The enigmatic High Energy tail of the Cosmic Ray Spectrum

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Enrique Zas University of Santiago de
Compostela Baeza February 5th 2008
The Ultra High Energy Realm
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Outline

• DAY 1
• Ultra High Energy Cosmic Rays
• Introduction and motivation
• Extensive Air Showers and detection
• Some preAuger data results
• Origin Astrophysical versus top-down
• The neutrino gamma ray proton connection
• UHE Neutrino detection
• Inclined showers
• Coherent radio pulses from showers
• DAY 2
• The Auger Observatory, results

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How do we learn about our large scale Universe?

• Mainly by light
• Directional gt imaging astronomy
• Extended in wavelengths
• Other particles challenge
• Neutrinos (Sun, SN 1979A)
• High energy charged particles
• Diffuse spectra important (cummulative)
• i.e. CMB Big Bang
• Interrelated fluxes through production and
  interactions

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Energy (eV) 10-8 10-6 10-4 10-2 1
102 104 106 108 1010 1012
1014 1016 1018 1020
Flux (cm2 s sr-1)
1012 1010 108 106 104 102 1 10-2
10-4 10-6 10-8 10-10 10-12 10-14 10-16
10-18 10-20
Diffuse spectra
CMB
CnB
g
Light
106 104 102 1 10-2 10-4 10-6
10-8 10-10 10-12 10-14 10-16 10-18 10-20
10-22 10-24 from M.T. Ressell M.S. Turner

Wavelength l (cm)
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The discovery Victor Hess (1912)

• Data
• Ionization increases with height
• Conclusion
• Radiation coming to Earth

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The Ultra High Energy Tail
Ankle
gt1020 eV 1 km-2 sr-1 century-1
T.K. Gaisser
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Ultra High Energy Cosmic RaysScience motivation

• Particle Physics
• Test interactions at (always) highest energies
• Test forward region
• Astrophysics
• Particle nature unknown (composition-origin)
• Interplay p, Fe, g, n related to unknown origin
  
• Acceleration (Bottom-up)
• Fragmentation (Top-down)
• Extragalactic sources gtCMB interactions
  (Cosmology-GZK)
• Large E gt Small angular deviations
• Astronomy
• Learn about B fields

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Nature always the source of highest energy
colisions
UHECR
LHC
Tevatron
HERA
Same cm energy
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Energy Flow along beam pipe

• Events triggered at accelerator experiments are
  those producing high-pT (large q) particles.
• Soft collisions produce mainly low-pT particles,
  which escape undetected in the beam pipe.

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LHCf an LHC Experiment to help UHECR physics
LHCf measurement of photons and neutral
pions and neutrons in the very forward region of
LHC Adding an EM calorimeter at 140 m from the
Interaction Point (IP1 ATLAS) For low luminosity
running
from Kakenhi agency in Japan
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At UHE Only Extensive Air Showers detected
spread over tens of km in length several km
radius
The atmosphere is a calorimeter 30 X0 (vertical)
/ 1000 X0 (horizontal)
Composition inferred from shower
developmentgtExtrapolate HE
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Require different techniques
Direct Balloon Satellite
compostion inferred HEP
compostion known (matter)
Indirect Air Showers
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p
6 km
1019 eV proton
p-
g e m
p0
p
n m
n m-
g
g
e e-
12 km
e
g
e-
m
g
e
n
e
n
6 km
Simulation by Clem Prike
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Heitler Model electromagnetic

• Each particle carries Eparent/2
• Stop _at_ Ecritical?c (85 MeV air)

d mean distance

d
...
?r 37 g cm-2 in air
(radiation length)
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After n steps N particles (e,e-,g)
Number of particles at maximum (end)

• Elaborate calculations
• Xmax ln Eo
• Eo Nmax
• 85 (gcm-2)/decade

Energy related to Nmax Nmax
Xmax nclr ln2 lr ln Eo/?c
Elongation rate
2.3 ?r
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Only two succesful techniques
Isotropic Fluorescence light from nitrogen
(aurora) (4 g per meter of track)
Fluorescence Technique
Particle array Technique
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The Fluorescence Technique
Energy
Geometry Timing
Calorimetric
E_at_2.19 MeV Ne(x)dx
direction (noise)
C.Song et al., Astropart. Phys. 14, 7 (2000)
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The particle array Technique
Er(600 m) r(1000 m)
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Two methods at comptetion

• Flourescence
• Calorimetric E (Xmax)
• Acceptance(E)
• Corrections(t)
• Absorption
• Cherenkov
• 10 duty cycle
• Fluor yield(T,p)
• Future (satellite)

• EAS arrays
• 1 layer calorimeter
• Geometric Acceptance
• Corrections
• Fluctuations
• Sampling
• 100 duty cycle
• Depth(T,p)
• Limited size ?

