IDAPP 2D Meeting, Ferrara, May 3 2007
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IDAPP 2D Meeting, Ferrara, May 3 2007. Claudio Di Giulio University of Roma Tor Vergata, INFN of Roma Tor Vergata. The origin and nature of cosmic rays above 10 19 eV is not understood…. 38° South, Argentina, Mendoza, Malargue 1.4 km altitude. The physics case.

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IDAPP 2D Meeting, Ferrara, May 3 2007

Claudio Di Giulio

University of Roma Tor Vergata,

INFN of Roma Tor Vergata

The origin and nature of cosmic rays above 1019 eV is not understood…

38° South, Argentina, Mendoza, Malargue 1.4 km altitude

The physics case

The physics case

  • Evidence for Ultra High Energy Cosmic Rays > GZK cutoff ?

  • Near sources (<50 Mpc) ?

  • Production-acceleration mechanism?

  • Composition?

  • Challenging rate: ≈ 1 / Km2 / sr / century above 1020 eV!

Auger aims to measure the properties of the highest energy cosmic rays with unprecedented precision.

Status southern observatory malargue argentina

Status Southern Observatory Malargue, Argentina

Surface Array

1600 detector stations

1.5 Km spacing

3000 Km2

Fluorescence Detectors

4 “Eye”

6 Telescopes per“Eye”

24 Telescopes total

Last L.A. pmt!!

(Malrgue Oct.2006)


~ 1300 SD tanks, AllFD data taking.

The auger hybrid detector concept

300-400 nm light from de-excitation of atmospheric nitrogen (fluorescence light) ≈ 4 γ’s / m /electron

1019 eV 1010 e

Cross-calibration, improved resolution, control of systematic errors

The Auger hybrid detector concept

  • Fluorescence Detector

  • E + longitudinal development

  • Time ≈ direction

  • ≈ 10% duty cycle

  • Surface Detector

  • Shower size ≈ E

  • Time ≈ direction

  • 100% duty cycle

The surface detectors

GPS antenna (fluorescence light)



Solar panels

Lateral Distribution Function

Battery box



Tank signal


Plastic tank with 12 tons of water

3 – nine inch



The Surface Detectors

Shower energy ~ S1000

FADC (fluorescence light)


100 s

The Fluorescence Detector

UV filter window

PMT camera

Corrector ring

Spherical surface camera

440 PMT with light collectors

Large 300x300 field of view

1.5º pixel fov

3.4 m spherical mirror

FD calorimetry (fluorescence light)

Nγ≈ Edep






Np.e.= ∑ Nγ(λ) A’ ε(λ) T (λ)

λ Ri2

Fluorescence Geometry Detector Atmosphere


  • Air as an electromagnetic-hadronic calorimeter medium: 25 radiation lengths, 15 interaction lengths

  • UHE cosmic ray high energy secondary hadrons interaction vs decay very good hadronic calorimeter “e/h” → 1 (only 10% of energy not in e.m. cascade)

  • Robust energy determination for UHECR, small syst.

FD Systematic uncertainties

Tot. ΔE/E ~25%





Alternative Profile Rec. Method: the “spot method” (fluorescence light)

Claudio Di Giulio – Rome Tor Vergata University

  • Based on a detailed description of the light distribution on the camera surface

Spot coming from

spherical aberration

Inclusion of the

shower lateral


(D.Gora et al.,




➾ Prediction of the expected ADC traces from the hypotized long. profile

➾ Cherenkov contribution from the hypotized profile: NO iteration

➾ Description of the signal on the camera borders and

accounts for camera inhomogeneities (Mercedes)

GAP-Note 2006-026

SD Energy calibration with hybrid events (fluorescence light)

ICRC 2005

ICRC 2007

  • S38 and EFD uncertainties assigned on event by event basis.

  • (my contribute in the Auger Energy Spectrum Working Group)

Simultaneous observation by Fluorescence and Surface Detectors: only ≈10% of events but extraordinary impact on the quality of our physics results!

ESD = A (S38)b

b ~ 1

The power of hybrid…..We DO NOT depend on shower simulation!

Calibration uncertainty improves with hybrid statistics.

FD “Test Beam” (fluorescence light)

Central Laser Facility

355 nm


SD tank

26 km

Optic fiber

CROSS CHECK OF DRUM CALIB (fluorescence light) .

  • Beam of up to 8 mJ 355 nm photons

  • Rayleigh scattered to the FD

  • Energy probe measurement of the beam with 10% uncertainty

CLF (355 nm) 30 Km  difficult

Roving (337 nm) 3 Km  safer

Drum (375 nm)

May 2005 (Roving+CLF)

August 2006 (Roving)

Confirmed FD

photometric calibration

at the level 10%

Analysis complicated by variable and poor atmospheric conditions

GAP-Note 2006-095

ICRC 2005 p.335-338

My contributes: (fluorescence light)

  • Study of “stereo” FD events (geometry and profile reconstruction) [1].

  • Study of CLF laser shots with FD [2] and cross-check of the FD optical calibration[4].

  • Study and implementation of new method for the shower profile reconstruction of the FD events [3].

  • Collaboration in the AIRFLY experiment.[5]

  • SD Calibration for ICRC 2007 Auger Energy Spectrum (under studying ).

[1] Eventi Stereo dell’Osservatorio Auger, Physics Degree Thesis Università degli Studi di Roma Tor Vergata. ROM2 F/2005/17

[2] ICRC 2005 (108): The central laser facility at the Pierre Auger Observatory.

[3]GAP-Note 2006-026: A New Methods for the Longitudinal Profile Reconstruction of the Auger Fluorescence Detector Events.

[4]GAP-Note 2006-026: Cross-check of the Fluorescence Detector optical calibration with laser shots.

[5]Astroparticle Physics: In press Accepted Manuscript Measurement of the pressure dependence of air fluorescence emission induced by electrons.