Speaker
Description
We analyze the radiative decay $P_c(4457)(3/2^-) \to P_c(4312)(1/2^-)\gamma$ by treating both pentaquark states as $S$-wave hadronic molecules. Using a chiral unitary approach with heavy-quark spin symmetry, we calculate photon couplings to meson-baryon components via nineteen $M1$ triangle loops. The transition is dominated by the $\bar D^{*0}\to\bar D^{0}\gamma$ loop, yielding a pure $M1$ transition ($E_\gamma = 143$~MeV) with a central width of $6.7$~keV (ranging between $2$ and $9$~keV). Introducing a soft Gaussian form-factor on the leading diagram reduces the full width to $\sim 4$~keV. We estimate the cascade rate for $\Lambda_b^{0}\to J/\psi\,p\,K^{-}\gamma$ and propose the pure $M1$ content, binding-energy dependence, and decay ratio compared to the $P_c(4440)$ as critical tests of these states' molecular nature.
