Measurement of the masses and widths of the ${\mathrm{\Sigma }}_c(2455{)}^{+}$ and ${\mathrm{\Sigma }}_c(2520{)}^{+}$ baryons

Using $980{\mathrm{fb}}^{-1}$ of data collected with the Belle detector operating at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider, we report the measurements of the masses, and the first measurements of the instrinsic widths, of the ${\mathrm{\Sigma }}_c(2455{)}^{+}$ and ${\mathrm{\Sigma }}_c(2520{)}^{+}$ charmed baryons. We find $M({\mathrm{\Sigma }}_c(2455{)}^{+})-M({\mathrm{\Lambda }}_c^{+})=166.17\pm 0.05_{-0.07}^{+0.16}\mathrm{MeV}/c^2$, $\mathrm{\Gamma }({\mathrm{\Sigma }}_c(2455{)}^{+})=2.3\pm 0.3\pm 0.3\mathrm{MeV}/c^2$, $M({\mathrm{\Sigma }}_c(2520{)}^{+})-M({\mathrm{\Lambda }}_c^{+})=230.9\pm 0.5_{-0.1}^{+0.5}\mathrm{MeV}/c^2$, and $\mathrm{\Gamma }({\mathrm{\Sigma }}_c(2520{)}^{+})={17.2}_{-2.1-0.7}^{+2.3+3.1}\mathrm{MeV}/c^2$, where the uncertainties are statistical and systematic, respectively. These measurements can be used to test models of the underlying quark structure of the ${\mathrm{\Sigma }}_c$ states.

Figure 1

The mass difference $M({\mathrm{\Lambda }}_c^{+}{\pi }^0)-M({\mathrm{\Lambda }}_c^{+})$ for the entire mass range of interest. The line shows the expected contribution from ${\mathrm{\Lambda }}_c(2625{)}^{+}\to {\mathrm{\Lambda }}_c^{+}{\pi }^0{\pi }^0$ decays assuming uniform three-body phase-space.

Figure 2

The mass difference $M({\mathrm{\Lambda }}_c^{+}{\pi }^0)-M({\mathrm{\Lambda }}_c^{+})$ in the region of the ${\mathrm{\Sigma }}_c(2455{)}^{+}$. The fit to the data is described in the text, and the lower line shows its contribution from the background function.

Figure 3

The mass difference $M({\mathrm{\Lambda }}_c^{+}{\pi }^0)-M({\mathrm{\Lambda }}_c^{+})$ in the region of the ${\mathrm{\Sigma }}_c(2520{)}^{+}$. The fit to the data is described in the text, and the lower line shows its contribution from the background function.