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The Ultra High Energy data
Flys Eye
Flys Eye
10 1 0.1
Flux E3 (1024 eV2 cm-2s-1sr-1 )
1017 1018
1019 1020 E(eV)
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Flys Eye
10 1 0.1
Flux E3 (1024 eV2 cm-2s-1sr-1 )
HiRes 2
1017 1018
1019 1020 E(eV)
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Flys Eye
qAgasa
10 1 0.1
Flux E3 (1024 eV2 cm-2s-1sr-1 )
HiRes 1
HiRes 2
1017 1018
1019 1020 E(eV)
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qAgasa
Flys Eye
10 1 0.1
Flux E3 (1024 eV2 cm-2s-1sr-1 )
Haverah Park
HiRes 1
HiRes 2
1017 1018
1019 1020 E(eV)
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Pre-Auger data disagreement

• Fluorescence data
• (Flys Eye HiRes)
• Suggests GZK cutoff
• No clustering evidence

• Array data
• (AGASA, HP, Yakutsk)
• No GZK cutoff seen
• Marginal clustering?

Both techniques Depend on Simulation
Int models but

• Detect events above 1020 eV
• Agree at UHE at the 2-s level

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Astrophysical Origin?
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Acceleration (2nd order Fermi 1949)
vout
vout
Magnetic cloud
Both gain and loss but head on encounters more
frequent Net acceleration
vin
v
vin
DE 4 v2 E 3 c2
Spectrum a E-g (g2.2-2.7)
1st order acceleration at shocks (more efficient)
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Acceleration size (L) MUST EXCEED radius (RI)
p RI lt L
Z e B cos q
RG
RI
E lt Ze c BL
Diffusive propagation in accelerating region
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The difficulty to accelerate particles
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Fragmentation origin? top-down scenarios
Acceleration is bypassed UHECR from decay into q
/ g that fragment

• CRs from decay of massive X particles (GUT)
• Topological defects (annihilation, colisions,
• Point Monopoles
• Lines Strings (superconducting, cusps,
  necklaces, ...)
• Surfaces Domain walls
• Acceleration (Bottom-up)
• Fragmentation (Top-down)
• X particles are massive remnants
• Could be part of cold dark matter
• CRs from decays of Z (n n CnB annihilations)

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The p(Fe)-g-n connection _at_ origin

• Acceleration

• Fragmentation

pg
q q X
p p0 p
p p0 p/- 0.03 0.3 0.65
pp
nm m
gg
p
nm ne e
g nm ne nm ne 2 2 1 2 1
p g n 0.09 2 6
p n 1 3
D threshold
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The Greisen-Zatsepin-Kuzmin cutoff
pgCMB n p
nm m
D1232 resonance
pgCMB p p0
gg
Pair production lower threshold
lower cross section
by Ralph Engel
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Expect Structure at a well defined energy
Threshold for eg 3 2.73 8.62 10-5 eV
(2mpmp)mp Ep 1020 eV
4 eg
GZK starts earlier (Wien tail)
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Astronomy is possible
Protons deviate small angles above 5 1019 eV
Using the Larmor radius
RL Z e c B cos q E One can estimate the
angular deflection in the galaxy Structured B
fields of order a few mG over scale distances of
order kpc Typical deviations are given by
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Neutrino detection
Ice AMANDA, IceCube Water Antares, km3Net, ...
Cherenkov light cone
muon
Detector
interaction
Lattice of Photomultipliers Optical Modules
Muon track direction from arrival time of
light Neutrino direction ? ?? ??? ? ? 0.7o /
E0.6(TeV) Atmospheric muons shielded by the Earth
neutrino
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UHE neutrinos Detection alternatives

• Inclined Showers Deep showers
• Downgoing neutrinos interacting in the atmosphere
• All flavors
• Earth-skimming neutrinos
• nt interacts at Earth crust
• t exits to atmosphere
• t decay generates an upcoming air shower
• Coherent Radio pulses
• Ice RICE, ANITA
• Salt Salsa
• Moon Glue, Lunaska
• Coherent sound (1500 km3, 100 hydroph/km3)

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Inclined showers Protons, nuclei, g Shower gs
es and e-s do not reach ground level Only
muons
Neutrinos interact deep gs es e-s reach
ground
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Down-Going Shower Rate
p sr
10 -16 s sr cm2-1
1000 1010 cm2
10-32 cm2
3 107 s
500 6 1023 cm-2
Events in 1 year and 1000 km2 0.3
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