Contribution invited talk
Hexaquarks under the microscope
Several new findings in the four, five and six quark systems have catalyzed new interest in the field of multiquark states (beyond the trivial $q\bar q$ and qqq systems). Very significant progress has recently been made in the 6q sector, on both the theoretical and experimental fronts. A resonance like structure observed in double-pionic fusion to the deuteron, at M = 2.38 GeV with $\Gamma$ = 70 MeV and $I(J^P )=0(3^+)$ has been consistently observed in a wealth of reaction channels, supporting the existence of a resonant hexaquark state - the $d^*(2380)$. Such a light hexaquark would have a very wide impact beyond hadronic physics. It was recently indicated that this new particle may set a limit on achievable neutron star masses, play a key role in the dynamics of neutron star merger events (including resultant gravitational wave emission) and has the potential to be an important intermediate step in the nuclear to quark-gluon plasma transition.
The talk will present the first results on $d^$ photoproduction, obtained with the Crystal Ball at MAMI along with our future plans to improve understanding of the d with electromagnetic probes at the JLab and Mainz MAMI. The $d^*$ is the only multiquark state which can be produced copiously at current facilities, offering unique access to information beyond its basic quantum numbers, particularly its physical size and internal structure. Further possible astrophysical implications will also be outlined.