Producing fully-charm structures in the $J/\psi$-pair invariant mass spectrum

Abstract

Very recently, the LHCb Collaboration reported the observation of several enhancements in the invariant mass spectrum of a $J/\psi$ pair between 6.2 and 7.4 GeV. In this work, we propose the dynamical mechanism to mimic the experimental data of a di-$J/\psi$ mass spectrum given by LHCb, which is based on the reactions, where all the possible combinations of a double charmonium directly produced by a proton-proton collision are transferred into a final state $J/\psi J/\psi$. We find that the LHCb experimental data can be well reproduced. We further extend our framework to study a di-${\rm Y}(1S)$ system, and give the line shape of a differential cross section of a partner process in a $b\bar{b}$ system on the invariant mass of ${\rm Y}(1S){\rm Y}(1S)$, which shows that there should exist possible enhancements near $m_{{\rm Y}(1S){\rm Y}(1S)}=$19.0, 19.3, 19.7 GeV in the ${\rm Y}(1S)$-pair invariant mass spectrum. These predictions can be tested in LHCb and CMS, which can be as a potential research issue in near future.

Comments: 5 pages, 1 table and 2 figures