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Ultra-high-energy cosmic-rays
Etienne Parizot (APC – Université Paris Diderot - France)
and the challenge of particle acceleration in the universe
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
2
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
1785: Coulomb notices the spontaneous discharge of electroscopes
1895-1900: discovery of the subatomic world: X-rays, electrons, radioactivity…
ionizing radiation !
1900: Wilson confirms spontaneous discharge of electroscopes in deep underground mines
natural radioactivity (Rutherford)
Cosmic rays timeline (ultra-brief) 3
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
1909: Wulf studies electroscopes spontaneous discharge at bottom and top of Eiffel Tower (320 m)
1910-1911: Pacini studies spontaneous discharge far from Earth crust (lake, sea)
not due to rock radioactivity
1911-1912: Hess studies spontaneous discharge at different altitudes, with balloon flights up to 5300 m (7 Aug. 2012)
radiation source from above! (+ Gockle, 1909)
anomalously small attenuation of irradiation!
Cosmic rays timeline (ultra-brief) 4
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
0 km
2 km
4 km
6 km
8 km
10 km
0 20 40 60 80Intensité du rayonnement
Synthèse des mesuresde Hess et de Kolhörster
(1912 - 1914)
radiation intensity
altitude
very penetrating!
Summary of Hess and Kohlörster observations (1912-1914)
« The result of these observations seems to be explained in the easiest way by assuming that an extremely penetrating radiation enters the atmosphere from above » (V. Hess)
Cosmic rays timeline (ultra-brief) 5
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Cosmic rays timeline (ultra-brief) 1912-1929: Millikan believes that “Hess rays” are gamma-rays
gives them the name of “cosmic rays” (1925)
1927-1929: Experiments with Geiger counters and cloud chambers with magnetic fields show that the particles are charged (Bothe, Kohlörster, Skobeltzyn)
But these are secondary particles (after interaction of primary cosmic rays in the atmosphere)
1928-1930: flux variation with latitude shows the primaries are charged (Clay, Compton)
1933: east/west asymmetry shows CRs’ charge is positive (Alvarez & Compton)
1941: CRs are composed mostly of protons
6
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Cosmic rays timeline (ultra-brief) Birth of the science of particle physics
■ Major discoveries ◆ Positron ⇒ antimatter !
◆ Muon
◆ Pions : π 0, π +, π -!◆ Kaons (K)
◆ Lambda (Λ)!
◆ Xi (Ξ)!
◆ Sigma (Σ)!
“strange” particles!
1932
1936
1947
1949
1949
1952
1953
(lifetime is much too long)!
7
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Key discovery: atmospheric showers 1938: Coincident detection of secondary particles over large areas from the
cascade induced by a single cosmic-ray event (Pierre Auger)
particle shower
atmospheric shower
1 very energetic particle
many secondary particles
8
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Very high energy cosmic rays Pierre Auger assesses the existence of cosmic rays of
unconceivably high energy:
The detection rate decreases rapidly with energy the flux decreases sharply, in E-2.7 or so, but with no evidence for a cutoff…
Lorentz factor: Γ > 106 E > 1015 eV
2 main reasons for this quest:
Search for higher and higher energies, with lower and lower fluxes, with larger and larger detectors…
Try to break through the magnetic mist! Challenging acceleration processes!
9
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
A wonder of the Physical world!
The cosmic-ray spectrum!
100 MeV
1021 eV
CR flux
Energy
32 o
rder
s of m
agni
tude
12 orders of magnitude
10
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!100 MeV
1021 eV
~ 1 particle / m2 / second
Energy
Flux
~ 1 particle / m2 / yr
~ 1 particle / m2 / billion years!
The cosmic-ray energy spectrum
32 o
rder
s of m
agni
tude
Out of equilibrium !!!
11
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
The cosmic-ray energy spectrum 12
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Georgi Zatsepin! Yakutsk (Sibérie)
Pierre Auger!
58 detectors covering 12 km2
Cherenkov tanks (water), 12 km2
Haverah Park (UK)
The quest for ultra-high-energy CRs 13
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
John Linsley! Volcano Ranch (New Mexico)
1962: a cosmic ray with E ≥ 1020 eV !!! Several joules = macroscopic energy !
