STAR refers to the Solenoidal Tracking instrument At RHIC (the Relativistic heavy Ion Collider). For momenta above 500 KeV/c charged kaons are not separated form pions within STAR's Main TPC(Time Projection Chamber) by track den- sity alone and they are poorly separated below 500 MeV/c, even when using information form other sources like the vertex tracker. Within the TPC large numbers of kaons and poins decay into muons (and undetected neutinos). Earlier work has shown parent pions and kaons whose decays are detected within a TPC may be distinguished uniquely form each other in a two-dimensional plot of muon-emission angle versus momentum difference (between each parent meson and its decay muon).
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