Calibration of the Underground Muon Detector of the Pierre Auger Observatory

Journal of Instrumentation

PAPER • OPEN ACCESS Calibration of the underground muon detector of the Pierre Auger Observatory

To cite this article: The Pierre Auger collaboration et al 2021 JINST 16 P04003

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This content was downloaded from IP address 129.13.72.195 on 01/06/2021 at 16:50 2021 JINST 16 P04003 April 6, 2021 close to the : 2 January 25, 2021 : December 16, 2020 : when far away, the 2 Published Accepted Received https://doi.org/10.1088/1748-0221/16/04/P04003 -modules, each segmented into 64 scintillators Published by IOP Publishing for Sissa Medialab 2 m : 2012.08016 Particle detectors; Detector alignment and calibration methods (lasers, sources, eV, the Pierre Auger Observatory is currently being equipped with an underground 5 . 2021 The Author(s). Published by IOP Publishing Ltd on behalf of : To obtain direct measurements of the muon content of extensive air showers with energy [email protected] c

16 Sissa Medialab. Original content from this work may be used under the 10 E-mail: intersection of the shower axisnecessary with broad the dynamic ground range is to achieved muchmodes by the less in simultaneous than the implementation one of read-out per two electronics:mode, acquisition m suited to the measure binary a high mode, numberof tuned of the them. to muon In detector count this modules: single work, wethen, first, muons, present the the the and end-to-end SiPMs ADC the calibration are channel calibrated ADC is bydata calibrated means acquisition. of using The the atmospheric laboratory binary and muons, channel, fieldof detected and measurements the in performed full parallel to calibration develop to the chain thecalibration implementation of procedure shower is both reliable binary to and workbe with ADC operated the channels continuously, high in are amount changing of presented environmental channels conditions, and in for discussed. the several UMD, years. Keywords: which The will particle-beams); Photon detectors for UV, visibleSi-PMTs, and G-APDs, CCDs, IR EBCCDs, photons EMCCDs, (solid-state) CMOS imagers, (PIN etc); diodes,Physics Performance Detectors APDs, of High Energy ArXiv ePrint Calibration of the underground muon detectorPierre of Auger the Observatory coupled to silicon photomultipliers (SiPMs).the Direct study of access both of to the the composition of shower primaryin muon cosmic the content rays and forward allows of direction. high-energy for hadronic As interactions the muon density can vary between tens of muons per m terms of the Creative Commons workAttribution must 4.0 maintain licence. attribution to Anyand the further DOI. author(s) distribution and of the this title of the work, journal citation The Pierre Auger collaboration Abstract muon detector (UMD), consisting of 219 10 above 2021 JINST 16 P04003 in 2 , and a denser array of 71 WCDs 2 eV can only be indirectly detected hit the scintillators without passing ◦ 15 10 eV. A hybrid technique is employed to do so, in 17 – 1 – 10 eV thanks to the installation of an even denser array of about 2 km 5 . 16 10 with a 750 m spacing (SD-750). More recently, the SD energy threshold has been 2 scintillation modules are buried at a depth of 2.3 m. The separation from the surface detector 2 The aim of the Pierre Auger Observatory [1], located near the town of Malargüe in Argentina, To provide a direct measurement of the muon content in air showers, an underground muon 4.1 Muon selection4.2 criteria and charge calculation Filling of charge histograms 12 14 through the WCD while probing the same shower density. The chosen depth, which corresponds to guarantees that even particles with zenith angles up to 45 is to measure cosmic rays with energies above detector (UMD) [2,3] is being219 deployed scintillator at modules co-located the at Auger 73 site. positions:hexagon, and 61 The positions at UMD of each the will position SD-750,10 consist forming of m of a the compact an SD-433. array of At a distance of at least 7 m from the WCD, three 1 Introduction Many questions remain openDue concerning the to origin their of lowby high- flux, measuring and cosmic extensive ultra-high-energy air rays cosmicatmosphere. showers with rays. produced Therefore, energy the when above nature they offlux, interact each is with primary difficult to cosmic molecules determine, ray, in orof hindering the the the muons composition full Earth’s produced of understanding in of theirmeasurements air data. global of showers However, these the scales muons total are with number thus thecosmic optimal rays. to mass understand number the chemical of composition the of primary primary particle. Direct which a fluorescence detector (FD)extensive and air a showers. surface The FD detector is (SD) composedthe are of edge 27 used of fluorescence in the telescopes combination distributed SD. to at Thea four detect SD 1500 sites m at consists spacing of an (SD-1500),over array covering of 28 a km 1600 total water-Cherenkov area detectors of (WCDs) with 3000 km which detectors are spaced by 433 m (SD-433). 5 Summary The Pierre Auger collaboration 21 extended down to 17 Contents 11 Introduction 2 Electronics features of the underground3 muon2 detector SiPM calibration and setup4 of the binary acquisition Calibration mode7 of the ADC acquisition mode 12 2021 JINST 16 P04003 , GeV 1 binary > close to the core to much less than 2 , is devoted to measuring a high number of ADC – 2 – with embedded wavelength-shifting optical fibers coupled to an array eV, as reported by other experiments [8,9], which shows that the models 18 4 cm × 10 1 cm × eV and 5 . when far away. Therefore, the UMD needs to work efficiently in a broad dynamic range 17 of overburden as determined by the local soil density, ensures that the electromagnetic 2 2 10 400 cm A key element for the reconstruction of the lateral distribution function is the conversion of The acquisition of the UMD data is performed in slave-mode, this is, only when triggered by The way to convert raw signals into a number of muons is different for the two acquisition modes. one per m UMD signals in units of muons,of which relies muons on at the calibration the described groundfrom in the this depends shower work. on core: The the it density can energy, vary primary between tens composition, of zenith muons per angle,and, m and to distance achieve this, two complementary working modes are implemented: one, dubbed used in simulations do not describedirection. accurately the high After energy hadronic the interactionsoptimize engineering-array in the the detector phase, forward performance based modifications on the inIn experience particular, the gained with photomultiplier-tubes design the were operation replaced were of with prototypes. and implemented SiPMs upgraded to to electronics improve the with detection animplemented efficiency, [10]. additional acquisition mode to extend the dynamic range were component of extensive air showers is largely absorbed while vertical muons with energy the associated SD stations. Theaxis shower with geometry the ground) (arrival and direction the and energythe are intersection signal reconstructed of with as data the a from shower function the of WCDsthe alone their by ground transverse analyzing distance is, to on the the showerof other axis [6]. hand, the reconstructed The shower with number muon of the density muonsall UMD at is UMD data stations obtained separately. and by A obtaining global reconstructing itsindividual estimator showers the value measured with at muon the 450 lateral SD-750 m array distribution (the aredistribution). minimized distance [7] with In at respect from a to which an previous fluctuations average work, lateral of usingnumber signals data of in of muons the in UMD data engineeringbetween is array, we larger confirmed than that those the expected from Monte-Carlo simulations of showers In the binary mode, the identification of particlesthe crossing the number detector relies of on its muons segmentation, is and higher determined than by a counting given threshold. signals, In segment-by-segment,of contrast, with all the an ADC segments amplitude mode simultaneously, relies converted oncharge the of afterward determination the to of signal the a produced charge explained number by in of a sections3 and4, muons single respectively. through muon. Finally, we the summarize The average and calibration conclude methods in section 5. for the2 two modes are Electronics features of the underground muonThe detector UMD electronics consist,a basically, Field-Programmable of: Gate (i) Array an (FPGA) that array houses of the SiPM acquisition with logic its and read-out a system, soft-core (ii) for 540 g/cm can reach the buried detectors. Eachstrips underground of module is segmented into 64of plastic-scintillation 64 silicon photomultipliers (SiPMs) [4,5], Hamamatsu S13361-2050. is tuned to count singlethem. muons, the We other, describe named inacquired detail in these both two modes modes correlates. in section2, where we also discuss how the signal 2021 JINST 16 P04003 effect. pile-up – 3 – A broad dynamic range is attained by the implementation of two acquisition modes, binary The ADC mode extends the saturation point of the detector: it is well-suited to measure a and ADC, which work simultaneously. Themuons binary can be mode directly benefits counted from as theit pulses detector neither above segmentation: relies a on certain deconvoluting threshold. theon total This the number mode precise of is optical particles very device robust fromhitting gain since a position of or single the its particle integrated-signal, on fluctuations, nor the scintillator and stripthe and is the fiber. almost corresponding light completely attenuation Another through independent advantage offluctuations is the in that the it number does ofmode not photons is per require limited impinging a by muon. the thickwill segmentation scintillator be Nevertheless, indistinguishable itself: to the and, control therefore, two binary only Poissonian muons counted acquisition once. arriving This at feature the is known same as strip simultaneously higher number of particlesof using the the total integrated charge signals ingrow the of with module. all the 64 Contrary number strips tothe of the as number binary impinging a acquisition of particles, single mode detected measurement the forfrom muons. which fluctuations an fluctuations in integrated However, signal the since in ADCuncertainties it terms mode in of relies decrease the an on with estimation average estimating charge, of the the the signal number number fluctuations of of are particles propagated muons. to The resolution of the ADC channel is data transmission and slow control,and communications. and (iii) Working an asgoverned interface a by for slave-detector, the that the WCD of event trigger,and acquisition the monitoring in second SD, data, the (T2) whose UMD onesand trigger stations formed 20 is chain triggers per locally second, has at respectively. differenttrigger: The each levels buried WCD. scintillators [11], when The are being averaged such synchronizedunderground at the rate a detector the of first modules first-level condition associated (T1) T1s is with andboth, it. met, binary T2s and Upon the is ADC, the WCD acquisition 100 arrivalinternal modes, sends of as memory such well a that a as signal can signal, the timestamp the accommodatedetermines with of that, traces data at the a of up each trigger, position, timestamp are to the stored 2048 data toof in are triggers. the an all retrievable T1s up to the Therefore, in about the the 20array. WCD s rate after are of On its triggered occurrence. triggers the by Most background othercentral muons hand, data and, all as acquisition WCDs such, server passing uncorrelatedfrom to the the among form array second-level the for triggers a permanent send storage. globaltriggers When their shower-trigger from a that the timestamp shower WCDs, trigger to initiates along takes with a the place, the muonserver. all data detector first- traces, and acquisition are second-level sent to the central data acquisition As far as strips with astatistically simultaneous treated signal and are corrected less [12], thanat the but segmentation, the as the soon same pile-up as effect time, the canpile-up the be 64 effect strips correction might in produce is a under-counting, nomight given knock-on produce longer module electrons signals have from in feasible signal two the and neighboring soilincreased strips the probability resulting or of binary in inclined saturating an the mode muons over-count detector. of is particles Therefore,of the as saturated. muons binary well mode that as is can an limited If be in the theshower detected number core at the that same can time, besegments which probed depend translates with on into it. the a number limitwhen Furthermore, of in measuring impinging the since closer particles, distance the to to the fluctuations the the resolution shower in of core. the the binary number mode of worsen hit 2021 JINST 16 P04003 , 1 cm × 4 cm × 4 cm – 4 – In the ADC acquisition mode the 64 SiPM signals are added up analogically and the result As the signal processing in binary and ADC modes is performed with different sets of electron- To study in detail how the two electronics relate one to another, we assembled in the laboratory The signals read by the SiPM depend on the optical-fiber length between the SiPM and the is amplified with low- andThe high-gain amplifiers low-gain with channel a extends ratiomuons the of when about dynamic 4 the range in binary of thein mode amplification the an factor. is UMD intermediate saturated. to rangeThe of measure The amplifier muon a outputs high-gain numbers, higher are channel, resulted number sampledDigital initially to at Converters of conceived perform (ADCs) 160 MHz resulting to similarly in (6.25 to work ns twoelectronics waveforms the sample of is time) 1024 binary samples. with shown channel. A two in schema 14-bitbottom, of the how Analog-to- the the upper read-out SiPM panel (a), the ofsingle binary muon. figure1. channel (b), and the In ADC the channel (c) lower respond panel, to a we simulated ics, show, differences from in the top response to tointroduce, the in same particular, physical different event are read-out expected. delays,ADC so The channels that different the do architectures start not timethe coincide: of ADC the trace as signals in is one binary delayed canthe and with following, see respect this in to time the the shift binary lowerelectronics. is one. panel very-well defined, of Nevertheless, stable figure1, as in we the time, shall start-time and shortly uniform of see across in thea different scintillator strip, identical toSiPM those used and in read-out the UMD, electronics,scintillator with strip. and an optical a The fiber muon muon coupled telescope consists to telescope of a movable two standard scintillator at segments different of positions along the 60% for single-muon signals and decreasesit inversely to reaches the 10% square at root ofhigher a the muon few number tens numbers, of particles; of the muonsallowing ADC for where mode measurements it of has particle matches significantly densitiesbinary the better closer acquisition resolution resolution to mode, of the than the core the 64 the withfast-shaper, binary SiPM and binary improved signals mode. precision. a mode, are discriminator, In built handled At the within independentlyIntegrated each through Circuits channel a of (ASICs). pre-amplifier, two 32-channeltime) The Application-Specific by discriminator the signal FPGA is intooutput sampled 64 is at above traces a 320 of fixed MHz discriminator 2048this (3.125 threshold, bits. ns and threshold sample a is In “0”-bit defined otherwise. each toefficiency. trace, As significantly explained a in reject “1”-bit section3, the results SiPM if noise the while fast-shaper preserving a high detection position where the muon impinges20000 on muons the produced scintillator. at Tobetween characterize different 1 these m positions signals, and on we 4.5displayed the measure m, in scintillator the in bottom-left strip, intervals panel corresponding of ofsummed and figure2. to 0.5 normalized m. lengths For to the the binary The total mode, number average each of of of events (solid-blue the these curves 2048-bit signals and traces left for is y-axis) each resulting length is with a SiPM coupled tofigure2. each segment. When a A muon schema impingesgate of on to the the inject telescope, setup a the isscintillator trigger SiPM presented strip: signals signal in are in the a correlated upper sequence the with of panelmode UMD an is positive of electronics. AND then samples obtained. in The the binary muon mode also and produces a a waveform in signal the in ADC the 4790 Time / ns 4750 4710 4670 2021 JINST 16 P04003 4620 Time / ns 4580 Discriminator (/5) Pre amp + Fast shaper Input muon (x50) Discriminator threshold 4540 4500 0

