1. Andrea CHIAVASSA and Elena CANTONI Universita` degli Studi di Torino
Measurement of the cosmic ray chemical composition based on the Nm/Nch ratio with the KASCADE-Grande experiment
Andrea CHIAVASSA and Elena CANTONI
Universita` degli Studi di Torino

2. KASCADE-Grande layout
KASCADE (200x200 m2)
e/g
4 Em
hadrons
Grande (700x700 m2)
Charged particles
Nch, Nm(Em>230 MeV)
~1173 days of data

3. Grande array resolution measured comparing
the event reconstruction with the KASCADE array
(NchG-NchK)/NchK
Nch accuracy < 15%
Systematic difference < 5%
Nm accuracy<20%
■ KASCADE stations
■ Grande stations
Apel et al. NIMA 620 (2010)

4. Fsim(i) = Sj aj fsim,j(i) Sj aj = 1
Measured Nm/Nch distributions (0°<q<24°) compared with
those obtained from a
complete EAS and detector simulation
Fsim(i) = Sj aj fsim,j(i)
Sj aj = 1
c2 = Si (Fsim(i)-Fexp(i))2/s2(i)
Fit results accepted if:
0.05<P(c2<c20)<0.95
H + HE&C + Si&Fe
QGSJetII-03 describes
the data
6.24<Log Nch<6.36

5. From aj to mass groups energy spectra
More than two mass groups needed in the whole energy range
Nj(k) = aj(k) Nexp(k)
Nj(k)  Fj(Nch)
Nch  E
F(Nch)  F(E)
Results depend on the QGSjet II-03 interaction model

6. No spectral breaks are introduced by the algorithm.
He+C true
He+C rec
simulation
Test spectra of the three mass groups reconstructed with the c2 analysis.
Results are not corrected for migration effects.
No spectral breaks are introduced by the algorithm.

7. - Spectrum of the heavy elements (Si+Fe) shows a knee like feature
- Spectra of the light (H) and intermediate (He+C) elements don’t show a knee like feature. Spectra seem to get harder above 1017 eV
 Si + Fe
▼ He + C
■ H
Data

8. Fitting function: Single power law: Data
K,Ek,g1,g2,e  free parameters
Data
K,g  free parameters
 Si + Fe

9.  Si + Fe Data g1 g2 Si+Fe c2s.p.l./dof = 9.29 c2func/dof = 2.06
Significance of the change of slope:
Ftest = (2single power law / m) / (2function / n), with m,n = dof single power-law, function
Variance = 2n2(m+n-2) / m(n-2)2(n-4)
Significance (in units of the standard deviation) = Ftest / √Variance
Si+Fe
c2s.p.l./dof = 9.29
c2func/dof = 2.06
Ftest = 4.52
Variance = 1.12
Significance = 4.3
▲ All particle
 Si + Fe
Data
Log(Ek/eV) g1 g2
Si+Fe
17.79±0.04
2.60±0.01
3.29±0.01

10. The change of slope of the heavy mass group spectra is observed also with other approaches
Data
DEk
○ Electron poor YCIC (J.C. Arteaga, #739)
○ Electron poor K (M. Bertaina, #312)
 Fe Nch-Nm Unfolding (D. Fuhrman,,#280)
 Fe+Si  This work

11. CONCLUSIONS
Primary composition obtained fitting the Nm/Nch distributions
Three mass groups can be separated
All mass groups present in the eV energy range
Change of slope of the heavy elements observed with this algorithm (4.3s) at Log(E/eV)=17.78±0.04
Relative abundances found in this work heavily depend on the hadronic interaction model  QGSjetII-03. While structures of the spectra don’t.