Astroparticle Physics
Claudia-Elisabeth Wulz
Institute of High Energy Physics, Vienna
TU Vienna
c/o CERN, Geneva
Part 1
Winter semester 2013/2014
Bibliography
D. Perkins: Particle Astrophysics (Second edition, 2011)
C. Grupen: Astroparticle physics (2010)
1
Subjects of these lectures
• Standard Model of particle physics
• Particles and radiation in the cosmos
• Expansion of the Universe
• Baryogenesis and nucleosynthesis
• Dark matter
• Dark energy
C.-E. Wulz
2
2
What is Astroparticle Physics?
New field at the intersection of particle physics,
astronomy and cosmology
• What is the Universe made of?
• How did it emerge and what is its future?
• Connection between the smallest and largest scales
C.-E. Wulz
3
What is Astroparticle Physics?
Astroparticle physics is the science of studying
the Universe through particles that arrive on
earth
First indications of particles from the cosmos:
Studies by Victor Hess (1912-1913)
Birth of neutrino astroparticle physics:
Neutrinos from sun studied in Homestake mine (1967)
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Victor Hess
1883 - 1964
1936
with C. Anderson
5
Homestake and the solar neutrino deficit
Beginning in the 1960s Ray Davis built an experiment to detect solar neutrinos
deep in the Homestake Mine in South Dakota, but he found only about a third
the number of neutrinos predicted by theorist John Bahcall.
HomestakeExperiment
610t C2Cl4
Result:
Measured flux:
Expected:
2.56 SNU
8.5 SNU
ne + 37Cl  37Ar + e6
Solar Neutrinos
ne production processes
p+p
+ + ne
p + e- + p  2H + ne
2H + p  3He + 
3He + 3He  4He + 2p
3He + 4He  7Be + 
3He + p  4He + e+ + n
e
7Be + e-  7Li + n
e
7Li + p  4He + 4He
7Be + p  8B + 
8B  8Be + e+ + n
e
8Be*  4He + 4He
2H
e+
Energies
(pp) 0 - 0.4 MeV
(pep) 1.4 MeV
Energy spectrum of solar neutrinos
(hep) 1.5 - 17 MeV
(Be) 0.38, 0.86 MeV
(B)
0 - 15 MeV
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Special relativity
and
basic units
8
relativistic kinematics
 elementary particles travel mostly at speeds
close to speed of light
 because their masses are small compared to typical
energies
  (almost) always use relativistic kinematics
 in particle physics, “special relativity” is
sufficient most of the time
 for massive astronomical bodies general relativity
becomes important
 remember a few basic formulae !
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relativistic kinematics
v
1/γ
1
10
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units: energy and mass
the electron-volt (eV)
+
1V
e-
-
 10-4 eV: 3 K cosmic background radiation
(~ 0.25 meV)
 10-2 eV: room temperature (~ 30 meV)
 eV: ionisation energy for light atoms
(13.6 eV in hydrogen)
 103 eV (keV): X-rays in heavy atoms
 106 eV (MeV): mass of electron me = 511
keV/c2
 109 eV (GeV): mass of proton (~1GeV/c2)
 ~ 100 GeV/c2: mass of W, Z
 ~ 200 GeV/c2: mass of top
E = mc
2
 1012 eV (TeV): range of present-day manmade accelerators
 1020 eV: highest energies seen for cosmic
particles
 1028 eV (1019 GeV/c2): ~ Planck mass
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units: mass and energy
 proton mass in kg: 1 / (6 × 1026 ) = 1.7 × 10-27 kg
 ~ 1 GeV/c2 = 109 eV/c2
 highest energy of cosmic particles: 1020 eV ~ 16 J
~ 1.7 × 10-16 kg
 Planck mass: 1028 eV ~ 1.7 × 10-8 kg
 Earth’s mass: : 6 × 1024 kg
 solar mass: 2 × 1030 kg
 our galaxy (Milky Way): 1042 kg
 including dark matter
 observable universe: ~1052 kg
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units: speed and distance
 velocity: speed of light
 ~ 3 * 108 m/s
 ~ 30 cm/ns
 all speeds are approximately equal to the speed of light in astro-particle
physics !
 all particles are “relativistic”
 distance (short): fm (femtometer)
 1 fm = 10-15 m
 sometimes also called “Fermi”
 distance (long):
 lightyear (~ 1016 m)
 parsec (“pc”, ~ 3 lightyears)




