Lattice QCD Study of Hadron Excitations Using All-to-All Quark Propagators with Improved Variance Reduction

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The masses of excited hadron resonances will be evaluated using computer simulations of quarks and gluons on a space-time lattice. These resonance states are being studied in several experiments, such as in the Hall B N* program and the GlueX experiment in Hall D at the Thomas Jefferson National Accelerator Facility. Such systems should also provide a wealth of information to help us understand the physics of quark confinement and hadron formation in quantum chromodynamics, the theory of the strong interactions and one of the fundamental forces of Nature. Understanding the physics of confining gluons is an important intellectual challenge; in fact, it is one of the seven so-called Millenium Prize problems announced by the Clay Mathematics Institute of Cambridge, Massachusetts. One of the most reliable means of investigating such systems is using Markov-chain Monte Carlo computations with quark and gluon fields defined on a space-time lattice. In the past, such calculations have been done with unrealistically large quark masses due to computational limitations. Current calculations have reduced the quark masses to nearly their physical values, causing the need to incorporate multi-hadron operators into the computations to become crucial. A new methodology for dealing with multi-hadron operators has been developed in the recent past, and this proposal plans to apply the new methodology to carry out the first calculations of the hadron masses using both single and multi-hadron operators. The proposed research incorporates the participation of two graduate students, and possibly one or more undergraduate students, whose educations will be enhanced not only by involvement in scientific projects at the forefront of nuclear theory, but also with high-technology training in the use of state-of-the-art parallel computing resources. The broader impacts of the proposed activities will be strengthened by posting results with simplified background information on publicly accessible web pages.