SuperNEMO Simulations Darren Price University of Manchester July, 2005

SuperNEMO Simulations

Darren Price

University of Manchesterhttp://www.hep.man.ac.uk/u/darren

July, 2005

SuperNEMO Simulations Darren Price NEMO Collaboration Meeting - 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 ~35m

– 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


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


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

foil centre


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

()


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

(2)


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)


2005

Calorimeter - backscattering Backscattered electrons from the (Bicron)

scintillators have the following energy distribution 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


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.)


2005

Tracking – Geiger hit distributions SuperNEMO simulation (LEFT) shows good

agreement with NEMO3 data (RIGHT)

NEMO 3 DATACertain geometrical

differences in NEMO3 slightly affect comparison


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


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)

signal/background(angular distribution)

Angular distributionBlue = 2vbb Green = 0vbb+2vbb

Ecut>2.73MeV


2005

Limit program - results Energy cut optimised using

MClimit program Shape information was used Using nuclear matrix

element |M| = 0.05 in analysis

Optimum energy cut found to be E>2.73MeV. Above is energy spectrum studied, to left is cut region.

Blue = 2vbb Green = 0vbb+2vbb

Result: n90=41, <m> <0.064, T1/2(0) > 6.01E+26


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 (00)

Studies of energy resolution against effective mass limit

Thesis completion: 09/2005

SuperNEMO Simulations

Darren Price

University of Manchesterhttp://www.hep.man.ac.uk/u/darren

July, 2005

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SuperNEMO Simulations Darren Price University of Manchester July, 2005