A. Aab’s research while affiliated with Radboud University and other places

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Publications (137)


Figure 8. Comparison of the í µí±‹ max distributions as reconstructed with the network (solid histograms) for proton (red) and iron (blue) showers and the simulated distribution (dashed histograms) for (a) EPOS-LHC and (b) Sibyll 2.3 for energies between 20 and 30 EeV.
Deep-learning based reconstruction of the shower maximum X max using the water-Cherenkov detectors of the Pierre Auger Observatory
  • Article
  • Full-text available

July 2021

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117 Reads

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51 Citations

Journal of Instrumentation

A. Aab

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P. Abreu

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A. Zepeda

The atmospheric depth of the air shower maximum Xmax is an observable commonly used for the determination of the nuclear mass composition of ultra-high energy cosmic rays. Direct measurements of Xmax are performed using observations of the longitudinal shower development with fluorescence telescopes. At the same time, several methods have been proposed for an indirect estimation of Xmax from the characteristics of the shower particles registered with surface detector arrays. In this paper, we present a deep neural network (DNN) for the estimation of Xmax. The reconstruction relies on the signals induced by shower particles in the ground based water-Cherenkov detectors of the Pierre Auger Observatory. The network architecture features recurrent long short-term memory layers to process the temporal structure of signals and hexagonal convolutions to exploit the symmetry of the surface detector array. We evaluate the performance of the network using air showers simulated with three different hadronic interaction models. Thereafter, we account for long-term detector effects and calibrate the reconstructed Xmax using fluorescence measurements. Finally, we show that the event-by-event resolution in the reconstruction of the shower maximum improves with increasing shower energy and reaches less than 25 g/cm2 at energies above 2×1019 eV.

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Extraction of the muon signals recorded with the surface detector of the Pierre Auger Observatory using recurrent neural networks

July 2021

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43 Reads

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31 Citations

Journal of Instrumentation

The Pierre Auger Observatory, at present the largest cosmic-ray observatory ever built, is instrumented with a ground array of 1600 water-Cherenkov detectors, known as the Surface Detector (SD). The SD samples the secondary particle content (mostly photons, electrons, positrons and muons) of extensive air showers initiated by cosmic rays with energies ranging from 1017 eV up to more than 1020 eV. Measuring the independent contribution of the muon component to the total registered signal is crucial to enhance the capability of the Observatory to estimate the mass of the cosmic rays on an event-by-event basis. However, with the current design of the SD, it is difficult to straightforwardly separate the contributions of muons to the SD time traces from those of photons, electrons and positrons. In this paper, we present a method aimed at extracting the muon component of the time traces registered with each individual detector of the SD using Recurrent Neural Networks. We derive the performances of the method by training the neural network on simulations, in which the muon and the electromagnetic components of the traces are known. We conclude this work showing the performance of this method on experimental data of the Pierre Auger Observatory. We find that our predictions agree with the parameterizations obtained by the AGASA collaboration to describe the lateral distributions of the electromagnetic and muonic components of extensive air showers.


Design and implementation of the AMIGA embedded system for data acquisition

July 2021

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506 Reads

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7 Citations

Journal of Instrumentation

The Auger Muon Infill Ground Array (AMIGA) is part of the AugerPrime upgrade of the Pierre Auger Observatory. It consists of particle counters buried 2.3 m underground next to the water-Cherenkov stations that form the 23.5 km ² large infilled array. The reduced distance between detectors in this denser area allows the lowering of the energy threshold for primary cosmic ray reconstruction down to about 10 ¹⁷ eV. At the depth of 2.3 m the electromagnetic component of cosmic ray showers is almost entirely absorbed so that the buried scintillators provide an independent and direct measurement of the air showers muon content. This work describes the design and implementation of the AMIGA embedded system, which provides centralized control, data acquisition and environment monitoring to its detectors. The presented system was firstly tested in the engineering array phase ended in 2017, and lately selected as the final design to be installed in all new detectors of the production phase. The system was proven to be robust and reliable and has worked in a stable manner since its first deployment.


