1. Results from the Pierre Auger Observatory
J. R. T. de Mello Neto
University of Chicago &
Universidade Federal do Rio de Janeiro
for the Pierre Auger Collaboration

2. Outline Introduction: the UHECRs
The Pierre Auger Observatory – an hybrid detector
Energy calibration
The model-independent energy spectrum
Hadronic models
Photon fraction limit
Anisotropy studies
Perspectives
Auger South enhancements
North Site
Auger contributions in the proceedings of ICRC 07 – Merida, Mexico

3. Cosmic rays flux vs. Energy
(nearly) uniform power-law spectrum spanning 10 orders of magnitude in E and 32 in flux!
structures :
~ 3 – eV: knee
change of source? new physics?
~ eV: ankle
transition galactic – extragalatic?
change in composition?
UHECR
one particle per century per km2
many interesting questions
S. Swordy

4. Open questions How cosmic rays are accelerated at ?
What are the sources?
How can they propagate along astronomical distances at such high energies?
Are they substantially deflected by magnetic fields?
Can we do cosmic ray astronomy?
What is the mass composition of cosmic rays?

5. Detection techniques Particles at ground level
large detector arrays (scintillators, water Cerenkov tanks, etc)
detects a small sample of secondary particles (lateral profile)
100% duty cicle
aperture: area of array (independent of energy)
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)
ex: AGASA

6. Detection techniques Fluorescence of N2 in the atmosphere
calorimetric energy measurement as function of atmospheric depth
only for E > 1017 eV
only for dark nights (10% duty cicle)
requires good knowledge of atmospheric conditions
aperture grows with energy, varies with atmosphere
ex: HiRes

7. The Auger Observatory: Hybrid design
A large surface detector array combined with fluorescence detectors results in a unique and powerful design;
Simultaneous shower measurement allows for transfer of the nearly calorimetric energy calibration from the fluorescence detector to the event gathering power of the surface array.
A complementary set of mass sensitive shower parameters contributes to the identification of primary composition.
Different measurement techniques force understanding of systematic uncertainties in each.

8. The Pierre Auger Collaboration
Czech Republic
France
Germany
Italy
Netherlands
Poland
Portugal
Slovenia
Spain
United Kingdom
Argentina
Australia
Brasil
Bolivia*
Mexico
USA
Vietnam*
*Associate Countries
~300 PhD scientists from
~70 Institutions and 17 countries
Aim: To measure properties of UHECR with
unprecedented statistics and precision

9. Pierre Auger South Observatory
3000 km2
1438 deployed
1400 filled
1364 taking data
~ 85%
All 4 fluorescence
buildings complete,
each with 6 telescopes
1st 4-fold on 20 May 2007
AIM: 1600 tanks
HYBRID DETECTOR

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

11. The fluorescence detector
Los Leones
telescope

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

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

14. θ~ 48º, ~ 70 EeV Typical flash ADC trace at about 2 km
18 detectors triggered
Typical flash ADC trace
at about 2 km
Detector signal (VEM) vs time (µs)
PMT 1
PMT 2
PMT 3
Now I would like to show you the observatory in action.
Here is an event of fairly high energy – about 70 EeV - at a moderate zenith angle of 48 degrees. Note that an EeV corresponds to 1 x 10^18 eV.)
At the left are the flash ADC traces of the detector stations that participated in the event. The horizontal axis is in nanoseconds while the vertical axis is in vertical equivalent muons. The three colors are the response to the three PMTs. As you see the signal goes out to 3 mircoseconds.
Here is the pattern of hits on the array with the size of the dot proportional to the log of the signal in the tank. The red arrow showed the reconstructed direction and core position.
The last frame shows the lateral distribution of detector signals from the core position.
Lateral density distribution
Flash ADC traces
Flash ADC traces µs

15. Hybrid Event
longitudinal
profile

16. Inclined Events offer additional aperture
 = 79 °

17. Energy spectrum from Auger Observatory
Based on fluorescence and surface detector data
First model- and mass-independent energy spectrum
Power of the statistics and well-defined exposure of the surface detector
Hybrid data confirm that SD event trigger is fully efficient above 3x1018 eV for θ<60o
Uses energy scale of the fluorescence detector (nearly calorimetric, model independent energy measurement) to calibrate the SD energy.

