Very Large Volume Neutrino Telescope Workshop

Athens 13 – 15 October 2009

Recent Results on Ultra High Energy Cosmic Rays

Alan Watson

University of Leeds

a.a.watson@leeds.ac.uk

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