“The Cosmic Ray composition in the knee region and the hadronic interaction models” G. Navarra INFN and University, Torino, Italy For the EAS-TOP Collaboration XIII International Symposium on Very High Energy Cosmic Ray Interactions Pylos Greece, September 2004

EAS-TOP at LNGS Campo Imperatore 2000 m a.s.l. 820 g. cm -2 data taking:

The Cosmic Ray primary spectrum THE HIGH ENERGY GALACTIC RADIATION KNEE DIRECT EXP.

EAS-TOP Energy range from the direct measurements up to above the knee: Cosmic Ray primary spectrum & composition Verification of the hadronic physics DETECTORS: HADRONS ATMOSPHERIC C.l. ELECTROMAGNETIC MUONS (E > 1 GeV) + MUONS (E > 1.3 TeV) Deep underground GS labs.: MACRO, LVD

EAS-TOP: THE CALORIMETER & MUON TRACKER 8 x 13 cm Fe layers; 144 m 2 streamer + q. proportional tubes

DETECTORS & METHODS Hadrons  E 0 ~ TeV Cherenkov light + TeV muons  p, He, CNO E 0 ~ 100 TeV e.m.  spectrum in “knee” region E 0 ~ TeV e.m. + GeV muons  composition in “knee” region e.m. + TeV muons  composition in “knee” region Verifications of methods and HE physics used e.m.  anisotropies & search for gamma primaries  CORSIKA-QGSJET 

Size and energy spectra: Ne Eo Astrop. Phys. 10 (1999) 1

Ne-N  distributions 3-component fit: L, CNO, H in  LogNe = 0.2 intervals of Ne  2 =  i (f c i – f exp i ) 2 /  i2 f c i = w L f sL i + w CNO f sCNO i + w H f sH i Simulations with  = 2.75 spectra L = “p” or “50%p + 50% He” ; CNO = N; H = Fe Fraction of events

The composition in the ‘knee’ region Mass group  Heavier primary spectra harder  E k  Z ?  l > 3.1  CNO ~ 2.75  Fe = 2.3 – 2.7

TeV muon multiplicity fits in MACRO (TeV  ) L = p + He H = Mg + Fe L+H Measured

EAS-TOP & MACRO (TeV  ) L = p + HeH = Mg + Fe Astrop. Phys., 20 (2004) 641

vs. E 0

particle and energy flux in p-p MACRO EAS-TOP E. M.

The hadronic interaction models (CORSIKA) Primary protons: N   N e   = ±  = ±  = ±  = 0.77 ± 0.02

Evolution of composition < N e -N    EXP = ±  EXTRCMP = 0.79 ± 0.02  MAX-VENUS = ± QGSJET: agreement with extrapolated direct measurements! NO INTERACTION MODEL CAN ACCOUNT FOR THE INCREASING N  vs. Ne WITHOUT INCREASING PRIMARY MASS

Component dominating at the “knee”? He – p spectra similar RUNJOB He spectrum harderJACEE From “direct” measurements: JACEE RUNJOB JACEE RUNJOB EAS-TOP

Astrop. Phys., 21 (2004) 223 Proc. 28 th ICRC, 1 (2003) 115 A different approach: EAS-TOP & MACRO

EAS-TOP (Cherenkov detector): total energy through the amplitude of the detected Cherenkov light signal. MACRO (muon  detector): EAS primaries with E n > 1.3 TeV/n EAS geometry through the  track ( r ~ 20 m,  ~ 1 0 uncertainties) MACRO and EAS-TOP are separated by m of rock: E   TeV

DATA SET  t = 7  s September 1998 – May 2000 Tot. Time T = 208 h 5 telescopes exposure   830 day m 2 sr angular window:  : 16 <  < 58, 127 <  < 210 MACRO events in T and  : with EAS-TOP in  t = 7  s: 3830 (expected accidental events < 3.0) Event coincidence is established off-line (GPS system -  T < 1  s) Coincidence Peak t MACRO –t Cherenkov (  s)  t = 7  s 7

E ≈ 80 TeV N  p ≈ N  He E ≈ 250 Tev N  p ≈ N  He ≈ N  CNO C.l. yield: p ~ He ~ CNO p He CNO Fe C.l. + TeV muon analysis Mg

p, He, ~ TeV InformationEAS-TOP & MACRO JACEERUNJOB J p+He (80 TeV) 18 ± 412 ± 38 ± 2 J p+He+CNO (250 TeV) 1.1 ± ± ± 0.1 J p / J p+He (80 TeV) 0.29 ± ± ± 0.20 J p+He / J p+He+CNO (250 TeV) 0.78 ± ± ± 0.25 J He (80 TeV) 12.7 ± ± ± 0.7 x m -2 s -1 sr -1 TeV -1 EAS-TOP & MACRO data EAS-TOP & MACRO data + p-flux p+Hep+He+CNO

The Cherenkov light LDF WITH JACEE FLUX Test of energy release in the atmosphere of QGSJET: R =  (42 m) /  (134 m) = Ne (370 g/cm 2 ) / Ne (505 g/cm 2 ) (R exp – R th )/R th = 0.14 ± 0.09

Ne and N  spectra Ne N 

Sec    Ik*10 7 Nk chi**2/df m-2s-1sr    / / / / / /11 chi**2/df (1slope)     / / / / /10 9.9/ /10 14/12 Agreement inside errors (~ 30%) 2 slopes Decreasing with increasing zenith angle Ne N  N   N e   = (  e –1) /(   -1) = 0.7 – 0.8 In agreement with models SAME BENDING COMPONENT ?

IF SAME BENDING COMPONENT in Ne and N  spectra We can identify it. We construct for each component (p, He, CNO, Mg, Fe) the energy spectrum fitting the size spectrum in the region of the knee. From such energy spectra we construct for each component the corresponding N  spectrum, to be compared with the measured one. The result of such comparison 

Muon size spectrum: measured and expected for different primaries on the base of the Ne spectrum If “Knee” on Helium primaries E k (He) = (3.5  0.3) eV VENUS QGSJET NEXUS

The primary spectrum from EAS-TOP

Natural evolution….. KASCADE-Grande

If : E k,Z = Z * E k,1 SEARCH FOR IRON “KNEE” AT ~ eV PRIMARY COMPOSITION: eV STUDY OF C.R. INTERACTIONS AT UHE N (> eV) ~ 250 (3 y data taking) At the threshold of Auger (High Resolution) P,He iron E knee = 3 – 4 PeV EAS-TOP/KASCADE

Hadron spectrum at 820 g/cm 2 & comparison with sea level (1033 g/cm 2 ) Calculated QGSJET Exp. KASCADE/EAS-TOP

E 0 = 0.5 – 50 TeV Proton spectrum at TOP Astrop. Phys. 19 (2003) 329 He contribution subtracted S(Eo) = (9.8  1.1 stat  1.6 sys ) 10 –5 (Eo/1000) –2.80  0.06 m -2 s -1 sr -1 GeV -1