I.P. Ivanenko

Observation Of Very High Energy Cosmic-ray Families In Emulsion Chambers At High Mountain Altitudes (i)

Characteristics of cosmic-ray hadronic interactions in the 1015 − 1017 eV range are studied by observing a total of 429 cosmic-ray families of visible energy greater than 100 TeV found in emulsion chamber experiments at high mountain altitudes, Chacaltaya (5200 m above sea level) and the Pamirs (4300 m above sea level). Extensive comparisons were made with simulated families based on models so far proposed, concentrating on the relation between the observed family flux and the behaviour of high-energy showers in the families, hadronic and electromagnetic components. It is concluded that there must be global change in characteristics of hadronic interactions at around 1016 eV deviating from thise known in the accelerator energy range, specially in the forwardmost angular region of the collision. A detailed study of a new shower phenomenon of small-pT particle emissions, pT being of the order of 10 MeV/c, is carried out and its relation to the origin of huge “halo” phenomena associated with extremely high energy families is discussed as one of the possibilities. General characteristics of such super-families are surveyed.

Observation of attenuation behaviour of hadrons in extremely high energy cosmic ray interactions: New hadronic state?

Abstract Experimental results are presented on high energy cosmic-ray hadron interactions recorded in homogeneous-type thick lead chambers (total thickness being 60 cm and 110 cm) exposed at the Pamirs (atmospheric depth 595 g/ cm 2 ). High energy cosmic-ray hadron flux is measured. The attenuation mean free path of the arriving cosmic-ray hadrons of E h γ ≥ 6 TeV measured in the chamber is obtained as 252 ± 30 g/cm 2 of lead. However, for the high energy hadrons ( E ( γ ) ≥ 10 TeV) constituting cosmic-ray families of the highest energy range, ΣE ( γ ) ≥ 700 TeV, which have been accumulated so far in the series exposures at the Pamirs and analysed by MSU group, the attenuation mean free path of hadrons in lead has turned out to be as short as 170 −26 +47 g/cm 2 with 95% CL by the maximum likelihood method. The present experimental result of such a short attenuation length of hadrons in cosmic-ray families is essentially consistent with that obtained for high energy hadrons ( E ( γ ) ≥ 10 TeV) constituting the “Chiron-type” families of ΣE ( γ )>100 TeV in the Chacaltaya two-storeyed chamber experiments. The anomalous transition characteristics of high energy hadrons in lead is found and examples are presented. The physical significance of the experimental results on extremely high energy hadron interactions is discussed.

Observation of a high-energy cosmic-ray family caused by a Centauro-type nuclear interaction in the joint emulsion chamber experiment at the Pamirs

Abstract An exotic cosmic-ray family event is observed in the large emulsion chamber exposed by the joint at the Pamirs (4360 m above sea level). The family is composed of 120 γ -ray-induced showers and 37 hadron-induced showers with individual visible energy exceeding 1 TeV. The decisive feature of the event is the hadron dominance: ΣE γ , ΣE ( γ ) h , 〈 E γ , 〈 E ( γ ) h 〉, 〈 E γ · R γ 〉 and 〈 E ( γ ) · R h 〉 being 298 TeV, 476 TeV, 2.5 TeV, 12.9 TeV, 28.6 GeV m and 173 GeV m, respectively. Most probably the event is due to a Centauro interaction, which occured in the atmosphere at ∼700 m above the chamber. The event will constitute the second beautiful candidate for a Centauro observed at the Pamirs.