Abstract
A phenomenon of abnormally weak absorption of very high energy cosmic ray hadrons in thick lead blocks is discussed. This phenomenon was first observed in a Tien Shan high altitude experiment to study hadronic cores of extensive air showers (EAS) with a deep ionization calorimeter and encouraged researchers to introduce the hypothesis of the so-called long-flying or penetrating cosmic ray component. A similar effect was detected later with deep uniform lead X-ray emulsion chambers (XREC) at the Pamirs, which we discuss in detail. To establish the nature of the phenomenon we are have carried out dedicated experiments at the Tien Shan and at the Pamirs by exposing two-storey XRECs with large air gaps. According to detailed simulation of the chamber response, these experiments are very sensitive to the production of charmed hadrons in the forward kinematic region and can prove a hypothesis that the phenomenon under study can be explained on the assumption of very high values of charm particle production cross section at 〈ELab〉 ~ 75 TeV in the forward kinematic region at xLab≳ 0.1 which are near the upper limit of recent results of collider experiments, i.e., σpp→c¯c~ 8 mb. The same factor makes it possible to fit all the features of the experimental hadron absorption curve observed by means of deep uniform lead XRECs, including its bending at a depth of ~ 70 c.u.
Highlights
A reduction of absorption rate of high energy hadron cascades while passing the lead material was observed for the first time in 1973 - 1974 by V.Yakovlev et al [1] at the Tien Shan High Mountain Research Station (TSS) of the P.N
At larger depths, t > 78 r.l., the absorption length of hadrons in lead changes and becomes as high as λ(a2b)s = 310 ± 36 g/cm2. It was suggested [6, 7] that both phenomena, i.e., excess ionization in the hadron calorimeter and hadron excess in the deep uniform X-ray emulsion chambers (XREC), result from high values of the cross section of leading charm particle (D mesons and Λ+c hyperons) production at energies ELab ∼ 50 TeV
Monte-Carlo simulations of both experiments, i.e., with the two-storey XREC and deep homogeneous lead XREC, were carried out under the assumption that incident cosmic ray hadrons at mountain altitudes are mainly represented by nucleons and pions with energies Eh ≥ 20 TeV which are produced by protons and nuclei of the primary cosmic ray radiation in the thick target (700 g/cm2) of the atmosphere above the chamber
Summary
A reduction of absorption rate of high energy (tens of TeV) hadron cascades while passing the lead material was observed for the first time in 1973 - 1974 by V.Yakovlev et al [1] at the Tien Shan High Mountain Research Station (TSS) of the P.N. It was suggested [6, 7] that both phenomena, i.e., excess ionization in the hadron calorimeter and hadron excess in the deep uniform XREC, result from high values of the cross section of leading charm particle (D mesons and Λ+c hyperons) production at energies ELab ∼ 50 TeV. That in the early 90-ies the measured values of charm production cross section were as s√mall as tens of μb at attainable accelerator energies ( s = 20 − 50 GeV) It means that charm production cross section should rapidly (almost linearly) increase with energy contradicting theoretical approaches available at that time
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