Decays of Roper-like singly heavy baryons in a chiral model

We present a chiral model describing decays of the Roper-like ${\mathrm{\Lambda }}_c(2765)$ and ${\mathrm{\Xi }}_c(2970)$ as well as those of the heavy quark spin-doublet $\{{\mathrm{\Sigma }}_c(2455),{\mathrm{\Sigma }}_c(2520)\}$ and $\{{\mathrm{\Xi }}_c^{\prime },{\mathrm{\Xi }}_c(2645)\}$, by focusing on chiral representations of diquarks inside the heavy baryons. Based on our chiral model together with the heavy quark spin symmetry, we derive a relation satisfied by axial charges of the heavy baryons that controls the magnitude of their one pion (kaon) decays. Besides, it is shown that the large decay widths of the Roper-like ${\mathrm{\Lambda }}_c(2765)$ and ${\mathrm{\Xi }}_c(2970)$, which cannot be implemented by conventional nonrelativistic quark models, are explained by reasonable values of the axial charges. In addition, we apply the chiral model to bottom baryons and predict decay widths of the undiscovered Roper-like ${\mathrm{\Xi }}_b$. We expect that our present investigation leads to elucidation of dynamical properties of the excited heavy baryons from the viewpoint of chiral symmetry.

Figure 1

Feynman diagrams for (a) ${\mathrm{\Lambda }}_c(2765)\to {\mathrm{\Sigma }}_c(2455)\pi$ and for (b) ${\mathrm{\Lambda }}_c(2765)\to {\mathrm{\Sigma }}_c(2520)\pi$.

Figure 2

Feynman diagrams for (a) ${\mathrm{\Sigma }}_c(2455)\to {\mathrm{\Lambda }}_c\pi$ and for (b) ${\mathrm{\Sigma }}_c(2520)\to {\mathrm{\Lambda }}_c\pi$.

Figure 3

$R=\sqrt{g_A^2+g_A^{\prime 2}}$ dependence of the decay widths of ${\mathrm{\Lambda }}_c(2765)$ (red) and ${\mathrm{\Xi }}_c(2970{)}^{+}$ (blue). The dashed lines are the corresponding experimental values (the central values) indicated in PDG.

Figure 4

Mass dependence of the decay width of Roper-like ${\mathrm{\Xi }}_b$. The vertical black line represents the mass of ${\mathrm{\Xi }}_b(6255)$ predicted in Ref. [27].

Figure 5

$R=\sqrt{g_A^2+g_A^{\prime 2}}$ dependence of the decay widths of ${\mathrm{\Lambda }}_b^0(6070)$ (red) and the Roper-like ${\mathrm{\Xi }}_b^{-}$ (blue). The red dashed line is the experimental values (the central value) indicated in PDG, and the vertical black line corresponds to $R=0.612$.

Figure 6

Feynman diagrams for (a) ${\mathrm{\Xi }}_c(2970)\to {\mathrm{\Sigma }}_c(2455)\overline{K}$, (b) ${\mathrm{\Xi }}_c(2970)\to {\mathrm{\Xi }}_c^{\prime }\pi$, and (c) ${\mathrm{\Xi }}_c(2970)\to {\mathrm{\Xi }}_c(2645)\pi$.

Figure 7

A Feynman diagram for ${\mathrm{\Xi }}_c(2645)\to {\mathrm{\Xi }}_c\pi$.