Z.M. Guseva

Intense bundles of particles in cores of nuclear-electromagnetic cascades in the atmosphere with energies around 100 PeV (gamma-families with halo)

An appreciable fraction of gamma-families are accompanied by a halo, a narrow bundle of high-energy particles (energy density > 20 TeV/mm2) recorded in X-ray emulsion chambers as a diffuse dark spot in the central region of a gamma-family. Gamma-families in the experiment “Pamir” are compared with simulations by three different codes of quark-gluon string model (MQ, MCO and QGSJet) based on extrapolating accelerator data up to energy Eo = 3 ∗ 1018 eV and under various assumptions on mass composition of primary cosmic rays (PCR). The spectrum of halo area, S, is analyzed, especially at S > 100 mm2. Simulations by different codes predict that at a PCR energy Eo ∼ 1018 eV the probability of initiating a halo with S ∼ 1000 mm2 is 60% for primary protons and 40% for Fe nuclei. The fraction of protons in PCR composition at E0 = 1016 ÷ 1017 eV is estimated.

Fraction of protons in primary cosmic rays according to data from the PAMIR experiment in consideration of the response of X-ray emulsion chambers

Adjusted data on the fraction of protons in the mass composition of primary cosmic rays (PCRs) in the energy range of 1015–1017 eV are presented. Adjustments are made according to detailed calculations of the response of the X-ray emulsion chamber in the PAMIR experiment. It is demonstrated that the fraction of protons in a PCR is 16–18% for E0 ≈ 1015–1016 eV and does not change within the error for E0 ≈ 1016–1017 eV.

Mass composition of primary cosmic radiation according to data on spectrum of “halo” areas

Spectrum of “halo” areas in gamma-hadron families with ∑ Eγ ≥ 500 TeV is analyzed. The comparison of experimental data and simulations by quark-gluon string model suggests an increasing contribution of nuclei heavier than protons and α-particles to the primary cosmic radiation (PCR) at energy E0 > 1016 eV. Such a model is consistent both with the accelerator data and those from X-ray emulsion chamber experiments under assumption that PCR mass composition is normal for E0

Studying the nature of the long-flying component of cosmic rays using X-ray emulsion chambers exposed in the Pamirs and Tien Shan

The origin of an excess of hadrons observed in deep homogeneous lead X-ray emulsion chambers (XRECs) at depths of more than 70 radiation length units is analyzed. Preliminary experimental data on the absorption of cosmic-ray hadrons in a two-storied XREC with a large air gap, exposed in the Tien Shan mountains, are presented. The chamber was designed to test the hypothesis that the main source of the excess of dark spots detected on X-ray films deep inside the XREC was substantial growth of the charmed-particle production cross section at energy Elab ∼ 75 TeV. The experimental data obtained using a two-storied REC and in experiments with deep homogeneous XRECs are compared to the results from calculations using the FANSY 1.0 model. The comparison shows qualitative agreement between the experimental and the model data, assuming high values of the charmed-particle production cross section when Elab ∼ 75 TeV in the forward kinematic region with xF ≥ 0.1.

Revised data on γ-families observed in X-ray emulsion chambers of the Experiment PAMIR

Recently essential efforts were made to improve measurement routine with X-ray films exposed in the X-ray emulsion chambers at the Pamirs. Analysis of X-ray emulsion response upon recorded events show that gamma-family energy and intensity in early publications were over estimated. The main physical results of the new analysis are presented.Recently essential efforts were made to improve measurement routine with X-ray films exposed in the X-ray emulsion chambers at the Pamirs. Analysis of X-ray emulsion response upon recorded events show that gamma-family energy and intensity in early publications were over estimated. The main physical results of the new analysis are presented.

Energy spectra of secondary particles in γ families and their sensitivity to the spectrum of primary cosmic rays

Spectra of secondary particles (γ-rays) in γ-families detected in the X-ray chambers in the Pamirs (H = 600 g cm−2) have been analyzed. These γ-ray spectra show a bend at the energy E*γ ≈ (ΣEγ)min, where (ΣEγ)min is the lowest total energy of γ-rays in the families above which γ-families were selected. The bend is not related to the knee in the spectrum of primary particles; it is due to the use of the ΣEγ selection criterion. The Eγ spectrum slope is sensitive to the spectrum of the primary cosmic rays in the region Eγ ≥ (ΣEγ)min.

Efficiency of the production of γ families with halos and the fraction of protons at an energy of 1016 eV

Abstractγ Families with halos detected in the “Pamir” experiment have been analyzed. Comparison of the experimental data with the results of calculation within the quark-gluon string model (MC0 code) made it possible to determine the efficiency of halo formation by protons, α particles, and heavy nuclei, as well as the fraction of protons in the mass composition of primary cosmic rays at an energy of 1016 eV. It is shown that halos are formed predominantly by protons. The fraction of protons in the mass composition of primary cosmic rays at an energy of 1016 eV is 20%.

The characteristics of gamma-hadron families induced by primary cosmic rays with an energy more than 10 PeV

Parameters R ¯ > , ER ¯ > of gamma-hadron families with a visible energy Σ E γ ≥ 100 TeV are analysed with the aim to prove their sensitivity to the mass composition of primary cosmic rays (PCR). The experimental values of these parameters are in agreement with the assumption that PCR become enriched with CNO nuclei at an energy ≥ 10 16 PeV.