18. Energy calibration
SD parameter S1000: interpolated tank signal at 1000 meters from the lateral distribution function
Determined for each SD event
It is proportional to the primary energy
Reduced measurement uncertainty (shower fluctuations dominate)
VEM = vertical equivalent muons from self calibration of the tank signal (from ambient muons)

19. Energy calibration (constant intensity cut)
How to relate S(1000 m) to E?
It depends on the atmospheric depth --> shower zenith angle, 
=0 one atm, = atm, shower is attenuated depending on the zenith angle;
Showers with the same energy developing at differente zenith angles produce different S1000 signals at ground level
The corresponding grammage of atmosphere along the shower axis (shower age) is different
Choose a reference zenith angle 38° (median of the Auger data set)
Make use of the isotropy of the observed CR flux
For a fixed I0 find S(1000) at each θ such that I(>S(1000)) = I0
All these steps have been taken by Auger!!!

20. Constant intensity cut
Integral number of events for cos2(θ) for the indicated minimum value of S(1000)
Same value of S1000 at higher zenith
angle correspond to a higher energy
Derived attenuation curve, CIC(θ), fitted with a quadratic function.
Normalized so that CIC(38°) = 1;
Define energy parameter S38= S(1000)/CIC(θ) for each shower :
“the S(1000) it would have produced if it had arrived at 38o zenith angle”

21. S38 (1000) vs. E(FD) 4 x 1019 eV Nagano et al, FY used
387 hybrid events

22. Energy calibration
Fractional difference between the SD and FD energy for the hybrid events;
Small relative dispersion
includes uncertainties in both the FD energy and the SD signal
S(1000) is intrinsecally a very good energy estimator
Reliable energy measurements when properly calibrated

23. Summary of systematic uncertainties
Note: Activity on several fronts to reduce these uncertainties
Fluorescence Detector Uncertainties Dominate
Invisible energy: fraction of the energy carried away by neutrinos and energetic muons (Monte Carlo dependent)
energy determination nearly independent of mass or model assumptions

24. Energy spectrum from SD < 60°
Exp Obs
> /
> /
Slope = ± 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 > eV ) and 4σ ( E > 1019 eV )

25. Slope = -2.7 ± 0.1

26. Hybrid Spectrum: clear evidence of the ‘ankle’ at ~ 4 x 1018 eV
- 3.1 ± 0.3

27. Energy spectra from Auger
The agreement between the spectra derived using three diferent methods is good
It is underpinned by the common method of energy calibration based on the FD measurements.

28. Astrophysical models and the Auger spectrum
models assume: an injection
spectral index, an exponential cutoff at an energy of Emax times the charge of the nucleus,
and a mass composition at the acceleration site as well as a distribution of sources.
Auger data: sharp suppression in the spectrum with a high confidence level!
Expected GZK effect or a limit in the acceleration process?

29. Composition from hybrid data
UHECR: observatories detect induced showers in the atmosphere
Nature of primary: look for diferences in the shower development
Showers from heavier nuclei develop earlier in the atm with smaller fluctuations
They reach their maximum development higher in the atmosphere (lower cumulated grammage, Xmax )
Xmax is increasing with energy (more energetic showers can develop longer before being quenched by atmospheric losses)

30. Composition from hybrid data
Xmax resolution ~ 20 g/cm2

31. composition from hybrid data
The results of all three experiments are compatible within their systematic uncertainties.
The statistical precision of Auger data already exceed that of preceeding experiments
( data taken during construction of the observatory)

32. test of hadronic models
Lateral distribution
function
Longitudinal profile
Assumption: universality of the eletromagnetic shower evolution
Test: number of muons needed to obtain a self consistent description of data

33. Universality of the e/m shower component
Sem parameterised as a function of the distance to ground DG = Xdet - Xmax
Predicted signal at 1000 m:
includes e/m signal for muon decays

34. constant intensity method
Cosmic ray
flux isotropic
Result accounting for shower fluctuations and detector resolution

35. expected tank signal at 1019 eV
from Auger hybrid data
from Auger data:
const. intensity method
Corresponding energy scale:
within current uncertainty of fluorescence detector energy scale
it corresponds to assigning showers a ~ 30% higher energy than done in the fluorescence detector-based Auger shower reconstruction!

