SIMULATION OF PHOTON PROPAGATION IN CALIBOB

Ciro Bigongiari

Monte-Carlo Meeting

Bologna 26-28 April, 2012

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History

Calibob was derived from KM3 code Nearly the same code The light source are pointlike source instead

of tracks On the assumption that the simulated light

sources are nearly monochromatic all the dependencies on the wavelength were removed in the past La, Ls, β(θ) and n didn’t depend on λ

Recently reintroduced the dependence on λ of La and Ls trying to improve the Data-MC agreement

17/05/2011

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LED Spectrum

17/05/2011

From AVAGO CB30 Datasheet

Peak wavelength ~470 nm

Sigma ~15 nm

Slightly asymmetric Values confirmed by measurements in Valencia labANTARES LED

LED angular emission

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R1 = 7.95 cm

R2 = 9.35 cm

d = 5.5 cm

Measured ‘zenith’ emission in air of one cleaved LED

Azimuthal distributiion is assumed uniform

AirGlass

Water

Top LED positions

Simulated the emission of the 6 Top LEDs

1) Measured emission of one LED2) Real LED positions3) Double refraction through the

glass cap

nGlass = 1.472nWater = 1.382

0º

90º

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Absorption length La =La(λ)

26 April 2012

λRef = 470 nm LRef = 60 m

WARNING: in this way LA can be larger than SmithBaker(λ).

The dependence of the absorption length on the photon wavelength is given by a scaled Smith&Baker parameterization

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Scattering Length

The overall scattering length is calculated using the Kopelevich parameterization

Vs = Vl = 0.01

26 April 2012

3.07.13.4 )550(**3120.0)550(**3400.1)550(*0017.0)(

nmVnmVnmL LSb

WARNING: These values are outside the range suggested by Mobley. They were chosen on the base of Test3

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Volume scattering function for large scatters β = β(θ,λ) is a function of scattering angle and

photon wavelength

26 April 2012

T.Pet

zold

m

easu

erem

nts

λ =

514

nm

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Scattering models There are two models implemented inKm3

The so called PARTIC model (where 0 < η < 1)

The so called MEDSEA model with 3 parameters

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)(*)1()(*)( PetzoldRayleigh

WARNING: In both models the β dependence on λ is neglected

),(*)1(),(*)( 21 gg HGHG

25-27 Sep 2007Collaboration Meeting 16

Scattering angle distribution

PARTIC

MEDSEA

Partic

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Estimate La, Lb and η

Simulate many MC samples with different combinations of La, Lb and eta We do have problem of disk space cal file

size ~ 20GB Use the same OM positions of one real

data run Compare hit arrival time distribution

with real data ones Minimize the χ2

26 April 2012

Example of time distribution comparison

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OM0

OM1

OM2

The agreement between data and the MC sample which minimizes the χ2 seems good

Floor 13 Floor 20

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Sorry No new results since Geneva meeting We found a problem in the minimizing

function which surely affects the results The problem is related to the bins with few entries

Investigating how much our previous results are affected

Maybe there is another problem related to the simulation strategy Fixed number of events Variable number of photons per event

26 April 2012

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Ciro’s doubts

Should we stick to the Smith&Baker or not ?

Should we take into account the wavelength dependence of the volume scattering function ?

Should we consider some more recent water model ?

26 April 2012

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Smith&Baker ?

26 April 2012

…………………………In the visible part of the spectrum, recent studies from Sogandares and Fry (1997) and Pope and Fry (1997), based on different measuring techniques, provided very precise measurements of pure water absorption from 380 to 700 nm. The results obtained by these authors emphasized that Smith and Baker (1981) formulation strongly overestimated the actual aw(λ) in particularly below 490 nm. At 380 nm Pope and Fry (1997) values are about 2 times lower.Such differences between Smith and Baker (1981) and Pope and Fry (1997) formulations have been attributed to biases in the former measurements induced by organic impurities absorption and scattering effects. Moreover, Pope and Fry (1997) confirmed the existence of seventh and eighth harmonics of the OH stretch at 449 and 401 nm and the presence of the absorption minimum at 420 nm as previously observed by Sogandares and Fry (1997). The data by Pope and Fry (1997) are currently considered as the reference value and are widely used in bio-optical modeling and remote sensing applications in the visible………(Vantrepotte&Mélin2006).

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Pope & Fry

26 April 2012

Appl

ied

Optic

s Vol

36 N

33

(199

7)

The absorption coefficient measured by Pope&Fry has a minimum at 420nm instead of 470nm of the Smith&Baker measurement. Moreover the Pope&Fry minimum is much lower.

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Pope&Fry vs Smith&Baker

26 April 2012

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VSF does depend on λ

26 April 2012

V.H

altr

in

Appl

.Opt

.38(

33)-

1999

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Water Models

There are some recently developed water models with a reasonably low number of parameters. For example Kopelevich’s Haltrin’s Morel’s Zege – Katsev – Prikcach

Should we try a more recent water model ? Can they be used for very deep waters ?

26 April 2012

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The End

26 April 2012

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Hale&Quarry

26 April 2012

25-27 Sep 2007Collaboration Meeting 28

Water PropertiesAbsorption length

Scattering length

29

Scattering Angle

26 April 2012Ciro Bigongiariη = 0.17 <cos(θ)> = 0.767

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Time of flight We are not only interested in the amount of

photons reaching the OMs but also in their arrival time distribution The refraction index is a function of photon wavelength

and water temperature, pressure and salinity. We fixed T = 13.1 ºC P = 220 bar S = 38.44 %0

26 April 2012

32 )1(*)1(*1*)(

DCBAnPhase

)(*1)()( '

Phase

PhaseGroup n

nn

A = 1.3201 B = 16.2561 C = -4382.0 D = 1.1455e6

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Refraction Index

26 April 2012

MEASURED LED ANGULAR DISTRIBUTIONS