The Kascade-Grande Experiment

Home , KASCADE

THE KASCADE-GRANDE EXPERIMENT

¡ ¢ ¡ ¢

M. Brüggemann , M. Stümpert , J. van Buren , T. Antoni , W.D. Apel ,

¢ £¤ ¢ ¥ ¢ £ ¡ ¢

F. Badea , K. Bekk , A. Bercuci , M. Bertaina , H. Blümer , H. Bozdog ,

¥ ¡ ¡

I.M. Brancus , P. Buchholz , C. Büttner , A. Chiavassa , K. Daumiller ,

¢ ¢ ¢ ¢ ¢ §

F. di Pierro , P. Doll , R. Engel , J. Engler , F. Fe ler , P.L. Ghia ¨ , H.J. Gils ,

¢ ¢ ¡ ©

R. Glasstetter © , A. Haungs , D. Heck , J.R. Hörandel , K.-H. Kampert ,

¢ ¢ ¢ ¢

H.O. Klages , Y. Kolotaev , G. Maier , H.J. Mathes , H.J. Mayer ,

¢ ¥ ¢ ¢

J. Milke , B. Mitrica , C. Morello ¨ , M. Müller , G. Navarra , R. Obenland ,

¢ ¢ £ ¡ ¥ ¢

J. Oehlschläger , S. Ostapchenko , S. Over , M. Petcu , S. Plewnia ,

¢ ¡ ¢ ¢ ¢

H. Rebel , A. Risse , M. Roth , H. Schieler , J. Scholz , T. Thouw ,

¥ ¢

G. Toma , G.C. Trinchero ¨ , H. Ulrich , S. Valchierotti , W. Walkowiak ,

¢ ¢ ¢

A. Weindl , J. Wochele , J. Zabierowski , S. Zagromski , D. Zimmermann ¡

Institut für Experimentelle Kernphysik, Universität Karlsruhe, 76021 Karlsruhe, Germany ¢

Institut für Kernphysik, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany ¥

National Institute of Physics and Nuclear Engineering, 7690 Bucharest, Romania ¦

Dipartimento di Fisica Generale dell’Università, 10125 Torino, Italy

Fachbereich Physik, Universität Siegen, 57072 Siegen, Germany

¨ Istituto di Fisica dello Spazio Interplanetario, CNR, 10133 Torino, Italy

Soltan Institute for Nuclear Studies, 90950 Lodz, Poland ¤

on leave of absence from Nat. Inst. of Phys. and Nucl. Engineering, Bucharest, Romania ¡ on leave of absence from Moscow State University, 119899 Moscow, Russia

Abstract The KASCADE-Grande experiment measures extensive air showers induced by

primary cosmic rays in the energy range . The major motiva- tion for KASCADE-Grande is the investigation of the so called "knee" in the energy spectrum of cosmic rays and its presumed rigidity dependence. A short overview of the experimental setup with focus on the Grande array and its new data acquisition system is given. As an example of analysis the reconstruction of the total muon number is presented.

Keywords: KASCADE-Grande, EAS, air showers, cosmic rays 2 1. Introduction The major goal of the KASCADE-Grande experiment [Haungs et al. 2003] is to study the knee in the primary cosmic ray energy spectrum [Hörandel J. 2004] and the composition around the knee. Therefore KASCADE-Grande measures air showers caused by primary cosmic ray particles hitting the earth’s atmosphere. Results so far by the smaller area KASCADE experiment indicate

a rigidity dependence of the individual components. Thus one could expect a

¡ ¢

£ ¤ knee corresponding to iron at © . KASCADE-Grande uses a multi- detector layout (Fig. 1) to measure as many air shower observables as possible, to achieve a high-quality reconstruction of extensive air showers. A brief description of the experiment, focusing on the new Grande array is given in section 2. In section 3 we describe an extension to the already existing data acquisition system. It will allow time dependent measurements of the

arriving particles in the shower disk, enabling an estimator for the electron to

¡ ¢ © muon ratio for high energies above £ ¤ . In section 4, the reconstruction of the total muon number is described, necessary to infer the mass of the primary cosmic ray particle with unfolding techniques using the electron and muon size spectra.

