Abstract
The origin of the cosmic ray hadron excess observed in a deep uniform lead X-ray emulsion chamber (XREC) at depths larger than 70 radiation lengths is analyzed. We present preliminary experimental data on the absorption of cosmic ray hadrons in the two-storey XREC with a large air gap exposed at the Tien Shan mountains. The design of the chamber was especially invented to prove the hypothesis on a substantial increase of the charm particle production cross section with energy at ELab ∼ 75TeV as the main source of the darkness spot excess observed on X-ray films. Experimental data obtained with both a 2-storey XREC and a deep uniform XREC are compared with simulation results calculated with the FANSY 1.0 model. The comparison reveals a qualitative agreement between experimental and simulated data under the assumption of high values of charm particle production cross section at ELab ∼ 75 TeV in the forward kinematic region at xLab > 0.1.
Highlights
A slowing down of the absorption of high energy hadron cascades was observed at the Tien Shan High-Mountain Research Station (TSS) in extensive air shower (EAS) experiments with the Big Ionization Calorimeter (BIC) of 36 m2 area (Fig. 1) which contained lead absorber of 850-g/cm2 thick [1, 2]
At larger depths t > 70 r.l., the absorption length of hadrons in lead changes and becomes as high as λa(1b)s = 340 ± 80 g/cm2 (Fig. 4). It was soon suggested [5, 6] that both phenomena, i.e., excess ionization in the hadron calorimeter and hadron excess in the deep uniform X-ray emulsion chamber (XREC), result from high values of the cross section of production of leading charm particles
Monte-Carlo simulations of both experiments, i.e., with the two-storey XREC and deep homogeneous lead XREC, were carried out assuming that the incident cosmic ray hadrons at mountain altitudes are mainly represented by nucleons and pions with energies Eh ≥ 20 TeV and that these 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
Mountain Research Station (TSS) in extensive air shower (EAS) experiments with the Big Ionization Calorimeter (BIC) of 36 m2 area (Fig. 1) which contained lead absorber of 850-g/cm thick [1, 2]. At larger depths t > 70 r.l., the absorption length of hadrons in lead changes and becomes as high as λa(1b)s = 340 ± 80 g/cm (Fig. 4) It was soon suggested [5, 6] 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 production of leading charm particles This means that the charm production cross section should rapidly (almost linearly) increase with energy that contradicted theoretical approaches available at that time To prove this hypothesis, a dedicated experiment was proposed [7] which employs a two-storey XREC with a large air gap between two vertically separated lead blocks of the chamber (Fig. 5). The same comparison is performed for experimental data of the Pamir experiment with deep (110-cm thick) uniform lead XREC
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