Relative Yields and Nuclear Modification of ψ^′ to J/ψ mesons in p+p, p(³He)+A Collisions at s_NN=200 GeV, measured in PHENIX

The PHENIX collaboration has measured the ratio of ψ^′ to J/ψ in p+p and p(³He)+A collisions at forward and backward rapidity. We find that in p+p collisions, the data are consistent with expectations from a modified color evaporation model of quarkonia formation. In p(³He)+A collisions, in the p(³He)-going direction, the ψ^′ to J/ψ ratio is the same as found in p+p within uncertainties. However, in the A-going direction, the weaker bound ψ^′ is suppressed by a factor of 2 compared to the J/ψ. Since these states are not fully formed until after they exit the nucleus, interactions between the fully formed charmonia and co-moving matter may be responsible for this effect, consistent with the higher particle density in the A-going direction relative to the p(³He)-going direction. This mechanism may compete with color screening in a deconfined plasma in A+A collisions to produce sequential suppression of excited quarkonia states.