The Meson Ds(2317)

The meson Ds(2317), discovered a couple of months ago in high energy electron-positron collisions at SLAC, possesses a mass of 2.317 GeV, some 170 MeV lighter than expected, at least according to prevalent theories of quark interactions. Hence physicists need a new explanation of how a charm quark attached to an antistrange quark should have this particular mass. In general, Ds and D mesons are a class of particles, each consisting of a charm quark attached to a light antiquark. (The subscript "s" pertains to all those D's containing a strange antiquark; "ordinary" D mesons consist of a charm quark and a down antiquark.) The Babar detection group at SLAC responsible for the experimental discovery (Aubert et al., Physical Review Letters, 20 June 2003; also see press release) suggests that the Ds(2317) might be a novel particle made of 4 quarks. But a pair of physicists in Portugal claim that in their model, assuming that the meson is indeed a charm/antistrange combination, the mass comes out in the right range if the strong-nuclear-force interactions responsible for the creation and annihilation of extra quark-antiquark pairs are taken into account. Using this model, Eef van Beveren (University of Coimbra) and George Rupp (CFIF Lab, IST, Lisbon) have successfully predicted meson masses in the past (such as the kappa meson, discovered at Fermilab (E791) at a mass of 800 MeV), while in the case of Ds mesons they predict a mass very near the Ds(2317) found already, and another at about 2.9 GeV (yet to be found). As to D mesons, they predict the equivalent of the Ds(2317) at a mass range of 2.1-2.3 GeV (for which preliminary evidence exists), and a heavier one at about 2.8 GeV (still undetected). According to van Beveren and Rupp, both pairs of Ds and D mesons are, in some sense, different aspects of the same underlying quark-antiquark state. (Physical Review Letters, upcoming article, see website or contact George Rupp, +351-21-841-9103)