Measurements of theA2−andA2+Mass Spectra

Abstract

Observations of the mass distribution of the $A_2$ meson produced in the reaction $\pi p\to A_{2}p$ are reported. The $A_2$'s were observed using a missing-mass technique. Measurements were made with 5- and 7-GeV ${\pi }^{-}$ as well as 5-GeV ${\pi }^{+}$ beams. For each beam setting more than 17000 $A_2$'s above background were observed with $0.20<~\mathrm{}\left|t\right|\mathrm{}<~0.29$ Ge${\mathrm{V}}^2$. The $A_2$ peaks are well described by a Breit-Wigner shape, whereas the dipole mass formula does not fit the data.