Deuteron photodisintegration in the energy region of the d*(2380) resonance

• Applicant: Professor Dr. Michael Ostrick
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465063196

Deuteron photodisintegration is one of the simplest reactions in nuclear physics.Experimental and theoretical investigations started even shortly after the discovery of the neutron in 1932. However, even today many key observables, in particular spin dependent ones, remain unmeasured, or have been only measured in rather limited or coarse kinematics. This is particularly evidenced at photon energies above 200~MeV where the substructure of the deuteron can be excited. This limits a detailed assessment of the reaction mechanisms, including the contributions of nucleon resonances, meson exchange currents as well as constraining potential roles of exotic hadrons, such as genuine six-quark states (hexaquarks). A candidate for such a hexaquark is the so-called d*(2380), a state with isospin I = 0, spin-parity JP = 3+ and a decay width of ~70 MeV which has been observed in elastic proton-neutron (pn) scattering and several inelastic pn fusion reactions. An unambiguous identification of the d*(2380) in an electromagnetic process would be an important next step and a prerequisite for future determinations of electromagnetic couplings and transition form factors. The photoexcitation from a deuteron target, gamma d -> d*(2380), requires a beam energy of 570 MeV, which is ideal for experiments at the Mainz Microtron (MAMI) where high intensity, energy-tagged photon beams from 100 to 1500 MeV with linear and circular polarization are routinely available.The project will implement a joint experimental and theoretical program aiming at systematic measurements of double-spin observables in deuteron photodisintegration and their interpretation via sophisticated models. The results will have an important impact not only in the physics of multi-quark exotic hadrons, but also in nuclear physics, as well as in astrophysics, where it is speculated that the d*(2380) might play a role in the dynamics of neutron stars.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Science Foundation, until 3/2022
• Cooperation Partner: Professor Dr. Alexander Fix, until 3/2022