Measurement of inclusive pi(0) production in hadronic Z(0) decays

An analysis is presented of inclusive \ pi^0 production in Z^0 decays measured with the DELPHI detector. At low energies, \ pi^0 decays are reconstructed by \linebreak 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 = 2 \cdot p_{\ pi}/\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 {q\ overlineq} and {b \bar b} events. The number of \ pi^0's per hadronicZ^0 event is N(\ pi^0)/ Z_{had}^0 = 9.2 \pm 0.2 \mbox{( stat)} \pm 1.0 \mbox{(syst)} and for {b \bar b}~events the number of \ pi^0's is {\mathrm N(\ pi^0)/ b \ overlineb} = 10.1 \pm 0.4 \mbox{( stat)} \pm 1.1 \mbox{(syst)} . The ratio of the number of \ pi^0's in b \ overlineb events to hadronicZ^0 events is less affected by the systematic errors and is found to be 1.09 \pm 0.05 \pm 0.01. The measured \ pi^0 cross sections are compared with the predictions of different parton showermodels. For hadronicevents, the peak position in the \mathrm \xi_p = \ln(1/x_p) distribution is \xi_p^{\star} = 3.90^{+0.24}_{-0.14}. The average number of \ pi^0's from the decay of primary \mathrm B hadronsis found to be {\mathrm N} (B \rightarrow \ pi^0 \, X)/\mbox{B hadron} = 2.78 \pm 0.15 \mbox{( stat)} \pm 0.60 \mbox{(syst)}.