Heavy flavor leptons provide an extra handle on the open heavy flavor mesons, since they come from semi-leptonic decays of D and B mesons with significant branching ratios. Once produced, leptons do not participate in the strong interaction in the later stages of the collision, and remain a clean probe into the whole evolution of the system. Apart from TPC and TOF, BEMC is used to improve electron identification, and MTD is used for muon detection.
J/psi suppression was one of the proposed QGP signatures in the early days. Later, various cold nuclear matter effects were brought up to complicate the interpretation of J/psi measurements. Still, the study of J/psi collective motion deepens our understanding of the coalescence mechanism and the charm quark collectivity. We also reconstructed Upsilon and observed the suppression of Upsilon(1S+2S+3S).
More than 99% of charm quarks hadronize into open charm, D mesons. So the measurement of D mesons is a must for the determination of charm cross section. Due to the short life time, the low production rate and the high combinatorial background, the direct reconstruction of D mesons is difficult with the TPC pointing resolution. HFT will be employed to reconstruct the displaced vertex and greatly suppress the combinatorial background. This will also enable the D0 flow analysis, to ascertain the charm quark collectivity. Other open heavy flavor hadrons like Ds and Lambdac will also be studied with HFT.