Observation of a narrow charmonium-like state in exclusive B+ -> K+ pi+pi- J/psi decays

TL;DR

The observation of a narrow charmoniumlike state produced in the exclusive decay process B+/--->K+/-pi(+)pi(-)J/psi, which has a mass that is very near the M(D0)+M(D(*0)) mass threshold.

Abstract

We report the observation of a narrow charmonium-like state produced in the exclusive decay process B+ -> K+ pi+pi- J/psi. This state, which decays into pi+pi- J/psi, has a mass of 3872.0+-0.6(stat)+-0.5(syst) MeV, a value that is very near the M_D + M_D* mass threshold. The results are based on an analysis of 152M B-Bbar events collected at the Upsilon(4S) resonance in the Belle detector at the KEKB collider. The statistical significance of the signal is in excess of 10 sigma.

Figures (4)

• Figure 1: Distribution of $M(\pi^{+}\pi^{-}\ell^{+}\ell^{-})-M(\ell^{+}\ell^{-})$ for selected events in the $\Delta E$-$M_{\rm bc}$ signal region for (a) Belle data and (b) generic $B$-$\bar{B}$ MC events .
• Figure 2: Signal-band projections of (a)$M_{\rm bc}$, (b)$M_{\pi^{+}\pi^{-}J/\psi}$ and (c)$\Delta E$ for the $X(3872)\rightarrow\pi^{+}\pi^{-}J/\psi$ signal region with the results of the unbinned fit superimposed.
• Figure 3: $M(\pi^{+}\pi^{-})$ distribution for events in the (a)$M(\pi^{+}\pi^{-}J/\psi)=3872$ MeV signal region. and (b) the $\psi^{\prime}$ region. The shaded histograms are sideband data normalized to the signal-box area. Note the different horizontal scales.
• Figure 4: Signal-band projections of (a)$M_{\rm bc}$ and (b)$M_{\gamma\chi_{c1}}$ for the $\psi^{\prime}$ region with the results of the unbinned fit superimposed. (c) and (d) are the corresponding results for the $M=3872$ MeV region.