WATER CHERENKOV DETECTOR ARRAY at the University of Puebla to study cosmic rays H. Salazar, J. Cotzomi, E. Moreno, T.Murrieta, B.Palma, E.Perez, L. Villaseñor FCFM-UAP

EAS-BUAP : Design and Preliminary Results of the water Cherenkov array Main goal: Contribute to the study of inclined showers and mass composition around the knee as well as educational training. *11+1 tanks filled with a layer of 12 cm high of liquid scintillator and 1 m 2 effective area, mounted in a rectangular grid (40x100m 2, 20m spacing). *3 Water Cherenkov detectors 2 m 2 effective area 1 Water Cherenkov Detector (WCD), 10m 2 effective area, 1.2m height.

Full array and operational detectors in red. All signals are collected in a central acquisition station. EAS-UAP: First Stage, scintillator detectors.

EAS-UAP Altitude ~2200 m above sea level, 800 g /cm 2 Location: 19 0 N and 90 0 W.

Energy range covered by the EAS- BUAP array: to eV.

The primary energy spectrum extends over many Orders of magnitude from GeV energies to 50 J. Power law spectrum with almost no structure Change in the spectral index at about 4 PeV(Knee) Slight steepening around 400PeV (second Knee) Flattening at the highest energies around 10EeV (Ankle) GZK Cutoff The origin of the Knee is still under discussion

Cosmic ray particles are most likely accelerated in strong shock fronts of supernova remnants (Fermi acceleration) Low Z(charge) particles are more likely to escape from the galaxy as compared to particles with high Z (gyromagnetic radii) The first Knee is due to the subsequent Cut-offs for all elements, starting with the proton component Second Knee could mark the end of the stable elements (Z=92)

EAS TOP

Italy Location: 2005 m a.s.l. (820 g/cm 2 ) 35 detector stations of scintillators 10m 2 Detector: Array, MACRO Observables: N e, muons Status: stopped

KASKADE

Germany Location: 500 m a.s.l. (1020 g/cm²). 252 scintillator detectors Area: 200 X 200 m² Detector: Array, tunnel GRANDE Observables: N e -N u, hadrons, muons Status: running in set-up

The trigger requires the coincidence of >4 signals in a rectangular sub-array with an area of 29  29 m 2. The measured trigger rate is 150 hour -1. Light-tight cylindrical container with inner reflective walls filled with liquid scintillator up to a height of 12 cm and one 5” PMT (EMI 9030A) facing down 70 cm above the surface of the liquid..

Day/Night temperature effect on rates

Calibration histograms EAS-UAP Scintillation detectors November 2004

Calibration histograms of the Water Cherenkov detectors

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

Angular distribution from Cherenkov detector arrival times A = 4  R² cos(  ) + 2hR sen(  )

Example of lateral distribution of electromagnetic particles from Scintillation detectors

Two examples of LDF for both: EM and VEM

Muon/EM separation in Water Cherenkov detectors For details see Villasenor L. talk at Rich 2004

Discussion on composition 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 number of charged particles in each detector using the single-particle charge spectrum to obtain the LDF of (vertical) showers and the water cherenkov detectors to obtain the LDF in VEM’s. The shower core is located by the center of gravity and by fitting the measured charged particle distribution to the NKG function. Muon/Electromagnetic content from: S( VEM )= N  *VEM + N em *VEM/W 1 S(Nt)= N  + W 2 N em, with W 1 ~24 and W 2 ~2.4 But simulation of the detection process is needed for fine tuning of these weigths!

CABAÑA ALT: 4560 N 18° 59’ 03.9’’ W 97° 18’ 44.7’’ ALT: 4558 N 18° 59’ 04.6’’ W 97° 18’ 45.4’’ CENTRO ALT: 4557 N 18° 59’ 03.7’’ W 97° 18’ 45.5’’ ALT: 4557 N 18° 59’ 04’’ W 97° 18’ 46.4’’ ALT: 4558 N 18° 59’ 02.9’’ W 97° 18’ 45.2’’ ARENA RAMPA NORTE SUR TOWARDS THE MOUNTAIN TEST ARRAY Thanks to INAOE- LMT for the site!

Cherenkov DETECTORS fluorescence detector Construction in progress: Hybrid Mountain Array to determine mass composition Acknowledgements to students! Eduardo Moreno, Jorge Cotzomi, Epifanio Lancho, Marcelino Anguiano, Saul Aguilar, Guillermo Ontiveros, Isabel Pedraza, Tirso Murrieta, Bianey Palma, Gonzalo Perez

Acknowledgements This work was done with partial support of the CONACY-G32739 E And University of Torino University of Puebla Fermilab Students: Eduardo Moreno Barbosa Jorge Cotzomi Paleta Epifanio Lancho Marcelino Anguiano Saul Aguilar Guillermo Ontiveros Isabel Pedraza Tirso Murrieta Bianey Palma Gonzalo Perez

Scintillator detetctor vs Small Water CD

Infill array: distribution of zenith angle