1. MEASUREMENTS OF COSMIC RAYS WITH PRIMARY ENERGIES UP TO 1020 eV
Recent results from the Pierre Auger Observatory
Danilo Zavrtanik
Pierre Auger Collaboration
University of Nova Gorica
Slovenia
I will talk mainly about:
P. Auger Observatory,
Progress in the observatory construction.
Performance of the detectors now in operation.
The quality of the data.
Results.
But let me start with a brief overview about UHECR
Institut fur Hochenegiephysik
Austrian Academy of Sciences
Wien, May 25, 2010 1

2. OUTLINE Brief overview of UHECR P. Auger Observatory Conclusions
Experimental method
Results
Spectrum
Composition
Photon flux
Arrival direction
Conclusions 2

3. WHY STUDY UHECRs? Measured spectrum extends to E > 1020 eV
Where and how are cosmic rays
accelerated to these energies
No known astrophysical sources
seem able to produce such
enormous energies
Chemical composition unknown
The high energy end of the
spectrum probes physics at
energies out of reach of any man
made accelerator
Possible new physics 3

4. WHY STUDY UHECRs? Accesible to experiment Astronomy with charged
Energy spectrum
Chemical composition
Arrival directions
Astronomy with charged
particles?
Problems
Very low rates call for giant
observatory
Protons and nuclei are charged and
therefore deflected by galactic and
intergalactic magnetic fields
 1 particle/km2/century or a few particles/km2/millenium 4

5. POSSIBLE SOURCES Bottom – Up (Astrophysical Acceleration Mechanisms)
Shock acceleration in extended objects or
catastrophic events
Acceleration in strong fields associated with
accretion disks and compact rotating galaxies
Collision of galaxies NGC4038 and NGC4039
as seen by Hubble Space Telescope

6. LIMITS TO ACCELERATION
Hillas plot
No good candidates
for ZeV accelerators
in the known Universe!

7. Models do not reproduce the measured flux which is too high !
POSSIBLE SOURCES
Top - Down Models
Exotic Mechanisms
Decay of topological deffects
Relic monopoles
Etc.
New Physics
Supersymmetric particles
Strongly interacting neutrinos
Decay of massive new long lived particles
Violation of LI
Models do not reproduce the measured flux which is too high !

8. PROPAGATION
All known particles except neutrinos undergo interactions with Cosmic Microwave Background
Example:
p + 2.7K  p + 0
 n + +
For energy > 5 x 1019 p N Δ+
γ2.7K p

9. Greisen-Zatsepin-Kuzmin Cut-off Size of the observable Universe
PROPAGATION
Greisen-Zatsepin-Kuzmin Cut-off
(Greisen ‘66, Zatsepin & Kuzmin ’66)
Particles > 5 x 1019 eV
must be < 50 Mpc away
Size of the observable Universe
~ MPc
Cut-off in the spectrum or
UHECR comes from our neighbourhood or
New physics at work

10. MAGNETIC FIELD DEFLECTION
Above 100 EeV Df < larger than experimental resolution!
A window to CR astronomy ?

11. EXPERIMENTAL TECHNIQUE
Measurement of extensive air showers
Calorimetry
Calorimeter – atmosphere
Read out
Fluorescence detectors
Particle detector array

12. EXPERIMENTS PRESENT PAST Yakutsk, Russia Volcano Ranch, USA
Scintillators, Atmospheric Čerenkov
PAST
Volcano Ranch, USA
Scintillators
Haverah Park, UK
Water Čerenkov
SUGAR, Australia
Fly’s Eye, USA
Atmospheric Fluorescence
AGASA, Japan
Scintillators, muon detectors
HiRes, USA
P. Auger, Argentina
Hybrid: Atmospheric Fluorescence, Water Čerenkov
Telescope Array
Atmospheric Fluorescence, Scintillator Array
FUTURE
AirWatch: OWL – JEM/EUSO - TUS
Atmospheric Fluorescence

13. PIERRE AUGER OBSERVATORY
A cosmic ray observatory designed for a high statistics study of The Highest Energy Cosmic Rays ( eV)
using
Two Large Air Shower Detectors
Mendoza, Argentina
(observatory fully operational)
Colorado, USA
(design and proposal in preparation)
The objective of the Pierre Auger Observatory is to make a full sky, high statistics, study of cosmic rays at the highest energies.
The Auger Observatory will consist of sites – one in each hemisphere at mid latitude – so as to have full sky coverage.
The southern site of the Auger Observatory is located in the province of Mendoza, Argentina near the city of Malargüe. The northern site will be in south east Colorado.

