Eur. Phys. J. C (2020) 80: 301
https://doi.org/10.1140/epjc/s10052-020-7874-1

Regular Article - Theoretical Physics

Resolving the low mass puzzle of

¹ School of Physical Science and Technology, Lanzhou University, Lanzhou, 730000, China
² School of Electrical and Electronic Engineering, Anhui Science and Technology University, Fengyang, 233100, China
³ Research Center for Hadron and CSR Physics, Lanzhou University and Institute of Modern Physics of CAS, Lanzhou, 730000, China

^* e-mail: xiangliu@lzu.edu.cn

Received: 2 March 2020
Accepted: 24 March 2020
Published online: 3 April 2020

Abstract

For the long standing low mass puzzle of , we propose an unquenched picture. Our calculation explicitly shows that the mass of the state can be lowered down to be consistent with the experimental data of by introducing the channel contribution. It means that the low mass puzzle of can be solved. What is more important is that we predict a mass inversion relation for the 2P states, i.e., the state is higher than the , which is totally different from the result of conventional quenched quark model. It provides a criterion to test such an unquenched scenario for . We expect the future experimental progress from the LHCb and Belle II.