Design and implementation of the AMIGA embedded system for data acquisition

July 2021

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14 Reads

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P. Abreu

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et. al

The Auger Muon Infill Ground Array (AMIGA) is part of the AugerPrime upgrade of the Pierre Auger Observatory. It consists of particle counters buried 2.3 m underground next to the water-Cherenkov stations that form the 23.5 km2 large infilled array. The reduced distance between detectors in this denser area allows the lowering of the energy threshold for primary cosmic ray reconstruction down to about 1017 eV. At the depth of 2.3 m the electromagnetic component of cosmic ray showers is almost entirely absorbed so that the buried scintillators provide an independent and direct measurement of the air showers muon content. This work describes the design and implementation of the AMIGA embedded system, which provides centralized control, data acquisition and environment monitoring to its detectors. The presented system was firstly tested in the engineering array phase ended in 2017, and lately selected as the final design to be installed in all new detectors of the production phase. The system was proven to be robust and reliable and has worked in a stable manner since its first deployment.


The FRAM robotic telescope for atmospheric monitoring at the Pierre Auger Observatory

June 2021

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55 Reads

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11 Citations

Journal of Instrumentation

FRAM (F/Photometric Robotic Atmospheric Monitor) is a robotic telescope operated at the Pierre Auger Observatory in Argentina for the purposes of atmospheric monitoring using stellar photometry. As a passive system which does not produce any light that could interfere with the observations of the fluorescence telescopes of the observatory, it complements the active monitoring systems that use lasers. We discuss the applications of stellar photometry for atmospheric monitoring at optical observatories in general and the particular modes of operation employed by the Auger FRAM. We describe in detail the technical aspects of FRAM, the hardware and software requirements for a successful operation of a robotic telescope for such a purpose and their implementation within the FRAM system.


FIG. 1. Number of muons as a function of the measured energy. The black line is the fitted hR μ i ¼ a½E=ð10 19 eVފ b . Markers on the top of the frame define the bins in which the fluctuations are evaluated. The numbers give the events in each bin. The effect of the uncertainty of the absolute energy scale is indicated by σ sys ðEÞ. The best-fit values for parameters a; b and the deviance per degree of freedom (n.d.f.) in the fit are shown on the lower right.
FIG. 2. Measured relative fluctuations in the number of muons as a function of the energy and the predictions from three interaction models for proton (red) and iron (blue) showers. The gray band represents the expectations from the measured mass composition interpreted with the interaction models. The statistical uncertainty in the measurement is represented by the error bars. The total systematic uncertainty is indicated by the square brackets.
FIG. 3. Data (black, with error bars) compared to models for the fluctuations and the average number of muons for showers with a primary energy of 10 19 eV. Fluctuations are evaluated in the energy range from 10 18.97 to 10 19.15 eV. The statistical uncertainty is represented by the error bars. The total systematic uncertainty is indicated by the square brackets. The expectation from the interaction models for any mixture of the four components p, He, N, Fe is illustrated by the colored contours. The values preferred by the mixture derived from the X max measurements are indicated by the star symbols. The shaded areas show the regions allowed by the statistical and systematic uncertainties of the X max measurement [39].
Measurement of the Fluctuations in the Number of Muons in Extensive Air Showers with the Pierre Auger Observatory

April 2021

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178 Reads

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86 Citations

Physical Review Letters

We present the first measurement of the fluctuations in the number of muons in extensive air showers produced by ultrahigh energy cosmic rays. We find that the measured fluctuations are in good agreement with predictions from air shower simulations. This observation provides new insights into the origin of the previously reported deficit of muons in air shower simulations and constrains models of hadronic interactions at ultrahigh energies. Our measurement is compatible with the muon deficit originating from small deviations in the predictions from hadronic interaction models of particle production that accumulate as the showers develop.


Figure 3. (Top) Dark-counts per second (cps) as a function of the discriminator threshold at different V bias for an individual SiPM. The dark-count rates and PE amplitudes shift towards higher values when rising the V bias . In the inset, we show one curve at the middle of the displayed range in the main plot and its derivative fitted with a Gaussian distribution to obtain the corresponding PE amplitude. (Bottom-left) V br determination for this specific SiPM. The linear extrapolation to 0 amplitude yields the value of V br . (Bottom-right) Dark-count rate (red squares) and cross-talk probability (black dots) as a function of the V bias .
Figure 6. 1 PE amplitude (left) and dark-count rate (right) as a function of the temperature of the highvoltage source measured in the laboratory. We display the results for measurements with and without the compensation mechanism on. The fitted slopes for the PE amplitude data are (−0.049 ± 0.003) PE/ • C and (−0.431 ± 0.002) PE/ • C, respectively.
Figure 10. 360000 background events which correspond to the equivalent of one hour of first-level triggered events. In orange (black) the time windows to search for muon (noise) signals are indicated. (Top) sum of binary channel traces. (Bottom) overlap of ADC channel traces. Note that the x-axis is shifted by about 170 ns, the time shift between the channels presented in the bottom-right panel of figure 2.
Calibration of the underground muon detector of the Pierre Auger Observatory

