Longitudinal Double-Spin Asymmetries for π⁰s in the Forward Direction for 510 GeV Polarized pp Collisions

Here, the STAR Collaboration reports measurements of the longitudinal double-spin asymmetry, ALL, for neutral pions produced at forward directions in polarized proton-proton collisions, at a center-of-mass energy of 510 GeV. Results are given for transverse momenta in the range 2 < p _T < 10 GeV/c within two regions of pseudorapidity that span 2:65 < η < 3:9. These results are sensitive to the polarized gluon parton distribution function, Δg(x), down to the region of Bjorken x ~ 10 ^-3. The asymmetries observed are less than +5 • 10 ^-3 in magnitude, and will help constrain the contribution to the spin of the proton from polarized gluons at low x, when combined with other measurements as part of a global analysis.