Improved determination of the sample composition of dimuon events   produced in {\boldmath $p\bar{p}$} collisions at {\boldmath $\sqrt{s}=1.96$}   TeV
  We use a new method to estimate with 5% accuracy the contribution of pion and kaon in-flight-decays to the dimuon data set acquired with the CDF detector. Based on this improved estimate, we show that the total number and the properties of the collected dimuon events are not yet accounted for by ordinary sources of dimuons which also include the contributions, as measured in the data, of heavy flavor, $\Upsilon$, and Drell-Yan production in addition to muons mimicked by hadronic punchthrough. 
CDF Collaboration
hep-ex