Combined analysis of the data on cross sections and spin density matrix elements for $K^*Σ$ photoproduction reactions

Abstract

In our earlier work [Phys. Rev. C \textbf{98}, 045209 (2018)], we analyzed the differential cross-section data from the CLAS Collaboration for the reactions $γp \to K^{*+}Σ^0$ and $γp \to K^{*0} Σ^+$ using an effective Lagrangian approach. We found that a satisfactory description of the data required the inclusion of the $s$-channel $Δ(1905)5/2^+$ resonance, in addition to $t$-channel exchanges of $K$, $κ$, and $K^*$, $s$-channel contributions from nucleons ($N$) and $Δ$, $u$-channel exchanges of $Λ$, $Σ$, and $Σ^*$, and a generalized contact term. In the present work, we extend our analysis to incorporate the data on spin density matrix elements from the LEPS Collaboration for the $γp \to K^{*0}Σ^+$ reaction at photon energies $E_γ = 1.85$--$2.96$ GeV. Our goal is to impose more stringent constraints on the theoretical model and obtain a more reliable understanding of the reaction mechanisms. We obtain two fits that describe the experimental data equally well. In both fits, the $Δ(1905)5/2^+$ resonance plays an important role. However, the contribution from $t$-channel $κ$ exchange is significant in one fit but negligible in the other. This finding contradicts earlier claims in the literature that the LEPS parity spin asymmetry $P_σ$ data support a dominant role of $κ$ exchange in $γp \to K^{*0}Σ^+$. We also present predictions for $P_σ$ at $E_γ= 8.5$ GeV, which may help clarify whether $κ$ exchange is indeed dominant in this reaction.

Figures (10)

• Figure 1: Generic structure of photoproduction amplitude for $\gamma N\to K^{*}\Sigma$. Time proceeds from left to right.
• Figure 2: Differential cross sections for $\gamma p \to K^{*+}\Sigma^0$ as a function of $\cos\theta$ (black solid lines) in model I. The scattered symbols denote the CLAS data in Ref. Wei:2013. The blue dashed, green dash-double-dotted, magenta dotted, and cyan dash-dotted lines represent the individual contributions from the $\Delta(1905)5/2^+$, $\Delta$, $\Lambda$, and $K^*$ exchanges, respectively. The numbers in parentheses denote the centroid value of the photon laboratory incident energy (left number) and the corresponding total c.m. energy of the system (right number), in MeV.
• Figure 3: Differential cross sections for $\gamma p \to K^{*0}\Sigma^+$ as a function of $\cos\theta$ in model I. Notations are the same as in Fig. \ref{['fig:dif1']} except that now the cyan dash-dotted lines represent the contributions from the $u$-channel $\Sigma^*$ exchange, the magenta dotted lines denote the contributions from the $u$-channel $\Sigma$ exchange, and the scattered symbols denote the CLAS data in Ref. Hleiqawi:2007ad.
• Figure 4: Differential cross sections for $\gamma p \to K^{*+}\Sigma^0$ as a function of $\cos\theta$ in model II. Notations are the same as in Fig. \ref{['fig:dif1']} except that the orange dot-double-dashed lines represent the contributions from the $\kappa$ exchange.
• Figure 5: Differential cross sections for $\gamma p \to K^{*0}\Sigma^+$ as a function of $\cos\theta$ in model II. Notations are the same as in Fig. \ref{['fig:dif2']} except that the orange dot-double-dashed lines represent the contributions from the $\kappa$ exchange.