First measurement of φ meson production in 30 GeV proton-nucleus reactions via di-electron decay at J-PARC

We present the first measurement of the production of the φ meson in 30 GeV proton-nucleus interactions on carbon and copper targets via the di-electron decay channel. The measurement was conducted at the high-momentum beamline of the J-PARC Hadron Experimental Facility, which was commissioned in 2020. The e+e− pairs were detected using the E16 spectrometer, during a commissioning run of the J-PARC E16 experiment. The φ mesons are successfully reconstructed on all experimental targets. The obtained yields are converted to the total production cross section, assuming a kinematical distribution of the event generator JAM. The total cross sections derived are 2.0 ± 0.9 (stat.) ± 1.0 (syst.) mb on the carbon target and 10.3 ± 4.4 (stat.) ± 4.4 (syst.) mb on the copper target. The mass-number dependence of the cross section is discussed using the parameter α, defined as σ∝Aα, resulting in α = 0.99 ± 0.38 (stat.) ± 0.34 (syst.). The extrapolation to A = 1, which means that the cross section of proton-proton reactions, is in good agreement with the existing measurements at comparable energies.