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Ultra-high-energy cosmic-rays and the challenge of particle acceleration in the universe Etienne Parizot (APC – Université Paris Diderot - France) 2 Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Cosmic rays timeline 3 (ultra-brief) 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) Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Cosmic rays timeline 4 (ultra-brief) 1909: Wulf studies electroscopes spontaneous discharge at bottom and top of Eiffel Tower (320 m) anomalously small attenuation of irradiation! 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! Glasgow, 13 Nov. 20012! (+ Gockle, 1909) — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Cosmic rays timeline 5 (ultra-brief) Summary of Hess and Kohlörster observations (1912-1914) 10 km altitude Synthèse des mesures de Hess et de Kolhörster (1912 - 1914) 8 km 6 km very penetrating! 4 km 2 km 0 km radiation intensity 0 20 40 60 Intensité du rayonnement 80 « 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) Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Cosmic rays timeline 6 (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 Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Cosmic rays timeline 7 (ultra-brief) Birth of the science of particle physics ■ Major discoveries 1932 ◆ Positron ⇒ antimatter ! 1936 ◆ Muon 1947 ◆ Pions : π 0, π +, π -! 1949 ◆ Kaons (K) 1949 ◆ Lambda (Λ)! 1952 ◆ Xi (Ξ)! 1953 ◆ Sigma (Σ)! Glasgow, 13 Nov. 20012! “strange” particles! (lifetime is much too long)! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Key discovery: atmospheric showers 8 1938: Coincident detection of secondary particles over large areas from the cascade induced by a single cosmic-ray event (Pierre Auger) 1 very energetic particle particle shower atmospheric shower many secondary particles Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Very high energy cosmic rays 9 Pierre Auger assesses the existence of cosmic rays of unconceivably high energy: E > 1015 eV Lorentz factor: Γ > 106 The detection rate decreases rapidly with energy the flux decreases sharply, in E-2.7 or so, but with no evidence for a cutoff… Search for higher and higher energies, with lower and lower fluxes, with larger and larger detectors… 2 main reasons for this quest: Glasgow, 13 Nov. 20012! Try to break through the magnetic mist! Challenging acceleration processes! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! A wonder of the Physical world! 10 CR flux 32 orders of magnitude The cosmic-ray spectrum! 1021 eV 100 MeV Glasgow, 13 Nov. 20012! 12 orders of magnitude Energy — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! The cosmic-ray energy spectrum 11 Flux 32 orders of magnitude ~ 1 particle / m2 / second Out of equilibrium !!! ~ 1 particle / m2 / yr 1021 eV 100 MeV Glasgow, 13 Nov. 20012! Energy ~ 1 particle / m2 / billion years! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! The cosmic-ray energy spectrum Glasgow, 13 Nov. 20012! 12 — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! The quest for ultra-high-energy CRs 13 Pierre Auger! Georgi Zatsepin! Yakutsk (Sibérie) 58 detectors covering 12 km2 Haverah Park (UK) Cherenkov tanks (water), 12 km2 Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! The quest for ultra-high-energy CRs John Linsley! 14 Volcano Ranch (New Mexico) 1962: a cosmic ray with E ≥ 1020 eV !!! Several joules = macroscopic energy ! Lorentz factor of 1011 v ≈ 0,99999999999999999999995 × c Glasgow, 13 Nov. 20012! 1 second 3500 years 1.5 m d(Earth,Sun) — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! The quest for ultra-high-energy CRs 15 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 !!!! Fly’s Eye, puis HiRes (Utah) Glasgow, 13 Nov. 20012! keeps up the dream of a “cosmic-ray astronomy”! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Which cosmic-ray sources behind the magnetic mist? As charged particles, cosmic rays are deflected by magnetic fields Larmor radius: rL = E/qBc 16 Proton E = 1015 eV B = 3 µG rL ~ 1/3 pc rL << size of the Galaxy Glasgow, 13 Nov. 20012! isotropization — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Which cosmic-ray sources behind the magnetic mist? 17 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… Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! 18 Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Breaking the magnetic mist at high E ? 19 Larmor radius ∝ E increasing energy Protons with E >> 1018 eV are not confined in the Galaxy rL >> size of the Galaxy pointing astronomy? Proton E = 1020 eV B = 1 nG rL ~ 100 Mpc larger than the horizon scale! ??? Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! 20 The “GZK effect” Major prediction by Greisen (1966) and Zatsepin &Kuz’min (1966) a few weeks after the discovery of the CMB UHE proton as seen in the + “cosmic frame” γ-ray photon as seen in the + “proton rest frame” CMB photon proton very low energy (T = 2.7 K) e- or π e+ In the proton rest frame, the gamma-ray loses energy to produce the secondary particles In the “cosmic frame”, the UHE proton loses energy! Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! [cross section] x [inelasticity] 21 1 production de pions Pion production 0,1 σκ (mbarn) 0,01 0,001 paires e+/ee+production /e- pair de production 0,0001 1 0-5 1 0-6 1 06 1 07 1 08 1 09 1 010 Eγ (en eV) Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Proton attenuation length 22 e+e– π attenuation length interaction length Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! 23 Proton horizons For different energies, the plot shows the fraction of protons (ordinate) coming from a distance smaller than the abscissa 1 20.4 0,8 20.2 P(d<D) 20.0 19.8 0,6 19.6 19.4 0,4 19.2 0,2 Protons 10 Glasgow, 13 Nov. 20012! 100 D(Mpc) 1000 — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! GZK cut-off for nuclei 24 Photo-dissociation through interactions with CMB photons γ-ray photon in the “nucleus rest frame” as seen in the “cosmic frame” energy losses! Glasgow, 13 Nov. 20012! + + CMB photon mass-dependent horizon scale… — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! 25 Helium horizons For different energies, the plot shows the fraction of He nuclei (ordinate) coming from a distance smaller than the abscissa 1 0,8 19.8 P(d<D) 19.6 0,6 19.4 19.2 0,4 0,2 He 10 Glasgow, 13 Nov. 20012! 100 D(Mpc) 1000 — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! 26 “CNO” horizons For different energies, the plot shows the fraction of C, N or O nuclei coming from a distance smaller than the abscissa 1 20.0 0,8 P(d<D) 19.8 0,6 19.6 19.4 19.2 0,4 0,2 CNO 10 Glasgow, 13 Nov. 20012! 100 D(Mpc) 1000 — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! GZK horizons for UHECRs 27 104 Proton Fe Helium Oxygen 103 Iron χ75 (Mpc) 102 He O H 101 100 10-1 1019 Glasgow, 13 Nov. 20012! 1020 E (eV) 1021 — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Fitting the UHECR spectrum Pure Fe sources Pure proton sources Fe only (at sources) Emax= Z × 1020.3 eV 1024 20 ≤ Z ≤ 26 12 ≤ Z ≤ 19 protons 1023 Pure Proton β=2.3 evolution : (1+z)5 1025 β = 2.3 E3Φ(E) (eV2m-2s-1sr1) E3Φ(E) (eV2m-2s-1sr1) 1025 28 1024 1023 9 ≤ Z ≤ 11 18,4 Glasgow, 13 Nov. 20012! 18,8 19,2 19,6 log10E eV 20 20,4 18,4 18,8 19,2 19,6 log10E eV 20 20,4 — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! UHECR phenomenology Modification of the composition Photo-dissociation + magnetic rigidity effects… Modification of the energy spectrum by the GZK effect Energy-dependent horizon within which the sources must be! Modification 29 of the arrival directions: Hopefully limited at UHE, but the deflections depend on particle charge! Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Main results of the Pierre Auger Observatory Energy cut-off confirmed with high statistics! km2 (3000 in Argentina) 30 Drastic reduction of the flux above ~ 6 1019 eV 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? Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Main results of the Pierre Auger Observatory Energy cut-off confirmed with high statistics! km2 (3000 in Argentina) 31 Drastic reduction of the flux above ~ 6 1019 eV 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? Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Main results of Auger 32 Disappointing image of the UHECR sky above 60 EeV No obvious accumulation of events in specific arrival directions…! no source identified! Glasgow, 13 Nov. 20012! Question still open! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Main results of Auger 33 However, the first evidence for anisotropies has been observed. But not easy to interpret and with moderate significance. Excess of correlation with local matter (~100 Mpc)! for E ≥ 6 1019 eV! The deflections are probably large (≥ 10°) ! 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…! Major challenge for the coming years!! Glasgow, 13 Nov. 20012! JEM-EUSO?! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Main results of Auger 34 Composition features… Atmospheric depth of maximum shower development! AVERAGE! SPREAD! Transition towards a heavier composition around 1019 eV…! Consistent with large deflections (and weak or no anisotropy)! (But maybe in conflict with other results in Northern hemisphere)! But relies on extrapolations of hadronic physics models! + details do not work perfectly well: more muons than predicted!! constraints for and from high-energy physics! Glasgow, 13 Nov. 20012! cf. LHC results!! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! UHECRs and high-energy physics - 1 35 unexplored hadronic physics Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! UHECRs and high-energy physics - 1 36 unexplored hadronic physics QGSJET, SYBILL, EPOS… Recent input from LHC results have been implemented to better constrain the models used in atmospheric shower simulations science in progress… Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! UHECRs and high-energy physics - 1 37 unexplored hadronic physics 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. Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! UHECRs and high-energy physics - 1 38 unexplored hadronic physics 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? Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Intermediate comment 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 highenergy 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!)… Progress in high-energy astrophysics and “astroparticle physics” is a key to progress in high-energy physics, and viceversa! Glasgow, 13 Nov. 20012! 39 — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Particle acceleration in the universe 40 Major question in high-energy astrophysics: Where do the cosmic rays come from? What are the sources? What is the acceleration mechanism? Energetics arguments indicate a link with supernovæ explosions (~20%-30% of their kinetic power) (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! Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Supernova remnants X-ray rims from synchrotron emission of TeV electrons in amplified magnetic field TeV gamma-ray emission Chandra (satellite X) Tycho (1572) 41 Red 0.95-1.26 keV, Green 1.63-2.26 keV, Blue 4.1-6.1 keV π0 decay (hadronic) ? Inverse Compton scattering (leptonic) ? Glasgow, 13 Nov. 20012! broad-band spectrum — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Diffusive shock acceleration Chandra (satellite X) 42 Tycho (1572) Supernova explosion (~ 3/century) supersonic ejecta: V = 104 km/s super-Alfvénic flow collisionless shock wave Red 0.95-1.26 keV, Green 1.63-2.26 keV, Blue 4.1-6.1 keV Key aspect of the shock wave = discontinuity in velocity! Vshock Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Diffusive shock acceleration Chandra (satellite X) 43 Tycho (1572) Supernova explosion (~ 3/century) supersonic ejecta: V = 104 km/s super-Alfvénic flow collisionless shock wave Red 0.95-1.26 keV, Green 1.63-2.26 keV, Blue 4.1-6.1 keV Key aspect of the shock wave = discontinuity in velocity! + magnetic turbulence! resonant interaction Vshock Glasgow, 13 Nov. 20012! between energetic particles and plasma waves — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Diffusive shock acceleration 44 Reflection off “magnetic walls” No energy gain, because a B field does not produce any work Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Diffusive shock acceleration 45 Simple analogy v Tennis ball bouncing off a standing wall v elastic bounce unchanged velocity Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Diffusive shock acceleration 46 Simple analogy v Tennis ball bouncing off a standing wall v elastic bounce unchanged velocity v v + 2V V unchanged velocity with respect to the racket elastic bounce ball acceleration Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Diffusive shock acceleration 47 Reflection off “magnetic walls” No energy gain, because a B field does not produce any work moving magnetic structure energy gain! V Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! 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!) Glasgow, 13 Nov. 20012! V — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Diffusive shock acceleration 49 Reflection off “magnetic walls” No energy gain, because a B field does not produce any work moving magnetic structure energy change [equivalent to the work of the induced E field…] Glasgow, 13 Nov. 20012! V — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Diffusive shock acceleration 50 Always head-on interactions across a shock wave! shock front n2, p2, T2 n1, p1, T1 v2 v1 downstream medium upstream 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 Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Diffusive shock acceleration 51 Always head-on interactions across a shock wave! shock front n2, p2, T2 n1, p1, T1 v2 v1 downstream medium upstream medium velocity discontinuity: Δv/c Energy gain at each shock crossing! compression ratio 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) universal power law spectrum in E-2 !! Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Limitations of shock acceleration 52 Magnetic turbulence and waves must be present on both sides of the shock shock front Vshock ~ easy downstream (shocked medium) waves resonantly produced upstream by energetic particles themselves tricky! 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) Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! 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” Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! “Hillas plot” Glasgow, 13 Nov. 20012! 54 — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! “Hillas plot” Glasgow, 13 Nov. 20012! 55 — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Limitations of shock acceleration Hillas criterion not so many candidates for ultra-highenergy cosmic rays (UHECRs)! “Optimistic view”: “Pessimistic view”: 56 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 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! Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Limitations of shock acceleration 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 energy losses - - - - 57 synchrotron radiation Inverse Compton scattering photo-pion production photo-dissociation Problem for large shocks… Problem for high-power regions… Can severely challenge the Hillas criterion! Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! New ideas for particle acceleration? 58 What about wake-field acceleration? See past and coming works by Tajima, Takahashi, Chen, Hillmann, Ebisuzaki… For instance, gamma-ray bursts are hugely powerful events 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… ?) Short timescale acceleration can we avoid losses? In any case, one should think about non linear effects… A new field within astrophysics, very little explored (if at all!)… Possible connections with iZEST community… Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Other possible connections 59 Exploration of high-energy physics Hadronic physics from UHECR interactions in the atmosphere (shower physics, cross sections, etc.) Exploring fundamental physics at 1020 eV 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? Exploring space-time structure… UHECRs propagate in space-time at an unexplored energy scale may feel small-scale structures Lorentz Invariance Violation… (“predicted” by most quantum gravity theories…) Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Lorentz Invariance Violation (LIV) Cf. talk by Professor Tajima this morning 60 (Abdo, et al, 2009) 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 IZEST? Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! 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 Ingredients: Interaction cross sections: 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! Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! LIV and the GZK cut-off 62 Different particles may have different “maximum attainable velocities”! Violation of Lorentz Invariance: Threshold and elasticity of photo-pion production Will be modified if c is different for the protons and the pions (simple kinematics!) Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! LIV and the GZK cut-off 63 Energy losses and GZK horizon will thus be different from those calculated in the standard case… (Stecker-Scully 2009) Proton attenuation length with LIV no LIV Proton energy Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! LIV and the GZK cut-off 64 Energy losses and GZK horizon will thus be different from those calculated in the standard case… (Stecker-Scully 2009) UHECR flux Flux recovery at ultra-high energy! with LIV no LIV UHECR energy Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! LIV and the GZK cut-off 65 Energy losses and GZK horizon will thus be different from those calculated in the standard case… (Stecker-Scully 2009) UHECR flux Flux recovery at ultra-high energy! with LIV Current limit no LIV Look for larger statistics at higher energy! Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Perspective 66 Go into space to increase the statistics at UHE energy JEM-EUSO! Large field-of-view UV telescope on the Kibo module of the International Space Station Observe 200 000 Glasgow, 13 Nov. 20012! km2 at once! Momentum is building up! 2017 ? — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)! Perspective 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 67 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) Glasgow, 13 Nov. 20012! — IZEST 2012 / UHECRs challenging particle acceleration in the universe —! E. Parizot (APC, Paris 7)!
