The Double Chooz Monte The Double Chooz Monte CarloCarlo

(selected topics !)(selected topics !)

Dario Motta (Irfu/SPP)Anatael Cabrera (APC)

Performance

Backgrounds

Detector Detector Monte Monte CarloCarlo

The Double Chooz Monte Carlo

● Scintillation and optical model● PMT geometry and optics● Read-out System simulation● User-friendly interfaces for event generation● Data-Base handling

Geant4-based, detailed detector description, however several extensions :

Optical ModelNote: Geant4 does not “understand”

molecules !➔ No native optical micro-model

Data-Base material optical

properties

Run-time optical model

Guidelines:● Flexibility● Detailed micro-physical modelmodeled as in: D. Motta, et al., NIMA 547 (2005), 368-388

Mineral OilAromaticFluorGd-compWLS

Tunable composition for all sub-volumes

Optical model : light emissionFluor and WLS choice => Emission & Re-emission spectra (≠) Primary (before any

interaction) emission spectrum depends on Fluor -> WLSenergy transfer:● radiative● non radiative● both channelsFluorimetric measurements says energy transfer mode

Example : PPO -> Bis-MSB mostly radiative(especially true @ low Bis-MSB concentrations)

Scintillation time profile

DC Measurements

4-exp fit

Geant4 allows only 2 time constants (fast + slow)

Optical model : light attenuation

Partial attenuation lengths calculated by using :● Molecular extinction coefficients (DC spectrophotometric measurements)● Concentrations in the mixture

Target scintillator

Optical model : wavelength-shift

Partial re-emission probabilities calculated by using :● Partial att. length (see above) to get the partial absorption probabilities● Molecular re-emission yields (from literature and fluorimetric measurements)

Optical model : the PMT

Faithful geometry through the GLG4sim “ThorusStack” class (non G4-native)

Hamamatsu 10'' Internal photon tracking

PMT optical model : definitions

θR

T

QE medium

A

CE (xpmt)

QE air ≠ QEmedium

QE air is the quantum efficiency typically measured with standard techniques

● QE()medium Probability for pe emitted in vacuum

● A() - QE()medium is lost● R() reflects and must be

tracked● T() is transmitted into

the PMT and must be tracked

● DE() = QE()medium x CE(x)

Optics of an absorbing thin filmThe experimental input for the

model(D. Motta & S. Schönert, NIMA 539 (2005), pp. 217-235)

+ photocathode thickness, which is quite typical : 20 - 30 nm

PMT Model● A() ; R() and T() calculated for any impinging photons QE()medium = QE()air x [A()/A(0)air] QE/A = const

Relevant QE Measured QE Calculated Assumed

= 410 nm

PMT Model : CE(x)photocathode

● Simplified 1d model : CE = CE(r), normalized to maximum● Complete 2d model DE = DE () discussed by Anatael● Convenient to make an accurate CE simulation in post-processing : (PEs killed by CE do not any longer need Geant4 !)

0 1,55 3,13 4,62 6,16 7,67 9,03 10,3611,9412,480.000

0.200

0.400

0.600

0.800

1.000

1.200R7081

R (cm)

CE

Thank you !

Yes, this is the end