Evidence for a Narrow Near-Threshold Structure in the $J/\psi \varphi$ Mass Spectrum in $B^{+}\to J/\psi \varphi K^{+}$ Decays

Evidence is reported for a narrow structure near the $J/\psi \varphi$ threshold in exclusive $B^{+}\to J/\psi \varphi K^{+}$ decays produced in $\overline{p}p$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. A signal of $14\pm 5$ events, with statistical significance in excess of 3.8 standard deviations, is observed in a data sample corresponding to an integrated luminosity of $2.7{\mathrm{fb}}^{-1}$, collected by the CDF II detector. The mass and natural width of the structure are measured to be $4143.0\pm 2.9(\mathrm{stat})\pm 1.2(\mathrm{syst})\mathrm{MeV}/c^2$ and ${11.7}_{-5.0}^{+8.3}(\mathrm{stat})\pm 3.7(\mathrm{syst})\mathrm{MeV}/c^2$.

Figure 1

(a) The mass distribution of $J/\psi \varphi K^{+}$; the solid line is a fit to the data with a Gaussian signal function and flat background function. (b) The $B^{+}$ sideband-subtracted mass distribution of $K^{+}{K}^{-}$ without the $\varphi$ mass window requirement. The solid curve is a $P$-wave relativistic Breit-Wigner fit to the data.

Figure 2

(a) The Dalitz plot of $m^2(\varphi K^{+})$ versus $m^2(J/\psi \varphi )$ in the $B^{+}$ mass window. The boundary shows the kinematic allowed region. (b) The mass difference, $\Delta M$, between ${\mu }^{+}{\mu }^{-}{K}^{+}{K}^{-}$ and ${\mu }^{+}{\mu }^{-}$, in the $B^{+}$ mass window. The dash-dotted curve is the background contribution and the red solid curve is the total unbinned fit.