Non-Photonic Electron Angular Correlations With Charged Hadrons From The STAR Experiment: First Measurement Of Bottom Contribution To Non-Photonic Electrons At RHIC

Experimental results from the Relativistic Heavy Ion Collider (RHIC) have established the creation of an extremely dense partonic matter in central Au+Au collisions at RHIC. The measurements of suppression of high transverse momentum particles and azimuthal anisotropy v₂ for light hadrons have indicated partonic energy loss in the produced matter and the development of partonic collectivity in a very early stage of the collision. The study of energy loss and elliptic flow for hadrons carrying heavy quarks will complement these measurements and provide further insight into properties of the produced medium.Recent experimental data from RHIC show that the nuclear modification factor of non-photonic electrons from heavy quark decays is comparable to that of light hadrons in central Au+Au collisions. This implies that heavy quarks lose a substantial amount of energy, in contradiction with existing theoretical predictions. The detailed comparison with experimental non-photonic electron energy loss depends on the relative contributions from D and B meson decays. Strong elliptic flow for non-photonic electrons has been observed recently, suggesting that charm quark carries a substantial amount of v₂. The non-photonic electron v₂ data show a tendency for the measured v₂ to decrease with P_T at high p_T region, which could be an indication of increasing contribution to non-photonic electrons from B meson decays. The full understanding of the non-photonic electron energy loss and elliptic flow requires the knowledge of the relative D and B meson decay contributions to non-photonic electrons.We here propose an innovative experimental method which uses the azimuthal correlations between non-photonic electrons and charged hadrons to estimate the relative contributions to non-photonic electron yield from D and B meson decays. Our method is based on the fact that for the same electron transverse momentum the near-side e-h azimuthal correlation from B decays is much wider than that from D decays. Correlations of non-photonic electrons with charged hadrons using PYTHIA Monte Carlo event generator in p+p collisions at = 200 GeV are studied. The measurement of azimuthal correlations between non-photonic electrons and charged hadrons in p+p collisions at = 200 GeV from the STAR experiment is presented. These analyses provide the first measurement of B meson semi-leptonic decay contribution to non-photonic electrons as a function of electron p_T for p_T > 2.5 GeV at RHIC.Within the present statistical and systematic errors, our data analysis based on PYTHIA model indicates that at p_T～4.0 - 6.0 GeV/c the measured B contribution to non-photonic electrons is comparable to the D contribution and that the measured B/(B + D) ratios as a function of transverse momentum from 2.5 to 6.5 Gev/c are consistent with the FONLL theoretical calculation. Together with the observed large energy loss of non-photonic electrons and the decreasing value for the non-photonic electron v₂ at high p_T in Au+Au collisions, the measured B/(B + D) ratios imply that the bottom quarks suffer considerable amount of energy loss in the dense QCD medium as well.