Inclusive observation of neutral pions from pion--proton collisions at 14 GeV/c

In the early 1970s inclusive momentum distributions of secondary particles created in energetic collisions between hadrons began to attract much theoretical and experimental attention. Bubble chamber experiments have produced excellent and extensive data on the charged secondary particles, mostly pions, from various kinds of hadron collision, but such experiments have difficulty in detecting neutral pions. A counter experiment designed to detect neutral pions and complement the bubble chamber data is described. This experiment detects the two gamma rays from neutral pion decay and measures the invariant mass, so that the parent particle is conclusively identified. Gamma ray spectrometers based upon large sodium iodide scintillation counters of excellent energy resolution are employed. Neutral pions are produced in liquid hydrogen by both positive and negative pions at a laboratory momentum of 14 GeV/c, and are detected over the ranges 0.25 to 1.0 in the Feynman scaling variable and 0 to 0.7 GeV/c in the transverse momentum. The results show that the cross section for production of neutral pions at large forward momenta is very small compared to the cross section for charged pions of the same polarity as the incident beam, but somewhat larger than the cross section for the beam-unlike charged pions. Transverse momentum dependences of the production cross sections are similar for neutral and charged pions. The ''Favored and Disfavored Fragmentation'' picture of hadronic collisions is supported by the data. A Triple Regge parameterization of the neutral pion inclusive cross section between 0.6 and 0.9 in the Feynman scaling variable also works reasonably well