Lorentz factor of 1011 v ≈ 0,99999999999999999999995 × c
1 second 3500 years 1.5 m d(Earth,Sun)
The quest for ultra-high-energy CRs 14
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
A 1020 eV atmospheric shower yields ~100 billion particles in the atmosphere!
By a clear, moonless night, one can detect the induced fluorescence light!
15 october 1993: 3.2×1020 eV !!!!
keeps up the dream of a “cosmic-ray astronomy”!
Fly’s Eye, puis HiRes (Utah)
The quest for ultra-high-energy CRs 15
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Which cosmic-ray sources behind the magnetic mist?
As charged particles, cosmic rays are deflected by magnetic fields
Larmor radius: rL = E/qBc
Proton
B = 3 µG rL ~ 1/3 pc E = 1015 eV
rL << size of the Galaxy isotropization
16
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Which cosmic-ray sources behind the magnetic mist?
No astronomy with cosmic rays sources are still not known!
≠ Source position is known Source position is unknown
Next slide: high resolution image of the sky seen in cosmic rays…
17
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
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E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Breaking the magnetic mist at high E ?
Larmor radius ∝ E
Protons with E >> 1018 eV are not confined in the Galaxy
Proton
B = 1 nG rL ~ 100 Mpc E = 1020 eV
rL >> size of the Galaxy pointing astronomy?
increasing energy
larger than the horizon scale!
???
19
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
proton γ-ray photon
e+
e-
UHE proton as seen in the “cosmic frame”
The “GZK effect” Major prediction by Greisen (1966) and Zatsepin &Kuz’min
(1966) a few weeks after the discovery of the CMB
+ CMB photon
very low energy (T = 2.7 K)
as seen in the “proton rest frame” + or π
In the proton rest frame, the gamma-ray loses energy to produce the secondary particles
In the “cosmic frame”, the UHE proton loses energy!
20
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
10-6
10-5
0,0001
0,001
0,01
0,1
1
106 107 108 109 1010
σκ
(mba
rn)
Eγ (en eV)
production de pions
production de paires e+/e-
[cross section] x [inelasticity]
Pion production
e+/e- pair production
21
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
e+e–
π
interaction length
attenuation length
Proton attenuation length 22
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
0,2
0,4
0,6
0,8
1
10 100 1000
P(d<D)
D(Mpc)
Protons
19.2
19.4
19.6
19.8
20.020.2
20.4
Proton horizons For different energies, the plot shows the fraction of protons
(ordinate) coming from a distance smaller than the abscissa
23
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
GZK cut-off for nuclei Photo-dissociation through interactions with CMB photons
in the “nucleus rest frame”
as seen in the “cosmic frame”
+
+
γ-ray photon
CMB photon
energy losses! mass-dependent horizon scale…
24
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
0,2
0,4
0,6
0,8
1
10 100 1000
P(d<D)
D(Mpc)
He
19.2
19.4
19.6
19.8
Helium horizons For different energies, the plot shows the fraction of He nuclei
(ordinate) coming from a distance smaller than the abscissa
25
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
0,2
0,4
0,6
0,8
1
10 100 1000
P(d<D)
D(Mpc)
CNO
19.2
19.4
19.6
19.8
20.0
“CNO” horizons For different energies, the plot shows the fraction of C, N or O
nuclei coming from a distance smaller than the abscissa
26
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
10-1
100
101
102
103
104
1019 1020 1021
ProtonHeliumOxygenIron
χ75
(Mpc
)
E (eV)
He OH
Fe
GZK horizons for UHECRs 27
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
1023
1024
1025
18,4 18,8 19,2 19,6 20 20,4
E3 Φ(E
) (eV
2 m-2
s-1sr
1 )
log10E eV
Pure Proton β=2.3
evolution : (1+z)5
1023
1024
1025
18,4 18,8 19,2 19,6 20 20,4
E3 Φ(E
) (eV
2 m-2
s-1sr
1 )
log10E eV
9 ≤ Z ≤ 11
protons
12 ≤ Z ≤ 19
20 ≤ Z ≤ 26
β = 2.3
Fe only (at sources)Emax= Z × 1020.3 eV
Pure Fe sources Pure proton sources
Fitting the UHECR spectrum 28
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
UHECR phenomenology
Modification of the energy spectrum by the GZK effect Energy-dependent horizon within which the sources must be!