200 200 600 400 Signal / mV / Signal (simulation) ADC channel – 5 – Binary channel . (Top) Schematics of the UMD electronics. (Bottom-a) Simulated SiPM response to a single-muon In the bottom-left panel of2, figure two optical-fiber effects can be inferred. The light produced Figure 1 signal. (Bottom-b) Simulation of theis binary mode re-scaled response for to illustration. the simulated(low- and muon. (Bottom-c) high-gains) Simulation The are discriminator of shown. pulse the ADC mode processing. The twoin ADC a outputs histogram whose peaks correspond(long-dashed-orange curves) to and the low-gain (short-dashed-red most curves) probable modes, bit theresulting to traces in are have averaged a the “1”. mean For waveformcurves (right the corresponding ADC y-axis) high- to of the the measurements muonADC at and signal. the 1 m binary In channels, and both introduced 4.5 by cases, m. different we time indicate The response of the general the timeafter electronics, shift a is between apparent. muon the impinges onas the it scintillator strip propagates is to attenuated theADC in SiPM: waveform decrease the the as optical histogram a fiber function peak and ofdifferent of loses the positions the optical-fiber intensity of length. binary the In channel strip addition,the and arrive photons photon at the produced propagation the maximum at in SiPM of the at the opticalshifted different fiber: when times measuring the due at time to different of the positions the delay on histogram introduced the and strips. by waveform maximums To better is illustrate this fact, we present 2021 JINST 16 P04003 Laboratory Field 5m , are shown as i , about 1 / 0.6 c. t Δ m h , between the start / i t ns Δ ) h 05 . 0 Muon telescope ± 67 . t) measured in the laboratory (black 5 Δ ( Scintillator strip w/ aluminium cover – 6 – 1m Optical fiber + connector SiPM + electronics 1 . (Top) Schematics of the laboratory setup used to characterize the UMD traces. (Bottom-left) Finally, we show in the bottom-right panel of figure2 the mean shift, Due to the refractive index of the material (n = 1.60), the speed of light in the core of the optical fiber is 62.5% of 1 This indicates that the photonsthe in vacuum. the optical fiber propagate at about 60% of thetimes speed of of the light binary in and ADCand channels only (black averaged circles); values the are time shown. shiftis The was five ADC standard calculated deviations start event above time by the is event, baseline. definedconstant and as We does the obtained not time depend that at on the which thealso time the position show signal shift where the the between mean muon channels impinges time is onsquare), shift the as calculated scintillator an strip. with example. data We In takenthe this with case, a muons as module impinge it deployed on is in the notto the possible scintillator, field the to we (red identify center assume the of the positionlaboratory. the on average For optical-fiber the module. completeness, strip length the where corresponding mean Thered start triangles data times in of from the the panel the ADC above, channel,it field to minus will illustrate are their be well-matched consistency explained with in with the section4,channels those start characterizing constitutes times the taken a of signal key in the point start binary. in the time As the and calibration the of time the shift ADC. betweenthe the speed in the vacuum.the material However, and the the speed path theselected of photons fiber the for follow signal when the propagating UMD is due is a the to convolution Saint-Gobain total of BCF-99-29AMC. internal the reflection in effect the from fiber the cladding. refractive The index of circles) and the field (red square) is shown in the lower part. in the bottom-right panel of figure2 optical-fiberthe length mean (blue start triangles). time ofwhere We the the define binary first the “1” channel start in as time the athe trace of function optical is of each fiber, found. the individual which The we trace slope estimated, as of by the this fitting time curve the corresponds data, to to the be signal speed in Figure 2 Average trace for the binary (solid-blueand and low-gain (short-dashed-red) left channels y-axis), measured ADC atright) high- different Signal (long-dashed-orange start optical-fiber and time lengths right as (1 y-axis), atriangles) to function 4.5 channels. of m). the The (Bottom- optical-fiber difference length, between for the the binary channel (blue start triangles) times and ( ADC (red 2021 JINST 16 P04003 ) ) br V cells − bias V , commonly ). Then, the = br br ov V V V and . To set up the SiPM, 2 bias V 2 mm × ) needs to be set. The minimum voltage for bias V , photons absorbed in the silicon produce electron- – 7 – 0 [13, 14]. varies from one SiPM to another, the first step of the > 2 br ov V V of each. To this aim, we first measure the dark-count rates with br unit to achieve a uniform response in each scintillator module and, V 2 , we vary the discriminator threshold of the binary channel, using ). When C. As an example, we show in the top panel of figure3 the dark counts ◦ bias ov V V ( and of the temperature and to the number of triggered cells, which we refer to as photo-equivalents (PE). ov ov V V . At each over-voltage bias V , in which different plateaus can be clearly identified. The width of the plateau is related to the Since the amplitude fluctuation of signals with a certain number of PEs is small, the rate of The purpose of the SiPM calibration in the UMD is to equalize the gain (hence The noise in SiPMs is mainly caused by spurious pulses produced in absence of light. In silicon, The direct dependency of the cross-talk probability with the temperature is rather weak, if any, compared to most of 2 bias of the 64 devices in eachtherefore, 10 m in the fullcalibration UMD is array. to determine As the different events varies slowly when the discriminator threshold isIn moved far contrast, from the when mean signal thenumber amplitude. discriminator of events threshold changes rapidly is andcorresponds near a to transition to the between the transition plateaus is mean between observed. the amplitude baseline The of first and the plateau 1 PE signal, signals, the the second to the transition a 10-bit digital-to-analog converterof (DAC) integrated SiPM into signals the per ASICs,reference second temperature and of above 25 we each count threshold theper level. second number (cps) as The a measurements functionV of are the performed discriminator threshold at for a oneseparation SiPM in measured amplitude with different between twotransition consecutive between integer these numbers signals. of PEs and corresponds to the the parameters in SiPMs. there is a probability forproduced carriers inside to the be active region generatedthat of by are not a thermal originated cell, agitation; by incident an if radiation avalanchecells as an may may dark electron-hole occur counts. be when pair initiated. Furthermore, electrons is optical are cross-talk Wemay recombined between refer escape during to from the the the avalanche triggered emitting pulses cell photons andresult, [13]. hit an These neighbor output cells of producing several PEs simultaneousradiation avalanches. may be or As obtained, a thermal despite noise. having only Infunction one SiPMs, of cell the the triggered dark-count by rate incident and cross-talk probability are increasing Furthermore, since signal fluctuations are rathereach small, number the of amplitude PE (and are charge) distinguishable distributionsof one for PE from another, in making individual it signals. possible to identify the number operated in Geiger mode; the cells are distributed over an area of 2 SiPM gain, noise and efficiency are proportionalreferred to the as difference between hole pairs, which trigger aimpinging diverging on avalanche of a carriers. cell,depends this Regardless on avalanche of the results the SiPM always number inproportional of gain. to the photons Therefore, same at macroscopic the current, SiPM which output, only the signal amplitude and charge are SiPMs to function corresponds to the breakdown voltage of the silicon junctions ( 3 SiPM calibration and setup ofEach the binary SiPM acquisition of mode the UMD is an arraya reverse of bias 1584 voltage across avalanche the photo-diodes SiPM terminals (also ( referred to as 2021 JINST 16 P04003 .

