Search for narrow six-quark states in the reactions $\gamma d\to \pi\gamma nn$

We study the reactions $\gamma d\to\pi\gamma NN$ with the aim to search for six-quark states, the decay of which into two nucleons is forbidden by the Pauli exclusion principle. These states with the masses $M<2m_N+m_{\pi}$ should mainly decay by emitting a photon. This is a new class of metastable six-quark states with the decay widths $<< 1$keV. The recent experiment at Proton Linear Accelerator of INR (Moscow) suggests a possibility of the existence of such states with masses 1904, 1926, and 1942 MeV. The proposed experiment at MAMI-C could provide an unique opportunity to observe such dibaryon states in mass region up to 2000 MeV and determine their masses and quantum numbers.