Observation of Prompt Single Muon Production of 400 GEV Protons

The observation of prompt single muon production from 400 GeV protons interacting in an iron target is reported. The experiment used a variable-density calorimeter made of iron plates and plastic scintillator as a target, followed by a large-acceptance muon identifier and an iron toroidal spectrometer. Single muon and dimuon events were separated with good efficiency using the muon identifier, and the rate of prompt single muons was measured by varying the density of the target-calorimeter, thereby changing the relative rate of prompt and non-prompt single muon production. Prompt single muon signals were observed in two different kinematic regions - pμ < 20 GeV/c, ptμ > 1 GeV/c and 10 GeV/c < pμ < 60 GeV/c, ptμ > 0.5 GeV/c. Approximate equality was found between the prompt 1μ+ and prompt 1μ- signal in the high p region (in the high pt region, only positive muons were accepted by the trigger). The observed cross section in both regions was~ 70 nb/nucleon, assuming linear A dependence for the production of the prompt muons. Hadronic production of charmed particles was the most likely source of the prompt muons; other possible sources could not account for the large rates observed. Three different models for charm production - uncorrelated D production, correlated DD production, and diffractive production of Λc-D pairs - are compared to the data and used to calculate cross sections. Within the DD model, the range of kinematic parameters allowed by the data is determined and the corresponding range of cross