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/0306408

N. G. Lehtinen et al. PRD 69 (2004)

S. W.Barwick et al. astro-ph/0503304

FORTE satellite

ANITA

antenna cluster

RICE

antenna

array

J. Alvarez-Muñiz, ARENA 2005

The MoonP.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 initiativesSaltdome Shower Array ZEchstein SAlt Neutrino

Array

A.M. van den Berg et al.

www.kvi.nl/~berg/zesana

salt pillarsP.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

Needs1) 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)

(ECritical, Radiation X0, RMoliere)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 ~ (EShower)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/0412128

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

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 Ke < 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 (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)

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

particlescharged

i EE

• Charged particle trajectories divided in small steps.

• Contributions to the E-field from all steps in the shower.

i

i

sin

] t ) cos n - 1 ( i exp[ t e 1iiii iv

Phase factors (different for each step)

charge

φi = ωδti (1 – nβi cosθ)

Perpendicular trackfrequenc

y

J. Alvarez-Muñiz, ARENA 2005

ZHS vs GEANT simulationsRemarkable agreement between two independent

codes !!!

100 e- showers

E=100 GeVGEANT 3.21 GEANT 4 ZHS

Total track [m] 577.9 587.9 589.2

Excess track [m]

123.5 122.7 122.2

e-+e+ @ maximum

142.0 150.0 141.0

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 2005

1D toy model

θ = θC → t12 = t13 = t14 + t45

L/v = L cosθC / (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 X0

J. Alvarez-Muñiz, ARENA 2005

1D toy model: cutoff (θ≠θC)

θ ≠ θC → t12 ≠ t13 → time delay due to long. develop.

Δt ~ L (cosθC - cosθ) / (c/n)

Destructive interference starts at cutoff ~ Δt-1

Cutoff frequency @ θ ≠ θC mainly determined by the longitudinal profile of the shower.

cutoff ( θ ≠ θC ) ~ [X0 ] [ n (cosθC - cosθ) ]-1

J. Alvarez-Muñiz, ARENA 2005

3D toy model: cutoff (θC)

Even @ θ=θC there is a Δt due to lateral

spread of shower Δt ~ R sin θC /(c/n)

Destructive interference should start at cutoff ~ Δt-1

Excess charge travelling at =1 in 3D along L ~ a few X0 with a lateral spread ~ RMoliere

Cutoff frequency @ θC mainly determined by the lateral profile of the shower.

cutoff ( θC ) ~ [ RM ] [ n sin θC ]-1

J. Alvarez-Muñiz, ARENA 2005

Heitler model: normalizationHeitler model

Track = T ~ [ X0 / ] [ 2 + 22 + … + 2N ] ~ Nmax [ X0 / ] ~ [X0/] [ EC ]-1

E-field ~ Tsinθ ~ [ X0 / ] sinθ [ EC ]-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

c

MS0M EE

XR

sinθE1

ρX

sinθ T fieldEc

0

n1n

sinθn1

cosθ2

CC

E-field normalization @ θ

Cutoff frequency @ θC 1n

1E

Xρ

2c0

c

ν

Cutoff frequency @ θ ≠ θC

J. A-M, E. Marqués, R.A. Vázquez & E. Zas

in preparation.

θcos n1 1

Xρ

0c

ν

J. Alvarez-Muñiz, ARENA 2005

Does the scaling predicted by the toy model work ?

J. Alvarez-Muñiz, ARENA 2005

Ice vs Salt

Longitudinal development

Lateral development at maximum

L0 = 39.1 cm

L0 = 10.8 cm

RM = 11.2 cm

RM = 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.

MediumGEANT4cut(θC)

[GHz]

Modelcut(θC)

[GHz]

GEANT4cut(90o)

[MHz]

Modelcut(90o)

[MHz]

GEANT4E10MHz(θC)

[V/MHz/ TeV]

ModelE10MHz(θC)

[V/MHz/ TeV]

Salt ~ 4.5 ~ 4.0 ~ 113.5 ~ 105.5 ~ 8.3 10-

11~ 1.2 10-

10

Moon ~ 6.5 ~ 5.6 ~ 82.5 ~ 90.9 ~ 8.6 10-

11

~ 1.2 10-

10

10 - 15 % 10 % 30 - 35 %

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:

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).