通过基矢光前量子化方法研究K介子

为研究K介子的性质，通过基矢光前量子化(BLFQ)方法获得K介子的光前波函数(LFWF)。使用的光前哈密顿量中包含了动能项、横向与纵向禁闭势以及夸克-胶子相互作用，其中横向禁闭势借鉴了光前全息量子色动力学(LFHQCD)模型的禁闭势。基矢空间包括领头阶与次领头阶的Fock空间。在前期工作的基础上，只引入了奇异夸克的质量作为唯一额外参数，使K>介子的质量与实验值相匹配。基于K介子领头阶Fock空间的LFWF，计算了K介子的部分子分布振幅(PDA)，其结果与量子色动力学(QCD)微扰论在零夸克质量近似下计算的结果相近。本工作得到的K介子的电磁形状因子(FF)与欧洲核子中心(CERN)超级质子同步加速器 (SPS)以及费米国家加速器实验室(FNAL)的实验结果一致。从领头阶Fock空间的LFWF计算出的电磁半径与粒子物理数据表(PDG)的实验值相近。计算出的K介子部分子分布函数(PDF)，QCD演化后，在实验能标下的K介子和$ \pi $介子中价夸克u的PDF之比与CERN-NA-003的实验数据在整体趋势上大体相符。此外，在计算出的K介子PDF中，价夸克携带的纵向动量之比，$ \langle x_{uv}\rangle/\langle x_{sv}\rangle $，约为$ 2/3 $，这个数值与Bethe-Salpeter equation(BSE)模型以及密西根州立大学格点QCD(MSULat)模型的计算结果相近。还计算了K介子的结构函数，发现与BLFQ考虑有效 Nambu–Jona-Lasinio相互作用(BLFQ-NJL)模型的结果有显著差别。K介子的结构函数有望在将来的电子离子对撞机(EIC)实验中得到观测与检验。

A Study of the Kaon from the Basis Light-Front Quantization Approach

We study the properties of the kaon through the light-front wave function(LFWF) obtained from the Basis Light-front Quantization(BLFQ) approach. Our Hamiltonian contains the kinetic energy terms, a transverse confining potential motivated by the light-front holographic quantum chromodynamics(LFHQCD) model, a complementary longitudinal confining potential, and the quark-gluon interactions based on quantum chromodynamics (QCD). Our basis space includes the lowest two Fock sectors. Based on the previous work, we tune the only additional strange quark mass parameter to match the resulting kaon mass with the experimental data. Based on the obtained leading Fock sector LFWF, we calculate the parton distribution amplitude(PDA) of the kaon which is in reasonable agreement with the one calculated from perturbative QCD in the massless quark limit. The obtained kaon form factor (FF) agrees with results from the Super Proton Synchrotron(SPS) experiment at the European Organization for Nuclear Research (CERN) and the Fermi National Accelerator Laboratory(FNAL) experiment. The electromagnetic radius (at the leading order Fock sector) is comparable to the one from the particle data group(PDG). In addition, the kaon parton distribution function(PDF), after QCD evolution, can be used to calculate the ratio of the kaon up quark PDF to that of the pion whose trend qualitatively agrees with that of the CERN-NA-003 experimental data. The obtained kaon PDF shows that the ratio between longitudinal momentum fractions of valence quarks, $ \langle x_{uv}\rangle/\langle x_{sv}\rangle $, is around 2/3, which agrees with results from the Bethe-Salpeter equation(BSE) model and the lattice QCD calculation in the Michigan State University(MSULat). We also calculate the structure function of the kaon which shows disagreement with the one from BLFQ-NJL calculation. This disagreement would be investigated in the future Electron-Ion Collider experiment(EIC).