The PHENIX Collaboration has measured the ratio of the yields of psi(2S) to psi(1S) mesons produced in p+p, p+Al, p+Au, and ^3He+Au collisions at sNN=200 GeV over the forward and backward rapidity intervals 1.2 < |y| < 2.2. We find that the ratio in p+p collisions is consistent with measurements at other collision energies. In collisions with nuclei, we find that in the forward (p-going or ^3He-going) direction, the relative yield of psi(2S) mesons to psi(1S) mesons is consistent with the value measured in p+p collisions. However, in the backward (nucleus-going) direction, the psi(2S) meson is preferentially suppressed by a factor of 2. This suppression is attributed in some models to the breakup of the weakly bound psi(2S) meson through final-state interactions with comoving particles, which have a higher density in the nucleus-going direction. These breakup effects may compete with color screening in a deconfined quark-gluon plasma to produce sequential suppression of excited quarkonia states.著者所属: 日本原子力研究開発機構(JAEA)