1. “Un altro modo di guardare il cielo”
NO – VE
Venezia - April 15-18, 2008
“Un altro modo di guardare il cielo”
Auger New Results G. Matthiae Universita’ e Sezione INFN di Roma “Tor Vergata”

2. Cosmic ray spectrum
year 2000
~ 1 / E3
1 particle/km2/century
LHC c.m.

3. Cosmic ray spectrum - 2008 ankle GZK AGASA: surface array
HiRes: fluorescence telescopes
Auger: Hybrid
Cosmic ray spectrum l
ankle
GZK

4. Greisen-Zatsepin-Kuzmin Interaction with CMB GZK cutoff
Above E ≈ 6*1019 eV, protons loose rapidly energy via pion photoproduction. Energy loss ≈ 15 % / interaction. Interaction length = 5 – 10 Mpc
p + γ CMB → n + π+
p + π0
∆+ production
{γ from π0 , ν from π+}
protons
e+e–
e+ e- pair production is
less effective, energy loss ≈ 0.1% / interaction
Produces a “dip” in the spectrum (Berezinsky)
Attenuation length 
Nuclei:
also photodissociation
Interaction length

5. PROTONS
1 EeV = 1018 eV

6. Horizon: maximum distance of the sources from which X % (for example 90 %) of the protons arrive on Earth with energy above a given value.
Energy (EeV)
100 Mpc

7. Auger hybrid detector Fluorescence Detector (FD)
Longitudinal development of the shower
Calorimetric measurement of the energy
Calibration of the energy scale
Only moonless nights
12% duty cycle !
Surface Detector (SD)
Front of shower at ground
Direction and “energy” of the shower

8. AUGER Observatory Total area ~3000 km2 nearly completed
350 S latitude
≈ 1400 m height ≈ 875 g/cm2
Total area
~3000 km2
Surface detectors (“water tanks”) 1.5 km spacing
24 fluorescence telescopes, 6 in each of 4 buildings
Very flat region with low population density
Good atmospheric conditions (clouds, aerosol)

9. Water Tank in the Pampa Communication antenna GPS antenna
Solar Panel
Electronics enclosure
40 MHz FADC, local triggers, 10 Watts
Communication antenna
GPS antenna
Battery
box
Plastic tank with 12 tons of water
three 9”
PMTs

10. Calibration:
Vertical Equivalent Muon (VEM) : ~ 90 p.e.
Time resolution
~ 12 ns
Selecting vertical muons
with telescope scintillation counters
Dia
Noche

11. ‘young’ shower strong e.m. component ‘old’ shower m signal dominates
Young & Old Shower
‘young’ shower
strong e.m. component
‘old’ shower
m signal dominates

12. The FD telescope (Schmidt optics) Field of view 30x30 degrees
Diaphragm
Spherical mirror
PMT camera
Shutter
UV Filter ( nm)

14. Fluorescence Telescope
Camera with 440 PMTs
Spherical mirror (R=3.4 m)

15. FD ABSOLUTE CALIBRATION
Drum: a calibrate light source
uniformly illuminates the FD camera
Mirror reflectivity,
PMT sensitivity etc.,
are all included!
Drum
~ 5 photons /ADC
10% error

16. molecular/Rayleigh & aerosol/Mie
Atmospheric attenuation / shoot on shower technique
LIDAR
Backscattering
Elastic bcks.
molecular/Rayleigh & aerosol/Mie
Laser
Mirror
DAQ

17. Central Laser Facility
FD “TEST BEAM”
Central Laser Facility
355 nm
Steerable laser
optical fiber
SD tank
Time correlation FD - SD

18. Longitudinal profile of showers from the FD telescopes Fit with empirical formula of Gaisser-Hillas Cherenkov light subtracted Calorimetric measurement of the energy.
4 par
Nmax ~ E , Xmax ~ log E

19. Correction for energy loss (neutrinos, muons)
p / Fe : 8 – 12 % at 1019 eV (10% ± 2%)
eventually important to know the composition

20. Study of composition – mass of the primaries
Xmax
Depth of the maximum

21. Xmax as a function of the energy{
Compilation
previous data

22. Photon – the experimental method
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

23. Limits on photon fraction (integral flux) PRELIMINARY
HP: Haverah Park
A1,A2: AGASA
Y: Yakutsk
~ 3 %

24. Neutrinos - Earth skimmingL W
10 km
hmax

25. Auger – no neutrino candidates

26. Xmax measured over two decades of energy
Syst error on Xmax < 15 g /cm2
(<A> ~ 5)
Mass composition: protons, light nuclei, Fe ?