diameter of our galaxy: 30 kpc (1021 m)
distance to Andromeda galaxy: ~ 0.8 Mpc (3 * 1022 m)
distance to Virgo cluster: ~ 18 Mpc (7 * 1023 m)
observable universe: ~ 30 Gpc (1027 m)
 related: redshift z = (λ – λ0) / λ0
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parsec:
Living on Earth may be
expensive, but it includes an
annual free trip around the
sun.
Ashleigh Brilliant
1 pc = 3.08567758 × 1016 m
1 AU (astronomical unit) = 149 597 871 km
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relations and constants
 waves
 λ*ν = c
 ω = 2π ν
 quantum mechanics
 h
Planck constant (“Planck’sches Wirkungsquantum”)
 h = h / 2π
 hν = hω = E
 numerical survival kit
 c=h=1
 as long as you need no “usual” units; and then, use:
 c ~ 3 * 108 m/s
 hc ~ 200 MeV * fm
speed of light




Avogadro’s number
~ 6 * 1026 protons / kg (~ GeV / kg)
e ~ 1.6 × 10−19 As (Coulomb)
1 eV ~ 104 K
1 Tesla = 10000 Gauss
Boltzmann’s constant
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“natural” units
 c=h=1
 c ~ length/time
 hc ~ energy*length
speed of light
  length ~ time ~ 1/energy
 1 GeV−1 ~ 10−16 m (=0.1 fm) ~ 10−24 s
 V = -G m1m2 / r
  G ~ m-2
 G = MPlanck-2
gravitational attraction
particles with this mass would at ~proton-size
distance have gravitational energy of ~proton
mass
 MPlanck ~ 1019 GeV
 LPlanck = 1/MPlanck ~ 10-31 m
 tPlanck = 1/MPlanck ~ 10-43 s
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gravitation is weak!
 Vgrav = - G m1m2 / r
= - MPlanck-2 m1m2 / r
~ - 10-38 m1m2 / r
gravitational potential
 Velec = (1 / (4πε0) ) q1e q2e / r
= (e2 / (4πε0 hc) ) q1q2 / r
= α q1q2 / r
~ (1/137) q1q2 / r
~ 10-2 q1q2 / r
electrostatic potential
α = fine structure constant
  Vgrav / Velec ~ 10-38 / 10-2 = 10-36
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Subjects of these lectures
• Standard Model of particle physics
• Particles and radiation in the cosmos
• Expansion of the Universe
• Baryogenesis and nucleosynthesis
• Dark matter
• Dark energy
• Development of structure
• Particle physics in stars and galaxies
C.-E. Wulz
20
20
Standard Model of
Particle Physics
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e-
the electron
Thomson
1897
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e-
p
the proton
Rutherford
1897
1914
1900-1924
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ep
 the photon
Planck
Einstein
Compton
1897
1900-1924
24
The Standard Model of Particle Physics
The Standard Model is a theory of the strong, weak and
electromagnetic forces, formulated in the language of quantum
gauge field theories, and of the elementary particles that take
part in these interactions. It does, however, not include gravity.
Interactions are mediated by the exchange of virtual particles.
Fundamental forces
FORCE
Strong (nuclear)
Weak (radioactive decay)
Electromagnetic
Gravitational
RELATIVE
STRENGTH
RANGE
1
10-15 m
10-6
10-18 m
a (10-2)
infinite
10-38
infinite
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Particle Content of the Standard Model
Matter particles:
Fermions (half-integer spin, s = ½ħ) and their antiparticles.
There are 3 families (generations) of fermion fields, which are identical
except for their masses. Fermions come as leptons and quarks.
Mediator particles:
Gauge bosons (integer spin, s = 1ħ).
There are 3 types of gauge bosons, corresponding to the 3 interactions
described by the Standard Model.
Higgs particle:
Needed to explain that the symmetries of the electroweak theory are
broken to the residual gauge symmetry of QED. Particles that interact
with the Higgs field cannot propagate at the speed of light and acquire
masses through coupling to the Higgs boson (s = 0ħ).
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27
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Gravitational interaction
Long-range force
Only attractive
Gravity is currently described by General Relativity
Different assumptions about the Universe at the macroscopic scale than
those made by quantum mechanics at the microscopic scale
Quantum gravity: theories that attempt to unify gravity with the other
forces (e.g. string theory, loop quantum gravity)
Examples of systems
Black holes
Universe
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Electromagnetic interaction
Long-range force
Much stronger than gravity but effectively shielded over long distances
Repulsive or attractive
Unified description of electricity and magnetism.
Examples of systems:
Atoms (electrons and nuclei)
Electromagnetic waves (light, radio waves)
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Weak interaction
Short-range force
Very weak
Only force that can change the flavor of quarks (e.g. d -> u)
Unified with electromagnetic force
CP violation (charge conjugation, parity not conserved)
Examples of systems
Neutrino interactions
Beta decays
Nuclear fusion
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ee+
the positron
(anti-matter)

