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