Chapter 9
Symmetry Violations and Quark Flavour
Physics
Konrad Kleinknecht and Ulrich Uwer
9.1 Introduction
9.1.1 Matter–Antimatter Asymmetry in the Universe
One of the surprising facts in our present understanding of the development of
the Universe is the complete absence of “primordial” antimatter from the Big
Bang about 13.7 billion years ago. The detection of charged cosmic-ray particles
by magnetic spectrometers borne by balloons, satellites, and the space shuttle
has shown no evidence for such primordial (high-energy) antibaryons; nor has
the search for gamma rays from antimatter–matter annihilation yielded any such
observation. In the early phases of the expanding Universe, a hot (10 32 K) and
dense plasma of quarks, antiquarks, leptons, antileptons and photons coexisted in
equilibrium. This plasma expanded and cooled down, and matter and antimatter
could recombine and annihilate into photons. If all interactions were symmetric with
respect to matter and antimatter, and if baryon and lepton numbers were conserved,
then all particles would finally convert to photons, and the expansion of the Universe
would shift the wavelength of these photons to the far infrared region.
This cosmic microwave background radiation was indeed observed by Penzias
and Wilson in 1965 [1], and its wavelength distribution corresponds exactly to
Planck black-body radiation at a temperature of 2.73 K (see Fig. 9.1). The density
of this radiation is about 5 × 10 2 photons/cm 3 .
K. Kleinknecht
Johannes Gutenberg-Universität, Mainz, Germany
Ludwig-Maximilians-Universität, München, Germany
U. Uwer ()
Heidelberg University, Heidelberg, Germany
e-mail: uwer@physi.uni-heidelberg.de
© The Author(s) 2020
H. Schopper (ed.), Particle Physics Reference Library,
https://doi.org/10.1007/978-3-030-38207-0_9
519
Symmetry Violations and Quark Flavour
Physics
Konrad Kleinknecht and Ulrich Uwer
9.1 Introduction
9.1.1 Matter–Antimatter Asymmetry in the Universe
One of the surprising facts in our present understanding of the development of
the Universe is the complete absence of “primordial” antimatter from the Big
Bang about 13.7 billion years ago. The detection of charged cosmic-ray particles
by magnetic spectrometers borne by balloons, satellites, and the space shuttle
has shown no evidence for such primordial (high-energy) antibaryons; nor has
the search for gamma rays from antimatter–matter annihilation yielded any such
observation. In the early phases of the expanding Universe, a hot (10 32 K) and
dense plasma of quarks, antiquarks, leptons, antileptons and photons coexisted in
equilibrium. This plasma expanded and cooled down, and matter and antimatter
could recombine and annihilate into photons. If all interactions were symmetric with
respect to matter and antimatter, and if baryon and lepton numbers were conserved,
then all particles would finally convert to photons, and the expansion of the Universe
would shift the wavelength of these photons to the far infrared region.
This cosmic microwave background radiation was indeed observed by Penzias
and Wilson in 1965 [1], and its wavelength distribution corresponds exactly to
Planck black-body radiation at a temperature of 2.73 K (see Fig. 9.1). The density
of this radiation is about 5 × 10 2 photons/cm 3 .
K. Kleinknecht
Johannes Gutenberg-Universität, Mainz, Germany
Ludwig-Maximilians-Universität, München, Germany
U. Uwer ()
Heidelberg University, Heidelberg, Germany
e-mail: uwer@physi.uni-heidelberg.de
© The Author(s) 2020
H. Schopper (ed.), Particle Physics Reference Library,
https://doi.org/10.1007/978-3-030-38207-0_9
519