Coherent radio pulses from high energy showers: A blooming field In the memory of a brilliantly original mind Enrique Zas Instituto Galego de Fisica de Altas Enerxias & Universidad de Santiago de Compostela 1 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Particles radiate (or induce radiation Cerenkov) •Radiation adds coherently for low enough frequencies •Power of coherent radiation scales with (shower particles) 2 •Showers have lots of particles => Interesting for UHE! Interference effects give rich diffraction patterns •Shower could be fully visualized if sufficiently well sampled !! (amplitude & phases in every direction) Signal: contributions from many (all) shower stages • Reduced fluctuations => good observable Antennas: cheap Radio detection: high duty cycle Main difficulty: dealing with noise 2 Coherent radio pulses from high energy showers EZ Heidelberg 2018
58 J. Jelley 58 extend Cherenkov to radio 61 G. Askary’an excess Q= ∆ q 65 In air: high ν 65 J. Jelley 8 “mechanisms” (ICRC65) Complex some are •Enhanced Cherenkov(Askary’an) limiting cases •Dipole Cherenkov of given situations •Synchrotron radiation •Transition radiation but it is all in •Coulomb field bremsstrahlung •Induction (by nearby charges) Maxwell’s laws! •Molecular transitions •Reflections of continuous waves (Doppler shifted) 67-70 Air: e + e - separation in B Geo dominant (Th & exp) 75 decline of field, steep ldf, storm interference … 90 ν detection: full calculations in ice (ZHS) New initiatives radio telescopes, air showers, ice, salt … 00 Lab measurements Air showers 1 st generation LOPES, CODALEMA, ANITA (GHz) 10 Full simulations (ZHS algorithm + MC) 2 nd generation LOFAR, AERA, Tunka-Rex (E,X max ) 20 Ambitious plans: GRAND, AugerRadio, phased arrays … 3 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Calculations are key: Based on simple solution Maxwell’s Equations in transverse gauge The transverse current is the divergenceless component (the transverse projection at large distances) Well known solution, Vector potential A gives us the radiated field Delta of Retarded time = με nc with 4 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Solve for simple case (constant speed) t 2 t 1 v δ t=t 2 -t 1 v=0 position 5 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Organize t and t’ and massage Fraunhofer approximation i.e. θ v δ t 6 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Substitute into solution for A Divergence at Cherenkov angle? NO!! We formally get derivative of Theta funciton Limit CHERENKOV Radiation Note A proportional to TRACKLENGTH 7 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Field single track: Time domain [J. Alvarez Muniz, A. Romero-Wolf, E.Z., PRD 81 , 123009 (2010)] Vector potential NOTE: “Acceleration” with a grain of salt Limit of large δ t gives Cerenkov radiation (by medium) Terms of adjacent sub-tracks give large cancellations E-field Time “Acceleration” “Decceleration” 8 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Fourier transform => ZHS [E.Z., F. Halzen, T. Stanev PRD45 (1992) 386] ω − ⋅ δ (Fraunhofer limit) − i ( k v ) t 1 e 1 − ω = ω i ( overall phase ) E ( ) i e v ⊥ ω − ⋅ R i ( k v ) [ ] − β θ ω if ω =0 sin ( 1 n cos ) t v δ δ v t t or θ = θ c ⊥ − β θ ω ⊥ ( 1 cos ) n t or δ t=0 trackl klength State -o f-the -art: simulatio ns AI RE S / CORSI K A + Zas-Halze n-Stane v alg o rithm (c lassic al e le c tro mag ne tism) 9 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Askary’an effect: excess charge G.A. Askaryan 10 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Unidimensional current J(z,t) = v Q(z) δ (z - vt) Vector potential A(t o bs , θ) ≈ v Q(ζ ) / R ζ → Retardation + time-compression : ro m z to time t o bs ( θ –d e pe nd e nt) F t o b s = z(1 - nc o s θ )/ c + t 0 t o b s = t 0 @ θ c Electric field E(t o bs , θ ) = d A(t o bs , θ )/ d to bs J. A-M, A. RW, E . Z, PRD 81 , 123009 (2010) 11 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Interesting for neutrino detection e showers & hadronic debris separate (LPM) Flavor tagging : ν e Measure y (energy transfer to hadrons) 12 Coherent radio pulses from high energy showers EZ Heidelberg 2018
