Ultra High Energy Cosmic Rays Ultra High Energy Cosmic Rays at Pierre Auger Observatoryat Pierre Auger Observatory

HernánHernán Wahlberg WahlbergUniversidad Nacional de La PlataUniversidad Nacional de La Plata

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OutlineOutline

Physics motivationPrevious detection of UHECR

SD: AGASAFD: HiRes

The Pierre Auger Observatory (PAO)Physics results from PAO

Energy spectrumCompositionAnisotropy

Conclusion and future prospects

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What do we want to know?What do we want to know?

Energy spectrumIs there a cut off (GZK) ?

Arrival directionIsotropic or correlated with astronomic sources ?

Mass compositionphotons , protons, nuclei, neutrinos ?

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1st Knee

1 m-2 second-1

Ankle

1 m-2 year-12nd Knee

Ultra-High Ultra-High Energy Energy

Cosmic RaysCosmic Rays

Energy spectrumEnergy spectrum

1 km-2 year-1

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TheThe Extreme Universe Extreme Universe

Pulsar

GRB

AGN

SNR

Radio Galaxy

• Several possible accelerators in nature up to 1020 eV

• Bottom-Up: Fermi acceleration

• Extremely difficult to accelerate above 1020 eV

• Top-Down: Decay of super heavy relics from early Universe -> photons and neutrinos predicted

E ~ Z BGLkpc

Possible acceleration sites

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Interaction of UHE protonsInteraction of UHE protons

Interaction of protons with intergalactic radiation fields.

The Greisen-Zatsepin-Kuzmin cut-offDominant mechanisms for energy loss

p + 2.7k + p + 0 n + +

If particles are observed > 5 x 1019 eV, then they must be local (GZK cut-off)

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Where they should not come Where they should not come from…from…

Constraint on the

proximity of

UHECR sources. Modification of

the spectrum.

If D>100 Mpc E< 100 1018 eV

regardless of the initial energy. If UHECR are due to know stable particles the must come for our

vicinity.

GZK energy cut-off

Proton mean energy vs. propagation distance

E=1019 eVE=1020 eV E=1018 eV

Is it possible to do particle Is it possible to do particle astronomy?astronomy?

Trajectory of protons in the Galaxy Galactic Magnetic Field ~ 2 µG

We can do point-source-search astronomy with UHECR

Detecting UHECRDetecting UHECR

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Shower developmentShower development

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DetectorsDetectors

Fluorescence light emitted by the atmospheric nitrogen excited by the shower passage10 % duty cycleLongitudinal profile is measured

Cherenkov light is emitted as relativist muons and electrons pass through the water100 % duty cycleLateral profile is measured

Previous experiments and Previous experiments and measurementsmeasurements

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AGASA - Surface Detector ArrayAGASA - Surface Detector Array

100 km2 scintillator arrayOperation 1991 – 2004Measure via footprint on ground.

High duty-cycle. Exposure is easily estimated Self-calibration with atmospheric muons.X Energy measurement relies on assumptions about interaction models.

Akeno Giant Air Shower Array

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M. Teshima

Bottom-upwith GZK Cutoff

Top-down?

New analysis!

Energy spectrum by AGASAEnergy spectrum by AGASA

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HiRes – Fluorescence DetectorsHiRes – Fluorescence Detectors

C. Finley

HiRes 1 HiRes 2

Nearly calorimetric energy measurement.X Low duty-cycle.X Aperture is not easily determined.X Atmospheric uncertainty X Fluorescence yield.

High Resolution Fly’s Eye (Utah)

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C. Finley

(1999-2004)(1996-2005)

Energy Spectrum by HiResEnergy Spectrum by HiRes

Consistentwith GZK Cutoff

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Energy SpectrumEnergy Spectrum

Ralph Engel

AGASA (SD)

HiRes (FD)

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The Pierre Auger ObservatoryThe Pierre Auger Observatory

The CollaborationThe CollaborationArgentina MexicoArgentina MexicoAustralia Australia

NetherlandsNetherlandsBoliviaBolivia** Poland PolandBrazil Slovenia Brazil Slovenia

Czech Rep. SpainCzech Rep. SpainFrance UK France UK Germany USAGermany USAItaly VietnamItaly Vietnam** **AssociateAssociate

63 Institutions, 63 Institutions, 369 Collaborators369 Collaborators

A new cosmic ray observatory designed for a high statistics study of the Highest Energy Cosmic Rays

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Hybrid instrumentsHybrid instruments

Calorimetric energy calibration form fluorescence detector transferred to the event gathering power of the surface array.

A complementary set of mass sensitive shower parameters.

