Particle Physics Phenomenology from Lattice QCD
Gregory Kilcup, The Ohio State University
Rajan Gupta, Los Alamos National Laboratory
Stephen Sharpe, University of Washington
Phillipe de Forcrand, Federal Institute of Technology (ETH),
Zürich
1998 Annual Report
Grand Challenge Projects
Particle Physics Phenomenology from Lattice QCD
Gregory Kilcup, The Ohio State University
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Research ObjectivesTo compute the theoretical rates for certain weak interaction decay modes of elementary particles, thereby helping constrain our knowledge of the Standard Model of particle physics. Computational ApproachWe use lattice gauge theory, a technique which discretizes space and time and models the quantum fluctuations in the vacuum by Monte Carlo. The propagation of quarks in random background fields is computed by solving discretized partial differential equations with conjugate gradients. These algorithms fit very naturally on parallel machines such as NERSC's T3E. AccomplishmentsOur primary focus continues to be on the weak decays of hadrons. One long-standing puzzle in the decay of kaons is the so-called "delta I=1/2 rule," which is the experimental observation that two seemingly similar decay processes actually proceed at vastly different rates. For the first time, we have been able to compute the relevant decay amplitudes and successfully reproduce the observed effect. We have also computed the matrix elements needed to interpret experiments on direct CP violation currently under way at Fermilab. In a related project, we have also performed a non-perturbative determination of the light quark masses. One of the major sources of uncertainty in many lattice QCD calculations is the use of the "quenched" approximation, in which one neglects the effects of virtual quark pairs which polarize the vacuum. Including these effects is feasible, but quite computationally intensive. |
We have made two steps to help alleviate this problem.
First, we are developing a promising new algorithm which speeds
up calculations that include virtual quarks. Second, we have established
a publicly available archive for gauge configurations at NERSC.
This "Gauge Connection" archive
allows the sharing and
re-use of the valuable unquenched configurations generated at
NERSC and elsewhere.
SignificanceTogether with results from particle physics experiments currently under way at labs in the U.S. and Europe, these calculations allow direct and detailed tests of the Standard Model of particle physics. At a minimum they will help determine some of the fundamental constants of nature. Eventually such tests may find small gaps in our current understanding of particle interactions, thereby giving us clues to the new physics which lies beyond. PublicationsG. Kilcup, R. Gupta, and S. Sharpe, "Staggered fermion matrix elements using smeared operators," Physical Review D 57, 1654 (1998).
D. Pekurovsky and G. Kilcup, "Weak matrix elements: On the
way to the delta I=1/2 rule and epsilon-prime/epsilon with staggered
fermions," Nuclear Physics B (Proc. Supp.) 63, 293
(1998).
P. de Forcrand, "UV filtered fermionic Monte Carlo,"
Nuclear Physics B (Proc. Supp.) (in press, 1998). |
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