Argonne National Laboratory

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Experimental Probes into the Essence of Matter

Physics Division Colloquium
Ralf Gothe, University of South Carolina
May 3, 2013 11:00AM to 12:00PM
Building 203
All visible matter that surrounds us is made of atoms, i.e. electrons and nuclei, and the latter are made of nucleons, which finally are made of quarks and gluons. Contrary to the recent discussions in the news, the Higgs boson, frequently called the God Particle, is not responsible for the generation of all mass. In fact, if it exists, it only generates the mass of the elementary quarks and electrons amounting to less than 2% of the total visible mass. Somewhat counter intuitively, the biggest part of the mass is not ab initio mass at all but energy, or more physically, the energy of the strong fields that bind the quarks into nucleons.

The mass-energy equivalence, E=mc2, formulated by Einstein allows us to understand that the more than 98% of the weight you see when you step on a scale is nothing, or more precisely vacuum filled solely with field energy. How Quantum Chromodynamics (QCD) generates these strong fields, and hence most of the mass, is still an unsolved problem that can be uniquely addressed by experiments at the Thomas Jefferson National Accelerator Facility (JLab) in Virginia. Pushing the idea of an electron microscope to higher and higher energies allows us to investigate nucleons and their excitations with higher and higher resolution via electron scattering experiments carried out at JLab.

A close collaboration of theorists and experimentalists has already started to shed light on some of the remaining, overarching, and most important problems of QCD, as defined by Nuclear Science Advisory Committee's Long-Range Plan, by providing new insights into the structure of the nucleon, the transition between meson/baryon and quark/gluon degrees of freedom, the nature of confinement, and the essence of mass.