Study of the lineshape of X (3872) using B decays to D0 D ¯ ∗0K
We present a study of the X(3872) lineshape in the decay B→X(3872)K→D0D¯∗0K using a data sample of 772×106 BB¯ pairs collected at the γ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The peak near the threshold in the D0D¯∗0 invariant mass spectrum is fitted using a relativistic Breit-Wigner lineshape. We determine the mass and width parameters to be mBW=3873.71-0.50+0.56(stat)±0.13(syst) MeV/c2 and ΓBW=5.2-1.5+2.2(stat)±0.4(syst) MeV, respectively. The branching fraction is found to be B(B+→X(3872)K+)×B(X(3872)→D0D¯∗0)=(0.97-0.18+0.21(stat)±0.10(syst))×10-4. The signal from B0 decays is observed for the first time with 5.2σ significance, and the ratio of branching fractions between charged and neutral B decays is measured to be B(B0→X(3872)K0)/B(B+→X(3872)K+)=1.34-0.40+0.47(stat)-0.12+0.10(syst). The peak is also studied using a Flatté lineshape. We determine the lower limit on the DD¯∗ coupling constant g to be 0.075 at 95% credibility in the parameter region where the ratio of g to the mass difference from the D0D¯∗0 threshold is equal to -15.11 GeV-1, as measured by LHCb.
