ψ(2S)衰变中强作用和电磁作用之间相对相角的测量

自然界已知的四种基本相互作用有：强相互作用、电磁相互作用、弱相互作用和万有引力。强相互作用和电磁相互作用是强度最大的两种，但其间的相对相位是夸克偶素研究的重要输入量，但在实验和理论上一直没有确定的结果。BESIII实验在粲偶素能区积累了大统计量的数据样本，为此相角的研究提供了前所未有的机会。.本项目拟利用BESIII积累的ψ(2S)扫描实验数据及共振态数据，从（1）e+e-->K+K-和（2）e+e-->ppbar的产生截面的线形，精确测量强相互作用和电磁相互作用之间的相对相角，为理解粲偶素衰变提供更多的实验信息。这种方法用于测量ψ(2S)衰变中的相角，属世界上首次，并期望给出唯一的，精确的，直接测量结果。此项目有助于深入理解粲偶素的衰变机制，若能从实验证实相角的普适性，将极大的推动物理学基础理论的发展。

There are four categories of interactions in the universe: strong interaction, electromagnetic interaction, weak interaction, and universal gravitation. Among them, the two largest interactions are strong and electromagnetic interactions. The relative phase between the two largest is an important input to the quarkonium studies, but there is no definite result neither from theory nor experiment. BESIII experiment accumulates the largest datasets in charmonium region and provides unprecedented opportunities for study of this phase. .This proposal suggests measuring the relative phase between the strong and the electromagnetic amplitudes precisely by studying the production cross section lineshapes of (1) e+e-->K+K- and（2）e+e-->ppbar, based on the largest ψ(2S) scan datasets and resonance datasets accumulated by BESIII. This will provide more experimental information of the charmonium decay mechanism. This method is the first time used for the phase measurement in ψ(2S) decays. The only one solution, precise and direct results are expected. This project will help to understand deeply the charmonium decay mechanism and will promote the development of elementary physics if the universality of the phase is verified from experiment.