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Simulations of radio emission from EM showers in different dense media

Simulations of radio emission from EM showers in different dense media. Jaime Alvarez-Muñiz. E. Marqués R.A. Vázquez E. Zas. Universidade de Santiago de Compostela, SPAIN. Motivation. Large amount of experimental work & initiatives on radio detection of n & CR in dense media Ice

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Simulations of radio emission from EM showers in different dense media

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  1. Simulations of radio emission from EM showers in different dense media Jaime Alvarez-Muñiz E. Marqués R.A. Vázquez E. Zas Universidade de Santiago de Compostela, SPAIN

  2. Motivation Large amount of experimental work & initiatives on radio detection of n & CR in dense media • Ice • Moon regolith • Salt • … Reliable simulations of radiopulses in dense media are needed.

  3. Ice FORTE satellite RICE antenna array ANITA antenna cluster I. Kravchenko et al. astro-ph/0306408 N. G. Lehtinen et al. PRD 69 (2004) S. W.Barwick et al. astro-ph/0503304

  4. TheMoon Cosmic Ray P.W. Gorham et al. PRL 93 (2004) GLUE Neutrino J. Bacelar et al. R. Protheroe, R. Ekers et al. Westerbork ATCA … also LOFAR on the surface of the Moon (H. Falcke et al.)

  5. Salt initiatives Saltdome Shower Array ZEchsteinSAltNeutrinoArray The Netherlands salt pillars P.Gorham et al. Salt dome … also the SaltNeutrinoDetector (M.Chiba, et al.) A.M. van den Berg et al. www.kvi.nl/~berg/zesana

  6. First bounds on n fluxes from radio !!!

  7. Needs • Reliable & well tested simulations of radioemission in ice, regolith, salt, etc… needed to: • Characterize the frequency spectrum & angular distribution of pulses. • Interpret data & obtain n bounds. • Desirable to have a simple model that relates: Medium properties Cherenkov radioemission (Z,r, n) Electric field (n,θ) (ECritical, Radiation X0, RMoliere) • Evaluate the capabilities of present & future initiatives without time consuming MC sims.

  8. The radio technique Attractive technique • Power ~ (EShower)2 • Cheap detectors • Broad freq. range • Large natural vols. of dense transparent media Coherent radio emission • lobs >> shower dimensions • Charge excess (Akar´yan)

  9. SLAC experiments: sand & salt Radioemission mechanism in dense media i.e. the Askar´yan effect confirmed !!! Pulse correl. to charge excess Agreement with expectations Polarized radiation E-field ~ Ebunch MC vs Data SAND D. Saltzberg et al. PRL 86 (2001) P.W. Gorham et al. astro-ph/0412128

  10. Two reliable simulation codes: ZHS and GEANT

  11. Monte Carlo simulations: ZHS e-, e+ & g as primaries • Bremsstrahlung & pair production • Multiple scattering (lateral spread) • Compton • Moller • Bhabha • e+ annihilation (excess charge) Special features • 4D code: (x,y,z,t) of each particle (phases) • Fast: can reach up to ~ 10 PeV energies. • Low threshold (Ke~ 100 keV Cherenkov thresh.) • Different screening of atomic potentials + LPM • Low energy corrections: density effect, etc… • Sums E-field of each e-, e+ track (Fraunhofer) 50 % of excess track in ice due to e- with Ke < 6-7 MeV Designed for ice. Has been adapted to other media: salt, sand, lunar regolith,… E.Zas, F.Halzen & T.Stanev, PRD 45 (1992)

  12. MC simulations: GEANT • Well-known, well-tested and widely used simulation package. • Same list of processes as in ZHS (implemented independently). • Two versions: GEANT 3.21 (FORTRAN) & GEANT 4 (C++). • Both Kansas & Santiago groups implemented the computation of radiopulses in GEANT. • In Santiago: GEANT4 simulations in ice, saltandlunar regolith. J. A-M, E. Marqués, R.A. Vázquez & E. Zas, PRD 68 (2003) J. A-M, E. Marqués, R.A. Vázquez & E. Zas in preparation. S. Razzaque et al., PRD 69 (2004)

