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The Pierre Auger Observatory

Explore the largest cosmic ray detector, Pierre Auger Observatory, designed to study UHECR and solve the GZK puzzle. Understand its hybrid detection system, current deployment status, and calibration methods.

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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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