Modification of the composition
Modification of the arrival directions:
Photo-dissociation + magnetic rigidity effects…
Hopefully limited at UHE, but the deflections depend on particle charge!
29
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Energy cut-off confirmed with high statistics!
Main results of the Pierre Auger Observatory
Is it the GZK cut-off (horizon effect) or the end of the acceleration process?
(or both?!)
Can we isolate sources in the sky before the spectrum ends?
Drastic reduction of the flux above ~ 6 1019 eV
(3000 km2 in Argentina)
30
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Energy cut-off confirmed with high statistics!
Main results of the Pierre Auger Observatory
Is it the GZK cut-off (horizon effect) or the end of the acceleration process?
(or both?!)
Can we isolate sources in the sky before the spectrum ends?
Drastic reduction of the flux above ~ 6 1019 eV
(3000 km2 in Argentina)
31
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Disappointing image of the UHECR sky above 60 EeV
Main results of Auger 32
No obvious accumulation of events in specific arrival directions…!
no source identified! Question still open!
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
However, the first evidence for anisotropies has been observed. But not easy to interpret and with moderate significance.
Main results of Auger
Excess of correlation with local matter (~100 Mpc)!
One will need to significantly increase the statistics at the highest energies, where the number of sources within the GZK horizon is very limited, in order to isolate sources in the sky…!
for E ≥ 6 1019 eV!
The deflections are probably large (≥ 10°) !
Major challenge for the coming years!! JEM-EUSO?!
33
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Composition features… Main results of Auger
Consistent with large deflections (and weak or no anisotropy)!Transition towards a heavier composition around 1019 eV…!
(But maybe in conflict with other results in Northern hemisphere)!
But relies on extrapolations of hadronic physics models!
constraints for and from high-energy physics!
+ details do not work perfectly well: more muons than predicted!!
cf. LHC results!!
Atmospheric depth of maximum shower development!
AVERAGE! SPREAD!
34
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
UHECRs and high-energy physics - 1
unexplored hadronic physics
35
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
UHECRs and high-energy physics - 1
unexplored hadronic physics
Recent input from LHC results have been implemented to better constrain the models used in atmospheric shower simulations
science in progress…
QGSJET, SYBILL, EPOS…
36
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
UHECRs and high-energy physics - 1
Discrepancy between models predictions and observations (number of muons: too many + no feature in energy!)
new physics or new constraints on: - cross sections - multiplicity - rapidity - etc.
unexplored hadronic physics
37
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
UHECRs and high-energy physics - 1
Experimental challenge: disentangle the muon component from the EM component
under study…
+ independent estimate of the composition
By anisotropy studies? By radio data? By astrophysics?
unexplored hadronic physics
38
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Historically, Cosmic Rays played a key role in High-Energy Physics, giving birth to Particle Physics, and allowing one to explore the physical world at an unprecedented energy scale.
Then their role decreased because of the poor control on and understanding of the “cosmic beam”, compared to the high-energy beams produced in man-made accelerators…
Today, UHECRs give access to a new realm of physics, beyond accelerator’s reach. But we still suffer from the poor understanding of the beam (and its extreme rarity!)…
Intermediate comment 39
Progress in high-energy astrophysics and “astroparticle physics” is a key to progress in high-energy physics, and vice-versa!
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Major question in high-energy astrophysics:
Energetics arguments indicate a link with supernovæ explosions (~20%-30% of their kinetic power)
Particle acceleration in the universe 40
What is the acceleration mechanism?
Where do the cosmic rays come from?
What are the sources?
(but it could be a coincidence, or it could be an indirect link)
We do know a mechanism to accelerate particles at the shock wave created by the supersonic (super-Alfvénic) supernova ejecta in the interstellar medium!
Diffusive Shock Acceleration
We do see energetic particles at the shock supernova fronts!
