Underground Scintillation Detectors Research Articles

Muons in EASs with E0 = 1019 eV According to Data of the Yakutsk Array

Lateral distribution functions of particles in extensive air showers with the energy {{E}_{0}} approx {{10}^{{19}}}{kern 1pt} eV recorded by ground-based and underground scintillation detectors with a threshold of {{E}_{mu }} approx {kern 1pt} 1.0 times {text{sec}}{kern 1pt} theta GeV at the Yakutsk array during the continuous observations from 1986 to 2016 have been analyzed using events with zenith angles θ ≤ 60°. Experimental functions have been compared to the predictions obtained with the QGSJet-01-d hadron interaction model by applying the CORSIKA code. The entire dataset indicates that cosmic rays consist predominantly of protons.

Design, upgrade and characterization of the silicon photomultiplier front-end for the AMIGA detector at the Pierre Auger Observatory

AMIGA (Auger Muons and Infill for the Ground Array) is an upgrade of the Pierre Auger Observatory to complement the study of ultra-high-energy cosmic rays (UHECR) by measuring the muon content of extensive air showers (EAS). It consists of an array of 61 water Cherenkov detectors on a denser spacing in combination with underground scintillation detectors used for muon density measurement. Each detector is composed of three scintillation modules, with 10 m2 detection area per module, buried at 2.3 m depth, resulting in a total detection area of 30 m2. Silicon photomultiplier sensors (SiPM) measure the amount of scintillation light generated by charged particles traversing the modules. In this paper, the design of the front-end electronics to process the signals of those SiPMs and test results from the laboratory and from the Pierre Auger Observatory are described. Compared to our previous prototype, the new electronics shows a higher performance, higher efficiency and lower power consumption, and it has a new acquisition system with increased dynamic range that allows measurements closer to the shower core. The new acquisition system is based on the measurement of the total charge signal that the muonic component of the cosmic ray shower generates in the detector.

Diseño, mejora y caracterización del front-end con fotomultiplicadores de silicio para los detectores de AMIGA del Observatorio Pierre Auger

AMIGA (Auger Muons and Infill for the Ground Array) es una mejora del Observatorio Pierre Auger con el objetivo de complementar el estudio de los rayos cósmicos de ultra alta energía (UHECR) mediante la medición del contenido muónico de las cascadas atmosféricas extensas (EAS). Éste consiste en un arreglo de 61 detectores de agua de efecto Cherenkov ubicado en un espacio más denso en combinación con detectores de centelleo enterrados bajo tierra utilizados para la medición de densidad de muones. Cada detector esta compuesto por tres módulos centelladores, con un área de detección de 10 m2 por módulo, enterrados a 2.3 m de profundidad, resultando un área total de detección de 30 m2. Fotomultiplicadores de silicio (SiPM) miden la cantidad de luz de centelleo generada por las partículas cargadas que atraviesan los módulos. En este trabajo, el diseño de la electrónica del front-end para procesar las señales de esos SiPMs, y los resultados de pruebas realizadas en el laboratorio como también en el sitio del Observatorio Pierre Auger son descriptos. Comparado con el diseño anterior, esta nueva electrónica muestra un mayor rendimiento, una mayor eficiencia y un menor consumo de potencia, e incluye además, un nuevo sistema de adquisición con un rango dinámico ampliado que permite realizar mediciones cercanas al núcleo de la lluvia. El nuevo sistema de adquisición esta basado en la medición de la carga total que la componente muónica de la lluvia cósmica genera en el detector.

Muons in Extensive Air Showers with Energy above 1017 eV According to the Long Standing Studies at the Yakutsk Array

lateral distribution of muons was studied in extensive air showers initiated by cosmic rays with energy above 1017 eV. The study is based on the experimental data of underground scintillation detectors with 1-GeV energy threshold collected during the continuous observational period lasting from 1986 to 2017. Experimentally measured values of muon density are compared to results of simulations performed for primary protons and iron nuclei within the framework of four ultra-high energy hadronic interaction models. The density of particles with 1-GeV threshold obtained in simulations was then converted to the signal of ground-shielded scintillation detectors of the array. Studying the features of the resulting muon lateral distribution has allowed us to reconstruct parameters of longitudinal development of extensive air showers.

