J. Alvarez-Muñiz, ARENA 2005 Simulations of radio emission from EM showers in different dense media E. Marqués R.A. Vázquez E. Zas Jaime Alvarez-Muñiz Universidade de Santiago de Compostela, SPAIN

J. Alvarez-Muñiz, ARENA 2005 Motivation Large amount of experimental work & initiatives on radio detection of  & CR in dense media –Ice –Moon regolith –Salt – … Reliable simulations of radiopulses in dense media are needed.

J. Alvarez-Muñiz, ARENA 2005 Ice I. Kravchenko et al. astro-ph/ N. G. Lehtinen et al. PRD 69 (2004) S. W.Barwick et al. astro-ph/ FORTE satellite ANITA antenna cluster RICE antenna array

J. Alvarez-Muñiz, ARENA 2005 The Moon P.W. Gorham et al. PRL 93 (2004) Cosmic Ray Neutrino R. Protheroe, R. Ekers et al. GLUE Westerbork J. Bacelar et al. … also LOFAR on the surface of the Moon (H. Falcke et al.) ATCA

J. Alvarez-Muñiz, ARENA 2005 Salt initiatives Sal tdome S hower A rray ZE chstein SA lt N eutrino A rray A.M. van den Berg et al. salt pillars P.Gorham et al. Salt dome The Netherlands … also the Salt Neutrino Detector (M.Chiba, et al.)

J. Alvarez-Muñiz, ARENA 2005 First bounds on fluxes from radio !!!

J. Alvarez-Muñiz, ARENA 2005 Needs 1)Reliable & well tested simulations of radioemission in ice, regolith, salt, etc… needed to: Characterize the frequency spectrum & angular distribution of pulses. Interpret data & obtain bounds. 2)Desirable to have a simple model that relates: Medium properties Cherenkov radioemission (Z, , n) (E Critical, Radiation X 0, R Moliere ) Electric field (,θ) Evaluate the capabilities of present & future initiatives without time consuming MC sims.

J. Alvarez-Muñiz, ARENA 2005 The radio technique   obs >> shower dimensions  Charge excess (Akar´yan) Coherent radio emission  Power ~ (E Shower ) 2  Cheap detectors  Broad freq. range  Large natural vols. of dense transparent media Attractive technique

J. Alvarez-Muñiz, ARENA 2005 SLAC experiments: sand & salt D. Saltzberg et al. PRL 86 (2001) P.W. Gorham et al. astro-ph/ Radioemission mechanism in dense media i.e. the Askar´yan effect confirmed !!! Pulse correl. to charge excessAgreement with expectationsPolarized radiation E-field ~ E bunch MC vs Data SAND

J. Alvarez-Muñiz, ARENA 2005 Two reliable simulation codes: ZHS and GEANT

J. Alvarez-Muñiz, ARENA 2005 Monte Carlo simulations: ZHS 50 % of excess track in ice due to e - with K e < 6-7 MeV e -, e + &  as primaries  Bremsstrahlung & pair production  Multiple scattering (lateral spread) Compton Moller Bhabha e+ annihilation 4D code: (x,y,z,t) of each particle (phases) Fast: can reach up to ~ 10 PeV energies. Low threshold (K e ~ 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) Special features (excess charge) Designed for ice. Has been adapted to other media: salt, sand, lunar regolith,… E.Zas, F.Halzen & T.Stanev, PRD 45 (1992)

J. Alvarez-Muñiz, ARENA 2005 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, salt and lunar 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)

J. Alvarez-Muñiz, ARENA 2005 Computation of E-field Charged particle trajectories divided in small steps. Contributions to the E-field from all steps in the shower. Phase factors (different for each step) charge φ i = ωδt i (1 – nβ i cosθ) Perpendicular track frequency

J. Alvarez-Muñiz, ARENA 2005 ZHS vs GEANT simulations Remarkable agreement between two independent codes !!! 100 e - showers E=100 GeVGEANT 3.21GEANT 4ZHS Total track [m] Excess track [m] e - +e maximum J. A-M, E. Marqués, R.A. Vázquez & E. Zas, PRD 68 (2003)

J. Alvarez-Muñiz, ARENA 2005 ZHS vs GEANT4 simulations Difference due to track splitting algorithm 10 GHz Freq. spectrum cutoff (θ) Normaliz. (,θ)

J. Alvarez-Muñiz, ARENA 2005 Simple model medium radio Predicts scaling of radiopulse with medium parameters

J. Alvarez-Muñiz, ARENA D toy model θ = θ C → t 12 = t 13 = t 14 + t 45 L/v = L cosθ C / (c/n) (definition of Cherenkov angle) All stages in the long. development of the shower are viewed at the same time → fully coherent emission: The spectrum increases as  with no cutoff frequency No phase factor associated to the position along the shower. Excess charge travelling at  =1 in 1D along L ~ a few X 0

