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Simulations for Double Chooz
Dario Motta (CEASaclay, France)
on behalf of the Double Chooz collaboration
MANDsim WorkshopManhattan (KS) 1415 June 2005
The Double Chooz CollaborationFrance
CEA/DAPNIA, Saclay: F. Ardellier, J.C. Barrière, M. Cribier, Th. Lasserre, A. Letourneau, D. Lhuillier, F. Marie, J.P. Meyer, A. Milsztajn, D. Motta, L. Scola, V. Sinev
Collège de France, Paris: B.Courty, H.de Kerret, D.Kryn, G.Mention, M.Obolensky, S.Sukhoten, D.Vignaud
Subatech, Nantes: S. Cormon, M. Fallot, T. Kirchner, J. Martino, K. Zbiri
ILL, Grenoble: H. Faust, P. Mutti
Germany
MaxPlanckInstitut Kernphysik, Heidelberg: Ch.Buck, F.DalnokiVeress, W. Hampel, F.X.Hartmann, S.Schönert, U.Schwan
Technische Universität, München: Ch.Grieb, M.Goeger, P.Huber, Ch.Lendvai, M.Lindner, L.Oberauer, W.Potzel, T.Schwetz, F.von Feilitzsch, W.Winter
Universität Tübingen: M.Bauer, J.Jochum, T.Lachenmaier, S.Scholl
Universität Hamburg: C.Hagner
Universität Aachen: ...
Italy
LNGS: C.Cattadori, A. Di Vacri, L.Pandola
Russia
Institute for Nuclear Research RAS: I.Barabanov, L.Bezrukov
Institute of Physical Chemistry RAS: N.Danilov, Y.S.Krylov
RRC Kurchatov Institute: A.Etenko, M.Skorokhvatov
USA
University of Alabama: J.Buzenitz, I.Stancu
Argonne National Laboratory: G.Drake, M.Goodman, J.Grudzinski, V.Guarino, D.Reyna, R.Talaga
Drexel University: C.Lane
Kansas State University: Glenn HortonSmith
Louisiana State University: S.Dazeley, T.Kutter, R.McNeil, W.Metcalf, R.Svoboda
University of Notre Dame: J.LoSecco
University of Tennessee: S.Berridge, W.Bugg, Yu.Efremenko, Yu.Kamyshkov, T. Handler, T. Gabriel, H. Cohn
Double Chooz:search for the mixing angle θ13
Marseille 14/03/05
Near detector Far detector
νe νe,µ,τ
antiνe flux (uranium 235, 238 & plutonium 239, 241)
Reaction: νe + p e+ + n, <E>~ 4 MeV, Ethreshold =1.8 MeV
Disappearance experiment: search for a departure from 1/D2 and shape distortionGoal: improve Chooz sensitivity 0.03
D1 = 100200 m D2 = 1,050 m
Improve the detector concept and backgrounds rejection
Detector Layout I
Acrylic Target vessel(r=1,2m, h=2,8m, t = 8mm)
Stainless steel Buffer(r= 2,92m, h = 5,84m, t = 3mm)MuonVeto (50 cm)
Steel Shield (20 cm)
Acrylic Gamma catcher vessel(r = 1,8m, h = 4 m, t = 12mm)
LS +
0,1
%Gd
LS
Detector Layout III
Marseille 14/03/05
7 m
Shielding: 20 cm steel
7 m
Muon VETO: scintillating oil (r+0.5 m – V = 80 m3)
Nonscintillating buffer: mineral oil (r+0.95m, , V = 100 m3)
γcatcher: 80% dodecane + 20% PXE(acrylic, r+0,6m – V = 28,1 m3)
PMTs supporting structure
ν target: 80% dodecane + 20% PXE + 0.1% Gd (acrylic, r = 1,2 m, h = 2,8 m, 12,7 m3)
nνe
p
Gd
Σγ ~ 8 MeV
511 keV
511 keVe+
Overview Double Chooz Simulation
● DCGLG4
● Optical model
● Detector response
● Gd γ spectra
● Cosmic muons and induced nbackground
● Outlook
DCGLG4sim Double Chooz GenericLand Geant 4 simulation● DCGLG4 is a derivation of GLG4sim
● GLG4sim contains major extensions of Geant4 => G. Horton Smith
● DCGLG4 implements
– Double Chooz geometry & materials– Detailed optical model of scintillator(s) & PMTs
● DCGLG4 profits from simulation expertise of KamLAND, Borexino, Chooz, LENS, ...
