In 2015, the PHENIX Collaboration has measured single-spin asymmetries for charged pions in transversely polarized p + p collisions at the center-of-mass energy of root s = 200 GeV. The pions were detected at central rapidities of vertical bar eta vertical bar < 0.35.
The single-spin asymmetries are consistent with zero for each charge individually, as well as consistent with the previously published neutral-pion asymmetries in the same rapidity range. However, they show a slight indication of charge-dependent differences which may suggest a flavor dependence in the underlying mechanisms that create these asymmetries.