Observation of chi_c and chi_b nuclear suppression via dilepton   polarization measurements
  We demonstrate that it is possible to use the polarization of vector quarkonia, measured from dilepton event samples, as an instrument to study the suppression of chi_c and chi_b in heavy-ion collisions, where a direct determination of signal yields involving the identification of low-energy photons is essentially impossible. A change of the observed J/psi and Upsilon(1S) polarizations from proton-proton to central nucleus-nucleus collisions would directly reflect differences in the nuclear dissociation patterns of S and P states and may provide a strong indication for quarkonium sequential suppression in the quark-gluon plasma. 
Pietro Faccioli and Joao Seixas
hep-ph