Mass Composition of Cosmic Rays with Energies above 1017 eV According to the Data from the Muon Detectors of the Yakutsk EAS Array

The lateral distribution of muons in extensive air showers with energies above 1017 eV detected by underground scintillation detectors with a threshold of 1.0 GeV at the Yakutsk array in 1986–2016 has been analyzed. The experimental data on the muon flux density at a distance of 300 m from the shower axis have been compared to the calculations within various models of hadron interactions at ultrahigh energies. The experimental data are in the best agreement with the QGSJet01 and QGSJet II-04 models. The mass composition of cosmic rays in the energy range of (1–30) × 1017 eV changes from middle nuclei to a purely proton composition.

Energy Spectrum of Ultrahigh-Energy Cosmic Rays according to Data from the Ground-Based Scintillation Detectors of the Yakutsk EAS Array

The energy spectrum of cosmic rays with energies E0 ≥ 1017 eV over the period of continuous observations in 1974–2017 is analyzed. A refined formula for estimating the primary particle energy is used for individual events. It is derived from our calculations of the responses of the ground-based and underground scintillation detectors of the Yakutsk extensive air shower array within the QGSjet-01-d, QGSjet-II-04, SIBYLL-2.1, and EPOS-LHC models by applying the CORSIKA package. The new estimate of E0 is appreciably lower than its previously used value.

Energy Spectrum of Ultrahigh-Energy Cosmic Rays according to Data from Ground-Based Scintillation Detectors of the Yakutsk EAS Array

Results obtained from an analysis of the energy spectrum of cosmic rays with energies in the region of $E_0 \ge 10^{17}$ eV over the period of continuous observations from 1974 to 2017 are presented. A refined expression for estimating the primary-particle energy is used for individual events. This expression is derived from calculations aimed at determining the responses of the ground-based and underground scintillation detectors of the Yakutsk array for studying extensive air showers (EAS) and performed within the QGSJET01, QGSJET-II-04, SIBYLL-2.1, and EPOS-LHC models by employing the CORSIKA code package. The new estimate of $E_0$ is substantially lower than its counterpart used earlier.

New estimates of extensive-air-shower energies on the basis of signals in scintillation detectors

New formulas for estimating the energy of inclined extensive air showers (EASs) on the basis of signals in detectors by means of an original method and detailed tables of signals induced in scintillation detectors by photons, electrons, positrons, and muons and calculated with the aid of the GEANT4 code package were proposed in terms of the QGSJETII-04, EPOS LHC, and GHEISHA models. The parameters appearing in the proposed formulas were calculated by employing the CORSIKA code package. It is shown that, for showers of zenith angles in the range of 20◦–45◦, the standard constant-intensity-cut method, which is used to interpret data from the Yakutsk EAS array, overestimates the shower energy by a factor of 1.2 to 1.5. It is proposed to employ the calculated VEM (Vertical Equivalent Muon) signal units of 10.8 and 11.4 MeV for, respectively, ground-based and underground scintillation detectors and to take into account the dependence of signals on the azimuthal angle of the detector position and fluctuations in the development of showers.

Revision of the energy calibration of the Yakutsk extensive air shower array

Responses of surface and underground scintillation detectors of Yakutsk array are calculated for showers initiated by primary particles with energy ${E}_{0}\ensuremath{\ge}1{0}^{17}\text{ }\mathrm{eV}$ within the frameworks of QGSJet01d, QGSJet-II-04, SIBYLL-2.1, and EPOS-LHC hadron interaction models. A new estimation of ${E}_{0}$ is obtained with the use of various methods. The resulting energy is lower compared to the obtained with earlier method by a factor of $\ensuremath{\sim}1.33$.

Units of signals in the surface and underground scintillation detectors of the Yakutsk array

Signals in the surface and underground scintillation detectors from the extensive air shower particles at the Yakutsk array are measured in some practical units. These units are signals in detectors caused by the near vertical muons. These signals from the near vertical muons in the surface and underground detectors have been simulated with the help of the GEANT4 package. These simulations follow up the real experimental calibration of the surface and underground detectors carried out at the Yakutsk array. Results of simulations show the noticeable difference of ~5% in energies deposited in these two types of detectors. This difference should be taken into account to interpret correctly data on the fraction of muons observed at the Yakutsk array and to make real conclusions about the composition of the primary cosmic radiation at ultra-high energies.

