Polarization asymmetry in high-p⊥inclusive production

We calculate the asymmetry $A_{\mathrm{LL}}$ for scattering of longitudinally polarized protons from a polarized target in an effort to discriminate among constituent models of inclusive high-transverse-momentum hadron and jet production. $A_{\mathrm{LL}}$ is defined by $A_{\mathrm{LL}}=\frac{(\frac{\mathrm{Ed}{\sigma }_L^{+}}{d^{3}p}-\frac{\mathrm{Ed}{\sigma }_L^{-}}{d^{3}p})}{(\frac{\mathrm{Ed}{\sigma }_L^{+}}{d^{3}p}+\frac{\mathrm{Ed}{\sigma }_L^{-}}{d^{3}p})}$, where ${\sigma }_L^{+}\left({\sigma }_L^{-}\right)$ is the $\mathrm{pp}$ cross section for the configuration in which the proton helicities are the same (opposite). For inclusive pion production the principal mechanism in the constituent-interchange model is quark-meson scattering, which leads to the prediction $A_{\mathrm{LL}}=0\mathrm{}$. However, in several recent models the mechanism for producing high-transverse-momentum pions involves processes such as quark-quark scattering for which it is expected that $A_{\mathrm{LL}}\ne 0$. In the present paper $A_{\mathrm{LL}}$ is calculated for inclusive production of pions and jets in the phenomenological effective-gluon model and also in a model based on quantum chromodynamics. Among the important ingredients of such calculations are the distribution functions for quarks in a polarized proton. A new model of these is developed and compared to the most recent SLAC data. It is shown that even in models where $A_{\mathrm{LL}}\ne 0$, the magnitude and sign of $A_{\mathrm{LL}}$ depend sensitively on the strong-interaction dynamics and hence can be used to discriminate among models of inclusive production.