April 2021

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172 Reads

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20 Citations

Journal of Instrumentation

To obtain direct measurements of the muon content of extensive air showers with energy above 101 eV, the Pierre Auger Observatory is currently being equipped with an underground muon detector (UMD), consisting of 219 10 m2-modules, each segmented into 64 scintillators coupled to silicon photomultipliers (SiPMs). Direct access to the shower muon content allows for the study of both of the composition of primary cosmic rays and of high-energy hadronic interactions in the forward direction. As the muon density can vary between tens of muons per m close to the intersection of the shower axis with the ground to much less than one per m when far away, the necessary broad dynamic range is achieved by the simultaneous implementation of two acquisition modes in the read-out electronics: the binary mode, tuned to count single muons, and the ADC mode, suited to measure a high number of them. In this work, we present the end-to-end calibration of the muon detector modules: first, the SiPMs are calibrated by means of the binary channel, and then, the ADC channel is calibrated using atmospheric muons, detected in parallel to the shower data acquisition. The laboratory and field measurements performed to develop the implementation of the full calibration chain of both binary and ADC channels are presented and discussed. The calibration procedure is reliable to work with the high amount of channels in the UMD, which will be operated continuously, in changing environmental conditions, for several years.


Figure 3. Schematic drawing of the input, architecture and output of the neural network. See the text for details.
Figure 4. Left: Loss as a function of the epoch, see Eq. 2.1. Right: Mean value and standard deviation of the difference between the integral of the true muon signal and the predicted muon signal for the validation set.
Figure 5. Examples of predicted muon traces for two simulated events with EPOS-LHC, for a electromagneticdominated signal (left) and muon-dominated signal (right). The prediction (black line) agrees well with the shape of the simulated muon trace (orange line) for a majority of the time bins. The blue thicker line corresponds to the total trace, the one measured by a WCD.
Figure 6. Left: Distribution of the difference between the integral of the predicted muon signal í µí±† í µí¼‡ and the integral of the true muon signal í µí±† í µí¼‡ . Right: Distribution of í µí±† í µí¼‡ and í µí±† í µí¼‡ for all the stations in the test set.
Figure 7. Left: Mean value (top) and standard deviation (bottom) of the difference between the predicted and values of the true muon signal as a function of energy. Right: Relative bias (top) and resolution (bottom) for the determination of the muon fraction as a function of the energy.
Extraction of the Muon Signals Recorded with the Surface Detector of the Pierre Auger Observatory Using Recurrent Neural Networks

March 2021

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148 Reads

The Pierre Auger Observatory, at present the largest cosmic-ray observatory ever built, is instrumented with a ground array of 1600 water-Cherenkov detectors, known as the Surface Detector (SD). The SD samples the secondary particle content (mostly photons, electrons, positrons and muons) of extensive air showers initiated by cosmic rays with energies ranging from 1017 10^{17}~eV up to more than 1020 10^{20}~eV. Measuring the independent contribution of the muon component to the total registered signal is crucial to enhance the capability of the Observatory to estimate the mass of the cosmic rays on an event-by-event basis. However, with the current design of the SD, it is difficult to straightforwardly separate the contributions of muons to the SD time traces from those of photons, electrons and positrons. In this paper, we present a method aimed at extracting the muon component of the time traces registered with each individual detector of the SD using Recurrent Neural Networks. We derive the performances of the method by training the neural network on simulations, in which the muon and the electromagnetic components of the traces are known. We conclude this work showing the performance of this method on experimental data of the Pierre Auger Observatory. We find that our predictions agree with the parameterizations obtained by the AGASA collaboration to describe the lateral distributions of the electromagnetic and muonic components of extensive air showers.


