Arreglo EAS-UAP para el Estudio de Rayos Cósmicos alrededor de 1015 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 EnergíasCINVESTAV-IPND.F.Sept. 20, 2005

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 1014 eV and Iron to 3 x 1015 eV)

Observing the mass composition of cosmic rays at the knee therefore provides an important clue to the origin of cosmic rays.

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 1015 eV.

Measuring the chemical composition of the cosmic rays at 1015 eV can test the different explanations.

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

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

DAQ System• Trigger: Coincidence of 3-4 central detectors (40mx40m) NIM y CAMAC.

Use digital Osciloscopes

as ADCs. Rate: 80

eventos/h

DAQ System

• Calibration Rate: 250 events/m2/s

Monitoring• Use CAMAC scalers to measure

rates of single partícles on each detector.

• Day-night variations <10%

/mean around 3%

Calibration

~74 pe

LabView basedDAS

MPV of EM peak = 0.12 VEMi.e. around 29 MeV, i.e., dominatedBy knock-on + decay electrons

Stopping muonat 0.1 VEM

Decay electronat 0.17 VEM = 41 MeV

Crossing muonat 1 VEM

Alarcón M. et al., NIM A 420 [1-2], 39-47 (1999).

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

Data Analysis

• Arrival directionsin sin = d/c(t2-t1)

Angular distribution inferred directly from the relative arrival times of shower frontin good agreement with the literature: cosp sen

Data Analysis

• Lateral Distribution Functions

mR

RRRRSKRS SSNKG

100)/(1)/)((),(

0

5.40

20

Energy Determination107.1

00 5.197)( EEN

mR

RRRRKRGreissen

400)/(1)/()(

0

5.20

75.0

EAS-TOP, Astrop. Phys,10(1999)1-9

The shower core is located as the center of gravity.

Ne, obtained for vertical showers. The fitted curve is Ik (Ne/Nek)

-, gives =2.44±0.13 which corresponds to a spectral index of the enerfy distributions of =2.6

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

Mass CompositionHybrid Array

3

24

int LEMLmuon

L

LiqSc

CEMCmuon

C

Cherekov

AAVEMq

AAVEMq

LL

LiqSc

CC

Cherekovmuon

CC

Cherekov

LL

LiqScEM

VEMAq

VEMAq

VEMAq

VEMAq

int

int

71

78

)(724

Solution:

IterationsStart with

Ne=82,300Nmu = 32700E0 = 233 TeV

IterationsEnd with

Ne=68000Nmu = 18200E0 = 196 TeV

Mass CompositionNon-Hybrid Array

24CEM

CmuonC

Cherekov AAVEMq

Do a three parameter fit to :

mRmR

RRRRKRRRRSKRNRS GreissenSS

NKGGreissenNKG

400100

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

1

0

5.21

75.01

5.40

20

Mass CompositionNon-Hybrid but Composite

ArrayTwo 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

VEMq

VEMq

A

VEMq

VEMq

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: