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Role of the $Λ^+_c(2940)$ in the $π^- p \to D^- D^0 p$ reaction close to threshold

We report on a theoretical study of the $π^- p \to D^- D^0 p$ reaction near threshold within an effective Lagrangian approach. The production process is described by $t$ channel $D^{*0}$ meson exchange, $s$-channel nucleon pole, and $u$ channel $Σ^{++}_{c}$ exchange. In our work, the final $D^0 p$ results from the ground $Λ^+_c(2286)$ state and also dominantly from the excited $Λ^+_c(2940)$ state which is assumed as a $D^{*0} p$ molecular state with spin parity $J^P = \frac{1}{2}^+$ or $\frac{1}{2}^-$. We calculate the total cross section of the $π^- p \to D^- D^0 p$ reaction. It is shown that the spin parity assignment of $\frac{1}{2}^-$ for $Λ^+_c(2940)$ gives a sizable enhancement for the total cross section in comparison with a choice of $J^p = \frac{1}{2}^+$. However, our theoretical result of the total cross section is sensitive to the value of the cutoff parameter involved in the form factor of the exchanged off-shell particles. Moreover, we also calculate the second order differential cross section and find it can be used to determine the parity of the $Λ^+_c(2940)$. It is expected that our model calculations can be tested by future experiments at J-PARC in Japan.