Association between the Dip in theπ−p→π0nHigh-Energy Angular Distribution and the Zero of theρTrajectory

Abstract

The angular distributions of ${\pi }^{-}p\to {\pi }^{0}n$ near the forward direction from 3 to 18 GeV/c measured by the Saclay-Orsay group displayed a dip near $t=-0.6\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ independent of energy. To analyze the data we assumed that the amplitude is dominated by the $\rho$-trajectory exchange, and we parametrized it with six parameters (two for the $\rho$ trajectory, two for the non-spin-flip residue, and two for the spin-flip residue). The data above 5 GeV/c with $\mathrm{}\left|t\right|\mathrm{}<~1.4$ are included in this analysis. We found a solution with ${\chi }^2=98\mathrm{}$ for a total of 62 points. The result for the $\rho$ trajectory is ${\alpha }_{\rho }=0.56(\pm 0.01)+1.08(\pm 0.03) t$. Our result shows that the observed dip can be explained by the necessary vanishing of the spin-flip amplitude when the exchange angular momentum passes through 0.