27. HiRes Final data 2007 Power law index E-γ
5.1 +/- 0.7
Power law index E-γ
HiRes Group: astro-ph/
V. Berezinski: shallow minimum (“dip”) from e +e- production
and pile-up of GZK particles

28. Auger - One event of high energy:~1020 eV, q ~60°
34 tanks
Lateral Distribution Function
LDF
Fit distance r from the core
S=A [r/rs (1+r/rs)] -β
rs = 700 m
A, β from fit (β= 2-2.5)
S(1000) energy estimator
Signal (VEM)

29. Energy calibration – hybrid events Energy obtained by the calorimetric measurement of the fluorescence detector. Simulation not needed.
661 events
S(1000)
6x1019 eV
Corrected to 380
EFD= a x S b
b = 1.08 ± 0.04
Error on the energy
19 % statistical
22% systematic (scale error) fluorescence yield/calibration

30. Energy spectrum (θ < 600) Exposure 7000 km2 sr yr (3% error) (~ 1 year Auger completed)
Exp. Observed
> 4x ±
> ±
Trigger efficiency =100 % above 3x1018 eV

31. Fit E-γ GZK cut off Detailed features of the spectrum better seen
by taking difference with respect to
reference shape Js = A x E-2.69
Fit E-γ
γ = 2.69 ± 0.02
GZK cut off
Slope γ above 4x1019 eV:
4.0 ± 0.4
HiRes:
5.1 ± 0.7

32. ENERGY SPECTRUM
0-60 degrees
60-80 degrees

33. Precision of the measurement of the direction
Vertical shower of energy 1019 eV activates 7-8 tanks

34. EVIDENCE OF ANISOTROPY AT HIGH ENERGY
High-energy events (E > 5.7x1019 eV) are correlated with AGNs
at distance less than about 75 Mpc Angular correlation (~ 30)
9 November 2007

35. Véron &Véron-Cetty catalogue 442 AGN (292 in f.o.v.)
z<0.018 (75 Mpc)
27 events E > 57 EeV
20 events correlate with AGN within 3.20
Galactic coordinates
Relative
exposure
Doublet from Centaurus A
(nearest AGN at ~ 4 Mpc)
Border of the
field of view
Super-galactic plane

36. ANALYSIS METHOD Three parameter scan to find the minimum of P
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 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

37. Maximum AGN redshift ( 0.018 corresponding to ~75 Mpc)
Set of parameters for the minimum P corresponding to maximum correlation with AGN
Angular separation ψ = 3.10
Maximum AGN redshift ( corresponding to ~75 Mpc)
Energy threshold : 57 EeV
p = 0.21
Number
of events
E > 57 EeV
Correlated
with AGN
ψ = 3.1 degree
Expected for
isotropy
Exploratory scan
1 Jan May 06 15 12
3.2
Second independent set
27 May 06–31 Aug 07 13 8
2.7
Full data set
(about 1.2 year full Auger) 27 20
5.6
Full data set excluding
region of the galactic plane
(|b| > 12 degree) 21 19
5.0
(1.7x10-3)
Probability of observed configuration if distribution is isotropic: 10-5
5 of the 7 events not correlated are close to the galactic plane

38. ANGULAR SEPARATION FROM THE CLOSEST AGN
The 6 events at low
galactic latitudes
|b| < 120
Isotropic flux
catalogue
incompleteness
larger deflections
in galactic B CR
AGN

39. Deflection in the galactic magnetic field
Simulation
(protons 60 EeV)
20 correlated events

42. Conclusions FUTURE Auger North (Colorado, US) to study
Auger observes the GZK steepening of the energy spectrum confirming HiRes results (very high energy events are of extra-galactic origin).
Correlation with AGNs (E > 57 EeV). Direct evidence of extra-galactic origin. Identification of the sources. ~ 25 events/year
Interplay of different observables
- Composition at very high-energy: protons or mixture of protons and light nuclei as indicated by Xmax ? <A>=5 ?
Shape of the GZK steepening.
Energy calibration (22% scale error at present)
Horizon ( calculation gives 75 Mpc  80 – 100 EeV).
Magnetic field deflection (small for protons !)
More statistics and better control of the systematic errors needed !
Auger North (Colorado, US) to study
northern sky (~ km2 = 7 x Auger South)
FUTURE

44. Zenith angle dependence of the energy estimator S(1000)

45. Shower parameters from Fluorescence Detector (single telescope)
Determination of the Shower-Detector Plane (SDP) is good
Time fit: t(χi) = t0 + Rp*tan [(χ0 - χi)/2]
Space reconstruction is inaccurate within the Shower Detector Plane.
shower t0 Rp χi χ0

46. Attenuation Rayleigh attenuation length: 23 km at sea level
Vertical Aerosol Optical Density
VAOD (h) = ∫ α(z) dz
Attenuazione: exp{-VAOD(h)}
Not a good night

47. Study of excess from the Galactic Center
Observation of an excess from the region of the Galactic centre at the level of 4.5 σ was reported by AGASA (1.22 ± 0.05) in angular cone of 20 degree radius.
The Auger Observatory is suitable for these studies because the Galactic centre (constellation of Sagittarius) lies well in the field of view of the experiment.
In the Auger data there is no indication of a statistically significant excess
Energy interval (eV) Nobs/Nexp Ratio (errors: stat, syst)
/ ± 0.02 ± 0.01
– / ± 0.02 ± 0.01
– / ± 0.03 ± 0.01

48. Effect of interaction with CMB V.Berezinsky et al.
protons
Effect of interaction with CMB
V.Berezinsky et al.
production of e+ e- pairs
photoproduction of pions

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