Understanding the nature of the hidden charm pentaquark(like) signals in the LHCb data for ${\mathrm{\Lambda }}_b^0\to J/\psi p{K}^{-}$ is a central problem of hadron spectroscopy. We propose a scenario completely different from previous ones such as hadron molecules and compact pentaquarks. We identify relevant double triangle mechanisms with leading or lower-order singularities. The associated anomalous threshold cusps at the ${\mathrm{\Sigma }}_c^{(*)}{\overline{D}}^{(*)}$ thresholds are significantly more singular than the ordinary ones. Then we demonstrate that the double triangle amplitudes reproduce the peak structures of $P_c(4312{)}^{+}$, $P_c(4380{)}^{+}$, and $P_c(4457{)}^{+}$ in the LHCb data, through an interference with other common mechanisms. Only the $P_c(4440{)}^{+}$ peak is due to a resonance with a width and strength significantly smaller than previously estimated. $P_c^{+}$ signals are expected in other processes, and the proposed model (partly) explains the current data, such as the GlueX $J/\psi$ photoproduction data with no $P_c^{+}$ signals and the LHCb ${\mathrm{\Lambda }}_b^0\to J/\psi p{\pi }^{-}$ data with a possible signal only from $P_c(4440{)}^{+}$. In general, the double triangle singularity is now a possible option to interpret resonancelike structures near thresholds.

• Received 16 March 2021
• Accepted 12 May 2021

DOI:https://doi.org/10.1103/PhysRevD.103.L111503

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society