Photoproduction of a Λ on ¹²C

The photoproduction of a Λ on ¹²C is investigated by using the recently developed Saclay-Lyon amplitudes for the γp⃗K⁺Λ reaction and the single-particle wave functions from a relativistic mean-field model of nuclei and Λ hypernuclei. With the nuclear transition matrix elements taken from a shell-model calculation, the predicted bound-Λ production cross sections are close to the ¹²C(γ,K⁺)_Λ¹²B reaction data. The dependence of the predictions on the model of γp⃗K⁺Λ amplitudes has been investigated. The cross sections of quasifree processes leading to an unbound Λ are also calculated in a simple three-body model. The predicted cross sections of the inclusive ¹²C(γ,K⁺) reaction reproduce the energy dependence of the data up to 1.1 GeV, but overestimate the magnitude by a factor of about 2.2. We discuss the extent to which this overestimation can be understood in terms of medium effects on the propagation of the outgoing K⁺ and Λ.