SuperNEMO Simulations
Darren Price
University of Manchester
http://www.hep.man.ac.uk/u/darren
July, 2005
Simulation details - geometry

Mylar-wrapped scintillators on 4
sides of detector:
–
–

Main calorimeters 2x250x360cm
Top and bottom calorimeters
20x250x2cm
Use foil (82Se) of width 250cm,
height 275cm, thickness ~35mm
– Foil 50cm from main scintillator,
touching top and bottom
scintillators

Wiring in tracking volume going from top to bottom in 3
bands (as in NEMO3)
– One band of wires close to scintillator, band near middle of
tracking and a band near the foil
– Geiger cell dimensions used from NEMO3
SuperNEMO Simulations
Darren Price
NEMO Collaboration Meeting - July 2005
Simulation details - cuts

We require two hits in the calorimeter to accept an
event, both of which must come from electrons
created at the primary vertex

Once backscattered, electron is ignored, so cannot
contribute to hit distribution, acceptance etc.

Require Emin>0.1MeV for each electron to accept
event

Need electrons to pass through at least 9 unique
Geiger cells to count as a possible hit in calorimeter
SuperNEMO Simulations
Darren Price
NEMO Collaboration Meeting - July 2005
Simulation details - acceptance

Acceptance ratio for
0vbb varies between
50% and 20%

Plot of acceptance
ratio with relation to
foil vertex creation to
the right

Currently working on
acceptances with
relation to energy cut
and number of Geiger
hits required
SuperNEMO Simulations
foil centre
Darren Price
NEMO Collaboration Meeting - July 2005
Calorimeter – energy plots (8% res.)

Sum of two
electron energies
at scintillator (MeV)
using a Gaussian
smearing function
corresponding to
an 8% energy
resolution at 1MeV
(0nbb)
SuperNEMO Simulations
Darren Price
NEMO Collaboration Meeting - July 2005
Calorimeter – energy plots (8% res.)

Sum of two
electron energies
at scintillator (MeV)
using a Gaussian
smearing function
corresponding to
an 8% energy
resolution at 1MeV
(2nbb)
SuperNEMO Simulations
Darren Price
NEMO Collaboration Meeting - July 2005
Calorimeter – energy plots (8% res.)

Sum of two electron
energies at
scintillator (MeV)
using a Gaussian
smearing function
corresponding to an
8% energy
resolution at 1MeV
for neutrinoless
double beta decay
with Majoron
emission (SI=1)
SuperNEMO Simulations
Darren Price
NEMO Collaboration Meeting - July 2005
Calorimeter - backscattering

Backscattered electrons from the (Bicron)
scintillators have the following energy distribution




SuperNEMO Simulations
Darren Price
Only electrons
backscattering for the
first time are recorded
(multiple backscatters
not included in this plot)
Backscattering ratio is
~12.4%
Mean backscattered
electron energy 680keV
Other materials also
studied
NEMO Collaboration Meeting - July 2005
Tracking – Geiger cells

Wires added to the simulation
– simulated octagonal cell wiring of NEMO3 with central anode
wire surrounded by 8 other wires
– low stepsize volume defined around each Geiger cell optimised
for speed of calculation and fidelity of Geiger hit simulation

Modular design of the tracking/wire volumes had to be
implemented to reduce the processing time for GEANT to
search through many volumes

Added a random generator to simulate Geiger cell efficiency
(96%)

Added code to ensure Geiger cell hits were unique (in case
of backscattering etc.)
SuperNEMO Simulations
Darren Price
NEMO Collaboration Meeting - July 2005
Tracking – Geiger hit distributions

SuperNEMO simulation (LEFT) shows good
agreement with NEMO3 data (RIGHT)
Certain geometrical
differences in NEMO3
slightly affect comparison
SuperNEMO Simulations
Darren Price
NEMO 3
DATA
NEMO Collaboration Meeting - July 2005
Limit program - details

Using a limit program (MClimit) (NIM.A434, p. 435-443, 1999)
created by Tom Junk (University of Illinois) I ran an analysis on
data generated from my simulation
– Input spectra of signal + background
– Get 90% confidence limits on effective neutrino mass, half-life.
– Program allows inclusion of systematic uncertainties and uses
shape information

Program takes multi-variable data to calculate limit – used:
– Energy spectrum
– Separation angle of the two generated electrons

Calculated the limit for 500kg.yrs
SuperNEMO Simulations
Darren Price
NEMO Collaboration Meeting - July 2005
Limit program - results


Using a 2-channel analysis of energy and angular distributions
did not affect outcome (angular distribution below left)
Signal / background for angular distribution almost constant at 1
– so no real benefit – (s/b plot below right)
Angular distribution
Blue = 2vbb
Green = 0vbb+2vbb
Ecut>2.73MeV
signal/background
(angular distribution)
SuperNEMO Simulations
Darren Price
NEMO Collaboration Meeting - July 2005
Limit program - results



Energy cut optimised using
MClimit program
Shape information was used
Using nuclear matrix
element |M| = 0.05 in
analysis
Result: n90=41, <mn> <0.064,
T1/2(0n) > 6.01E+26
Optimum energy cut found to be
E>2.73MeV. Above is energy
spectrum studied, to left is cut region.
Blue = 2vbb Green = 0vbb+2vbb
SuperNEMO Simulations
Darren Price
NEMO Collaboration Meeting - July 2005
Current work

Acceptance studies varying Geiger cell hit requirements, foil
dimensions, energy cuts

Studies of wire diameter on electron energy loss

Working on limit calculation for Majoron emission process
(0nbbc0)

Studies of energy resolution against effective mass limit

Thesis completion: 09/2005
SuperNEMO Simulations
Darren Price
NEMO Collaboration Meeting - July 2005
SuperNEMO Simulations
Darren Price
University of Manchester
http://www.hep.man.ac.uk/u/darren
July, 2005