Study ofπ−p→ωn, φnat 2.10 BeV/c

Abstract

In a bubble-chamber experiment at 2.10 BeV/c we have determined the cross section $\sigma ({\pi }^{-}p\to \omega n)=1.41\mathrm{}\ne 0.18$ mb by fitting the neutral and the charged effective-mass spectra for events of the type ${\pi }^{-}p\to {\pi }^{+}{\pi }^{-}n\left(m\right)\mathrm{}{\pi }^0$, $m\ge 1$, with appropriate phase-space and resonance effective-mass distributions. Cross sections for other contributing reactions are also given. The cross section $({\pi }^{-}p\to \phi n)={{19}_{-8\mathrm{}}}^{+9\mathrm{}}$ μb (statistical error) was obtained by using the maximum-likelihood method to determine the cross section corresponding to a peak (at the $\phi$ mass 1019.5 MeV) in the $K^{+}{K}^{-}$ effective-mass spectrum of $K^{+}{K}^{-}n$ events. The relative probability of the cross section being zero is 0.07. We conclude that $\sigma ({\pi }^{-}p\to K^{+}{K}^{-}n)$ is between 75 and 150 μb at 2.10 BeV/c. The $K$-pair events studied include events both with and without a visible $K$ decay. The nondecay-event identification procedure included a visual bubble-density estimation. We calculate an $\omega -\phi$ mixing angle of 42.1±1.8° (statistical error) using a quark-model prediction by Alexander, Lipkin, and Scheck. This mixing-angle prediction agrees well with values calculated from $\mathrm{SU}\left(3\right)\mathrm{}$ mass formulas. The input data for this calculation are our $\phi n$ cross section (at c.m. energy 2.20 BeV) and the $\omega n$ cross section at c.m. energy 1.96 BeV which we estimated from ${\pi }^{+}n\to \omega p$ data.