Different measurement techniques force understanding of systematic uncertainties

A unique and powerful designSurface detector array

+fluorescence detectors

1600 Water Tanks1.5 km spacing3000 km2

4 Eyes (6x4 telescopes)

#S

#SS

Full sky Full sky coveragecoverage

N

Northern Augerin Colorado

Southern Augerin Argentina

Low population density.

Favourable atmospheric conditions (clouds, rain, light, aerosol).

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The southern location (MalargThe southern location (Malargüüe–e–Argentina)Argentina)

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Six Telescopes looking at 30Six Telescopes looking at 30oo x 30 x 30oo each each

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The Fluorescence Detector

3.4 meter diameter segmented mirror

Aperture stop and optical filter

440 pixel camera

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Atmospheric Monitoring and Atmospheric Monitoring and CalibrationCalibration

Lidar at each fluorescence eye

Central Laser Facility

Drum for uniform camera illumination – end to end calibration .

Absolute CalibrationAtmospheric Monitoring

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The Surface Array The Surface Array Detector StationDetector Station

Communications antenna

Electronics enclosure

3 – nine inchphotomultipliertubes

Solar panels

Plastic tank with 12 tons of water

Battery box

GPS antenna

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Flash ADC traces

Lateral density distribution

Hybrid Event Hybrid Event ΘΘ~ 30º,E ~ 8x10~ 30º,E ~ 8x101818 eVeV

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Tim

e μ

sec

Angle Χ

Hybrid Event Hybrid Event ΘΘ~ 30º, E~ 8x10~ 30º, E~ 8x101818eVeV

Tanks

Pixels

Energy

Energy spectrumEnergy spectrum

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The energy converterThe energy converter

Hybrid events Compare ground parameter S(1000) with the fluorescence detector energy.

Transfer the energy converter to the surface array only events.

S(1000) at 38o

1 EeV 10 EeV 100 EeV

Arisaka

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PreliminaryPreliminary energy spectrum energy spectrum E E33 (2006) (2006)

Mass compositionMass composition

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Primaries and shower Primaries and shower developmentdevelopment

photons protons iron

Xmax

R

Δt N° particles

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Hadrons vs. photonsHadrons vs. photonsSeparating photon showers from events initiated

by nuclear primaries is much easier than distinguishing light and heavy primaries!

AUGER: Photon discrimination with Xmax using HYBRID events.

<2005: Upper limits to the photon fraction only with ground arrays.

Best limit so far!

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Real data vs. photon simulationReal data vs. photon simulationData Set:

Hybrid events (Jan04 – Feb 06)

E>1019 eV

29 events satisfy the selection criteria.

For each event, high

statistics shower

simulations.

Event 1687849:

Xmax = 780 + 28(stat) + 23(syst) g cm-2

MC photons :

<Xmax>= 1000 g cm-2 , rms=71 g cm-2

Differences between photon prediction and data range from 2.0 to 3.8 standard deviations.

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Photon fraction upper limit Photon fraction upper limit (E>10EeV)(E>10EeV)

Astropart.Phys.27:155-168,2007.

Arrival directionArrival direction

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Angular resolution of Auger SDAngular resolution of Auger SD

>10 EeV

>3 EeV

>1 EeV

HiRes (Stereo)

AGASACrucial for anisotropy

studies

Hybrid angular resolution

0.5 º (mean)

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Anisotropy around galactic enterAnisotropy around galactic enter

AGASA 4.5 σ SUGAR 2.9 σ

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Auger around galactic centre Auger around galactic centre

Astropart.Phys.27:244-253,2007.

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Sky map of Auger data setSky map of Auger data set

Galactic Coordinates

Auger latitude = -36

Preference view to the

Galactic center.

Limited coverage in

Northern region

If super-GZK events come from a finite set of local sources in the North we could miss them…

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ConclusionsConclusions

Pierre Auger Observatory statusSD: 30 times larger than AGASA. (>3/4 complete)FD: 4 stations of HiRes-like telescopes. (4/4 complete.)

Hybrid observation is giving critical information to determine the energy and composition.

First estimate of the energy spectrum. GZK feature?Upper limit to photon fraction using FD technique for the first time. New limits soon with SD technique.

Anisotropy studiesno hints of anisotropies in the region of the GC.No excess of events from the GP or SGP.

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Future plansFuture plans

Complete Auger South end 2007. Use rapidly expanding data set to enable

Improvement in the energy assignment.High statistics study of the spectrum in the GZK region.Anisotropy studies and point source searches.Composition studies.

Reduce systematic uncertainties. Exploit events beyond a zenith angle of 60º.

– search for neutrinos Begin work on Auger North.