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The Pierre Auger Observatory

The Pierre Auger Observatory. Nicolás G. Busca Fermilab-University of Chicago. FNAL User’s Meeting, May 2006. Ultra High Energy CR (UHECR) spectrum. Trans GZK events?. Ankle. Cosmic Ray (CR) Spectrum.

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The Pierre Auger Observatory

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  1. The Pierre Auger Observatory Nicolás G. Busca Fermilab-University of Chicago FNAL User’s Meeting, May 2006

  2. Ultra High Energy CR (UHECR) spectrum Trans GZK events? Ankle Cosmic Ray (CR) Spectrum The GZK puzzle: UHECR lose energy very quickly by collisions with the CMB, so they should come from nearby sources. But there are no known nearby sources of CR! (1 particle per km2-century) FNAL LHC by S. Swordy

  3. The Detection principle: observe the CR shower in the atmosphere. We try to observe 1 particle per km2 per century. Such a low flux can only be detected with extremely large detectors: the atmosphere is an essential component!

  4. The Pierre Auger Observatory • Is the largest ground array detector of cosmic rays • It’s goal is to study UHECR (E>1018eV) • It’s design ensures high statistics and a experimentally based energy calibration • Detector resolutions are also experimentally determined. Systematic uncertainties are traceable. Questions addressed by Auger: • What are UHECR? • Where do they come from? • Are they accelerated or do they come from super heavy particle decay? • Shape of the spectrum…

  5. The Hybrid Detector • Auger combines two detection techniques: • Ground array of water cherenkov detectors (the surface detector or “SD”) • The SD provides high statistics ~100% duty cycle. • 24 fluorescence telescopes (the fluorescence detector or “FD”) The FD has only a 10% duty cycle: operates only on clear moonless nights. It provides a direct measurement of the primary energy.

  6. PAO current deployment status • 950 stations operating, >1200 deployed (no electronics yet) • 18 fluorescence telescopes • Aperture ~ 2000 km2sr • Official data taking started in Jan. 2004 • Expect deployment completion in 2007 60 km

  7. Water tank features: • 12 tons of purified water • 3 PMTs measure light deposited by shower particles • electronics 25ns FADC • self-calibration using atmospheric muon flux • power supplied by solar panels • GPS timing and positioning radio antenna GPS solar panel electronics PMT purified water battery box The SD 1600 water cherenkov detectors, 3000 km2 ~60km

  8. An example SD event Timing information is used to reconstruct the shower direction The SD samples a transverse section of the shower. Timing allows for a direction measurement. The signal amplitude characterizes the energy of the shower. shower front SD stations Event 1225537 A fit to a lateral distribution function determines amplitude 6km E ~ 80EeV

  9. The FD 4 buildings with 6 telescopes each • The camera: • Array of 440 pmt (1.5deg each) Sketch of a fluorescence telescope: spherical mirror camera diaphragm

  10. An example hybrid event Highest signal tank pixels

  11. SD-FD energy calibration Calibration curve from hybrid events:

  12. The current Auger Spectrum (first 2 years of data) • Features: • No composition assumption for 3EeV<E<25EeV • No assumption on hadronic interaction models • Assumes no dramatic composition change occurs above 25EeV • 30% energy systematic uncertainty at low energies and 50% at high energies (due to extrapolation of calibration curve)

  13. other Results I didn’t have time to talk about: • Sources and anisotropy studies: • No excess from the Galactic Centre as claimed by AGASA and SUGAR (Lettesier-Selvon et al., 2005). • No excess from galactic/super-galactic plane • Photon Flux: • < 26% at above 10EeV • Auger as a gamma-ray burst observatory: • Detection capabilities complementary to satellite detectors (Allard et al., 2005)

  14. Some answers and prospects… • Is there a GZK suppression in the spectrum? • Not enough statistics to address this question yet. Aperture • will multiply by ~3 once the observatory is finished. • Where do CR come from? • No evidence for individual sources, correlations with • the galactic plane or global anisotropy. • What are CR anyways? • < 26% of photons above 1019eV. Prospects to study • composition by exploiting other capabilities of the detector. • Prospects • Auger North: site selected, R&D phase.

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