p
n
Anderson
Dirac
1897
1914
1900-1924
1932
1937
1947
31
31
Weak interaction
Occurs for example in radioactive b-decay (e.g. 31H  23He) :
Particles without the strong interaction are called LEPTONS
(e.g. electron, muon, neutrino).
The weak interaction is mediated by the INTERMEDIATE
VECTOR BOSONs (W±, Z). These are almost 100x as heavy as
the proton and were detected in 1983 at the experiments UA1
and UA2 at the CERN SppS collider.
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Nobel Prize 1984
C. Rubbia
S. van der Meer
“…for their decisive contributions to the large project which led to the
discovery of the field particles W and Z, communicators of weak interaction”
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W -> en at the UA1 experiment
C.-E. Wulz
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34
34
Z -> e+e- at the UA1 experiment
ino
C.-E. Wulz
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35
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Strong interaction
Short-range force
Very strong
Holds quarks (and nuclei) together
Mediated by gluons
Neither gluons nor quarks are free particles (“Confinement”)
Particles that experience the strong force are called hadrons
Examples of systems
Proton and other atomic nuclei
36
Strong interaction
Gluons and quarks carry a charge (“COLOR”)
QUANTUM CHROMODYNAMICS
Existing particles are colorless, however.

u
u

d
Proton

u
u
d
p
+

d
d

u
d

d
u
d
Neutron
37
Yukawa Theory
Protons and neutrons in nuclei are
attracted by a field. The field quantum
should have properties conform with the
strong interaction, it must therefore be
relatively heavy due to the short range of
the strong force. Yukawa predicted that
its mass should be around 300 me. It was
called meson (mass between me and mp).
Particles with compatible properties were indeed found in
cosmic rays. However, there were discrepancies in the
measurements of masses and lifetimes. In addition, only a
weak interaction with atomic nuclei was found. What was
found were muons.
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• Hess
• Anderson,
Neddermeyer
µ
e-
the muon

p
n
e+
Who ordered
this ?
1897
1914
1900-1924
1937
1932
39
39
Marietta Blau
1894 - 1970
Developed a photographic method based in nuclear
emulsions to study cosmic rays, which led to the
discovery of new particles. With her method the
pion was discovered in 1947 by Cecil Powell et al.,
and much later, in 2000, the tau neutrino. Powell
received the Nobel prize in 1950. Blau should
probably have shared it with with due to her decisive
contributions. She was nominated for the prize twice
by Erwin Schrödinger.
Marietta Blau at
the “Institut für
Radiumforschung”
in Vienna about
1925
40
p+  + + n

