V. G. Denisova

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 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.

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.

Coplanar emission of neutral and charged components of gamma-hadron families at energies 1015 – 1017 eV

Separate treatment of γ —quanta and hadrons in γ − h families and considerably increased statistic of experimental events enabled us to determine some new features of the mechanism responsible for the coplanar emission phenomenon of most energetic secondaries in nuclear interactions at 10 15 ÷ 10 17 eV. The influence of selection criteria and methodical distortions on the search for coplanar events is analyzed. It is shown that model combining the semihard diffraction of the projectile hadron and, probably, generation of baryons of new higher-color quark sextet can produce the experimental effects rather than well-known physical factors.

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.