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
X-ray rims from synchrotron emission of TeV electrons in amplified magnetic field
Supernova remnants 41 Chandra (satellite X)
Red 0.95-1.26 keV, Green 1.63-2.26 keV, Blue 4.1-6.1 keV
Tycho (1572)
TeV gamma-ray emission
broad-band spectrum
π0 decay (hadronic) ?
Inverse Compton scattering (leptonic) ?
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Diffusive shock acceleration 42
Chandra (satellite X)
Red 0.95-1.26 keV, Green 1.63-2.26 keV, Blue 4.1-6.1 keV
Tycho (1572)
Supernova explosion (~ 3/century)
supersonic ejecta: V = 104 km/s
Key aspect of the shock wave = discontinuity in velocity!
super-Alfvénic flow
collisionless shock wave
Vshock
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Diffusive shock acceleration 43
Chandra (satellite X)
Red 0.95-1.26 keV, Green 1.63-2.26 keV, Blue 4.1-6.1 keV
Tycho (1572)
Supernova explosion (~ 3/century)
supersonic ejecta: V = 104 km/s
Key aspect of the shock wave = discontinuity in velocity!
super-Alfvénic flow
collisionless shock wave
Vshock
+ magnetic turbulence! resonant interaction between energetic particles
and plasma waves
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Diffusive shock acceleration 44
Reflection off “magnetic walls”
No energy gain, because a B field does not produce any work
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Diffusive shock acceleration 45
elastic bounce unchanged velocity
v
v
Simple analogy
Tennis ball bouncing off a standing wall
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Diffusive shock acceleration 46
elastic bounce unchanged velocity
v
v
Simple analogy
Tennis ball bouncing off a standing wall
v V
v + 2V unchanged velocity���with respect to the racket
elastic bounce ball acceleration
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Diffusive shock acceleration 47
Reflection off “magnetic walls”
No energy gain, because a B field does not produce any work
V
moving magnetic structure
energy gain!
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Diffusive shock acceleration 48
Reflection off “magnetic walls”
No energy gain, because a B field does not produce any work
moving magnetic structure
or energy loss!
( drop shot in tennis!) V
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Diffusive shock acceleration 49
Reflection off “magnetic walls”
No energy gain, because a B field does not produce any work
V
moving magnetic structure
energy change
[equivalent to the work of the induced E field…]
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Diffusive shock acceleration 50
Always head-on interactions across a shock wave! shock front
n1, p1, T1 v1
n2, p2, T2 v2
upstream medium downstream medium
velocity discontinuity: Δv/c
• In the downstream rest frame, the upstream medium is coming towards the particles that cross the shock
• In the upstream rest frame, the downstream medium is coming towards the particles that cross the shock
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Diffusive shock acceleration 51
Always head-on interactions across a shock wave! shock front
n1, p1, T1 v1
n2, p2, T2 v2
upstream medium downstream medium
velocity discontinuity: Δv/c
Energy gain at each shock crossing!
Balance between exponential energy growth and constant probability of escaping away from the shock (due to the global drift along the flow in the shock rest frame)
compression ratio
universal power law spectrum in E-2 !!
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Limitations of shock acceleration 52
Magnetic turbulence and waves must be present on both sides of the shock
shock front
Vshock
waves resonantly produced upstream by energetic particles themselves tricky!
~ easy downstream (shocked medium)
It works: we do see particle acceleration at collisionless shocks! (supernovæ, extragalactic, interplanetary, etc.)
important problem for relativistic shocks! Challenging for ultra-high-energy cosmic rays (UHECR)
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Limitations of shock acceleration 53
Keep the particle inside the accelerator!
Shocks fronts are not infinite planes!
Key limitation, due to the size of the accelerator The Larmor radius of the particle must be smaller than the size of the accelerator
In fact, diffusion-advection at the shock implies: (“work of an effective induced E field”)!
so-called “Hillas criterion”
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
“Hillas plot” 54
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
“Hillas plot” 55
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Limitations of shock acceleration 56
Hillas criterion not so many candidates for ultra-high-energy cosmic rays (UHECRs)!
“Optimistic view”: sources are among the few candidates the particle acceleration process works
at its maximum possible efficiency we roughly see the end of the
acceleration spectrum
“Pessimistic view”: Adding refinements and taking into account actual conditions will reduce the maximum energy and make the process fail for UHECRs
Optimistic in another way! it just requires other ideas for particle acceleration in the universe!
