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Colorado, USA
(in planning)
Gregory Snow / University of Nebraska
The Pierre Auger Observatory
Capturing Messengers from the
Extreme Universe
A new cosmic ray observatory designed for a high
statistics study of the
The Highest Energy Cosmic Rays
Using
Two Large Air Shower Detectors
Mendoza, Argentina
(construction nearing completion)
1

The Auger Collaboration
67 Institutions, 369 Collaborators
Argentina Netherlands
Australia Poland
Bolivia * Portugal
Brazil Slovenia
Czech Republic Spain
France United Kingdom
Germany USA
Italy Vietnam *
Mexico
* associate
True International Partnership
- by non-binding agreement -
No country, region or
institution dominates – No
country contributes more than
25% to the construction.
2

Many
experiments
have
contributed
Flux (m 2 sr s eV) -1
Power law with
structure
The Cosmic Ray Spectrum
Energy (eV)
Supernova
shock can
generate up
to ~10 15 eV
Transition from
galactic to
extra-galactic?
Most interesting,
but:
•Rare
• Don’t know
acceleration
mechanism
• Point back
possible
3

Conventional – Bottoms-Up
Possible Sources
• Hot spots in radio galaxy lobes?
• Accretion shocks in active
galactic nuclei? - Colliding
galaxies?
• Associated with gamma ray
bursts?
Exotic – Top-Down
• Annihilation of topological
defects?
ν’s
γ’s • Cold dark matter?
signatures
• Evaporation of mini black holes?
4

Propagation
in the Cosmic Microwave Background
Space becomes opaque to protons of energy > 5 * 10 19 eV because of
the cosmic microwave background - Greisen-Zatsepin-Kuzmin
(GZK) suppression. Cosmic ray protons with 10 20 eV must come
from less than about 50 Mps.
proton +photon CMB -> pion + nucleon
Recent data at the
end of the spectrum
GZK cut off?
5

10 18 eV
protons
Propagation
magnetic fields
At energies near 10 20 eV protons magnetic deflection is small – Cosmic
ray protons should point back to the source. Charged particle
astronomy becomes possible.
10 20 eV protons
5 ×10 19 eV ~ bottom end of pointing capability (about 10 o )
6
J. Cronin

N
Interaction with the atmosphere
A look at air showers
Shower Max
Depth in the Atmosphere
Shower front
10 11 Particles
at surface
Sea level
EM shower
Shower core -
hard muons
γ ~ 89% ⎫
⎬ 10 MeV
e ± ~ 10% ⎭
µ ~ 1% 1GeV
7

Detecting Cosmic Ray Air Showers
Fly’s Eye
Surface Array
Air shower
measurements are
made by two
techniques
1) Surface Arrays
2) Fluorescence
Telescopes (Fly’s
Eyes)
8

Can’t see small
showers far
away, need
good model of
atmosphere
Features of the
Air Shower Detector Techniques
Surface Array
µ‘s come first,
100% duty cycle
γ’s,e’s shower
Well-defined acceptance
causing delay
Uniform sky coverage
Simple robust detectors
Mass determination using rise time, muon/em (*)
Energy determination requires simulation
Fluorescence Detector
Calorimetric energy measurement
Direct view of shower development
Good angular resolution (< 1 o )
Correction for atmospheric attenuation
Aperture requires simulation (*)
10% duty cycle (moonless nights only)
Fe vs. proton
more µ-rich
9

Pierre Auger Observatory
Science Objectives
Cosmic ray spectrum above 10 19 eV
• Shape of the spectrum in the region of the GZK feature
Arrival direction distribution
• Search for departure from isotropy – point sources
Composition
• Light or heavy nuclei, photons, neutrinos, exotics(?)
Design Features
High statistics (aperture >7000 km 2 sr above 10 19 eV in each
hemisphere)
Full sky coverage with uniform exposure
Hybrid configuration – surface array with fluorescence detector
coverage
10

The Hybrid Design
Surface detector array + Air fluorescence detectors
A unique and powerful design
• Nearly calorimetric energy
calibration of the fluorescence
detector transferred to the
event gathering power of the
surface array.
• A complementary set of mass
sensitive shower parameters.
• Different measurement
techniques force understanding
of systematic uncertainties
• Determination of the angular
and core position resolutions
11

The Observatory Plan
Surface Array
1600 detector stations
1.5 km spacing
3000 km 2
Fluorescence Detectors
4 Telescope enclosures
6 Telescopes per
enclosure
24 Telescopes total
12

Battery box
The Surface Array
Detector Station
Communications
antenna
Electronics
enclosure
3 – nine inch
photomultiplier
tubes
GPS antenna
Solar panels
Plastic tank with
12 tons of water
13

Deploying the Surface Detectors
14

FD telescopes in closed
environment
The Fluorescence Detector
11 square meter
segmented mirror
440 pixel camera
Aperture stop
and optical filter
Corrector lens
minimizes spherical
aberrations, filter
brackets 350 nm
fluorescence light 15

The Fluorescence Detector
Los Leones
16

Atmospheric Monitoring and Calibration
Atmospheric Monitoring
Used to “shoot
the shower”
Simulates hybrid
event – some light to tank
Central Laser
Facility
Lidar at each
fluorescence eye
Precisely calibrated light
source
Absolute Calibration
Drum for uniform
camera illumination –
end to end calibration .
Lidar (Light Detection and Ranging)
measures back-scattered light→atmos. density profile 17

Status of the Observatory
1190 out of 1600 surface
detector stations
deployed
Three of four
fluorescence buildings
operational each with 6
telescopes
18

Aerial Photos of Fluorescence Buildings
November 2006
19

Thanks to Cristina Raschia
Building the Observatory
20

Deployment Sequence
Thanks to Cyril Lachaud
21

Deployment Sequence
Thanks to Cyril Lachaud
22

Surface Detector
Event
Θ~ 48º, ~ 70 EeV
70 × 10 18 eV
Typical flash ADC
trace
Detector signal
(VEM) vs time (ns)
PMT 1
PMT 2
PMT 3
Flash ADC traces
Flash ADC traces
Lateral density
distribution
18
tanks
S(1000) best estimate of
shower energy, min.
fluctuations
23

Surface Detector Event
Θ~ 60º, ~ 86 EeV
Flash ADC Trace
for detector late in
the shower
Flash ADC
traces
PMT 1
PMT 2
PMT 3
Lateral
density
distribution
34
tanks
24

y [km]
Hybrid Event
Θ~ 30º, ~ 8 EeV
Shower plane from FD
28
26
24
22
20
18
16
14
12
10
SD core position
8
10 15 20 25 30
x [km]
)]
2
dE/dX [GeV/(g/cm
FD pulse heights
corrected for
atmospheric effects,
Cerenkov light
elevation [deg]
30
25
20
15
10
5
20
18
16
14
12
10
8
6
4
2
6
× 10
60 65 70 75 80 85 90
azimuth [deg]
400 500 600 700 800 900
2
slant depth [g/cm ]
Depth in atmosphere
Integral under Gaisser-Hillas fit gives FD energy, which is corrected by
~10% (simulation) due to shower particles penetrating earth
25

Hybrid Event
Θ~ 30º, ~ 8 EeV
Flash ADC
traces
Example Event 3
A hybrid event – 1021302
Zenith angle ~ 30º, Energy ~ 8 EeV
Lateral density
distribution
26

Same Hybrid Event
Θ~ 30º, ~ 8 EeV
These 2 plots give energy,
angle, and core position
Time µ sec
Tanks
Fitted Electromagnetic
Shower
Pixels
from Fly's Eye 1985
Angle χ in the shower-detector plane
27

A Tri-ocular Event!
~20EeV
28

A Big Event - One that got away!
Shower/detector plane
outside of array
Fluorescence Mirror
Energy
Estimate
>140 EeV
No correction for aerosols, could be as high as 2 × 10 20 eV
29

Laser
Beam
Performance: Angular Resolution
Angle in laser beam /FD detector plane
Hybrid Angular resolution
(68% CL)
0.6 degrees (mean)
Entries 269
σ(ψ) = 1.24º
Hybrid Data
Hybrid-SD only space angle difference
Surface array Angular resolution (68% CL)
< 2.2º for 3 station events (E< 3EeV, θ < 60º )
< 1.7º for 4 station events (3

Laser Data
Performance: Resolution of Core Position
Laser position – Hybrid and FD only (m)
Core position resolution
+500
-500
Hybrid Data
Entries 501
Mean
5.8 ± 6.5 m
RMS 147 m
Hybrid – SD only core position
– Hybrid: < 60 m Surface array: ~150 m
Entries 501
Mean 68 ± 8 m
RMS 173 m
31

Cosmic Ray Air Shower Measurements
Energy – if surface array only
11 tank event
Surface Array:
Measure radial particle density
distribution and match to simulated
distribution.
simulation
Clem Pryke
32

Cosmic Ray Air Shower Measurements
Energy – fluorescence detectors
Fluorescence Detectors:
Measure the light produced
by the shower
350 nm
From fluorescence yield experiment
Fully calibrated calorimetric measurement
Note how shower max moves deeper in
atmosphere for higher energy shower
33

Cumulative number of events
January 04
July 04
The First Data Set ICRC2005 in India
January 05
Collection period – 1 January
2004 to 5 June 2005
Zenith angles - 0 - 60º
Total acceptance – 1750km 2 sr yr
(~ AGASA)
Surface array events (after
quality cuts)
Current rate - 18,000 / month
Total -~180,000
Hybrid events (after quality cuts)
Current rate – 1800 / month
Total ~ 18000
ICRC2005 contributions available on Auger web site
http://www.auger.org
34

Enhancement toward south
pole due to oversampling
Sky Map of Data set
Galactic Coordinates
Where we don’t
see from the
south
35

Energy Determination and the Spectrum
The energy scale is based on fluorescence measurements
without reliance on a specific interaction model or
assumptions about the composition.
The detector signal size at
1000 meters from the
shower core - called
the ground parameter
or S(1000) - is
determined for each
surface detector event
using the lateral
density function.
S(1000) is proportional
to the primary energy.
Only model-dependent ingredient is the ~10% correction
for shower particles penetrating earth
Zenith angle ~ 48º
Energy ~ 70EeV
36

Energy Determination and the Spectrum
The energy converter:
Compare ground
parameter S(1000)
with the fluorescence
detector energy.
Transfer the energy
converter to the
surface array only
events.
Log (E/EeV)
Hybrid Events
Strict event selection:
track length >350g/cm2
Cherenkov contamination

Auger Energy Spectrum
∆E/E~30%
∆E/E~50%
38

J. Bellido
Systematic Errors in the FD (Hybrid)
Energy Normalization
~ 30%
50% at higher energy
is from extrapolation
of energy converter
39

Auger reserves
making specific
claim until
more statistics
Comparison with HiRes1, AGASA
Auger spectrum
similar to HiRes
which is consistent
with GZK suppression
1) M. Takeda et al. Astroparticle Physics 19, 447 (2003)
2) R.U. Abbasi et al. Phys Lett B (to be published)
8
6
Stat. errors only
3
40

Galactic center
No excess approaching
significance of AGASA, SUGAR reports
Galactic plane
Auger data Jan 2004-
Mar 2006
Overdensity significance
Circles represent regions of previously reported excesses from AGASA, SUGAR.
Sugar = Sydney University Giant Air Shower Recorder
x
41

Photon Limit
Integral (E>E0) photon fraction limit based on shower depth (X max )
measured in 29 quality hybrid events above 10 19 eV
Auger data Jan 2004-Feb 2006
Models
predict
lines
HP, A1, A2 == previous limits from Haverah Park, AGASA data.
2007: Improved limits/detection(?) using surface detector observables.
Start to probe model predictions (Z-burst, SuperHeavy Dark Matter, Topological
Defects) yielding photon primaries, also extend limits to higher energies.
42

Malargüe
Outreach
43

Northern Auger
Objectives:
– Complete sky coverage/ Increased aperture
• Anisotropy – source searches (charged particle
astronomy)
• More detailed spectrum near the GZK feature
• Increased aperture for earth skimming neutrinos.
• Design
– Increase the array size from 3000 to 10000 Km 2
– Simpler surface detectors (1 PMT)
– Greater average spacing
– 12 FD telescopes
– Simpler communications system
– Possible new technologies
(Radio, radar detection)
for even greater aperture
44

• Requirements
– Large flat area w/clear, dark sky
– Remote, but easy access
– Latitude, Altitude
– Infrastructure
• Site identified in Colorado
– Around Lamar (38 o N, 102 o 30’ W )
– Over 4000 sq miles (84x48 miles)
– 1200-1400 m.a.s.l
– 3 hs drive from DIA
Northern Auger Site
45

Summary
• The Observatory is approaching completion.
• With 25% of a full Auger-year exposure, we have:
– Defined our empirical spectrum analysis strategy and
produced our first model-independent spectrum
– Performed first studies of anisotropies in the sky
– Set limits on photon primaries
Future Plans
• Complete Auger South by mid 2007
• Fully understand our instruments.
• Use rapidly expanding data set (x7 in two years) to enable
– Improvement in the energy assignment
– High statistics study of the spectrum in the GZK region
– Anisotropy studies and point source searches.
– Composition studies
• Reduce systematic uncertainties.
• Exploit events beyond a zenith angle of 60º
– search for neutrinos and exotics
• Begin work on Auger North
46

Backup Slides
47

Cosmic Ray Air Shower Measurements
Some Sensitivity to Neutrinos
Tau neutrinos can interact
in the mountains or in the
crust of the earth to
produce taus that decay and
shower over the detector.
τ Lifetime ~40 km for 10 18 eV ν τ
Large zenith angle
(>60 degrees) hadron
showers have lost most
of their electromagnetic
component.
Low rate ~1/year
48

The Cosmic Ray Observatory Project
(CROP) in Nebraska
Gregory Snow
UNL Department of Physics and Astronomy
September 22, 2006
49

CROP article in Lincoln Journal Star, 7 August 2003
50

A few facts
• Funded by $1.34 Million NSF grant, 2000-2007
• Co-PIs Greg Snow and Dan Claes
• 26 Nebraska and 5 Colorado schools enlisted and trained
in summer workshops of duration 2-4 weeks, about
5 new schools per summer
• Venture into Colorado was a joint effort by CROP,
WALTA, ALTA
• Hosted 2 one-day meetings each academic year for
participants from all years to report results, exchange
faulty equipment, receive equipment and software
upgrades, refresh training or train new students
• External evaluation of this period has shown that CROP
has accomplished most of its educational and scientific
goals listed in the original proposal
• CROP has also served as a great training ground for
staff (undergrad, grad students) at UNL
51

Highlighted squares = participating schools
52

The Chicago Air Shower Array
• CROP uses retired detectors from the Chicago Air Shower Array
• 1089 boxes each with:
• 4 scintillators and photomultiplier tubes (PMT)
• 1 high voltage and 1 low voltage power supply
• Two removal trips (September 1999, May 2001) yielded over
2000 scintillator panels, 2000 PMTs, 500 low and power supplies
53

U.S. Army Photo
The CROP team at Chicago Air
Shower Array (CASA) site
September 30,
199954

To PC
serial port
GPS receiver
input
5 Volt
DC power
CROP data acquisition electronics card
Developed by Univ. Nebraska, Univ. Washington, Fermilab (Quarknet)
Programmable
logic device
• 43 Mhz (24 nsec) clock interpolates
between 1 pps GPS ticks for trigger time
• TDC’s give relative times of 4 inputs with
75 picosecond resolution
Time-to-digital
converters
Event
counter
Discriminator
threshold
adjust
Four analog
PMT inputs
55

Summer 2004 Workshop Activities
Detector assembly and testing
56

Each school made new rooftop enclosures
57

Excellent extensive air shower
data taking run overnight
58

New enclosures making it to rooftops
Weights, important !!
Westside High School
Omaha, NE
59

NALTA
The North American Large-Scale Time-Coincidence Array
http://csr.phys.ualberta.ca/nalta/
• Includes links to individual project
Web pages
WALTA ALTA
CHICOS
SALTA
CROP
PARTICLE
Pierre Auger northern
hemisphere site in
southeast Colorado
SCROD
TECOP
60

Aiming toward a worldwide network
of cosmic ray detectors
61