Measurement of inclusive π0 production in hadronic Z 0 decays

An analysis is presented of inclusive π⁰ production in Z ⁰ decays measured with the DELPHI detector. At low energies, π⁰ decays are reconstructed by using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to $x_p={2cdot p?/{sqrt s}=0.75}$) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for qq? and bb? events. The number of π⁰’s per hadronic Z ⁰ event is $N(?^0)/Z_{had} ^0=9.2pm 0.2({? stat})pm 1.0 ({? syst})$ and for bb? events the number of π⁰’s is ${? N}(?^0)/{? b?r b}=10.1pm 0.4({? stat})pm 1.1 ({? syst})$. The ratio of the number of π⁰’s in bb? events to hadronic Z ⁰ events is less affected by the systematic errors and is found to be 1.09 ±0.05 ±0.01. The measured π⁰ cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in the $xi_{? p}={? ln}(1/{? x_p})$ distribution is $xi_p^{?ar}=3.90_{-0.14}^{+0.24}.$ The average number of π⁰’s from the decay of primary B hadrons is found to be N(B → π⁰ X)/B hadron = 2.78 ± 0.15(stat) ± 0.60(syst).