Productions of X (3872)/Zc (3900) and X2 (4013)/Zc (4020) in y (4220) and y (4360) decays

The two excited vector charmonium states Y(4220) and Y(4360) are difficult to understand as pure cc¯ charmonium states. Since they are located close to the mass thresholds of D¯D1 and D¯∗D1, they can be viewed as D¯D1 and D¯∗D1 molecules. Furthermore, recent studies indicate that the exotic states X(3872)/Zc(3900) and X2(4013)/Zc(4020) are the isoscalar/isovector D¯D∗ and isoscalar/isovector D¯∗D∗ molecules, respectively. In this work, in the molecular picture, we employ the triangle diagram mechanism to study the productions of Zc(3900) and X(3872) in the pionic and radiative decays of Y(4220), as well as their heavy-quark spin symmetry partners - i.e., the productions of Zc(4020) and X2(4013) in the pionic and radiative decays of Y(4360). Using the effective Lagrangian approach, we obtain the ratios of the branching fractions B[Y(4360)→Zc(4020)π]/B[Y(4220)→Zc(3900)π]=1.2±0.3 and B[Y(4360)→X2(4013)γ]/B[Y(4220)→X(3872)γ]=0.5±0.1, almost independent of model parameters, which indicate that the productions of X2(4013) and Zc(4020) in the radiative and pionic decays of Y(4360) are likely to be measured in the future. The experimental studies of the predicted decay modes will help to verify the molecular nature of X(3872), Zc(3900), and Y(4220). We hope that the present work can stimulate experimental and further theoretical studies on these decay modes.