Measurement of inclusiveπ ⁰ production in hadronicZ ⁰ decays

Abstract

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 _had =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/x_p) distribution isξ* _p =3.90 ^+0.24_−0.14 . 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).