$A_N$ 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

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.