for

bias Cross-talk probability / % / probability Cross-talk V bias PE. In V 5 . 3 2.5 2 1.5 1 0.5 0 = 57.58 V. / V > bias , can be easily 45 bias is then adjusted V V 55.5 determination for = 57.58 V bias bias br V bias V V V 55 40 . . (Bottom-right) Dark-count PE = (38.3 ± 0.1) / DAC counts PE = (38.3 ± 0.1) bias Threshold / DAC counts br 54.5 V V 35 54 0

400 200 600 Dark-count rate / cps / rate Dark-count 53.5 Cross-talk Dark counts V in this example. The ) 53 , making their response uniform.

0.3 0.6 0.5 0.4 . Dark-count rate / Mcps / rate Dark-count . With a linear fit to the measured amplitudes, we ov 0 br V – 8 – ± V 68 = . / V 51 59 bias ( bias V V 58.68 58 for the different SiPMs, the dark-count rate measurements allow us also ov 0.03) V V 57 55.39 . The dark-count rate is estimated as the rate of signals with amplitude = (51.68 for each SiPM, which is br 56 . bias br V V V , as shown in the bottom-left panel of figure3. The mean amplitude increases linearly bias as expected, and is zero for V bias . (Top) Dark-counts per second (cps) as a function of the discriminator threshold at different bias V

50 35 30 25 45 40

V PE Amplitude / DAC counts DAC / Amplitude PE Besides equalizing The dark-count rate thus allows us to build the mean amplitude of the 1 PE signal as a function Dark-count rate / cps / rate Dark-count for each SiPM, so that all of them get the same to quantify the SiPM noise.squares We show and in y-axis the on bottom-right the panelfunction of left) of figure3 andthe cross-talk dark-count probability rate (red (black dots and y-axis on the right) as a of the identified in the middle between the first2.5 and PEs second are plateau. represented, as The an sets example, ofprocedure in amplitude for the values figure finding for 1 with the and black dashed PEwith lines. amplitudes, a To we Gaussian better distribution illustrate present the whose in meanBy the corresponds inset repeating to the a this amplitude curve process of with 1 withdifferent PE its all for derivative the fitted curves we can determine the signal amplitude of 1 PEwith for thus obtain an individual SiPM. The dark-count rates and PEIn amplitudes the shift towards inset, higher values we when show rising one the with curve a at Gaussian the distribution middle to of obtainthis the specific the displayed SiPM. corresponding range The in PE linear the extrapolation amplitude. to main 0rate (Bottom-left) plot amplitude (red yields and squares) the its and value derivative of cross-talk fitted probability (black dots) as a function of the between 1 and 2 PE signals, etc. The 1 PE signal amplitude, which depends on Figure 3 2021 JINST 16 P04003 , 45 bias 30 V 28 40 26 V in the figure). Threshold / DAC counts 24 2 was optimized by . PE Amplitude / DAC counts ov 55 22 V