Possible composition of the primary particles at ultrahigh energies observed at the Yakutsk array

The composition of the primary cosmic radiation should be studied by various alternative approaches. A promising way is to exploit a dependence of the fraction of muons in an extensive air shower on the atomic number of the primary nuclei. A comparison of the fraction of muons at 600 m from the shower axis observed at the Yakutsk array in the vertical air showers at ultra-high energies with results of simulations in terms of QGSJET-II and Gheisha-2002d models carried out with the help of the CORSIKA 6.616 and GEANT4 codes showed rather heavy composition of the primary radiation. But some errors in these models should be taken into account. At last, one has to allow for the fact that signals in the surface and underground scintillation detectors of the Yakutsk array from various particles of extensive air showers are measured in different units. All these corrections taken together show the proton composition of the primary radiation in the energy region of ~2.·1018 – 1019 eV. At lower energies a composition is heavier. The change from the heavy composition to the primary protons occurs in the energy interval of 9.·1017 – 2.·1018 eV. It is not excluded that at energies above 1.1·1019 eV the composition may be also heavier as illustrated by a trend of data.

The composition of the primary particles at energies 3×1017–3×1019 eV observed at the Yakutsk array

Signals in the surface and underground scintillation detectors of the Yakutsk array from particles of extensive air showers and a fraction of muons at 600 m from the vertical shower axis have been simulated. Calculations have been carried out in terms of QGSJET-II and Gheisha-2002d models with the help of the CORSIKA 6.616 and GEANT4 codes at energies 3×1017–3×1019 eV. A comparison of the results of these simulations with data observed at the Yakutsk array shows rather heavy composition of the primary radiation in this energy region. But it was shown that the number of muons is underestimated by ∼15% if the QGSJET-II model was used at energies above 100 GeV and by ∼ 10% if the Gheisha-2002d model was used at energies below 100 GeV. Besides, signals in the surface and underground detectors from a muon differ by 3%. A comparison of the results with these corrections taken into account with data favors rather a light (maybe a proton-dominated) composition of the primary radiation in the energy region of 2.3×1018–1.14×1019 eV. In the energy interval of 3×1017–2.3×1018 eV, the composition is heavier. At energies above 1.14×1019 eV, a composition may also be heavier as illustrated by a trend of data.

Signals in the underground scintillation detectors of the Yakutsk array from muons of extensive air showers

A model of the underground part of the Yakutsk array was developed. The signals from muon scintillation detectors were calculated using the GEANT4 code within this model. It was shown that the signals strongly fluctuate and may be several times higher that the mean ionization energy losses by a single muon. These large losses imitate high muon multiplicity in the case of a low muon density. It was also shown that there are many gamma particles near the shower axis, which significantly contribute to signals in underground detectors and thus make data interpretation difficult.

Changes in the chemical composition of primary cosmic radiation at ultrahigh energies

The signals from particles of extensive air showers in the energy region of 1017–1020 eV in both the surface and underground scintillation detectors of the Yakutsk array are calculated using the CORSIKA 6.616 and GEANT4 software packages and compared with experimental data. It is shown that a transition from a heavy primary composition to proton primaries at energies (1–2.6) × 1018 eV and from primary protons again to heavy primaries at energies above 1.3 × 1019 eV might be observed.

CNO andpepneutrino spectroscopy in Borexino: Measurement of the deep-underground production of cosmogenicC11in an organic liquid scintillator

Borexino is an experiment for low energy neutrino spectroscopy at the Gran Sasso underground laboratories. It is designed to measure the mono-energetic $^7$Be solar neutrino flux in real time, via neutrino-electron elastic scattering in ultra-pure organic liquid scintillator. Borexino has the potential to also detect neutrinos from the \emph{pep} fusion process and the CNO cycle. For this measurement to be possible, radioactive contamination in the detector must be kept extremely low. Once sufficiently clean conditions are met, the main background source is $^{11}$C, produced in reactions induced by the residual cosmic muon flux on $^{12}$C. In the process, a free neutron is almost always produced. $^{11}$C can be tagged on an event by event basis by looking at the three-fold coincidence with the parent muon track and the subsequent neutron capture on protons. This coincidence method has been implemented on the Borexino Counting Test Facility data. We report on the first event by event identification of \emph{in situ} muon induced $^{11}$C in a large underground scintillator detector. We measure a $^{11}$C production rate of 0.130 $\pm$ 0.026 (stat) $\pm$ 0.014 (syst) day$^{-1}$ ton$^{-1}$, in agreement with predictions from both experimental studies performed with a muon beam on a scintillator target and \emph{ab initio} estimations based on the $^{11}$C producing nuclear reactions.