Evolution of collisions and QGP

Extreme density and temperature allow the transition for the ordinary matter to the deconfined phase, in which quarks and gluons are free from their parent hadrons and they can interact with each other. Such conditions can be reached by ultrarelativistic heavy ion collisions. Different phases of evolution of the matter are predicted according to theoretical … Continue reading Evolution of collisions and QGP

Lattice QCD calculations

Due to the asymptotic freedom, the coupling constant of QCD is a diminishing function as the energy scale increases according to the following equation, already stated (*): . Therefore, the high-energy or equivalently the short-distance behavior can be described by a perturbative expansion, but a perturbative approach to the QCD fails at large distances where the begins to … Continue reading Lattice QCD calculations

The QCD phase diagram

A phase diagram aims to describe the behaviour of matter at different conditions depending for example from variables such as pressure and temperature. In the QCD phase diagram the interactions between particles are ruled by the quantum chromodynamics. The QCD phase transition scheme, in fact, is yet under studies and one of the targets of … Continue reading The QCD phase diagram

Symmetries of the QCD

An important feature of the QCD is the conspicuous amount of symmetries of its lagrangian. First and foremost, its lagrangian is invariant under local gauge transformations, i.e. one can redefine the quark fields indipendently at every point in the space-time, without changing the physical content of the theory. This determines a number of implications in … Continue reading Symmetries of the QCD

Colour confinement

The term confinement indicates that coloured free particles do not exist in Nature. Besides valence quarks, a hadron contains a population of more quarks and gluons. From the (b) side of the Figure in the previous post (*) it is possible to infer that the strong interaction between two quarks enhances with the increasing of their … Continue reading Colour confinement

Couplings and asymptotic freedom

Each of the four fundamental interactions can be characterized by a dimensionless parameter expressed in terms of universal constants, the coupling constant. In the lagrangian of strong interactions, the coupling constant is parameterized by the gauge coupling parameter,, giving in natural units . However, in a general field theory, the effective coupling constant is not a constant, … Continue reading Couplings and asymptotic freedom

Ultrarelativistic heavy-ion collision experiments

Why to make particles collide? Okay, if you're on this website you probably do not need to know this and you already have an idea of the physics studied at the and by other particles accelerator experiments. Strongly interacting particles at very high temperatures and energy densities compose a new state of matter called quark-gluon … Continue reading Ultrarelativistic heavy-ion collision experiments