1. for the Pierre Auger Collaboration
Results on Ultra-High Energy Cosmic Rays from the Pierre Auger Observatory
Valerio Verzi
INFN Roma Tor Vergata
for the Pierre Auger Collaboration

2. COSMIC RAYS SPECTRUM (2008)l
Flux x E2.5
UHECR
~ 1020 eV
1 particle/km2/century!

3. WHERE DO COME FROM? only few candidates B R B E AGN 1018 eV 1020 eV
Centaurus A B R E B
AGN at only 3.4 Mpc •
AGN
Trajectory in galactic and inter-galactic B
1018 eV
1020 eV
Hillas diagram R
more details in G.Farrar’s talk
Back to origin!

4. Greisen-Zatsepin-Kusmin (GZK)
Interaction with CMB
Modification of the spectrum
p gCMB → N p D+
l=5÷10 Mpc
GZK cutoff
UHECR sources must be closer than Mpc!

5. ATMOSPHERIC SHOWERS 10 li 30 X0 at ground millions of particles
… detectors in coincidence

6. AUGER – HYBRID DETECTOR
Fluorescence Detector (FD):
fluorescence light from the N2 de-excitation
(+) Longitudinal shower development
calorimetric measurement of E
sensitivity to CR mass (Xmax)
(-) Duty cicle ~ 10% FD
Surface Detector (SD):
detection of the shower front at ground
(+) Duty cicle ~ 100% (important for UHECR)
(-) Shower size at ground  E (systematics)
calibration from FD SD

7. PIERRE AUGER OBSERVATORY
Malargue - Argentina
SD water
Cherenkov detec.
on a 1.5 km
hexagonal grid
3000 km2
FD 4 x 6 fluorescence telescopes
50 km

8. PIERRE AUGER OBSERVATORY
Malargue - Argentina
SD water
Cherenkov detec.
on a 1.5 km
hexagonal grid
3000 km2
Installation
completed
this year
FD 4 x 6 fluorescence telescopes
50 km

9. SD TANKS
1.5 km

10. FLUORESCENCE TELESCOPE

11. WATER TANK Communication antenna GPS antenna Electronics enclosure
40 MHz FADC, local triggers, 10 Watts
Solar Panel
three 9”
PMTs
Plastic tank with 12 tons of water
Battery
box

12. TANK SIGNAL  m-response ~ track e/g-response ~ energy ‘young’ shower
PMT m
diffusive
Tyvek
m-response ~ track
e/g-response ~ energy
1.2 m ~ 3 Xo
Cerenkov
light
water
‘young’ shower
strong e.m. component
‘old’ shower
m signal dominates

13. SD SHOWER RECONSTRUCTION
1.5 km
shower front
Shower front from particle arrival times
Core position and S(1000) from LDF (NGK) fit
Signal (VEM)
Distance from the core (m)

14. SD SHOWER RECONSTRUCTION
1.5 km
shower front
Shower front from particle arrival times
Core position and S(1000) from LDF (NGK) fit
Signal (VEM)
Shower axis resolution
Distance from the core (m)
E > 1019 eV
~ 10
zenit (degrees)

15. SD SHOWER RECONSTRUCTION
1.5 km
shower front
Shower front from particle arrival times
Core position and S(1000) from LDF (NGK) fit
Signal (VEM)
S(1000) ~ E
Distance from the core (m)
FD calorimetric measurement
No simulations!

16. FD TELESCOPE
Spherical mirror m radius of curvature
Schmidt optics

17. FD TELESCOPE
2.2 m diameter diaphragm corrector ring, UV optical filter
Schmidt optics

18. FD TELESCOPE
Camera (focal surface) PMT’s 30ox30o FOV pixel = 1.5o spot: 15 mm (0.5o)
Schmidt optics

19. FD EVENT
bin=100 ns

20. FD ENERGY SCALE dE Energy deposit dX Nγ Fluorescence yield from
Airfly
spectrum
Fluorescence yield from
laboratory measurements
5 photons/MeV at 337 nm
Shower energy uncertainty ~ 15%

21. FD ENERGY SCALE Atmospheric transmission Nγ Nγ Atmospheric monitoring
at diaphragm
Atmospheric monitoring
aerosols, clouds, density profiles
(Lidar, Central Laser Facility,
Ballons, …)
Shower energy uncertainty ~ 5%

22. FD ENERGY SCALE Nγ Nγ Drum absolute calibration
PMT’s signal
at diaphragm Nγ
Drum absolute calibration
uniform camera illumination
with a calibrated light source
~ 5 g/ADC
Shower energy uncertainty ~ 10%

