Measurement of inclusive π 0 production in hadronic Z 0 decays

An analysis is presented of inclusiveπ 0 production inZ 0 decays measured with the DELPHI detector. At low energies,π 0 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 $$x_p = 2 \cdot p_\pi /\sqrt s = 0.75$$ ) 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 forqq andbb events. The number ofπ 0’s per hadronicZ 0 event isN(π 0)/Z 0 =9.2±0.2(stat)±1.0(syst) and forbb events the number ofπ 0’s is N(π 0)/bb=10.1±0.4(stat)±1.1(syst). The ratio of the number ofπ 0’s inbb events to hadronicZ 0 events is less affected by the systematic errors and is found to be 1.09±0.05±0.01. The measuredπ 0 cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in theξ p=ln(1/xp) distribution isξ* p =3.90 −0.14 +0.24 . The average number ofπ 0’s from the decay of primary B hadrons is found to be N(B→π 0 X)/B hadron=2.78±0.15(stat)±0.60(syst).