Speaker
Description
New high-statistics total cross-section data for the $\gamma p \rightarrow J/\psi p$ reaction from GlueX experiment do not show direct evidence of the exotic $P_c(4312)^+$ state observed by the LHCb Collaboration. There is, however, a noticeable ``dip'' structure in the GlueX data near the energy corresponding to the mass of the observed LHCb state. We perform a fit to the GlueX data and find that the dip could be the result of destructive interference between the $P_c(4312)^+$ resonance and an associated non-resonant background. There are other possible explanations for this structure, including effects related to open charm thresholds; however the LHCb state is still compatible with the GlueX results. Further study will require additional statistics beyound the approximately 320 pb$^{-1}$ of the GlueX data set. One exciting new opportunity will b the the High-p Experiment at J-PARC, which is capable of measuring the $\pi^- p \rightarrow J/\psi n$ reaction. This will dramatically improve our understanding of the dynamics of $c\bar{c}$ production at the threshold and offer a new way to confirm the LHCb Pc states. Additionally, it will allow a high-precision determination of the $J/\psi$-$p$ scattering length independent from any assumptions of vector meson dominance.
