Auger Muons And Infill For The Ground Array Research Articles

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.

Composition determination of cosmic rays from the muon content of the showers

The origin and nature of ultra high energy cosmic rays remains being a mystery. However, great progress has been made in recent years due to the observations performed by the Pierre Auger Observatory and Telescope Array. In particular, it is believed that the composition information of the cosmic rays as a function of the energy can play a fundamental role for the understanding of their origin. The best indicators for primary mass composition are the muon content of extensive air shower and the atmospheric depth of the shower maximum. In this work we consider a maximum likelihood method to perform mass composition analyses based on the number of muons measured by underground muon detectors. The analyses are based on numerical simulations of the showers. The effects introduced by the detectors and the methods used to reconstruct the experimental data are also taken into account through a dedicated simulation that uses as input the information of the simulated showers. In order to illustrate the use of the method, we consider AMIGA (Auger Muons and Infill for the Ground Array), the low energy extension of the Pierre Auger Observatory that directly measures the muonic content of extensive air showers. We also study in detail the impact of the use of different high energy hadronic interaction models in the composition analyses performed. It is found that differences of a few percent between the predicted number of muons have a significant impact on composition determination.

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.

Preliminary results of the AMIGA engineering array at the Pierre Auger Observatory

The Auger Muons and Infill for the Ground Array (AMIGA) aims to both extend the detection range of the Pierre Auger Observatory down to energies ~ 1016.5 eV and to measure the muon content of extensive air showers. To accomplish these goals, its detection system is composed of an array of coupled water-Cherenkov and scintillation detectors deployed in a graded triangular grid of 433 and 750 m spacings. At each position, the scintillation detector is buried 2.3 m deep so as to shield it from the air shower electromagnetic component and thus only measure the muon component. These muon detectors have 30 m2 area split into modules, each of them highly segmented in 64 plastic-scintillator strips with an embedded wavelength-shifter optical fiber to transport light to an optical sensor located at the center of the module. During the engineering array phase (finished in November 2017) two module areas (5 m2 and 10 m2) and two optical sensors (photo-multiplier tubes and silicon-photomultipliers) were tested. In this work, we present the final performance of the muon detectors equipped with silicon-photomultipliers which were thereafter selected as the baseline design for the AMIGA production phase. Analyses and results are based both on laboratory and field measurements.

Direct Measurement of the Muon Density in Air Showers with the Pierre Auger Observatory

As part of the upgrade of the Pierre Auger Observatory, the Auger Muons and Infill for the Ground Array (AMIGA) underground muon detector extension will allow for direct muon measurements for showers falling into the SD-750 array. We optimized the AMIGA muon reconstruction procedure by introducing a geometrical correction for muons leaving a signal in multiple detector strips due to their inclined angle of incidence and deriving a new unbiased parametrization of the muon lateral distribution function. Furthermore, we defined a zenith-independent estimator ρ35 of the muon density by parametrizing the attenuation of the muonic signal due to the atmosphere and soil layer above the buried detectors and quantified the relevant systematic uncertainties for AMIGA. The analysis of one year of calibrated data recorded with the prototype array of AMIGA confirms the results of previous studies indicating a disagreement between the muon content in simulations and data.

Estimating the mass of cosmic rays by combining radio and muon measurements

The Auger Engineering Radio Array (AERA) is a radio detector at the Pierre Auger Observatory and it is dedicated to measure the radio emission of cosmic-ray air showers. AERA is co-located with the underground muon detectors of the Auger Muons and Infill for the Ground Array (AMIGA). This provides a perfect setup to experimentally test the benefits of combining muons and radio emission for estimating the primary mass. We have investigated this combination using air-shower simulations. We compared the performance for mass separation of this new method to alternative methods in which the electrons and muons are measured with particle detectors at the surface. Forshowers with zenith angles below 50° the new method is of comparable performance, and for showers more inclinedthan 50° it is clearly superior. Therefore, measuring the radio signal in addition to the muons significantly improves the mass sensitivity compared to techniques using solely particle measurements.

Photovoltaic monitoring system for Auger Muons and Infill for the Ground Array

AbstractThis study is devoted to characterizing the operation of the entire photovoltaic system installed in one of the Auger Muons and Infill for the Ground Array (AMIGA) stations, a complimentary detector for the Pierre Auger Observatory, the largest cosmic‐ray air shower array in the world, 3000 km2, powered exclusively by solar energy. To understand charge and discharge cycles, the whole system behavior under different climatic conditions and to determine its limitations, the design of a new prototype for monitoring the whole system online is a fundamental part of this contribution. Also, it is demonstrated that the configuration of solar charge controllers in parallel is able to manage panels of different powers and brands and that the monitoring system allows analyzing periods with adverse weather conditions.

