Latest Results from the KASCADE-Grande experiment Andrea Chiavassa Universita` degli Studi di Torino 4th Roma International Conference on Astroparticle Physic Roma, 22-24 May 2013

Knee is due to the light component of cosmic rays Change of slope of the heavy component observed at 8x1016 eV Knee interpretation either by acceleration limit in galactic sources or by propagation effects Not yet identified the transition to extragalactic primaries

KASCADE-Grande experiment Karlsruher Institut für Technologie

KASCADE-Grande detectors & observables Grande array  cover an area of 0.5 km2, detecting EAS with high resolution Detector Detected EAS component Detection Technique Detector area (m2) Grande Charged particles Plastic Scintillators 37x10 KASCADE array e/g Electrons, g Liquid Scintillators 490 KASCADE array m Muons (Emth=230 MeV) 622 MTD Muons (Tracking) (Emth=800 MeV) Streamer Tubes 4x128 Shower core and arrival direction Shower Size (Nch number of charged particles) Grande array m Size (Em>230 MeV) KASCADE array m detectors m density & direction (Em>800 MeV) Streamer Tubes

KASCADE-Grande accuracies with a subsample of common events KASCADE + Grande 100% efficiency ■ KASCADE stations ■ Grande stations Apel et al. NIMA 620 (2010) 202-216

All particle energy spectrum Combination of Nch and Nm Five different angular bins k parameter evaluates chemical composition, used as a weight in the expression correlating Nch and E Based on QGSJet II-02 Astroparticle Physics 36, (2012) 183

Energy spectra measured in the five angular bins Spectrum cannot be described by a single power law Hardening above 1016 eV Steepening close to 1017 eV significance 2.1s Comparison of the KG spectrum with different experiments Astroparticle Physics 36, (2012) 183

Approach to Chemical Composition

Unfolding Analysis objective is to compute the spectra of NNucl mass groups. Ni number of events expected in the bin : pn is obtained from full EAS and detector simulation (based on QGSJet II) sn EAS development fluctuations rn, reconstruction resolution, including systematic reconstruction effects en, trigger efficiency

QGSJet II-02 Spectra of five mass groups obtained applying the unfolding technique to the KASCADE-Grande data. Only the heavier mass group spectrum (Fe) shows a significant steepening

Spectra agree well with those obtained applying the unfolding technique to KASCADE data. Both data sets are analyzed with the QGSJetII-02 hadronic interaction model

Event by event separation in two mass groups by the Nch/Nm ratio Two different ways of taking into account the EAS attenuation in atmosphere

YCIC is constant with E (E > full efficiency) For a specific hadronic interaction model YCIC increases with primary mass choice of YCIC  choice of a primary mass For a particular primary element YCIC increases when calculated by a model generating EAS with higher Nm  for the same primary mass the choice of YCIC is shifted

Energy spectra of the samples obtained by an event selection based on the k parameter Spectrum of the electron poor sample  k>(kC+kSi)/2  steepening observed with increased significance  3.5s Spectrum of electron rich events  can be described by a single power law  hints of a hardening above 1017 eV g1 = -2.76±0.02 g2 = -3.24±0.05 Eb = 1016.92±0.04 Phys. Rev. Lett. 107 (2011) 171104

Steepening observed at the same energy independently of the cut choice Spectra obtained with the two different strategies agree Steepening observed at the same energy independently of the cut choice The steepening of the electron poor sample is enhanced cutting at higher YCIC values YCIC event selection Phys. Rev. Lett. 107 (2011) 171104

Investigations of the electron rich sample Statistics increased by 36% adding new data sets and increasing the effective area To enhance possible structures of the electron rich sample  k < (kC+kHe)/2 Phys. Rev. D 87, 081101(R) (2013)

Spectra obtained enhancing the electron-rich event selection show a clearer hardening above 1017 eV Phys. Rev. D 87, 081101(R) (2013)

g1 = -3.25±0.05 g2 = -2.79±0.08 Eb = 1017.08±0.08 Nmeas = 579 Nexp = 467 P(N>Nmeas)≈7.23x10-09 5.8s significance Phys. Rev. D 87, 081101(R) (2013)

Conclusions Eb(light) ≠ Eb(heavy) g1(light) = g2(heavy) KASCADE-Grande data taking stopped in November 2012. All particle spectrum: Hardening ~1016 eV Steepening ~8x1016 eV Steepening of the heavy primaries spectrum at 1016.92±0.04 eV. Slope index changes from 2.76±0.02 to 3.24±0.05 Hardening of the light primaries spectrum at 1017.08±0.08 eV. Slope index changes from 3.25±0.05 to 2.79±0.08 Eb(light) ≠ Eb(heavy) g1(light) = g2(heavy) g2(light) ≈ 2.7