Where does the mass of the proton? 95% of the energy of quarks and gluons, replied physicists of the Center for Theoretical Physics in Marseille (1). Led from the standard model which describes the interactions between elementary particles, their calculations show that the mass of the proton due mainly to the energy carried by all these small "elements" that are the quarks and gluons, through the famous formula Einstein's E = mc2. This feat confirmed the validity of a theory to portray the strong interactions between particles. Published in Science on 21 November 2008, this work has been achieved thanks to supercomputers among the most powerful in the world. They can consider the arrival of a

new theory in fundamental physics beyond the current model, with potential discoveries in the field of weak interactions of quarks. In the nuclei of atoms are protons and neutrons. They are themselves made of quarks and gluons, kinds of small sub-fundamental structures. However, the mass of gluons is zero. And, contrary to what one might expect, the mass of the quarks that make up a proton is only 5% of the mass of the latter. Where therefore the remaining 95%? A team of physicists French, German and Hungarian just to prove that these result 95% of energy due to movements of quarks and gluons, and their interactions. Following a mass energy is a somewhat confusing result, translated yet by the famous Einstein formula E = mc2 out the equivalence between mass and energy. So far hypothesis, this result is for the first time corroborated. The researchers, led by Laurent in France Lellouch, CNRS research director at the Center for Theoretical Physics, relied on more than twenty years of research by physicists around the world. Based on the equations of quantum chromodynamics (2), ie the theory that describes the strong interactions, they managed to calculate the mass of protons, neutrons and other particles of the same type (3). Result, the masses obtained by calculation are in excellent agreement with those measured experimentally. Researchers confirm that the standard model is correct to describe the origin of the mass of particles and therefore more than 99% of the visible universe, including the Sun, Earth, ourselves and all objects surround us. To achieve their ends, the researchers used an approach where space-time is seen as a crystal in four dimensions, composed of sites spaced along rows and columns. Their main challenge was to arrive at a solution that suits our continuous space-time, while controlling all sources of uncertainties related to calculations on the network. In practical terms, this marks the maturing of numerical methods relevant to the study of interaction. It should play a fundamental role in the new era of physics that opens with the Large Hadron Collider. Indeed, check the model of interaction could help to identify new effects associated with weak interactions of quarks are masked by the strong interactions. This calculation is one of the largest numerical to date. A true performance that has required the resources of Blue Gene supercomputers of the Institute of development and resources in scientific computing (IDRIS) of CNRS and the Forschungszentrum Jülich, but also farms calculation of the University of Wuppertal and Central Theoretical Physics in Marseille. otes: (1) CNRS / University of the Mediterranean / University of Provence / University of Toulon (2) According to this standard model theory, quarks are confined in the particles they are and have a property called "color" blue, green or red, similar to the electric charge of electrostatic force. (3) This includes "light hadrons", which are particles composed of quarks and gluons (such as protons and neutrons). References: Ab-initio Determination of Light Hadron Masses. S. Dürr, Z. Fodor, J. Frisian, C. Hoelbling, R. Hoffmann, SD Katz, S. Krieg, T. Kurth, L. Lellouch, T. Lippert, KK Szabo, G. Vulvert. Science. November 21 2008.