1

The Pierre Auger ObservatoryCapturing Messengers from the

Extreme UniverseA new cosmic ray observatory designed for a high

statistics study of theThe Highest Energy Cosmic Rays

UsingTwo Large Air Shower Detectors

Mendoza, Argentina(construction nearing completion)

Colorado, USA(in planning)

Gregory Snow / University of Nebraska

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The Auger Collaboration67 Institutions, 369 Collaborators

Argentina NetherlandsAustralia PolandBolivia* PortugalBrazil Slovenia Czech Republic SpainFrance United Kingdom Germany USAItaly Vietnam*

Mexico

* associate

True International Partnership - by non-binding agreement -

No country, region or institution dominates – No country contributes more than 25% to the construction.

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The Cosmic Ray Spectrum

Energy (eV)

Flux

(m2 sr

s e

V)-1

Manyexperimentshavecontributed

Power law withstructure

Supernovashock cangenerate upto ~1015 eV

Transition fromgalactic toextra-galactic?

Most interesting,but:• Rare• Don’t know

accelerationmechanism

• Point backpossible

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Possible SourcesConventional – Bottoms-Up

• Hot spots in radio galaxy lobes?

• Accretion shocks in active galactic nuclei? - Colliding galaxies?

• Associated with gamma ray bursts?

Exotic – Top-Down

• Annihilation of topological defects?

• Cold dark matter?

• Evaporation of mini black holes?

ν’sγ’ssignatures

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Propagationin the Cosmic Microwave Background

Space becomes opaque to protons of energy > 5 * 1019 eV because of the cosmic microwave background - Greisen-Zatsepin-Kuzmin(GZK) suppression. Cosmic ray protons with 1020 eV must come from less than about 50 Mps.

proton +photonCMB -> pion + nucleon

Recent data at theend of the spectrum

GZK cut off?

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Propagationmagnetic fields

At energies near 1020 eV protons magnetic deflection is small – Cosmic ray protons should point back to the source. Charged particle astronomy becomes possible.

1018 eV protons

1020 eV protons

J. C

roni

n

5 ×1019 eV ~ bottom end of pointing capability (about 10o)

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Interaction with the atmosphereA look at air showers

Shower Max

N

Sea level

γ ~ 89% ⎫ ⎬ 10 MeV e± ~ 10% ⎭

µ ~ 1% 1 GeV

1011 Particlesat surface

Shower front Shower core -hard muons

EM shower

Depth in the Atmosphere

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Detecting Cosmic Ray Air Showers

Fly’s Eye

Surface Array

Air shower measurements are made by two techniques

1) Surface Arrays

2) Fluorescence Telescopes (Fly’s Eyes)

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Surface Array100% duty cycleWell-defined acceptanceUniform sky coverageSimple robust detectorsMass determination using rise time, muon/em (*)Energy determination requires simulation

Fluorescence DetectorCalorimetric energy measurementDirect view of shower developmentGood angular resolution (< 1o)Correction for atmospheric attenuationAperture requires simulation (*)10% duty cycle (moonless nights only)

Features of the Air Shower Detector Techniques

µ‘s come first,γ’s,e’s showercausing delay

Can’t see smallshowers faraway, needgood model ofatmosphere

Fe vs. protonmore µ-rich

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Pierre Auger Observatory

Science Objectives

Cosmic ray spectrum above 1019 eV • Shape of the spectrum in the region of the GZK feature

Arrival direction distribution• Search for departure from isotropy – point sources

Composition• Light or heavy nuclei, photons, neutrinos, exotics(?)