36. test of hadronic models
two other methods, one using golden hybrid events and another using inclined showers, give consistent results with the constant intensity method ;
Auger hybrid data: test of hadronic interaction models up to ultra-high energy ( Elab > 1019 eV, )
The number of muons measured in data is about 1.5 times bigger than that predicted by QGSJET II for proton showers!
Universality of eletromagnetic shower evolution indicates energy scale compatible with that of fluorescence detectors.

37. Top down models acceleration models (astrophysics):
active galactic nuclei, gamma-ray bursts...
not easy to reach > 100 EeV;
photon fractions typically < ~ 1%
non-acceleration models (particle physics)
UHECR: decay products of high-mass particles (> 1021eV)
super-heavy dark matter (SHDM): from early universe and concentraded on the halo of galaxies and clusters of galaxies
topological defects (TD) produced throughout the universe
UHECR produced as secondary particles (hadronization process) and are most photons and neutrinos, with minority of nucleus
photon fraction typically > ~ 10%
SHDM: CR from our galaxy, photons with a hard energy spectrum
TD: sources distributed in the universe, photons interact with CMB
(expect smaller photon fraction)

38. UHE photons status in 2005
HP: Haverah Park Ave et al.,2000; event rates
A1, A2: AGASA 1000 m Shinozaki et al., 2002; M. Risse et al., 2005
Models: ZB,SHDM,TD - Gelmini et al SHDM' – Ellis et al., 2005
cosmic ray photon fraction: check nonacceleration models
upper limits so far: surface detectors only !?
needed: cross check by fluorescence technique (Xmax in hybrids)

39. variables for composition (photons)
Showers with greater Xmax have a time distribution in the SD which is more spread (geometrical effect)
Energetic muons ( spherical shower front)
larger values of Xmax related to smaller values of Rc.
Photons: greater time spread and smaller radius of curvature
Data lying above the dashed line
( the mean of the distribution for photons)
are identfied as photon candidates.
No events meet this requirement.

40. photon limits
A = Agasa
HP = Haverah Park
Y = Yakutsk

41. Angular resolution Surface detector Hybrid data: better
angular resolution, ~ 0.7o
@ 68% c.l. in the EeV
energy range
Events with E > 10 EeV :
6 or more SD stations
All these steps have been taken by Auger!!!

42. Galactic center
Galactic Center is a “natural” site for cosmic ray acceleration
Supermassive black hole
Dense clusters of stars
Stellar remnants
SNR (?) Sgr A East
SUGAR excess is consistent with a point source, indicating neutral primaries
Neutrons would go undeflected, and neutron decay length at 1018 eV is comparable to the distance to the Galactic center (~8.5 kpc)
Chandra

43. Source at the Galactic center
AGASA
Significance (σ)
20o scales
1018 – eV
22% excess
Cuts are a posteriori
Chance probability is not well defined
N. Hayashida et al., Astroparticle Phys. 10 (1999) 303

44. Source at Galactic center
SUGAR
5.5o cone
1018 – eV
85% excess
J.A. Bellido et al., Astroparticle Phys. 15 (2001) 167

45. results for the galactic center
test of AGASA: obs/exp = 2116/2159.5
R = 0.98 ± 0.02 ± 0.01
NOT CONFIRMED (with 3x more stats)
test of SUGAR: obs/exp = 286/289.7
R = 0.98 ± 0.06 ± 0.01
NOT CONFIRMED (with 10x more stats)
Galactic Center as a point source (σ=1.5°):
obs/exp = 53.8/45.8
R = 1.17 ± 0.10 ± 0.01
NO SIGNIFICANT EXCESS
upper limit on the flux of neutrons coming from GC:
Galactic Plane: NO SIGNIFICANT EXCESS
AGASA
5°, top-hat
SUGAR
G.P.
astro-ph/
(Astropart. Phys., 2007)
(check proceedings
ICRC 07 for an update)
Φs < 0.08 ξ km-2 yr-1 at 95% C.L.

