Status, Performance and Perspectives of the Auger Observatory

Stefano Argirò 1 for the Auger Collaboration

1 University of Torino, Italy, and INFN

Physics caseThe Auger ObservatoryPerformancePreliminary AnalysisConclusions

EPS 2003

Status, Performance and Perspectives of the Auger Observatory

Air Showers generated by primaries with E>1020 eV exist20 events observed in the past 40 yr

Standard Astrophysical models cannot easily account for such E

Astrophysical sources must be near GZK cutoff at 50 Mpc for E>1020 eV

Near sources should be identified by point source astronomy

High magnetic rigidity of the primaries

0 pp CMB

Stefano Argirò, “Status ... of the Pierre Auger Observatory”

Physics Case

• What is the source of CR of such energies ?• Are sources uniformly distributed ?• What is the composition of the primaries ?• Is GZK violated ?

The experimental situation is rather controversial:

The Pierre Auger Observatory responds with:

• Difficulty of the measurements• Low statistics

• Precision Measurements Hybrid Detector • Large area 3000 + 3000 km2

• Full sky coverage (Harmonic Analysis)

• Sensitivity to -induced showers !

1 particle/yr/km2 E>1019

0.01 particle/yr/km2 E>1020


The UHECR Problem

Physics (oversimplified) scenarios

Anisotropy – point sources Astroph objects

Isotropy decay of superheavy relicsor other new physicsUniformly distributed Astroph sourcesbut depending on composition & magnetic fields

Composition:

gamma new physics

heavy NS, very near sources

GZKViolated

Conserved

near Astroph sourcesnew physics

far Astroph sources

Distribution of arrival directions

proton goto GZK

features of the spectrum

Experimental evidence Meaning

Integrated exposure

No

. of

Ev

ents

(E

> 1

020eV

)

1,000

100

10

1100

1000

10000

100000

1000000

1985 1990 1995 2000 2005 2010 2015 2020

Year

Inte

gra

ted

Ap

ertu

re (

km^

2*st

r *ye

ar)

Fly’s Eye

AGASA

HiRes

Auger(N+S)

EUSO


#S

#S

Northern siteNorthern siteMillard CountyMillard County

Utah, USAUtah, USA


Auger Sites

1600 Water Cerenkov Detectors, 1.5 km spacing

24 Fluorescence Telescopes + extensive atmospheric monitoring

3000 km2 of instrumented area

Southern Site

Northern Site: configuration to be detailed

MalarguePopulation : 15000

Lat : -35, Long: -69, Elevation: 1430 m


The Pierre Auger Observatory

PreProductionPreProduction ArrayArray

EngineeringEngineering ArrayArray

Surface ArraySimple and reliable detectors100% duty cycleEnergy Determination relies on simulation

Fluorescence Detector

Quasi calorimetric energy measurementTracks directly shower developement10-15 % duty cycleSistematics from atmospheric transparency

Combination

Cross CalibrationBetter control of systematicsSuperior Angular resolutionIndependent measurement of

EnergyComposition: /e , Xmax


The Hybrid Detector Concept

Solar panel

Commantenna

GPSantennaThree 8”

PM Tubes

Plastic tank 12 m3 of de-ionized water

White light diffusing liner


electronic box40 Mhz sampling12+12 bit FADCLocal Trigger

The Surface Detector

SD Calibration

Detect presence ofhump from atmosphericmuons with a specialtrigger.

Scale to Vertical EquivalentMuon measuredon a sample tankequipped with scintillators


30° x 30 ° fovSchmidt optics440 pixels1.5 ° Ø pixel12 bit FADC10 Mhz fs

< 4 g/cm2

Digital trigger

Fluorescence Detector


Aperture

Mirror


FD Calibration Absolute: End to End Calibration

The Drum device installed at the aperture uniformly illuminates the camera with light from a calibrated source (1/month)

Alternative techniques for cross checks• Scattered light from laser beam• Statistical

Relative: UV LED + optical fibers (1/night)


All agreed within 10%for the EA

N Photons at diaphragm FADC counts

Mirror

Camera Calibratedlight source

Diffusely reflective drum

Atmospheric Monitoring

Crucial for an accurate energy measurement

• Wheather stations• Horizontal Attenuation Monitors• Aerosol Phase Function Monitors• Cloud Monitors• Balloon launches• Lidar systems


Rayleigh (molecular) scattering and Mie (aerosol) scatteringare the physical process to be accounted for.