Design Features

High statistics (aperture >7000 km2 sr above 1019eV in each hemisphere) Full sky coverage with uniform exposureHybrid configuration – surface array with fluorescence detector coverage

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The Hybrid Design

• Nearly calorimetric energy calibration of the 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

• Determination of the angular and core position resolutions

Surface detector array + Air fluorescence detectorsA unique and powerful design

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The Observatory Plan

Surface Array1600 detector stations1.5 km spacing3000 km2

Fluorescence Detectors4 Telescope enclosures6 Telescopes per

enclosure24 Telescopes total

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The Surface ArrayDetector Station

Communicationsantenna

Electronics enclosure

3 – nine inchphotomultipliertubes

Solar panels

Plastic tank with12 tons of water

Battery box

GPS antenna

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Deploying the Surface Detectors

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The Fluorescence Detector

11 square meter segmented mirror

Aperture stop and optical filter

440 pixel camera

Corrector lensminimizes sphericalaberrations, filterbrackets 350 nmfluorescence light

FD telescopes in closedenvironment

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The Fluorescence Detector Los Leones

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Atmospheric Monitoring and Calibration

Lidar at each fluorescence eye

Central Laser Facility

Drum for uniform camera illumination –end to end calibration .

Absolute Calibration

Atmospheric Monitoring

Lidar (Light Detection and Ranging)measures back-scattered light→atmos. density profile

Used to “shootthe shower”

Simulates hybridevent – some light to tank

Precisely calibrated lightsource

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Status of the Observatory

1190 out of 1600 surface detector stations deployed

Three of four fluorescence buildings operational each with 6 telescopes

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Aerial Photos of Fluorescence BuildingsNovember 2006

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Building the Observatory

Thanks to Cristina Raschia

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Deployment Sequence

Thanks to Cyril Lachaud

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Deployment Sequence

Thanks to Cyril Lachaud

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Surface Detector Event

Θ~ 48º, ~ 70 EeV

Flash ADC tracesFlash ADC traces

Lateral density distribution

Typical flash ADC trace

Detector signal (VEM) vs time (ns)

PMT 1

PMT 2

PMT 3

70 × 1018 eV

S(1000) best estimate ofshower energy, min.

fluctuations

18tanks

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Lateral density distribution

Surface Detector Event Θ~ 60º, ~ 86 EeV

Flash ADC traces

Flash ADC Trace for detector late in the shower

PMT 1

PMT 2

PMT 3

34tanks

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Hybrid Event Θ~ 30º, ~ 8 EeV

x [km]10 15 20 25 30

y [k

m]

8

10

12

14

16

18

20

22

24

26

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]2slant depth [g/cm400 500 600 700 800 900

)]2d

E/d

X [

GeV

/(g

/cm

2

4

6

8

10

12

14

16

18

20

610×

azimuth [deg]60 65 70 75 80 85 90

elev

atio

n [

deg

]

5

10

15

20

25

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Shower plane from FD

SD core position

FD pulse heightscorrected foratmospheric effects,Cerenkov light

Depth in atmosphere

Integral under Gaisser-Hillas fit gives FD energy, which is corrected by~10% (simulation) due to shower particles penetrating earth

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Example Event 3 A hybrid event – 1021302

Zenith angle ~ 30º, Energy ~ 8 EeV

Flash ADC traces

Lateral density distribution

Hybrid Event Θ~ 30º, ~ 8 EeV

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Fitted Electromagnetic Shower

from Fly's Eye 1985

Tim

e µ

sec

Angle χ in the shower-detector plane

Same Hybrid EventΘ~ 30º, ~ 8 EeV

Tanks

Pixels

These 2 plots give energy,angle, and core position

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A Tri-ocular Event!~20EeV

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A Big Event - One that got away!

Shower/detector plane

outside of array Fluorescence Mirror

Energy Estimate

>140 EeV

No correction for aerosols, could be as high as 2 × 1020 eV

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Performance: Angular Resolution

Surface array Angular resolution (68% CL)< 2.2º for 3 station events (E< 3EeV, θ < 60º )< 1.7º for 4 station events (3<E<10 EeV)< 1.4º for 5 or more station events (E>10 EeV)

Hybrid Angular resolution(68% CL)

0.6 degrees (mean)

Hybrid-SD only space angle difference

Hybrid Data

Angle in laser beam /FD detector plane

Laser Beam

Entries 269

σ(ψ) = 1.24º

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Performance: Resolution of Core Position

Hybrid – SD only core position

Hybrid DataLaser Data

Laser position – Hybrid and FD only (m)

-500

+500

Entr

ies

501

M

ean

5.

