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Using the high performance computing resources available
to us as a Department of Energy Grand Challenge Applications
Group, we have been computing ``
'', a fundamental constant
of nature. This parameter describes the decay of particles
called ``B-mesons,'' which are the subject of intense
scrutiny at experimental particle physics laboratories
throughout the world today, and which will be the main focus of
attention at the so-called ``B Factory'' under construction
by the Department of Energy at Stanford Linear Accelerator
Center. Computation of the parameter 
is crucial to understanding
the results of many such experiments.
Our calculations are performed using a ``lattice.'' We divide
the continuum of space and time into a finite number of points, do
numerical computations with the corresponding finite number of
variables, and then try to take the limit where the spacing
between the points (``a'') approaches zero, so that the
continuum of space and time is regained. The figure shows the
current status of these calculations in two versions of the theory.
We believe we have the best results in the world within both the
``quenched approximation'' and the more realistic version which includes
virtual quarks. The current result for 
is
The figure shows the current 
data,
both quenched and including virtual quarks, together with a
preliminary extrapolation of the quenched results to the continuum.
The main thrust of this work is clearly basic research. Yet our work has had important practical consequences. Our codes provide stress tests of all key features of parallel computers: integer and floating-point operations, inter-node communications, and I/O. We were able to uncover several problems with the Intel Paragon and iPSC/860 which had not been detected by Intel diagnostic software or by other users. Large sections of our code are now incorporated in standard Intel diagnostic software.vs. lattice spacing
The diamonds are from quenched lattices; the crosses are from lattices with virtual quarks. The fit is to the diamonds only, and the square is the extrapolated point.