A discussion on the anomalous threshold enhancement of – couplings and peak* *Supported in part by the National Nature Science Foundations of China (12335002). This work is also supported by the Fundamental Research Funds for the Central Universities

Abstract

The attractive interaction between and has to be strong enough if X(6900) is of the molecule type. We argue that since decays predominantly into a pair, the interactions between and may be significantly enhanced owing to the three point loop diagram. The enhancement originates from the anomalous threshold located at GeV , whose effect propagates into the s-channel partial wave amplitude in the vicinity of GeV. This effect may be helpful in the formation of the peak.