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Roma Meeting: June 2007
Recent results from the Pierre Auger Observatory
(and comparisons with AGASA and HiRes)
Alan Watson
University of Leeds
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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
The Pierre Auger Collaboration
Aim: To measure properties of UHECR with unprecedentedstatistics and precision – necessary even if no disagreement
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Array of water-Cherenkov or scintillation detectors
Fluorescence in UV →
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Shower Detection Methods
OR
300 – 400 nm
Nitrogen fluorescence
The Design of the Pierre Auger Observatory marries these two well-established techniques
AND
~1°
Due to Enrique Zas
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Present situation Present situation (April 13, 2007)(April 13, 2007)
1410 (1357 filled) SDstations deployed with 1304 taking data (300507) OVER 80%All 4 fluorescence buildings complete,each with 6 telescopes
AIM: 1600 tanks
30 May 2007
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GPS Receiverand radio transmission
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UV optical filter(also: provide protectionfrom outside dust)
Camera with 440 PMTs (Photonis XP 3062)
Schmidt Telescope using 11 m2 mirrors
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θ~ 48º, ~ 70 EeV
Flash ADC tracesFlash ADC traces
Lateral density distribution
Typical flash ADC trace
at about 2 km
Detector signal (VEM) vs time (µs)
PMT 1
PMT 2
PMT 3
-0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 µs
18 detectors triggered
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Lateral density distribution
θ~ 60º, ~ 86 EeV
Flash ADC traces
Flash ADC Trace for detector late in the shower
PMT 1
PMT 2
PMT 3
-0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 µs
35 detectors triggered
Much sharper signalsthan in more vertical events leads toν- signature
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79 degrees
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Laser Facilities Laser Facilities (April 13, 2007)(April 13, 2007)30 May 2007
There are also2 laser facilities,CLF and XLF
Steerable YAG lasersto mimic 100 EeV
CLF
XLF
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The Central Laser Facility of the Pierre Auger Observatory
355 nm, frequency tripled, YAG laser, giving < 7 mJ per pulse: GZK energy
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Atmospheric Monitoring
Balloon probes (T,p)-profiles
LIDAR at each FD building
light attenuation lengthAerosol concentration (Mie scattering)
steerable LIDAR facilities located at each FD eye
• LIDAR at each eye
• cloud monitors at each eye
• central laser facility
• regular balloon flights
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Pixel geometryshower-detector plane
Signal and timingDirection & energy
FD reconstruction
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ti
Geometrical Reconstruction
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Angular and Spatial Resolution from Central Laser Facility
Laser position – Hybrid and FD only (m)Angle in laser beam /FD detector plane
Mono/hybrid rms 1.0°/0.18° Mono/hybrid rms 570 m/60 m
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ARRIVAL DIRECTION DISTRIBUTION FROM AUGER
• No significant emission from Galactic Centre
• No broadband signals – e.g. Dipole – at any energy above 1 EeV e.g 1 < E < 3 EeV, Amplitude < 0.7%
• No clustering of the type claimed by AGASA
• No signal from BL Lacs as possibly seen by HiRes
Summary:Previous Claims have not been confirmed
BUT, two ‘prescriptions’ are currently being tested – but I cannot tell you what they are
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Energy Determination with Auger
The detector signal at 1000 m from the shower
core
– S(1000)
- determined for each surface detector event
S(1000) is proportional to the primary energy
The energy scale is determined from the data and does not depend on a knowledge of interaction models or of the primary composition – except at level of few %.