14. ~ 450 physicist from ~ 100 institutions
P. AUGER COLLABORATION
Argentina
Australia
Bolivia
Brazil
Croatia
Czech Republic
France
Germany
Italy
Mexico
Netherlands
Poland
The Observatory is being built by an eclectic mix of high energy physicists, low energy physicists, cosmic ray physics and a few astronomers from 63 institutions in 17 countries.
The Auger collaboration is unique among large international science projects in that there is no dominant country or institution – indeed a true partnership.
The only cosmic ray experiment of a size of a High energy physics collaboration.
Portugal
Slovenia
Spain UK
USA
Vietnam
~ 450 physicist from ~ 100 institutions
18 countries 14

15. SOUTHERN OBSERVATORY HYBRID DETECTOR SD FD World largest array
~ surface detectors with 1.5 km spacing FD
4 fluorescence buildings with 6 telescopes each
World largest array
3.000 km2 area
1 Auger year = 30 AGASA years (SD)
Here is a summary of construction progress.
The blue area shows the areas where detector stations have been installed. Over half of the array has been deployed.
Three fluorescence enclosures and their 18 telescopes are in operation. The fourth fluorescence enclosure is under construction.
As you see the Observatory is still very much work in progress. We have been taking data while construction continues. 15

16. Event timing and direction determination
SURFACE DETECTOR ARRAY
Event timing and direction determination
Shower timing Shower angle
Particle density Shower energy
Muon number Measure of
Pulse rise time primary mass 16

17. WATER ČERENKOV DETECTOR17

18. FLUORESCENCE DETECTOR
Shower ~ 90% electromagnetic
Ionization of nitrogen measured directly
Calorimetric energy measurement
Measure of shower development 18

19. FLUORESCENCE DETECTOR
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.
May 3, 2009

20. HYBRID OPERATION
May 3, 2009

21. SPECTRUM

22. ENERGY MEASUREMENT Fluorescence detector Surface detector array
Measure light intensity along the track and integrate.
Nearly calorimetric, model and mass independent.
Surface detector array
Particle density S at fixed distance to the shower core is related to the shower energy via simulations.
S(1000)‏
Signal Size [VEM]
Distance to shower core [m] 23

23. ENERGY DETERMINATION Energy scale is determined from data
Aperture is determined by geometry of surface detector array.
Hybrid data is used to establsh conection between S(1000) and shower energy as measured by FD
Correction for elevation angle relies on measured data only (CIC).
Energy scale is free of simulations.
hybrid events
Here is a plot of S(1000) – corrected for zenith angle - vs. hybrid reconstructed fluorescence energy from which the energy converter can be obtained.
Note that the systematic error grows when extrapolating this rule to 100 EeV!
Our rapidly increasing data set and reduced systematic uncertainties will be able to dramatically improve the precision of the energy scale.
Ground parameter
Energy from FD 24

24. ENERGY SPECTRUM (< 600)
Spectral index changes from ± 0.02 ± 0.06 to 4.2 ± 0.4 ± 0.1.
Comparison of spectrum to unbroken power law (TP test): 6 σ.
Confirms observation of similar suppression in HiRes data.
Consistent with longstanding prediction by Greisen and Zatsepin-Kuzmin (GZK) that cosmic ray flux is attenuated above ~ 6×1019 eV due to interaction with CMB
Implications if GZK: cosmic rays above ~ 6×1019 eV originate within 100 Mpc.
This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 25

25. SYSTEMATIC ERRORS
Systematic uncertainties in the air fluorescence yield currently dominate but efforts to reduce this error are underway.
This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 26

