Hybrid Extensive Air Shower Detector Array at the University of Puebla to Study Cosmic Rays

(EAS-UAP)O. Martíneza, E. Morenoa, G. Péreza, H. Salazara, L. Villaseñora,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 m2 cross section and 12 liquid scintillator detectors of 1 m2 distributed in a square grid with a detector spacing of 20 m over an area of 4000 m2. 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, 2005. M. Alarcon, et al., Nucl. Instrum. And Meths A 420 (1999) 39-47.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) 251-254.M. Aglietta et al., Phys. Lett. B, 337 (1994) 376-382.

HE.1.2

EAS-UAP Array(19º N, 90ºW, 800g/cm2)

PMT EMI 9030 A

PMT Electron tubes 9353 KExperimental 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 1014 - 1016 eV

DAQ System

Trigger: Coincidence of 4 central detectors (40mx40m)

NIM y CAMAC. Use of digital Osciloscopes as ADCs

Rate: 80 eventos/h

MonitoringUse CAMAC scalers

to measure rates of

single partícles on

each detector.

Day-night variations

<10%

/mean around 3%

Calibration (Control Experiments)

~74 pe

Decay electronat 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 VEMi.e., dominated by EM particles ~ 10 MeVAngular Distribution

Angular distribution inferred directly from the relative arrival times of shower front.Zenithal distribution in good agreement with the literature: cosp sen Flat azimuthal distribution

Lateral Distribution Functions

mR

RRRRSKRS SSNKG

100

)/(1)/)((),(

0

5.40

20

mR

RRRRKRGreissen

400

)/(1)/()(

0

5.20

75.0

Energy Determination

107.100 5.197)( EEN EAS-TOP, Astrop. Phys,

10(1999)1-9

Ne, obtained for vertical showers. The fitted

curve is Ik (Ne/Nek) -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

3

24

int LEMLmuon

L

LiqSc

CEMCmuon

C

Cherekov

AA

VEM

q

AA

VEMq

LL

LiqSc

CC

Cherekovmuon

CC

Cherekov

LL

LiqScEM

VEMA

q

VEMA

q

VEMA

q

VEMA

q

int

int

71

78

)(724

Iterations Process. Start with Ne=82,300, Nmu = 32700, E0 = 233 TeV

Iteration Process. End with Ne=68000, Nmu = 18200, E0 = 196 TeV

Mass Composition Non-Hybrid Array

24CEM

CmuonC

Cherekov AA

VEM

q

Do a three-parameter fit to :

mR

mR

RRRRKRRRRSKRNRS GreissenSS

NKGGreissenNKG

400

100

)/(1)/()/(1)/)(()(),(

1

0

5.21

75.01

5.40

20

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., VEMC’=0.5VEMC

12

24

'

' EMmuon

CC

Cherekov

EMmuon

CC

Cherekov

VEMAq

VEMAq

)2

(1

)(24

'

'

'

'

C

Cherekov

C

Cherekov

Cmuon

C

Cherekov

C

Cherekov

CEM

VEM

q

VEM

q

A

VEM

q

VEM

q

A

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: