Direct experimental test of scalar confinement
  The concept of Lorentz scalar quark confinement has a long history and is still widely used despite its well-known theoretical faults. We point out here that the predictions of scalar confinement also conflict directly with experiment. We investigate the dependence of heavy-light meson mass differences on the mass of the light quark. In particular, we examine the strange and non-strange D mesons. We find that the predictions of scalar confinement are in considerable conflict with measured values. 
Theodore J. Allen, M.G. Olsson, Jeffrey R. Schmidt, Sinisa Veseli, Yu   Yuan