Recent results from Pierre Auger Observatory J. R. T. de Mello Neto Universidade Federal do Rio de Janeiro XI International Conference on Hadron Spectroscopy – HADRON 05 CBPF- Rio de Janeiro

Outline Open questions The Auger Observatory The detector’s performance The model-independent energy spectrum Anisotropies Blind source search Photon fraction limit Perspectives Ref: Auger contributions in the proceedings of ICRC 05 – Pune, India

S. Swordy Cosmic flux vs. Energy Roughly a single power law Indication of Fermi shock acceleration mechanism? Spectrum extends beyond the energies that can be produced with shock acceleration in known shocks. UHECR one particle per century per km 2 many interesting questions

Open questions How cosmic rays are accelerated at ? What are the sources? How can they propagate along astronomical distances at such high energies? Are they substantially deflected by magnetic fields? Can we do cosmic ray astronomy? What is the mass composition of cosmic rays?

GKZ suppression Cosmic rays E = eV interact with 2.7 K photons In the proton frame Proton with less energy, eventually below the cutoff energy E GZK = 5x eV Universe is opaque for E > E GZK ! Photon-pion production Photon dissociation

Detection techniques Particles at ground level large detector arrays (scintillators, water Cerenkov tanks, etc) detects a small sample of secondary particles (lateral profile) 100% duty cicle aperture: area of array (independent of energy) primary energy and mass compostion are model dependent Fluorescence of N 2 in the atmosphere calorimetric energy measurement as function of atmospheric depth only for E > eV only for dark nights (14% duty cicle) requires good knowledge of atmospheric conditions aperture grows with energy, varies with atmosphere

The Auger Observatory: Hybrid design A large surface detector array combined with fluorescence detectors results in a unique and powerful design; Simultaneous shower measurement allows for transfer of the nearly calorimetric energy calibration from the fluorescence detector to the event gathering power of the surface array. A complementary set of mass sensitive shower parameters contributes to the identification of primary composition. Different measurement techniques force understanding of systematic uncertainties in each.

Pierre Auger South Observatory 3000 km 2

A surface array station Communications antenna GPS antenna Electronics enclosure Solar panels Battery box 3 photomultiplier tubes looking into the water collect light left by the particles Plastic tank with 12 tons of very pure water

Electronics temperature and VEM charge evolution over a week in April 2005 Surface detector Station 102 Los Leones Coihueco Los Morados Loma Amarilla Trigger rates: T1: First level trigger T2: Second lever trigger T2: Second lever trigger ToT: Time over Threshold ToT: Time over Threshold

Surface detector Correlation of the trigger rate with temperature: T ± 0.03 % per degree T ± 0.05 % per degree ToT 0.20 ± 0.50 % per degree SD array operates with stable trigger threshold even with 20 degrees daily temperature variations Surface detector array on-time in 2004: 94.3% Evolution of the physics event rate as a function of time. It is roughly related to the number of active stations by 0.9 event per day per station

The fluorescence detector Los Leones telescope

The fluorescence telescope 30 deg x 30 deg x 30 km field of view per eye

Atmospheric monitoring and FD detector calibration Atmospheric monitoring Central Laser Facility (laser optically linked to adjacent surface detector tank) Atmospheric monitoring Calibration checks Timing checks Absolute calibration Drum for uniform illumination of each fluorescence camera – part of end to end calibration. Lidar at each fluorescence eye for atmospheric profiling - “shooting the shower”

Fluorescence detector Absolute calibration has been performed with a precision of 12%, with improvements planned to reduce this uncertainty to 8% The estimated systematic uncertainty in the reconstructed shower energy is 25%, with activity underway to reduce this significantly

Hybrid detection Golden events: independent triggers Simultaneus detection in the sky and in the ground Sub-threshold events: FD promoted triggers

Hybrid detector The hybrid analysis benefits from the calorimetry of the fluorescence technique and the uniformity of the surface detector aperture

Construction progress 1208 surface detector stations deployed 951 with eletronics and sending data Three fluorescence buildings complete each with 6 telescopes In construction

Angular resolution Hybrid events: 0.6° Surface detector: 2.2° for 3-fold events (E < 4 EeV) 1.7° for 4-fold events (3 < E < 10 EeV) 1.4° for 5 or more stations (E > 8 EeV) SD only Comparison hybrid and SD only  = 1.54 ± 0.05  / 14  = 1.30 ± 0.04  / 14 SD  Hyb  = 1.2 SD  Hyb  = 1.1  = 1.24 ± 0.07  / 14  = 0.98 ± 0.06  / 12 Sd  Hyb  = 0.66 Sd  Hyb  = 0.72

