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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

a.a.watson@leeds.ac.uk

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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

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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