The pion, the mediator of the nuclear force proposed in 1935 by Yukawa. The first particle discovered in the cosmic rays looked like the pion, but was later found to be a lepton, the muon. Experiments at high altitudes on cosmic rays led finally to the discovery of the pion. More experiments soon showed other surprises, the strange particles.

How the properties of the charged pion have been measured.

The discoveries of the charged leptons and of the neutrinos.

How, in 1928, A. M. Dirac found the fundamental relativistic wave equation and the Dirac Lagrangian. Dirac’s fundamental predictions of the existence for each fermion of an antiparticle with the same mass but opposite ‘charges’. How the positron and the antiproton were discovered. The important concepts of helicity and chirality.

The Majorana equation for completely neutral fermions.

The toolbox for subnuclear physics.

How the Lorentz transformations can be found from basic properties of space-time, independently of electromagnetism, as in the usual presentations. Lorentz-invariance is a common property of all the fundamental interactions.

Clear discussion of the fundamental concepts of energy, momentum and mass; of their relations; and of their transformations between reference systems, in particular the laboratory and centre of mass frames.

The sources of high-energy particles, cosmic rays and the different types of accelerators. The progress of our knowledge is fully linked to the experimental ‘art’ of detector design and development. Detectors are made of matter, solid or liquid, or gaseous. The interactions of charged and neutral high-energy particles with matter are described. The principal types of detector and the principles of their operation are introduced.

The fascinating new world inside the nucleon, of quarks, gluons and colour, the nuclear strong force. How quantum chromodynamics (QCD) was discovered: probing the nucleons with scattering experiments and with increasing energy e+e− colliders, where quarks and gluons appear as hadronic jets.

The colour charges are three. Being the gauge of QCD non-Abelian, the gluons, not only the quarks, are ‘coloured’. How colour charges bind three quarks or a quark–antiquark pair forming hadrons that have zero overall colour charges.

The QCD coupling constant runs as the fine-structure constant, but with increasing momentum transfer, it decreases, instead of growing. Quarks become ‘free’, when they are very close to each other. Only a very small fraction of the proton mass is due to the quark masses, 99% being the energy of the colour field. The QCD vacuum, the status of minimum energy, a very active medium indeed, beautiful to study.

When matter first appeared in the universe, in the first microsecond after the Big Bang, quarks and gluons moved freely in a hot ‘soup’, the quark–gluon plasma. It is created in the laboratory in the ultra-relativistic heavy ion colliders and theoretically analysed with lattice QCD

This short chapter touches on the limitations of the SM. The SM does not include gravity, and it does not explain the major components of the mass–energy budget of the universe, dark matter and dark energy, the latter being probably the cosmological constant. CP violation in the quark sector is too small to explain the matter–antimatter asymmetry of the Universe, but, if confirmed, the non-SM CP violation in the neutrino sector might be large enough. The ‘strong CP violation’ problem might be solved with the existence of a very light particle, the axion; experiments are reaching the requested sensitivity. Supersymmetric particles present in some extensions of the SM have been searched for, but not found so far.

The SM contains too many free parameters: the masses of the fermions and of the bosons, and the mixing angles. The masses of the fermions, from neutrinos to the top quark, span 13 orders of magnitude. Why such big difference? Why is mixing small in the quark sector, and large in the neutrino sector? Why do the proton and the electron have exactly equal (and opposite) charges? Why are there just three families? Are there any spatial dimensions beyond the three we know? And so on.

In classical electrodynamics (CED), the most important quantities are the electric and magnetic fields, which directly determine the forces. In quantum electrodynamics (QED), the potentials are the most important quantities; they determine the energy and momentum exchange between the EM field and matter. Gauge invariance, which in CED is just a mathematical curiosity, becomes fundamental in QED, ruling the gauge symmetry that determines the interaction itself.

The Lamb experiment that opened the way is discussed in detail.

Feynman diagrams are graphic representations of mathematical expressions of scattering or decay amplitudes. Without going into the mathematics, we use them to visually suggest the underlying physics. We show how the propagator describes virtual particles, and how uncertainty and relativity principles, joined, imply the existence of antimatter.

The fine-structure constant, which is the dimensionless expression of the electromagnetic charge, depends on the momentum transfer between the probe and the target charge in the scattering experiment we are performing. The ‘running’ of the coupling constants is a property of all the interactions.

The highest precision measurements and theoretical predictions of the magnetic moments of the electron and of the muon. The precision frontier to search for new physics.

The principle of relativity requires that no interaction can propagate instantly. Gravitational waves (GW) must exist, propagating with the same speed as light. The specific characters of GW are predicted by Einstein’s general relativity (GR). After decades of efforts to develop detectors, on 11 February 2016, the LIGO and Virgo Collaboration published the discovery of a GW.

The elements of GR relevant for GW production, propagation and detection. How the GR field, which is the dimensionless metric tensor, differs from the other fundamental fields, which have physical dimensions. The instruments and the discovery. After the first observation, dozens of gravitational signals have been detected, the vast majority from merging black holes and one, on 17 August 2017, from the merger of neutron stars. In this case, electromagnetic signals are expected, and have been detected, providing unique information to astrophysics and to fundamental physics as well. The measurement of the speed of the GW and the establishment of a bound on the mass of the graviton.

Oscillations between members of flavoured, electrically neutral meson pairs and the CP violation are phenomena strictly connected with the mixing. However, CP is more general, having been observed also in the decay of charged mesons.

CP violation was first observed in the neutral K system. We see the states of definite strangeness, those of definite CP and those with definite mass and lifetime. The oscillation between the former states, the mathematical expressions and the experimental evidence.

The oscillations and CP violation in the B0 system, and the beautiful experimental results obtained at dedicated high-luminosity electron–positron colliders, the ‘beauty factories’. Beauty physics at the dedicated experiment LHCb at LHC, in particular for the B0, that is not accessible to beauty factories. Examples of CP violation in B0. The recent discovery of CP violation in the charm sector.

How the many different measurements can be put together to test the SM with the unitary triangle.