ultra high energy cosmic rays at pierre auger observatory hernán wahlberg universidad nacional de...
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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
• 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
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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
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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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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 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
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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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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.
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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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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.