Measurements of $h_c({}^{1}P_1)$ in ${\psi }^{\prime }$ Decays

We present measurements of the charmonium state $h_c({}^{1}P_1)$ made with $106\times {10}^6$ ${\psi }^{\prime }$ events collected by BESIII at BEPCII. Clear signals are observed for ${\psi }^{\prime }\to {\pi }^0{h}_c$ with and without the subsequent radiative decay $h_c\to \gamma {\eta }_c$. First measurements of the absolute branching ratios $\mathcal{B}({\psi }^{\prime }\to {\pi }^0{h}_c)=(8.4\pm 1.3\pm 1.0)\times {10}^{-4}$ and $\mathcal{B}(h_c\to \gamma {\eta }_c)=(54.3\pm 6.7\pm 5.2)\%$ are presented. A statistics-limited determination of the previously unmeasured $h_c$ width leads to an upper limit $\Gamma (h_c)<1.44\mathrm{MeV}$ (90% confidence). Measurements of $M(h_c)=3525.40\pm 0.13\pm 0.18\mathrm{MeV}/c^2$ and $\mathcal{B}({\psi }^{\prime }\to {\pi }^0{h}_c)\times \mathcal{B}(h_c\to \gamma {\eta }_c)=(4.58\pm 0.40\pm 0.50)\times {10}^{-4}$ are consistent with previous results.

Figure 1

(a) The ${\pi }^0$ recoil-mass spectrum and fit for the $E1$-tagged analysis of ${\psi }^{\prime }\to {\pi }^0{h}_c$, $h_c\to \gamma {\eta }_c$. (b) The ${\pi }^0$ recoil-mass spectrum and fit for the inclusive analysis of ${\psi }^{\prime }\to {\pi }^0{h}_c$. Fits are shown as solid lines, background as dashed lines. The insets show the background-subtracted spectra.