Astroparticle Physics Claudia-Elisabeth Wulz Institute of High Energy Physics, Vienna TU Vienna c/o CERN, Geneva Part 1 Winter semester 2013/2014

1 Bibliography D. Perkins: Particle Astrophysics (Second edition, 2011) C. Grupen: Astroparticle physics (2010)

2 C.-E. Wulz2 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 2

3 C.-E. Wulz 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

4 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 ( ) Birth of neutrino astroparticle physics: Neutrinos from sun studied in Homestake mine (1967) 4

Victor Hess with C. Anderson 5

6 Result: Measured flux: 2.56 SNU Expected: 8.5 SNU e + 37 Cl  37 Ar + e - Homestake- Experiment 610t C 2 Cl 4 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.

7 p + p  2 H + e + + e (pp) MeV p + e - + p  2 H + e (pep) 1.4 MeV 2 H + p  3 He +  3 He + 3 He  4 He + 2p 3 He + 4 He  7 Be +  3 He + p  4 He + e + + e (hep) MeV 7 Be + e -  7 Li + e (Be) 0.38, 0.86 MeV 7 Li + p  4 He + 4 He 7 Be + p  8 B +  8 B  8 Be + e + + e (B) MeV 8 Be *  4 He + 4 He e production processes Energies Solar Neutrinos Energy spectrum of solar neutrinos

Special relativity and basic units 8

9 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 !

10 relativistic kinematics 1 v 1/γ

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e-e- 1V the electron-volt (eV)  eV: 3 K cosmic background radiation (~ 0.25 meV)  eV: room temperature (~ 30 meV)  eV: ionisation energy for light atoms (13.6 eV in hydrogen)  10 3 eV (keV): X-rays in heavy atoms  10 6 eV (MeV): mass of electron m e = 511 keV/c 2  10 9 eV (GeV): mass of proton (~1GeV/c 2 )  ~ 100 GeV/c 2 : mass of W, Z  ~ 200 GeV/c 2 : mass of top  eV (TeV): range of present-day man- made accelerators  eV: highest energies seen for cosmic particles  eV (10 19 GeV/c 2 ): ~ Planck mass units: energy and mass

13  proton mass in kg: 1 / (6 × ) = 1.7 × kg  ~ 1 GeV/c 2 = 10 9 eV/c 2  highest energy of cosmic particles: eV ~ 16 J ~ 1.7 × kg  Planck mass: eV ~ 1.7 × kg  Earth’s mass: : 6 × kg  solar mass: 2 × kg  our galaxy (Milky Way): kg  including dark matter  observable universe: ~10 52 kg units: mass and energy

14 units: speed and distance  velocity: speed of light  ~ 3 * 10 8 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 = m  sometimes also called “Fermi”  distance (long):  lightyear (~ m)  parsec (“pc”, ~ 3 lightyears)  diameter of our galaxy: 30 kpc (10 21 m)  distance to Andromeda galaxy: ~ 0.8 Mpc (3 * m)  distance to Virgo cluster: ~ 18 Mpc (7 * m)  observable universe: ~ 30 Gpc (10 27 m)  related: redshift z = (λ – λ 0 ) / λ 0

15 parsec: Living on Earth may be expensive, but it includes an annual free trip around the sun. Ashleigh Brilliant 1 pc = × m 1 AU (astronomical unit) = km

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17 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 * 10 8 m/s speed of light  hc ~ 200 MeV * fm  ~ 6 * protons / kg (~ GeV / kg) Avogadro’s number  e ~ 1.6 × 10 −19 As (Coulomb)  1 eV ~ 10 4 K Boltzmann’s constant  1 Tesla = Gauss

18 “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 m 1 m 2 / rgravitational attraction  G ~ m -2  G = M Planck -2 particles with this mass would at ~proton-size distance have gravitational energy of ~proton mass  M Planck ~ GeV  L Planck = 1/M Planck ~ m  t Planck = 1/M Planck ~ s

19 gravitation is weak!  V grav = - G m 1 m 2 / rgravitational potential = - M Planck -2 m 1 m 2 / r ~ m 1 m 2 / r  V elec = (1 / (4πε 0 ) ) q 1 e q 2 e / r electrostatic potential = (e 2 / (4πε 0 hc) ) q 1 q 2 / r = α q 1 q 2 / r α = fine structure constant ~ (1/137) q 1 q 2 / r ~ q 1 q 2 / r  V grav / V elec ~ / =

20 C.-E. Wulz20 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 20

21 Standard Model of Particle Physics 21

the electron e-e- Thomson

the proton e-e Rutherford p

the photon  Planck Einstein Compton e-e- p

25 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 FORCERELATIVE STRENGTH RANGE Strong (nuclear) m Weak (radioactive decay) m Electromagnetic  (10 -2 ) infinite Gravitational infinite

26 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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28 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

29 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)

30 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

the positron (anti-matter) e-e  1914 e+e+ p 1932 n Anderson Dirac

32 Occurs for example in radioactive  -decay (e.g. 3 H  3 He) : LEPTONS Particles without the strong interaction are called LEPTONS (e.g. electron, muon, neutrino). INTERMEDIATE VECTOR BOSONs 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

33 “…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

34 C.-E. Wulz34 W -> e at the UA1 experiment 34

35 C.-E. Wulz35 ino Z -> e + e - at the UA1 experiment 35

36 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

37 Gluons and quarks carry a charge (“COLOR”) QUANTUM CHROMODYNAMICS Existing particles are colorless, however. u d  Proton u  d u d  u   ududd  + Neutron d Strong interaction

38 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 m e. It was called meson (mass between m e and m p ). 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.

the muon e-e  1914 µ p 1932 n 1937 Hess Anderson, Neddermeyer e+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 Blau should probably have shared it with with due to her decisive contributions. She was nominated for the prize twice by Erwin Schrödinger

41  +   + +  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  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 + + e +    -  e - + e +  - -  600  m  e

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+K+ ++ 3 cm lead } Charged V event: K +   + +  Rochester, Butler: K 0     K +       K +      etc. Anderson et al.:       

43 “Strange Particles” were indeed strange as they were produced copiously (typical time scale s), but decayed relatively slowly (time scale 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. “Strangeness” 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   +  +  K  +  Strangeness is not conserved in their decay, e.g.   p  +  .

44 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.

45 The Quark Model Elementary building blocks of matter: 1964: Gell-Mann, Zweig

46 Quark Model Mesons are made of quark-antiquark pairs, baryons consist of 3 quarks. S: Strangeness (S = - 1 for s quark)

47 Meson octet - -   (ud)   (sd) K 0 (ds)K + (us)   (du)    (uu,dd,ss)   (su) Gell-Mann, Ne’eman (1961) The eightfold way

48 n (udd)p (uud)   (dds)   (uus)   (uds)  (uds)   (dss)   (uss) Baryon octet The eightfold way

49   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   (ddd)   (udd)   (uud)   (uuu)   (dds)   (dss)   (sss)   (uss)   (uus)   (uds) Quarks: spin 1/2! Pauli principle -> COLOR (O.W. Greenberg) The eightfold way

50 The Omega Minus Brookhaven, 1964

51 Glashow, Salam, Weinberg (1978) 3 families (generations) of quarks and leptons: e ()  ()  () + antiparticles 12 leptons udud () cscs () tbtb () [ + 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