Neutriner och Universum

1
Neutriner och Universum

• Preliminaries Units in Physics
• A short review of Quantum Mechanics and the
  Standard Model of Particle Physics
• Neutrino discovery and properties
• Neutrino oscillations
• Neutrino sources and detection
• A short review of the Big Bang model of Cosmology
• Neutrinos in Astrophysics
• Neutrinos from the cosmos
• High energy neutrino astrophysics
• Neutrino telescopes

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UNITS !

• All physics quantities have units (gr, eV, erg,
  cm2/s). This is what differenciates us from
  mathematics
• Following the units at each step when solving a
  problem can point out something done wrong

• It crashed on the approaching manouver

because one engineering team used metric units
while another used English units for a key
spacecraft operation
3
ENERGY RANGES IN PARTICLE PHYSICS

• Energy unit in particle physics eV
  (electronvolt) and multiples
• keV 103 eV (kilo)
• MeV 106 eV (Mega)
• GeV 109 eV (Giga)
• TeV 1012 eV (Tera)
• PeV 1015 eV (Peta)
• EeV 1018 eV (Exa)
• If you drop a pen (50gr, 1 m height), the energy
  it has when reaching the floor is 3.1x1018 eV.
  Since a plastic pen has 3x1020 atoms (approx.),
  this corresponds to an energy of 10-2 eV per atom
• (thats why we use other units, SI, for
  macroscopic objects, for example 1 Joule 6.2
  x1018 eV)

4
Some typical energies in eV
Room temperature thermal energy of a molecule
.......................... 0.04 eV Visible
light photons.....................................
.............................. 1.5-3.5
eV Energy for the dissociation of an salt
molecule into Na and Cl- ions...................
..................................................
........................ 4.2 eV Ionization
energy of atomic hydrogen ........................
.................... 13.6 eV Approximate
energy of an electron striking a color television
screen............................................
.......................................
20,000 eV High energy diagnostic medical
X-ray photons.......................... 200,000
eV .

(0.2 MeV) Flying mosquito
.. 1 TeV Higest
energy achieved at CERN LHC proton accelerator
. 7 TeV
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Quantum Mechanics in one transparency

• QM deals with wave functions, Y(r,t,a1...an), ai
  being whatever additional quantum numbers are
  necessary to describe the particle spin, L ...
• The Y's are vectors in a vector space (Hilbert
  space).
• concept of basis, ui
• superposition principle FS ui is also a
  state vector
• Measurable quantities are eigenstates of
  observables (Hermitian operators in the space of
  Y) H Y e Y
• The time evolution of a system is governed by the
  Hamiltonian,
• Y(r,t,a1...an) e -iH/t Y(rr0,t0,a1...an)
• QM can only predict probabilities of the
  different possible outcomes of a measurement on a
  system, based on probability densities calculated
  from Y2

Important for oscillations
Important for oscillations
ref. Cohen-Tannoudji, vol1, ch.3
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The Standard Model in two transparencies

• The Standard Model of particle physics is a
  Quantum Field Theory.
• Quantum field theories are used to describe
  relativistic, many-particle systems. They are an
  extension of QM (second quantization).
• A field is defined at every point in space-time
  with a continuous function of the space-time
  coordinates, F(xm) m1,,4
• Particles are understood as field excitations,
  ie. quanta, at a given space-time point where the
  field has non-zero value.
• There are several types of fields according to
  their behaviour under a Lorentz transformation
  scalar, vector, tensor and spinor.
• The SM contains 24 elementary particles (plus
  antiparticles)
• e, m, t ne, nm, nt
  u, d, c, s, t, b g, g(8), Z0,
  W-

leptons
quarks
bosons
all normal matter made of u, d and e-.
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The SM in two transparencies (II)

• The dynamics and interactions of particles are
  described by a Lagrangian
• The equations of motion are derived from the
  Lagrangian
• The SM describes correctly the interactions of
  particles under three of the four fundamental
  forces
• electromagnetic, nuclear strong, nuclear weak.
  (gravitation not included)
• which are mediated by the bosons g, g, Z0,
  W-.
• Is Lorentz invariant (invariant under space-time
  translations)
• (Is gauge invariant under U(1)EM x SU(2)weak x
  SU(3)strong)
• Lepton number (number of leptons-antileptons)
  is conserved in any interaction (for particles
  L1, for antiparticles L -1, for non-leptons
  L0), as well as charge, spin and energy.
• Mass is not explained. It is added ad-hoc through
  the Higgs mechanism, which requires the
  existence of an additional particle, the Higgs
  boson, that has not been observed yet.

