4 A Comprehensive Four - Quark Interpretation of D s ( 2317 ) , D s ( 2457 ) and D s ( 2632 )

The recently observed new member of the charm-strange family D s (2632) which has a surprisingly narrow width is challenging our theory. D s (2317) and D s (2457) which were observed earlier have similar behaviors and receive various theoretical explanations. Some authors use the heavy hadron chiral effective theory to evaluate heavy-light quark systems and obtain a reasonable evaluation on the masses of D s (2317) and D s (2457). An alternative picture is to interpret them as four-quark or molecular states. In this work, we are following the later and propose a unitive description for all the three new members D s (2632), D s (2317) and D s (2457) and at least, so far our picture is consistent with the data. 1. Introduction Recently, the SELEX collaboration reported a new observation of a narrow resonance D s (2632) with a mass of 2632 ± 1.6 MeV/c 2 and total width < 17 MeV [1]. This resonance is the heaviest member, so far, of the charm-strange family. D s (2632) and the other two resonances D s (2317) and D s (2457), which were observed earlier[2, 3, 4], constitute an exotic group which is obviously distinguished from the ordinary D s (1968) and D * s (2112) by the masses, narrow total widths and decay modes. The total decay widthes of these states seem to be too small to be understood in the regular q ¯ q ′ structure. If the newly observed resonances D s (2632) were of a simple quark structure of c¯ s, one would expect that the heavier the resonance is, the shorter its lifetime should be, but the observation seems not to follow this pattern. These unusual features challenge our present theory. There have been some theoretical models proposed to interpret the structures of D s (2317) and D s (2457) which are most likely to possess spin-parity as 0 + and 1 + respectively [5, 6]. For example, Cahn and Jackson [7, 8] studied the new forms of the spin-orbit and tensor forces in the heavy-light quark system and applied the technique to the D s (2317) meson. In the special models, a mass difference was predicted which is close to the experimental data. Especially, two groups independently work on the spectra by using the heavy hadron chiral effective theory [9, 10]. In their work, they study the heavy-light quark hadrons where …