A comparative measurement of ϕ→K+K− and ϕ→μ+μ− in In–In collisions at the CERN SPS

Abstract The NA60 experiment at the CERN SPS has studied ϕ meson production in In–In collisions at 158 A GeV via both the K + K − and the μ + μ − decay channels. The yields and inverse slope parameters of the m T spectra observed in the two channels are compatible within errors, different from the large discrepancies seen in Pb–Pb collisions between the hadronic (NA49) and dimuon (NA50) decay channels. Possible physics implications are discussed.