Hybrid Analysis with the Pierre Auger Observatory

1
Recontres de Moriond
Hybrid Analysis with the Pierre Auger Observatory
David Newton University of Leeds dn_at_ast.leeds.ac.u
k
La Thuile, March 2005
2
Measured Energy Spectrum
3
Summary of some of the problems with the energy
spectrum

• At low energies SD apertures can be in error
• At high energies FD apertures are uncertain
• Model/mass uncertainties in conversion from SD
• Fluorescence Yield
• Absolute calibrations of FD and SD
• BUT
• EVENTS ABOVE 100 EeV DO EXIST

4
The Hybrid Concept
300-400 nm light from de- excitation of
atmospheric nitrogen (fluorescence light)

• Fluorescence Detector
• Energy longitudinal development
• Time -gt direction

• Surface Detector
• Shower size -gt Energy
• Time -gt direction

5
Hybrid Reconstruction
Using timing from one station FD data gives
angular reconstruction equivalent to stereo
detection
6
Hybrid events equivalent to stereo events and
superior to mono events
7
Hybrid Benefits

• Gives 2 independent energy measurements
• Only SD timings are used in geometric
  reconstruction. SD signals are independent and
  can be used to calculate separate energy
  measurement
• Cross check of energy measurements
• identify systematics in each technique
• 10 duty cycle, but...
• Use quality hybrid events to 'train' the SD
  events
• Gives high quality SD events with 100 duty cycle

8
Hybrid Benefits...

• Calibration can work both ways
• Low quality FD events ( large atmospheric
  attenuation uncertainty) can use the SD energy to
  normalise the longitudinal profile
• All FD events will be hybrid
• Easy to compute aperture
• Low energy threshold
• Only require timing information from 1 SD station
• High resolution measurements down to 1 EeV

9
Hybrid Benefits...

• Combine FD and SD parameters used for primary
  identification.
• Xmax , LDF slope parameter , Muon Ratio, FADC
  analysis...

10
A tour through event 673411. A hybrid event and
a stereo event (nearly). Here is what one finds
on the SD event display.
From Coi-hueco-gt
From Los Leones-gt
11
Fluorescence Display
Event 673411
Coi-hueco (6 pixels)
Los Leones (29 pixels)
12
Event 673411
Hybrid Reconstruction
Mono fit
Hybrid fit
lt- SD times
lt- SD times
lt- FD times
lt- FD times
Hybrid (Los Leones)
Surface Difference
Easting 465960 80
465830
130 m Northing 6090234 20
6090308 -74
m Theta 36.7 deg
35.9 deg 0.8
deg Phi 185.8 deg
186.7 deg -0.9 deg
13
Event 673411
Ne maximum 1.4x1010
Ne maximum 7x1010 for energy 1020 eV
FD energy 2x1019 eV
(preliminary) SD energy 2.1x1019
eV
14
Summary...

• Data taking and analysis in conjunction with
  installation and calibration
• Hybrid observations will give high statistics,
  high quality events
• Unambiguously determine the cosmic ray spectrum
  above 1018 eV
• structure of the ankle
• GZK features
• Primary identification.

15
Measurements at Malargue of the deviation of
grams/cm2 with respect to US std atmosphere
Measurement of horizontal attenuation of the
atmosphere at the Auger site. Attenuation varies
between 8 km and 18.5 km
16
(No Transcript)
17
Bad night
Average night
VAOD Vertical Aerosol Optical Depth
26 km
lt- Celeste
Central Laser Facility (vertical beam optical
fibre to Celeste)
18
Event 721353
19
Hybrid Benefits...
Primary Identification Plot of Xmax v N(muon)
for simulated Iron and proton primaries
Diagonal line on 2D scatter plot, gives better
separation of proton/iron components than
relying on Xmax or N(muon) alone. Could use
additional information (risetimes, LDF ...)
20
(No Transcript)
21
Surface Detectors

• Energy calculation is model dependent
  systematic uncertainty
• Aperture is generally easy to calculate
• although problematic at threshold energy

22
PAO Status

• 12 Fluorescence Telescopes fully operational
• 700 surface detectors operational
• Completion of Observatory in early 2006
• Data taking and analysis in conjunction with
  installation and calibration
• First results August 2005

23
Fluorescence Detectors

• Energy Measurement is calorimetric model
  independent, but...
• Need constant calibration of optics,
  electronics...
• atmospheric modelling
• light attenuation, re-scattered light from
  aerosol, Rayleigh scattering
• Aperture is difficult to calculate
• especially at high energy

24
FD Calibration
25
(No Transcript)
26

Estimate cloud fraction / FD camera pixel
Coihueco
Los Leones
27
Extensive Air Showers
1018 eV lt E lt 1021 eV
28
Why Do We Study High EnergyCosmic Rays?

• Offer a unique window on the ultra high energy
  universe
• No known acceleration mechanism beyond 1015 eV
• Predicted Greisen-Zatsepin-Kuzmin (GZK)
  steepening?
• p g2.7K -gt D -gt p p0
  
  
  -gt n p
• If E gt 4 x 1019 eV 50 from within 130 Mpc
• If E gt 1020 eV 50 from within 20 Mpc

29
We'd Like to Know...

• Where they come from.
• Discrete sources?
• Anisotropies?
• Isotropic?
• Extragalactic?
• What they are?
• Nature of the primary
• The shape of the energy spectrum

30
Surface Detectors

• Angular reconstruction from fit of the shower
  front to the detector trigger times
• Fit Lateral Distribution Function to get ground
  parameter -gt energy(models)

31
Fluorescence Detectors
Angular Reconstruction
Stereo detection (2 telescopes) improves the
angular reconstruction
32
Fluorescence Detectors
Energy reconstruction...
Energy found by integrating under the curve
33
The Observatory

• 3000 km2 on completion

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

34
The Surface Detectors
35
The Fluorescence Telescope
The Camera440 PMTs on a spherical surface
36
The Schmidt optics
Spherical aberration
Coma aberration
C
C
C
F
spot
Diaphragm
Coma eliminated
C
Spherical focal surface
37
The FD camera
Light collectors to recover border inefficiencies
mercedes star with aluminized mylar reflecting
walls
440 PMTs on a spherical surface
90 cm
38
(No Transcript)