ar X iv : h ep - p h / 06 05 31 7 v 1 2 9 M ay 2 00 6 Is the Y ( 4260 ) just a coupled - channel signal ? Eef

The DsD ∗ s , D ∗D∗, and D∗ sD ∗ s P -wave channels in the energy region of the Y (4260) charmonium structure are studied in a coupled-channel model applied to J = 1−− cc̄ resonances. The three channels exhibit enhancements that peak at 4.27 GeV, 4.26 GeV, and 4.33 GeV, respectively, having widths ranging from 80 to 200 MeV. However, no S-matrix poles are found, other than those associated with the ψ(2D, 4160) and ψ(4S, 4415). The conclusion is that the observed Y (4260) signal(s) in ππJ/ψ is (are) probably associated with the opening of the aforementioned channels, resulting in a resonance-like structure caused by the tail of the ψ(3S, 4040) resonance, roughly midway between the mentioned P -wave thresholds and a sharp kinematical minimum at about 4.4 GeV present in both the experimental and the model scattering amplitude. The surprising new J = 1−− charm-anticharm Y (4260) enhancement recently discovered in ππJ/ψ by the BABAR collaboration [1], with mass ≈ 4.26 GeV and width ≈ 90 MeV, later confirmed and also seen in ππJ/ψ as well as KKJ/ψ by the CLEO collaboration [2], has been studied in a variety of theoretical models [3], namely as a standard vector charmonium state (4S) [4], mesonic or baryonic molecule [5], gluonic excitation (hybrid) [6], or cqc̄q̄ state [7]. In the present paper, we shall present arguments for an again completely different, yet nonexotic interpretation of the Y (4260). In Ref. [8], a coupled-channel model for quarkonium systems was presented, which reproduced fairly well the then known charmonium and bottomonium states, while in Ref. [9], using a more realistic transition potential, also the hadronic widths were reasonably reproduced. Here, we employ the original model of Ref. [8], leaving the parameters unaltered. This yields the spectrum shown in the first figure in Fig. 1, in which one observes the ψ(1D, 3770), ψ(3S, 4040), ψ(2D, 4160), and ψ(4S, 4415), 3.8 4.0 4.2 4.4 10 20 30 40 √ s(GeV) σ (G e V − 2 ) 4.25 4.30 4.35 0.1 0.2 0.3 √ s(GeV) σ (G e V − 2 ) Figure 1: The J = 1−− cc̄ spectrum of Ref. [8]. as well as a newly predicted ψ(3D, 4550) J = 1−− cc̄ state. For energies in the interval 4.2 GeV to 4.4 GeV, no enhancement is visible (second figure). In Table 1, channel threshold LMM relative couplings GeV to lcc̄ = 0 to lcc̄ = 2 D D 3.73400 1 1/36 1/108 Ds Ds 3.93660 1 1/72 1/216 D D∗ 3.87540 1 1/9 1/108 Ds D ∗ s 4.08040 1 1/18 1/216 D∗ D∗ 4.01680 1 7/36 1/270 D∗ s D ∗ s 4.22420 1 7/72 1/540 D∗ D∗ 4.01680 3 7/60 D∗ s D∗ s 4.22420 3 7/120 Table 1: The various meson-meson channels (MM) included in this analysis, and their relative squared couplings [10] to J = 1−− cc̄ states in S and D wave.