Observation of a Near-Threshold $\omega J/\psi$ Mass Enhancement in Exclusive $B\to K\omega J/\psi$ Decays

We report the observation of a near-threshold enhancement in the $\omega J/\psi$ invariant mass distribution for exclusive $B\to K\omega J/\psi$ decays. The results are obtained from a $253{\mathrm{fb}}^{-1}$ data sample that contains $275\times {10}^6$ $B\overline{B}$ pairs that were collected near the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^{+}{e}^{-}$ collider. The statistical significance of the $\omega J/\psi$ mass enhancement is estimated to be greater than $8\sigma$.

Figure 1

(a) $M_{\mathrm{bc}}$ distributions for $B\to K\omega J/\psi$ candidates in the $\Delta E$ and $\omega \to {\pi }^{+}{\pi }^{-}{\pi }^0$ signal regions. (b) $\Delta E$ distribution for events in the $M_{\mathrm{bc}}$ and $\omega$ signal regions. (c) $M({\pi }^{+}{\pi }^{-}{\pi }^0)$ distribution for events in the $M_{\mathrm{bc}}$ and $\Delta E$ signal regions. The curves are the results of fits described in the text; the arrows indicate the signal region for each quantity.

Figure 2

Dalitz-plot distribution for $B\to K\omega J/\psi$ candidate events. The dotted line indicates the boundary of the $M(K\omega )>1.6\mathrm{GeV}$ selection requirement.

Figure 3

$M_{\mathrm{bc}}$ distributions for $B^{-}\to K^{-}\omega J/\psi$ candidates in the $\Delta E$ signal region for 40 MeV-wide $\omega J/\psi$ invariant mass intervals. The curves are the results of fits described in the text.

Figure 4

$B\to K\omega J/\psi$ signal yields vs $M(\omega J/\psi )$. The curve in (a) indicates the result of a fit that includes only a phase-space-like threshold function. The curve in (b) shows the result of a fit that includes an $S$-wave Breit-Wigner resonance term.