= 0

40 30 20 10 Entries bias V . V( ov 5 . V 3 = ov V 4 5

10 10 Dark-count rate / cps / rate Dark-count – 9 – 45 30 28 40 PE, due to the fact that events produced by thermal ﬂuctuations 26 1 850 kcps, depending on the SiPM temperature. The discriminator > 24 ∼ PE Amplitude / DAC counts 22

thus results, on the one hand, in a higher gain and efficiency, but also, 20 10 40 30 Entries ov , the typical value of cross-talk probability is about 2% and that of dark-count V ov V . Dark-count rate as a function of the discriminator threshold for the 64 SiPMs of a typical scintillator Increasing the The effect of the SiPM equalization can be appreciated in figure4, where we illustrate the result The procedure described above was performed in the laboratory but it can be repeated at any PE and that with amplitude

2 Dark-count rate / cps / rate Dark-count > balancing these parameters [5].efficiency and With a laboratory sufficiently measurements low noise we are have achieved with shown that both a high on the other end, in higher noise. During the engineering array phase, the Figure 4 module, before (left) and after1 (right) PE the are calibration. also shown Histograms in of the the insets. signal Solid amplitude lines corresponding between data to points areturn, shown the to cross-talk ease the probability comparison. is derived from the ratio between thecan rate have of more signals than with 1 amplitude PEsee amplitude from only if the cross-talk figure, signals both are the produced dark-count effectively. rate As one and can the cross-talk probability depends on the given that, as mentioned before, the SiPM noise depends on the of the calibration performed onrate one curves scintillator for module, the as 641 an PE SiPMs example. amplitude as histograms, We a show beforethe the function (left) histograms dark-count of is and the reduced after by discriminator (right) auniformity threshold factor calibration. of about and, the two in after detector The calibration, response. the standard whichthe insets, Note deviation reflects curves, that the of the where expected lines points better are correspond displayed tois to the smaller ease data than the the taken. comparison minimum After between stepthat calibration, of the while 1 dispersion DAC a count, of large which the dispersion corresponds gain the on to middle the the DAC of gain resolution. a should Note plateau berejecting where avoided, dark the the counts. chosen dark-count rate discriminator As is threshold cancounts rather in be in constant inferred minimizes the from the gain the effect top haveprocedure. it panel no has of impact on figure3, in variations the of performance a few and ADC are acceptabletime for in the the full field, calibration with the module removed from normal data acquisition. In fact, given that the threshold of the binary mode isthe then threshold chosen results to in reduce a the betterbalance impact background to of reduction reduce this but residual the also noise. dark-count loss ratethe Increasing of muon measurements signal. telescope while studies 2.5 keeping PE [15]. about gives 99% the of best the muons from rate, at 0.5 PE, is between 450 For the selected 2021 JINST 16 P04003 8 6 and the gain constant. Such ov every year. The 4 V ◦ . In the left panel ov Mean br V 20 V , the 2 bias V 0 2 - 4 - 1 , to maintain the value of 4 3 2

10 10 Entries 10 10 bias V – 10 – increases and, for a ﬁxed 28 br V , which is the temperature dependence of 26 C ◦ with the temperature. The UMD operates in an outdoor ambient: / br PE Amplitude / DAC counts V , according to the temperature variation: set at a reference value of 24 bias V 22 20 Field Laboratory . (Left) PE amplitude obtained in the laboratory and in the ﬁeld for 512 SiPMs. (Right) PE amplitude , it compensates by 54 mV The calibration procedure has been applied, in the laboratory, to more than 6400 SiPMs: in The SiPM gains, determined with the calibration, are however subjected to drifts, due to the C

◦ 18 2 Entries 10 10 decrease. It is apparent howon. the The PE remaining amplitude variation is of stabilizedthe about when acceptable 2 the range, DAC counts and compensation in does mechanism the not is whole have temperature an range impact is on well the within detector performance. In the right panel gain drifts must be compensated by readjusting an adjustment is done automatically, byis exploiting a integrated mechanism into of the temperature compensation high-voltagethe that source high (C11204-01 voltage, by i.e., Hamamatsu). This mechanism adjusts of figure6, we presentthe the temperature signal of amplitude the at high-voltagewith 1 source PE (black measured (averaged circles) in over the the 64and laboratory temperature SiPMs) the without as compensation. temperature (red increases, a squares) then function When and the of the compensation mechanism is off the right panel of figure5 eachwe corresponding module show results that well-centered to the zero. distributionallows This us of shows to that the the obtain PE calibration a effectively amplitudes uniform(4.5 minus gain, standard the the deviation), mean maximum which, deviation of well fromdetector within the performance. the mean acceptable This being range, calibration of does procedure 3SiPMs not DAC counts guarantees of have a the an sufficient UMD impact array. uniformity on to the work in all well-known dependence of 25 Figure 5 for 6400 SiPMs; for each set of electronics, the mean amplitude of each module wasstrategy centered to to calibrate the zero. SiPM array andperforming the binary the channel is calibration based in on the thebe analysis of seen laboratory thermal in noise, or the the left field panelwith of is, dark-count figure5 for measurementswhere any on we purpose, showand a the indistinct. in sample histograms the of field of This the (solid-red 512 can PE line),difference amplitudes, SiPMs, after between obtained calibration. the in two The measurements the two being distributions laboratorythe always are smaller (dashed discriminator well-superimposed, than the threshold blue 0.5 DAC counts. levels line) using We2.5 compare PE the corresponds mean to of 61 DAC counts. these histograms: in both cases the level of even if it is buried 2.3 m deep, it is exposed to temperature variations of about 2021 JINST 16 P04003 . C 44 ov V C and ◦ 42 PE/ ) Temperature / 40 , is contained 003 . ◦ 0 42 ± 38 049 and . 0 ◦ (about 0.6 V). Therefore, (− 36 30 ov V 34 32 w/o compensation w/ compensation 30 1

