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

Latest improvements in astronomical equipment had recently realized in a series of brilliant discoveries and rise
interest to a question of nuclear matter at extreme conditions. These conditions can be achieved in neutron stars and at
various catastrophic astrophysical phenomena, like neutron star mergers, black hole collapses etc... The key
parameter which describes nuclear matter at moderate densities is the symmetry energy. It can be extracted by
measurement of the neutron skins of a range of nuclei. Our group leads such measurements utilizing the high intensity
photon beam of Mainz MAMI facility with hermetic Crystal Ball (CB) detector, a highly segmented photon and
particle calorimeter. A UoY led programme of "skin" measurements on various isotopes (including the flagship
measurement of 48Ca) will be obtained in late 2018 with further beamtime possible in 2019. Due to the nice
performance and large acceptance of the CB detector, one can measure essentially all photo-induced reactions on
nuclear 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 the
interaction of the recently discovered d*
(2380) hexaquark. Recent UoY led papers indicate this new particle sets a
limit on achievable neutron star masses, plays a key role in the dynamics of neutron star merger events (including
resultant gravitational wave emission) and may act as an important intermediate step in nuclear to quark-gluon plasma
transition in nuclear matter. To advance these exciting studies it is crucial to constrain the basic properties of the
d*
(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 on
nuclei. The simplest example of such reaction would be yC
12 --> d
*+ 10N --> pi
0 pi
0 C
12* with C
12* --> C
12 +
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 by
comparing the intensity of various nuclear excited state population.