Cosmic rays rays at at PeV PeV energies energies with with Cosmic GAMMA Experiment Experiment GAMMA Anatoly Erlykin on behalf of the GAMMA collaboration Vulcano Workshop May 2010
ARAGATS scientific station (late autumn) Hill sides of the Mt. Aragats, Armenia, 65 km from Yerevan Elevation: 3200 m a.s.l. (700 g/cm 2 of atmospheric depth) Geographical coordinates: Latitude = 40.470 N, Longitude = 44.180 E
Creation and evaluation of the GAMMA Construction of the GAMMA was begun in the middle of 80th in the frame of joint project ANI of the Moscow Lebedev Institute and Yerevan Physics Institute. Ambitious project for studying CR at 0.1 – 1000 PeV including - Hadron calorimeter 1600 sq. m. – study of EAS hadron component (half-built) - Surface part of scintillation detectors – electromagnetic component - Underground part: muon scintillation detectors – muon component big electromagnet, weight 3000 ton (half-built) After the collapse of the Soviet Union in the beginning of 90 th construction was practically stopped for about 5 years. Nevertheless in the end of 90 th we succeed to create (in the framework of ANI project) the GAMMA installation with Surface part of scintillation detectors Carpet of underground muon scintillation detectors Start for operation - in 1998
Investigation of Cosmic Rays and Gamma Rays at 10 14 -10 17 eV Main topics ( most of them in progress ) Study of EAS characteristics - Lateral distributions of EAS electrons and muons; - Dependence of age parameter S from shower size N ch ; - Dependence of number of muons N µ from shower size N ch ; - EAS size spectra
Investigation of Cosmic Rays and Gamma Rays at 10 14 -10 17 eV Main topics ( most of them in progress ) Study of EAS characteristics - Lateral distributions of EAS electrons and muons; - Dependence of age parameter S from shower size N ch ; - Dependence of number of muons N µ from shower size N ch ; - EAS size spectra Particle physics - Study of cascade processes in atmosphere - Investigation of multi-core showers
Investigation of Cosmic Rays and Gamma Rays at 10 14 -10 17 eV Main topics ( most of them in progress ) Study of EAS characteristics - Lateral distributions of EAS electrons and muons; - Dependence of age parameter S from shower size N ch ; - Dependence of number of muons N µ from shower size N ch ; - EAS size spectra Particle physics - Study of cascade processes in atmosphere - Investigation of multi-core showers Astrophysical problems, gamma-astronomy - Study of energy spectrum and mass composition of primary cosmic radiation at energies 0.1-100 PeV - Estimation of diffuse flux of primary gamma rays - Search for astrophysical sources
GAMMA at present (after several modifications) Surface part (electromagnetic component) • 33 stations on R = 0, 18, 28, 50, 70 and 100 meters with 3 plastic scintillation detectors (S=1m 2 ) in each station. Total number – 116 The area – ~ 30.000 m 2 • 33 fast-timing channels for estimation of the EAS angular characteristics Underground part (muon component) • Carpet of muon scintillation detectors with total number – 150 and energy threshold E µ > 5 GeV)
GAMMA facility 0.09m 2
Recent results (2007) Rigidity-dependent CR energy spectra in the knee region [ Astroparticle Physiscs, 28 (2007) 169 ] On the base of EAS data the energy spectra and elemental composition of the PCR are derived in the 1 – 100 PeV. The reconstruction of spectra carried out using an EAS inverse approach in the frameworks of the SIBYLL2.1 and QGSJET0.1 interaction models and the hypothesis of power-law primary energy spectra with rigidity-dependent knees.
The measured variable distributions in comparison with expected dependences from SIBYLL and QGSJET interaction models
R i 50 m < Detected and expected particle density spectra measured by surface and underground scintillators for different shower sizes Good agreement besides the muon density for shower size N ch > 10 7
EAS truncated muon size spectra EAS size spectra for three zenith for three zenith angle intervals angle intervals
EAS size spectra for different EAS truncated muon size spectra truncated muon size thresholds for different shower size thresholds
Dependence of the average EAS Average EAS truncated muon age parameter on EAS size size versus EAS size
Dependence of the average EAS Average EAS truncated muon age parameter on EAS size size versus EAS size
The reconstruction of the primary energy spectra is carried out using an inverse approach for simulated data base (SIBYLL2.1 and QGSJET01 interaction models and the hypothesis of power-law primary energy spectra with rigidity-dependent knees. B.Wiebel & P.Biermann, 24 th ICRC (1995) A.Lagutin et al., 29 th ICRC (2005) Extrapolation of balloon and satellite data to ~ 10 3 TeV
Conclusion I Conclusion I Rigidity-dependent spectra describe the EAS data at least up to E~100 PeV. The abundances and energy spectra obtained for primary p, He, O-like and Fe-like nuclei strongly depend on interaction model. The SIBYLL interaction model is preferable in terms of consistency of the extrapolation of derived primary spectra with direct measurements in the energy range of satellite and balloon experiments. The derived all-particle primary energy spectra only weakly depend on interaction model. An anomalous behavior of the muon size and age parameter for EAS size N ch > 10 7 is observed and requests additional analysis.
