Systematics in the Pierre Auger Observatory

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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