Charged-pion cross sections and double-helicity asymmetries in polarized p+p collisions at s=200 GeV

Le résumé fourni par la source

We present midrapidity charged-pion invariant cross sections, the ratio of the ${\ensuremath{\pi}}^{\ensuremath{-}}$ to ${\ensuremath{\pi}}^{+}$ cross sections and the charge-separated double-spin asymmetries in polarized $p+p$ collisions at $\sqrt{s}=200\text{ }\mathrm{GeV}$. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. The charge-separated pion asymmetries presented here sample an $x$ range of $\ensuremath{\sim}0.03--0.16$ and provide unique information on the sign of the gluon-helicity distribution.

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