Using 980 ${rm fb}^{-1}$ 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 $Sigma_c(2455)^+$ and $Sigma_c(2520)^+$ charmed baryons. We find $M(Sigma_c(2455)^+)-M(Lambda_c^+) = 166.17pm 0.05^{+0.16}_{-0.07} {rm MeV}/c^2$, $Gamma(Sigma_c(2455)^+) = 2.3 pm 0.3 pm 0.3 {rm MeV/c^2}$, $M(Sigma_c(2520)^+)-M(Lambda_c^+) = 230.9 pm 0.5 ^{+0.5}_{-0.1} {rm MeV}/c^2$, and $Gamma(Sigma_c(2520)^+) = 17.2^{+2.3 +3.1}_{-2.1 -0.7} {rm MeV}/c^2$, where the uncertainties are statistical and systematic, respectively. These measurements can be used to test models of the underlying quark structure of the $Sigma_c$ states.
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