High energy events The highest energy SD event (86 EeV) Properties of the 20 most energetic events

A Hybrid event

Spectrum: previous claims Continuation beyond the GZK limit? Extragalatic sources distributed uniformly AGASA M. Takeda et al., PRL 81 (1998) 1163

Spectrum: previous claims HiRes HiRes mono spectrum consistent with GZK suppresion HiRes Collab., arXiv:astro-ph/ Fit to unbroken power law: Fit taking into account GZK suppression:

Energy spectrum for Auger Observatory Based on fluorescence and surface detector data First model- and mass-independent energy spectrum Power of the statistics and well-defined exposure of the surface detector Hybrid data stablishes conection between ground parameter S and shower energy Hybrid data confirm that SD event trigger is fully efficient above 3x10 18 eV for θ<60 o Energy scale of the fluorescence detector (nearly calorimetric, model independent energy measurement)

Constant intensity cut Cosmic rays are nearly isotropic: Constant intensity cut ↔ constant energy cut For a fixed I 0 find S(1000) at each θ such that I(>S(1000)) = I 0 The relative values of S(1000) give CIC(θ) Normalized so that CIC(38 o ) = 1; 38 o is the median zenith angle Define the energy parameter S 38 = S(1000)/CIC(θ) for each shower : “the S(1000) it would have produced if it had arrived at 38 o zenith angle”

Energy spectrum for Auger Observatory Constant Intensity CutCorrelation FD-SD

Energy spectrum for Auger Observatory Estimated Spectrum Percentage deviation from the best-fit power law Error bars Poisson statistics Systematic uncertainty: double arrows at two different energies

Energy spectrum for Auger Observatory No events above in spectrum Two sigma upper limit is consistent with AGASA flux With current level of statistics and systematics, no solid conclusion is possible

Source at the Galactic center AGASA 20 o scales – eV N. Hayashida et al., Astroparticle Phys. 10 (1999) 303 Significance (σ) Cuts are a posteriori Chance probability is not well defined 22% excess

Source at Galactic center J.A. Bellido et al., Astroparticle Phys. 15 (2001) 167 SUGAR 85% excess – eV 5.5 o cone

Source at the Galactic Center Significance Coverage map 1.5 o scale 3.7 o scale (SUGAR like)13.3 o scale (AGASA like)

Source at the Galatic center AGASA Original Cuts (1.0 – 2.5 EeV) top hat 20°1155 / ratio = 1.00 ± 0.03 Enlarge energy range (0.8 – 3.2 EeV) top hat 20°1896 / SUGAR (0.8 – 3.2 EeV) top hat 5°144 / 150.9ratio = 0.95 ± 0.08

Point sources at the Galactic center SD only: Gaussian filtering 1.5 degree exp/obs 24.3/23.9 if  S   CR then for 0.8 EeV < E < 3.2 EeV  S < 2.5    m -2 s 95 % Hybrid : Top hat window 1.0 degree Exp/obs 4/3.4 if  S   CR then for E > 0.1 EeV  S < 1.2   m -2 s 95 % Excess / Significance maps build using the individual pointing direction of the events.  uncertainty in CR flux  Iron/proton detection efficiency ratio

Galactic plane and Super Galactic plane A) GP 1-5 EeV 5077 / B) SGP > 5 EeV 241 / C) SGP > 10 EeV 68 /67.4

Prescription results For each target: specify a priory probability levels and angular scales avoids uncertainties from “penalty factors” due to a posteriori probability estimation Targets: low energy: Galactic center and AGASA-SUGAR location high energy: nearby violent extragalactic objects

Blind search for point sources Exposure map Events map Galactic coordinates 1 – 5 EeV smoothed top-hat window 5 o HEALPIX pixielization

Blind search for point sources Li, Ma ApJ 272, (1983) significance All distributions consistent with isotropy

Primary photon fraction upper limit Limited by statistics, Considerable increase in a near future. Obtain a bound at higher energy

Primary photon fraction upper limit Further exploit surface detector observables

Conclusions January June 2005 SD Array: Unprecedented statistics in southern hemisphere (anisotropy) Unprecedented statistics in southern hemisphere (anisotropy) Exposure 1750 km 2 sr yr (1.07 total AGASA) Exposure 1750 km 2 sr yr (1.07 total AGASA) On time 94.3% On time 94.3% Gain one order of magnitude within the next two years (1500 physical events per day) Gain one order of magnitude within the next two years (1500 physical events per day)Hybrid: Unprecedented core location and direction precision  excellent shower development and energy measurements (energy spectrum & photon limits) This is just the beginning! We have a lot of work ahead, including the Auger North Observatory! Thanks!