Spin effects in high-Pperpendicularto2 elastic scattering

Recent experiments found large unexpected spin forces in high-Pperpendicularto2 proton-proton elastic scattering by using a polarized proton target and sometimes a polarized proton beam. If both protons are unpolarized then one can only measure the differential elastic cross-section. If either the beam or the target is spin-polarized then one can measure the one-spin parameter A, which is called the analyzing power or the left-right asymmetry. If both the beam and the target are polarized then one can measure two-spin quantities such as Ann, the spin-spin correlation parameter. Recall that Ann parameterizes the spin-spin force while A measures the spin-orbit force. (orig.)