Investigating the puzzle of scalar mesons in QCD and their connections to nonperturbative Higgs dynamics

该奖项为研究低于20亿电子伏特的标量介子的性质和夸克子结构及其对低能量子色动力学（QCD）相关问题的影响的项目目标提供旅行资金和计算资源。关于最轻的标量介子，有一个众所周知而又相当令人困惑的方面，那就是包含奇异夸克和非奇异夸克的态的质量排序似乎是相反的：假定的K_0^*(800)介子（带有一个奇异夸克）比a_0（980）介子（只包含非奇异夸克）轻。这导致人们猜测这些标量介子主要是四夸克态，而不是夸克-反夸克态。这项研究将包括比较强耦合体系中不同的近似方案，以及用双夸克和四夸克来解释奇异态。该方法将采用来自手性朗朗日量的有效场论方法，其参数将由SLAC粒子数据组出版物中的实验数据确定。由实验数据构建的部分波振幅将用于确定双夸克方法的有效性以及不同的统一方案。利用这些方法，理论上可以更好地理解低质量标量介子的性质。更广泛的影响是，通过更好地理解低能量标量介子，人们有望对标准模型中的非摄动希格斯动力学有所了解。我们也希望这一分析能对BaBar合作中较重介子的衰变有所帮助。该项目将使他所在学院的本科生能够参与到他的研究项目的各个方面。

This award provides travel funds and computational resources toward the project objective of investigating the properties and the quark substructure of the scalar meson below two gigaelectronvolts and their impacts on related issues in low-energy Quantum Chromodynamics (QCD). A well-known, and quite puzzling, aspect of the lightest scalar mesons is that there seems to be a reverse mass ordering of states containing strange and non-strange quarks: the putative K_0^*(800) meson (with a strange quark) is lighter than the a_0(980) meson (containing solely non-strange quarks). This has led to the speculation that these scalar mesons are predominantly tetraquark, and not quark-antiquark states. The research will involve comparing different approximation schemes in strongly coupled regimes and interpreting exotic states in terms of diquarks and tetra quarks. The approach will be the method of effective field theories coming from chiral Langrangians whose parameters will be determined from experimental data found in the Particle Data Group publication from SLAC. Partial wave amplitudes that have been constructed from experimental data will be used to determine the usefulness of the diquark approach as well as different unitarization schemes. Using these methods the properties of the low mass scalar mesons will be better understood theoretically. The broader impacts are that it is hoped by better understanding the lower energy scalar mesons one will get some insight into the non-perturbative Higgs dynamics in the Standard Model. It is also hoped that this analysis can be helpful in understanding the decay of heavier mesons by the BaBar collaboration. The PI will make his research accessible for the undergraduates at his institution to take part in various aspects of his research project.