Hovsepyan, G

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29th International Cosmic Ray Conference Pune (2005)  6, 93-96  The Size Spectra of Extensive Air Showers in the “Knee” region  Measured by Maket-ANI detector  G. Hovsepyana, A. Chilingariana, G. Gharagyozyana, S. Ghazaryana, E. Mamijanyana,b,  L. Melkumyana and A. Piloyanc (a)  Cosmic Ray Division, Yerevan Physics Institute, Alikhanyan Brothers 2, Yerevan 36, Armenia (b) Moscow Lebedev Institute, Leninsky pr.56, Moscow 117924, Russia (c) Yerevan State University, A.Manukyan st.2, Yerevan 5, Armenia Presenter: G.Hovsepyan (hgg@crdlx5.yerphi.am), arm-hovsepyan-G-abs1-he12-poster  The MAKET-ANI detector is operating at altitude 3200 m. at slope of mt. Aragats in Armenia. More than million showers with size greater than 105 were registered by the MAKET-ANI detector in 1999-2004. Detector has effectively collected the cores of EAS, initiated by primaries with energies of 5·1014-3·1017 eV. After calculating the detector response function and accounting on the registration efficiency we present the EAS size spectra in 5 azimuth angle intervals. Taking into account reach statistics and high quality of data, it can serve for the estimation of the attenuation lengths and phenomenological characteristics of the strong interaction of primary cosmic rays with atmosphere.      1. Calculation of the detector response function  The description of physical results from MAKET-ANI detector is given in [1-5]. In present report we consider methodological biases influence the accuracy of size spectra – the most important outcome of Extensive Air Shower (EAS) experiments and basis of physical inference on energy spectra and theories of Cosmic Ray (CR) origin and acceleration:   Ω⋅⋅⋅= dSTdNndNNdJeiee ),( θ                                                          (1) where ni – is the number of shower detected within T time-span in the ith size interval , in the solid angle of dΩ = Sin(θ) d θ dφ,  on surface of  S=Seff Cos(θ).  Sources of biases in intensity estimation are the arbitrary binning, according to shower size, age and angle of incidence.  The inter-bin migration of observed events was estimated using simple event-generator. We simulate size spectra with constant power index γ = -2.5 in energy range from Nethr  ≥  3.8·104.  The age distribution was taken alike measured one and axes were randomly choused in rectangular area of   Smax = 40x88 m2, see Figure 1. The angular distribution  follows Cosρ (θ),  where  ρ=(X0/Λ),  X0 =700 g/cm2,   and Λ =140 g/cm2. 108 events were generated. For each shower with fixed size, age and angles of incidence (input parameters of simulation), the number of shower particles at detector location were determined using Nishimura-Kamata-Greizen (NKG) function (vector ki 0, i=1, 92). Then the obtained ki 0 values were distorted according to experimental accuracies and experimental data handling procedures to determine the “experimental” EAS parameters – shower size, age, core position and angle of incidence. Sure the reconstructed parameters did not coincide with input ones.  The inter-bin migration of showers was enumerated by the “migration” function ξ(Ne,θ,)= ni/ ni 0 ,  where ni is a number of showers  in particular bin, and ni 0  - number of showers simulated with input parameters fallen in this bin. To keep the efficiency of registration (ni/ ni 0 ratio) higher than 0.95 (see Figure 1), we select appropriate areas of shower collections, so called “belts”.In Figure 1 these   areas are shown as belt1, belt2, etc, corresponding efficiencies are shown in Figure 2.   94       G.Hovsepyan et.al  We collect showers from the maximal area Seff, providing chosen level of the efficiency (>95%), also we keep condition of maximal allowable distortion of age parameter (<0.02). To check detector response function obtained with simple model, we used the CORSIKA code [6,7] to simulated events for different nuclei, slope of energy spectra, knee position. Obtained results pointed on model-independence of used detector response function and correct account of experimental distortions – the accuracy of reconstructed spectral index was not worse than 0.01-0.015.   .  Figure 1.. The MAKET-ANI  detector. The nested rectangular surfaces represent shower selection areas      Figure 2 .  The efficiency of shower registration, dependent on shower size and collection area                                                                                        The Size Spectra…                                                                        95  2. The size Spectra  The  size spectra, corrected on response function, were approximated by   [8]                                  δγδγθθ /))(1()(),( ∆− +⋅= kneeeeeeeNNNAdNNdJ                                    (2) Here A(θ)  - shows angular dependence of spectra  , ∆γ  change of power index  γ1-γ,   where γ and γ1 – spectral indexes before and after the knee, Neknee - knee position, and δ – the sharpness of the knee.   In   the Table 1 are depicted   parameters of approximation (2) of the size spectra, measured by MAKET-ANI detector for 5 uniform by Sec(θ) intervals. In Figure 3 the size spectra are presented in the graphic form along with size spectra measured by KASCADE experiment   [9].  Table 1.  The size spectra measured  by  Maket-ANI detector.                                                            With   response      ∆θo      γ       ∆γ    Neknee       A       δ   χ 2/ndf 0  - 23.5     2.53±0.002 0.45±0.02 1.58·106±8·104 641.9±11   7.1±1.7 1.1/19 23.8-32.4    2.52±0.002 0.43±0.02 1.33·106±6·104 333.3±8.5 11.6±3.0 1.9/17 32.4-38.5    2.47±0.003 0.47±0.03 1.08·106±8·104 114.4±3.8   3.9±0.8 1.2/19 38.5 - 43   2.45±0.003 0.45±0.03 0.86·106±6·104  53.6±2.6   4.4±1.6 0.8/17 43 - 46.8    2.44±0.006 0.48±0.04 0.70·106±6·104  29.2±2.2   4.7±1.4 0.9/16  The numbers indicate the effective atmosphere depth, corresponding to different zenith angles of incidence. Knee positions for both Maket-ANI and KASCADE data were calculated by formula (2).  Figure 3. The size spectra of MAKET-ANI and KASCADE  [9] experiments   96       G.Hovsepyan et.al  3. Discussion  EAS size spectra at  the  atmosphere depth of  700 g/cm2  are presented with great statistics  (more than 1.2 ·106 events). Remarkable coincidence of spectra measured by MAKET and KASCADE detectors and large slant-depth available from joint data give well establishes ground for estimation of attenuation length. Taking into account MAKET results in selection of light and heavy primaries [5] we can pose the problem of estimation of phenomenological parameters of strong interaction of primary nuclei with atmosphere for energies till 1016 eV.   4. Acknowledgements  We thank the staff of Aragats mountain Cosmic Ray Observatory  for help in operation of Maket-ANI experiment. We thank also   ANI collaboration members for their fruitful cooperation over many years. This work was supported by Armenian Government grant , ISTC grant A – 1058.  Reference  [1] E. Bazarov .et al. Voprosy Atomnoi Nauki i Tekhniki.(VANiT) ser. Nucl.Phis.Reser. , v.5(31), p.3-16 (in Russian)  (1986) [2] G. Gharagyozyan  for the ANI collab.,  Proc. of the Workshop ANI98, FZKA 6215, p.51,  Forschungszentrum  Karlsruhe,   (1998)        [3] A.Chilingaryan  et al.,26-th ICRC, Salt-Lake City, v.1 , 240 (1999) [4] A.Chilingarian  et al.  Proc. 27-th ICRC, Hamburg,  v. 2,  p. 590  (2001) [5] A.Chilingarian, et al., ApJ, 603:L29-L32  (2004 ) [6] D.Heck  et al. FZKA report 6019, Forschungzentrum, Karlsruhe, 1998 [7] N.Kalmikov , S. Ostapchenko, A.Pavlov, Nucl.Phis.B.(Proc.Suppl.), 52B, 17  (1997) [8] L.Haroyan , S. Ter-Antonyan, hex-ep/0003006  [9] R.Glasstetter  for the KASCADE collaboration,  Proc. 25-th ICRC,  Durban, vol. 2  (1997) 

The Size Spectra of Extensive Air Showers in the "Knee" region Measured by Maket- ANI detector

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