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 physicists 18 countries ~90 Institutions Spokesperson: Giorgio Matthiae

Auger Exposure nearly doubled since Mérida 12,790 km 2 sr yr > eV: 4440 (HiRes stereo: 307 > 5 x eV: 59 : 19 > 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 eV

f f = E tot /E em E tot (log 10 (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 Lodz ICRC 2009 Above 3 x 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 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 monocular and stereo methods agree very well” Abassi et al: AstroParticle Phys

HiRes Mono HiRes Stereo Auger Combined Power Law before ankle 3.25 ± ± ± 0.04 Power Law (intermediate) 2.81 ± ± ± 0.02 Power Law above suppression 5.1 ± ± ± 0.2 log E (ankle) ± ± ± 0.01 log E (suppression) ± ± ± 0.03 Comparison of Slopes and break points for HiRes and Auger

Residuals with respect to slope of 2.74 through this data point at log e = 18.65

ANISOTROPY Situation as at November 2007: Science and Astroparticle Physics 27 events

22 The Auger Sky above 60 EeV Comparison 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. X max bracketed in HiRes-2 FOV Energy > l eV Loose chi-sq profile fit and X max uncertainty cuts. Large fraction of the data used – in contrast to Auger approach HiRes

Elongation rate corrected for detector acceptance and comparison with previous results

X max fluctuations data and p QGSJET02: HiRes X max resolution Auger – from above

J Belz (HiRes): Blois June 2009

Fukushima: Rapporteur Talk at Lodz

Probably now little doubt that a steepening in the cosmic ray spectrum has been found - HiRes and Auger data agree reasonably well BUT, it may be premature to jump to the conclusion that this 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 the ground are in error: The data are surely telling us something

Energy Estimates are model and mass dependent Takeda et al. ApP 2003

Comment and Speculation Effort should be made to understand why ground array energy estimates are not in agreement with energy spectra 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 predictions of neutrino fluxes

Reminder: Initial Estimate of Temperature was 3.5 +/- 1 K Do we already have evidence for exotic physics?

Differential Spectra: Sample data AG/Au = 2.30 AG/HiR = 1.76 AG/Au = 3.75 AG/HiR = 2.90

Integral Rates Scintillator Arrays agree Fluorescence Calibrated spectra agree

Hillas: Phil Trans R Soc London Could the difference between fluorescence calibrated data and model data be due to loss of energy in the inner regions of the shower? Should not overlook problems with particle physics at highest energies

f f = E tot /E em E tot (log 10 (eV)) Fluorescence Measurements are NOT model or mass independent