NA60 results on charm and intermediate mass dimuons' production in In–In 158 GeV A−1collisions

The high granularity pixel vertex tracker of the NA60 experiment can distinguish between prompt muon production and semi-leptonic decays of open charm. This clarifies the origin of the dimuon excess measured by NA50 in the 1.2–2.7 GeV/ c 2 mass range in Pb–Pb collisions. Preliminary results from NA60, obtained in In–In collisions at 158 GeV/nucleon, have shown that the excess is due to prompt dimuons. We present here the most recent results, obtained using the full statistics, with a significant improvement of the off-vertex decay tagging capabilities, due to a better detector alignment. Results on multiplicity and p T dependences of both charm and prompt dimuon contributions are presented here for the first time.