8 ±

6.5

m

R

MS

147

m

Entries 501 Mean 68 ± 8 m RMS 173 m

Core position resolution

– Hybrid: < 60 m Surface array: ~150 m

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Cosmic Ray Air Shower MeasurementsEnergy – if surface array only

Surface Array: Measure radial particle density

distribution and match to simulateddistribution.

Cle

m P

ryke

simulation

11 tank event

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Cosmic Ray Air Shower MeasurementsEnergy – fluorescence detectors

Fluorescence Detectors: Measure the light produced

by the shower

From fluorescence yield experiment

350 nm

Fully calibrated calorimetric measurementNote how shower max moves deeper inatmosphere for higher energy shower

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The First Data Set ICRC2005 in India

Collection period – 1 January 2004 to 5 June 2005

Zenith angles - 0 - 60ºTotal acceptance – 1750km2 sr yr

(~ AGASA)Surface array events (after

quality cuts)Current rate - 18,000 / monthTotal -~180,000

Hybrid events (after quality cuts) Current rate – 1800 / monthTotal ~ 18000

Cumulative number of eventsJa

nuar

y 04

July

04

Janu

ary

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ICRC2005 contributions available on Auger web sitehttp://www.auger.org

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Sky Map of Data set

Galactic Coordinates

Enhancement toward southpole due to oversampling

Where we don’tsee from thesouth

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Energy Determination and the Spectrum

The detector signal size at 1000 meters from the shower core - called the ground parameter or S(1000) - is determined for each surface detector event using the lateral density function. S(1000) is proportional to the primary energy.

The energy scale is based on fluorescence measurements without reliance on a specific interaction model or assumptions about the composition.

Zenith angle ~ 48º

Energy ~ 70EeV

Only model-dependent ingredient is the ~10% correction for shower particles penetrating earth

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Energy Determination and the Spectrum

10EeV

1 EeV

Hybrid EventsStrict event selection:track length >350g/cm2Cherenkov contamination <10%

Linearity preservedfor more recentevents at higherenergy too

The energy converter:

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

Transfer the energy converter to the surface array only events.

Log

(E/E

eV)

Log S(1000)

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Auger Energy Spectrum

∆E/E~30%

∆E/E~50%

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Systematic Errors in the FD (Hybrid) Energy Normalization

~ 30%50% at higher energyis from extrapolationof energy converter

J. Bellido

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Comparison with HiRes1, AGASA

1) M. Takeda et al. Astroparticle Physics 19, 447 (2003)

2) R.U. Abbasi et al. Phys Lett B (to be published)

Auger spectrumsimilar to HiReswhich is consistentwith GZK suppression

Auger reservesmaking specificclaim untilmore statistics

3

68

Stat. errors only

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Galactic centerNo excess approaching

significance of AGASA, SUGAR reportsAuger data Jan 2004-Mar 2006

Circles represent regions of previously reported excesses from AGASA, SUGAR.

Ove

rden

sity

sign

ifica

nce

Galactic plane

x

Sugar = Sydney University Giant Air Shower Recorder

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Photon LimitIntegral (E>E0) photon fraction limit based on shower depth (Xmax)

measured in 29 quality hybrid events above 1019 eV

Auger data Jan 2004-Feb 2006Modelspredictlines

HP, A1, A2 == previous limits from Haverah Park, AGASA data.2007: Improved limits/detection(?) using surface detector observables.Start to probe model predictions (Z-burst, SuperHeavy Dark Matter, Topological Defects) yielding photon primaries, also extend limits to higher energies.

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MalargüeOutreach

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Northern Auger

Objectives:– Complete sky coverage/ Increased aperture

• Anisotropy – source searches (charged particle astronomy)

• More detailed spectrum near the GZK feature• Increased aperture for earth skimming neutrinos.