0.6 0.4 1.2 0.8 Dark-count rate / Mcps / rate Dark-count – 11 – C, respectively. ◦ PE/ ) 002 . C) is stronger than that produced by the variation of the 0 ◦ . 1 PE amplitude (left) and dark-count rate (right) as a function of the temperature of the high- . Mean rate per SiPM (left y-axis) and mean electronics temperature (right y-axis) averaged every w/o compensation w/ compensation ± The temperature range probed in the laboratory, between about 431 , when the compensation mechanism is off, two opposite effects contribute to the variation of . 0 ov (− Figure 7 hour in an exampleJanuary scintillation of 2020 module corresponds in to a operation period in in which the the field. corresponding position was The notof in gap figure6 acquisition. betweenwe show mid-December the and average dark-countwithout rate as the a compensation function mechanism. of thefor temperature For measured both comparison, with measurements. and the same Since temperatureV the range dark-count is rate displayed increases boththe with total rate: the an SiPM increase temperature withHowever, and in the the temperature given of ranges, the the silicon fluctuation and(about of a the decrease 12 dark-count with rate the due fall to of thethe the temperature dark-count rate variation fluctuation behaves similarly whencompensation measuring mechanism. with and without the temperature Figure 6 voltage source measured in thecompensation laboratory. mechanism on. We display The the fitted results slopes for for the measurements PE with amplitude and data without are the within that experienced during operationshow in the variations the of field, the as temperaturescintillation one of module the can during electronics see more (right than in y-axis), three figure7. years averaged every of hour, operation: The in the red one daily and squares yearly modulations are 2021 JINST 16 P04003 PE averaged over all the SiPMs 5 . 2 > – 12 – , a modulation of the background rate is observed, despite the ov V PE were produced, “1”s in the corresponding binary traces were obtained. In the . The factor 2 in noise level between the warmest and coolest months of the years 5 . ov 2 V > We used the muon telescope to collect 16000 signals at different positions of the scintillator translates into a probability betweentrace. 13% and This 25% will of not havingcan have noise be a producing rejected significant a by impact “1” setting in a in the cut, the explained muon binary in number section estimation,4.1. since4 these signals Calibration of the ADC acquisitionIn mode the ADC channel, the numbersignal of to muons the is estimated mean byobtain normalizing charge the the latter of charge for a each of UMD the singleapproach module. recorded used muon. To for this the aim, calibration we Therefore, of exploitthe the the atmospheric UMD WCD muons, [16]. goal modules. with This As of the approach explained same the in isbut section2, however more ADC it the challenging depends trigger calibration for of on is each the UMD first-levelUMD to module trigger are is of not in the autonomous, associated fact WCD. mostlysignals The uncorrelated: in signals the in in the UMD WCD the are andto largely majority in select due of the single-muon to signals the noise. and events usehigh However, triggered them we rate by to show calibrate in of the the this WCDs, the ADC section the during first-level channel, how data thanks WCD it acquisition, to trigger histograms is the of (100 sufficiently possible triggers the per muon-chargeis second). distribution, from extracted. which The the average procedure Two charge ingredientsperformed aims with need at the to filling, binary be channel,the and defined ADC the first: channel. calculation of the their strategy integrated charge, for performed the with 4.1 selection of muons, Muon selection criteria andAt charge the calculation lowest trigger level, the bulk ofAs the signals no recorded amplitude in the filter ADCthreshold are is due in to implemented SiPM the in dark binary counts. the mode),more ADC than each 0.5 acquisition of Mcps mode the of dark-count (such 64muons, rate. SiPMs as we contributes make To the reduce to use discriminator such of the backgroundwe the baseline while build binary fluctuation selecting an channel. signals with internal due second-level When trigger to in a based the first-level on trigger binary the is trace. signal received width, fromnoise To defined the signals define as by WCD, such the using a number a trigger, of laboratorysection2 we “1”s setup,and first including shown characterized a in the muon the widtharray telescope, is upper of similar coupled single-muon panel to to and that of an described optical figure2.counts. fiber, in with The In the SiPM other this array 63 and configuration, being binary passive only channel and one were contributing calibrated SiPM only as with in explained dark strip, the in section3. in the sametime way as window explained around in the section2.window trigger were time classified To as characterize given noise. the by Theamplitude muon the other signal, telescope. 63 SiPMs we were defined Signals also a turned produced on: away when from dark this counts with in the same module (blacktemperature, dots independently of and the left y-axis).stability of Since the dark-count rate depends on the SiPM left panel of figure8, we display the histogram of the widths of the single-muon signal (solid-black apparent. We also show the rate of signals with an amplitude 2021 JINST 16 P04003 Field Laboratory s. μ – 13 – . Binary channel. (Left) histograms of signal widths due to single muons (black), SiPM noise Based on these measurements, to select a muon we set a condition on the width of the signal, requiring morethree than standard deviation four from “1”s theSiPM average (left noise duration. with arrow less than in 1% This of(right cut muon the arrow signal rejects in loss. figure), the thus figure), Similarly, we which which also more allows setbiases us corresponds than an to in upper select the 95% cut about to muon of 99% of 12 charge of about samples estimation the the also due single-muon shown signals, to avoiding as shower events grey with dashed severalUMD lines particles. in in The the the two field, right cuts we are panel. measuredthe the latter, To we average verify width expect the to of observe applicability binary wider of signals signals these in than a cuts the module mean to found as the in an the example. laboratory, since In knock-on Figure 8 (long-dashed red), and SiPM plus opticalsingle-muon fiber-scintillator signals noise as (short-dashed a blue). function (Right)displayed of mean as the width error of optical-fiber bars. length.indicated The The in red one number square of standard samples corresponds deviation (3.125 from to ns). the the mean result is obtained with fieldline), data. based The on widths the are measurementsan made effect at of all the positions. attenuationwe in show The the the spread behavior optical of of fiber, the theof as average distribution the illustrated width optical-fiber is in of the length. in the right part single-muonthat, The signal panel as error (black of expected, circles) bars figure8, longer as represent where (shorter) aof one signals function such standard are a deviation. detected spread, closer One thethe to can distribution left (farther clearly is panel from) see well-separated the of from SiPM. figure8.widths that of In the due spite The noise to long-dashed signals noise in redblue signals, the one histogram 63 also is SiPMs corresponds shown due not to in coupled to the tonoise noise-signals and the distribution in of optical the the of fiber, muon SiPM while the signal coupled the arean short-dashed to well-distinguished: average the the width optical distribution of relative fiber. to 7.8 the The samplesthat muon widths (24.4 due signal ns) of has to with the the SiPM a SiPM-noise0.7 standard samples has deviation (2.2 ns). of an 1.5 average Note samples width thatis (4.7 the of ns) the noise convolution 3.0 while samples in of the two (9.4 ns) SiPM contributions:3 samples, coupled with the and to standard SiPM a the deviation tail, dark-count optical noise, with fiberto a the (blue the mean peak histogram) at optical-fiber/scintillator of about system which 6 [17]. is samples,those at not due Even about related to muons, though to it the the cannot SiPMs, latterirreducible be which background efficiently generates we is rejected signals attribute however without rather shorter losing small, muon than yieldingin signals. a a 5% The module probability effect when of of considering over-counting this a the muon whole trace of 6.4 2021 JINST 16 P04003 4.5 Field 4 Distance / m 3.5 Laboratory 3 2.5 2 1.5 1

