Study of excited charm-strange baryons with evidence for new baryons ${\Xi }_c(3055{)}^{+}$ and ${\Xi }_c(3123{)}^{+}$

We present a study of excited charm-strange baryon states produced in $e^{+}{e}^{-}$ annihilations at or near a center-of-mass energy of 10.58 GeV, in a data sample with an integrated luminosity of $384{\mathrm{fb}}^{-1}$ recorded with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ storage rings at the Stanford Linear Accelerator Center. We study strong decays of charm-strange baryons to ${\Lambda }_c^{+}{K}_S^0$, ${\Lambda }_c^{+}{K}^{-}$, ${\Lambda }_c^{+}{K}^{-}{\pi }^{+}$, ${\Lambda }_c^{+}{K}_S^0{\pi }^{-}$, ${\Lambda }_c^{+}{K}_S^0{\pi }^{-}{\pi }^{+}$, and ${\Lambda }_c^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$. This study confirms the existence of the states ${\Xi }_c(2980{)}^{+}$, ${\Xi }_c(3077{)}^{+}$, and ${\Xi }_c(3077{)}^0$, with a more accurate determination of the ${\Xi }_c(2980{)}^{+}$ mass and width. We also present evidence for two new states, ${\Xi }_c(3055{)}^{+}$ and ${\Xi }_c(3123{)}^{+}$, decaying through the intermediate-resonant modes ${\Sigma }_c(2455{)}^{++}{K}^{-}$ and ${\Sigma }_c(2520{)}^{++}{K}^{-}$, respectively. For each of these baryons, we measure the yield in each final state, determine the statistical significance, and calculate the product of the production cross section and branching fractions. We also measure the masses and widths of these excited charm-strange baryons.

Figure 1

(a) Scatter plot of $M({\Lambda }_c^{+}{\pi }^{+})$ versus $M({\Lambda }_c^{+}{K}^{-}{\pi }^{+})$, and (b,c) projections of the $M({\Lambda }_c^{+}{K}^{-}{\pi }^{+})$ distributions, in two ranges of $M({\Lambda }_c^{+}{\pi }^{+})$, for data (points with error bars) summed over all five reconstructed ${\Lambda }_c^{+}$ decay modes combined. The curves correspond to the two-dimensional fit results. The $M({\Lambda }_c^{+}{\pi }^{+})$ ranges are (b) within 3.0 natural widths of the ${\Sigma }_c(2455{)}^{++}$ mass, and (c) within 2.0 natural widths of the ${\Sigma }_c(2520{)}^{++}$ mass. These $M({\Lambda }_c^{+}{\pi }^{+})$ ranges are delineated by the horizontal lines on the scatter plot in (a). The projections of the combined background-PDF components are illustrated by the dashed curves.

Figure 2

(a) Scatter plot of $M({\Lambda }_c^{+}{\pi }^{-})$ versus $M({\Lambda }_c^{+}{K}_S^0{\pi }^{-})$, and (b,c) projections of the $M({\Lambda }_c^{+}{K}_S^0{\pi }^{-})$ distribution, in two ranges of $M({\Lambda }_c^{+}{\pi }^{-})$, for data (points with error bars) summed over all five reconstructed ${\Lambda }_c^{+}$ decay modes combined. The curves correspond to the two-dimensional fit results. The $M({\Lambda }_c^{+}{\pi }^{-})$ ranges are (b) within 3.0 natural widths of the ${\Sigma }_c(2455{)}^0$ mass, and (c) within 2.0 natural widths of the ${\Sigma }_c(2520{)}^0$ mass. These $M({\Lambda }_c^{+}{\pi }^{-})$ ranges are delineated by the horizontal lines on the scatter plot in (a). The projections of the combined background-PDF components are illustrated by the dashed curves.

Figure 3

Distributions of (a) $M({\Lambda }_c^{+}{K}_S^0)$ and (b) $M({\Lambda }_c^{+}{K}^{-})$, for all five reconstructed ${\Lambda }_c^{+}$ decay modes combined. The curves correspond to fits with no signal PDFs. Signals were searched for around the invariant-mass values indicated by the dashed vertical lines.

Figure 4

Distributions of (a) $M({\Lambda }_c^{+}{K}_S^0{\pi }^{-}{\pi }^{+})$ and (b) $M({\Lambda }_c^{+}{K}^{-}{\pi }^{+}{\pi }^{-})$, for all five reconstructed ${\Lambda }_c^{+}$ decay modes combined. The curves correspond to fits with no signal PDFs. Signals were searched for around the invariant-mass values indicated by the dashed vertical lines.