Cross Sections and Beam Asymmetry for $K^{+}{\Sigma }^{*-}$ Photoproduction from the Deuteron at $E_{\gamma }=1.5–2.4\mathrm{GeV}$

The $\Sigma (1385)$ resonance, or ${\Sigma }^{*}$, is well known as part of the standard baryon decuplet with spin $J=\frac{3}{2}$. Measurements of the reaction $\gamma p\to K^{+}{\Sigma }^{*0}$ are difficult to extract due to overlap with the nearby $\Lambda (1405)$ resonance. However, the reaction $\gamma n\to K^{+}{\Sigma }^{*-}$ has no overlap with the $\Lambda (1405)$ due to its charge. Here we report the first measurement of cross sections and beam asymmetries for photoproduction of the ${\Sigma }^{*-}$ from a deuteron target. The cross sections at forward angles range from 0.4 to $1.2\mu \mathrm{b}$, with a broad maximum near $E_{\gamma }\simeq 1.8\mathrm{GeV}$. The beam asymmetries are negative, in contrast with positive values for the $\gamma n\to K^{+}{\Sigma }^{-}$ reaction.

Figure 1

Mass spectra calculated using the missing mass technique for: (a) detected $K^{+}{\pi }^{-}$; (b) detected $K^{+}$ only; (c) same as (a) but cut on the $\Sigma (1385)$ peak shown by the dashed lines in (b); (d) same as (b) but cut on the $\Lambda$ peak shown by the dashed lines in (a).

Figure 2

Cross sections for the reaction $\gamma n\to K^{+}{\Sigma }^{*-}$ as a function of photon energy. Each plot is for the angle bin in $\cos {\theta }_{\mathrm{cm}}$ as shown. The curve is from the model of Ref. [5] and the shaded region extends over the given angular range.

Figure 3

Azimuthal angle $\varphi$ dependence of the asymmetry given by Eq. (1) for $K^{+}{\Sigma }^{-}$ (left) and $K^{+}{\Sigma }^{*-}$ (right) photoproduction from the deuteron. Three energy bins are shown: 1.5–1.8 GeV (top), 1.8–2.1 GeV (middle), and 2.1–2.4 GeV (bottom). The curves are fit to the function $A\cos 2\varphi$.

Figure 4

Linear beam asymmetry $\Sigma$ for the reactions $K^{+}{\Sigma }^{-}$ (top) and $K^{+}{\Sigma }^{*-}$ (bottom) photoproduction from the deuteron as a function of photon energy. The open points in the top plot are weighted averages from Ref. [11], which are offset from the bin center for visibility. The curve is from the model of Ref. [5].