Speaker
Prof.
Paolo Camerini
(Univ. Trieste & INFN Trieste)
Description
The $K^-_{stop} A$ $\rightarrow$ $\Sigma^\pm\pi^\mp A'$ reaction is studied on light nuclei, $A=$
$^{6,7}Li$, $^9Be$, $^{13}C$ and $^{16}O$.
The outgoing $\Sigma$'s and $\pi$'s are detected using the FINUDA spectrometer, which
operated at the DA$\Phi$NE $e^+e^-$ facility (LNF). The $\Sigma^\pm$ hyperons are reconstructed via the
$n \pi^\pm$ decay with the neutrons detected by TOFONE, a large volume plastic scintillator array. The
two final $\pi^\pm$ mesons are reconstructed by means of the FINUDA tracker, which consists of 5
position sensitive layers. Final $\Sigma^\pm \pi^\mp$ pairs are selected requiring
topological cuts for the $n \pi^\pm$ correlated pairs, where the $n \pi^\pm$ pairs are requested to
have $\Sigma^\pm$ invariant mass. \\ The $\Sigma^\pm\pi^\mp/ K^-_{stop}$ emission rates are reported as
a function of $A$. These rates are compared to previous experimental measurements. They are also used
to calculate the $\gamma$ ratio ($\gamma=\Sigma^+\pi^-/\Sigma^-\pi^+$) which strongly increases when the
kaon is absorbed on an in-medium proton instead of a free proton. This effect is related to the
sub-threshold behavior of the $\bar{K}N$ interaction. \\ The momentum spectra of prompt pions and free
sigmas are also discussed as well as the $\Sigma^\pm \pi^\mp$ missing mass behavior.
In this case, the $\Sigma^\pm \pi^\mp$ channel is filled by two resonances $\Sigma(1385)$ and
$\Lambda(1405)$ as well as by the $\Sigma^\pm
\pi^\mp$ quasi-free reaction whose phase space develops in the same region as the two resonances.
Primary author
Prof.
Paolo Camerini
(Univ. Trieste & INFN Trieste)