ν e + N → e + jet E( ν e ) = 10 EeV E(hadron jet) = 2 EeV E(electron) = 8 EeV 13 Coherent radio pulses from high energy showers EZ Heidelberg 2018
14 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Pulseahead of time! Path difference θ > θ c L Emission out of phase path difference = λ => diffraction minimum like in a single slit L ~ slit width 15 Coherent radio pulses from high energy showers EZ Heidelberg 2018
The slit diffraction analogy If current is “thin”: θ c ω i ∫ ω ∝ ikz E ( ) dzQ ( z ) e R FT with ω = ( − θ ) k 1 n cos c Great scaling properties : reduced fluctuations integrated emission (“calorimetric”) 16 Coherent radio pulses from high energy showers EZ Heidelberg 2018
E sh (TeV) 17 Coherent radio pulses from high energy showers EZ Heidelberg 2018
E sh (TeV) 18 Coherent radio pulses from high energy showers EZ Heidelberg 2018
E sh (TeV) 19 Coherent radio pulses from high energy showers EZ Heidelberg 2018
d θ c Blow up of shower front Path difference = d sin θ c In Cherenkov direction: d sin θ = λ Interference minimum at lower λ (higher frequency) 20 Coherent radio pulses from high energy showers EZ Heidelberg 2018
21 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Why is the atmosphere so different? The Cherenkov angle is small ~ 1 0 Opposite charges cancel!! J ┴ = Q v ┴ ~ 0.2N e c sin θ ~ 0.003 N e c (Askary’an) B → transverse current ~ v ┴ drift ~ qB ┴ / ρ ~ 0.04c O. Scholten et al. ApP29(2008)94 J ┴ = Q v ┴ drift ~ 0.04 N e c (geomagnetic) often dominant Depends on sin( α ) [angle between shower axis and B field] 22 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Polarization of two components is different Ge o mag ne tic F ro m e xc e ss c harg e Sho we raxis B v J geo Askaryan However new complex issues: Loss of symmetry (mixed patterns) There is a varying refractive index There is curvature of the atmosphere … 23 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Lessons from experiments 24 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Many activities pursued >89 On Moon from Earth: GLUE, ATCA, LUNASKA, LOFAR … R.D. Dagkesamanskii, I.M. Zheleznykh, Sov. Phys. JETP Lett. 50(1989)259 … >96 In Ice: Rice, ARA, ARIANNA … G. Frichter; D.Besson; D. Seckel; … >00 On “lab”: SLAC (Silica Sand, Salt, Ice, Air+B), Utah (ARAcalTA) … P. Gorham, D. Saltzberg et al. PRL86(2001)2802 … >03 In air: LOPES, CODALEMA, AERA, LOFAR, Tunka-Rex… D.Ardouin; H. Falcke … >03 In ice from air: ANITA … P. Gorham, et al. PRL96(20006)171101 >10 in air microwave: MIDAS, CROME, EASIER, MAYBE ... P. Privitera; A. Lettessier-Selvon; R. Smida; V. Verzi, … 25 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Buitnik, S. et al. Nature 531 (2016) 70 X max reliably measured ! 26 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Energy in radio is an excellent energy estimator ! The Pierre AugerCollaboration, PRL 116, 241101 (2016); PRD 93 122005 (2016) 27 Coherent radio pulses from high energy showers EZ Heidelberg 2018
36 km high P. Gorham, et al. PRL105(2010)151101 14 events CR detected! Why GHz radiation? ν 28 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Diameter 1000 times larger BUT θ c VERY small d θ c Blow up of shower front Path difference = d sin θ c At θ c coherence up to the GHz in spite of scale factor!! 29 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Insight from time delays Alvarez-Muñiz, et al. PRD 86 (2012) 12300 Observer at position such that shower center (0,0) is viewed viewed at Cherenkov angle Antarctica proton 10 19 eV 30 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Blow up of central region 31 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Different spectra as we get away from Cher angle Inner cone ψ =0.7 0 ψ =0.62 0 ψ =0.55 0 ψ =0.48 0 ψ =0.4 0 ψ =0.33 0 ψ =0.25 0 ψ =0.18 0 ψ =0.11 0 32 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Inner cone ψ =0.7 0 ψ =0.62 0 ψ =0.55 0 ψ =0.48 0 ψ =0.4 0 ψ =0.33 0 ψ =0.25 0 ψ =0.18 0 ψ =0.11 0 33 Coherent radio pulses from high energy showers EZ Heidelberg 2018
Inner cone ψ =0.7 0 ψ =0.62 0 ψ =0.55 0 ψ =0.48 0 ψ =0.4 0 ψ =0.33 0 ψ =0.25 0 ψ =0.18 0 ψ =0.11 0 34 Coherent radio pulses from high energy showers EZ Heidelberg 2018
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