Recent results 2008 An all-particle primary energy spectrum in the 3-200 PeV energy range [ J.Phys. G: Nucl. Part. Phys. 35 (2008) 115201 ] On the basis of extended EAS data set from the GAMMA experiment an all-particle primary CR energy spectrum in the 3- 200 PeV energy range was obtained by a multi-parametric event-by-event evaluation of the primary energy. The energy evaluation method has been developed using the EAS simulation with the SIBYLL interaction model taking into account the response of the GAMMA detectors and reconstruction uncertainties of EAS parameters.
Energy estimator Energy estimator where N ch , N µ , s, cos θ – experimentally measured parameters The best energy estimations as a result of χ 2 min (E 0 ,E 1 ) were achieved for the 7-parametric fit: where x = LnN ch , y = LnN µ (R<50m), c = cos( θ )
Verification Δδ ≈ b / (E PeV ) 0.5 δ ≈ 1 ± Δδ ( Ε ) The boundary lines corresponds to approximations with upper and low limits b ≈ +0.10 and b ≈ -0.17 The shaded area corresponds to approximations b ≈ +0.09 and b ≈ -0.15 and were used to estimate errors for reconstruction of the all- particle energy spectrum Mean biases versus energies of the primary proton (p) and iron (Fe) nuclei and the uniformly mixed p, He, O, Fe composition (All)
σ A (E) ≈ σ (E) σ = 0.14, Δσ = 0.03 Errors of the energy estimator versus primary energy E 0 for 4 primary nuclei and uniformly mixed (All) composition. The cross symbols are taken from our Previous data computed for the mixed composition and shower core selection criteria R<25m !!! Such high accuracies of the energy evaluation regardless of primary nuclei are a consequence of the high mountain location of the GAMMA facility (700 g/cm 2 ), where the correlation of primary energy with the detected EAS size is very high (about 0.95) !!!
E 0 -E 1 scatter plots of simulated primary energy E 0 and estimated energy E 1 (N ch ,N µ ,s, θ ) for 4 primary nuclei
Zenith Angular Distribution R<50m, θ <45 0 Detected zenith angular distributions for different energy thresholds. The lines correspond to simulated distributions with the same statistics . The agreement of detected and simulated distributions gives an additional support to the consistency of energy estimates in the whole measurement range. The anisotropic spectral behavior at low energy (less than 3 PeV) is explained by the lack of heavy nuclei at larger zenith angles.
All-Particle Energy Spectrum All-Particle Energy Spectrum GAMMA05: R < 25m; Q < 30 0 GAMMA07: R < 50m; Q < 45 0 All-particle energy spectrum in comparison with the results of EAS inverse approach (GAMMA-06, KASCADE, KASCADE-Grande), our preliminary data and results of other experiments 24
Dependence of the average EAS Average EAS truncated muon age parameter on EAS size size versus EAS size
Possible origin of irregularities Rigidity-dependent primary-energy spectra cannot describe the phenomenon of ageing of EAS at energies (5-10) x 10 16 eV which was observed in mountain-altitude experiments. It is reasonable to assume that an additional flux of heavy nuclei (Fe- like) is responsible for the bump at these energies. Besides, the sharpness of the bump points out the local origin of this flux from compact object. We carried out the test of this hypothesis using the inverse approach on the base of GAMMA data and the hypothesis of two- component origin of cosmic ray flux: so-called Galactic component is the power-law energy spectra with rigidity-dependent knees at energies E k =E R ·Z and power indices γ = γ 1 and γ = γ 2 for E < E k and E > E k respectively; so-called pulsar component is an additional power-law energy spectrum with cut-off energies E c,Fe and indices γ p = γ 1,p and γ p = γ 2,p for E < E c,Fe and E > E c,Fe respectively.
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