Measurement of the Σπ photoproduction line shapes near the Λ(1405)

Le résumé fourni par la source

The reaction $\ensuremath{\gamma}+p\ensuremath{\rightarrow}{K}^{+}+\ensuremath{\Sigma}+\ensuremath{\pi}$ was used to determine the invariant mass distributions or ``line shapes'' of the ${\ensuremath{\Sigma}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$, ${\ensuremath{\Sigma}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$, and ${\ensuremath{\Sigma}}^{0}{\ensuremath{\pi}}^{0}$ final states, from threshold at 1328 $\mathrm{MeV}/{c}^{2}$ through the mass range of the $\ensuremath{\Lambda}(1405)$ and the $\ensuremath{\Lambda}(1520)$. The measurements were made with the CLAS system at Jefferson Lab using tagged real photons, for center-of-mass energies $1.95<W<2.85$ GeV. The three mass distributions differ strongly in the vicinity of the $I=0$ $\ensuremath{\Lambda}(1405)$, indicating the presence of substantial $I=1$ strength in the reaction. Background contributions to the data from the ${\ensuremath{\Sigma}}^{0}(1385)$ and from ${K}^{*}\ensuremath{\Sigma}$ production were studied and shown to have negligible influence. To separate the isospin amplitudes, Breit-Wigner model fits were made that included channel-coupling distortions due to the $N\overline{K}$ threshold. A best fit to all the data was obtained after including a phenomenological $I=1$, ${J}^{P}=1/{2}^{\ensuremath{-}}$ amplitude with a centroid at $1394\ifmmode\pm\else\textpm\fi{}20$ $\mathrm{MeV}/{c}^{2}$ and a second $I=1$ amplitude at $1413\ifmmode\pm\else\textpm\fi{}10$ $\mathrm{MeV}/{c}^{2}$. The centroid of the $I=0$ $\ensuremath{\Lambda}(1405)$ strength was found at the $\ensuremath{\Sigma}\ensuremath{\pi}$ threshold, with the observed shape determined largely by channel coupling, leading to an apparent overall peak near 1405 $\mathrm{MeV}/{c}^{2}$.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.