J. Alvarez-Muñiz, ARENA D toy model: cutoff (θ≠θ C ) θ ≠ θ C → t 12 ≠ t 13 → time delay due to long. develop. Δ t ~ L (cosθ C - cosθ) / (c/n) Destructive interference starts at cutoff ~ Δt -1 Cutoff θ ≠ θ C mainly determined by the longitudinal profile of the shower. cutoff ( θ ≠ θ C ) ~ [  X 0 ] [ n (cosθ C - cosθ) ] -1

J. Alvarez-Muñiz, ARENA D toy model: cutoff (θ C ) θ=θ C there is a Δt due to lateral spread of shower Δt ~ R sin θ C /(c/n) Destructive interference should start at cutoff ~ Δt -1 Excess charge travelling at  =1 in 3D along L ~ a few X 0 with a lateral spread ~ R Moliere Cutoff θ C mainly determined by the lateral profile of the shower. cutoff ( θ C ) ~ [  R M ] [ n sin θ C ] -1

J. Alvarez-Muñiz, ARENA 2005 Heitler model: normalization Heitler model Track = T ~ [ X 0 /  ] [ … + 2 N ] ~ N max [ X 0 /  ] ~ [X 0 /  ] [ E C ] -1 E-field ~ Tsinθ ~ [ X 0 /  ] sinθ [ E C ] -1 Coherent E-field is known to scale with the excess track projected onto the direction perpendicular to the observer´s direction. NOTE: Implicitely assumes that particles travel parallel to shower axis.

J. Alvarez-Muñiz, ARENA 2005 Summary of scaling relations E-field θ Cutoff θ C Cutoff θ ≠ θ C J. A-M, E. Marqués, R.A. Vázquez & E. Zas in preparation.

J. Alvarez-Muñiz, ARENA 2005 Does the scaling predicted by the toy model work ?

J. Alvarez-Muñiz, ARENA 2005 Ice vs Salt Longitudinal developmentLateral development at maximum L 0 = 39.1 cm L 0 = 10.8 cm R M = 11.2 cm R M = 5.9 cm Excess charge in e- showers, E=10 TeV [GEANT4 simulations]

J. Alvarez-Muñiz, ARENA 2005 Ice vs Salt Frequency spectrum GEANT4 simulations J. A-M, E. Marqués, R.A. Vázquez, E. Zas in preparation.

J. Alvarez-Muñiz, ARENA 2005 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. Medium GEANT4 cut (θ C ) [GHz] Model cut (θ C ) [GHz] GEANT4 cut (90 o ) [MHz] Model cut (90 o ) [MHz] GEANT4 E 10MHz (θ C ) [V/MHz/ TeV] Model E 10MHz (θ C ) [V/MHz/ TeV] Salt~ 4.5~ 4.0~ 113.5~ ~ ~ Moon~ 6.5~ 5.6~ 82.5~ 90.9~ ~ %10 % % Assumption that tracks are parallel to shower axis

J. Alvarez-Muñiz, ARENA 2005 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: % level (cutoff frequencies) % level (pulse normalization). Assumption that tracks are parallel to shower axis (pulse normalization depends on projection of tracks onto perpendicular to observer´s direction).

J. Alvarez-Muñiz, ARENA 2005 Ice vs Salt vs Moon Angular distribution J. A-M, E. Marqués, R.A. Vázquez, E. Zas in preparation. GEANT4 simulations

J. Alvarez-Muñiz, ARENA 2005 Shopping list 1)Reliable & well tested simulations in ice, regolith, salt, etc… needed:  Good understanding & comprehensive charact. of freq. spectrum & θ distr.  Interpret data & obtain bounds.  Evaluate the capabilities of present & future initiatives. 2)Desirable to have a simple model that relates: Medium properties Shower development Cherenkov radioemission (Z, , n) (E Critical, Radiation X 0, R Moliere ) Longitudinal & lateral distr. of charged pcles. Electric field (ω,θ)

J. Alvarez-Muñiz, ARENA 2005 Summary of scaling relations Radiation length Critical energy Moliere radius E-field θ C Cutoff θ C Cutoff θ ≠ θ C J.A-M, E.Marqués, R.A.Vázquez & E.Zas in preparation. Particle Data Book

J. Alvarez-Muñiz, ARENA 2005 Ice vs Salt vs Moon Medium  [g/cm 3 ] L 0 [cm] R Moliere [cm] θ C [deg] E critical [MeV] Ice ~ 73.0 Salt ~ 38.5 Moon ~ 40.0

J. Alvarez-Muñiz, ARENA 2005 Aims of this talk Report on simulation work that was done in Santiago. ZHS simulations GEANT simulations Remarkable agreement between them Simple model of radio emission from showers: Scaling of radiopulse emission with medium parameters. density refraction index atomic number Ice, salt, moon regolith, sand, etc… }