  13. Computation of E-field • Charged particle trajectories divided in small steps. • Contributions to the E-field from all steps in the shower. Perpendicular track frequency charge Phase factors (different for each step) φi= ωδti (1 – nβi cosθ)

  14. ZHS vs GEANT simulations Remarkable agreement between two independent codes !!! J. A-M, E. Marqués, R.A. Vázquez & E. Zas, PRD 68 (2003)

  15. ZHS vs GEANT4 simulations Freq. spectrum Difference due to track splitting algorithm ncutoff (θ) Normaliz. (n,θ) 10 GHz

  16. Simple model medium radio Predicts scaling of radiopulse with medium parameters

  17. 1D toy model Excess charge travelling at b=1 in 1D along L ~ a few X0 θ = θC→ t12 = t13 = t14 + t45 L/v = L cosθC / (c/n) (definitionofCherenkov angle) No phase factor associated to the position along the shower. All stages in the long. development of the shower are viewed at the same time→ fully coherent emission: The spectrum increases as n with no cutoff frequency

  18. 1D toy model: ncutoff (θ≠θC) θ ≠ θC→ t12 ≠ t13 → time delay due to long. develop. Δt~L (cosθC - cosθ) / (c/n) Destructive interference starts at ncutoff~ Δt-1 Cutoff frequency @ θ ≠ θCmainly determined by the longitudinal profile of the shower. ncutoff (θ≠θC ) ~ [r / X0 ][ n (cosθC - cosθ) ]-1

  19. 3D toy model: ncutoff (θC) Excess charge travelling at b=1 in 3D along L ~ a few X0 with a lateral spread ~ RMoliere Even @ θ=θC there is a Δt due to lateral spread of shower Δt~R sin θC /(c/n) Destructive interference should start at ncutoff~ Δt-1 Cutoff frequency @ θCmainly determined by the lateral profile of the shower. ncutoff (θC ) ~ [ r / RM ][ n sin θC ]-1

  20. Heitler model: normalization Heitler model Coherent E-field is known to scale with the excess track projected onto the direction perpendicular to the observer´s direction. Track = T~ [ X0 / r ] [ 2 + 22 + … + 2N ] ~ Nmax[ X0 / r ] ~ [X0/r] [ EC]-1 E-field ~ Tsinθ~ [ X0 / r ] sinθ [ EC ]-1 NOTE: Implicitely assumes that particles travel parallel to shower axis.

  21. Summary of scaling relations E-field normalization @ θ Cutoff frequency @ θC Cutoff frequency @ θ≠θC J. A-M, E. Marqués, R.A. Vázquez & E. Zas in preparation.

  22. Does the scaling predicted by the toy model work ?

  23. IcevsSalt Excess charge in e- showers, E=10 TeV [GEANT4 simulations] Longitudinal development Lateral development at maximum L0 = 39.1 cm L0 = 10.8 cm RM = 11.2 cm RM = 5.9 cm

  24. IcevsSalt GEANT4 simulations Frequency spectrum J. A-M, E. Marqués, R.A. Vázquez, E. Zas in preparation.

  25. Scaling model vs GEANT4 simulations • Normalize scaling relations (toy model) to GEANT 4 simulations in ice. • Compare toy model predictions in Moon & Salt to GEANT 4 sims. 10 - 15 % 10 % 30 - 35 % Assumption that tracks are parallel to shower axis

  26. Conclusions • Remarkable agreement between ZHS & GEANT 3.21 & GEANT 4. • Simulations in ice, salt, lunar regolith with ZHS & GEANT4 performed. • We developed a simple model that relates shower development in dense media & radio emission. • We established the scaling of radioemission with medium parameters. • It works at a: • 10-15 % level (cutoff frequencies). • 30-35 % level (pulse normalization). Assumption that tracks are parallel to shower axis (pulse normalization depends on projection of tracks onto perpendicular to observer´s direction).

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