes


SNO fluxes

84 external-source neutrons

From event rates to neutrino fluxes:

6 -2 -1in units: 10 cm s 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)


Determination of neutrino fluxesfrom SNO measurements

Number of interactions of a neutrino of flavor x:

Assuming the spectrum of 8B neutrinos:

and knowing cross sections one can find: x

mass x time-of-exposure fluxcross section


SNO Results phase 1+2

Hime, Nu06 /e μ 1.00.85.05SSM

to compare

with:

SNO – final phase


Neutron counters in SNOCounters 2-3 m long.36 strings on 1x1 m grid



Results of all the solar experiments


Solar neutrino experiments

Homestake S.Dakota USA 615 37Cl(νe,e-)37Ar 1968 stopped

SAGEGalex/GNO

Baksan, RussiaGran Sasso, Italy

50 30

71Ga (νe,e-)71Ge 71Ga (νe,e-)71Ge

1990 stopped

1992 stopped

Kamiokande Kamioka, Japan 2000 νxe- → νxe- 1986 stopped

Super Kamiokande

Kamioka, Japan 50000 νxe- → νxe- 1996

SNO Sudbury, Canada

8000 νed→ e- ppνxd → νx npνxe- → νxe-

1999 stopped

2001 stopped

1999 stopped

Borexino Gran Sasso, Italy

300 νxe- → νxe- 2007soon

KamLand Kamioka, Japan 1000 reactor antineutrinos

2001

Name Location Mass Reaction Start


Odkrycie oscylacji neutrin atmosferycznych w Super-

Kamiokande


Atmospheric NeutrinosWeak decays are sources of neutrinos:

, K mesons decay on the way to Earth

some muons also decay but many reach the surface (mμ=106 MeV; cτ=659 m)


Atmosph


Neutrino events in Super-K

μUpward stopping μ

different energy scale different analysis technique different systematics

Upward through-going muons

μinteractions in rocks belowthe detector

Contained events:Fully contained

FCPartially contained

PC

e/μ identificatio

n

all assumed to be μ

All have to be separatedfrom „cosmic” muons

(3Hz)


Neutrino energy spectraFully contained

FCPartially contained

PC

e/μ identification

all assumed to be μ

Interactions in rocks

μ

Upμ stop

Upμ thru

μ


e-like:

μ-like:

electronsgammas

muonscharged pionsprotons

0 2

ee μμ

iT

iT

Hit times are correctedfor Cherenkov photontime of flight.

Particle Identification

1 2e N e N mostly

mostly1 2N Nμ μ


Super-K: particle identification

the variable „PID”describes howdiffuse a ring is

points: DATAhistogram: MC simulation


• 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. 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 simulationsThe 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


Data MC1ring e-like 772 707.8 μ-like 664 968.2

Sub-GeV (Fully Contained) Evis < 1.33 GeV, Pe > 100 MeV, Pμ > 200 MeV

Data MC1-ring e-like 3266 3081.0 μ-like 3181 4703.9

Multi-GeV

Fully Contained (Evis > 1.33 GeV)

Partially Contained (assigned as μ-like)

Super-Kamiokande results (contained)

( / ) 0.638 0.016 0.050( / )

dataSub

MC

eRe

μμ

0.0300.028

( / ) 0.658 0.078( / )

dataMulti

MC

eRe

μμ

913 1230.0

We take ratios to cancel out errors on absolute neutrino fluxes:

Too few muon neutrinos observed!


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) 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


Double ratios in various experiments

most experiments observed muon deficits


Atmosph


Zenith angle distributionse-like1 ring

μ-like1 ring

μ-likemulti- ring upward going μ

Sub-GeV

Multi-GeV

up down

Red: MC expectationsBlack points: DataGreen: next lectures

Missing are the muonneutrinos passingthrough the Earth!

Interpretation of the zenith angle distributions

Let’s try to find interpretation of the deficitOf νμ after passing the Earth ......

Looks like μ disappearance...

What happens to muon neutrinos?

Let’s suppose an oscillation: xμ

We see that νe angular distribution is as expectedbut what is x

x e

Oscillations of muon neutrinos

Looks like μ oscillates:..

μ

N X

N Xμ

μ

Remember that we identify neutrinos by the corresponding charged lepton which they produce:

But look at the masses: μ 106 MeV τ1777MeV

Does neutrino have enoughenergy to produce τ?

cross sections Total CC cross sections for:

N X

N X

compared with μ


Atmospheric neutrino experiments

The largest statistics of atmospheric neutrino eventswere 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 MACROand SOUDAN detectors. The results were consistentwith neutrino oscillations.

Discovery of neutrino oscillations

Documents

Transcript of Discovery of neutrino oscillations