First measurement of AN at in polarized proton–proton elastic scattering at RHIC

We report on the first measurement of the single spin analyzing power ( A N A N ) at s = 200 GeV , obtained by the PP2PP experiment using polarized proton beams at the Relativistic Heavy Ion Collider (RHIC). Data points were measured in the four momentum transfer t range 0.01⩽|t|⩽0.03 (GeV/c) 2 0.01 ⩽ | t | ⩽ 0.03 ( GeV / c ) 2 . Our result, averaged over the whole |t| | t | interval is about one standard deviation above the calculation, which uses interference between electromagnetic spin-flip amplitude and hadronic non-flip amplitude, the source of A N A N . The difference could be explained by an additional contribution of a hadronic spin-flip amplitude to A N A N .