Production of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>P</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math> states in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi mathvariant="normal">Λ</mml:mi><mml:mi>b</mml:mi></mml:msub></mml:math> decays

Abstract

We develop a model for the production of the ${P}_{c}$ states observed at LHCb in ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}J/\ensuremath{\psi}p{K}^{\ensuremath{-}}$ decays. With fewer parameters than other approaches, we obtain excellent fits to the $J/\ensuremath{\psi}p$ invariant mass spectrum, capturing both the prominent peaks, and broader features over the full range of invariant mass. A distinguishing feature of our model is that whereas ${P}_{c}(4312)$, ${P}_{c}(4380)$, and ${P}_{c}(4440)$ are resonances with ${\mathrm{\ensuremath{\Sigma}}}_{c}^{(*)}{\overline{D}}^{(*)}$ constituents, the nature of ${P}_{c}(4457)$ is quite different, and can be understood either as a ${\mathrm{\ensuremath{\Sigma}}}_{c}{\overline{D}}^{*}$ threshold cusp, a ${\mathrm{\ensuremath{\Lambda}}}_{c}(2595)\overline{D}$ enhancement due to the triangle singularity, or a ${\mathrm{\ensuremath{\Lambda}}}_{c}(2595)\overline{D}$ resonance. We propose experimental measurements that can discriminate among these possibilities. Unlike in other models, our production mechanism respects isospin symmetry and the empirical dominance of color-enhanced processes in weak decays, and additionally gives a natural explanation for the overall shape of the data. Our model is consistent with experimental constraints from photoproduction and ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}{\overline{D}}^{(*)0}{K}^{\ensuremath{-}}$ decays and it does not imply the existence of partner states whose apparent absence in experiments is unexplained in other models.

Topics & Concepts