Nuclear Matter at High Densities - Elucidating the Properties of Hadronic Resonances in the Nuclear Medium

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Latest improvements in astronomical equipment had recently realized in a series of brilliant discoveries and riseinterest to a question of nuclear matter at extreme conditions. These conditions can be achieved in neutron stars and atvarious catastrophic astrophysical phenomena, like neutron star mergers, black hole collapses etc... The keyparameter which describes nuclear matter at moderate densities is the symmetry energy. It can be extracted bymeasurement of the neutron skins of a range of nuclei. Our group leads such measurements utilizing the high intensityphoton beam of Mainz MAMI facility with hermetic Crystal Ball (CB) detector, a highly segmented photon andparticle calorimeter. A UoY led programme of "skin" measurements on various isotopes (including the flagshipmeasurement of 48Ca) will be obtained in late 2018 with further beamtime possible in 2019. Due to the niceperformance and large acceptance of the CB detector, one can measure essentially all photo-induced reactions onnuclear targets in parallel to the main "skin" measurements. This gives access to another high profile programme -elucidating the properties of hadronic resonances in the nuclear medium. Of particular importance is constraining theinteraction of the recently discovered d*(2380) hexaquark. Recent UoY led papers indicate this new particle sets alimit on achievable neutron star masses, plays a key role in the dynamics of neutron star merger events (includingresultant gravitational wave emission) and may act as an important intermediate step in nuclear to quark-gluon plasmatransition in nuclear matter. To advance these exciting studies it is crucial to constrain the basic properties of thed*(2380) in-medium for the first time.We propose a new method to look for in-medium d*(2380) production using incoherent 2(pi)0 production onnuclei. The simplest example of such reaction would be yC12 --> d*+ 10N --> pi0 pi0 C12* with C12* --> C12 +y(4.4 MeV) reaction. The requirement for an extra photon from excited nuclei ensures in-medium d*(2380)production, filters out major backgrounds and allows to determine in-medium electromagnetic properties bycomparing the intensity of various nuclear excited state population.