1. Arreglo EAS-UAP para el Estudio de Rayos Cósmicos alrededor de 10 15 eV Humberto, Salazar, Oscar Martínez, César Alvarez, L. Villaseñor* + Estudiantes del Grupo de la FCFM-BUAP Facultad de Físico-Matemáticas, Benemérita Universidad Autónoma de Puebla, Apartado Postal 1364, Puebla, Pue., 72000, México *On leave of absence from Institute of Physics and Mathematics, University of Michoacan, Morelia, Mich., 58040, México Coloquio del Grupo de Altas Energías CINVESTAV-IPN D.F. Sept. 20, 2005

10.  At an energy of approximately 3 PeV the spectral index steepens (“knee”).  To understand the reason for the knee, one must understand the source, acceleration mechanism, and propagation of cosmic rays.  First-order Fermi acceleration has a cutoff energy (protons to 10 14 eV and Iron to 3 x 10 15 eV)  Observing the mass composition of cosmic rays at the knee therefore provides an important clue to the origin of cosmic rays.

11. Source  Supernova shock-wave Fermi acceleration is correct + Unknown mechanism i.e., rotating compact magnetic objects (neutron stars or black holes) at higher energies = kink due to overlap between the two mechanisms with progressive change in chemical composition as the knee is approached. Propagation  Smooth energy distribution up to the highest cosmic-ray energies with unknown loss mechanism beginning at about 10 15 eV.  Measuring the chemical composition of the cosmic rays at 10 15 eV can test the different explanations.

12. EAS Array  Area: 4000 m^2  10 Liquid Ssintillator Detectors (Bicron BC-517H)  4 Water Cherenkov Detectors PMT Electron tubes 9353 K PMT EMI 9030 A

13. 2200m a.s.l., 800 g/cm2. Located at Campus Universidad Autonoma de Puebla Hybrid: Liquid Scintillator Detectors and water Cherenkov Detectors Energy range 10^14- 10^16 eV

14. DAQ System Trigger: Coincidence of 3-4 central detectors (40mx40m) NIM y CAMAC. Use digital Osciloscopes as ADCs. Rate: 80 eventos/h

15. DAQ System Calibration Rate: 250 events/m2/s

17. Monitoring Use CAMAC scalers to measure rates of single partícles on each detector. Day-night variations <10%  /mean around 3%

18. Calibration

19. ~74 pe

20. LabView based DAS

21. MPV of EM peak = 0.12 VEM i.e. around 29 MeV, i.e., dominated By knock-on + decay electrons

22. Stopping muon at 0.1 VEM Decay electron at 0.17 VEM = 41 MeV Crossing muon at 1 VEM Alarcón M. et al., NIM A 420 [1-2], 39-47 (1999).

23. Cherenkov Liquid Scint Muons deposit 240 MeV in 1.20m high water and only 26 MeV in 13 cm high liquid, while electrons deposit all of their energy i.e., around 10 MeV. Therefore for 10 Mev electrons we expect: Mu/EM=24 for Cherenkov Mu/EM=2.6 for Liq. Scint. Muon/EM Separation

24. Data Analysis Arrival direction sin  sin  = d/c(t 2 -t 1 )

25. Angular distribution inferred directly from the relative arrival times of shower front in good agreement with the literature: cos p  sen 

26. Data Analysis Lateral Distribution Functions Energy Determination EAS-TOP, Astrop. Phys, 10(1999)1-9 The shower core is located as the center of gravity.

27. N e, obtained for vertical showers. The fitted curve is I k (N e /N ek ) - , gives  =2.44±0.13 which corresponds to a spectral index of the enerfy distributions of  =2.6

28. Cherenkov Liquid Scint Muons deposit 240 MeV in 1.20m high water and only 26 MeV in 13 cm high liquid, while electrons deposit all of their energy i.e., around 10 MeV. Therefore for 10 Mev electrons we expect: Mu/EM=24 for Cherenkov Mu/EM=2.6 for Liq. Scint. Muon/EM Separation

29. Mass Composition Hybrid Array Solution:

30. Iterations Start with Ne=82,300 Nmu = 32700 E0 = 233 TeV Iterations End with Ne=68000 Nmu = 18200 E0 = 196 TeV

31. Mass Composition Non-Hybrid Array Do a three parameter fit to :

32. Mass Composition Non-Hybrid but Composite Array Two Identical types of Cherenkov Detectors one filled with 1.20 m of water and the other with 0.60 m, i.e., VEM C’ =0.5VEM C i.e., do independent fits of  EM and  muon to NKG and Greissen LDF, respectively, where:

33. Conclusions We have checked the stability and performed the calibration of the detectors. We have measured and analyzed the arrival direction of showers. We determine the energy of the primary by measuring the total number of charged particles obtaining by integration of the fitted LDF. Study of Muon/Electromagnetic ratio is underway: