Simulations of QCD on ultrafine grids

Abstract

Fully realistic numerical calculations of the effects of the strong force are now possible using the techniques of lattice QCD. This method enables us to simulate theinteractions between subatomic particles called quarks and gluons at distance scales of a tenth of a femtometre and, from this, build up an accurate picture of the quark bound states called hadrons. Hadrons can be studied experimentally whereas freequarks are never seen, so the linkage between the two must be made by theory. In this way lattice QCD is becoming established as a precision tool for strong interactionphysics and for testing the Standard Model against experiment. Bottom quarks, being much heavier than the light up, down and strange quarks are inprinciple sensitive to much shorter distance scales if they are to be treated fully relativistically. Very fine lattices offer a huge numerical challenge but tests against experiment for hadrons made of these quarks are particularly important, becausethey may offer a window into Beyond the Standard Model physics. Here we propose to perform lattice QCD calculations on ultrafine lattices with a spacing of three hundredths of a femtometre and including the effect of sea up, down and strange quarks. This will allow analysis of fully relativistic bottom quarks for the first time and comparison both to experiment and to effective theories for heavy quarks that have been used up to now. It will open the way for more accurate calculations for hadrons made of bottom quarks in the future.