 In their paper, however, the authors remarked that though the results were approximate, the charm-strange excited mesons formula_15 could be abnormally narrow (long-lived) since the principal decay mode, formula_16, could be kinematically suppressed (or altogether blocked) owing to the mass of the kaon.They could then be readily observed.In 2003 the formula_17 was discovered by the BABAR collaboration, and was seen to be surprisingly narrow, with a mass gap above the formula_18 of formula_19 MeV, within a few percent of the Bardeen-Hill model prediction.