23. only a 10% model dependent correction
FD ENERGY SCALE dE dX
E ~ eV
Expected profile:
fitted Gaisser-Hillas
function
Xmax~ 810 g/cm2
Ecal Xmax X E
Ecal
Ecal E
only a 10% model dependent correction
Shower energy uncertainty ~ 4%
Log E

24. SD CALIBRATION USING FD ENERGY
HYBRID SHOWERS
S(1000,q=380)
with CIC
LINEAR FIT
50 VEM ~ 1019 eV
661 events
Statistical uncertainty
7% at 1019 eV
15% at 1020eV
PRL 101, (2008)
FD syst. uncertainty (22%) dominates

25. AUGER SCIENCE
SPECTRUM
COMPOSITION
SOURCES

26. ENERGY SPECTRUM - q<600
Data up to
31/08/07
Aperture
7000 km2 sr yr
~ 1 year Auger
completed
2 x HIRES
4 x AGASA
PRL 101, (2008)
Full efficiency above eV
 3% uncertainty on aperture

27. ENERGY SPECTRUM - q<600
Data up to
31/08/07
Exp. Observed
> 4x ±
> ±
Aperture
7000 km2 sr yr
~ 1 year Auger
completed
2 x HIRES
4 x AGASA
PRL 101, (2008)
Full efficiency above eV
 3% uncertainty on aperture
Evidence of GZK cutoff

28. ENERGY SPECTRUM - q<600
Fit E-γ
HiRes: 5.1 ± 0.7
γ = 2.69 ± 0.06
γ = 4.2 ± 0.4
difference with respect
to reference shape
Js = A x E-2.69
GZK cut off

29. ENERGY SPECTRUM Comparison of the three Auger spectra - consistency
0-60 degrees
Different reconstruction
60-80 degrees
Exposure from simulation
Ankle
ICRC 07

30. Auger combined compared to Hires and Agasa
Fairly agreement within systematic uncertainties
ICRC 07

31. AUGER SCIENCE
SPECTRUM
COMPOSITION
SOURCES

32. ELONGATION RATE
(< A> ~ 5)
Change of slope
correlation
with ankle ?
preliminary
Systematics
< 15 g /cm2
Not proton dominated composition at the highest energies

33. SENSITIVITY TO PHOTON SHOWERS
Fluorescence Detector
Xmax from shower
longitudinal profile.
(SD) Shower front curvature A g
Surface Detector
Shape of the front of the shower
(SD) Shower front thickness A g

34. PHOTON FRACTION LIMIT ~ 3 % preliminary HP: Haverah Park A1,A2: AGASA
Top Down models:
Super Heavy
Dark Matter
Relic of “topological
defects”
HP: Haverah Park
A1,A2: AGASA
Y: Yakutsk
Astro. Ph. 29 (2008), 243.
Astro. Ph. 27 (2007), 155.

35. NEUTRINO FLUX LIMIT 87 degrees Signature: very inclined
showers with high e.m.
signal component
hadronic showers:
signal dominated
by muon component
PRL 100 (2008),
87 degrees

36. AUGER SCIENCE
SPECTRUM
COMPOSITION
SOURCES

37. GALACTIC CENTER ANISOTROPIES
H.E.S.S.: TeV g-ray from Sagittarius A*
Excess in previous experiments GC
AGASA 2.5s
SUGAR 2.9s
Auger:
larger exposure
GC lies well in the f.o.v.
No statistically significant excess in Auger data
angular windows:
AGASA and SUGAR
10° and 20° around the GC (charged CR’s)
1° around the GC
0.1 < E < 1 EeV (photons)
1 < E < 10 EeV (neutrons)

38. EVIDENCE OF ANISOTROPY
Correlation of the Highest-Energy (>5.7x1019 eV) Cosmic Rays with Nearby (<75 Mpc) Extragalactic Objects
Centaurus A
Science 318 (2007), 939.
Astro. Ph. 29 (2008), 188.