● DCGLG4 provides feedback for GLG4 debugging, test, improvement
DCGLG4 Detector Construction
● Simplified geometry (concentric cylinders)
No chimney, no tank supports, no filling lines, no sloping top/bottom
● All materials implemented
● Hamamatsu 8inch PMTs
● Buffer tank “100 % black”
“Self illuminated” view
DCGLG4 Optical ModelThe Strategy
Mineral Oil
Aromatic
Fluor
Gdcomp
WLS
DataBase materials optical properties
Optics simulateddetector
(4 volumes => 4 independent liquids)
Guidelines:● Flexibility● Detailed physicsmodeled as in: D. Motta, et al., Physics/0502086, accepted for publication in NIMA
Scintillator composition (all parameters free !!)
Light Emission : Spectra
Fluor and WLS choice Emission & Reemission spectra (≠)
Emission spectrum depends on Fluor WLS energy transfer:● radiative● non radiative
It's your choice ...
Examples:● PPO BisMSB radiative● BPO BisMSB non radiative
Fluorimetric measurements tells you whether radiative or non radiative transfer
(Data from MPIKHeidelberg)
Light Emission : Light Yield
● Aromatic/Oil fraction● Fluor concentration● GdCompund concentration
LYFree parameter for each volume of the simulation
(Data from MPIKHeidelberg)
Attenuation
Attenuation : extinction coefficients x concentrations
Important to separate contributions :Abs ≠WLS !!
(example for typical formulation Double Chooz scintillator)
Re Emission
Determined by :● Prob. Abs. by fluorescent species (Fluor & WLS)
● Fluorescing probabilities
– QE
– cutoff
(example for typical formulation Double Chooz scintillator)
Re – Emission probability
Photons reemitted according to the WLS spectrum
What can we do with this ?
● Chose our liquids as we like, and see:– Aromatic (e.g. PXE, PC, ...)– Oil (e.g. Dodecane, mineral oil)– Fluor (e.g PPO, BPO, pTP, ...)– WLS (e.g BisMSB, BPO, ...)
– GdCompound (Gd(acac)3, Gd(dpm)3, GdA3, ...)
All concentrations / volume fractions free !
The simulation accesses the database and builds its optics runtime
Yes ... But what exactly?
● Tune PXE/Dodecane ratio and see ...● Change PXE with PC and see ...● Change PPO with another fluor and see ...● Simulate optical impurities and see ...● Tune the LY of target and γ – catcher● ...
New optical properties adjusted with minimal intervention from the user
PMTsManaged by :● GLG4TorusStack● GLG4_PMT_LogicalVolume● GLG4PMTOpticalModel(see also Glenn HortonSmith)
GLG4PMTOpticalModel implements model thin absorbing photocathode with complex refractive index, as described in:D. Motta & S. Schönert, NIMA 539 (2005), pp. 217235)
PMTs Optical Model
A PMT is not just its QE ! The model
Predictions● A (θ,λ)● R (θ,λ)● T (θ,λ)
Complex refractive index + thickness(from experiments)
The predictions
Applications DCGLG4 Optical Model
We will discuss some examples related to :
● Scintillator optimization
● Detector response
● Study scenarios scintillator degradation
● PMT orientation
Scintillator Optimization
● PPO vs BPO (LY BPO ~ 1.051.10 LY PPO, however abs ↑)
Result: BPO disfavored● PXE – Dodecane ratio
(less PXE convenient for acrylics)● BisMSB concentration
PXE LY Light Output20% 100% 100%15% 96% 97%10% 92% 94%
Assumptions :● PPO > BisMSB radiative (wrong, but easier to simulate)● Primary LY independent of bisMSB● QEPPO = 100 % , cutoff = 390 nm● QEBisMSB = 94 %, cutoff = 430 nm
Scenarios Degradation Scintillator● What is the impact of a considered or observed
degradation of the scintillator ?– Which are the wavelengths that really matters?– When spectrophotometric effects become observable?
