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

The physics case Evidence for Ultra High Energy Cosmic Rays > GZK cutoff ? Near sources (<50 Mpc) ? Production-acceleration mechanism? Composition? Challenging rate: ≈ 1 / Km 2 / sr / century above eV! Auger aims to measure the properties of the highest energy cosmic rays with unprecedented precision.

Status Southern Observatory Malargue, Argentina ~ 1300 SD tanks, All FD data taking. Last L.A. pmt!! (Malrgue Oct.2006) CLF Surface Array 1600 detector stations 1.5 Km spacing 3000 Km 2 Fluorescence Detectors 4 “Eye” 6 Telescopes per“Eye” 24 Telescopes total

The Auger hybrid detector concept Fluorescence Detector E + longitudinal development Time ≈ direction ≈ 10% duty cycle nm light from de- excitation of atmospheric nitrogen (fluorescence light) ≈ 4 γ’s / m /electron eV e Surface Detector Shower size ≈ E Time ≈ direction 100% duty cycle Cross-calibration, improved resolution, control of systematic errors

The Surface Detectors Communications antenna Electronics enclosure Solar panels Battery box 3 – nine inch photomultiplier tubes Plastic tank with 12 tons of water GPS antenna S 1000 Tank signal Lateral Distribution Function Shower energy ~ S 1000

3.4 m spherical mirror UV filter window Corrector ring PMT camera The Fluorescenc e Detector FADC trace 100  s Spherical surface camera 440 PMT with light collectors Large 30 0 x30 0 field of view 1.5º pixel fov

FD calorimetry 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. N p.e. = ∑ N γ (λ) A’ ε(λ) T (λ) λ R i 2 Fluorescence Geometry Detector Atmosphere yield FD Systematic uncertainties Tot. ΔE/E ~25% N γ (λ) RiRi A T(λ) ε(λ) N γ ≈ E dep ~15% ~10% 40

Alternative Profile Rec. Method: the “spot method” Based on a detailed description of the light distribution on the camera surface Claudio Di Giulio – Rome Tor Vergata University f PMT (2) f PMT (1) Spot coming from spherical aberration Inclusion of the shower lateral size (D.Gora et al., astro-ph/ ) ➾ 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

SD Energy calibration with hybrid events The power of hybrid….. We DO NOT depend on shower simulation! E SD = A (S 38 ) b b ~ 1 Calibration uncertainty improves with hybrid statistics. ICRC 2005 ICRC 2007 S 38 and E FD 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!

FD “Test Beam” Central Laser Facility 355 nm laser Optic fiber SD tank 26 km

CROSS CHECK OF DRUM CALIB. 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 Beam of up to 8 mJ 355 nm photons Rayleigh scattered to the FD Energy probe measurement of the beam with 10% uncertainty GAP-Note ICRC 2005 p

My contributes: 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 : A New Methods for the Longitudinal Profile Reconstruction of the Auger Fluorescence Detector Events. [4]GAP-Note : 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.