Speaker
Description
Nature has two sources of mass. One is the Higgs boson, which is responsible for every mass scale that appears explicitly in the Standard Model Lagrangian. The Higgs was discovered at CERN in 2012; and with that discovery, the Standard Model became complete.
However, in connection with everyday matter, the material which constitutes our computers and ourselves, the Higgs produces little more than 1% of the mass. Some agent, far more powerful than the Higgs mechanism, is responsible for the remaining 99%, i.e. for the vast bulk of visible mass in the Universe. This is the phenomenon of emergent hadron mass (EHM) and it is characterized by the size of the proton’s mass, mp ≈ 1 GeV, which is roughly 2000-times the size of the electron mass. Uncovering the source and revealing the impacts of EHM stand as some of the greatest challenges in modern science.
Within the Standard Model, the proton is supposed to be described by quantum chromodynamics (QCD), a Poincaré-invariant local gauge theory of gluons (gauge fields) and quarks (matter fields); but no one can really be certain because, even fifty years after its formulation, there is no solution to QCD. Of course, there is a perturbative definition of the theory, valid at high energies. However, a perturbative approach cannot be used to compute any bound-state mass or radius, etc. And there is another challenge; namely, the pion. Discovered more than 70 years ago, the Standard Model describes the pion as a bound-state of a quark+antiquark pair. It is a hadron, like the proton; yet, the pion is atypically light, with a mass on the same scale as the μ lepton. It is a rare thing for a single theory in Nature to produce such a large disparity in masses from “nothing”: in the perturbative formulation of QCD, the gluons are massless and the quarks/antiquarks in the pion and proton possess masses that are less-than 1% of mp.
Solving the riddle posed by EHM is today the primary focus of experiments in nuclear and particle physics at the world’s leading accelerator facilities and the impetus behind construction of an electron ion collider in the USA and planning for such a facility in China. This presentation will describe a paradigm for understanding EHM within the Standard Model; and explain how a synergistic effort in experiment, phenomenology, and theory is capable of validating the picture. The sketch begins with the emergence of a mass for gluons, QCD’s gauge bosons – something that many imagined to be impossible; and culminates with an explanation of how deep ploughing structural studies of the pion and kaon, Nature’s lightest hadrons, may deliver answers to the profound questions that probe for the origin of 99% of the visible mass in the Universe.