39. EVIDENCE OF ANISOTROPY
Véron &Véron-Cetty catalogue
442 AGN (292 in f.o.v.)
z<0.017 (71 Mpc)
27 events
E > 57 EeV
3.20 radius
galactic
coordinates
Doublet from Centaurus A
Border of the f.o.v.
Relative exposure
Super-galactic plane

40. ANALYSIS METHOD Fix candidate sources and maximum angular distance yCR
Source y
Fix candidate sources and maximum angular distance y
Probability p that one event
from isotropic flux is close (<y)
to at least one source
p = fraction of “Auger sky” covered
by windows y centred on sources
Prob. >k of the N events from isotropic flux correlate
by chance with sources (<y)

41. ANALYSIS METHOD Fix candidate sources and maximum angular distance yCR
Source y
Fix candidate sources and maximum angular distance y
Probability p that one event
from isotropic flux is close (<y)
to at least one source
p = fraction of “Auger sky” covered
by windows y centred on sources
Prob. >k of the N events from isotropic flux correlate
by chance with sources (<y)
Three parameter scan to find the maximum anisotropy (minimum of P)
1- Minimum CR energy (->N)
minimize deflections in B
2- Maximum source distance zmax
GZK
3- Maximum angular separation y
deflections in B and angular resolution

42. RESULTS
Absolute minimum
y = 3.20
zmax = (71 Mpc)
E > 57 EeV
Selected events
Events correlated
Expected for isotropy 27 20
5.6
1.2 year
full Auger
Isotropy hypothesis rejected with at least 99% confidence level
exploratory scan (01/01/04- 27/05/06)
confirmation on an independent data set (27/05/06- 31/08/07)

43. WHAT ABOUT NOT CORRELATED EVENTS?
Events with low
galactic latitudes
|b| < 120
Isotropic flux
catalogue
incompleteness
larger deflections
in galactic
magnetic field CR
closest AGN
Selected events
Events correlated
Expected for isotropy
Full data sample 27 20
5.6
|b| > 120 21 19
5.0
6 events less
with 5 not correlated

44. THE ANGULAR SEPARATION Y
angular resolution ~ 10 < y (=3.20)
y determined by galactic and inter-galactic magnetic fields
Simulation including galactic magnetic field
simulated protons (isotropy)
27 observed events
y=3.20

45. THE ANGULAR SEPARATION Y
angular resolution ~ 10 < y (=3.20)
y determined by galactic and inter-galactic magnetic fields
Simulation including galactic magnetic field
simulated protons (isotropy)
27 observed events
y=3.20
deflection
correlated events are likely protons
but elongation rate suggests a mixed composition at the highest energies …

46. CONNECTION TO THE GZK CUT OFF
events E > eV
spectrum
sources < 71 Mpc
flux reduced by 50%
but …

47. CONNECTION TO THE GZK CUT OFF
events E > eV
spectrum
sources < 71 Mpc
flux reduced by 50%
but …
GZK Horizon is ~200 Mpc
maximum distance of the sources from which 90 % of the protons arrive on Earth with energy above a given value.
90%

48. CONNECTION TO THE GZK CUT OFF
events E > eV
spectrum
sources < 71 Mpc
flux reduced by 50%
but …
GZK Horizon is ~200 Mpc
maximum distance of the sources from which 90 % of the protons arrive on Earth with energy above a given value.
90%
For an +30% energy estimator the Horizon would be ~100 Mpc

49. CONNECTION TO THE GZK CUT OFF
events E > eV
spectrum
sources < 71 Mpc
flux reduced by 50%
but …
GZK Horizon is ~200 Mpc
maximum distance of the sources from which 90 % of the protons arrive on Earth with energy above a given value.
90%
For an +30% energy estimator the Horizon would be ~100 Mpc
Uncertainty on energy scale ~ 25%

50. CONCLUSIONS
Auger is fully operational: exposure ~ 1 year of Auger completed
UHECR anisotropy
angular distribution similar to that of AGN within ~ 70 Mpc sources are of extra-galactic origin
primaries are likely protons which interact with CMB radiation (GZK)

51. CONCLUSIONS
Auger is fully operational: exposure ~ 1 year of Auger completed
UHECR anisotropy
angular distribution similar to that of AGN within ~ 70 Mpc sources are of extra-galactic origin
primaries are likely protons which interact with CMB radiation (GZK)
evidence of GZK cut-off in the spectrum confirming
HIRES data
no photon and neutrino candidates
(disfavour TOP-DOWN models)

52. CONCLUSIONS
Auger is fully operational: exposure ~ 1 year of Auger completed
UHECR anisotropy
angular distribution similar to that of AGN within ~ 70 Mpc sources are of extra-galactic origin
primaries are likely protons which interact with CMB radiation (GZK)
evidence of GZK cut-off in the spectrum confirming
HIRES data
no photon and neutrino candidates
(disfavour TOP-DOWN models)
but …
Xmax studies disfavour a proton dominated composition at the highest energies
Consistency or not with the GZK horizon?
Two events from CenA, none from Virgo. Why?
Need more statistics (~ 70 events/year above 4x1019 eV)
and better control of systematics