FIG. 1. Number of muons as a function of the measured energy. The black line is the fitted Rµ = a (E/(10 19 eV)) b . Markers on the top of the frame define the bins in which the fluctuations are evaluated. The numbers give the events in each bin. The effect of the uncertainty of the absolute energy scale is indicated by σsys(E).
FIG. 2. Measured relative fluctuations in the number of muons as a function of the energy and the predictions from three interaction models for proton (red) and iron (blue) showers. The gray band represents the expectations from the measured mass composition interpreted with the interaction models. The statistical uncertainty in the measurement is represented by the error bars. The total systematic uncertainty is indicated by the square brackets.
FIG. 3. Data (black, with error bars) compared to models for the fluctuations and the average number of muons for showers with a primary energy of 10 19 eV. Fluctuations are evaluated in the energy range from 10 18.97 eV and 10 19.15 eV. The statistical uncertainty is represented by the error bars. The total systematic uncertainty is indicated by the square brackets. The expectation from the interaction models for any mixture of the four components p, He, N, Fe is illustrated by the colored contours. The values preferred by the mixture derived from the Xmax measurements are indicated by the star symbols. The shaded areas show the regions allowed by the statistical and systematic uncertainties of the Xmax measurement [42].
Measurement of the fluctuations in the number of muons in extensive air showers with the Pierre Auger Observatory

February 2021

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100 Reads

We present the first measurement of the fluctuations in the number of muons in extensive air showers produced by ultra-high energy cosmic rays. We find that the measured fluctuations are in good agreement with predictions from air shower simulations. This observation provides new insights into the origin of the previously reported deficit of muons in air shower simulations and constrains models of hadronic interactions at ultra-high energies. Our measurement is compatible with the muon deficit originating from small deviations in the predictions from hadronic interaction models of particle production that accumulate as the showers develop.


Figure 3. One of the images taken by the Auger FRAM during a Mode A altitude scan, in this case covering a well-known region of the Milky Way around the star í µí¼‚ Carinae and its surrounding nebula (seen left of the center). A single 30-second exposure in the Johnson B filter can be used to measure the brightness of hundreds of stars simultaneously in such a rich area.
Figure 6. The FRAM enclosure with one half open and one closed. Inside is an older version of the FRAM setup with the Meade SCT and Paramount ME mount.
Figure 8. Spectral characteristics of the key components of the wide-field system -transmissivity of the lens and the filters and quantum efficiency of the CCD -as measured in an optical laboratory.
The FRAM robotic telescope for atmospheric monitoring at the Pierre Auger Observatory

January 2021

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150 Reads

FRAM (F/Photometric Robotic Atmospheric Monitor) is a robotic telescope operated at the Pierre Auger Observatory in Argentina for the purposes of atmospheric monitoring using stellar photometry. As a passive system which does not produce any light that could interfere with the observations of the fluorescence telescopes of the observatory, it complements the active monitoring systems that use lasers. We discuss the applications of stellar photometry for atmospheric monitoring at optical observatories in general and the particular modes of operation employed by the Auger FRAM. We describe in detail the technical aspects of FRAM, the hardware and software requirements for a successful operation of a robotic telescope for such a purpose and their implementation within the FRAM system.


Citations (61)


... These output signals are sampled by a Field-Programmable Gate Array at 320 MHz, corresponding to a sampling interval of 3.125 ns, resulting in a binary trace of 2048 bits stored in the front-end memory. The backend electronics handles all calibration, control, and monitoring tasks [45]. Additionally, the surface electronics, common to all UMD station modules, interfaces with the SD electronics to check for a trigger and retrieve and transfer the binary traces upon an event data request. ...

Reference:

Search for a diffuse flux of photons with energies above tens of PeV at the Pierre Auger Observatory
Design and implementation of the AMIGA embedded system for data acquisition

Journal of Instrumentation

... In practice, extracting mass sensitive parameters by combining SSD and WCD measurements has proven to be complicated process often heavily leveraging universality [129,130] or the use of DNNs [131]. Unfortunately, it has also so far proven to be more difficult than originally hoped, with only marginal increases in mass sensitivity observed in simulations [132], as compared to WCDs alone [22,133]. It is likely that this situation will improve as hadronic interaction models gain in accuracy and expertise is brought to bear on the problem of mass reconstruction with an SSD + WCD hybrid detector through the AugerPrime upgrade of the Pierre Auger Observatory [21]. ...

