This report describes the size reduction of the particle data output file(s) for Auger simulations. This reduction is achieved by a (random) selection of the shower core position relative to the triangular grid of detectors, as for all shower particles in the observation plane it is checked whether they arrive in the neighbourhood of a corresponding detector position. Only hitting particles are kept for the output. All other particles falling onto the Argentinian pampa far from any detector are skipped

Heck, Dieter

Oehlschläger, Jürgen

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  KIT SCIENTIFIC WORKING PAPERS    20The AUGERHIT Option of the Air Shower Simulation Program CORSIKA   by Jürgen Oehlschläger1, Dieter Heck1   1 Institute for Nuclear Physics, Karlsruhe Institute of Technology (KIT)    Impressum Karlsruher Institut für Technologie (KIT) www.kit.edu    Diese Veröffentlichung ist im Internet unter folgender Creative Commons-Lizenz  publiziert: http://creativecommons.org/licenses/by-nc-nd/3.0/de  2014  ISSN: 2194-1629  IIIAbstractThe AUGERHIT Option of the Air Shower Simulation Program CORSIKAThis report describes the size reduction of the particle data output file(s) forAuger simulations. This reduction is achieved by a (random) selection of theshower core position relative to the triangular grid of detectors, as for all showerparticles in the observation plane it is checked whether they arrive in the neigh-bourhood of a corresponding detector position. Only hitting particles are kept forthe output. All other particles falling onto the Argentinian pampa far from anydetector are skipped.ZusammenfassungDie AUGERHIT-Option des Luftschauer-SimulationsprogrammsCORSIKADieser Bericht beschreibt die Reduzierung der Größe der Teilchenausgabe-datei(en) bei Auger-Simulationen. Diese Reduzierung wird durch eine (zufällige)Wahl der Lage des Schauerzentrums relativ zu dem Dreieck-Gitter der Detektorenerreicht, weil für alle Schauerteilchen in der Beobachtungsebene geprüft wird,ob sie in der Nähe einer passenden Detektorposition niedergehen. Nur solcheTeilchen werden in die Ausgabedatei geschrieben. Alle anderen Teilchen, die indie argentinische Pampa weitab von einem Detektor fallen, werden weggelassen.IVVContents1 Introduction 12 Core Selection 13 Hitting Particles 34 Shower Core 35 File Size Reduction 56 Example 6References 8VI11 IntroductionRecently the CORSIKA Extensive Air Shower simulation code [1] has been ex-tended for parallel processing [2, 3] on multi-node machines. This developmentenables the full simulation (without thinning procedures) of even the highest en-ergies for the Pierre Auger Observatory (PAO) [4] in elapsed times of less than aday. At energies above 1019 eV the number of particles reaching the observationlevel exceeds 5 · 109 resulting in a particle data output file size above a TeraByte.This file size is too large for an easy handling, especially when the outputs ofthe different CPU-slaves of a parallelized run have to be merged into one particledata output file.With respect to a precalculated core position within the triangular grid struc-ture of the PAO all particles falling outside of detectors will be skipped and onlythe particles hitting detectors will be written to the particle data output file. Bythese means a significant reduction of the particle data output file size to about0.1% can be achieved.2 Core SelectionBefore starting the simulation the shower core position relative to the triangulargrid of the PAO-detectors has to be defined. To reduce the overall computing timeup to 20 core locations can be chosen for each single shower event with a quasi-random distribution using a SOBOL random generator [5]. Correspondingly thearray of PAO-detectors is placed up to 20 times in the observation plane relativeto the shower center and the coordinates of all particles hitting close to a detectorare stored. Instead of selecting the core positions at random, alternatively theycan be selected in the steering input using the additional keyword AUGHIT (see[6], parameters xshcore, yshcore in meters). Up to 20 shower core positions may beselected by separate input lines in arbitrary sequence. For the random selectionthe first parameter MAUGPOS of the keyword AUGSCT (see [6], default value20) defines how often each shower is used. The x- and y-coordinates of all corelocations are stored within the event header of the particle data output file becausethey must