Muon counting using silicon photomultipliers in the AMIGA detector of the Pierre Auger observatory

AMIGA (Auger Muons and Infill for the Ground Array) is an upgrade of the Pierre Auger Observatory designed to extend its energy range of detection and to directly measure the muon content of the cosmic ray primary particle showers. The array will be formed by an infill of surface water-Cherenkov detectors associated with buried scintillation counters employed for muon counting. Each counter is composed of three scintillation modules, with a 10 m2 detection area per module. In this paper, a new generation of detectors, replacing the current multi-pixel photomultiplier tube (PMT) with silicon photo sensors (aka. SiPMs), is proposed. The selection of the new device and its front-end electronics is explained. A method to calibrate the counting system that ensures the performance of the detector is detailed. This method has the advantage of being able to be carried out in a remote place such as the one where the detectors are deployed. High efficiency results, i.e. 98% efficiency for the highest tested overvoltage, combined with a low probability of accidental counting (∼2%), show a promising performance for this new system.

The Auger Engineering Radio Array and multi-hybrid cosmic ray detection

The Auger Engineering Radio Array (AERA) aims at the detection of air showers induced by high-energy cosmic rays. As an extension of the Pierre Auger Observatory, it measures complementary information to the particle detectors, fluorescence telescopes and to the muon scintillators of the Auger Muons and Infill for the Ground Array (AMIGA). AERA is sensitive to all fundamental parameters of an extensive air shower such as the arrival direction, energy and depth of shower maximum. Since the radio emission is induced purely by the electromagnetic component of the shower, in combination with the AMIGA muon counters, AERA is perfect for separate measurements of the electrons and muons in the shower, if combined with a muon counting detector like AMIGA. In addition to the depth of the shower maximum, the ratio of the electron and muon number serves as a measure of the primary particle mass.

Prototype muon detectors for the AMIGA component of the Pierre Auger Observatory

AMIGA (Auger Muons and Infill for the Ground Array) is an upgrade of the Pierre Auger Observatory to extend its range of detection and to directly measure the muon content of the particle showers. It consists of an infill of surface water-Cherenkov detectors accompanied by buried scintillator detectors used for muon counting. The main objectives of the AMIGA engineering array, referred to as the Unitary Cell, are to identify and resolve all engineering issues as well as to understand the muon-number counting uncertainties related to the design of the detector. The mechanical design, fabrication and deployment processes of the muon counters of the Unitary Cell are described in this document. These muon counters modules comprise sealed PVC casings containing plastic scintillation bars, wavelength-shifter optical fibers, 64 pixel photomultiplier tubes, and acquisition electronics. The modules are buried approximately 2.25 m below ground level in order to minimize contamination from electromagnetic shower particles. The mechanical setup, which allows access to the electronics for maintenance, is also described in addition to tests of the modules' response and integrity. The completed Unitary Cell has measured a number of air showers of which a first analysis of a sample event is included here.

A composition dependent energy scale and the determination of the cosmic ray primary mass in the ankle region

At present there are still several open questions about the origin of the ultra high energy cosmic rays. However, great progress in this area has been made in recent years due to the data collected by the present generation of ground based detectors like the Pierre Auger Observatory and Telescope Array. In particular, it is believed that the study of the composition of the cosmic rays as a function of energy can play a fundamental role for the understanding of the origin of the cosmic rays.The observatories belonging to this generation are composed of arrays of surface detectors and fluorescence telescopes. The duty cycle of the fluorescence telescopes is ∼10% in contrast with the ∼100% of the surface detectors. Therefore, the energy calibration of the events observed by the surface detectors is performed by using a calibration curve obtained from a set of high quality events observed in coincidence by both types of detectors. The advantage of this method is that the reconstructed energy of the events observed by the surface detectors becomes almost independent of simulations of the showers because just a small part of the reconstructed energy (the missing energy), obtained from the fluorescence telescopes, comes from simulations. However, the calibration curve obtained in this way depends on the composition of the cosmic rays, which can introduce biases in composition analyses when parameters with a strong dependence on primary energy are considered. In this work we develop an analytical method to study these effects. We consider AMIGA (Auger Muons and Infill for the Ground Array), the low energy extension of the Pierre Auger Observatory corresponding to the surface detectors, to illustrate the use of the method. In particular, we study the biases introduced by an energy calibration dependent on composition on the determination of the mean value of the number of muons, at a given distance to the showers axis, which is one of the parameters most sensitive to primary mass and has an almost linear dependence with primary energy.

The low-energy extensions of the Pierre Auger Observatory

The Pierre Auger Observatory was designed to measure ultra-high energy cosmic rays above 1018eV with high accuracy using a hybrid air shower detection technique. A Surface Detector (SD) with 1600 water-Cherenkov stations on a 1500 m triangular grid covers an area of 3000 km2. The atmosphere above the array is viewed by a Fluorescence Detector (FD) with 24 telescopes at 4 sites in the periphery of the SD. As an enhancement to this baseline design, in order to reach a lower energy threshold below 1017eV, the Collaboration has implemented extensions to the Observatory. The SD extension is AMIGA (Auger Muons and Infill for the Ground Array), an infilled area with detectors at a smaller spacing than in the main array and with buried scintillator counters. The FD is complemented by HEAT (High Elevation Auger Telescopes), with 3 additional telescopes that are tilted upwards to extend the elevation range. The importance of these extensions of the Auger Observatory is that they allow to study the energy range where the transition from a Galactic to an extra-Galactic origin of cosmic rays may occur. The current status and initial results from these extensions are discussed.