ICRW, Aragats2007

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GAMMA Experiment
Study of structure of the primary cosmic ray
energy spectrum around the knee at energies 1
100 PeV
R.Martirosov on behalf of the GAMMA collaboration
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_____________ ICRW, Aragats-2007
XV ISVHECRI Paris 2008
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GAMMA experiment, Mt. Aragats, 3200m a.s.l.,
Armenia
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At present

• Surface part
• 33 stations on the five concentric circles with
  R 0, 18, 28, 50, 70 and 100 meters with 3
  scintillation detectors (S1m2) in each station.
  Total number (including 9 small detectors) 108
• The area 3.14x104 m2
• - 33 timing channels for estimation of the EAS
  angular characteristics
• Underground part
• Carpet of muon detectors with total number 150
  and energy threshold Eµ gt 5 GeV)

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The shower size thresholds of the 100 efficiency
are equal to Nch 3 x 105 and Nch 5 x105 at
the EAS core location within R lt 25 m and R lt 50
m respectively. The time delay is estimated by
the pair-delay method to give the time resolution
of about 4-5 ns. The EAS detection efficiency
(Pd) and the corresponding shower parameter
reconstruction errors are equal to Pd 100,
?? 1.50, ?Nch/ Nch 0.05-0.15, ?s
0.05, ?x and ?y 0.7-1.0 m. The reconstruction
errors of the truncated muon shower size for Rµ lt
50 m from the shower core are equal to ?Nµ/ Nµ
0.2-0.35 at Nµ 105-103 respectively.
The
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The simulated EAS data base
To obtain the parametric representation for the
unbiased (d 1) energy estimator E1 of the
primary energy E0 we simulated showers database
using CORSIKA6031 EAS simulation code with the
SIBYLL interaction model for H, He, O and Fe
primary nuclei.

• Emax 5103 PeV
• ? lt 450
• Ee gt 1 MeV
• E? gt 150 MeV
• E? gt 4 GeV (e?)

SIBYLL2.1
N 4 x 1.5?104
11/23/2009
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Event-by-event analysis and All-Particle Energy
Spectrum The best energy estimations were
achieved for the 7-parametric fit
were x Ln(Nch), y Ln(N?), c cos(? ), s is
the shower age and energy E1 is in GeV.
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Verification
d 1 ? Dd(E)
The average biases versus energies (E E0 and E
E1) of the primary proton (p), iron (Fe) and
uniformly mixed p, He, O, Fe composition. The
boundary lines corresponds to approximation ?? ?
b/(EPeV)0.5 were b 0.10 and b -0.17 for the
upper and lower limits respectively. The shaded
area corresponds to b 0.09 and b - 0.15 and
were used to estimate the errors for the
reconstruction of the all-particle energy
spectrum.
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Verification
sA(E) s(E)
The dependence of standard deviation s(E0) of
systematic errors of energy evaluation on
primary energy E0 for 4 primary nuclei (p, He, O
and Fe) and uniformly mixed composition 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 about
0.95-0.99.
11/23/2009
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The E0-E1 scatter plot of simulated primary
energy E0 and estimated energy E1(Nch, N?, s, ?)
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Zenith Angular Distribution
Rlt50m, ?lt450
The independent test of energy estimates can be
done by detected zenith angle distributions which
have to be isotropic for different energy
thresholds. The lines correspond to simulated
isotropic distributions with the same statistic.
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All-Particle Energy Spectrum
GAMMA05 R lt 25m Q lt 300 GAMMA07 R lt 50m Q lt
450
4 standard deviation at 7.4x107 GeV
The obtained energy spectrum agrees within errors
with KASCADE, AKENO and TIBET-III data both in
the slope and in the absolute intensity
practically in the whole measurement range.
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Possible origin of irregularities
Irregularities of the all-particle energy
spectrum in the knee region are observed by many
others experiments and explained by both the
rigidity-dependent knee hypothesis and
contribution of pulsars in the Galactic cosmic
ray flux for energy range (1-100)x106 GeV. As
regards the observed bump at about (6-8)x107 GeV
there are some other indications in
KASCADE-Grande, TIBET-III and TUNKA experiments
but with larger statistical uncertainties at
level 1.5-2.0 standard deviation. 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 (pulsar). We carried out
the test of this hypothesis using the
parameterized inverse approach on the basis of
the GAMMA facility EAS database and the
hypothesis of two-component origin of cosmic ray
flux.
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EAS size spectra
Truncated muon size spectra
The folded (expected) shower spectra (filled
symbols) were computed on the basis of
parameterization and CORSIKA EAS simulated data
set for H, He, O, Fe. You can see also the
derived expected elemental shower spectra (lines)
for primaries H, He, O, Fe.
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All-particle spectra and pulsar Fe component
Resulting expected energy spectra for the
Galactic H, He, O and Fe nuclei (thin lines)
along with the all-particle energy spectrum (bold
line with shaded area.) The thick dash-dotted
line corresponds to derived energy spectrum of
the additional Fe component. The all-particle
energy obtained on the basis of the GAMMA EAS
data and the event-by-event multi-parametric
energy evaluation method is also shown.
It is seen that the shape of the two-component
all-particle spectrum (bold line with shaded
area) calculated with parameters taken from the
fit of EAS size spectra agrees within errors with
results of the event-by-event analysis (symbol)
that points out the consistency of applied
spectral parameterization with GAMMA data.
11/23/2009
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All-particle spectra and pulsar Fe component
The average logarithm primary nuclei mass number
derived from rigidity-dependent primary spectra
(so-called Galactic component, dashed line) and
2-component model prediction taking into account
additional pulsar component (solid line).
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CONCLUSION

• Multi-parametric event-by-event energy
  evaluation method
• provided high accuracies (10-15) for energy
  evaluation of
• primary nuclei regardless of nuclei mass number
  in 5-200 PeV
• energy region

• All-particle energy spectrum are obtained using
  GAMMA facility EAS database. The all-particle
  spectrum in the range of statistical and
  methodical errors agrees with the same spectrum
  obtained using EAS inverse approach in 5-70 PeV
  energy region.
• High accuracies of energy evaluations and small
  statistical errors point out to the existence of
  explicit irregularity (bump) of energy spectrum
  in the 70-80 PeV region.

• The bump can be associated with an additional
  Fe-component
• from magnetosphere of pulsars.

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• These results are available on
• Journal of Physics G Nuclear Part. 35 (2008)
  115201
• Poster presented by Alexandr Garyaka on this
  Symposium
• Primary cosmic ray energy spectrum in terms of
  the
• GAMMA muon data
• We hope for confirmation from other experiments
• KASCADE-Grande, Tibet-III, GRAPES-III and others

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GAMMA Experiment
COLLABORATION
ARMENIA Yerevan Physics Institute R.Martirosov,
A.Garyaka RUSSIA Moscow Lebedev
Institute A.Erlykin, N.Nikolskaya USA L.Jones,
University of Michigan S.Ter-Antonyan, Southern
University, Baton Rouge France Y.Gallant,
University of Montpellier J.Procureur, University
of Bordeaux

11/23/2009
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GAMMA TEAM
GAMMA Experiment
Thanks
http//gamma.yerphi.am
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(No Transcript)
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GAMMA Experiment
TUNKA experiment
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Sharpness of the knee
?1 2.7
?2 3.2
E2.7?F(E)
? 2
? 4-5
Polar Cap Component
Outer Gap Component MHD acceleration
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E, PeV