Topic: Origin of Visible Mass in the Universe
Speaker: Prof. Craig D. Roberts
Coordinates: Classroom 2103, 16:00, Friday, Mar. 10
Abstract: Nuclear and particle physics communities, in China and internationally, are operating, building, and planning an array of high-luminosity, high-energy facilities. The goal is to discover the source of the mass of visible material in the Universe. That matter is chiefly built from the nuclei that can be found on Earth, themselves composed of neutrons and protons (nucleons) bound together by the exchange of π-mesons (pions). Thus, some of the mass is generated by the much-celebrated Higgs boson via couplings to matter in the Standard Model (SM) Lagrangian. However, concerning nucleons and pions, the Higgs-generated mass component is only a small part. Regarding the nucleon–a system with mass mN ≈ 940 MeV, yet built from three light valence quarks, ∑q=light quarks mq ≈ 9MeV, Higgs boson couplings are directly responsible for ＜1% of its mass: the remainder has its origin in some other mechanism. The story for the pions, each composed of a light quark and a light antiquark, is very subtle because pions are the SM's (would-be) Nambu-Goldstone bosons, whose emergence can be traced to the same source as 99% of the nucleon mass. This “other”, dominant source is called emergent hadron mass (EHM); and elucidating its origins and impacts may be viewed as the principal challenge in strong interaction physics for the next generation. This presentation will sketch a contemporary picture of how science may understand EHM, the origin of 99% of visible mass in the Universe.