2nd Workshop on The Proton Mass; At the Heart of Most Visible Matter

The subject of understanding the proton mass in terms of its constituents, as naive as it may sound, is of paramount importance to the field of Hadronic/Nuclear physics. The emergence of hadron masses from quarks and gluons is one of the most fascinating subjects in coherence physics and a cornerstone of QCD. In a tour de force, calculations of the baryon mass spectrum in lattice QCD has been successfully carried out, however developing the intuition of how the mass of each hadron emerges finds many pathways as noticed in the workshop held at Temple University in March of 2016 ( https://phys.cst.temple.edu/~meziani/proton-mass-workshop-2016/ ). How the mass of the proton emerges from its constituents is a natural and familiar question shared by many colleagues from other areas of physics where the mass of key systems is commonly described in terms of the mass of their constituents. While the mass of a hadron in QCD is an emergent phenomenon it is nevertheless important to cast our answer in terms of the energy/mass of the constituents in order to facilitate communication with the public in a familiar way. This is now crucial as the nuclear physics community in the U.S. and elsewhere embarks in the justification of building ever larger experimental facilities in the quest of understanding QCD and the structure of hadronic/nuclear matter from basic principles. In the U.S. such a facility is the electron ion collider (EIC) project which has been endorsed by the US nuclear physics community as the next construction project after the completion of FRIB. The science justification of this project will soon undergo an evaluation by a committee from the US National Academy of Science to cement its raison d'être. The quality and importance of the problems addressed by Nuclear physics, especially those involving a true understanding of the inner workings of QCD need to identify connections and pathways to others area of physics. The "mass of the proton" is one theme amenable to emphasize what remain to be understood in QCD as a worthwhile goal that can be appreciated by the wider physics community not just the practitioners of hadronic/nuclear physics.