The Pierre Auger Project

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The Pierre Auger Project
Claudine Colnard, Matic Andrija , Talai Mohamed
Cherif, Valverde Hermosila Manuel
Summer School on Particle and Nuclear Astrophysics
Nijmegen, The Nederlands August 17-29, 2003
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What we "know" about Ultra High Energy cosmic Rays

Observed spectrum above eV


Evidence for Utra High Energy Cosmic Rays gt GZK
cut-off ?
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What we do not know (but would like to )

• Where does the spectrum end?
• Primary nature (composition)?
• Nucleus, proton?
• Are there gamma rays or neutrinos?
• What is the source of UHECR?
• Bottom-Up or Top-Down scenario?

Pierre Auger Observatory
A Study of The Highest Energy Cosmic Rays 1019 -
1021 eV Energy Spectrum - Direction - Composition
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Auger Philosophy
Uniform sky coverage 2 sites located in each
hemisphere Argentina, USA need high
statistics large detection surface 2?3000
km² Hybrid detector - fluorescence detector -
surface array (water Cerenkov tanks)
Good energy and direction resolution Good
sensitivity to composition
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Auger Southern Site

• Argentina Pampa Amarilla, Mendoza
• 35o S latitude
• 69o W longitude
• 1.4 km altitude
• 875 g/cm2
• Low population density (lt 0.1 / km2), Pampa
  amarilla
• Favourable atmospheric conditions (clouds,
  rain, light, aerosol)

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The hybrid detector
300- 400 nm light from fluorescence of
atmospheric nitrogen

• Fluorescence Detector
• Longitudinal development
• Intensity E
• Duty cycle 10-15
• (moonless and cloudless nights)

• Surface Detector
• Shower size E
• Time direction
• Duty cycle 100

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The Observatory
3000 km2 covered aperture 7400 km2 .sr
Fluorescence detectors 4 peripheral eyes (6
telescopes each) 11000 PMTs
Surface detectors 1600 Cerenkov tanks 1.5 Km
spacing 4800 PMTs

Wireless RF Communication system
65 km
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Why a hybrid detector?
The same cosmic ray shower is measured by two
independent detector systems
Cross calibration - complementary measure of the
energy and direction of the primary - allows for
redundancy cheks of interesting events - allows
to study (and reduce) systematics Increase
composition sensitivity Uniform
exposure Hadronic cascades - muon and
electromagnetic densities combined with the
longitudinal profile put constraints on the
hadronic interaction models Cost - cost per
event is lower than a stereo fluorescence
detector design
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The Auger Surface Detector
Water Cerenkov tank Polyethylene tank 10 m2 x
1.2 m of purified water, diffusing walls 3 PMTs
Photonis 9 Autonomous unit solar
panelbattery, GPS timing, communication
antenna modest power consumption (10 W)
Commantenna
Solar panel and electronic box
GPSantenna
Three 8 PM Tubes
Battery box
White light diffusing liner
12 m2 of de-ionized water
Plastic tank
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The FD telescope

• Schmidt optics (eliminates coma) Spherical
  mirror Rcurv 3.4 m
  2.2 m diameter diaphragm, corrector ring,
  
• 30o x 30o aperture spot size
  from spherical aberration 15 mm
• Focal surface 20 x 22 hexagonal
  PMT (Photonis XP3062) Pixel angular size
  1.5o (45 mm)

Diaphragm, UV Filter, Corrector ring
Spherical mirror
PMT camera
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High statisitcs
1 Auger year 30 AGASA, 10 Hires years
5000 events/year E gt 1019 eV 500
events/year E gt 5x1019 eV 50
- 100 events/year E gt 1020 eV
Expected rates
Sky above after 3 years
Spectrum after 20 months
15 sources of equal densities randomly distributed
Efficiency gt 90 (Egt10 Eev)
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Performances
Energy resolution
Array
alone Hybrid mode 100 Eev 15
10 10 Eev 30
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Angular resolution
Array
alone Hybrid mode 100 Eev 0.5º
0.20º 10 Eev 1º
0.35º
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The Auger Collaboration

• Argentina Italy
• Australia Mexico
• Bolivia Poland
• Brazil Russia
• Czech Republic Slovenia
• Peoples Republic of China Spain
• France United Kingdom
• Germany USA
• Greece Vietnam
• 50 Institutions, gt250 Scientists

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Costs and Funding

• South 54M US
• North 46M US
• Total 100M US
• In kind contributions 80
• Detector Components
• Infrastructure (host countries)
• Common Fund 20
• Photomultiplier tubes
• Site buildings

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Status

• The Auger southern site is now under
  construction.
• 40 surface detectors over 40 km2
• 2 fluorescence telescopes (Los Leones,
  Coihueco)
• In 2003 installation and commissioning of 12 FD
  telescopes and 500 additional tanks
• Southern site to be completed by 2005
• Construction of the Auger northern detector will
  begin in 2 to 3 years.

