Electron Shower Size Spectra Reconstructed with KASCADE-Grande Data

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Proceedings of the 30th International Cosmic Ray Conference ID 601 Rogelio Caballero, Juan Carlos D’Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.) Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008 Vol. 4 (HE part 1), pages 211–214

30TH INTERNATIONAL COSMIC RAY CONFERENCE

Electron shower size spectra reconstructed with KASCADE-Grande data

F. COSSAVELLAc, W.D. APELa,J.C.ARTEAGAa, F. BADEAa,K.BEKKa,M.BERTAINAb, J.BLUMER¨ a,c,H.BOZDOGa,I.M.BRANCUSd,M.BRUGGEMANN¨ e, P. BUCHHOLZe,A.CHIAVASSAb , K.DAUMILLERa, V. DE SOUZAc, F. DI PIERROb , P. DOLLa,R.ENGELa,J.ENGLERa,M.FINGERc, D.FUHRMANNf , P.L. GHIAg ,H.J.GILSa,R.GLASSTETTERf ,C.GRUPENe,A.HAUNGSa,D.HECKa, J.R.HORANDEL¨ c, T. HUEGEa, P.G. ISARa,K.-H.KAMPERTf ,D.KICKELBICKe,H.O.KLAGESa, Y. KOLOTAEVe, P. LUCZAKh,H.J.MATHESa,H.J.MAYERa,C.MEURERa,J.MILKEa,B.MITRICAd, A.MORALESa,C.MORELLOg ,G.NAVARRAb,S.NEHLSa,J.OEHLSCHLAGER¨ a,S.OSTAPCHENKOa, S.OVERe,M.PETCUd, T. PIEROGa,S.PLEWNIAa,H.REBELa,M.ROTHa,H.SCHIELERa,O.SIMAi, M.STUMPERT¨ c,G.TOMAd,G.C.TRINCHEROg ,H.ULRICHa,J. VAN BURENa , W. WALKOWIAKe, A.WEINDLa,J.WOCHELEa,J.ZABIEROWSKIh. a Institut fur¨ Kernphysik, Forschungszentrum Karlsruhe, Germany b Dipartimento di Fisica Generale dell’Universita` Torino, Italy c Institut fur¨ Experimentelle Kernphysik, Universitat¨ Karlsruhe, Germany d National Institute of Physics and Nuclear Engineering, Bucharest, Romania e Fachbereich Physik, Universitat¨ Siegen, Germany f Fachbereich Physik, Universitat¨ Wuppertal, Germany g Istituto di Fisica dello Spazio Interplanetario, INAF Torino, Italy h Soltan Institute for Nuclear Studies, Lodz, Poland i Department of Physics, University of Bucharest, Romania [email protected]

Abstract: KASCADE-Grande, located at Forschungszentrum Karlsruhe, is a multi-detector experiment for the measurement of extensive air showers induced by primary cosmic rays in the energy range of 1014 1018 eV. With its 0.5 km2 large ﬁeld detector, in combination with the muon detectors of the KASCADE− array, it allows the reconstruction of both the total electron and muon numbers, which are important observables for estimating the mass and the energy of the primary particles. In this work we will present the status of the electron size spectrum as well as the 2-dimensional (Ne Nµ) shower size spectrum after 626 days of effective data taking. −

Introduction particles up to energies of 1018 eV. Each station consists of 16 scintillation detectors (80 80 × × The field array of the original KASCADE [1] ex- 4 cm3), arranged in a 4 4 grid, with a total sur- × periment consists of 252 detectors stations placed face of 10 m2 sensitive to the charged particles of on a grid of 200 200 m2. Due to the low flux the shower. With the present set-up Grande mea- × 10 2 1 1 2 of cosmic rays in the order of 10− m− s− sr− sures densities up to 800 charged particles/ m , for energies above 1017 eV, the collective area of while the muon component of the shower is es- KASCADE is not sufficient for investigations in timated from the 622 m2 muon detectors of the this energy range. Thus, the Grande array [2], with KASCADE array, with an energy threshold for its 37 detector stations organised in 18 hexago- muons of 230 MeV. Full efficiency for the coinci- nal trigger cells of 7 stations each, is the natural dent KASCADE-Grande array is reached with a 7 extension of KASCADE over an area of approxi- out of 7 stations coincidence (0.5 Hz) at log(Ne) ≈ mately 0.5 km2, suitable for detection of primary 6.3 (corresponding roughly to a primary energy of

