A. V. Stepanov

New complex EAS installation of the Tien Shan mountain cosmic ray station

In this paper we present a description of the new complex installation for the study of extensive air showers which was created at the Tien Shan mountain cosmic ray station, as well as the results of the test measurements made there in 2014-2016. At present, the system for registration of electromagnetic shower component consists of ∼100 detector points built on the basis of plastic scintillator plates with the sensitive area of 0.25m2 and 1m2, spread equidistantly over ∼104 m2 space. The dynamic range of scintillation amplitude measurements is currently about (3 − 7) · 104, and there is a prospect of it being extended up to ∼106. The direction of shower arrival is defined by signal delays from a number of the scintillators placed cross-wise at the periphery of the detector system. For the investigation of nuclear active shower components there was created a multi-tier 55m2 ionization-neutron calorimeter with a sum absorber thickness of ∼1000g/cm2, typical spatial resolution of the order of 10cm, and dynamic range of ionization measurement channel about ∼105. Also, the use of saturation-free neutron detectors is anticipated for registration of the highand lowenergy hadron components in the region of shower core. A complex of underground detectors is designed for the study of muonic and penetrative nuclear-active components of the shower. The full stack of data acquisition, detector calibration, and shower parameters restoration procedures are now completed, and the newly obtained shower size spectrum and lateral distribution of shower particles occur in agreement with conventional data. Future studies in the field of 1014 − 1017eV cosmic ray physics to be held at the new shower installation are discussed.

Quasifree proton scattering on halo nuclei as a tool for studying the neutron-halo structure

An experimental method is proposed for investigating the structure of the two-neutron halo in quasifree proton scattering on clusters of halo nuclei. This scattering process is studied in inverse kinematics by using a 6He beam incident to a stack of track emulsions. Preliminary data on the reaction 6He + p → 4He + p + X are compared with the results of simple kinematical calculations for quasifree proton scattering on the clusters forming the halo of the 6He nucleus.

Are there tachyons in extensive air showers

The results obtained by studying double-front extensive air showers in which more than 107 particles are contained and in which the fronts are separated by a time interval of Δt ∼ 100 ns are presented. Serious difficulties in explaining “delayed” showers are revealed. In this connection, a hypothesis that the “leading” showers are initiated by tachyons produced in the first interaction of primary particles is proposed.

The Role of Configurations of Neutron Halo in the Formation of the Model Vertex Function for Description of the Two-Neutron Transfer Reaction

The nuclear vertex functions for virtual decay of halo nuclei 6He → α + n + n (11Li-9Li + n + n) for dineutron and cigarlike configurations of the neutron halo have been analytically investigated using the diagram method of direct nuclear reactions. These vertex functions describe the one-step process of two-neutron transfer. It is shown that the angular and energy distributions of the reaction products (α particles, 9Li, etc.) in different ranges of variables correspond to different structural elements of the halo. The vertex function describing the two-step process of halo neutron transfer has also been analyzed.

Observation of Vavilov-Cherenkov radiation and EAS charged particles at large zenith angles

Extensive air showers (EASes) at zenith angles of 70–80 degrees with Vavilov-Cherenkov radiation having two and three maxima were registered at the Tian Shan Mountain Station of the Lebedev Physical Institute. In each such event, the subsequent maxima came with a time delay of 100 or more nanoseconds. Extensive air showers at a zenith angle of 70° with charged particles and Vavilov-Cherenkov radiation were also registered.

A method of space-time correlation functions for describing the quasifree knockout of valence neutrons from a halo nucleus

Expressions for the distribution functions of products of the valence neutron knockout reaction (p, p’n) for halo nuclei were obtained using a method of space-time correlation functions. An analysis of the efficiency of this reaction as a method for investigating the structure of a neutron halo is given. The fraction of events in which the internal motion in a neutron complex remains unperturbed in the case of the quasifree knockout of the complex from a halo nucleus by protons with an energy of several tens of MeV was calculated. An expression for the spectrum of outgoing protons was obtained and analyzed.

Comparative analysis of the information content of exclusive (p, p′n) and inclusive (p, p′) experiments with nuclei featuring one- and two-neutron halos

Expressions for the distributions of products originating from (p, p′n) and (p, p′) reactions on halo nuclei involving one and two valence neutrons in the quasifree-collision mode are obtained by the method of spacetime correlation functions. A comparative analysis is given to the information content of experiments with these nuclei within both exclusive (p, p′n) and inclusive (p, p′) approaches.

Delayed muons in extensive air showers and double-front showers

The results of a long-term experiment performed in the period between 1995 and 2006 with the aid of the MUON-T underground (20 mwe) scintillation facility arranged at the Tien Shan mountain research station at an altitude of 3340 m above sea level are presented. The time distribution of delayed muons with an energy in excess of 5 GeV in extensive air showers of energy not lower than 106 GeV with respect to the shower front was obtained with a high statistical significance in the delay interval between 30 and 150 ns. An effect of the geomagnetic field in detecting delayed muons in extensive air showers was discovered. This effect leads to the asymmetry of their appearance with respect to the north-south direction. The connection between delayed muons and extensive air showers featuring two fronts separated by a time interval of several tens of to two hundred nanoseconds is discussed. This connection gives sufficient grounds to assume that delayed muons originate from the decays of pions and kaons produced in the second, delayed, front of extensive air showers.

Studying of the neutron halo structure in quasi-free proton scattering from 6He Halo nucleus

An experimental method based on an analysis of the neutron-neutron correlations in reactions induced by halo nuclei in nuclear photoemulsion is proposed for studying the two-neutron halo structure. Photoemulsion stacks were exposed to a beam of radioactive 6He nuclei. Preliminary data on interaction of the 6He halo nucleus to hydrogen are compared with the results of the kinematic calculation for the reaction of quasi-free proton scattering from clusters making up the 6He halo nucleus. A fraction of quasi-free scattering events with “survival” of the dineutron is evaluated for scattering of protons by the dineutron configuration of the 6He nucleus.

STUDY OF QUASI-FREE SCATTERING OF PROTONS BY CLUSTERS OF 6He HALO NUCLEUS

To investigate the structure of two-neutron halo we propose an experimental method of studying neutron-neutron correlations by measuring reactions induced by halo projectile in nuclear photoemulsions. The obtained preliminary data on interaction of halo nucleus 6He with hydrogen are compared with results of simple kinematical calculations for the reaction of quasi-free scattering of proton by the clusters existing in halo nucleus 6He.