Measurement of the analyzing power in inclusive, high-x(F) charged pion production with a 200 GeV/c polarized proton beam
The analyzing power, A$\sb{\rm N},$ in inclusive $\pi\sp{+}$ and $\pi{-}$ production by a 200 GeV/c polarized proton beam was found to have a striking $x\sb{F}$ dependence in which the magnitude of A$\sb{\rm N}$ increases from 0 to 0.42 for the $\pi\sp{+}$ data and decreases from 0 to $-0.38$ for the $\pi\sp{-}$ data for increasing $x\sb{F}$ over the kinematic range $0.2 \le x\sb{F} \le 0.9$ and 0.2$GeV/c \le p\sb{T} \le 2.0GeV/c.$ The higher values of $x\sb{F}$ and $p\sb{T}$ in these kinematic ranges insure that the measured particle came from an interaction of the beam and target through a direct channel and that quark scattering through gluon exchange is the dominant interaction. The charged pions were identified and tracked with a large forward multi-particle spectrometer based upon a Helium gas threshold Cherenkov counter. A simple parton recombination model correctly predicts the signs of the spin parameters measured in this experiment. It also correctly predicts the magnitudes of the $\pi\sp{+}$ and $\pi\sp\circ$ analyzing power at high $x\sb{F}$ but the $\pi\sp{-}$ analyzing power is twice the predicted value. The $\pi\sp{+},$ $\pi\sp{-},$ and $\pi\sp\circ$ analyzing powers were also measured with a polarized anti-proton beam. These data and their interpretation with the simple model suggest that the transverse spin of the proton can be correlated with its quarks in certain kinematic regions, however, the details are still not well understood.
Particle physics, Elementary particles, High energy physics
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