Photoproduction of $\hat{I}›$ and $\hat{I}{\pounds }^0$ hyperons off protons with linearly polarized photons at $E_{\hat{I}}^3=1.5-3.0$ GeV

Abstract

We report the measurement of the ${\hat{I}}^{3}p\to K^{+}\hat{I}›$ and ${\hat{I}}^{3}p\to K^{+}\hat{I}{\pounds }^0$ reactions at SPring-8. The differential cross sections and photon-beam asymmetries are measured at forward $K^{+}$ production angles using linearly polarized tagged-photon beams in the range of $E_{\hat{I}}^3=1.5$--3.0 GeV. With increasing photon energy, the cross sections for both ${\hat{I}}^{3}p\to K^{+}\hat{I}›$ and ${\hat{I}}^{3}p\to K^{+}\hat{I}{\pounds }^0$ reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at $E_{\hat{I}}^3=1.5$--3.0 GeV. The forward peaking in the angular distributions of cross sections, a characteristic feature of $t$-channel exchange, is observed for the production of $\hat{I}›$ in the whole observed energy range. A lack of similar feature for $\hat{I}{\pounds }^0$ production reflects a less dominant role of $t$-channel contribution in this channel. The photon-beam asymmetries remain positive for both reactions, suggesting the dominance of $K^{\ast }$ exchange in the $t$ channel. These asymmetries increase gradually with the photon energy, and have a maximum value of +0.6 for both reactions. Comparison with theoretical predictions based on the Regge trajectory in the $t$ channel and the contributions of nucleon resonances indicates the major role of $t$-channel contributions as well as non-negligible effects of nucleon resonances in accounting for the reaction mechanism of hyperon photoproduction in this photon energy regime.

published version, two-column format, 10 pages, 8 figures