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The elusive neutrino

Piet MuldersVrije Universiteit

Amsterdam

mulders@nat.vu.nlhttp://www.nat.vu.nl/~mulders

Fysica 2002 Groningen

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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

What is a neutrino?

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Matter

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The periodic table

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Matter

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Matter

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Atomic nuclei Isotopes Radioactivity

alphabeta gamma

After 15 min.1930: W. Pauli1956: Reines & Cowan

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Matter

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The buildingblocks of thesubatomicworld

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What is special with neutrinos?

No mirror image (only lefthanded)Barely interacting (crossing the earth without problems)

Origin of neutrinos ?

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Origin of neutrinos Weak decay of atomic nuclei (Sun/reactors):

…n… …p… + e + e (righthanded antineutrino) …p… …n… + e + e

(lefthanded neutrino) Cosmic rays (decay of the pion)

+ (rechtshandig antineutrino) + (linkshandig neutrino)

Remnants of the big bang just as photons (T = 2.7 K background) one finds about 500 neutrinos per cm3 for all three kinds of neutrinos (e, and )

How do we know all of that?

Brokenmirrorsymmetry

Wu et al.1957(looking atCobalt nuclei)

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From the largest microscope in the world: CERN

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Antiparticles

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Standard model

3 families of particles

4 fundamental forces

Carriers of the forces

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Weak interactions

Force particles play a role in: Interactions Pair creation Annihilation

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Example: neutron decay

Neutron beta-decay

At the quark level

n p + e + e

d u + e + e

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Three kinds of neutrinos!

Z0 decay into: quark pairs (except top quarks!) lepton pairs

ee, , neutrino pairs

lifetime is inverse of decay probability

i

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cross sections

GF ~ /MW2

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Collission lengths of neutrinos

Neutrino puzzles

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Questions about neutrinos How heavy are

neutrinos? Where are the

solar neutrinos? (compared to the SSM)

How can we detect Neutrinos?

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Neutrino detectorsSuper Kamiokande

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Super Kamiokande

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Detection via cherenkov light emitted by particles moving “faster” than light

(from antares experiment)

Neutrino detection techniques

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Neutrino oscillations in the atmosphere

Neutrinos from cosmic rays come from decay of pions. These are neutrinos

If the neutrino is a quantummechanical superposition of neutrinos en one gets oscillations

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Vacuum oscillations

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Neutrino oscillations in the atmosphere

Superkamiokande found oscillations by looking at the zenith angle dependence

Results are consistent with oscillations with m2 ~ 2 - 3 x 10-

3 eV2 and sin2 2 ~ 1V ~ 1250 km

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My first reaction:

Interview inAik door Wilm Geurts enJoost van Mameren

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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)

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Dirac and Majorana fermions

Fermion(general)DiracneutrinoMajorananeutrino

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Dirac and Majorana fermions

Although it seems as if the Majorana solution restores mirror symmetry, this is NOT true

Lefthanded neutrino interacts with lefthanded electronRighthanded neutrino interacts with righthanded positron

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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

Solar neutrinos

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Solar neutrinos in SNO(Sudbury Neutrino Observatory)

All neutrinos (x = e, )x + p x+ px + d x+ p + nx + e- x + e- (via Z0-exchange)

Electron neutrinose + d e- + p + pe + e- e+ e-

(via Z0 and W)

E < 15 MeV

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Solar neutrino oscillations Matter contains

protons, neutrons and electrons.

Oscillations arise because e interacts differently with matter dan

Basis states e and

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Solar neutrino oscillations

SNO showed that the missing e appear as different type, most probably

e = [2 x 107 m]/(/water) ~ 2 x 105 m (for a density of /water ~ 100)

V = [2.5 x 103 m](E[GeV]/m2[eV2]) Thus for E ~ 1 MeV and m2 ~ 6 x 10-5 eV2 one

finds that V ~ e and thus one can have the situation of a resonance with maximal oscillations!

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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/cm3) light is slowed down more than that neutrinos move slower than light in vacuum!

Vlight = 1/n’ ~ 1 – 2 N f(k,=0)/E2

Vneutrino = 1 – m2/2E2

m2 = 10-5 eV2

E = 1 GeVv = 1 – 10-23

x = 3 x 10-15 m/yr

Nevertheless high-energy neutrinos might be the messengers that help solving cosmological puzzles!

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An underwater laboratory

Towards huge volumes of the order of a km3

ANTARES(mediterraneanSea)

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Event simulation

ANTARES

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Event simulation

AMANDA

(South Pole)

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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

END