Deep-learning based reconstruction of the shower maximum X max using the water-Cherenkov detectors of the Pierre Auger Observatory

Journal of Instrumentation

... A simple water-Cherenkov detector, such as the one used at the Pierre Auger Observatory cannot distinguish directly between the electromagnetic and muonic components, but it has been proven that machine learning techniques might provide very good resolution in extracting the muonic component from the total signal [22] for certain distances to the air-shower axis and energies of the primary particles. The reconstruction of the number of muons in air showers can be further improved by separating horizontally the optical volume of the detectors in two: the upper layer would be more sensitive to the electromagnetic component, while the bottom layer would contain more light produced by muons. ...

Extraction of the muon signals recorded with the surface detector of the Pierre Auger Observatory using recurrent neural networks
  • Citing Article
  • July 2021

Journal of Instrumentation

... With a ph(F)otometric Robotic Atmospheric Monitor, FRAM, the overall atmospheric optical depth can be derived. A CCD camera with a photographic lens on an equatorial mount provides wide-field images of stars which can be compared to their cataloged brightness [62,63]. This passive method does not inferfer with any other observation technique and is used for characterizing the conditions at possible observatory sites, for example, see Fig. 24. ...

The FRAM robotic telescope for atmospheric monitoring at the Pierre Auger Observatory
  • Citing Article
  • June 2021

Journal of Instrumentation

... The observed offset is larger than the expected differences by up to −15 g cm −2 from studies using various hadronic interaction models [23,28]. This indicates that the current generation of hadronic interaction models may not describe the measured data entirely, which is consistent with previous analyses that suggest inadequacies in the description of muon profiles [14,33,41,42], as well as the longitudinal profiles in general [43]. ...

Measurement of the Fluctuations in the Number of Muons in Extensive Air Showers with the Pierre Auger Observatory

Physical Review Letters

... Recently, SiPMs have been used in various space applications, including measuring transient gamma rays [2], detecting high-energy cosmic rays [3], and detecting coincident gamma-ray bursts with gravitational wave events [4]. Additionally, SiPMs are used in terrestrial applications, such as communications [5], astrophysics [6], and quantum optics [7]. ...

Calibration of the underground muon detector of the Pierre Auger Observatory

Journal of Instrumentation

... The observatory's main objectives of scientific study are to find ultra-high energy sources of cosmic rays, measure the cosmic ray energy spectrum, and uncover the mass composition of cosmic rays. Throughout its years of operations, the Pierre Auger collaborators have also found other uses for the experiment, such as measuring proton-air cross-section, measurement of upper atmosphere lightning called ELVES [53], and searching for neutrinos [54]. The Pierre Auger Observatory began operation in 2004 while it was only partially built. ...

A 3-Year Sample of Almost 1,600 Elves Recorded Above South America by the Pierre Auger Cosmic-Ray Observatory
  • Citing Article
  • January 2020

... The underground muon detector consists of scintillators deployed next to the water Cherenkov detectors that constitute these denser arrays [8]. At each position, three 10 m 2 modules are buried at a depth of 2.3 m to shield electromagnetic particles [13]. ...

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

Journal of Instrumentation

... Atmospheric cosmic rays (CRs) with high energies have been detected using the EAS [1]. Physicist Pierre-Victor Auger of France was the first to find EAS in 1930 when he increased the amount of atmospheric particles [2]. ...

Reconstruction of events recorded with the surface detector of the Pierre Auger Observatory
  • Citing Article
  • October 2020

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et. al

... The estimated muon density is defined as the number of muons over the projected area of a module to account for the decrease of its sensitive area with the air-shower zenith angle. To reconstruct the incoming direction of the primary particle and the lateral distribution function (LDF) [48] of the air showers we use the signals from the WCDs. The LDF is described by the Nishimura-Kamata-Greisen (NKG) function [49,50] from which we extract the shower size, S(r ref ), defined as the value at an optimal distance, r ref . ...

Reconstruction of events recorded with the surface detector of the Pierre Auger Observatory

Journal of Instrumentation