Energy Independence of the Collins Asymmetry in p↑p Collisions

The STAR experiment reports new, high-precision measurements of the transverse single-spin asymmetries for π± within jets, namely the Collins asymmetries, from transversely polarized p↑p collisions at √s = 510 GeV. The energy-scaled distribution of jet transverse momentum, xT = 2pT,jet/√ s, shows a remarkable consistency for Collins asymmetries of π± in jets between √s = 200 GeV and 510 GeV. This indicates that the Collins asymmetries are nearly energy independent with, at most, a very weak scale dependence in p↑p collisions. These results extend to high-momentum scales (Q² ≤ 3400 GeV²) and enable unique tests of evolution and universality in the transverse-momentum-dependent formalism, thus providing important constraints for the Collins fragmentation functions.