26. INCLINED EVENT
This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 28

27. INCLINED SHOWERS
This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 29

28. SPECTRUM - INCLINED EVENTS
This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 30

29. SPECTRUM COMPARISON
This slide shows a comparison of the Auger spectrum with that of AGASA and HiRes 1 (mono). The Auger points are about 25% below those of AGASA and slightly lower ~ 10% than HiRes. 31

30. CHEMICAL COMPOSITION

31. CHEMICAL COMPOSITION
Speed of air shower development depends on the mass of the primary: a heavier nucleus induces earlier shower development.
FDs measure the height of the shower maximum directly, but intrinsic fluctuations in the depth of shower maximum are large, so an identification of the primary on an event-by-event basis is not possible.
Signal rise time in SD analysis is in progress
Study mean height of shower maximum for a large data sample.
Elongation rate (mean shower maximum vs. energy) indicates the dominant chemical component, but we have to compare to simulations to interpret the data (strong model dependence!). 33

32. CHEMICAL COMPOSITION Too early for conclusions!
Signal rise time in SD analysis is in progress
Proton primaries determined by patterns in sky distribution – new interactions to explain composition measurements
Heavy primaries determined by patterns in sky distribution – new source models to explain heavy dominance.
Too early for conclusions! 34

33. PHOTON FLUX

34. TOP – DOWN MODELS DISFAVORED !
PHOTON FLUX
TOP – DOWN MODELS DISFAVORED !

35. ARRIVAL DIRECTIONS

36. ARRIVAL DIRECTIONS
Here is the raw distribution of arrival directions for the data set on the sky in galactic coordinates.
Note the over sampling in the southern hemisphere where the detector is located and the hole in the north
The V-C catalog is likely to be incomplete near the Galactic plane also the Galactic magnetic field is stronger in the disk. Out of the 7 events out of the correlation, 5 are within 12º of the Galactic Plane.
Cutting on the Galactic Plane (|b|<12º) the minimum reads :
P = 2x10-10 at E=57 EeV, z=0.017 and  =3.2º,
with 19 of of 21 events in correlation where 5 are expected
Short article published in Science 318 (2007)
Long article published in Astroparticle physic 29 (2008) 188. 38

37. ARRIVAL DIRECTIONS Acceleration sites
Can we say something about the sources?
They are not in the Milky Way
They are likely astrophysical
AGN are plausible acceleration sites
More data are needed to identify the sources and their characteristics
Here is the raw distribution of arrival directions for the data set on the sky in galactic coordinates.
Note the over sampling in the southern hemisphere where the detector is located and the hole in the north 39

38. CORRELATIONS WITH AGNs
Here is the raw distribution of arrival directions for the data set on the sky in galactic coordinates.
Note the over sampling in the southern hemisphere where the detector is located and the hole in the north 40

39. CORRELATIONS WITH AGNs
Here is the raw distribution of arrival directions for the data set on the sky in galactic coordinates.
Note the over sampling in the southern hemisphere where the detector is located and the hole in the north
Signal strength for AGN correlations is not as strong as the first data suggested.
Probability psignal of correlating with an AGN appears to settle on a value around the null hypothesis corresponds to p0 = 0.21
Results still shows good correlation with matter.
Several events close to Centaurus A. 41

40. FUTURE Much more statistics needed. Full sky coverage. AUGER NORTH
~ km2
Design report finished
Needs more work 42

41. AUGER NORTH
Needs more work
SIZE OF SLOVENIA 43

42. FUTURE - EXPOSURE
Needs more work 44

43. CONCLUSIONS Pierre Auger Observatory Physics Results
Exposure is now 17,000 km2 sr yr.
Current SD statistics: >106 events above 1017 eV.
Detector systematics are understood and being reduced.
Physics Results
Energy spectrum
Statistically significant change in spectral index near GZK region.
Mass composition
Hybrid elongation rate sugests mass mixture.
Arrival direction anisotropy
New data do not favor previous claims of correlations with local AGNs
Still good evidence for correlations with mass distribution
Needs more work 45

44. 46