Unraveling Mysteries of Ultra-High Energy Cosmic Rays with the Pierre Auger Observatory

1. Detectingultrahighenergy cosmicrayswith the Pierre Auger Observatory Tome Antičić

2. What we (don’t) know about UHECRs • Cosmic rays are high energy charged particles which rain down on our planet. • 85% protons, 12% He nuclei, 2% electrons, 1% heavier nuclei. • Ultra-High Energy Cosmic Rays are those which have energies in excess of 1018 eV (1 EeV). • We know: • their energies (up to 1020 eV). • their overall energy spectrum • We don’t know: • where they are produced(Local or cosmological) • how they are produced/accelerated (Top-down or bottom-up) • How can they propagate along astronomical distances at such high energies(GZK) • what they are made off (protons, heavier nuclei, photons,neutrinos) • exact shape of the energy spectrum • `Are they substantially deflected by magnetic fields • Can we do cosmic ray astronomy??

3. Cosmic ray flux vs energy Highest energy event: 3.2 x 1020 eV Fly’s Eye in Utah in 1991 • (nearly) uniform power-law spectrum spanning 10 orders of magnitude in E and 32 in flux! • structures : • ~ 3 – 5 1015 eV: knee • change of source? new physics? • ~ 3 1018 eV: ankle • transition galactic – extragalatic? • change in composition? The Auger project is focused on the highest energies. many Joules in one particle! …a tennis ball at 60 km per hour • UHECR • one particle per century per km2

4. Candidates of Sources for Bottom-up Models

5. Unified models of AGNs

6. Cosmic microwave background interaction p + CMB  p + 0  n + + • For energy > 5 * 1019 Greisen, Zatsepin-Kuzmin (GZK) Cut Off Particles > 5 * 1019 eV must be < ~ few*50 Mpc away

7. Magnetic Field Charged particles are randomized by the interstellar magnetic field in the Milky Way (~0.5kpc, 2μG) the intergalactic magnetic field at the highest energies(1.0Mpc, 1nG) At ~1020 eV one could perhaps do cosmic ray astronomy in the nearby universe. Low-energy cosmic ray sky

8. How UHE Cosmic Rays interact with the atmosphere?

15. electrons/positrons photons Big Mess! muons neutrons Seems hopeless...

16. Ground level detectors • large detector arrays (scintillators, water Cerenkov tanks, etc) • detects a small sample of secondary particles (lateral profile) • 100% duty cicle • aperture: area of array • differences in arrival times—› trajectory • total amount of muons —› indicator for primary type • primary energy and mass composition are model dependent (rely on Monte Carlo simulations based on extrapolations of the hadronic models constrained at low energies by accelerator physics) • Shower is sampled at one altitude only, development of the shower in the atmosphere is not seen. • 111 Electron Detectors • 100 km2 • 27 Muon Detectors • Operation 1991 - 2004 ex: AGASA 0 4km

17. Flourescence detectors • Charged particles of theshower excitenitrogen molecules, which fluoresce in the UV (80% between 300 and 450 nm).. • Fluorescence light can be detected with photomultipliers observing the night sky - the shower is seen by a succession of tubes. • Air fluorescence detectors observe shower development in the atmosphere and provide a nearly calorimetric energy estimate (the amount of light is proportional to the number of particles in the shower). • Large instantaneous detector volume. • Operation on clear, moonless nights with good atmospheric conditions, so small duty cycle about 10%. • only for E > 1017 eV • requires good knowledge of atmospheric conditions(aerosols, atmospheric monitoring necessary: T, P, clouds) • aperture grows with energy • Shape, direction, shower maximum Xmax -> CR direction, primary type • Showers from heavier nuclei develop earlier in the atm with smaller fluctuations • Xmax is increasing with energy HiRes: fluorescence detector [350 km2 sr]

18. Pierre Auger Observatory Auger north is planned in Colorado 1938 Pierre Auger discovers Extensive air showers 17 Countries 70 Institutions ~400 Scientists Auger south is here. Malargue is a small town on the high plains not far from a ski area in the Andes.

19. Pierre Auger Observatory Hybrid Detector • Auger combines a surface detector array (SD) and fluorescence detectors (FD). • 1600 surface detector stations with 1500 m distance. • 4 fluorescence sites overlooking the surface detector array from the periphery. • 3000 km2 area. • 1 Auger year = 30 AGASA years (SD). http://www.auger.org

20. A surface array station Communications antenna GPS antenna Electronics enclosure Solar panels Battery box 3 9 inch photomultiplier tubes looking into the water collect light left by the particles Plastic tank with 12 tons of very pure water