• Design– Increase the array size from 3000 to 10000 Km2

– Simpler surface detectors (1 PMT)– Greater average spacing– 12 FD telescopes– Simpler communications system– Possible new technologies(Radio, radar detection) for even greater aperture

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Northern Auger Site

• Requirements– Large flat area w/clear, dark sky– Remote, but easy access– Latitude, Altitude– Infrastructure

• Site identified in Colorado – Around Lamar (38o N, 102o 30’ W )

– Over 4000 sq miles (84x48 miles)– 1200-1400 m.a.s.l– 3 hs drive from DIA

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Summary• The Observatory is approaching completion.• With 25% of a full Auger-year exposure, we have:

– Defined our empirical spectrum analysis strategy and produced our first model-independent spectrum

– Performed first studies of anisotropies in the sky– Set limits on photon primaries

Future Plans• Complete Auger South by mid 2007• Fully understand our instruments.• Use rapidly expanding data set (x7 in two years) 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 and exotics• Begin work on Auger North

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Backup Slides

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Cosmic Ray Air Shower MeasurementsSome Sensitivity to Neutrinos

Large zenith angle (>60 degrees) hadronshowers have lost mostof their electromagneticcomponent.

Tau neutrinos can interactin the mountains or in thecrust of the earth toproduce taus that decay andshower over the detector.

τ Lifetime ~40 km for 1018 eV ντ Low rate ~1/year

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The Cosmic Ray Observatory Project (CROP) in Nebraska

Gregory SnowUNL Department of Physics and Astronomy

September 22, 2006

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CROP article in Lincoln Journal Star, 7 August 2003

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A few facts• Funded by $1.34 Million NSF grant, 2000-2007• Co-PIs Greg Snow and Dan Claes• 26 Nebraska and 5 Colorado schools enlisted and trainedin summer workshops of duration 2-4 weeks, about5 new schools per summer

• Venture into Colorado was a joint effort by CROP,WALTA, ALTA

• Hosted 2 one-day meetings each academic year forparticipants from all years to report results, exchangefaulty equipment, receive equipment and softwareupgrades, refresh training or train new students

• External evaluation of this period has shown that CROPhas accomplished most of its educational and scientificgoals listed in the original proposal

• CROP has also served as a great training ground forstaff (undergrad, grad students) at UNL

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Highlighted squares = participating schools

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The Chicago Air Shower ArrayThe Chicago Air Shower Array

• CROP uses retired detectors from the Chicago Air Shower Array• 1089 boxes each with:

• 4 scintillators and photomultiplier tubes (PMT)• 1 high voltage and 1 low voltage power supply

• Two removal trips (September 1999, May 2001) yielded over 2000 scintillator panels, 2000 PMTs, 500 low and power supplies

54U.S. Army Photo

The CROP team at Chicago Air Shower Array (CASA) site

September 30,1999

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CROP data acquisition electronics cardDeveloped by Univ. Nebraska, Univ. Washington, Fermilab (Quarknet)

5 VoltDC power

To PCserial port

Discriminatorthreshold

adjust

GPS receiverinput

Eventcounter

Programmablelogic device

Time-to-digitalconverters

Four analogPMT inputs

• 43 Mhz (24 nsec) clock interpolates between 1 pps GPS ticks for trigger time

• TDC’s give relative times of 4 inputs with75 picosecond resolution

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Summer 2004 Workshop ActivitiesDetector assembly and testing

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Each school made new rooftop enclosures

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Excellent extensive air showerdata taking run overnight

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New enclosures making it to rooftops

Westside High SchoolOmaha, NE

Weights, important !!

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NALTAThe North American Large-Scale Time-Coincidence Array

CROP

Pierre Auger northern hemisphere site insoutheast Colorado

SCRODSALTA

CHICOS

WALTA ALTA

http://csr.phys.ualberta.ca/nalta/• Includes links to individual projectWeb pages

TECOP

PARTICLE

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Aiming toward a worldwide networkof cosmic ray detectors