Production of charm and bottom quarks in $p+p$ collisions at 200GeV
The measurement of electrons from semi-leptonic decay of heavy flavor in $p+p$ collisions at $\sqrt{s}$=200 GeV has been carried out with the PHENIX detector in the RHIC Year-2005 and Year-2006 run. This measurement provides a good test of the perturbative QCD and the important base line to study the medium created in Au+Au collisions at RHIC. The behavior of bottom in the medium is expected to be largely different from that of charm. Therefore, the determination of the fraction of bottom in the electrons from heavy flavor is necessary to understand the behavior of heavy quarks in the matter. The first separate measurement of charm and bottom via partial reconstruction of $D/\bar{D} \to e^{\pm} K^{\mp} X$ decay has been carried out in $p+p$ collisions. It is found that there is the considerable contribution from bottom in the electrons from heavy flavor above 3 GeV/$c$. The total cross section of bottom is also determined to $\sigma_{b\bar{b}}= 3.2 ^{+1.2}_{-1.1}(stat) {}^{+1.4}_{-1.3}(sys) \mu b$. It is found that the perturbative QCD predictions of charm and bottom production are consistent with the measurement of charm and bottom at PHENIX. In addition, this result indicates the not only charm but also bottom quarks lose a large fraction of their energy in the medium.