● Degradation implemented DCGLG4sim– Stability measurements and aging tests– If some degradation shows up, data converted into
additional attenuation lengths– Monte Carlo outcome in the new scenario
PMT Orientation tilted or non tilted ?
Alias : how to get the best from a cylindrical geometry ?
● Several luxurylevels defined (G. HortonSmith):– 0 => QEλ (no angular dependence; R=T=0)
– 1 => QEλ(no angular dependence; rough model for R,T)
– 2 => QE(λθ), R(λθ), T(λθ) (full model)
Note : simplistic simulations equivalent to luxury0 approach
(only geometrical coverage considered)
● Caveat: Folding of PMT radial response missing !!
Results PMTtilt
Lux level tilted pe/MeV Ratio0 no 150,30 yes 164,7 1,0961 no 193,71 yes 195,5 1,0092 no 191,22 yes 196,2 1,026
Conclusions :● precise modeling of PMTs does matter!● tilting is anyway better than nontilting
Warning :● PMT radial response can substantially change the result
Summary & Outlook Optical Model● Detailed and flexible implementation scintillator optical properties
● Feedback with the scintillator and calibration groups
– Optimization of the formulation
– Set specifications for optical stability
– Where and how precisely to calibrate
● Detailed optical model PMTs
● To do list
– continue debugging validation
– improve geometry (chimney, supports, ...)
– reflective buffer tank
– Optimize PMT disposition, study light concentrators for the edges
Gd Radiative Spectra(from Karim Zbiri, Subatech Nantes)
Basic Class : G4NeutronHPCaptureUse of Evaluated Nuclear Data File (ENDF)⇒ High precision for the neutron capture ⇒ Bad description of photon evaporation ?
Question: how can we check ?Answer: comparing with experimental spectra, if not with CHOOZ 1 simulation!
=>Implementation of new class :GdNeutronHPCapture
Gd Radiative Spectra(from Karim Zbiri, Subatech Nantes)
Two interesting isotopes : Gd155(14.73%) and Gd157(15.68%) + neutron +
Gd*156 Gd*158
(E*=8.46 MeV) (E*=7.87 MeV)Gamma spectra : double or multiple cascades
Double cascades of Gd*156 :7.33 and 1.17 MeV (probability of 1%)6.44 and 2.18 MeV (probability of 1.3%)
Double cascades of Gd*158 :6.74 and 1.11 MeV (probability of 3.7%)5.88 and 1.99 MeV (probability of 1.8%)5.62 and 2.25 MeV (probability of 1.3%)
Gd Radiative Spectra(from Karim Zbiri, Subatech Nantes)
Multiple cascadesAssumption: transitions of energy ε from level energy E to :● Ground state● First excited state (E1st*= 1 MeV), always followed by a transition to ground
state.● Continuum of levels with density (with minimum energy of 2E1st*=2MeV)
of the form:
Assumption:● Emission’s probability of 1 gamma proportional to ε3
● All transitions are dipolar (E1)
ea E−2 E1 st*− a = 37
Gd Radiative Spectra(from Karim Zbiri, Subatech Nantes)
Probability of different transitions :
1Transition to the ground state : A = E3
2Transition to the first excited state : B = (EE1st*)3
3Transition to the continuum : C = ∫0
E−2 E1 st*
3 ea E−2 E1 st*− d
(*)L. V. GROSHEV, A.M. DEMIDOV, V.N. LUTSENKO, V.T. PALEKHOV« Atlas » Moscou (1958)
a = 37
Gd Radiative Spectra(from Karim Zbiri, Subatech Nantes)
Egamma(MeV)
● Spectra are different at low and high energies● Effect on the neutron response under evaluation● Work in progress to finalize the model and compare with experimental data