Zenith angle ~ 48º
Energy ~ 70 EeV
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A Hybrid Event
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S38 vs. E(FD)
387 hybrid events
Absolute value of FDcalibration uncertain ~ 14%
Nagano et al, FY used
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10 EeV S(1000)
Precision of S(1000) improvesas energy increases
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(Outdated) Summary of FD systematic uncertainties
%
Note: Activity on several fronts to reduce these uncertainties
(to be updated)
~ 14%
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Summary of systematic uncertainties
Note: Activity on several fronts to reduce these uncertainties
New version from Bruce Dawson’s Merida talk
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5165 km2 sr yr ~ 0.8 full Auger year
Exp Obs>1019.6 132 +/- 9 58
> 1020 30+/- 2.5 2
Spectrum from Surface Detectors
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Ankle? Comparisons of residualsagainst an arbitrary spectrum
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Spectrum from very inclined events
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Calibration curve for Inclined showers
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Energy Spectrum from 60 °< < 80°: 734 events
1510 km2 sr yr
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Blue: < 60°Black: inclined
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ti
A ‘hybrid’ spectrum
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Triggering probability for Hybrid Events
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Lunar Cycles
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Hybrid Spectrum: clear evidence of the ‘ankle’ at ~ 4 x 1018 eV
-3.1 +/- 0.2
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Energy Estimates aremodel and mass dependent
Takeda et al. ApP 2003
Surface Detectors
Recent reanalysis has reduced number > 1020 eVto 6 events
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Teshima: Roma 2006
38HiRes Group: astro-ph/0703099
- 5.1 +/- 0.7
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17.0 17.5 18.0 18.5 19.0 19.5 20.0 20.51E-38
1E-37
1E-36
1E-35
1E-34
1E-33
1E-32
1E-31
1E-30
1E-29
1E-28
1E-27
J (
m2 s
r s e
V)-1
log E (eV)
Auger Combined HiResI HiResII
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18.0 18.5 19.0 19.5 20.0 20.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5(J
/Js )
- 1
log E (eV)
Auger HiRes I HiRes II
x3
x2
x1
Plot of residuals of individual spectra compared to standard, Js = A E-2.6
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Immensely important IF it was to be establishedthat slopes at highest energy are different in northern (- 5.1+/- 0.7) and southern hemispheres (- 4.1 +/- 0.4)
But, MUCH TOO EARLY TO DRAW CONCLUSIONS
• Uncertainties about HiRes aperture
• Poorer energy and angular resolution in HiRes than Auger
• Low number of events – and no more to come to from HiRes
• Issue will be addressed with more Auger data
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The HiRes aperture is noteasy to compute and requiresassumptions about the spectral indexand the mass composition in regionswhere it has not been measured.
astro-ph/0703099
Physics Letters B 2005
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Exposure
AGASA ~1700
HiResI “3-4 times AGASA”
Auger
6675
1019 0.49 0.29 0.22
827 564 1473
> 4 x 1019 0.04 0.015 0.10
65 49 66
> 7x 1019 0.014 3.6 x 10-3 2 x 10-3
24 13 13
> 1020 6 x 10-3 1.0 x 10-3 3 x 10-4
11 4 2
Integral Rates: km-2 yr-1 sr-1
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Variation of Depth of Maximum with Energy
Inferring the Primary Mass: Crucial for Interpretation
******
******
******
******
Xmax
log E
p
Fe
Key is energy per nucleon
protonsnucleineutrinosphotons
all are expected at some level- at different energies
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46Fluctuations in Xmax yet to be explored and exploited
Elongation Rate measured over 2 decades in energy
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and few photons at high energy
AnkleFluctuations in Xmax to be exploited
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49Jump to 66
50Berezinsky et al Phys Rev D 74 (2006)
Steepening affected by over- and under-densities
Comparison of data with models of origin and propagation
Berezinsky et al. argue that the dip is caused by γ + p p + e+ + e-
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Knee
>1019 eV1 km-2 sr-1 year-1
air-showers
after Gaisser
Hadronic Physics
Ankle
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Models describe Tevatron data well - but LHC model predictions reveal large discrepancies in extrapolation.
Could there be surprises in the hadronic physics?
James L. Pinfold IVECHRI 2006 13
ET (LHC)
E(LHC)
54 Prospects from LHCf
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LHC measurement of TOT expected to be at the
1% level
– useful in the extrapolation up to UHECR energies
The p-p total cross-section
10% difference in measurements ofTevatron Expts:
James L. Pinfold IVECHRI 2006 14
(log s)
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Summary:• Spectrum: ankle and steepening seen in model-
independent measurement and analysis
• But what does this all mean? Is the ankle marking a galactic/extra-galactic change?
Have we seen the GZK effect?Or is it a ‘bump’ from a more local effect?Are the accelerators just ‘tired’?
Can we deduce much from propagation models?
• Measuring MASS is crucial: mixed at highest energy?
• Need a point source (or some evidence of anisotropy) – and/or more insight about hadronic interactions
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