NUMERICAL STUDY OF LATTICE QUANTUM CHROMODYNAMICS

晶格QCD的数值模拟为确定强子弱振幅的强相互作用修正提供了一种可行的方法，这对于解释包括CP破坏起源在内的基本粒子弱相互作用尚未解决的问题至关重要。本研究的目的是在这个方向上对晶格QCD进行系统的研究。1994年，我们将自己发明的无规固定壁源方法应用于π - n σ项和质子自旋夸克含量问题。这两种矩阵元素都接受海夸克环的贡献，如何评估这些贡献代表了一个普遍的问题，也出现在弱矩阵元素计算中。我们发现该方法效果很好，得到的值与实验结果一致，首次有力地表明QCD成功地解释了这些在粒子理论中长期争论的可观测值。同年，我们还开始准备富士通VPP500/80矢量并行超级计算机，计划于1995年1月安装在KEK。在1995年1月至3月期间，编写了各种晶格QCD码，并进行了密集测试。1995年4月，我们在VPP上对强子的各种弱矩阵元进行了大规模的点阵QCD计算。目前的计算情况如下。(1) K介子B参数是固定Cabibbo-Kobayashi-Maskawa夸克混合矩阵的基本量之一。用科古特-苏斯金德夸克作用对这个量的计算正在进行中。目前已经收集了6个格间距值的数据，并计划再计算一个格间距值。这些数据应能使B参数精确外推到连续体极限。基于今年开发的手性沃德恒等式方法，威尔森夸克作用的类似计算也在进行中。(2)另一个对CP违和研究很重要的参数是B介子衰变常数。1995年初夏进行的初步计算显示统计上有很大的波动。试验了一种减小误差的模糊源方法，并于1995年底开始了新的计算。已经收集了两个晶格间距值的数据，并计划在不久的将来开始进一步计算减少晶格间距。这将使我们能够估计衰减常数的连续m值。(3) Clover夸克作用的实验已经完成，有望更快地接近连续体极限。真正的计算将在(2)中的Wilson计算完成后立即开始。我们期望能在1996年夏天之前公布这些计算的最后结果。少

Numerical simulations of lattice QCD provides a viable method for determination of the strong interaction corrections to weak amplitudes of hadrons, which is crucial for elucidating unsolved problems of weak interactions of elementary particles including the origin of CP violation. The objective of the present research is to carry out a systematic study of lattice QCD in this direction.In 1994 we applied the method of wall source without gauge fixing, previously developed by us, to the problem of pi-N sigma term and the quark content of proton spin. Both these matrix elements receive contributions from sea quark loops, and how one can evaluate these contributions represents a general problem that also appear in weak matrix element calculations. We found that the method works well, and that the values obtained are consistent with experiments, strongly indicating for the first time that QCD successfully explains the values of these observables long debated in particle theory.In the same … More year we also started preparations for Fujitsu VPP500/80 vector parallel supercomputer, which was scheduled to be installed at KEK in January 1995. A variety of lattice QCD codes were written, and tested intensively in the period January-March 1995.In April 1995 we have initiated large scale lattice QCD calculations of a variety of weak matrix elements of hadrons on VPP.The present status of the calculations are as follows.(1) The K Meson B parameter is one of the fundamental quantity for fixing the Cabibbo-Kobayashi-Maskawa quark mixing matrix. A quenched calculation of this quantity with the Kogut-Susskind quark action is well underway. So far data for 6 values of lattice spacings have been collected, and a calculation for one more value of lattice spacing is planned. Together the data should allow a precision extrapolation of the B parameter to the continuum limit. A similar calculation with the Wilson quark action, based on the method of chiral Ward identities developed this year, is also underway.(2) Another parameter important for CP violation studies is the B meson decay constant. An initial calculation made in the early summer of 1995 revealed large statistical fluctuations. A method of smeared source for reducing the error was tested, and a new calculation has been started late 1995. Data for two values of lattice spacing have been collected and a further calculations with reduced lattics spacing is planned to start soon. This will allow us to estimate the continue m value of the decay constant.(3) Tests of Clover quark action, expected to have a faster approach to the continuum limit, has been completed. Real calculations will start as soon as the Wilson calculation in (2) will be finished.We expect to be able to publish final results of these calculations by summer of 1996. Less