Michael Prouza Center for Particle Physics Institute of Physics Academy of Sciences of the Czech Republic Prague Studies of the ultra-high energy cosmic ray composition at the Pierre Auger Observatory Michael Prouza Center for Particle Physics Institute of Physics Academy of Sciences of the Czech Republic Prague

The Pierre Auger Observatory Participating countries: Argentina, Australia, Bolivia *, Brazil, Czech Republic, France, Germany, Italy, Mexico, Netherlands, Poland, Portugal, Slovenia, Spain, United Kingdom, USA and Vietnam * * - associated countries More than 250 PhD scientists from more than 60 institutions from 15 (+2) countries. Participating countries are in cyan. 2/21

Pierre Auger Observatory Southern hemisphere: Malargüe, Mendoza province, Argentina Northern hemisphere (planned): Lamar, Colorado, USA The construction of the southern site in Argentina is (almost) completed. See for details Lifetime of the observatory: yrs 3/21

The Pierre Auger Observatory = hybrid detector of cosmic rays The array of surface Cherenkovov detectors is accompanied with system of fluorescence telescopes, which observes faint UV/visible light during clear nights. This fluorescence light origins as by-product during the interactions of shower particles with the atmosphere. Scheme of hybrid detector function 4/21

Ground detectors of the Pierre Auger Observatory Ground detectors: Covered surface: 3000 km 2 Number of detectors: 1600 Type of detector: Detector of Cherenkov radiation, each consisting of litres of ultrapure water and equipped with 3 photomultipliers. Spacing between detectors: 1.5 km. 5/21

11 square meter segmented mirror Aperture stop and optical filter 440 pixel camera Fluorescence detectors of the Pierre Auger Observatory Fluorescence telescopes: Number of telescopes: 24 Mirrors: 3.6 m x 3.6 m with field of view 30º x 30º, each telescope is equipped with 440 photomultipliers. 6/21

Evolution of the hybrid detector Production of scientific data since late /21

Outlook Comparison of integrated aperture Integrated exposure (1 Jan 2004 – 31 Dec 2008): 12,790 km 2 sr yr 8/21

Auger Energy Spectrum For more details see arXiv: /21

Auger Energy Spectrum 10/21

Mass Composition For more details see arXiv: Or talk by Michael Unger: 11/21

Shower Profile 12/21

FD mass-sensitive parameters Average Shower Maximum, Shower-to-shower fluctuations, RMS(X max ) 13/21

FD mass composition results 14/21

SD mass-sensitive parameters Signal risetime, t 1/2 15/21

SD mass-sensitive parameters Deviation to average risetime, Δ (θ - zenith angle) For more details see arXiv: Or Hernan Wahlberg’s talk at ICRC’09, Lodz 16/21

SD mass-sensitive parameters Risetime asymmetry, b/a (t 1/2 /r = a + b cos ζ; ζ - shower plane azimuth) XAsymMax, sec θ position, where b/a is maximal 17/21

Mass composition summary Elongation rate flattens at high energy Fluctuations decrease with energy Two options (both can be simultaneously true): 1.) Cosmic rays heavier at high energy 2.) Hadronic models at UHE energy need modification 18/21

3.8% 2.4% 3.5% 2.0% 5.1% 31 % Photon limit Piotr Homola (Pierre Auger Coll.), ICRC’09, Lodz; arXiv /21

COSMOGENIC s Neutrino limit J. Tiffenberg (Pierre Auger Coll.), ICRC’09, Lodz; arXiv /21

Anisotropy D. Hague (Pierre Auger Coll.) & J. De Mello Neto (Pierre Auger Coll.), ICRC’09, Lodz; arXiv AGN correlation Search for intrinsic anisotropy 21/21