53. FUTURE DEVELOPMENT Auger North (Colorado, US) Full sky coverage
(talk of prof. J.Bluemer)
Full sky coverage
Array: square miles
≈ km2 ≈ 7 x Auger South)
events above 4x1019 eV (GZK cutoff)
Auger South: ~ 70 events/year
Auger North: ~ 500 events/year

55. BACK UP SLIDES

56. TANK CALIBRATION Online calibration with background muons (2 kHz)
Vertical m
PMT m
diffusive
Tyvek
Online calibration with background muons (2 kHz)
1.2 m ~ 3 Xo
Cerenkov
light
water
muon peak VEM peak
scintillator
1 VEM ≈ 100 p.e.

57. TIME RESOLUTION Doublets
Dia
Noche
11m
Doublets
Low energy events (~ 1017 eV) used to compare the time measurement of each tank
GPS intrinsic time resolution 8 ns
Time precision of each individual tank ~ 12 ns

58. SD-TANK TRIGGER SD-EVENT TRIGGER
Threshold Trigger
~ 20 Hz
Time Over Threshold Trigger
~ Hz
5 s
SD-EVENT TRIGGER
hottest tank surrounded by 6 working stations

59. SD SHOWER RECONSTRUCTION
distance from the core
size parameter
Lateral distribution function (LDF)
NGK
slope parameter
(β(q)= 2-2.5)
S(1000) and the core position from the fit
core
Signal (VEM)
S(1000)
34 tanks
distance from the core (m)

60. SD CALIBRATION USING FD ENERGY
vertical shower
inclined shower
for the same energy and mass
S(1000;0)> S(1000;q) Xg
Xg/cosq
Attenuation curve derived with constant intensity cut technique
ground
for each shower determine
the signal that would
have had at 380
S38 = S(1000,380)

61. SD CALIBRATION USING FD ENERGY
LINEAR FIT
19%
measurement of the energy resolution
16%-S38
8%-EFD
PRL 101, (2008)

62. SD APERTURE Aperture 7000 km2 sr yr (3% error)
Full efficiency above 3x1018 eV
~ events
above eV
Aperture 7000 km2 sr yr (3% error)

63. ELONGATION RATE

64. Comparison with PAO data, without and with acceptance

65. ELONGATION RATE

66. ELONGATION RATE
p - EPOS
Fe - EPOS
Fe - QGSJETII
p - QGSJETII
proton
iron
The mass spectrum is not proton dominated at the highest energies
Ambiguous interpretation: uncertainties of hadronic interactions at highest energies

67. GALACTIC CENTER ANISOTROPIES
Angular window
Windows centred in the GC:
Nobs/Nexp
Ratio (err.: stat, syst)
search for photons
1.30 (G)
192.1 / 191.2
1.00 ± 0.07 ± 0.01
100
5663 / 5657
1.00 ± 0.02 ± 0.01
200
22274 / 22440
0.99 ± 0.01 ± 0.01
0.80 (G)
16.9 / 17.0
0.99 ± 0.17 ± 0.01
1463 / 1365
1.07 ± 0.04 ± 0.01
5559 / 5407
1.03 ± 0.02 ± 0.01
GC lies well in the
Auger f.o.v.
0.1 < E < 1 EeV
search for neutrons
1 < E < 10 EeV

68. ANISOTROPY 15 12 3.2 13 8 2.7 27 20 5.6 21 19 5.0 Events Expected for
correlated
Expected for
isotropy
Exploratory scan
1 Jan May 06
zmax = 0.018
E > 56 EeV
y = 3.10 15 12
3.2
Test on an independent data set
27 May Aug 07 **
running prescription 13 8
2.7
Full data set
1.2 year full Auger *
zmax = (71 Mpc)
E > 57 EeV
y = 3.20 27 20
5.6
Full data set excluding
region of the galactic plane
(|b| > 120) 21 19
5.0
*Probability to see such anisotropy
with an isotropic flux = 10-5
5 of the 7 events not correlated
are close to the galactic plane **

69. Red dots: 13 HiRes events (claim consistent with isotropy)
Black dots: 27 Auger events

70. GZK and mass composition
Only protons and not too light nuclei are able to reach the Earth
for energies above ~ 60 EeV