The nature of X(3900) and recognition of open charm effects

Abstract

We identify open charm effects in a direct production process $e^{+}{e}^{-}\to J/\ddot{I}ˆ\ddot{I}{€}^0$. A unique feature of this process is that the $D{\bar{D}}^{\ast }+c.c.$ threshold is located at a relatively isolated energy region, i.e. $\sim 3.876\mathrm{GeV}$, which is far away from the well-established charmonia $\ddot{I}ˆ(3770)$ and $\ddot{I}ˆ(4040)$. Therefore, the cross section line-shape of this reaction provides an opportunity for singling out the open charm effects. A model-independent narrow enhancement between the thresholds of $D^0{\bar{D}}^{\ast 0}+c.c.$ and $D^{+}{D}^{\ast -}+c.c.$ is predicted. This study can also help understand the X(3900) enhancement recently observed by the Belle and BaBar Collaboration in $e^{+}{e}^{-}\to D\bar{D}+c.c.$ We also show that the open charm effects play a crucial role for our understanding of the long-standing "$\ddot{I}\ddot{I}€$ puzzle".

6 pages and 2 eps figures; Proceeding of Sixth International Conference on Quarks and Nuclear Physics - QNP 2012, Paris