Coplanar Production of Pions at Energies above 10 PeV According to Pamir Experiment Data

Phenomenon of coplanar emission of secondary particles in superhigh energy nuclear interactions is investigated through the study of structure of γ−ray families detected in Pamir emulsion chamber experiment. To increase sensitivity of γ−family structure to anisotropy of the interaction predominantly contributing to the observed family, decascading of electromagnetic cascades into initial γ−rays and their subsequent coupling in π 0 -mesons were performed. The probability to observe super energy families with aligned multi-core structures composed of 4 or 5 highest energy reconstructed neutral pions is higher than that predicted in QGSJet model by 3.5 standard deviations. The energy-lateral characteristics of the aligned multi-core pion structures favors the hypothesis of high pT production of coplanar pions (pT ∼ 3 TeV/c). The estimated energy threshold for production of coplanar events is as high as E0 ∼ 8 PeV.