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First giant airshower
hit 20 out of the 30 active surface detectors on
May 23rd 2002
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Summary

• Auger Project has some exciting science.
• Strong collaboration organized.
• Thirty of the surface detectors equipped with
  electronics have worked under stable conditions
  since January 2002
• More than 70 air showers detected in hybrid mode
  
• A few hundreds of events with estimated energies
  above 1 EeV (1018 eV) observed by the surface
  array alone.

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Systematics in the Pierre Auger Observatory

• Bruce Dawson
• University of Adelaidefor the Pierre Auger
  Observatory Collaboration

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Introduction

• Fluorescence - a technique with great rewards,
  but a lot of work required!
• Will concentrate on energy measurement (e.g.
  composition has an additional set of systematics)
• All good experiments build in CROSS-CHECKS, Auger
  no exception. Clearly, most important
  cross-check is the Hybrid nature of Auger, but
  many others.

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The Observatory

• Mendoza Province, Argentina
• 3000 km2, 875 g cm-2
• 1600 water Cherenkov detectors 1.5 km grid
• 4 fluorescence eyes -total of 24 telescopes each
  with 30o x 30o FOV

65 km
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Engineering Array
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Simulated Hybrid Aperture
Stereo Efficiency
Hybrid TriggerEfficiency
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Hybrid Reconstruction Quality
Statistical errors only!
statisticalerrors only
zenith angles lt 60O

• 68 error bounds given
• detector is optimized for 1019eV, but good Hybrid
  reconstruction quality at lower energy

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Steps to good energy reconstruction

• Geometry
• Calibration atmosphere and optical
• Analysis
• Light collection
• Cherenkov subtraction
• Fitting function
• Missing energy
• Fluorescence yield

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Geometry Reconstruction

• eye determines plane containing EAS axis and eye
• plane normal vector known to an accuracy of
  0.2o
• to extract Rp and y, eye needs to measure angular
  velocity w and its time derivative dw/dt
• but difficult to get dw/dt, leads to degeneracy
  in (Rp,y)
• degeneracy broken with measurement of shower
  front arrival time at one or more points on the
  ground
• eg at SD water tank positions

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Geometry Reconstruction

• Simulations at 1019eV
• Reconstruct impact parameter Rp. Dramatic
  improvement with Hybrid reconstruction

(Will check with stereo events)
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Atmosphere Systematics

• light transmission corrections(Rayleigh and
  aerosol scattering)AIM know corrections to
  better than 10
• air density profile with height(mapping height
  to depth Rayleigh scattering)AIM know
  overburden at a given height to better than 15
  g/cm2

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Distance from pixels to track
MC 1019eV events over full arrayClosest
triggering eye
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VARIABLE !!
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• Horizontal attenuation monitors (50km)
• Steerable LIDARs - total optical depth
• Vertical lasers near centre of array - vertical
  distribution of aerosols
• Cross-checks

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Aerosol measurements
(John Matthews ICRC 2001)
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LIDAR System
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LIDAR System
Tests near Torino
System at Los Leones
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Some simulations

• Simulations 1000 1019eV showers landing within
  Auger full array. Generate with fixed aerosol
  parameters
• horizontal attenuation length (334nm) al 25
  km
• scale height of aerosol layer
  ha 1.0 km
• height of mixing layer hm 0 km
• First, reconstruct events with different aerosol
  assumptions

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Dependence on Aerosol Parameters

• (generated with al25km, ha1.0km, hm0km)
• reconstruct with 19km 1.0km
  0km DE/E 8 DXmax 7 g/cm2
• reconstruct with 40km 1.0km
  0km DE/E -9 DXmax -9 g/cm2
• reconstruct with 25km 2.0km
  0km DE/E 10 DXmax -2 g/cm2
• reconstruct with 25km 1.0km
  0.5km DE/E 12 DXmax 8 g/cm2

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Atmosphere Density Profile

• Density profile of atmosphere determines mapping
  from height to depth, and Rayleigh scattering
• MC generated with vertical overburden 873
  g/cm2and one of the US Standard Atmospheres.
  Will maintain scale height.
• reconstruct with vertical overburden 900
  g/cm2 DE/E 2.2 DXmax 19
  g/cm2
• reconstruct with vertical overburden 845
  g/cm2 DE/E - 3.3 DXmax - 19
  g/cm2

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Radiosonde

• Balloon-borne radiosondes are planned to monitor
  the atmospheres density and temperature
  profile
• First flight in August 2002 at Malargue.
• A series of flights in the austral spring,
  summer, winter and autumn will determine the
  suitability of re-scaled standard atmospheres,
  and variability.

