A. S. Malgin

Neutrons from muons underground

Results of many-year experimental investigations of neutrons originating from cosmic-ray muons at depths of 25, 316, 570, 3650, and 5200 mwe are presented. Mechanisms of neutron generation by muons underground are outlined qualitatively. Methods of relevant measurements are described in detail, and the resulting properties of neutrons, including their total yield, flux, energy spectrum, multiplicity, and spatial distribution, are reported.

Universal formula for the muon-induced neutron yield

The experimental data on the yield of muon-induced neutrons for liquid scintillator, iron and lead accumulated during 60 years of muon interaction underground study have been analyzed. A universal formula connecting the yield with muon energy loss in the matter and neutron production in hadronic and electromagnetic showers is presented.

Search for the νμ→ντ Oscillation with the OPERA Hybrid Detector

This work reviews the status of the international OPERA experiment aimed at searching for the νμ → ντ oscillation. Development of the emulsion techniques in the preceding DONUT and CHORUS experiments is described. A brief overview of the NOMAD experiment is given, in which properties of ντ interactions were thoroughly investigated. Characteristics of the CERN-Gran Sasso (CNGS) neutrino beam are given, the structure of the OPERA hybrid detector and the functions of its subsystems are considered, and the automatic emulsion scanning technique is briefly reviewed. Uncertainties in reconstruction of event parameters using the electronic and emulsion detectors are discussed and the procedure adopted in the experiment for identification of ντ interactions is described. The main sources of background in the search for νμ → ντ oscillation are considered. Topologies of the first two ντ candidates observed in the OPERA emulsion detector are presented. Possibilities of increasing the ντ interaction selection efficiency using multidimensional criteria are briefly discussed.

Analysis of Experimental Data on the Neutron Yield from Muons

Experimental data accumulated over 60 years of studying the yield of cosmogenic neutrons in a liquid scintillator (YLS), iron (YFe), and lead (YPb) were analyzed. This analysis revealed that the main part of the results on the yield YLS were overestimated by about 30%. With allowance for this circumstance, all experimental data can be described by the dependence Y(Ēµ, A) = bnAβĒµα, where the product bnĒµα stands for the energy spent by a muon on neutron production. The exponents of α = 0.78 and β = 0.95 are determined by the properties of the medium and by neutron production in showers.

On the cosmic ray muon positive excess problem

Predictions on the positive excess based on data from cosmic ray experiments, data from accelerators and on ideas in the frames of modern theoretical QCD models are given up to 105 GeV. An estimation of the accuracy of these calculations is better than 3% for a wide energy interval.

Measurement of neutron number generated by cosmic-ray muons in iron using the LVD

The experiment to measure the neutrons numbers generated by muons in iron (Fe) and lead (Pb) carried out using LVD. A full Monte Carlo simulation of the actual geometric configuration of the experiment is performed. The first measurement results are obtained. The measured yield of neutrons produced by muons with an energy of 280 GeV in iron is 16 × 10−4 n/μ/(g cm−2).

LVD Experiment: 25 Years of Operation

The current status of the LVD (large volume detector) experiment aimed at search for neutrinos from the gravitational collapse of stellar cores is described. Within the period of observations from June 1992 to February 2017, no gravitational collapse was found in the Milky Way Galaxy and Magellanic Clouds, including hidden ones (not ejecting the envelope). The LVD collects data for 99% of the live time. A limit on the frequency of supernova bursts within a distance of 25 kpc was set at a level of 0.1 event/yr. The most recent results obtained by studying the muon component of cosmic rays are presented.

Seasonal variations in the muon-induced neutron flux and background of natural radioactivity at the Gran Sasso Underground Laboratory

Cosmic ray muons at average energies of 280 GeV and muon-induced neutrons are detected by the LVD (Large Volume Detector). An analysis of seasonal variations in the neutron flux, based on data collected over 15 years, is presented. Measuring of the seasonal variations in the specific number of neutrons generated by muons allows us to determine the magnitude of variations in the average energy of the muon flux at the depth of the LVD’s location. The source of the seasonal variations in the total neutron flux is a change in the intensity and average energy of the muon flux. An analysis of the long-term monitoring of the LVD’s low-energy background is also presented.

Characteristics of neutrons produced by muons in a standard rock

Characteristics of cosmogenic neutrons, such as the yield, production rate, and flux, were determined for a standard rock. The dependences of these quantities on the standard-rock depth and on the average muon energy were obtained. These properties and dependences make it possible to estimate easy the muon-induced neutron background in underground laboratories for various chemical compositions of rock.

A comparative analysis of light collection in a scintillation counter with a volume of 1.5 m3 with diffuse and mirror reflection

Measurement and calculation results show that light collection of scintillation counters used in the Large Volume Detector has features of light collection similar to an ideal counter with mirror reflection. A comparison of the characteristics of light collection with diffuse reflection and reflection from a relief specular surface suggests that specularly reflecting cover is preferred in a counter of present design.