Astroparticle Physics

Claudia-Elisabeth WulzInstitute of High Energy Physics, ViennaTU Viennac/o CERN, Geneva

Part 1Winter semester

2013/2014

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Bibliography

D. Perkins: Particle Astrophysics (Second edition, 2011)

C. Grupen: Astroparticle physics (2010)

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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

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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

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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 Hess1883 - 1964

1936with C. Anderson

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Result:Measured flux: 2.56 SNUExpected: 8.5 SNU ne + 37Cl 37Ar + e-

Homestake-Experiment

610t C2Cl4

Homestake and the solar neutrino deficitBeginning 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.

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p + p 2H + e+ + ne (pp) 0 - 0.4 MeV

p + e- + p 2H + ne (pep) 1.4 MeV2H + p 3He + 3He + 3He 4He + 2p3He + 4He 7Be + 3He + p 4He + e+ + ne (hep) 1.5 - 17 MeV7Be + e- 7Li + ne (Be) 0.38, 0.86 MeV7Li + p 4He + 4He7Be + p 8B + 8B 8Be + e+ + ne (B) 0 - 15 MeV8Be* 4He + 4He

ne production processesEnergies

Solar Neutrinos

Energy spectrum of solar neutrinos

Special relativityand

basic units

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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

1

v 1/γ

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+

-e-

1V

the electron-volt (eV)

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

1012 eV (TeV): range of present-day man-made accelerators

1020 eV: highest energies seen for cosmic particles

1028 eV (1019 GeV/c2): ~ Planck mass

units: energy and mass

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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

units: mass and energy

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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 speed of light hc ~ 200 MeV * fm

~ 6 * 1026 protons / kg (~ GeV / kg) Avogadro’s number e ~ 1.6 × 10−19  As (Coulomb) 1 eV ~ 104  K Boltzmann’s constant 1 Tesla = 10000 Gauss

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“natural” units c = h = 1

c ~ length/time speed of light hc ~ energy*length

length ~ time ~ 1/energy 1 GeV−1 ~ 10−16 m (=0.1 fm) ~ 10−24 s

V = -G m1m2 / r gravitational attraction G ~ m-2

G = MPlanck-2

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 gravitational potential = - MPlanck

-2 m1m2 / r

~ - 10-38 m1m2 / r

Velec = (1 / (4πε0) ) q1e q2e / r electrostatic potential = (e2 / (4πε0 hc) ) q1q2 / r = α q1q2 / r α = fine structure constant ~ (1/137) q1q2 / r ~ 10-2

q1q2 / r

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

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Standard Model of Particle Physics

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1897

the electrone-

Thomson

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1897

the proton

e-

1900-1924

1914

Rutherfordp

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1897

the photon

1900-1924

Planck Einstein

Compton

e-

p

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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 forcesFORCE RELATIVE

STRENGTHRANGE

Strong (nuclear) 1 10-15 m

Weak (radioactive decay) 10-6 10-18 m

Electromagnetic a (10-2) infinite

Gravitational 10-38 infinite

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Particle Content of the Standard ModelMatter 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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Gravitational interaction

Long-range forceOnly attractiveGravity is currently described by General RelativityDifferent assumptions about the Universe at the macroscopic scale than those made by quantum mechanics at the microscopic scaleQuantum gravity: theories that attempt to unify gravity with the other forces (e.g. string theory, loop quantum gravity)

Examples of systemsBlack holesUniverse

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Electromagnetic interaction

Long-range forceMuch stronger than gravity but effectively shielded over long distancesRepulsive or attractiveUnified description of electricity and magnetism.

Examples of systems:Atoms (electrons and nuclei)Electromagnetic waves (light, radio waves)

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Weak interactionShort-range forceVery weakOnly force that can change the flavor of quarks (e.g. d -> u) Unified with electromagnetic forceCP violation (charge conjugation, parity not conserved)

Examples of systemsNeutrino interactionsBeta decaysNuclear fusion

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1897

the positron (anti-matter)

e-

1900-1924

1914

e+

p

1932

n

1937

1947

Anderson

Dirac

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Occurs for example in radioactive b-decay (e.g. 3H 3He) :

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.

1 2

Weak interaction

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“…for their decisive contributions to the large project which led to the discovery of the field particles W and Z, communicators of weak interaction”

Nobel Prize 1984

C. Rubbia S. van der Meer

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W -> en at the UA1 experiment

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inoZ -> e+e- at the UA1 experiment

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Strong interactionShort-range forceVery strongHolds quarks (and nuclei) togetherMediated by gluonsNeither gluons nor quarks are free particles (“Confinement”)Particles that experience the strong force are called hadrons

Examples of systemsProton and other atomic nuclei

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Gluons and quarks carry a charge (“COLOR”) QUANTUM CHROMODYNAMICS

Existing particles are colorless, however.

u d ÞProton

uÜ

d u d ÞuÜ »» »»u d u dd

p+ Neutron

d

Strong interaction

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Yukawa TheoryProtons 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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the muon

e-

1900-1924

1914

µp

1932

n

1937

• Hess• Anderson, Neddermeyer

e+

Who ordered this ?

Marietta Blau

Marietta Blau at the “Institut für Radiumforschung” in Vienna about 1925

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.

1894 - 1970

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p+ + + n

Lattes, Powell, Occhialini, Muirhead (1947)Pic du Midi Observatory

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-+ne+n

--

p

600 m

e

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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}Charged V event:

K+ + + n

Rochester, Butler:K0 p p

K+ p p p

K+ n etc.

Anderson et al.:L p

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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 10-

10 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 .

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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

Elementary building blocks of matter:

1964: Gell-Mann, Zweig

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Quark Model

Mesons are made of quark-antiquark pairs, baryons consist of 3 quarks.

S: Strangeness (S = - 1 for s quark)

48Meson octet

- -

p (ud)

K0 (sd)

K0 (ds) K+ (us)

p (du)p0, h

(uu,dd,ss)

K (su)

- -

- -

- - -

-

Gell-Mann,Ne’eman (1961)

The eightfold way

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n (udd) p (uud)

S (dds) S (uus)S0 (uds)

L (uds)

X (dss) X0 (uss)

Baryon octet

The eightfold way

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L has the same quark content as the proton, but different energy level, in analogy to the hydrogen atom in different levels of excitation.

Baryon decuplet

L (ddd) L0 (udd) L (uud) L (uuu)

S* (dds)

X* (dss)

W (sss)

X*0 (uss)

S* (uus)S*0 (uds)

Quarks: spin 1/2!Pauli principle-> COLOR(O.W. Greenberg)

The eightfold way

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The Omega Minus

Brookhaven, 1964

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Glashow, Salam, Weinberg (1978)3 families (generations) of quarks and leptons:

ene

( ) n

( ) tnt

( ) + antiparticles 12 leptons

ud( ) c

s( ) tb( )[ + antiparticles ] x 3 colors 36 quarks

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)

Particles of the Standard Model