Fake Muon Background

We estimate the fake muon background by applying fake muon probablilities to third tracks in our J/&psi+track sample. First we determine the particle composition of the third tracks by using dE/dx (energy loss) and TOF (time of flight) measurements. The extraction of pion fractions using dE/dx can be seen in Figure 5. Kaons and protons are not seperated by dE/dx, so we used TOF (Figure 6) measurements in the 2.0-3.0 GeV/c momentum region to determine a proton fraction of 15% which we then extrapolate into the momentum region occupied by our third tracks. A summary of pion and kaon+proton fractions can be seen in Figure 7.

Figure 5: The dE/dx significance distributions for 3-5 GeV/c momentum ranges of tracks in the J/&psi+track sample.

Figure 6: Tof pull distribution for the tracks from J/&psi+track sample. This data is evidence for a combined pp contribution of approximately 15%.

Figure 7: The fractions of pion and combined (kaon+proton) particles on the J/&psi+track sample within 3-9 GeV/c region. F_&pi is derived from the fit and F_K+p = 1 - F_&pi. For further analysis we assign that F_pp = 0.15 ± 0.04, F_K = 1 - F_&pi - F_pp.

Having determined the third track particle composition we determine fake muon probablilites for the kaons, pions and protons that make up the third track sample. For kaons and pions we look at D^*+->D⁰&pi⁺->K^-&pi⁺&pi⁺ decays where the pions and kaons from the D⁰ decay are positively identified by the sign of the bachelor pion from the D^*+ decay. We look for D⁰ daughters that are identified as muons to determine our fake muon rate. The D⁰ mass peaks before and after muon matching can be seen in Figure 8. For protons we place an upper limit on the fake muon rate by looking at Lambda->p&pi decays where the proton is identified as the higher momentum particle. A summary of the fake rates can be seen in Figure 9.

Figure 8: Top Left: D⁰ mass distribution for K^- legs. Top Center: D⁰ mass distribution for K⁺ legs. Top Right: D⁰ mass distribution for &pi^± legs. Bottom Left: D⁰ mass distribution for K^- legs identified as muons. Bottom Center: D⁰ mass distribution for K⁺ legs identified as muons. Bottom Right: D⁰ mass distribution for &pi^± legs identifed as muons.

Figure 9: Summary of fake muon probablilites

We apply the particle fractions and fake muon rates to the the J/&psi+track sample. In the 4.0-6.0 GeV/c² mass window we see a predicted background of 16.3 ± 2.9 events.