600 m
e
Marshak, Bethe:
Muons could be decay products of
heavier particles, which in turn
could be Yukawa’s mesons.
Indeed p mesons (pions) were
identified with Yukawa’s field
quanta. Their decay products, the
muons, do not have strong
interactions. They generally decay
before reaching the surface of the
earth into electrons and two
neutrinos (as the energy of the e is
not constant - 3-body decay):
+  e++ne+n-
-  e-+n-e+n
p
Lattes, Powell, Occhialini, Muirhead (1947)
Pic du Midi Observatory
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1947 it appeared as if the biggest problems in elementary particle physics
were more or less understood, apart from the role of the muon (I. Rabi:
“Who ordered that?”).
The discovery of “Strange Particles” changed the picture …
K+
}
3 cm lead
+
Rochester, Butler:
K0  p   p 
K+  p   p   p 
K+     n etc.
Anderson et al.:
L p
Charged V event:
K+   + + n
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“Strange Particles” were indeed strange as they were produced copiously
(typical time scale 10-23 s), but decayed relatively slowly (time scale 1010 s). This means that production and decay mechanisms are different.
Strange particles are produced by the strong interaction, but they decay
through the weak interaction.
Gell-Mann and Nijishima attributed a property called “Strangeness” to
each particle, which is conserved in the strong interaction, but which is
not conserved in the weak interaction. Therefore strange particles are
only produced in pairs, such as p  + p+  K0 + L Strangeness is not
conserved in their decay, e.g. L  p + p  .
43
Willis Lamb in his Nobel speech 1955:
When the Nobel Prizes were first awarded in 1901, physicists knew
something of just two objects which are now called « elementary
particles»: the electron and the proton. A deluge of other « elementary »
particles appeared after 1930; neutron, neutrino, μ meson, π meson, heavier
mesons, and various hyperons. I have heard it said that « the finder of a
new elementary particle used to be rewarded by a Nobel Prize, but such a
discovery now ought to be punished by a $10,000 fine ».
Something similar was said by Enrico Fermi (to Leon Lederman) in
connection with hadron spectroscopy:
Young man, if I could remember all the names of these particles, I would
have become a botanist.
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The Quark Model
1964: Gell-Mann, Zweig
Elementary building blocks of matter:
45
Quark Model
S: Strangeness (S = - 1 for s quark)
Mesons are made of quark-antiquark pairs, baryons consist of 3 quarks.
46
The eightfold way
K0 (ds)
K+ (us)
Gell-Mann,
Ne’eman (1961)
p0, h
- (uu,dd,ss)
p (du)

K
(su)
p (ud)

-0 K (sd)
Meson octet
47
The eightfold way
n (udd)
p (uud)
S0 (uds)
S (dds)
S (uus)
L (uds)
X (dss)
X0 (uss)
Baryon octet
48
The eightfold way
L (ddd)
L0 (udd)
L (uud)
S*0 (uds)
S* (dds)
X* (dss)
L (uuu)
S* (uus)
X*0 (uss)
L has the same quark content as
the proton, but different energy
level, in analogy to the hydrogen
atom in different levels of
excitation.
W (sss)
Baryon decuplet
Quarks: spin 1/2!
Pauli principle
-> COLOR
(O.W. Greenberg)
49
The Omega Minus
Brookhaven, 1964
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Particles of the Standard Model
Glashow, Salam, Weinberg (1978)
3 families (generations) of quarks and leptons:

n
t
b
t
nt
( ) ( ) ( ) + antiparticles 12 leptons
u
[ ( d ) ( ) ( ) + antiparticles ] x 3 colors 36 quarks
e
ne
c
s
4 mediator particles of the electroweak interaction:
3 intermediate vector bosons (W±, Z) + 1 photon ()
8 mediator particles of the strong interaction:
8 gluons (g)
1 particle to generate mass:
Higgs boson (H)
51