Nuclear and Particle Physics Franz Muheim 1

NeutrinosNeutrinos

Pauli postulates NeutrinoDiscovery of neutrino flavours

Electron, muon and tau neutrinosNeutrino Interactions

Cross sections

Neutrino massDirect measurement

Neutrino oscillationsLepton flavour violationFormalism

Solar neutrinosHomestake, Super-K and SNO

Atmospheric neutrinosSuper-K

Discovery of Neutrino Massneutrino oscillations

Cosmology

OverviewOverview

Nuclear and Particle Physics Franz Muheim 2

PauliPauli’’ss Letter Letter

Particle Physics in 1930Only 3 knowns fundamental particles: e-, p, γContinuous energy spectrum of e- in beta decay

Pauli postulates NeutrinoDear radioactive Ladies and Gentleman“ … desperate remedy to save … the law of

conservation of energy”“ … that there could exist … neutrons”“in beta decay a neutron is emitted in addition to

the electron“

1934 name - “neutrino” coined by Fermi1932 neutron discovered by Chadwick

eA

ZAZ eXX ν++→ −

+1

Pauli

Nuclear and Particle Physics Franz Muheim 3

Neutrino InteractionsNeutrino Interactions

Neutrinospoint-like leptonsdo not interact strongly, no colour chargecharge Q = 0 → no electromagnetic interactions Only weak interactions by coupling to W± and Z0

Expect very small detection rates“ I have done a terrible thing. I have postulated a

particle that cannot be detected.” PauliInverse Beta Decay

Cross section

Mean Free Path60 light years of water for 1 MeV anti-neutrino

1 ν in 1011 interacts when crossing the earthRequire huge rates as neutrino sources

+

−

+→+

+→+

enp

epn

e

e

ν

ν

( ) 22

44 cmMeV

105 ⎟⎠⎞

⎜⎝⎛⋅≈+→+ −+ ννσ

Eenpe

3-2319 cm1034.3nyearslight 60cm1061⋅==≈⋅≈=

ANZ

nA

σλ

Nuclear and Particle Physics Franz Muheim 4

Discovery of NeutrinosDiscovery of Neutrinos

Electron Neutrino νe discovered 1956 byAnti-neutrino source Reines and CowanNuclear reactor --- anti-ν flux 6·1020 s-1

Target and Detector --- 400 l liquid scintillatorWater and Cadmium ChlorideDetection of anti-neutrinoe+ annihilates with atomic e-n Cd reaction delayed by 20 µsDelayed coincidences only produced by signal

Muon Neutrino νµ 1962 at Brookhaven byPion beam Ledermann, Steinberger, SchwartzIron absorber --- only muons survive

νµ and νe are different

Tau Neutrino ντ 2000 at Fermilab - Donut p on tungsten targetproduce Ds mesons

CdCdnCdee

enpe

γ

γγ

ν

→→

→

+→+−+

+

*

neppen

nppn

+→++→+

+→++→+

→→

+−

+−

−−++

µµ

µµ

µµ

νν

µνµν

νµπνµππ

seet don'

observe

beam-

µτ

τ

τ

ννµτ

τν

ντ

++→

+→+

+→

−−

−

++

XN

Ds

Nuclear and Particle Physics Franz Muheim 5

Neutrino PhysicsNeutrino Physics

Neutrino SourcesNatural radioactivity – e.g. rocksCosmic rays hitting the atmosphereNuclear reactorsParticle acceleratorsSun - nuclear fusion reactor

Flux on earth ~1011 cm-2s-1

100 billions/sec through your finger nailNeutrino Mass

No apparent “reason” for neutrino to be masslessall other fermions have mass

Direct mass measurementsBeta decay energy spectrum

Kurie plotlinear

Endpoint modified by resolutionand non-zero νe massTritium Beta Decay Mass m(νe) < 3 eV

Neutrino OscillationsNo apparent “reason” for neutrinos not to oscillateinto each other

MeV7.26224 4 +++→ +eeHep ν

eeHeH ν++→ −33

( )

ee

eeF

EEEdE

d

EEEGdEd

−∝Γ

−=Γ

02

2203

2

12π

Nuclear and Particle Physics Franz Muheim 6

Neutrino OscillationsNeutrino Oscillations

Lepton flavour conservationLe, Lµ, Lτ are conserved separatelyNeutrinos with mass can mix – weak eigenstatesare linear superpositions of mass eigenstates

Le, Lµ, Lτ not absolutely conservedLe, Lµ, Lτ Violation too small to observe BF < 10-40

2 Neutrino flavoursEasy to understand, can be expanded to 3 generations

Time evolution

Intensity I(t) for initial νe beam

Neutrino energy E and mass difference ∆m122

Neutrino Oscillation Probabilities

Distance from source L [m], E[MeV] and ∆m122 [eV2]

