We estimate the valence quark contributions for the ${\gamma }^{*}Y\to {\Lambda }^{*}$ ($Y=\Lambda$, ${\Sigma }^0$) electromagnetic transition form factors. We focus particularly on the case of ${\Lambda }^{*}=\Lambda (1670)$ as an analogue reaction with ${\gamma }^{*}N\to N(1535)$. The results are compared with those obtained from chiral unitary model, where the ${\Lambda }^{*}$ resonance is dynamically generated and thus the electromagnetic structure comes directly from the meson cloud excitation of the baryon ground states. The form factors for the case $Y={\Sigma }^0$ in particular, depend crucially on the two real phase (sign) combination, a phase between the $\Lambda$ and ${\Lambda }^{*}$ states, and the other, the phase between the $\Lambda$ and ${\Sigma }^0$ radial wave functions. Depending on the combination of these two phases, the form factors for the ${\gamma }^{*}{\Sigma }^0\to {\Lambda }^{*}$ reaction can be enhanced or suppressed. Therefore, there is a possibility to determine the phase combination by experiments.

• Received 13 February 2012

DOI:https://doi.org/10.1103/PhysRevD.85.093014