Z c (3900): What has been really seen?
Miguel Albaladejo (Instituto de Física Corpuscular (IFIC), Centro Mixto CSIC-Universidad de Valencia, Institutos de Investigación de Paterna, Aptd. 22085, Valencia, E-46071, Spain); Feng-Kun Guo (State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 100190, China, Helmholtz-Institut für Strahlen- und Kernphysik, Bethe Center for Theoretical Physics, Universität Bonn, Bonn, D-53115, Germany); Carlos Hidalgo-Duque (Instituto de Física Corpuscular (IFIC), Centro Mixto CSIC-Universidad de Valencia, Institutos de Investigación de Paterna, Aptd. 22085, Valencia, E-46071, Spain); Juan Nieves (Instituto de Física Corpuscular (IFIC), Centro Mixto CSIC-Universidad de Valencia, Institutos de Investigación de Paterna, Aptd. 22085, Valencia, E-46071, Spain)
The Zc±(3900)/Zc±(3885) resonant structure has been experimentally observed in the Y(4260)→J/ψππ and Y(4260)→D¯⁎Dπ decays. This structure is intriguing since it is a prominent candidate of an exotic hadron. Yet, its nature is unclear so far. In this work, we simultaneously describe the D¯⁎D and J/ψπ invariant mass distributions in which the Zc peak is seen using amplitudes with exact unitarity. Two different scenarios are statistically acceptable, where the origin of the Zc state is different. They correspond to using energy dependent or independent D¯⁎D S -wave interaction. In the first one, the Zc peak is due to a resonance with a mass around the DD¯⁎ threshold. In the second one, the Zc peak is produced by a virtual state which must have a hadronic molecular nature. In both cases the two observations, Zc±(3900) and Zc±(3885) , are shown to have the same common origin, and a D¯⁎D bound state solution is not allowed. Precise measurements of the line shapes around the DD¯⁎ threshold are called for in order to understand the nature of this state.