Rayleigh is easy to measure, but Mie is not.

Status

Engineering Array Phase completed35 Surface Detector Tanks2 Fluorescence Telescopes

Production phase started

100 tanks positioned with production electronics200 by end of September400 by Jan 20041600 by Jul 2005

2 telescopes commissioned with production electronics3+2 by end 2003 (stereo detection by end of 2003)6+6 by first quarter 2004

2 eye buildings completed

Successful Detectionof Hybrid events


Performance

SD : 6000 triggers since Dec 2001 600 shower candidates E>1018

120 with more than 5 tanks

FD: 1000 triggers 500 real showers 50 have quality such that energy can be roughly estimated

many laser shots for detector studies

77 hybrid events


Geometrical Reconstruction

SD


))()((1

0exp, coreicoreii yyvxxuc

Tt cossinu

22,exp,

2 /)(iti imeasi tt

core 100m

, 1

sinsinv

nsit

5030

xcore, ycore from barycenter of triggered tanksweighted by signal

, from minimization of

, from arrival times

Shower frontShower corehard muons

EM shower


FD Geometrical Reconstruction

SDPShower Axis

hit station tSD

Shower Front

Rp

t0

impact point

i0

FD

Two Steps:

• Shower Detector Plane• Axis

SDPThe Plane that minimizes the sum of the square angular differences from the direction of the hit pixels

222 /)2

^( ii sdpisdp nr

Nsdp 0.3Stefano Argirò, “Status ... of the Pierre Auger Observatory”

FD Mono:Axis

)2

tan( 00exp,

ipi c

Rtt

22exp,,

2 /)( iii measi tt

core 800m, 1

Tests with laser shotsthrown at known direction(aiming at a star)

The Time Fit

FD stereo: intersectionof SDP

Hybrid Reconstruction

Problem of the time fit:

3 parameter fit from an almost linear function between time and positionaccuracy depends on geometry (toward/outward)

Additional constraint from time of stations

core 30 m, 0.3

Hybrid resolution


Analysis Example

= 54.3 ± 0.5

= -77.8 ± 0.8

n = 11

E = 2035 EeV#184599,Friday April 2002.




Lateral Distribution


Energy from S100010 events/curve

Signal Fluctuations


Longitudinal Profile

)(4

)()(2

rTtcrA

XLXS

)()( XnhF ey

Received light at aperture, emitted between X and X+X:

Atmospheric Transmission Trayleigh T aerosol

Fluorescence yield function Fy from lab measurements

Cerenkov contamination subtracted by an iterative procedure

e-m energy estimation: dXXnX

EE e

r

cem )(

From Gaisser-Hillas fit to profileStefano Argirò, “Status ... of the Pierre Auger Observatory”

run 505 ev 544theta 55.6 °phi 122.7 °X 9.8 KmY 8.8 KmR 13.1 km

Eem 1.3 1019 eV


FD Event Display


run 531 ev 68theta 48.1°phi -135.6 °X 4.4 KmY 19.0 KmR 19.5 km

Eem 3.3 1019 eV


Conclusions


The Engineering Array proved that:

The Detector design is sound

The technical difficulties are sorted out

We are able to calibrate and operate the detectors smoothly

We are able to take consistent data and perform a thoroughand consistent analysis

The Challenge:

Timely completion of the Southern Observatory

Startup of Northern Observatory

Tevatron LHC

D. Bergman, ICHEP 2002


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Status, Performance and Perspectives of the Auger Observatory

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