Congresso del Dipartimento di Fisica

Highlights in Physics 200511–14 October 2005, Dipartimento di Fisica, Università di Milano

The Pierre Auger observatory: a hybrid detector looking for the ultra high energy cosmic raysC. De Donato*, F. Sánchez*,†, D.V. Camin*,† and V.Grassi*,†

* Dipartimento di Fisica, Università di Milano† INFN – Sezione di Milano

Science Objectives

Cosmic ray spectrum above 1019 eV • Shape of the spectrum in the region of the GZK

featureArrival direction distribution• Search for departure from isotropy – point

sourcesComposition• Light or heavy nuclei, photons, neutrinos,

exotics(?)

Design Features

High statistics :aperture >7000 km2 sr above 1019eV in each hemisphere

Full sky coverage with uniform exposure

Hybrid configuration – surface array (water-Cherenkov tanks) with fluorescence detector coverage: High resolution in energy and

geometric reconstruction Complementary set of mass

sensitive shower parameters Crossed calibration through two

different measurement techniques Max hybrid efficiency above 1019eV

for zenith angle <60° 100% monocular detection 60% stereo detection

Diaphra

gm 2

.2 m

Corrector ring 25 cm

UV Filter (300-400 nm)

20x22 PMT’s camera(Ø=1.5°)

3.5 m x 3.5 m segmented mirrorRc=3.4 m, focal lenght=1.743

20x22 PMT’s camera

Plastic tank12 tons of de-ionized water3 – nine inch

photomultipliertubes

Battery box

Solar panels

Electronics box

Communications and GPS antennas

White-light diffusing liner

Fluorescence Detectors•4 FD stations (3 completed)•6 telescopes per station•24 Telescopes total•Duty cycle 10%•Longitudinal profile of the shower

Surface Array•1600 detector station (905 deployed)•1.5 km spacing•3000 km2

•Duty cycle 100%•Lateral distribution of the shower front

Mendoza, Argentina (construction underway)

Colorado, USA (in planning)

Galaxy distribution 7-21 Mpc

Fitted Electromagnetic Shower

from Fly's Eye 1985

Tim

e μ

sec

Angle Χ in the shower-detector plane

Tanks

Pixels

Hybrid EventΘ~ 30º, ~ 8 EeV

First Data Set Collection period – 1 January 2004 to 5 June 2005 Zenith angles - 0 - 60º Total acceptance – 1750 km2 sr yr (~ AGASA) Surface array events (after quality cuts)

Current rate - 18,000 / month Total -~180,000

Hybrid events (after quality cuts) Current rate – 1800 / month Total ~ 18000

CLF

DRUM Absolute calibration

Drum illuminator Atmospheric monitorng

LIDAR Central Laser Facility

(CLF)

LIDAR

The Pierre Auger Observatory has been conceived to study the cosmic ray spectrum in the Ultra High Energy region (above 1018 eV). Although the existence of such energetic particles is now beyond doubt, their nature has not been explained yet. To solve this enigma the esperiment will measure the properties of the highest energy cosmic rays with unprecedent statistical precision combinig two traditional and independent techniques in an unique and innovative hybrid detector.

Participating Countries (*Associate)

Argentina Czech Republic Mexico SpainAustralia France Netherlands United KingdomBolivia* Germany Poland USABrazil Italy Slovenia Vietnam*

Italian groups:Catania, L’Aquila, Lecce, Milano, Napoli, Roma, Torino

63 Institutions, 369 Collaborators

Aligned tanks

1.5

km