Search for the $h_c$ meson in $B^{\pm }\to h_c{K}^{\pm }$

We report a search for the $h_c$ meson via the decay chain $B^{\pm }\to h_c{K}^{\pm }$, $h_c\to {\eta }_c\gamma$ with ${\eta }_c\to K_S^0{K}^{\pm }{\pi }^{\mp }$ and $p\overline{p}$. No significant signals are observed. We obtain upper limits on the branching fractions for $B^{\pm }\to {\eta }_c\gamma K^{\pm }$ in bins of the ${\eta }_c\gamma$ invariant mass. The results are based on an analysis of $253{\mathrm{fb}}^{-1}$ of data collected by the Belle detector at the KEKB $e^{+}{e}^{-}$ collider.

Figure 1

The $M_{\mathrm{bc}}$ distributions in the $\Delta E$ signal region and the $\Delta E$ distributions in the $M_{\mathrm{bc}}$ signal region for the ${\eta }_c\to K_S^0{K}^{-}{\pi }^{+}$ (left) and ${\eta }_c\to p\overline{p}$ modes (right) in 100 MeV bins of $M({\eta }_c\gamma )$ for $3.17<M({\eta }_c\gamma )\le 3.67\mathrm{GeV}/c^2$. The distributions are shown in the increasing order of $M({\eta }_c\gamma )$ from the top to the bottom. The solid curves are the results of the fits. The dashed curves represent background components from $B$ decays.

Figure 2

The $M_{\mathrm{bc}}$ distributions in the $\Delta E$ signal region and the $\Delta E$ distributions in the $M_{\mathrm{bc}}$ signal region for the ${\eta }_c\to K_S^0{K}^{-}{\pi }^{+}$ (left) and ${\eta }_c\to p\overline{p}$ modes (right) in 100 MeV bins of $M({\eta }_c\gamma )$ for $3.22<M({\eta }_c\gamma )\le 3.72\mathrm{GeV}/c^2$. The distributions are shown in the increasing order of $M({\eta }_c\gamma )$ from the top to the bottom. The solid curves are the results of the fits. The dashed curves represent background components from $B$ decays.

Figure 3

The $M({\eta }_c\gamma )$ distributions for both ${\eta }_c$ modes. The points with error bars are the data in the $M_{\mathrm{bc}}$ and $\Delta E$ signal region; the solid histogram is the $M_{\mathrm{bc}}$ sideband data in the region $5.20<M_{\mathrm{bc}}<5.26\mathrm{GeV}/c^2$; the hatched histogram shows the expected contribution for a signal with a branching fraction at the observed upper limit for a resonance with $M({\eta }_c\gamma )=3.527\mathrm{GeV}$.

Figure 4

Upper limits at 90% C.L. on the branching fractions for $B^{+}\to h_c{K}^{+}$ as a function of the $h_c$ mass, assuming $\mathcal{B}(h_c\to {\eta }_c\gamma )=0.5$. The dashed lines with arrows show the upper limits for mass bins shifted by $50\mathrm{MeV}/c^2$ with respect to the nominal ones. The dotted lines represent the theoretical range for the branching fraction obtained by Colangelo, Fazio and Pham [15].