be available in the analysis of the simulated shower.2 2 CORE SELECTION-3000-2000-10000100020003000-3000 -2000 -1000 0 1000 2000 3000x (m)y (m)dradius = 35 mFigure 1: Traces of hits on the three stripes parallel to the detector rows. Thewidth of the stripes is 2 dradius = 70 m, the distance between the detectors (at thecrossing point of the traces) amounts to 1500 m.33 Hitting ParticlesThe decision whether a particle may hit a detector of the PAO uses a simple andfast procedure to keep the simulation time as low as possible. Without controllingthe directional details of each particle it is sufficient to require that it falls onto acircular area with a radius of dradius = 35 m (default value of the second parameterof the keyword AUGSCT) around the detector center. With the dimensions of theactive volume of the PAO-detector tanks with 1.2 m height and 3.54 m diameterthis area is touched by particles with a zenith angle up to ≈ 88◦ for skimming thetank volume at its upper circular edge.With the triangular structure of the detector array it may be favourable to lookfor each particle to fall onto a stripe of width 2 dradius which connects the de-tectors on the x-axis (West-East) of the coordinate system. Equivalently it mayhit onto a stripe parallel to this axis in the distance rowdist between the detectorrows. See the black traces in Fig. 1. With the distance between the detectorsr = 1500 m this row distance calculates torowdist = r ·√3/2 ≈ 1299 m .In a second step it is checked whether the particles fall on one of the parallelstripes which are rotated by 60◦ counter-clockwise relative to the x-coordinate.These hits are marked in red in Fig. 1. The third parallel stripe pattern (in greenin Fig. 1) is rotated by 60◦ clockwise. If the particles simultaneously hit all threestripe patterns the area of hits results in a hexagon around a detector. This isdrawn in Fig. 2. By this method it is guaranteed that all particles landing withina maximum distance of dradius to a detector are kept for the particle data outputfile, while the bulk of particles falling outside are discarded from writing.4 Shower CoreParticles close to the shower core at distances less than 200 m (default of the thirdparameter CUTRAD of the keyword AUGSCT, see [6] for details) are discarded,as at such small distances the detectors become overloaded and therefore cannotregister any hitting particle. A similar suppression of particles too close to theshower core is already available in CORSIKA in the thinning option [6].4 4 SHOWER CORE-50-40-30-20-1001020304050-50 -40 -30 -20 -10 0 10 20 30 40 50x (m)y (m)dradius = 35 mFigure 2: Traces of hits on the hexagonal area around a detector. The detectordiameter (drawn in pink) amounts to 3.54 m. The diameter of the black circleinscribing the hexagon amounts to 2 dradius = 70 m. The width of the stripesis indicated by the limiting dotted lines in black (West-East), red (60◦ rotatedcounter-clockwise), and green (60◦ rotated clockwise).55 File Size ReductionFor particles with uniform distribution on the surface detector array the size reduc-tion of the particle data output file may be calculated from the ratio of the activehexagon area F (see the area filled with blue dots in Fig. 2) to the total area be-tween the detectors. It is sufficient to use only the sixth part of the active hexagonand to consider the area A of one triangle spanned by three detector stations at itscorners (see Fig. 1):A = 0.5 · r · rowdist = 0.5 · r · r ·√3/2 = 0.25 · r2 ·√3 ,with r the triangles side length and rowdist the triangles height. Within eachcorner of such a triangle we have 1/6 portion of an active hexagon area, withinwhich a circle of radius dradius may be inscribed (see black circle in Fig. 2)F/6 = d2radius/√3 .As we have to consider 3 such portions (one in each corner of the triangle withdetectors at the corners) the reduction ratio ratio results inratio =A3 · F/6=0.25 · r2 ·√33 · d2radius/√3which simplifies toratio = 0.25 · r2/d2radius .With the distance between the detectors of r = 1500 m and the default size ofthe active hexagon (dradius = 35 m of inscribed circle) a reduction ratio of ≈ 460is attained for uniformly distributed particles.Moreover, as in the direct neighbourhood of the shower core up to a distance(radius) of 200 m (default value) all particles are rejected from output (becauseof overload of the detectors) in practical cases the reduction ratio will even bemarkedly higher. But this reduction ratio has to be divided by the number of theselected core positions, which is restricted to 20. Adopting the default valuesof the detector geometry and the sensitive area and using each shower with 20different core positions relative to the triangular PAO-detector grid structure theparticle data output file size will be reduced at minimum by a factor of 23.6 6 EXAMPLE6 ExampleAs example we used a shower with the specifications listed in Table 1 employingthe PARALLEL option of CORSIKA without thinning. Each shower is used 20times with the shower core locations distributed at random. The scatter of the 20shower core locations is shown in Fig. 3. By the usage of the SOBOL pseudo-random generator [5] events with overlapping detector areas are prohibited.Table 1: Parameters of simulated example.parameter valueprimary particle protonprimary energy 1018.5 eVzenith angle 18◦azimuth angle -63.4◦observation level 1452 menergy cuts hadrons 100 MeVmuons 50 MeVelectrons 250 keVgamma 250 keVmagnetic field horizontal 19.5 µTvertical -14.17 µTinteraction models high energy QGSJET-II-4low energy GHEISHAAUGSCT parameters number of scatters 20 (randomly selected)stripes half 55 mwidth dradiuscore cut radius 200 mFor all other parameters default values have been usedThe results of the simulations without/with the AUGERHIT option are sum-marized in Table 2. With identical random seeds the two runs produce the sameparticles arriving at ground. The markedly different accumulated processing timeshave to be attributed to the different number of WRITE commands to be executedin the two cases. Most stringent is the reduction of the summed particle data utputfile size shrinking from 392 GB without the AUGERHIT option to only 6.9 GBwith the AUGERHIT option. Even for the larger radius of dradius = 55 m theattained reduction factor of ≈ 57 reaches more than the double of the prognosiscalculated in Sect. 5.7Table 2: Properties of example simulated with a multi-core processor system.without withAUGERHIT optionused processors 128 128accumulated processing time 40.5 d 22.7 dsummed particle data output file size 392.1 GB 6.9 GBreduction factor 56.8-1500-1000-500050010001500-1500 -1000 -500 0 500 1000 1500x (m)y (m)dradius = 55 mFigure 3: Scatter positions (red crosses) of the shower center relative to the hexag-onal grid of detectors (black circles with 2 dradius = 110 m diameter).8 REFERENCESReferences[1] D. Heck, J. Knapp, J.N. Capdevielle, G. Schatz, and T. Thouw,CORSIKA: A Monte Carlo Code to Simulate Extensive Air Show-ers, Report FZKA 6019, Forschungszentrum Karlsruhe (1998),available from: https://web.ikp.kit.edu/corsika/physics description/corsika phys.html[2] D. Heck, R. Engel, T. Pierog, G. Thiara, S. Karla, H. Singla, G. Poghosyan,D. Seldner, and F. Schmitz, Challenges of simulating air showers atultra-high energy, Proc. of Workshop Computational Methods in Scienceand Engineering (SimLabs@KIT 2010), Karlsruhe (Germany), (2010)87; http://digbib.ubka.uni-karlsruhe.de/volltexte/documents/1794913[3] S. Sharma, G. Poghosyan, T. Pierog, D. Heck, J. Oehlschläger, and R. En-gel, MPI-Runner for CORSIKA Simulations (Algorithms), available withthe CORSIKA files in subdirectory doc/MPI-Runner PHYSICS.pdf;S. Sharma and G. Poghosyan, User Guide of MPI-Runner for par-allel CORSIKA simulations on computing systems supporting MessagePassing Interface, available with the CORSIKA files in subdirectorydoc/MPI-Runner GUIDE.pdf[4] J. Abraham et al. (Auger Coll.), Properties and performance of the proto-type instrument for the Pierre Auger Observatory, Nucl. Instr. Meth. A 523(2004) 50; Trigger and aperture of the surface detector array of the PierreAuger Observatory, Nucl. Instr. Meth. A 613 (2010) 29[5] W.H. Press, S.A. Teukolsky, W.T. Vetterling, and B.P. Flannery, NumericalRecipes in FORTRAN 77: The Art of Scientific Computing, 2nd ed., Cam-bridge University Press, Cambridge (U.K.), (1992)[6] D. Heck and T. Pierog, Extensive Air Shower Simulations with COR-SIKA: A User’s Guide, available from: https://web.ikp.kit.edu/corsika/usersguide/corsika tech.html KIT Scientific Working Papers ISSN 2194-1629www.kit.eduKIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association

The AUGERHIT Option of the Air Shower Simulation Program CORSIKA

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The AUGERHIT Option of the Air Shower Simulation Program CORSIKA

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