Electromagnetic form factor of pion from Nf = 2 + 1 dynamical flavor QCD
Electromagnetic form factor of pion from Nf = 2 + 1 dynamical flavor QCD
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DOI：
10.1007/jhep04(2011)122
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发表时间：
2011-02
影响因子：
5.4
通讯作者：
O. Nguyen;K. Ishikawa;A. Ukawa;N. Ukita
中科院分区：
文献类型：
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作者：
O. Nguyen;K. Ishikawa;A. Ukawa;N. Ukita
本文计算了Nf = 2+ 1味格点QCD中π介子的电磁形状因子。在32.3 × 64格点体积上，计算了由Iwasaki规范作用量和Wilson-clover夸克作用量产生的PACS-CS规范场组态，格点间距a= 0. 0907（13）fm在物理点。利用部分扭转边界条件技术测量了形状因子，以达到小动量传递以及整数动量的周期性边界条件。为了减少误差，还采用了随机壁源技术和对进入和离开的夸克所携带的动量的明智选择。分析M π <$411 MeV和296 MeV的π介子质量的形状因子数据，我们发现NNLO SU（2）手征微扰理论拟合得出< r 2>= 0。441±0。046 fm 2的π介子电荷半径在物理π介子质量。虽然误差较大，但与实验值0. 452±0。011调频2.低于M π <$300 MeV，我们发现，在π介子的两点和三点函数的统计波动变得太大，提取统计上有意义的平均值在32 - 3空间体积。我们在夸克质量接近物理点的64 4格点上进行了一个样本计算，这表明通过将格点尺寸扩大到M π L <$4，在物理点上的形状因子计算变得可行。
We present a calculation of the electromagnetic form factor of the pion in N f= 2+ 1 flavor lattice QCD. Calculations are made on the PACS-CS gauge field configurations generated using Iwasaki gauge action and Wilson-clover quark action on a 32 3× 64 lattice volume with the lattice spacing estimated as a= 0. 0907 (13) fm at the physical point. Measurements of the form factor are made using the technique of partially twisted boundary condition to reach small momentum transfer as well as periodic boundary condition with integer momenta. Additional improvements including random wall source techniques and a judicious choice of momenta carried by the incoming and outgoing quarks are employed for error reduction. Analyzing the form factor data for the pion mass at M π≈ 411 MeV and 296 MeV, we find that the NNLO SU (2) chiral perturbation theory fit yields< r 2>= 0. 441±0. 046 fm 2 for the pion charge radius at the physical pion mass. Albeit the error is quite large, this is consistent with the experimental value of 0. 452±0. 011 fm 2. Below M π≈ 300 MeV, we find that statistical fluctuations in the pion two-and three-point functions become too large to extract statistically meaningful averages on a 32 3 spatial volume. We carry out a sample calculation on a 64 4 lattice with the quark masses close to the physical point, which suggests that form factor calculations at the physical point become feasible by enlarging lattice sizes to M π L≈ 4.