( )( )tiEt

tiEt

222

111

exp)0()(exp)0()(

−=−=

νννν

i

iii

iiiii

pmpE

mEmpE

2

2

222

+≈⇒

>>+=

EmEEE

mmm

2/21212

21

22

212

∆≈−≡∆⇒

−≡∆

( ) ( )⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛ −

−+=2

sincossin4sincos)0()( 12222222 tEEItIee

θθθθνν

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛−

=⎟⎟⎠

⎞⎜⎜⎝

⎛

2

1

cossinsincos

νν

θθθθ

νν

µ

e

( )

( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛ ∆=→

⎟⎟⎠

⎞⎜⎜⎝

⎛ ∆−=→

]MeV[]m[]eV[27.1sin2sin

]MeV[]m[]eV[27.1sin2sin1

21222

21222

ELmvvP

ELmvvP

e

ee

θ

θ

µ

Nuclear and Particle Physics Franz Muheim 7

Solar NeutrinosSolar Neutrinos

Standard Solar Model (SSM)Predicts rates and solar neutrino energy spectrapp flux below 0.42 MeV8B νe up to 14 MeVpp cycle

Homestake ExperimentFirst observed solar neutrinos in 1970s Davies100,000 gallons of cleaning fluid C2Cl4

Measurement

0.5 Ar atoms/day2.56±0.23 SNU

SSM prediction1.5 Ar atoms/day7.7±1.3 SNU

Puzzle - What is wrong?Experiment, SSM, Neutrinos

AreCle3737 +→+ −ν

1 SNU = 1 interaction1036 target atoms/sec

Bahcall

Nuclear and Particle Physics Franz Muheim 8

Solar Neutrinos IISolar Neutrinos II

Super-Kamiokande50,000 tons of water, 11,000 phototubesunderground inside a mine in Japan, started 1997

νe DetectionElastic scattering

Directionalsensitivity

Measurements(0.465 ± 0.005 + 0.016 -0.015) x SSMνe definitely from sunSignal from centre of sun

Puzzle - What is wrong?Homestake experimentconfirmedExperiment, SSM, Neutrinos

−− +→+ ee ee νν

Nuclear and Particle Physics Franz Muheim 9

Solar Neutrinos IIISolar Neutrinos III

SNO --- Sudbury Neutrino Observatory1000 tons of heavy water (D2O)10,000 photo multipliers tubes

SensitivitySNO is able to measure νe - Charged Currentbut also νµ and ντ (νi=e,µ,τ ) - Neutral Current

Measurements 2003 results31% of SSM

100% of SSM

31 % of solar ν’s arrive as νe at earth 100% of solar ν’s detected if νµ and ντ are included

Puzzle - What is wrong?Experiment, SSM, Neutrinos

νe change to νµ in flight

ii

ii

e

pnDee

eppD

νννν

ν

++→+

+→+

++→+−−

−

(NC)current Neutral (ES) scattering Elastic

(CC)current Charged

Neutrino OscillationsNeutrino Oscillations

Nuclear and Particle Physics Franz Muheim 10

Atmospheric NeutrinosAtmospheric Neutrinos

Cosmic RaysProtons hit nuclei in upper part of atmosphereProducing chain of particlescopious source of neutrinosMain decay sequence

and

Expect 2 νµ for each νe~1990 1st indications for ”too few νµ”

Super-KamiokandeCan discriminate νµ from νe

Recoil muon produces clean ringRecoil e- produces fuzzy ring

XeNXN e +→++→+ −− νµν µ

µ

µ

ννµ

νµπ

ee++

++

→

→

µ

µ

ννµ

νµπ

ee−−

−−

→

→

XeNe +→+ −νXN +→+ −µν µ

Nuclear and Particle Physics Franz Muheim 11

Atmospheric Neutrinos IIAtmospheric Neutrinos II

Measurements1998 Super-KamiokandeObserve significant deficit of νµand agreement for νe

Neutrino Disappearanceνµ traversing the earthi.e arriving at the detector from below disappear

Atmospheric neutrinos First Evidence for νµ change to ντ in flight Neutrino Oscillations

Neutrino OscillationsNeutrino Oscillations

Nuclear and Particle Physics Franz Muheim 12

Discovery of Neutrino MassDiscovery of Neutrino Mass

Atmospheric Neutrino OscillationsAtmospheric νµ change into ντOscillationprobabilityFit data for best values of mass difference ∆m23

2

and mixing angle θµτFind θµτ ≈ 450 and

∆m232 ≈ 2.4·10-3 eV2

Neutrinos have MassSolar Neutrino Oscillations

Super-Kamiokande, SNOKamland – reactor anti-νeFind θeµ ≈ 330 and

∆m122 ≈ 8.0·10-5 eV2

Neutrino massMinimum mν ~ 0.05 eV2 scenarios

CosmologyBig Bang large nr. of neutrinos Neutrinos are hot dark matter candidates

Supernova 1987AKamiokande and IMBObserved ~ 10 neutrinos

( ) ( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛ ∆=→

]MeV[]m[]eV[27.1

sin2sin2

22

ELm

vvP µτµττµ θ