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The Standard Model particles
g
Q2/3
0
Q-1/3
Q0
2 Ws W, W-
Q-1
8 gluons
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The Standard Model forces
If g electromagnetic If Z, W weak If g strong
Feynmann diagram
10
Brief history of the neutrino

• The neutrino (turned out to be ne) was introduced
  to explain the energy spectrum of electrons from
  the radioactive decay of certain nuclei.
• b decay

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Brief history of the neutrino (II)
1934 - Enrico Fermi develops a comprehensive
theory of radioactive decays, including Pauli's
hypothetical particle, which Fermi coins the
neutrino (Italian "little neutral one"). With
inclusion of the neutrino, Fermi's theory
accurately explains many experimentally observed
results.
Without the neutrino, the energy of the electron
in b-decays should be always the same, and equal
to the difference of masses of the nuclei
involved (simply from energy conservation of a
3-body system)
Note that in 1930 the only known particles were
the e, the p and the photon (the neutron was
discovered in 1932).
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The Fermi theory

• 4-fermion point-interaction.
• Probability to decay
• P g YeYnYeYn

p
n
e-
n
and today
W-mediated weak interaction. Probability to
decay in terms of quarks P Gf
Yegm(1-g5)YnYpgm(1-gag5)Yn With Gf depending
on Mw
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the discovery of the (e-)(anti)neutrino

• 1956, Clyde Cowan and Fred Reines idea use the
  neutrinos emitted in nuclear reactors. (26 years
  after Pauli's proposal!)

• Detector 11m from reactor core, 12m
  underground
  Tank of 200 l of water, 40 kg of CdCl viewed by
  110 photomultiplier tubes
• Reaction
• ne p (H20) ? n e
• n 108Cd ? 109Cd ? 109Cd g
• e e (H20)? g g

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the discovery of the (e-)(anti)neutrino

• Detected about 3 events/hour (from a flux of
  1013/cm2 s)
• Reines got the Nobel price in 1995 (39 years
  after the experiment!)
• (Cowan died in 1974) http//nobelprize.org/p
  hysics/laureates/1995/reines-lecture.pdf
• Note that Pauli got the price in 1945 but for the
  discovery of the exclusion principle.

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neutrinos in the SM

• Originally(), neutrinos were considered massless
  
• They are elementary spin ½ fermions
• They come in three 'flavours' (ne, nm and nt
  type)
• They are electrically neutral.
• They feel only the weak interaction. (and the
  gravitational)
• They would be described in the SM by the massless
  Dirac equation.
• But There is nothing in the SM that requires
  neutrinos to be massless
• Indeed, that the neutrinos have mass was
  discovered in 1998 through the effect of neutrino
  oscillations (more later)

() Not by Pauli, who proposed that neutrinos
would have a mass of the same order as the
electron mass
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(known)sources of neutrinos

• the Atmosphere the Sun
  nuclear reactors

Excited fragments that b decay
n 235U
particle accelerators
p X p n
(90x90 r.a, dec)
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other sources of neutrinos

• Neutrinos from the Big Bang about 300/cm2
• from ee- ? n n in the first few seconds
• Neutrinos from natural radioactivity the Earth
  contains radioactive isotopes that b decay
• Neutrinos from humans Our body also contains
  radioactive isotopes, 40K for example. We emit
  about 340 milllion neutrinos per day (assuming a
  body content of 20 mg of 40K)

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key concepts from this lecture

• Units in high energy physics
• Known elementary particles today and interactions
• The need for the neutrino in the 30s
• Neutrino properties
• Neutrino sources reactions producing neutrinos