Production of $P_c$ states in $\Lambda_b$ decays

TL;DR

This paper presents a new model for the production of Pc states in Lambda_b decays, fitting experimental data well and proposing mechanisms for their nature, with implications for future experimental discrimination.

Contribution

The model uses fewer parameters, respects isospin symmetry, and explains the Pc states' nature and production without predicting unobserved partner states.

Findings

Excellent fit to J/psi-p invariant mass spectrum

Different interpretations for Pc(4457) proposed

Consistent with various experimental constraints

Abstract

We develop a model for the production of the Pc states observed at LHCb in Lambdab - Jpsi p K- decays. With fewer parameters than other approaches, we obtain excellent fits to the Jpsi-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 Pc(4312), Pc(4380), and Pc(4440) are resonances with Sigmac*-D* constituents, the nature of Pc(4457) is quite different, and can be understood either as a Sigmac-D* threshold cusp, a Lambdac(2595)-D enhancement due to the triangle singularity, or a Lambdac(2595)-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 colour-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 Lambdab - Lambdac-D(*)0 K- decays and it does not imply the existence of partner states whose apparent absence in experiments is unexplained in other models.