2. The KASCADE-Grande experiment The KASCADE-Grande experiment is located at the Forschungszentrum Karlsruhe, Germany, at 110m above sea level, corresponding to an average ] 5 4 3 KASCADE m 100 [ 2 1 11 Grande-stations 0 10 9 8 7 6

-100 14 13 16 15 12 y-coordinate -200 Piccolo-stations 21 22 20 19 18 17 -300 DAQ

26 25 24 23 27 -400

33 30 29 28 -500 32 31 Cluster 16 37 -600 36 35 34 -700 -600 -500 -400 -300 -200 -100 0 100 x-coordinate [m]

Figure 1. The arrangement of the KASCADE-Grande detectors

The KASCADE-Grande experiment 3

¡ ¢ £ vertical atmospheric depth of 1022 . For studies of the hadronic core of extensive air showers KASCADE-Grande uses a central detector containing a large hadron sampling calorimeter. Further components of the central detector measuring the muonic part of the core of EAS are also available. A muon tracking detector north of the central detector building measures muon tracks and densities outside the core. The original KASCADE array of 252 detector stations located around the central detector measures densities and arrival times of electrons and muons. See table 1 and Ref. [Antoni et al. 2003] for further details.

Table 1. The detectors of the KASCADE-Grande experiment with the detected particle types and their sensitive area.

Detector Particles Sensitive area ( ¤ ¥ )

§ ¨

Grande array e/ ¦

Piccolo e/ ¦

KASCADE array

Liquid scintillators e

§ Plastic scintillators ¦ ,

Central detector

Trigger plane ¦ ,

MWPCs/LSTs ¦ ,

§ Calorimeter Hadrons,

With its extension the KASCADE-Grande experiment is able to measure

¡ ¢ £ ¤ primary particles up to . This is achieved with 37 detector stations from

the former EAS-Top experiment forming the Grande array. These stations are

¢ ¡ ¢

arranged in a ¢ hexagonal grid with an average distance of .

Each station houses 16 scintillation detectors arranged in a grid. These

¢ ¢

¡ ¢ detectors consist of plastic scintillators ( ) read out by photomul-

tiplier tubes. The signals of the 16 PMTs are summed up, ampliﬁed (high gain

¡ " # $ % & # ¢ channel, ! ) and shaped before they are sent to the central data

acquisition. The four central scintillators are equipped with additional PMTs

¢ ' # $ % & # ¢

with a 20 times lowered gain (low gain channel, ! ). Therefore

¢ ¢ ( ¢ ¢ ¢ & # % ¢ the Grande array reaches a large dynamic range of ¢ . In the central data acquisition the 37 stations are connected to 18 trigger hexagons. Programmable trigger conditions are used to start TDC-measurements which are stopped by the individual stations. The energy deposit is determined by digitizing the signals of the stations using peak sensing ADCs. The obtained arrival times and particle densities are used to reconstruct the shower core, the total number of charged particles, the arrival direction and the shape of the shower front. 4 3. The KASCADE-Grande FADC-DAQ-System Apart from the data acquisition (DAQ) system taking data since Novem- ber 2003 the collaboration decided to build a Flash-ADC (FADC) based DAQ system for the Grande array. This system will sample the full pulse shape cre- ated by the photomultiplier tubes. Having the complete pulse shape recorded a correction for noise in order to improve the data quality is possible and new shower observables to be used in the analysis can be derived. In particular an intrinsic electron to muon separation at individual detector stations will be possible. Since the data will be transmitted optically, it will be resistant against pickup noise. The FADC system is a modular system of custom made electronics. The main parts of the system are described in the following paragraphs.

Digitizer board: One digitizer board will be installed in each station. It digitizes continuously two analog photomultiplier signals by two chan- nels with 4 FADCs each. The FADCs work with 12 bit resolution and an effective sampling frequency of 250 MHz. A comparator compares each signal sample with a programmable threshold. If the current sample

exceeds the threshold, a 1 s long digitization period is triggered. If necessary this period is extended to prevent dead-time. The signals arriving at the FADCs are delayed compared to the ones seen by the comparator.