5 0

35 30 25 20 15 10 Width / 6.25 ns 6.25 / Width – 14 – Std. Dev. . ADC channel. (Left) histogram of the single-muon signal width measured with the ADC in the The second ingredient required for the calibration procedure is the calculation of the integrated charge for the selected muon,needs by to means be optimized of to the reduce contributions ADCcauses from channel. the fluctuations noise in due To to the do thechannel, ADC that, SiPM dark-count an baselines. we rate which integration studied window By the usingamplitude width the above of two laboratory the times data muon the acquiredsignal signal, standard widths with deviation defined is the of displayed as in the ADC the the baseline.the left number signal panel width The of of (black figure9, circles) distribution ADC as with of a bins thestandard function the right with of deviation). muon- panel the an Also, optical-fiber showing length the in (error behavior this bars of to case, correspond the to the light one signal attenuation becomes of narrower thewindow as optical for the fiber. single-muon distance signals Based increases, on as due thisthe three measurement, left standard we deviations panel, defined from grey the the dashed integration red mean line square width in corresponds (grey the arrow to right in thecompatibility one), with mean which the width corresponds measurement obtained to in the 32 from samples laboratory. measurements (200 ns). in the The 4.2 field, showing its Filling of charge histograms The core of the calibration procedure isby to atmospheric periodically muons. fill histograms To of explain the thefrom signal strategy, charge the produced we binary start channel from (top) figure andand10, the summed where ADC we (bottom), over show recorded one the following hour asimilar traces of WCD features: first-level operation trigger a in rather thenoise, uniform field and distribution (360000 an of events). accumulation, signals due Thethe along to two WCD. particles, the Note histograms at trace, that a show due in time tocorresponding the that to random corresponds summed high-amplitude detector to ADC signals, that most traces of likely undershoots due the are to trigger observed, air from shower after events. the trigger time, Figure 9 laboratory. (Right) Mean widthmuon. of Results from the the single-muon laboratory (black signalbars circles) are and as presented. field a (red The squares) function widths with are of one standard indicated the deviation in as position number error of of samples the (6.25 ns). impinging electrons from the soilthermore, also the deposit laboratory energy setup in isenergy more the deposit efficient than scintillators, at inclined thus selecting muons as vertical producingfigure found muons, more as in which the a light. leave field. red a square, The smaller is Fur- resulting still measurement, well-consistent shown with in that the obtained in the laboratory. 2021 JINST 16 P04003 – 15 – . 360000 background events which correspond to the equivalent of one hour of first-level triggered To identify single-muon signals in the traces, we first search for “1”s in a window around The choice of the window size to search for muons and noise is important. Narrowing the size the trigger, illustrated with orangedescribed lines above, looking in for the a topwindow. sequence If panel. of this criterion more Then is than wethe satisfied, four window, we apply and and set then the as less we selection the locate than the start criterion time twelve start-time time shift “1”s of of between the within the binary ADC binary this trace and trace bycharge, ADC including the we channels, the use first presented information the “1” on in integration within the window section2. ofand 32 Finally, samples illustrated to in extract by the the the ADC signal trace orangeeffective (200 lines to ns), remove as in most explained the of above the bottomsystem. noise panel. from Therefore, we the repeat As SiPM, the above-described but already procedure, not applyingfrom mentioned, it that in the this from a trigger time procedure the window optical time separated is fiber/scintillator windowcontributes (represented to by the black lines traces:subtract in from the we the calibration bottom use data. panel) this where window only to noise estimate thewould reduce optical the fiber/scintillator number noise ofTo to noise illustrate signals, this but effect, it wethe would show, single-muon also in search reduce criteria, the the in left number theone panel of noise (orange muon window of circles), of signals. figure as the11, a traceswindow, (black function the the squares) of number number and the of of in window the events events, size. signal grows satisfying linearly As with there its are size. no muon For the signals in signal the window, the noise number of Figure 10 events. In orange (black) thebinary time channel windows traces. to search for (Bottom)170 ns, muon overlap the (noise) of time signals ADC shift are between channel indicated. the traces. channels (Top) presented sum in Note of the that bottom-right the panel x-axis of figure2. is shifted by about 2021 JINST 16 P04003 pC with a standard deviation of ) 1 . 0 ± 3 . 5 ( – 16 – pC. This corresponds to the mean charge deposited in the UMD by omnidirectional overburden. The mean muon energy in showers measured with the UMD varies from ) . Number of events in noise and signal-with-noise windows (left) and number of muon events 1 2 . 0 ± To extract data for the ADC calibration, an algorithm is set up in each UMD module in the In figure 12 we present the muon charge histogram (green curve) obtained with the described 1 . 3 ( field, which runs in parallel tothe the traces air shower that data acquisition. match This the algorithm muon is designed selection to select criteria, both for the signal and noise window. This muons, and therefore includes the540 g/cm contribution of secondary knock-onabout electrons 2 GeV far produced from in the shower the coreelectrons up to to about the 30 GeV when total close. chargeon The is contribution average not of about knock-on expected 10% to variation largelyenergetic is depend muons expected on close in the to the distance the estimationFor to core of the the with the analysis shower respect axis: of particle to cosmic-ray density those,mean showers, for atmospheric less muon dividing the energetic, charge far the most measured from in total thean the charge same estimation impact seen underground of point. module in the will muon a give, density at UMD at first module the order, surface. by the procedure and a window of 20histogram samples. (dashed This black) histogram from has the been total obtainedand charge by noise. histogram subtracting (dotted the orange) The noise that mean contains charge both signal obtained in this case is Figure 11 (right) for each window sizepresented. is displayed. The ratio between the number of signal and noise eventsevents is increases also more rapidly thanvalue, in the the curve becomes case parallel of to that pureany due more noise, to to only up noise, the to thus number indicating about ofwhere that 35 events. no we samples. muons This show contribute fact Above the can this difference becircles): in better the observed it number in increases the of right forpresent events panel the between windows of ratio noise up figure between and the to11, signal numberwindow 35 windows of samples, size. (green signal The then and asymptotic noise it behavior to events becomesnumber (blue zero of indicates squares) constant. noise that, as events when grows a proportionally increasing In function faster the ofthe than addition, window calibration the the size, procedure, number we the we of thus signal choose events. alines), To window implement for size which of 80% 20 of samples the (indicated eventslarge with are enough muons gray-dashed number and of 20% events, are about noise.due 1200 Such to for a noise. the choice analyzed allows us period, to minimizing keep the a contamination 2021 JINST 16 P04003 pC eV. ) 5 . 01 16 . 0 10 ± 12 . 0 ( pC and 18 ) 0.1) pC 0.1) pC 0.1) pC 0.1) pC 01 . Charge / pC 0 16 ± C. In both cases, the mean of all 14 14 ◦ . 0 Signal + Noise Noise Mean = (2.2 RMS = (1.6 Signal Mean = (5.3 RMS = (3.1 ( pC, which indicates that the method is ) 12 1 . 0 ± C and 43 10 ◦ 5 . 0 ( 8 – 17 – 6 4 2 0 pC with a standard deviation of ) 01 0 . 20 80 60 40

