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Major Breakthrough in Lattice Quantum Chromodynamics


Prof. Ian Shipsey

In the February 12 issue of Nature featured an article by Purdue Physics Professor Ian Shipsey on a major breakthrough in Lattice Quantum Chromodynamics, a method that uses Teraflop scale computing to calculate the strong nuclear force that binds the sub atomic particles known as quarks into protons and neutrons and a host of heavier particles produced at particle accelerators.

The theory of fundamental particles called the standard model is able to account for all of the currently observed particles and their interactions. However despite its success it leaves many questions unanswered. For example, although the observable universe is made of matter, and there is no evidence for significant quantities of antimatter, equal amounts of both should have been created in the Big Bang. When matter and anti-matter meet they annihilate each other: if a small asymmetry did not exists at the time of the Big Bang there would be no matter in the universe today. Physicists speculate that new physical phenomena are responsible for the asymmetry. One of the most sensitive ways to search for these phenomena is to carefully measure the pattern of the radioactive disintegration rates of heavy quarks. The standard model constrains but does not determine the pattern while new phenomena can alter it significantly. But for almost forty years the pattern has been obscured because the binding effect of the strong force modifies the disintegration rates of the quarks and the correction factors to allow for it have been impossible to calculate reliably. In recent work Lattice Quantum Chromodynamics practitioners have succeeded in calculating nine previously measured binding effects with high precision for the first time.

The next step is to predict the binding effects of bound states including charm quarks before the CLEO-c experiment at Cornell University, of which Shipsey is the co-Spokesperson, can measure them. If calculations and experiments agree, it will be a powerful validation of the technique, which can then be confidently applied to data from many other current and future experiments. The success of the lattice approach is also relevant to other areas of particle physics, in nuclear physics and in astrophysics. If all goes well physicists may soon learn about the phenomena that give rise to the asymmetry between matter and antimatter that permits us to exist.