Failure ofs-Channel Helicity Conservation inA1−Production

A study of the ${A_1}^{-}$ density-matrix elements shows that $s$-channel helicity is not conserved in the process ${\pi }^{-}p\to {A_1}^{-}p$ between 5 and 25 $\frac{\mathrm{GeV}}{c}$. Instead the ${A_1}^{-}$ density-matrix elements have simple behavior in the $t$-channel helicity frame. A new analysis of the ${A_1}^{-}$ cross section as a function of the incident ${\pi }^{-}$ momentum is also presented.