Evidence of a new excited charmed baryon decaying to ${\Sigma }_c(2455{)}^{0,++}{\pi }^{\pm }$

Abstract

We present the study of ${\bar{B}}^0\to {\Sigma }_c(2455{)}^{0,++}{\pi }^{\pm }\bar{p}$ decays based on $772\times 10^6$ $B\bar{B}$ events collected with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The ${\Sigma }_c(2455{)}^{0,++}$ candidates are reconstructed via their decay to ${\Lambda }_c^{+}{\pi }^{\mp }$ and ${\Lambda }_c^{+}$ decays to $p{K}^{-}{\pi }^{+},p{K}_S^0,$ and $\Lambda {\pi }^{+}$ final states. The corresponding branching fractions are measured to be $\mathcal{B}({\bar{B}}^0\to {\Sigma }_c(2455{)}^0{\pi }^{+}\bar{p})=(1.09\pm 0.06\pm 0.07)\times 10^{-4}$ and $\mathcal{B}({\bar{B}}^0\to {\Sigma }_c(2455{)}^{++}{\pi }^{-}\bar{p})=(1.84\pm 0.11\pm 0.12)\times 10^{-4}$, which are consistent with the world average values with improved precision. A new structure is found in the $M_{{\Sigma }_c(2455{)}^{0,++}{\pi }^{\pm }}$ spectrum with a significance of $4.2\sigma$ including systematic uncertainty. The structure is possibly an excited ${\Lambda }_c^{+}$ and is tentatively named ${\Lambda }_c(2910{)}^{+}$. Its mass and width are measured to be $(2913.8\pm 5.6\pm 3.8)$ MeV/$c^2$ and $(51.8\pm 20.0\pm 18.8)$ MeV, respectively. The products of branching fractions for the ${\Lambda }_c(2910{)}^{+}$ are measured to be $\mathcal{B}({\bar{B}}^0\to {\Lambda }_c(2910{)}^{+}\bar{p})\times \mathcal{B}({\Lambda }_c(2910{)}^{+}\to {\Sigma }_c(2455{)}^0{\pi }^{+})=(9.5\pm 3.6\pm 1.6)\times 10^{-6}$ and $\mathcal{B}({\bar{B}}^0\to {\Lambda }_c(2910{)}^{+}\bar{p})\times \mathcal{B}({\Lambda }_c(2910{)}^{+}\to {\Sigma }_c(2455{)}^{++}{\pi }^{-})=(1.24\pm 0.35\pm 0.10)\times 10^{-5}$. Here, the first and second uncertainties are statistical and systematic, respectively.

Comments: 7 pages, 3 figures, 1 table; accepted for publication as a Letter in Physical Review Letters