Speaker
Description
The J-PARC E16 experiment aims to experimentally observe modifications of vector meson mass spectra in a nuclear medium, which are expected as a consequence of the partial restoration of chiral symmetry at finite density. In the experiment, vector mesons are produced by the 30 GeV proton beam at J-PARC on nuclear targets, and their di-electron decay is detected to obtain the invariant mass spectrum. Because the electrons do not suffer from final-state strong interactions with the nuclear medium, unlike hadronic decay modes, this enables a clean measurement of the invariant mass spectrum without distortion.
The E16 experiment completed its final commissioning run in June 2024 and started physics data taking in November 2025. From the analysis of the commissioning data, we confirmed that the vector mesons, in particular the $\phi$ meson, can be successfully reconstructed, with the $e^+e^-$ pairs collected despite 100 times more hadronic background. Furthermore, the production cross section of the $\phi$ meson was estimated from the obtained $\phi$ yield, assuming the production kinematics suggested by the event generator JAM.
In this presentation, after giving an overview and current status of the E16 experiment, we report the results from the 2024 commissioning run.