This allows to record 112 ns before the signal. The data of 1 s sampling cycle together with the timestamp of the KASCADE-Grande experiment forms one data package. This data package is transmitted over an optical ﬁbre to the central DAQ station, where it is received by the receiver board. A scheme of the concept is depicted in Fig. 2. Receiver board: The counterpart of the digitizer board is a receiver board located in the DAQ station receiving data packages from up to 8 detector stations. Five receiver boards will be installed in the DAQ station. The task of the board is to translate the incoming optical signals back into electronic signals and to forward them to the PCI-interface which forms the connection of the FADC system to the computers. PCI-Interface: The PCI-Interface writes the data via direct memory access (DMA) into the PC-memory. The data transfer rate achieved is 85 MB/s which has to be compared with an expected data rate of 20 MB/s. Event building: In addition to the PCs buffering the digitized detector signals, a master PC will be used to scan the data packages for coincident timestamps and request all data within a programmable time window around the coincidence. With this procedure the data rate is reduced The KASCADE-Grande experiment 5

Detector HutDAQ Station

KASCADE Grande Timestamp PC

RING BUFFER COMPARATOR depth

comparator threshold

Photomultiplier Signal DELAY START READOUT OPTICAL FLASH ADC LINK

data taking 1µs +1µs EXTEND DATA TAKING signal over threshold? self triggering!

Figure 2. Schematic overview of the FADC concept [Over 2004]

from initial 37 2.5 MB/s to ﬁnal 100 KB/s. In this estimation 2.5 MB/s correspond to the data rate of one detector station with an average event rate of 2.5 kHz and a FADC single event size of 1kB.

4. Reconstruction of Total Muon Number The new Grande array measures the charged component, enabling to reconstruct the energy of air showers in the range 30 PeV to 1 EeV. To deduce the mass composition of cosmic rays, one is interested in the muon component of

extensive air showers measured by 192 shielded scintillation detectors in the

' ¢ ¢ ' ¢ ¢ ¢ sized KASCADE array. Together with the shower core and arrival direction provided by the Grande array, a lateral distribution function is ﬁtted to the measured muon densities to obtain the total muon number of the

extensive air shower. To reduce the effect of misreconstructed cores, a ﬁducial

" ¢ ¢ " ¢ ¢ ¢

area of is deﬁned, which translates in a measurement of the

' ( " ' muon density in a radial distance of ¢ to the shower core for 68%

of the showers.

¡ ¢

¨ In the energy range E eV where Grande has 100% trigger efﬁ- ciency, the systematic error of the reconstructed total muon number is constant at around 20% (see Fig. 3). Though it depends, like the muon number itself, on the primary particle. The statistical error decreases as expected with increasing primary energy. Furthermore the systematic error shows a dependency on the core distance to the KASCADE array, ranging from 30% for showers close to the array to 10% at larger radii. 6 µ MC -1 103

N Nµ-Nµ ∆ sr trigger threshold

∆ N = µ MC proton -1 0.6 Nµ s p stat. error -2 Fe iron m

3 µ N

0.4 ⋅

µ dj dN

0.2

KASCADE-Grande 0°-18°

0 KASCADE 0°-18° ° ° KASCADE-Grande 18 -25 preliminary syst. error -0.2 KASCADE 18°-25° 102 16 16.5 17 17.5 18 4 4.5 5 5.5 6 6.5 7 log10(E0/eV) muon number log10(Nµ)

Figure 3. Uncertainties in reconstruction Figure 4. Reconstructed muon size spectrum of total muon number

The shown differential muon size spectrum in Fig. 4 is based on a data set of 5.4 10 ¨ events, taken from December 2003 to April 2004. The effective time of combined data taking of the Grande array and the KASCADE array was approximately 117 days. As one can see there is a good agreement between the two measured ﬂuxes in the overlap area in both shown zenith angle

ranges. Furthermore also the spectral structure shows reasonable continuation.

Around a total muon number of log N 5 one sees a decrease and then a re-increase of the index of the spectrum, corresponding to the knee in the light component of the energy spectrum and the relative increase of the heavy component. Further investigation of reconstruction systematics is necessary for both the reconstruction of high energetic showers with the KASCADE array and for showers with a reconstruction combining the information of both arrays.

5. Summary The Grande array as an extension of the KASCADE-Grande experiment is taking data for nearly one year now. A new data acquisition system will give further improvements on the reconstruction of air shower observables. First analysis show a good agreement between data from the KASCADE and the Grande array and provide enhanced capabilities of the Grande array.

References Antoni, T. et al. - KASCADE Coll., Nucl. Instr. and Meth. A513, 490-510, (2003) Haungs, A. et al. - KASCADE-Grande Coll., ICRC (Tsukuba) 2, 985, (2003) Hörandel J., 2004 Proc. 14th ISCRA, these proceedings S. Over - Development and comissioning of data acquisition systems for the KASCADE-Grande experiment, diploma thesis, Siegen University (2004)