Zb structures in a constituent quark model coupled-channels calculation

The Z(b) (10610)(+/-) and Z(b) (10650)(+/-) are two bottomoniumlike structures discovered in the pi h(b) (mP), pi Upsilon(nS) and B*(B) over bar(*) + H.c. invariant mass spectra, where m = {1,2} and n = {1,2,3}. Their nature is puzzling due to their charge, which forces its minimal quark content to be b (b) over baru (d) over bar (bbd). Thus, it is necessary to explore tour-quark systems in order to understand their inner structure. Additionally, their strong coupling to channels such as pi Upsilon and the closeness of their mass to B*(B) over bar(*) thresholds stimulates a molecular interpretation. Within the framework of a constituent quark model which satisfactorily describes a wide range of properties of (non)conventional hadrons containing heavy quarks, we perform a coupledchannels calculation of the I-G (J(PC)) = 1(+) (1(+-)) hidden-bottom sector including B(*)(B) over bar* + H.c., pi h(b), and pi Upsilon, channels. We analyze the line shapes in the different channels, describing the Upsilon(5S) -> pi B-(*())(B) over bar (()*() )by means of the P-3(0) model. Since our description of the line shapes is promising, we perform the same coupled-channels calculation for the Z(b) 's with J(--) where J = {0, 1, 2}. This allows us to obtain a fair description of the corresponding line shapes. The study of the analytic structure of the S-matrix suggests that the experimental Z(b) structures arise as a combination of several poles with J(PC) = 0(--), 1(+/--)and 2(--) quantum numbers nearby the B (B) over bar* and B*(B) over bar* thresholds.

Automated summary

The Z(b) (10610)(+/-) and Z(b) (10650)(+/-) are bottomoniumlike structures with puzzling charge properties, potentially involving four-quark systems. Coupled-channels calculations and line shape analysis suggest a molecular interpretation and provide description of their line shapes.