the auger observatory for high-energy cosmic rays g.matthiae university of roma ii and infn for the...
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The Auger Observatoryfor High-Energy Cosmic Rays
G.MatthiaeUniversity 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 >
GZK cutoff
• Quest for nearby sources (<50 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
• Low population density (< 0.1 / km2), “Pampa amarilla”
• Favourable atmospheric conditions (clouds, rain, light, aerosol)
35o S latitude
69o W longitude
≈ 1.4 km altitude
≈ 875 g/cm2
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The hybrid concept
Fluorescence Detector
•Longitudinal development
•Time ≈ direction
300- 400 nm light from fluorescence of atmospheric nitrogen
Surface Detector
• Shower size ≈ E
• Time ≈ direction
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The Observatory
• FD (4 peripheral eyes, 6 telescopes each) 11000 PMTs
• 1600 SD Cherenkov tanks (spacing 1.5 km) 4800 PMTs
3000 km2 covered
aperture 7400 km2 sr
Wireless RF Communication system
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• ΔE/E < 10 %
• Direction < 1o
• Ground impact point < 50 m
• Xmax < 20 g/cm2
Fraction of stereo FD
Expected rates ~ 5000 events/year E > 1019 eV ~ 500 events/year E > 5x1019 eV ~ 50 - 100 events/year E > 1020 eV
Shower reconstruction
Performances
FD duty cycle12 – 15 %
43
2
2,3,4
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15 g/cm2
17 g/cm2
ΔXmax
2.5 %7.0%4.2 %18 % ΔE/E
30 m40 m30 m80 mΔ core
0.401.000.402.00 Δθ
HybridSurfaceHybridSurface
1019 eV 1020 eV
Hybrid vs. Surface Detector
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Observatory Infrastructure
Office and CDAS building
Assembly building
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The Surface Detector
Water Cherenkov tankPolyethylene tank
10 m2 x 1.2 m of purified water, diffusing walls
3 PMTs Photonis 9’’
Autonomous unit: solar panel+battery, GPS timing, communication antenna
modest power consumption (10 W)
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Los Leones FD building
• 6 telescopes• Communication tower
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The FD telescope
Spherical mirror
PMT camera
Diaphragm, UV Filter,
Corrector ring
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)
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The FD telescope at Los Leones
PMT camera
Front End
electronics
mirror
HV+LV
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The FD camera
90 cm
440 PMTs on a spherical surface
Light collectors to recover border inefficiencies
“mercedes star” with aluminized mylar reflecting
walls
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• Installation and commissioning of tanks and telescopes,
• Communications
• Hybrid trigger and timing, CDAS
• Internet connection with data mirroring in US and Europe, data analysis
• First showers observed May 2001
The Engineering Array
Central Campus, Malargue
Los Leones FDeye
40 SD tanks
30o, FD 2 telescopes Aims
• December 2001–March 2002 stable data taking ≈ 80 hybrid events
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First hybrid event FD on line display
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FD – SD matching
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11-fold event
11 tanks triggered
April 2002
Preliminary energy estimate!
E ~ 2.6 x 1019 eV
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atmospheric corrections, FD pixel calibration, fluorescence yield, Gaisser-Hillas fit…
E= 1.3 x 1019eV, Smax= 9.2 x 109, Xmax = 670 g/cm2
Shower longitudinal development
atmospheric depth (g/cm2)
Preliminary energy estimates!
part
icle
num
ber
(107 )
atmospheric depth (g/cm2)
E= 1.5 x 1019eV, Smax= 1.0 x 1010, Xmax = 746 g/cm2
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Preliminary energy estimate
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Outlook • A large part of the Auger Observatory infrastructure near Malargue, Argentina already built.
• The Engineering Array goals were successfully accomplished. We can operate the hybrid system, hybrid trigger, wireless
communications
• Mass production of the components has started.
• In 2003 installation and commissioning of 12 FD telescopes and 500 additional tanks).
• Observatory to be completed by 2005.