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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)
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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
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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
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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
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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 ?
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Smith&Baker ?
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…………………………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
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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
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VSF does depend on λ
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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
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Hale&Quarry
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25-27 Sep 2007Collaboration Meeting 28
Water PropertiesAbsorption length
Scattering length
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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
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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
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MEASURED LED ANGULAR DISTRIBUTIONS