COSMIC RAY ORIGINS

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COSMIC RAY ORIGINS
Stella Bradbury, University of Leeds, U.K.

• g-ray sources
• Ultra High Energies
• introduction to charged cosmic rays
• Extensive Air Shower detection techniques
• problems posed by existence of UHE cosmic rays
• next generation experiments

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Following Hess Pfotzer used Geiger counters
separated by lead blocks to measure intensity of
radiation at up to 30 km above sea level
The intensity of radiation passing through the
lead continued to increase with altitude (A) ?
primary cosmic rays? The total amount of incident
radiation peaked and fell off (B) ? secondary
particles?
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A 10 GeV proton passing through several 1.3cm
slabs of lead
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Variation of intensity of ultra radiation with
the Earth magnetic latitude - Clay (1932)
Amsterdam
Genoa
Jakarta
Jakarta

• Data taken by Berlage

• Cosmic rays are charged particles

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Vallarta 1932
Early calculation of pCR paths in the
terrestrial B field
Curves are shown for proton energies of
2 GeV - 40 GeV
Need to go to higher energies to recover true
source direction
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Cosmic ray balloon experiment, 1992 IMAX
Time of flight scintillators aerogel Cherenkov
counters magnetic spectrometer ? velocity vs.
rigidity ? mass
Identified 16 mass-resolved cosmic ray p , as
expected from collisions in interstellar medium
pCR Hnucleus ? 3 p p
p / p 10-4 at 10 GeV
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• Discovery of Extensive Air Showers
• in 1938 Pierre Auger was testing a new
  coincidence unit for a 10ms resolving time
• found coincidence rate between Geiger counters
  separated by up to 300m was much higher than
  expected by chance

Simultaneous tracks appear in cloud chambers 5m
apart
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Secondary particles reaching the ground must be
generated by Ultra High Energy cosmic rays!
1 particle / m2 / year
1 particle / km2 / year
Tevatron LHC
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EXTENSIVE AIR SHOWER TECHNIQUES
Particle Detector Arrays
primary

• blocks of scintillator or water tanks spaced
  30 m - 1500 m apart
• air shower particles reaching the ground
  generate scintillation or Cherenkov light for
  energy measurement
• arrival time of shower front across detector
  array gives arrival direction to within a few
  degrees

shower trajectory
shower core
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Haverah Park 1962 - 1987
12 km2 array of water Cherenkov tanks
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Airshower recorded at Haverah Park generated by a
primary cosmic ray of energy gt 1020eV
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Array layout was dictated by the local residents
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Simulated particle distribution for a 1019 eV
proton arriving from a shallow angle of 80º from
the vertical
Fit to a similar Haverah Park air shower
event Ave et al. PRL 85, 2244 (2000)
Rely on comparison with simulations - need e.g.
good data on hadron production cross-sections
from accelerator experiments such as HARP
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Toasting the experiments success - with 25 year
old water
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Haverah Park Group went to South Pole (1987
-1997) to search for Supernova 1987A and other
possible sources towards galactic centre
Loading a scintillator block banana sledge to
the left
No, they didnt find any sources !
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KASCADE

• at Karlsruhe
• best for 1015eV composition studies
• layered scintillator huts separate e-, g, m
  components

• Central hadron calorimeter - iron concrete
  multi-wire proportional chambers at base

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Fluorescence Detectors

• air is a weak scintillator - nitrogen
  fluorescence _at_ 350nm
• shower tracks generated by ? 1017eV cosmic rays
  observable

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Energy threshold is 1017eV, approx. 100 - 1000
times higher than a particle detector
array BUT Fluorescence is isotropic ? can detect
air showers which impact anywhere within 20km
radius
Flys Eye Detector (U. of Utah) 880
photomultipliers

• Idea to view sky from all angles to
• exploit huge collection area
• track path of shower development

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The Flys Eye fluorescence detector overlooking
Dugway, Utah, 1981 - 1991
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x 1010
3 x 1020 eV Flys Eye event
Calorimetric measurement, DE/E 20 - requires
careful study of atmospheric transmission
conditions !
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Summary of UHE Spectrum, August 2001
4 x 1019 eV
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Projected arrival directions of cosmic rays gt
4x1019 eV Hillas, Nature 395, 15 (1998).
Statistically isotropic.
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Problems posed by UHE CR
PROBLEM I If particles are gt 4 x 1019 eV, then
they must be local (GZK cut-off) p
g2.7K ? D ? p p or n p Local
depends on energy gt 4 x 1019 eV 50
from within 390 million light years gt 1020
eV 50 from within 60 million light
years So ANISOTROPIES might be expected from
nearby sources
2.7 K microwave background
Looks like 200 MeV g ray to a 1020eV p
6x10-4eV/photon
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PROBLEM II Difficult to accelerate
Greisens argument (1965) (i) accelerator size
L gt Larmor radius (ii) synchrotron losses lt
energy gain
Shock Acceleration Emax k Ze B L bc with
k lt 1, b speed of scattering centres
Supernova remnant age, size and shock speed ?
Emax Z x 1014eV typically
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Nothing below the blue line can accelerate p to
1020eV
Are UHE cosmic rays iron nuclei?
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Mean logarithmic mass vs. particle energy
From Haverah Park, 49 events above 1019 eV, g
/ p ? 40
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Super Heavy Relic Particles - UHE CR progenitors?

• Super heavy relic particles may be created in
  early Universe
• May make up some of the cold dark matter
• Typical Mass 1012 GeV and lifetime 1020
  years ?

• Predictions of large fluxes of p, ?, ? as
  products of decay
• no acceleration required - top down
• avoids GZK cut-off
• Numbers depend on specific type of super-heavy
  relic

Sarkar and Toldra, Nucl Phys B621 495 2002 and
hep-ph/0206217
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Dark matter relic n are so damned hard to detect
- Kai Zuber
Z burst scenario - resonant annihilation of a UHE
cosmic neutrino on a relic (anti-) neutrino
resonance E MZ2 / 2 mni 4.2
x1021eV (1eV / mni)

• close to highest UHE cosmic ray energies for mn
  1 eV
• avoids GZK cut-off

TESTS 1 Anisotropy because of distribution of
matter in galaxy? 2 Are photons present
in large numbers above 1019 eV?
Final suggestion to avoid GZK cut-off with g 2.7
K through change in collision kinematics
failure of Lorentz invariance for 1020eV p ?
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Next Generation Experiments
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Genesis of the Pierre Auger Observatory
1990 Review If community does not build 1000
km2 then a reviewer in
10 years time will give much the same
story 1991 Jim Cronin to Alan Watson
You are not ambitious enough we must build
5000 km2 1992 First major meeting in Paris
in Spring 1992 1995 6 month design study at
Fermi Lab Choice of Argentina as the
Southern Site 1996 Choice of Utah for the
Northern Site March 1999 Ground Breaking
Ceremony in Argentina
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The Hybrid Concept

• Fluorescence Detector
• Longitudinal development
• Time ? direction

• Surface Detector
• Shower size ? E
• Time ? direction

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The Auger South Site
Picture by Peter Walker
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A Cherenkov tank - holds 12 tons of water
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Testing the liner for leaks!
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The first Fluorescence Detector site
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Fluorescence Detector
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Data are gathered from the water tanks using a
purpose built Wireless LAN, based on
cellular telephone technology. Signals are sent
to the antennae on the tower and then by
conventional microwave links to the computer in
Malargue. It is decided whether a group of tanks
has interesting data. If so, more detailed
information is requested and then transmitted.
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The Engineering Array
30o, FD 2 telescopes
40 SD tanks

• Installation and commissioning of tanks and
  telescopes
• Communications
• Hybrid trigger and timing
• Internet connection with data mirroring in US
  and Europe, data analysis
• First showers observed May 2001

Los Leones FD eye
Central Campus, Malargue

• December 2001March 2002 stable data taking
  80 hybrid events

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An early event in the fluorescence detector
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Longitudinal profiles of fluorescence events
E 1.3 x 1019eV, Smax 9.2 x 109,
Xmax 670 g/cm2
E 1.5 x 1019eV, Smax 1.0 x 1010,
Xmax 746 g/cm2
particle number (107)
particle number (107)
atmospheric depth (g/cm2)
atmospheric depth (g/cm2)
Preliminary energy estimates!
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Estimate of contamination of the fluorescence
signal by direct Cherenkov light for an air
shower profile
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The corrected profile
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an 11-fold Event 184599q 54 r(1000m) 7
VEM/m2 station pairs 31 45
34 48
Surface Detector, April 2002
Green hit before red
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4 Stations of the 11-fold event
31 34 hit before 45 48 - shower arrived at
shallow angle
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• Next stage of Auger project will be
  pre-production array (100 - 120 tanks) plus two
  full fluorescence detectors. This should be
  operational early in 2003. Meanwhile...

HiRes 15M U.S./Australian twin Flys Eye
project

• two fluorescence detectors separated by 13 km
• operating since 2000
• expect 300 events per year above 1019eV

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A HiRes flys eye facet
A binocular event
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Extreme Universe Space Observatory

• Aims to
• detect 104 events/year gt 1020eV
• look for GZK effect structure in spectrum
• map arrival directions in both hemispheres
• observe possible high energy cosmic n
• detect atmospheric phenomena

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• EUSO - external payload on ISS Columbus Exposed
  Payload Facility
• Phase A Study to be completed December 2002
• 2.5m Fresnel lens 2x105 pixel camera view an
  airmass of 2 x 1012 tons with pixel size 0.8 km ?
  0.8 km

OWL - similar concept to EUSO but free-flying on
a pair of satellites at 640km altitude
Also being installed on the International Space
Station AMS-02 Alpha Magnetic Spectrometer for
direct detection of antimatter cosmic ray nuclei
(He, C) from an anti region of the Universe
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And finally are high energy n from accreting
active galactic nuclei not such a new idea after
all?
Crivelli, 1430 - 1494