Hadron Physics and QCD: Just the Basic Facts

TL;DR

This paper reviews how Quantum Chromodynamics (QCD) explains the origin of most visible mass in the universe through phenomena like confinement and dynamical chiral symmetry breaking, highlighting recent theoretical and experimental insights.

Contribution

It clarifies the roles of confinement and DCSB in mass generation and challenges previous notions about condensates, advancing understanding of QCD's fundamental mechanisms.

Findings

DCSB generates over 98% of the universe's visible mass.

Confinement ensures condensates are contained within hadrons.

Observable consequences of confinement and DCSB are actively being measured.

Abstract

With discovery of the Higgs boson, the Standard Model of Particle Physics became complete. Its formulation is a remarkable story; and the process of verification is continuing, with the most important chapter being the least well understood. Quantum Chromodynamics (QCD) is that part of the Standard Model which is supposed to describe all of nuclear physics and yet, almost fifty years after the discovery of quarks, we are only just beginning to understand how QCD moulds the basic bricks for nuclei: pious, neutrons, protons. QCD is characterized by two emergent phenomena: confinement and dynamical chiral symmetry breaking (DCSB), whose implications are extraordinary. This contribution describes how DCSB, not the Higgs boson, generates more than 98% of the visible mass in the Universe, explains why confinement guarantees that condensates, those quantities that were commonly viewed as constant mass-scales that fill all spacetime, are instead wholly contained within hadrons, and elucidates a range of observable consequences of confinement and DCSB whose measurement is the focus of a vast international experimental programme.