$A_N$ at small negative values of $\xf$ in the reaction $p+p(pol) \to \pi^0+X$ at 70 GeV and universal threshold in inclusive pion production

TL;DR

This paper reports measurements of single spin asymmetry in polarized proton-proton collisions producing neutral pions at 70 GeV, revealing asymmetry growth at small negative Feynman-x and supporting the universal threshold hypothesis.

Contribution

It provides new experimental data on SSA at small negative $x$ in polarized proton collisions, confirming the universal threshold in inclusive pion production.

Findings

SSA reaches -16% at -0.4<xf<-0.25

Asymmetry increases in absolute value with decreasing xf

Results support the universal threshold in pion asymmetries

Abstract

The talk continues the series of Single Spin Asymmetry (SSA) $\pi^0$ inclusive measurements carried out at Protvino 70 GeV accelerator. The asymmetry in the polarized target fragmentation region grows up in absolute value with $\xf$ decreasing and equals to $(-16 \pm 5)%$ at $-0.4<\xf<-0.25$. The result of the current experiment is in agreement with the universal threshold in pion asymmetries.