Very Large Volume Neutrino Telescope Workshop
Athens 13 – 15 October 2009
Recent Results on Ultra High Energy Cosmic Rays
Alan Watson
University of Leeds
Outline:
Results on Energy Spectrum: HiRes and Auger
Results on Anisotropy
Mass Composition
Implications for UHE neutrino astronomy
- but will not discuss Auger limits on neutrinos
1390 m above sea-level or ~ 875 g cm-2
400 physicists18 countries~90 Institutions
Spokesperson: Giorgio Matthiae
Auger Exposure nearly doubled since Mérida
12,790 km2 sr yr> 1019 eV: 4440 (HiRes stereo: 307> 5 x 1019 eV: 59 : 19 > 1020 eV: 3 : 1)
• HiRes Aperture: X 4 at highest energies
• X 10 AGASA • TA area about ¼ Auger and exposure 0.5 AGASA
A Hybrid Event
Energy Estimate- from area under curve+ Missing energy
(2.1 ± 0.5) x 1019 eV
1.17
1.07
f
f = Etot/Eem
Etot (log10(eV))
785 EVENTS
Auger Energy Calibration
log E (eV)
8
Energy Spectrum from Auger Observatory
Five-parameter fit: index, breakpoint, index, critical energy, normalization
Schuessler
HE 0114
SD + FD
LodzICRC 2009
Above 3 x 1018 eV, the exposure is energy independent: 1% corrections in overlap region
9
The Auger Energy Spectrum – compared with models
Schuessler
HE 0114
ICRC
2009
Lodz
Above 3 x 1018 eV, the exposure is energy independent: ~1% corrections in overlap region
HiRes Spectrum: Sokolsky,Trondheim
• Monocular spectra - HiRes I and II
• HiRes I - largest statistics, limited elevation angle viewing = high threshold energy
• HiRes II - better low energy response
• Stereo spectrum - best geometrical and energy resolution – use as reference
Monocular and Stereo Aperture
Stereo Geometrical Resolution
Mono and Stereo Spectra
Mono – HR1 and HR2
Stereo
“The spectra measured using the monocularand stereo methods agree very well” Abassi et al: AstroParticle Phys 32 53 2009
HiRes Mono HiRes Stereo
Auger Combined
Power Law before ankle
3.25 ± 0.01 3.31 ± 0.11 3.26 ± 0.04
Power Law (intermediate)
2.81 ± 0.03 2.74 ± 0.05 2.59 ± 0.02
Power Law above suppression
5.1 ± 0.7 5.5 ± 1.8 4.3 ± 0.2
log E (ankle) 18.65 ± 0.05 18.56 ± 0.06 18.61 ± 0.01
log E (suppression)
19.75 ± 0.04 19.76 ± 0.11 19.46 ± 0.03
Comparison of Slopes and break points for HiRes and Auger
Residuals with respect to slope of 2.74through this data point at log e = 18.65
ANISOTROPYSituation as at November 2007: Science and Astroparticle Physics
27 events
22
The Auger Sky above 60 EeVComparison with Swift-BAT AGN density map
Simulated data sets based on isotropy (I) and Swift-
BAT model (II) compared to data (black line/point).
Aublin
HE 0491
ICRC Lodz 2009
Mass Composition Indications
• Most unexpected result from Pierre Auger Observatory so far
Some Longitudinal Profiles measured with Auger
More Longitudinal Profiles measured with Auger
Data and MC Cuts
• Zenith angle < 70 deg
• Psuedo-distance to HiRes-2 > 10 km.
• Xmax bracketed in HiRes-2 FOV
• Energy > l018.2 eV
• Loose chi-sq profile fit and Xmax uncertainty cuts.
Large fraction of the data used – in contrast to Auger approach
HiRes
Elongation rate corrected for detector acceptance andcomparison with previous results
Xmax fluctuations data and p QGSJET02: HiRes
Xmax resolution
Auger – from above
J Belz (HiRes): Blois June 2009
Fukushima: Rapporteur Talk at Lodz
Probably now little doubt that a steepeningin the cosmic ray spectrum has been found - HiRes and Auger data agree reasonably well
BUT, it may be premature to jump to the conclusion thatthis is really the GZK-effect – energy limit in sources?
Anisotropy is the key – but many more data needed
BUT: What can we learn from the AGASA data?
I do not believe that the measurements on theground are in error: The data are surely telling us something
Energy Estimates aremodel and mass dependent
Takeda et al. ApP 2003
Comment and Speculation
•Effort should be made to understand why ground arrayenergy estimates are not in agreement with energyspectra that are based on fluorescence detection
• Does the multiplicity become very large at the highest energies?
Maxima would be higher in atmosphere
Fluctuations would be smaller
More rapidly rising cross-section cannot be excluded
Need measurements closer than 300 m from core
Summary
• Suppression of spectrum slope above 40 EeV seems certain – but is it really GZK-effect?
• Anisotropy suggests around 40% correlation with local matter density above 55 EeV
• Composition situation is puzzling. Heavy nuclei at higher energies are not excluded. Big HiRes/Auger differences
Large fraction of heavy nuclei would impact on predictionsof neutrino fluxes
G Burbidge: ICRC Calgary 1967: Rapporteur Talk
Reminder: Initial Estimate of Temperature was 3.5 +/- 1 K
Do we alreadyhave evidence for exotic physics?
Differential Spectra: Sample data
AG/Au = 2.30AG/HiR = 1.76
AG/Au = 3.75AG/HiR = 2.90
Integral Rates
1331
24 2 4
827 44 5642937
Scintillator Arrays agree
Fluorescence Calibrated spectra agree
Hillas: Phil Trans R Soc London 277 413 1974
Could the difference between fluorescence calibrated data and modeldata be due to loss of energy in the inner regions of the shower?
Should not overlook problems with particle physics at highest energies
1.17
1.07
f
f = Etot/Eem
Etot (log10(eV))
Fluorescence Measurements are NOT model or mass independent