Ciro Bigongiari Monte-Carlo Meeting Bologna April, 2012

Photon fate 26 April 2012Ciro Bigongiari 2 Photon emitted by a light source (muon track, optical beacon, etc.) can be: 1.Absorbed 2.Elastically scattered  Same λ but different direction 3.Inelastically scattered  Different λ and different direction 1.For our purpose we can include this case in the absorption one 4.Eventually they may reach a photon detector Photon Path Light source Optical Module Sea water Scattering point Absorption point

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/ Ciro Bigongiari

LED Spectrum 17/05/2011Ciro Bigongiari 4 From AVAGO CB30 Datasheet Peak wavelength ~470 nm Sigma ~15 nm Slightly asymmetric Values confirmed by measurements in Valencia lab ANTARES LED

LED angular emission 06/02/2012C.Bigongiari 5 R 1 = 7.95 cm R 2 = 9.35 cm d = 5.5 cm Measured ‘zenith’ emission in air of one cleaved LED Azimuthal distributiion is assumed uniform Air Glass Water Top LED positions Simulated the emission of the 6 Top LEDs 1)Measured emission of one LED 2)Real LED positions 3)Double refraction through the glass cap n Glass = n Water = º 90º

Absorption  There is a constant probability a per unit path length that a photon is absorbed.   L a ~ 50m  Detector size R ~ 500m  Simulating photon absorption is highly inefficient and very time consuming  Absorption is simulated by weighting photons  Each detected photon is weighted with where PL is the photon PathLength 26 April 2012Ciro Bigongiari 6

Absorption length L a =L a ( λ ) 26 April 2012Ciro Bigongiari 7 λ Ref = 470 nm L Ref = 60 m WARNING: in this way L A can be larger than SmithBaker( λ). The dependence of the absorption length on the photon wavelength is given by a scaled Smith&Baker parameterization

Scattering (I)  To define completely the scattering we need the probability that a photon is scattered at angles ( θ,φ) w.r.t. the original direction  This probability can be factorized in two terms  The probability to be scattered per unit path length b  The probability to scatter at angles ( θ,φ) β = β ( θ,φ)  For isotropic media, like water, there is no dependence on φ β = β ( θ)  Having a constant probability b per unit path length that a photon is scattered the amount of direct photons decreases  26 April 2012Ciro Bigongiari 8

Scattering (II)  There are two contributions to the elastic scattering:  Rayleigh scattering  Due to small scatters  Mie scattering  Due to large scatters  So, there are two scattering lengths L b and two scattering functions β = β ( θ) 26 April 2012Ciro Bigongiari 9

Rayleigh Scattering 26 April 2012Ciro Bigongiari 10 I = Beam intensity  It’s worthwhile to notice the strong dependence on photon wavelength λ  Blue light is much more affected than red one  The scattering function β = β ( θ) is backward/forward symmetric

Mie Scattering  The intensity of Mie scattered radiation is given by the summation of an infinite series of terms.  Mie scattering is roughly independent of wavelength  Mie scattering is much larger in the forward direction than in the reverse direction.  The greater the particle size, the more of the light is scattered in the forward direction. 26 April 2012Ciro Bigongiari 11

Scattering Length  The overall scattering length is calculated using the Kopelevich parameterization Vs = Vl = April 2012Ciro Bigongiari 12 WARNING: These values are outside the range suggested by Mobley. They were chosen on the base of Test3

Volume scattering function for large scatters  β = β( θ,λ) is a function of scattering angle and photon wavelength 26 April 2012Ciro Bigongiari 13 T.Petzold measueremnts λ = 514 nm

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 26 April 2012Ciro Bigongiari 14 WARNING: In both models the β dependence on λ is neglected

25-27 Sep 2007Collaboration Meeting 15 Henyey-Greenstein Θ Scattering angle g =

25-27 Sep 2007Collaboration Meeting 16 Scattering angle distribution PARTIC MEDSEA Partic

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 χ 2 26 April 2012Ciro Bigongiari 17

Example of time distribution comparison 06/02/2012C.Bigongiari 18 OM0 OM1 OM2 The agreement between data and the MC sample which minimizes the χ 2 seems good Floor 13 Floor 20

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 2012Ciro Bigongiari 19

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 2012Ciro Bigongiari 20

Smith&Baker ? 26 April 2012Ciro Bigongiari 21 ………………………… 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 a w ( 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).

Pope & Fry 26 April 2012Ciro Bigongiari 22 Applied Optics Vol36 N33 (1997) 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.

Pope&Fry vs Smith&Baker 26 April 2012Ciro Bigongiari 23

VSF does depend on λ 26 April 2012Ciro Bigongiari 24 V.Haltrin Appl.Opt.38(33)-1999

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 2012Ciro Bigongiari 25

The End 26 April 2012Ciro Bigongiari 26

Hale&Quarry 26 April 2012Ciro Bigongiari 27

25-27 Sep 2007Collaboration Meeting 28 Water Properties Absorption length Scattering length

Scattering Angle 26 April 2012Ciro Bigongiari 29 η = 0.17  = 0.767

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 barS = % 0 26 April 2012Ciro Bigongiari 30 A = B = C = D = e6

Refraction Index 26 April 2012Ciro Bigongiari 31