Single-spin production asymmetries from the hard scattering of pointlike constituents

Abstract

When one takes into account the transverse momenta of the constituents in a polarized proton, there exists a kinematic, "trigger-bias," effect in the formulation of the QCD-based hard-scattering model which can lead to single-spin production asymmetries. It seems convenient to represent the coherent spin-orbit forces in a polarized proton by defining an asymmetry in the transversemomentum distribution of the fundamental constituents. It may then be possible to organize the hard-scattering model so that the kinematic constraints of hard 2-2 scattering provide the leading contribution at large transverse momentum to asymmetries of the type ANdo(hpt+jet+x), ANd0(hpr + "~''xx), where pt denotes a transversely polarized proton and "a" represents any spinless meson composed of light quarks. This approach provides testable relationships between different asymmetries.

Azimuthal and single spin asymmetries in hard scattering processes

“…The inclusion of k ⊥ effects and TMD functions can in principle lead to sizable SSA's; however, if the TMD functions are symmetric in the azimuthal direction, A N would be still negligible. It was then originally suggested by Sivers [18,19] that there could exist a correlation between the azimuthal distribution of an unpolarized parton and the spin of its parent hadron. That is, we could have the following nonvanishing asymmetry:…”

A New Mechanism for Generating a Single Transverse Spin Asymmetry

“…Hence our STSA-generating mechanism is distinctively different from the Collins [27] and Sivers [15,16] effects, and is more akin to (though still different from) the higher-twist mechanisms of [17][18][19][20][21][22][23][24][25][26].…”

“…To test whether such scenario is feasible within the CGC/saturation perturbative framework one has to calculate the higher order corrections to the polarization-dependent light-cone wave function squared (15). The corrections would need a generate a relative complex phase between the corrected and uncorrected wave functions, in agreement with the initial proposal of [22,23].…”

“…(32a) from Eq. (27) we employed the lowest-order (order-α s ) spin-dependent part of the light-cone wave function squared (15), which happens to be symmetric under the z ↔ y interchange: hence, in our case, to obtain a contribution to the STSA the interaction with the target had to be z ↔ y anti-symmetric. However, it is possible that higher-order corrections to the light-cone wave function squared would lead to a z ↔ y anti-symmetric contribution.…”

Electroproduction of neutral pions in the Hall A at the Jefferson Laboratory; Electroproduction de pions neutres dans le Hall A au Jefferson Laboratory

“…The nucleon-polarized TMD f ⊥ 1T , the so-called Sivers function is accessed through semi-inclusive deep inelastic scattering on a transversely polarized nucleon [54]. The total unpolarized quark distribution is given, for a polarized nucleon p ↑ :…”