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Limitations of shock acceleration 57
Acceleration (energy gain) competes with energy losses!
The longer the particle stay in the accelerator, the higher the probability to interact with ambient fields or particles
Problem for large shocks… Problem for high-power regions…
Can severely challenge the Hillas criterion!
energy losses - synchrotron radiation - Inverse Compton scattering - photo-pion production - photo-dissociation
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
New ideas for particle acceleration? 58
What about wake-field acceleration?
For instance, gamma-ray bursts are hugely powerful events
See past and coming works by Tajima, Takahashi, Chen, Hillmann, Ebisuzaki…
They emit in a few seconds the total energy radiated by the Sun in 10 billion years! Ultra-relativistic outflows and huge amount of high-energy photons in a small volume (1046 J in a few tens of km… ?)
In any case, one should think about non linear effects… A new field within astrophysics, very little explored (if at all!)…
Short timescale acceleration can we avoid losses?
Possible connections with iZEST community…
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Other possible connections 59
Exploration of high-energy physics
Exploring fundamental physics at 1020 eV
Hadronic physics from UHECR interactions in the atmosphere (shower physics, cross sections, etc.)
Highest-energy particles in the universe can we use them as the cosmic rays were used in the first half of the XXth century to discover new structures and new physics?
Lorentz Invariance Violation… (“predicted” by most quantum gravity theories…)
Exploring space-time structure… UHECRs propagate in space-time at an unexplored energy scale may feel small-scale structures
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Lorentz Invariance Violation (LIV) 60
Cf. talk by Professor Tajima this morning
Different propagation timescales for the different photon energy
Constraints from astrophysical observations of the energy/time structures in the light curves of distance sources
Or studies with “infinitesimal” timescales on “human-scale” distance
(Abdo, et al, 2009)
IZEST?
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
LIV and the GZK cut-off 61
Lorentz Invariance Violation and the GZK cut-off
The GZK cut-off in the UHECR spectrum is due to energy losses from the interactions between UHECRs and CMB photons
Interaction cross sections:
Ingredients: well known and measured at the relevant energies
Photon energy distribution: very well-known in the cosmic frame: CMB black body spectrum!
But the calculation assumes that we know how to make a Lorentz transform with a Lorentz factor of 1011 !
The energy of the photons may not transform as we think! That would change the effective energy threshold for pion production, and thus the energy scale of the cut-off!
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
62
Different particles may have different “maximum attainable velocities”!
LIV and the GZK cut-off
Violation of Lorentz Invariance:
Will be modified if c is different for the protons and the pions (simple kinematics!)
Threshold and elasticity of photo-pion production
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
63
Energy losses and GZK horizon will thus be different from those calculated in the standard case…
LIV and the GZK cut-off
Proton attenuation length
(Stecker-Scully 2009)
Proton energy
no LIV
with LIV
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
64
Energy losses and GZK horizon will thus be different from those calculated in the standard case…
LIV and the GZK cut-off
UHECR flux (Stecker-Scully 2009)
UHECR energy
no LIV
with LIV
Flux recovery at ultra-high energy!
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
65
Energy losses and GZK horizon will thus be different from those calculated in the standard case…
LIV and the GZK cut-off
UHECR flux (Stecker-Scully 2009)
Look for larger statistics at higher energy!
no LIV
with LIV
Flux recovery at ultra-high energy!
Current limit
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Perspective 66
Go into space to increase the statistics at UHE energy
Momentum is building up! 2017 ?
JEM-EUSO!
Large field-of-view UV telescope on the Kibo module of the International Space Station
Observe 200 000 km2 at once!
E. Parizot (APC, Paris 7)!Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —!
Perspective 67
UHECRs offer an interesting way to explore high-energy physics and fundamental physics at the highest energies known
The acceleration of particles in the universe is challenging and not well understood
new ideas are welcome!
There are extreme environments in the universe where non linear electromagnetic effects might be important must be studied !
This moment is timely for explorative interactions between the IZEST community and the high-energy astrophysics and astroparticle physics communities
(new instruments and capabilities under view)
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