Prompt Electron Production in Electron-Positron Annihilations at 29 GeV

[摘要]

We have studied the production of prompt electrons in high statistics sample (118 pb^-1) of multihadron events produced in electron positron annihilations at 29 Gev. The experiment was performed using the DELCO facility on the PEP storage ring at SLAC. Electron identification was done primarily with a large acceptance threshold Čerenkov counter. Both the momentum and the transverse momentum spectra are measured in terms of a differential cross section for electrons having momenta in the range 0.5 < P < 5.5 Gev/c. We measure the inclusive cross section in this momentum range to be 35.8±3.1 pb. The final distribution of candidates in the P – P_⊥ plane are fit well using a Monte Carlo having a combination of bottom and charm quark decays with the semielectronic branching ratios of (15.0±2.9)% and (8.9±1.4)%. We observe no evidence of electron production from new sources and determine a cross section upper limit of 11.6 pb (90% CL) for this process. We find that the fragmentation functions are hard for both b and c quarks, characterized by the values b> = 0.77±0.05 and c> = 0.68±0.06, where z is the fraction of the heavy quark's energy that is retained by the primary hadron containing the heavy quark. The fragmentation function is fit well by the form D_q(z) = N/[z(1- (1/z) – (∈_q/1-z))²] with ∈_b = .018^+.024_-.011 and ∈_c = .053^+.061_-.029. Finally we observe events having two electrons with an inclusive cross section of 2.8±1.3 pb for this process, which is consistent with the rate expected from the measured semielectronic rates.

[发布机构] University:California Institute of Technology;Department:Physics, Mathematics and Astronomy

[关键词] Physics