development of a scintillation simulation for carleton exo project rick ueno under supervision of...
TRANSCRIPT
Development of A Scintillation Simulation for Carleton EXO Project
Rick UenoUnder supervision of Dr. Kevin Graham
Outline Introduction Theory Detector Design Monte Carlo Simulation Empirical Position and Energy
Reconstruction Algorithm Results Conclusion
Introduction
EXO: Enriched Xenon Observatory Neutrinoless double beta decay (0υββ)
Massive neutrino = Majorana particle? Neutrino hierarchy? Effective Majorana neutrino mass?
Enriched 136Xe gas Both the source and detector Produces scintillation signals
Theory: Neutrino Neutrino = neutrally
charged lepton Suggested by Pauli to
explain continuous spectrum of beta decay
Neutrally charged third “ghost” particle carries some energy away
epn e
Theory: Neutrino Oscillation If neutrinos have mass, then weak eigenstate can be
written as a linear superposition of mass eigenstates
Where Uli is a 3 x 3 neutrino mixing matrix. If tau neutrino is neglected for simplicity:
Transition Probability in the vacuum
ilil U
cossin
sincosU
E
LmP
4sin2sin
222
Theory: 0υββ decay 0υββ decay occur only if
massive neutrinos are Majorana particles
Effective Majorana mass
Measured quantity is half-life of 0υββ decay
j
ejjUmm 2
22
2
2
01
2/1 , mMg
gMZEGT F
A
VGT
SNO and Super-K measures Δm2, but hierarchy is still unknown
Theory: Neutrino Mass
Theory: Xenon Gas Acts as both the source
(produces electrons by the decay process) and a detector (produces scintillation light)
Scintillation process Incoming particle loses
energy to form dimers The de-excitation of dimer
emits photons at wavelength centred around 178nm
http://hepwww.rl.ac.uk/ukdmc/iop98njts/index.htm
Detector Design A simple scintillation counter was designed to
study the scintillation process alone Motivation:
Predicting total light yield of gaseous xenon Reconstruction of position and energy for a
better energy resolution when coupled with the existing TPC (Time Projection Chamber) component
Study of how response varies with different gas mixtures (such as addition of quenching gases)
Detector Design: Overall Design Consists of a stainless steel “T”, two
PMTs on either side, wavelength shifter (WLS) on the PMT window
Detector Design: PMT 136Xe produces UV photon of
178nm Possibility: Regular PMT
with WLS or UV-sensitive PMT
We already have equipment to coat materials with WLS (Tetraphenyl Butadiene, TPB)
MC Simulation: Detector Construction MC Simulation using Geant4 was developed The detector design is simplified to a cylindrical
geometry PMT is represented
by a cylindrical tube with a photo-cathode at the end of a glass plate
y
x
z
12”
MC Simulation:Default Initial Values
Property Values
Photon energy 7.07 eV (≈ 178nm)
Scintillation yield 29000 photons / MeV
Absorption length 100 cm
Prompt scintillation timing constant
2.2 ns
Late scintillation timing constant
4.5 ns
Initial Particle Alpha particle
Initial Momentum Random direction
MC Simulation:Event Detection and Outputs
PMT and WLS has some wavelength-dependent efficiency The simulation should be as realistic as
possible The program reads an input data file
containing efficiency data corresponding to a wavelength
Result is outputted into a data file to be analysed
Empirical Position and Energy Reconstruction Algorithm
Reconstruction of initial position and energy Input: Signal output of two PMTs Output: Reconstructed position and energy of
the particle
ReconstructionProgram
PMT1 Hits, PMT2 Hits
Reconstructed Position and Energy
Empirical Algorithm: Position Reconstruction Looking at the
distribution of ratio between PMT1 and total signal as a function of z position
Gives a smooth curve
Can be readily used to reconstruct the initial position in z direction
11 exp1 zahits
hits
total
PMT
1
1ln
1
az
Empirical Algorithm: Energy Reconstruction Looking at the total
signal normalized by the signal at z = 0 as a function of z position
Can approximate to a 4th order polynomial
Used to estimate the hits if the event occurred at the centre of the detector
432 54321 zczczczccratio
ratio
hitshits total
centre
Empirical Algorithm: Energy Reconstruction
Looking at the total signal at the centre as a function of energy
Gives a linear relation
But a0=0 Rearranging the
equation, initial energy is reconstructed
Eaahitscentre 10
ratioa
hits
a
hitsE totalcentre
11
Empirical Algorithm:Radial dependency
The detected signal as a function of position across the diameter of detector shows deficiency up to ~40% near the wall of the detector
Empirical Algorithm:Radial dependency
Predict that the z-position reconstruction has smaller effect than energy reconstruction
Results of independent test simulations
Three test scenarios were simulated with alpha particles with initial energy of 5.4 MeV at various positions
Results:Test Scenario 1
Starting position at (0,0,0) cm Both reconstructed position and energy
agrees nicely
Results:Test Scenario 2
Starting position at (0,0,-10) cm Both reconstructed position and energy are
fairly consistent
Results:Test Scenario 3
Starting position at (5,0,5) cm Reconstructed energy is much lower than
expected
Results:Summary
Test Scenario
1 2 3
Reconstructed Position (cm)
-0.02354 -10.35 4.571
Sigma 0.3619 0.2947 0.3687
Reconstructed Energy (MeV)
5.41 5.065 4.284
Sigma 0.214 0.2825 0.2134
Conclusion Baseline simulation was developed using
Geant4 The reconstruction algorithm was
developed Works well if the event occurs at the centre Problem when the initial event is off-centre
Future plans Xenon gas and additives Implement into existing TPC system