120 100 Entries ± 09 . pC with a standard deviation of 6 ) ( 01 . 0 . Charge histograms for a window size of 20 samples. The calibration histogram (solid green) ± 09 . To develop the calibration method, correlations between the binary and ADC channels were 6 ( 5 Summary In this work, we have discussedof the the method developed Pierre to Auger calibrate Observatory. thesegmentation: underground A each muon key module detector characteristic is of divided the intothe UMD scintillator-based 64 is detector segments, the coupled is direct to measurement its of a high the set muon of content 64 in SiPMs. air showers The with energy aim above of first studied using a dedicatedcoupled laboratory to setup, a SiPM consisting and of of a aresponse movable scintillator of muon telescope. the strip two This with channels allowed optical us, toand on fiber start vertical the time. muons one hand, at On to the different study other positions, the the hand, two in it channels. terms allowed us of to signal fully amplitude characterize the intrinsic time shift between robust and its output quite uniform. This is achieved by implementinglow two particle acquisition densities modes: as found a far frommuon binary densities, the mode, such shower core, as suitable and those for close an measuring to ADCcalibration the mode, is shower tuned the core. to conversion For from measure both high raw channels, signals the to ultimate the scope number of of the muons. respectively, which translates into a fluctuationuniformity of of the the mean calibration charge has of beenof about tested 2%. over 21 Furthermore, modules the in the field obtaining a mean charge histogram was Figure 12 is filled by subtracting thewindow. charge histogram in the noise window from the charge histogram ininformation, the along trigger with the triggeranalysis timestamp, is is performed stored offline: in anthese a data. external server, calibration To and assess histogram the the canhave performance subsequent filled be of calibration this filled histograms calibration with by method data selectingperiods under obtained temperature a with with variations, one time average we module electronic range during several of temperatures weeks in of two 32 2021 JINST 16 P04003 – 18 – Having characterized the relevant electronics features, we then proceed to explain the calibration Next, we presented the calibration of the ADC channel. In this case, the aim of the calibration In conclusion, we presented the methods to perform the UMD end-to-end calibration. We Argentina — Comisión Nacional de Energía Atómica; Agencia Nacional de Promoción of the binary channel. The firstof step is the to UMD equalize the array SiPM which gainsobtained and is by guarantee of a counting uniform utmost signals response importance abovemethod a since, based certain in on threshold, this the measurement segment channel, of by thevoltage dark-count for segment. rates, number each in of which SiPM, We muons we implemented and first is a thenmost determine of we the the set reverse bias SiPM a noise. thresholdit for By allows the applying us binary the to achieve channel method a to to PEAlso, more 2.5 amplitude PE, than we with which 6400 a have filters SiPMs, maximum demonstrated deviation weeither from have that in the verified the mean the that of laboratory performance 3 or DACnoise. of the counts. field, Finally, the we thanks showed calibration that to the the is well-knownsuccessfully chosen drifts stabilized the strategy in by the based the same gains, temperature on due compensation when the to mechanismwhich analysis temperature integrated applied reduces of variations, into the are the thermal electronics, temperature dependence by a factor of about 9. is to provide thecan average be charge obtained of by theatmospheric scaling signal muons, the detected of underground. total a Because chargeby single the the measured associated muon, UMD water-Cherenkov detector, in only is so a not a part that triggered ofand UMD the autonomously, most the available but signals of module. correspond number them to correspond muons of to Tothe muons uncorrelated this information noise. in aim To the overcome we binary such use amplitude a channel and large to background, the select we duration use muon of signals.with the binary a The signals, muon selection have criteria, telescope. been based definedabout We on after 1% have the a of shown muon study that in signal loss. the theythe signal laboratory reject Once in more the muons ADC are than channel selected 95% iswhich with identified of corresponds and the to the the binary charge the SiPM channel, is mean computed the noisemeasured width using start with in an of time the integration the of laboratory window single-muon and signal verifiedmean in plus charge the three of field. standard single Finally, deviations, to muons, as obtain wedetector an fill noise. unbiased a estimation charge of This histogram the of methodthe the was calibration signal tested is subtracted in stable of over different that time UMD due and to modules, uniform the over also the over array. time,proved denoting that these that methods are robust tounder work with the the temperature high variations amount of expected channels inapplied to the to operate field. and the stable 73 The stations methods (219 described modules) in of this the work UMD will array. be Acknowledgments The successful installation, commissioning, andnot operation of have the been Pierre possible Auger without Observatoryistrative the would staff strong in commitment Malargüe. andfinancial effort We support: are from the very technical grateful and to admin- the following agencies andCientífica organizations y for Tecnológica (ANPCyT);cas Consejo (CONICET); Nacional Gobierno de Investigaciones de Científicas la y Provincia Técni- de Mendoza; Municipalidad de Malargüe; NDM 2021 JINST 16 P04003 – 19 – Holdings and Valle LasAustralia Leñas; — in the gratitudemento Australian for Científico their Research continuing e Council; cooperationdação Tecnológico Brazil over (CNPq); de land — Amparo Financiadora access; ConselhoFoundation à de Nacional (FAPESP) Pesquisa Estudos de Grants do eMinistério Desenvolvi- No. Projetos Estado da 2019/10151-2, (FINEP); de Ciência, No. Fun- RioGrant Tecnologia, No. 2010/07359-6 MSMT de Inovações CR LTT18004, and LM2015038, e Janeiro LM2018102, CZ.02.1.01/0.0/0.0/16_013/0001402, ComunicaçõesCZ.02.1.01/0.0/0.0/18_046/0016010 No. (FAPERJ); and (MCTIC); 1999/05404-3; São CZ.02.1.01/0.0/0.0/17_049/0008422; Czech Paulo France Republicde — Research — Calcul Centre IN2P3/CNRS;gional Centre Ile-de-France; National de DépartementDépartement la Physique Sciences Recherche Nucléaire de Scientifique et l’Univers (SDU-INSU/CNRS);No. (CNRS); Corpusculaire LABEX Institut ANR-10-LABX-63 Conseil (PNC-IN2P3/CNRS); within Lagrange the de Ré- Investissements d’Avenir Paris Programme11-IDEX-0004-02; Germany Grant — (ILP) Bundesministerium No. Grant für ANR- Bildung und Forschung (BMBF);Forschungsgemeinschaft Deutsche (DFG); Finanzministerium Baden-Württemberg; Helmholtz AllianceAstroparticle Physics for (HAP); Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF);isterium Min- für Innovation, Wissenschaftterium und für Forschung Wissenschaft, des Forschungtuto Landes und Nazionale Nordrhein-Westfalen; Kunst Minis- di des Fisicadell’Istruzione, Landes Nucleare dell’Università e Baden-Württemberg; (INFN); della Istituto Italy Ricercatero (MIUR); Nazionale — degli CETEMPS Affari di Isti- Esteri Center (MAE); of Astrofisica México — Excellence; (INAF);No. Consejo Minis- 167733; Nacional Ministero de Universidad Ciencia Nacional y Autónoma Tecnología de (CONACYT) MéxicoNetherlands (UNAM); — PAPIIT DGAPA-UNAM; The Ministry ofentific Education, Research Culture (NWO); Dutch and nationalPoland Science; e-infrastructure -Ministry Netherlands with of the Organisation Science support forence of and Sci- Centre, SURF Higher Grants No. Cooperative; Education, 2013/08/M/ST9/00322, No. grant5–2013/10/M/ST9/00062, 2016/23/B/ST9/01635 No. and UMO-2016/22/M/ST9/00198; No. DIR/WK/2018/11; HARMONIA Portugal National —and Sci- Portuguese FEDER funds national within funds Programapara Operacional a Ciência Factores e de a Competitividade Tecnologia (COMPETE);search, through the Romania Program — Fundação Nucleu within Romanian MCI Ministry (PN19150201/16N/2019 of and PN19060102) EducationIII-P1-1.2-PCCDI-2017-0839/19PCCDI/2018 and and project within PN- Re- PNCDI III; SloveniaAgency, — grants Slovenian P1-0031, Research P1-0385, I0-0033, N1-0111;y Spain Competitividad — Ministerio (FPA2017-85114-P and de PID2019-104676GB-C32), Economía, Industria 2017/07), Xunta de Junta Galicia de (ED431C Andalucía (SOMM17/6104/UGR,Nacional Temática P18-FR-4314) de Astropartículas Feder (FPA2015-68783-REDT) and Funds, María de RENATA Maeztu Red Unitlence of (MDM-2016-0692); Excel- U.S.A. — Department of Energy,No. Contracts No. DE-FR02-04ER41300, DE-AC02-07CH11359, No. DE-FG02-99ER41107ence Foundation, and Grant No. No. 0450696; DE-SC0011689;European The Particle National Grainger Physics Foundation; Sci- Latin Marie American Curie-IRSES/EPLANET; Network; and UNESCO. 