46. Overdensity search (galactic center)
1 EeV < E <10 EeV
0.1 EeV < E < 1 EeV
significance
Li, Ma ApJ 272, (1983)
All distributions
consistent with
isotropy

47. anisotropy searches
All-sky blind searches for sources: NO EXCESS FOUND
Right-ascension (RA) distribution of the events is remarkably isotropic!
Upper limit of 1.4% on the first harmonic amplitude (dipole in the RA modulation)
Angular coincidences between Auger events and BL Lac objects (as possibly seen by HiRes) was not confirmed;
Search for clustering (as seen by AGASA), no strong excess was observed
Scan in angle and energy: hints of clustering at larger energies and intermediate angular scales
Large scale distribution of nearby sources?
Chance probability of such a signal from an isotropic flux ~ 2% (marginally significant)

48. Anisotropy studies New results are coming out! Stay tuned!
For each target: specify a priory probability levels and angular scales
avoids uncertainties from “penalty factors” due to a posteriori probability estimation
Targets:
low energy: Galactic center and AGASA-SUGAR location
high energy: nearby violent extragalactic objects
(ICRC 05)
New results are coming out! Stay tuned!

49. other physics topics to be explored
Neutrinos
Gamma ray burst detection
Measurement of the primary cosmic ray cross section;
and many others ...

50. Conclusion e perspectives
More events > 10 EeV than from AGASA or HiRes
and close to more than their total
AND with superior angular and energy resolution
Auger South: about 90% complete
Detector working very well ( SD: 97% uptime)
First rate physics results: spectrum, composition, anisotropy and many others
Auger statistics will totally dominate after another year !!

51. Future for Auger Collaboration
Complete Auger-South in ~ 6 months and provide reliable and extensive experimental data for many years
Commence construction of Auger South upgrades:
HEAT: high elevation FD (to 60°)
AMIGA dense SD array plus muon detectors
Submit Auger-North proposal within a year

52. Backup slides

53. GKZ suppression Universe is opaque for E > EGZK ! EGZK= 5x 1019 eV
Cosmic rays E = 1020 eV interact with 2.7 K photons
In the proton frame
Nuclei
Proton with less energy, eventually below the cutoff energy
EGZK= 5x 1019 eV
Photon-pion production
Photon dissociation
Universe is opaque for E > EGZK !

55. Comparison of
Auger and HiRes
apertures
3-fold
5-fold
Linear
x 10 between 1 and 10 EeV
Depends on assumptions
about Models, Mass and
Spectrum slope
logarithmic

56. The Hybrid Era Hybrid SD-only FD-only Angular Resolution Aperture
Energy
Hybrid SD-only FD-only
mono
(stereo – low N)
~ 0.2° ~ 1 - 2° ~ 3 - 5°
Flat with energy AND E, A, spectral
mass and model (M) free slope and M
dependent
A and M free A and M A and M free

57. Super-Heavy Dark Matter
produced during inflation; Mx ~ 1023 eV, clumped in galactic halo (overdensity ~ 105)
lifetime ~ y: decay (SUSY-QCD) -> pions -> UHE photons (and neutrinos)
little processing during propagation: decay spectrum at Earth
Similar shapes for ZB (Weiler, 1982) e TD (Hill 1983 ) models
signature for exotics
Fit to AGASA data (Gelmini et al, 05)
Spectrum for
γSHDM and pSHDM
P: nucleonic component
at lower energy
Photons dominate
E > 5 x 1019 eV