21. Aligned water tanks

22. Six Telescopes viewing 30°x30° each • 4 FD sites, each with 6 telescopes • FD telescope: • 3.5 x 3.5 m segmented, sperical mirror • camera with 440 hexagonal photomultiplier tubes records arrival time and amount of light at each pixel • FOV: 30° x 28.6° • can view EAS up to 20km distance • zenith angles 0°-60°

23. The fluorescence telescope 30 deg x 30 deg view per telescope

24. Extracting information from an EAS • Tank timing • Arrival direction • Number of particles in tanks • Total Energy • Telescope image (digital camera like) • Arrival direction • Light detected • Total Energy • Redundant measurement for cross-checks

25. •LIDAR at each eye •cloud monitors at each eye • central laser facility • regular balloon flights Atmospheric Monitoring steerable LIDAR facilities located at each FD eye Central laser facility (fiber linked to tank) LIDAR at each FD building • light attenuation length • Aerosol concentration Balloon probes  (T,p)-profiles

26. Central campus with visitors center Assembly building, yard

27. http://www.auger.org.ar

28. Fluorescence Detector Event • Signal and timing time

29. Typical flash ADC trace at about 2 km Detector signal (VEM) vs time (µs) Lateral density distribution PMT 1 PMT 2 PMT 3 Surface Detector Event 18 detectors triggered θ~ 48º, ~ 70 EeV Flash ADC traces Flash ADC traces -0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 µs

30. Hybrid Event longitudinal profile

31. S38 (1000)vs. E(FD) 4 x 1019 eV 387 hybrid events

32. First 4-fold hybrid on 20 May 2007 First hybrid qudriple event! Signal in all four FD detectors and 15 SD stations! 20 May 2007 E ~ 1019 eV

33. RESULTS- energy spectrum Exp Obs >1019.6 132 +/- 9 51 > 102030 +/- 2.5 2 Slope = -2.62 ± 0.03 Calibration unc. 18% FD syst. unc. 22% 5165 km2 sr yr ~ 0.8 full Auger year • sharp suppression in the spectrum is seen for the last energy decade • pure power law is rejected with 6σ ( E > 1018.6 eV ) and 4σ( E > 1019 eV )

34. RESULTS- GZK cuttoff confirmed Residuals from a standard spectrum -3.30 ± 0.06 -2.62 ± 0.03 - 4.1 ± 0.4

35. RESULTS- Auger Chemical Composition Probably not pure protons

36. AGN Cen A II. The UHECR Sky is anisotropic RESULTS- Auger Highest-energy Sky Map New data confirms correlation with AGN clustering. Chance probability: 2× 10-3 • 472 AGN with z < 0.018 (red crosses), 27 cosmic ray arrival directions with 3.1º circle, color indicates relative exposure, position of CenA (white cross).

37. What does this mean? • The highest-energy cosmic-ray sky is anisotropic!(sources still unclear) • Intergalactic B-field small, cosmic rays good messengers for mapping the nearby universe • Astrophysics! • UHECR source identification, study • Timely concurrent operation with gamma-ray, neutrino, and low-energy photon observatories • UHECR astronomy possible! The beginning of “charged particle astronomy”!

38. sampling the sky with few events

39. Low-energy cosmic ray sky Cosmic Ray Astronomy? 0º 5º

40. FUTURE- Proposed Layout in Southeast Colorado

41. Down-going neutrinos Implications for Neutrino Astrophysics Old hadronic shower Young neutrino shower

42. Earth-skimming neutrinos Implications for Neutrino Astrophysics

43. Auger (and HiRes) neutrino limits Implications for Neutrino Astrophysics Pierre Auger Collaboration 2008, PRL submitted, arXiv:0712.1909(HiRes limits from: K. Martens for the HiRes Collaboration 2007, arXiv: 0707.4417)

44. Coherent Geosynchrotron Radio Pulses in Earth Atmosphere UHECRs produce particle showers in atmosphere Shower front is ~2-3 m thick ~ wavelength at 100 MHz e± emit synchrotron in geomagnetic field Emission from all e± (Ne) add up coherently Radio power grows quadratically with Ne EarthB-Field~0.3 G shower fronte± ~50 MeV Geo-synchrotron coherentE-Field • Initial motivation through prediction of Cherenkov-like radio emission process (Askaryan 1962).

45. Advantages of Radio Emission from Air Showers Cheap detectors High duty cycle (24 hours/day) Low attenuation, good calibratability (also distant and inclined showers) Bolometric, i.e. good energy measurement (integral over shower evolution) Interferometry gives precise directions Complementarity with SD gives composition But, does it work? Problems before 2001: No theoretical understanding No experimental understanding since 1974 .

46. LOPES:LOFAR Prototype Station 250 particle detector huts 30 Radio Antennas40-80 MHzraw RF data buffer LOPES Collaboration: MPIfR Bonn, ASTRON, FZ Karlsruhe, RU Nijmegen, KASCADE Grande