Transcript Document
Fysica 2002 Groningen
The elusive neutrino
Piet Mulders Vrije Universiteit Amsterdam [email protected]
http://www.nat.vu.nl/~mulders 1
What is it all about Neutrinos, quantum mechanics, relativity What are neutrinos?
Where do we find neutrinos?
How to catch neutrinos?
Neutrino puzzles How heavy are neutrinos?
Solar neutrinos 2
What is a neutrino?
Matter 4
The periodic table 5
Matter 6
Matter 7
Atomic nuclei Isotopes Radioactivity alpha beta gamma 1930: W. Pauli 1956: Reines & Cowan After 15 min.
8
Matter 9
The building blocks of the subatomic world 10
What is special with neutrinos?
No mirror image (only lefthanded) Barely interacting (crossing the earth without problems) 11
Origin of neutrinos ?
Origin of neutrinos Weak decay of atomic nuclei …n… …p… Cosmic rays p p + m m + …p… + e …n… + e + (Sun/reactors): + n e (righthanded antineutrino) + n e (lefthanded neutrino) (decay of the pion) + n m + n m (rechtshandig antineutrino) (linkshandig neutrino) Remnants of the big bang just as photons (T = 2.7 K background) one finds about 500 neutrinos per cm 3 for all three kinds of neutrinos ( n e , n m and n t ) 13
How do we know all of that?
Broken mirror symmetry Wu et al.
1957 (looking at Cobalt nuclei)
From the largest microscope in the world: CERN 16
Antiparticles 17
Standard model 3 families of particles 4 fundamental forces Carriers of the forces 18
Weak interactions
Force particles play a role in:
Interactions
Pair creation
Annihilation
19
Example: neutron decay
Neutron beta-decay
n p + e + n e
At the quark level
d u + e + n e 20
Three kinds of neutrinos!
Z 0
decay into: quark pairs
(except top quarks!)
lepton pairs
e + e , m + m , t + t neutrino pairs
lifetime is inverse of decay probability
1/t = G G = S G
i
21
cross sections G F ~
a
/M W 2
22
Collission lengths of neutrinos 23
Neutrino puzzles
Questions about neutrinos How heavy are neutrinos?
Where are the solar neutrinos? (compared to the SSM) 25
How can we detect Neutrinos?
Neutrino detectors Super Kamiokande 27
Super Kamiokande 28
Neutrino detection techniques Detection via cherenkov light emitted by particles moving “faster” than light (from antares experiment) 29
Neutrino oscillations in the atmosphere Neutrinos from cosmic rays come from decay of pions. These are n m neutrinos If the n m neutrino is a quantummechanical superposition of neutrinos n 1 en n 2 one gets oscillations 30
Vacuum oscillations 31
Neutrino oscillations in the atmosphere l
V ~ 1250 km
Superkamiokande found oscillations by looking at the zenith angle dependence Results are consistent with n m n t oscillations with D m 2 ~ 2 - 3 x 10 and sin 2 2 q ~ 1 -3 eV 2 32
My first reaction:
Interview in Aik door Wilm Geurts en Joost van Mameren
33
What are the consequences * For particles with mass both righthanded and lefthanded species exist! This is only * possible if the neutrino is its own antiparticle (like the photon, but different from the electron) (I do not discuss sterile neutrinos) 34
Dirac and Majorana fermions
Majorana neutrino
35
Dirac and Majorana fermions Although it seems as if the Majorana solution restores mirror symmetry, this is NOT true Lefthanded neutrino interacts with lefthanded electron Righthanded neutrino with righthanded interacts positron 36
CP violation
Mixing between mass and weak-interaction eigenstates for quarks AND neutrinos Complex phases (at least requiring 3x3 mixing) leads for both cases to CP violation
37
Solar neutrinos
Solar neutrinos in SNO (Sudbury Neutrino Observatory) E n < 15 MeV
All neutrinos (x = e,
m, t
)
n x n n n x x e + p + e + e (via Z 0 + d n x n x n x n e + p + p + n + e n (via Z e + d 0 -exchange)
Electron neutrinos
e- + p + p + e and W) 39
Solar neutrino oscillations Matter contains protons, neutrons and electrons.
Oscillations arise because n e interacts differently with matter dan n m 40
Basis states n e and n m
Solar neutrino oscillations SNO showed that the missing n probably e n m appear as different type, most l e = [2 x 10 7 m]/( r / r water ) ~ 2 x 10 5 (for a density of r / r water ~ 100) = [2.5 x 10 3 m](E[GeV]/ D m 2 [eV 2 ]) m l V Thus for E ~ 1 MeV and finds that l V ~ l e D m 2 ~ 6 x 10 -5 eV 2 one and thus one can have the situation of a resonance with maximal oscillations!
Why not go the easy way?
Just observa a supernova emitting photons and neutrinos and look which arrive first! Particles with mass after all move slower than light!
Surprise! Neutrinos from SN 87A arrived first!
Explanation: the velocity of light in matter is smaller than the velocity in vacuum In spite of a rather low density (in the galaxy about 5/cm 3 ) light is slowed down more than that neutrinos move slower than light in vacuum!
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V light = 1/n’ ~ 1 – 2
p
N f(k,
q
=0)/E 2
V neutrino = 1 – m
n
2 /2E 2
m 2 = 10 -5 eV 2 E = 1 GeV v = 1 – 10 -23 D x = 3 x 10 -15 m/yr
Nevertheless high-energy neutrinos might be the messengers that help solving cosmological puzzles!
An underwater laboratory
ANTARES
(mediterranean Sea) Towards huge volumes of the order of a km 3 46
Event simulation
ANTARES
47
Event simulation
AMANDA
(South Pole) 48
Concluding remarks Neutrinos have mass, but its tiny of the order of 0.05 - 0.001 eV (cf electron with mass of 511,000 eV) Mass eigenstates are different from weak-interaction states (oscillations) Explanation of solar neutrino puzzle No solution for ‘dark matter’ problem New possibilities in astrophysics 49