2021 JINST 16 P04003 , 798 Nucl. 545 , 2008 IEEE ]. 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Vicha 37 36 62 49 Observatorio Pierre Auger and Comisión NacionalUniversidad de Tecnológica Energía Nacional Atómica, — Malargüe, Facultad Regional Argentina BuenosUniversity Aires, of Buenos Adelaide, Aires, Adelaide, Argentina S.A., Australia Université Libre de Bruxelles (ULB), Brussels,Vrĳe Belgium Universiteit Brussels, Brussels, Belgium Centro Brasileiro de Pesquisas Fisicas, Rio deCentro Janeiro, Federal de RJ, Educação Brazil Tecnológica Celso SuckowUniversidade da de Fonseca, São Nova Paulo, Friburgo, Escola Brazil deUniversidade Engenharia de de São Lorena, Paulo, Lorena, Instituto SP, Brazil de FísicaUniversidade de de São São Paulo, Carlos, Instituto São de Carlos, Física,Universidade SP, Estadual São Brazil de Paulo, SP, Campinas, Brazil IFGW, Campinas,Universidade SP, Brazil Estadual de Feira de Santana, FeiraUniversidade de Federal do Santana, ABC, Brazil Santo André, SP,Universidade Brazil Federal do Paraná, Setor Palotina, Palotina, Brazil Universidade Federal do Rio de Janeiro, InstitutoUniversidade Federal de do Física, Rio Rio de de Janeiro Janeiro, (UFRJ),Universidade RJ, Federal Observatório Brazil Fluminense, do EEIMVR, Valongo, Volta Rio Redonda, de RJ,Universidad Janeiro, Brazil de RJ, Medellín, Brazil Medellín, Colombia Universidad Industrial de Santander, Bucaramanga, Colombia Charles University, Faculty of Mathematics and Physics, Institute of Particle and Nuclear Physics,Institute Prague, of Czech Physics of the CzechPalacky Academy University, RCPTM, of Olomouc, Sciences, Czech Prague, Republic Czech Republic CNRS/IN2P3, ĲCLab, Université Paris-Saclay, Orsay, France Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), Sorbonne Université, Université deUniversité Grenoble Paris, Alpes, CNRS, Grenoble Institute of Engineering Université Grenoble Alpes, LPSC-IN2P3, Centro Atómico Bariloche and Instituto BalseiroCentro (CNEA-UNCuyo-CONICET), de San Investigaciones Carlos en de Láseres Bariloche, y Argentina Departamento Aplicaciones, de CITEDEF Física and and CONICET, Villa Departamento Martelli, de Argentina Ciencias de la Atmósfera y losIFLP, Universidad Océanos, Nacional FCEyN, de Universidad La de Plata andInstituto CONICET, de La Astronomía Plata, y Argentina Física delInstituto Espacio de (IAFE, Física CONICET-UBA), de Buenos Rosario Aires, Argentina (IFIR) — CONICET/U.N.R. and Facultad de CienciasInstituto Bioquímicas de y Tecnologías Farmacéuticas en Detección y Astropartículas (CNEA, CONICET, UNSAM), and Universidad Tecnológica Instituto de Tecnologías en Detección yObservatorio Astropartículas (CNEA, Pierre Auger, CONICET, Malargüe, UNSAM), Argentina Buenos Aires, Argentina 1 2 3 Buenos Aires and CONICET, Buenos4 Aires, Argentina 5 6 U.N.R., Rosario, Argentina 7 Nacional — Facultad Regional Mendoza8 (CONICET/CNEA), Mendoza, Argentina 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Republic 30 31 32 33 CNRS-IN2P3, Paris, France 34 Grenoble 38000, France A. Weindl A. Yushkov V. Verzi E. Varela Z. Szadkowski P. Tobiska M. Tueros J. Souchard A. Streich S. Sehgal F.G. Schröder 2021 JINST 16 P04003 – 23 – Université Paris-Saclay, CNRS/IN2P3, ĲCLab, Orsay, France Bergische Universität Wuppertal, Department of Physics, Wuppertal,Karlsruhe Germany Institute of Technology, Institute for ExperimentalKarlsruhe Particle Institute Physics of (ETP), Technology, Institut Karlsruhe, für Germany ProzessdatenverarbeitungKarlsruhe und Institute Elektronik, of Karlsruhe, Technology, Institute Germany for AstroparticleRWTH Physics, Aachen Karlsruhe, University, Germany III. Physikalisches Institut A,Universität Hamburg, Aachen, II. Germany Institut für Theoretische Physik,Universität Siegen, Hamburg, Department Germany Physik — ExperimentelleGran Teilchenphysik, Siegen, Sasso Germany Science Institute, L’Aquila, Italy INFN Laboratori Nazionali del Gran Sasso,INFN, Assergi Sezione (L’Aquila), Italy di Catania, Catania, Italy INFN, Sezione di Lecce, Lecce, Italy INFN, Sezione di Milano, Milano, Italy INFN, Sezione di Napoli, Napoli, Italy INFN, Sezione di Roma “Tor Vergata”, Roma,INFN, Italy Sezione di Torino, Torino, Italy Istituto di Astrofisica Spaziale e FisicaOsservatorio Cosmica Astrofisico di di Palermo Torino (INAF), (INAF), Palermo, Torino, Italy Italy Politecnico di Milano, Dipartimento di ScienzeUniversità e del Tecnologie Salento, Aerospaziali Dipartimento , di Milano, Matematica Italy Università e dell’Aquila, Fisica Dipartimento “E. di De Scienze Giorgi”, Fisiche Lecce, eUniversità Italy Chimiche, di L’Aquila, Catania, Italy Dipartimento di FisicaUniversità e di Astronomia, Milano, Catania, Dipartimento Italy di Fisica,Università Milano, di Italy Napoli “Federico II”, Dipartimento diUniversità di Fisica Palermo, “Ettore Dipartimento Pancini”, Napoli, di Italy Fisica eUniversità di Chimica Roma “E. “Tor Segrè”, Vergata”, Dipartimento Palermo, Italy diUniversità Fisica, Torino, Roma, Dipartimento Italy di Fisica, Torino, Italy Benemérita Universidad Autónoma de Puebla, Puebla,Centro México de Investigación y de EstudiosUnidad Avanzados del Profesional Interdisciplinaria IPN en (CINVESTAV), México, Ingeniería y D.F., México Tecnologías Avanzadas del Instituto Politécnico Nacional Universidad Autónoma de Chiapas, Tuxtla Gutiérrez, Chiapas,Universidad Michoacana México de San Nicolás deUniversidad Hidalgo, Nacional Morelia, Autónoma Michoacán, de México México, México,Universidad D.F., Nacional México de San Agustin deInstitute Arequipa, of Facultad de Nuclear Ciencias Physics Naturales PAN, Krakow, y Poland University Formales, of Arequipa, Peru Łódź, Faculty of Astrophysics, Łódź,University of Poland Łódź, Faculty of High-Energy Astrophysics,Laboratório Łódź, de Poland Instrumentação e Física Experimental de Partículas — LIP and Instituto“Horia Superior Hulubei” Técnico National — Institute IST, for PhysicsInstitute and of Nuclear Space Engineering, Science, Bucharest-Magurele, Romania Bucharest-Magurele, Romania University Politehnica of Bucharest, Bucharest, Romania Center for Astrophysics and Cosmology (CAC), UniversityExperimental of Particle Nova Physics Gorica, Department, Nova J. Gorica, Stefan Slovenia Universidad Institute, de Ljubljana, Granada Slovenia and C.A.F.P.E., Granada, Spain Instituto Galego de Física de Altas Enerxías (IGFAE), Universidade de Santiago deIMAPP, Compostela, Radboud Santiago University Nĳmegen, de Nĳmegen, The Netherlands KVI — Center for Advanced RadiationNationaal Technology, University Instituut of voor Groningen, Kernfysica Groningen, en The Hoge Netherlands Stichting Energie Astronomisch Fysica Onderzoek (NIKHEF), in Science Nederland Park, (ASTRON), Amsterdam, Dwingeloo, The The Netherlands Netherlands 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 (UPIITA-IPN), México, D.F., México 65 66 67 68 69 70 71 72 Universidade de Lisboa — UL,73 Lisboa, Portugal 74 75 76 77 78 79 Compostela, Spain 80 81 82 83 2021 JINST 16 P04003 – 24 – Universiteit van Amsterdam, Faculty of Science, Amsterdam,Case The Western Netherlands Reserve University, Cleveland, OH, U.S.A. Colorado School of Mines, Golden, CO,Department U.S.A. of Physics and Astronomy, LehmanLouisiana College, State City University, University Baton of Rouge, New LA, York,Michigan U.S.A. Bronx, Technological NY, University, U.S.A. Houghton, MI, U.S.A. New York University, New York, NY, U.S.A. Pennsylvania State University, University Park, PA, U.S.A. University of Chicago, Enrico Fermi Institute, Chicago,University of IL, Delaware, U.S.A. Department of PhysicsUniversity and of Astronomy, Wisconsin-Madison, Bartol Department Research Institute, of Newark, Physics, DE, Madison, U.S.A. WI, U.S.A. (a) Fermi National Accelerator Laboratory, U.S.A. (b) Max-Planck-Institut für Radioastronomie, Bonn, Germany (c) School of Physics and Astronomy,(d) University of Fermi National Leeds, Accelerator Leeds, Laboratory, United Fermilab, Kingdom Batavia,(e) IL, also U.S.A. at Karlsruhe Institute of(f) Technology, Karlsruhe, Colorado Germany State University, Fort Collins, CO,(g) U.S.A. now at Hakubi Center for(h) Advanced also Research at and University Graduate of School Bucharest, of Physics Science, Department, Kyoto University, Bucharest, Kyoto, Romania Japan 84 85 86 87 88 89 90 91 92 93 94