AMIGA – A direct measurement of muons in Pierre Auger Observatory

PASC Winter School

Sesimbra, 19th December, 2007

P. Gonçalves, M. Pimenta, E. Santos, B. Tomé

Contents:

Introduction Science motivations AMIGA Detector Detector performance simulations at LIP Conclusions and prospects

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Introduction

AMIGA – Auger Muons and Infill for the Ground Array It’s an enhancement of the Pierre Auger Observatory. It will allow to:

study at full efficiency the region of the 1017 eV and up to the 1019 eV.

Perform a direct measurement of the muonic component of the showers.

Project still in development phase. Completion in 2009.

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Science Motivation

Infer about the primary cosmic ray composition. Improve the understanding of the physical origin of the second

knee and ankle. Determine the maximum energy attainable for our Galaxy.

Provide an independent measurement of the lateral distribution profiles of the several cosmic shower components (muonic vs. electromagnetic).

Study new physics unavailable at particle acelerators.

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AMIGA layout

Small area with buried muon counters and nearby Surface Detectors (SD).

The detectors are placed into triangular grids of 750 m (and 433 m) spacing. The 750 m array covers an

area of 23.5 km2 and is fully efficient for E > 3.5 x 1017 eV (42 detectors).

The 433 m array covers an area of 5.9 km2 and is fully efficient for E > 1017 eV (24 detectors) (In study).

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AMIGA layout (II)

Each muon detector will be deployed at a depth of 2.5 m to 3 m near a SD.

The trigger will be given by the SD array.

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The Muon Detector Area of 30 m2.

64 polysterene slabs: 4 m long 4.1 cm large and 1 cm thick. Have a middle groove which lodge

an optical fibre. The slabs are co-extruded with a

reflective coating.

The fibres are bundled and read by a 64 channel MAPMT.

Stores signals above a given threshold in 25 ns time bins.

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Specific problem to access the multihit patterns from a muon

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Muon Counter Simulations

Shower simulation with CORSIKA. A Geant4 simulation to:

track down the particles from the Earth surface until a depth of 3m where the detectors were placed.

obtain the energy deposited in the scintillators.

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CORSIKA simulation

Particles from the air shower which reach the Earth surface:

1 – photons

2- positrons

3 – electrons

5 – anti-muons

6 - muons

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Background

Particles from the air shower which reach the buried detector:

1 – photons2 - positrons3 – electrons5 – anti-muons6 - muons

Primary particles Secondary particles

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Multi-hit events

Ideally we should have a slab with deposited energy per muon… However, there are additional signals from secondary particles created

by muons.

Number of slabs with deposited energy per muon

Pattern of multi-hit events caused by secondary particles

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A study in energy

If we look at the deposited energy we can eliminate most of the background.

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A study in signal

But when we look at the same plot in electronic signal…

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Detector Efficiency Estimated efficiency of 80% to 90% ~ 10 % of multi-hits

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Conclusions and prospects

AMIGA is on the final stage of R&D. Conclusion foreseen in 2009. A study of the signal induced by muons was

performed. Signal contamination of ~10%.

The physics potential of AMIGA will be pursued.

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