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where the normalisation factor C(s) depends on the shower age s. From simulations, values of 1 α =1.5, β =3.6 and r0 = 40 m werefoundas op- timum for the radial distances relevant for Grande. 0.8 efficiency For the lateral distribution of muons, a modified 0.6 proton - 20 stat cut Lagutin function [6]: iron - 20 stat cut 7/7 trigger p1 p2 0.4 0.28 r r 4/7 trigger ρµ = Nµ r2 r 1+ r 0 0 · 0 · 2 p3 r# $ # $ 0.2 1+ 10 r · 0 % # $ & 0 4 4.5 5 5.5 6 6.5 7 7.5 is used, with r0 = 320 m and p1, p2, p3 respec- tively -0.69, -2.39 and -1, also found by simulation. Log(Ne) The analysis procedure develops in several steps. Figure 1: Reconstruction efficiency for showers First, the total muon number and total number of between 1014 and 1018 eV, with zenith angles charged particles are separately obtained fitting the respective lateral distributions. In a second step the smaller than 40◦. Requiring a 7/7 trigger at Grande with muon number successfully reconstructed by contribution of muons to the densities of charged particles measured by Grande is taken into ac- KASCADE, a full efficiency is reached at Ne = 2 106 . Applied data quality cuts require at least count: a likelihood fit compares for each detector 20× active Grande detector stations, for which case the measured number of particles with the expected the efficiency is plotted for proton and iron. number given by the sum of electrons and muons estimated from the corresponding lateral distribution functions. The combined fit of the muonic and electromagnetic components is delivering in the fi- 16 few times 10 eV) as shown in Fig. 1, where pri- nal step the shower size Ne, the age parameter s, mary iron reach for a bit smaller electron number the muon size Nµ, the position of the shower core full efficiency. This is due to the fact that we trigger and the arrival direction of the shower. To test the to charged particles, where also muons contribute, reconstruction procedure and estimate the uncer- in particular for small showers. tainty, showers generated by CORSIKA, with the KASCADE-Grande main goals are the investiga- QGSJetII interaction model, have been used as in- tion of the position of the expected iron knee and put for a detailed GEANT [7] simulation of the ap- the nature of the second knee. paratus. Approx. 260,000 proton and iron showers in the energy range of 1014 1018 eV, with − zenith angles between 0◦ and 40◦, have been anal- Shower reconstruction ysed with the same procedure used for real data. In order to reduce effects of misreconstructed shower Analysis of Grande array data provides informa- cores at the edges of the Grande array, a fiducial tion on core position, arrival direction and the total area of 190, 000 m2 centered in the middle of ≈ number of charged particles (Nch) in the shower Grande has been chosen. The results for spatial re- [3]; the information on muon densities comes in- solution are shown as a function of the shower size stead from the KASCADE array. in Fig. 2: above the threshold of 2 106 electrons × The lateral distribution of electrons has been stu- the core resolution is better than 12 m and shows died through detailed CORSIKA [4] simulations no significant dependence on the primary particle. and is described best in case of KASCADE- The points mark the mean deviation from the true Grande by a modified NKG-function [5]: value in percent, while the error bars describe the s α s β spread of the distribution. Fig. 2, left part, displays r − r − ρ = N C(s) 1+ the accuracy of the reconstructed electron num- e e · · r · r ! 0 " ! 0 " ber: the statistical uncertainty, expressed by the er-

212 30TH INTERNATIONAL COSMIC RAY CONFERENCE

Size reconstruction accuracy Core reconstruction accuracy 0.8 25

0.6 Ne/Ne Δ 20 0.4

0.2 15 core resolution [m] -0

10 -0.2

-0.4 5 -0.6

-0.8 0 6 6.5 7 7.5 8 6 6.5 7 7.5 8 Log(Ne) Log(Ne)

Figure 2: Left: reconstruction accuracy of the reconstructed electron number as function of the true electron number. The errors bars indicate the spread of the distribution (statistical error). Right: reconstruction 14 18 accuracy of the core position. Showers between 10 and 10 eV with zenith angles smaller than 40◦ have been considered, corresponding to proton (circles) or iron (square symbol) primaries.

ror bars, is around 25% at threshold and decreases tematic uncertainty yet, and no correction for the slightly with increasing shower size as expected, biases introduced by the reconstruction procedure while the bias decreases from 0 to -15%. For de- is applied. Clearly, we are still missing statistics tails about the muon reconstruction see [8]. at the highest energies, i.e. at N > 3 107, espe- e · Comparison of measured events reconstructed in- cially for inclined events, but the capability of the dependently by both Grande and KASCADE con- experiment can be determined. ﬁrms the values we obtained [3]. The features appearing in the spectra at log(Ne) 7.3 are currently under investigation, in order≥ to exclude possible effects of misreconstructed total Size spectra muon number on the estimation of the shower size. The spectra are based on a data set of 1.9 106 We present in this work a preliminary ver- well reconstructed events inside the ﬁducial× area. sion of the shower size spectrum measured by The effective time of combined data taking with KASCADE-Grande. Fig. 3 shows the spectra both KASCADE array and Grande is equivalent for six different zenith angular ranges, each cor- to 626 days. With the capability of reconstruct- responding to a change of the slant depth of ing both, muon and electron numbers, it is possible 2 3 50 g cm− , multiplied by Ne in order to better to investigate the two-dimensional size spectrum appreciate possible features. The errors represent like in KASCADE. In Fig. 4 the two-dimensional pure statistical uncertainty due to the number of spectrum for zenith angles between 18◦ and 25◦ events in each bin, there is no estimation of a sys- is shown. The dashed lines show an estimation of

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Preliminary Preliminary ] )]

-1 9 e 1018 eV sr

-1 5 8.5 3 s 10 1017 eV 10 -2 8 [m 3 e 1016 eV

N 7.5 ×

e 4 10 7 102 1015 eV dI/dN 6.5 18 ° electron number [Log(N 6 25 ° 103 0-18 ° 18-25 ° 5.5 10 25-30 ° 30-34 ° 5 34-37 ° 2 4.5 10 37-40 ° 4 1 6 6.5 7 7.5 8 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 electron number [Log(N )] muon number [Log(N )] e µ

Figure 3: Differential shower size spectra for ﬁve Figure 4: Reconstructed electron and muon different zenith angle ranges. number distribution of air showers measured by KASCADE-Grande in the zenith range 18◦ 25◦. The dashed lines indicate average lines of constant− energy derived from CORSIKA simulations the primary energy based on simulations with the interaction model QGSjet01 [5].

[2] A. Haungs et al. KASCADE-Grande Col- Conclusions lab., Proc of 28th ICRC, Tsukuba (2003) 2, 985. In this paper, it has been shown that it is pos- [3] F.Di Pierro et al. KASCADE-Grande Col- sible with the current setup of the KASCADE- lab., Proc. of 30th ICRC, Merida (2007). Grande experiment to measure cosmic ray showers [4] D.Heck et al., Report FZKA 6019, 18 up to 10 eV, although up to now only few events Forschungszentrum Karlsruhe (1998). have been detected at these energies. Size spectra [5] R.Glasstetter et al. KASCADE-Grande for different zenith angular ranges have been pre- Coll., Proc. of the 29th ICRC 6 (2005), sented as well as an example of electron vs muon p. 293-296. numbers distribution. At the moment the statistics [6] J.van Buren et al. KASCADE-Grande Coll., are too small to make further concise statement of Proc. of the 29th ICRC 6 (2005), p. 301- spectrum and mass composition for energies above 304. 17 10 eV, moreover the reconstruction procedure [7] GEANT - Detector Desc. and Sim. Tool, needs still some minimal reﬁnements. In future CERN Program Library Long Writeup, the two-dimensional spectrum will be the starting W5013, CERN (1993). point for the application of an unfolding analy- [8] J.C. Arteaga et al. KASCADE-Grande Col- sis that will lead to the determination of spectra lab., Proc. of 30th ICRC, Merida (2007). for different mass groups (as done for KASCADE [9] T.Antoni et al. KASCADE Coll., As- [9]). trop. Phys. 24 (2005), p. 1-25.

References

[1] T.Antoni et al. KASCADE Coll., Nucl. In- str. Meth., A 513, 490 (2003)

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