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Abstract

In a bubble-chamber experiment at 2.10 BeV/c we have determined the cross section $\ensuremath{\sigma}({\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\omega}n)=1.41\ensuremath{\ne}0.18$ mb by fitting the neutral and the charged effective-mass spectra for events of the type ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}n(m){\ensuremath{\pi}}^{0}$, $m\ensuremath{\ge}1$, with appropriate phase-space and resonance effective-mass distributions. Cross sections for other contributing reactions are also given. The cross section $({\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\varphi}n)={{19}_{\ensuremath{-}8}}^{+9}$ \ensuremath{\mu}b (statistical error) was obtained by using the maximum-likelihood method to determine the cross section corresponding to a peak (at the $\ensuremath{\varphi}$ mass 1019.5 MeV) in the ${K}^{+}{K}^{\ensuremath{-}}$ effective-mass spectrum of ${K}^{+}{K}^{\ensuremath{-}}n$ events. The relative probability of the cross section being zero is 0.07. We conclude that $\ensuremath{\sigma}({\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}n)$ is between 75 and 150 \ensuremath{\mu}b 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 $\ensuremath{\omega}\ensuremath{-}\ensuremath{\varphi}$ mixing angle of 42.1\ifmmode\pm\else\textpm\fi{}1.8\ifmmode^\circ\else\textdegree\fi{} (statistical error) using a quark-model prediction by Alexander, Lipkin, and Scheck. This mixing-angle prediction agrees well with values calculated from $\mathrm{SU}(3)$ mass formulas. The input data for this calculation are our $\ensuremath{\varphi}n$ cross section (at c.m. energy 2.20 BeV) and the $\ensuremath{\omega}n$ cross section at c.m. energy 1.96 BeV which we estimated from ${\ensuremath{\pi}}^{+}n\ensuremath{\rightarrow}\ensuremath{\omega}p$ data.

Study ofπ−p→ωn, φnat 2.10 BeV/c

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