Experimental investigation of vector mesons in medium through dielectron decay at J-PARC

Spontaneous breaking of the chiral symmetry in Quantum Chromodynamics plays a crucial role in generating hadron mass. Theoretical studies suggest that this broken symmetry may be partially restored even at normal nuclear density, leading to measurable differences in hadron masses. The J-PARC E16 experiment was designed to measure the spectral change of vector meson in a nuclear medium. It measures e + e − invariant mass spectra in 30 GeV p +A collisions at J-PARC. Importantly, the mass depends not only on momentum but also on polarization. Polarization dependence can, in principle, be experimentally investigated. We describe the experiment’s status and discuss a method of measuring polarization-dependent mass.