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Optical Calibration
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Drum Calibration

• 375nm LEDs
• NIST calibrated Silicon detector
• uniformly illuminates aperture with full range of
  incoming angles
• in future will also use range of colours
• absolute calib to 7 now, hope to improve to 5

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Relative calibration Xenon
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Laser shots at 3km - cross check on absolute
calibration
and also are checking with piece by piece
calibration.
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Reconstruction
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UV-Filter 300-400 nm
installed at Los Leones (Malargüe) and taking data
11 m2 mirror
camera440 PMTs
corrector lens
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No coma, good light collection
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Hybridevent.Dec 2001- March2002
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Light Flux at Camera
optical spot 0.5 deg diam

• Aim to collect all signal without too much noise
  or multiple scattered light.
• Effect of multiple scattered light? Halo?
• currently a 10-15 systematic, is being studied

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REAL event
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Dependence on Cherenkov Yield

• MC generated with nominal Cherenkov yield
• (easy calculation if you know the density profile
  of atmosphere and the energy spectrum of
  electrons)
• reconstruct with Cherenkov yield up by 30
  DE/E - 4.8 DXmax - 9 g/cm2
• reconstruct with Cherenkov yield reduced by
  30 DE/E 5.3 DXmax 9 g/cm2
• (These are averages. Clearly, the error for each
  event depends on its geometry).

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CORSIKA Check
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Cherenkov correction

• clearly depends on more than yield calculation,
  also
• atmospheric scattering
• geometry
• important problem that needs study, since all
  events have some contamination
• stereo will be an important aid

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PRELIMINARY
shower size (arb units)
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PRELIMINARY
shower size (arb units)
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Profile
T. Abu-Zayyad et al Astropart. Phys. 16, 1 (2001)
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Missing energy correction

• unavoidable 5 systematic
• currently being checked with new CORSIKA

Ecal calorimetric energyE0 true energy from
C.Song et al. Astropart Phys (2000)
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Conclusion

• cant provide an error budget now - many of the
  systematics are under study, and we need real
  (stereo) data to study many of them
• have indicated our goals in terms of two major
  players - the atmosphere (10) and optical
  calibration (5). These must be obtained early.
• cross-checks are vital
• then there is the fluorescence yield

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The Auger Observatoryfor High-Energy Cosmic
Rays
G.Matthiae University of Roma II and INFN For the
Pierre Auger Collaboration

• The physics case
• Pierre Auger Observatory - hybrid system
  Surface and Fluorescence Detectors
• The Engineering Array - first results

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The physics case

• Evidence for Ultra High Energy
  Cosmic Rays gt GZK cutoff

• Quest for nearby sources (lt50 Mpc)
• Production-acceleration mechanisms?
• Challenging rate
• 1 / km2 / sr / century above 1020 eV!

Auger will measure the properties of the highest
energy cosmic rays with unprecedented precision
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The Pierre Auger Observatory

• A world-wide Collaboration
• Full sky coverage two Observatories (North and
  South) (Malargue, Argentina, approved and
  financed, under construction)
• Hybrid detector concept The same cosmic ray
  shower is measured by two independent detector
  systems
  Cross-calibration, improved resolution, control
  of systematic errors
• Large scale detector
• Giant array of 1600 Cherenkov tanks, covering
  3000 km2 ,
• 24 Fluorescence Detector telescopes
  
• 1 Auger year 30 AGASA, 10 Hires
  years

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Malargue, Argentina
35o S latitude 69o W longitude 1.4 km
altitude 875 g/cm2

• Low population density (lt 0.1 / km2), Pampa
  amarilla
• Favourable atmospheric conditions (clouds, rain,
  light, aerosol)

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The hybrid concept
300- 400 nm light from fluorescence of
atmospheric nitrogen

• Fluorescence Detector
• Longitudinal development
• Time direction

• Surface Detector
• Shower size E
• Time direction

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The Observatory

• 3000 km2 covered
• aperture 7400 km2 sr

• FD (4 peripheral eyes, 6 telescopes each)
  11000 PMTs
• 1600 SD Cherenkov tanks (spacing 1.5 km)
  4800 PMTs

Wireless RF Communication system
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Performances

• Expected rates

5000 events/year E gt 1019 eV 500
events/year E gt 5x1019 eV 50 -
100 events/year E gt 1020 eV
FD duty cycle 12 15
Fraction of stereo FD

• Shower reconstruction

• ?E/E lt 10
• Direction lt 1o
• Ground impact point lt 50 m
• Xmax lt 20 g/cm2

2,3,4
2
4
3

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Hybrid vs. Surface Detector
1019 eV 1020 eV
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First hybrid event FD on line display
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Shower longitudinal development
atmospheric corrections, FD pixel calibration,
fluorescence yield, Gaisser-Hillas fit
E 1.5 x 1019eV, Smax 1.0 x 1010,
Xmax 746 g/cm2
E 1.3 x 1019eV, Smax 9.2 x 109,
Xmax 670 g/cm2
particle number (107)
atmospheric depth (g/cm2)
atmospheric depth (g/cm2)
Preliminary energy estimates!
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Preliminary energy estimate
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Management Organization