Dependence of the ${}^{12}$C($\vec{\gamma }$,pd) reaction on photon linear polarisation

The sensitivity of the ${}^{12}$C$(\vec{\gamma },pd)$ reaction to photon linear polarisation has been determined at MAMI, giving the first measurement of the reaction for a nucleus heavier than ${}^3$He. Photon asymmetries and cross sections were measured for $E_{\gamma }$=170 to 350 MeV. For $E_{\gamma }$ below the $\mathrm{\Delta }$ resonance, reactions leaving the residual ${}^9$Be near its ground state show a positive asymmetry of up to 0.3, similar to that observed for ${}^3$He suggesting a similar reaction mechanism for the two nuclei.