Hybrid Extensive Air Shower Detector Array at the University of Puebla to Study Cosmic Rays (EAS-UAP) O. Martínez a, E. Moreno a, G. Pérez a, H. Salazar a, L. Villaseñor a,b. (a) Facultad de Fisico-Matematicas, Benemerita Universidad Autonoma de Puebla, Puebla, Pue., 72000, Mexico (b) Instituto de Fisica y Matematicas, Universidad Michoacana de San Nicolas de Hidalgo, Morelia, Mich., 58040, Mexico Abstract We describe the performance of a hybrid extensive air shower (EAS) detector array built on the Campus of the University of Puebla (19oN, 90oW, 800 g/cm2) to measure the energy, arrival direction and composition of primary cosmic rays with energies around the knee of the cosmic-ray energy spectrum. The array consists of 6 water Cherenkov detectors of 1.86 m 2 cross section and 12 liquid scintillator detectors of 1 m 2 distributed in a square grid with a detector spacing of 20 m over an area of 4000 m 2. We discuss and report on measurements and reconstruction of the LDF for the electromagnetic and muonic components of extensive air showers. We also discuss the ways in which the hybrid character of the array can be used to study inclined EASs, i.e., zenithal angle > 60 degree; and also to measure mass composition of the primary cosmic rays, i.e., by estimating the relative contents of muons with respect to the EM component. a) Referencias H. Salazar and L. Villaseñor, Nucl. Instrum. and Meths A, Proc. RICH2004 Conference, M. Alarcon, et al., Nucl. Instrum. And Meths A 420 (1999) J. Nishimura, Handbuch der Physik XLVI/2, (1967) 1. H. Salazar, O. Martínez, E. Moreno, J. Cotzomi, L. Villaseñor, O. Saavedra, Nuclear Physics B (Proc. Suppl.) 122 (2003) M. Aglietta et al., Phys. Lett. B, 337 (1994) HE.1.2 EAS-UAP Array (19º N, 90ºW, 800g/cm2) PMT EMI 9030 A PMT Electron tubes 9353 K Experimental Setup 2200m a.s.l., 800 g/cm2. Located at Campus Universidad Autonoma de Puebla Hybrid: Liquid Scintillator Detectors and water Cherenkov Detectors Energy range eV DAQ System Trigger: Coincidence of 4 central detectors (40mx40m) NIM y CAMAC. Use of digital Osciloscopes as ADCs Rate: 80 eventos/h Monitoring Use CAMAC scalers to measure rates of single partícles on each detector. Day-night variations <10%  /mean around 3% Calibration (Control Experiments) ~74 pe Decay electron at 0.17 VEM = 41 MeV Indoors WCD: MPV of EM peak = 0.12 VEM ~ 29 MeV, i.e., dominated by knock-on + decay electrons Outdoors WCD: MPV of EM peak = 0.12 VEM ~ 29 MeV, i.e., dominated by EM particles ~ 10 MeV WCD 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. For 10 Mev electrons we expect: Mu/EM=24 for Cherenkov Mu/EM=2.6 for Liq. Scint. Outdoors Liquid Scintillator Detector: MPV of EM peak = 0.30 VEM i.e., dominated by EM particles ~ 10 MeV Angular Distribution Angular distribution inferred directly from the relative arrival times of shower front. Zenithal distribution in good agreement with the literature: cos p  sen  Flat azimuthal distribution Lateral Distribution Functions Energy Determination EAS-TOP, Astrop. Phys, 10(1999)1-9 N e, obtained for vertical showers. The fitted curve is I k (N e /N ek ) -g, gives g=2.44±0.13 which corresponds to a spectral index of the enerfy distributions of g=2.6 Mass Composition Hybrid Array Iterations Process. Start with N e =82,300, N mu = 32700, E 0 = 233 TeV Iteration Process. End with N e =68000, N mu = 18200, E 0 = 196 TeV Mass Composition Non-Hybrid Array Do a three-parameter fit to : 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: 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: