Ultra High Energy Cosmic Rays
Ultra high energy cosmic rays (UHECR)
LHC Heavier
elements
Lighter elements
• Energy?
• Composition?
• Origin?
Why are UHECR interesting?
• New energy scale – new physics?
• Acceleration mechanisms
• The GZK cutoff
+ +
CMB ∆ p+π n+π γ
+
p → → 0 /
How can they be detected?
Not by direct detection methods!
Use the atmosphere as a calorimeter and detect the huge amount of
secondaries!
Movie!
The shower foot-print
Lateral distribution Energy distribution
+ fluorescence light emitted isotropically + cherenkov radiation emitted forwardly
Different detection techniques
Particle detectors
Flourescence detectors
• Shower particles ionize nitrogen molecules in the air, which re-emits UV-light isotropically
• High energy threshold (~1 EeV)
• Requires extremely good weather conditions
• Detects the shower particles as they reach the ground
• The shower is sampled with a large number of small detectors
• The shower is only detected at one point in the development -> large fluctuations
• Large exposure
• Detects the cone of Cherenkov radiation that is beamed in the forward direction
• Ch. light intense close to the shower axis -> low energy threshold (~1TeV)
• Makes it possible to reconstruct the shower development
Cherenkov detectors
Present and future experiments
AGASA
Fly’s Eye
AUGER!
EUSO
Present Status
Energy Spectrum AGASA Sky Map
Detectors
• Surface Arrays
• Flourescence Detectors
Surface arrays I
Arrival direction reconstructed geometrically
• Scintillators
• Water tanks
Every detector records:
• time of hit
• integrated light yield
fit the arrival times to a shower plane!
Surface arrays II
Reconstruct the energy of the primary particle Problem!
The lateral distribution of particles (ldf) for different energies of the primary cosmic ray is known
Algorithm:
• reconstruct the incident angle
• find the shower core: weighted mean
• plot the measured particle densities versus distance to core,
• do a fit to the ldf
Fluctuation of the
”age” of the air showers at ground!
(E, r,θ )
d d =
The AUGER array
Surface Array
1600 detector stations 1.5 km spacing
3000 km2
Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per
enclosure 24 Telescopes total
The Surface Array Detector Station
Communications antenna
Electronics enclosure
3 – nine inch photomultiplier tubes
Solar panels
Plastic tank with 12 tons of water Battery box
GPS antenna
Motivations for the SD design
• 1.5 km spacing
• 10m2 top area
• 1.2 m depth
larger, more uniform coverage
• Cylindrical
uniform acceptance
• GPS for timing
< 10 ns time resolution
• 3 downward looking PMTs
uniform response
Fully eff. > 1019eV
AGASA Auger-SD µ± e± γ
Detector Response
γ ~1GeV ~10MeV ~10MeV
µ± e±
~1GeV ~10MeV ~10MeV
5cm Plastic
1.2m Water
10MeV ~10MeV ~1MeV 240MeV ~10MeV ~10MeV
Energy Deposit
AGASA vs. Auger-SD
• Both use VEM as one unit, but they are different.
– AGASA 10MeV equivalent – Auger-SD 240MeV equivalent
• Easier to calibrate in Auger (24 times bigger signal than AGAS
• For EAS, Auger is more sensitive to energy carried by muons.
• Gamma rays deposit more energy in Auger-SD.
– AGASA ~10%
– Auger-SD ~100%
• Auger is totally calorimetric for EM Showers. (AGASA is not.)
• Acceptance is more uniform in Auger-SD (as a function of Zenith Ang
Flourescence Detectors
Air Fluorescence Air Fluorescence Detector
Detector
~ 10 W
Every pixel element detects:
• time
• amount of light
Shower reconstruction I
First step: to geometrically
reconstruct the direction of the air shower
Shower reconstruction II
Second step: to derive the shower profile – the shower size as a
function of the atmospheric depth penetrated
Shower size ~ em. light ~ det. light
Two quantities can be extracted from the shower profile:
• energy of the primary particle (~ shower size)
• a statistical measure on the composition of the primary p.
(depends on the shower max.)
The first fluorescence detector
The Cornell experiment
• 50x10 PMTs, each 6x6 degrees
• each module equipped with 0.1m2 Fresnel lins as light collector
The Latest (Auger) detector
11 square meter
segmented mirror optical filter 440 pixel camera
• 1.5m2 light collection area
• 1.5 degrees pixel size
• 440 pixel camera
• 30x30 degrees field of view
Combining the two –
”a Hybrid detector”
Air showers detected in
complementary ways, allows:
• improved angle/core – reconstruction
• removes fluctuations in energy determination by the SA
Calibration
VEM – Vertical Equivivalent Muon
[ x x]dx
P P
l
d = ∫ −
0
0 exp α( )
What needs to be calibrated?
• SD: PMT ADC counts -> deposited energy Cosmic ray muons
• FD: PMT ADC counts -> light flux
Camera illuminated with light source of known intensity
• Atmospheric absorption Lidar system
… and more
Future plans for UHECR-experiments
AUGER
• muon counters
• FD calibration thing
• radio antennas
• AUGER NORTH
OTHER EXPERIMENTS
• the Telescope Array (completed in 2007)
• JEM/EUSO
