MaGe: a Monte Carlo framework for the GERDA and Majorana experiments Luciano Pandola INFN,...

MaGe: a Monte Carlo framework for the GERDA and

Majorana experiments

Luciano PandolaINFN, Laboratori Nazionali del Gran Sasso

for the MaGe development group

Geant4 WorkshopHebden Bridge, UK 13 September 2007

13 September, 2007 Geant4 Workshop – Hebden Bridge

Search for neutrinoless decay of 76Ge

0: (A,Z) (A,Z+2) + 2e-

Neutrinoless 2-decay violates the lepton

number conservation: ΔL=2

76Ge

76Se

Q = 2039 keV

Explore the Dirac/Majorana nature of neutrino and the absolute mass

scaleVery rare process:

T1/2 > 1025 y

New generation experiments require unprecedented low-

background conditions and large masses!

Two experiments with 76Ge, GERDA (Europe-Russia) and Majorana (US-Japan) have been

proposed for next generation (100 kg

scale). They will explore the feasibility of a

world-wide ton-scale 76Ge experiment


Common issues in Monte Carlo’s

GERDA and Majorana have very similar requirements

and issues in terms of Monte Carlo simulations for background and sensitivity

studies

1. To provide a physics simulation package to aid in the optimal design, operation and analysis of data.

2. It must persist over the long lifetime of the experiments.

3. It must be well-maintained, documented, and robust.

4. Maintain record of results.

functionality

OO and abstraction capabilities of C++ and STL for flexibility

1. Energy deposition of particles from radioactive sources, cosmic rays, and signal sources.

2. Pulse-shape formation in crystals, different segmentation schemes, and crystal geometries.

3. Electronics.4. Shielding (neutron absorption and muon

tagging).5. Radioactive decay chains and

emissions.6. Signal: double-beta decay7. Activation in detector material.

physics

Geant4 meets all physics requirements, has OO

structure, well established

MaGe framework


What’s MaGe ?

MaGe is a Geant4-based Monte Carlo simulation package dedicated to experiments searching for 02 decay of 76Ge

(and low-background experiments in general). It is developed jointly by the Majorana and GERDA simulation

groupsIdea: to share a common simulation framework with an abstract set of interfaces, while each experiment adds its concrete implementations (geometry, output, etc...).

No constraints to both sides (geometry, physics, etc.) each component can be independently re-

written

The whole package can be configured and tuned by

macros without accessing the code accessible to new users

and non experts of C++


MaGe block structure

Takes care of all common

parts that are not

experiment-specific

MJ output GERDA output

Event generators, description of

physics processes, properties of the

materials, management

Majorana

geometry

GERDA geomet

ryMaGe

The common CVS repository allows easy and parallel development of the code (Geant4 philosophy)

tunable and customizable by macro

Different formats supported (AIDA interfaces, ROOT, ASCII-

based)


Why to develop MaGe ?

Basic documentation available, paper in preparation

avoids duplication of the work for the common parts of the simulations (generators, physics, materials, management)

can provide the complete simulation chain (including pulse shape)

allows a more extensive validation of the simulation with experimental data coming from both experiments also Geant4 validation

Why MaGe?

can be run by script and is flexible for experiment-specific implementation of geometry and output

is suitable for the distributed development


Some common tools in MaGe

Generators

Radioactive isotopes and 2

Cosmic ray muons

Neutrons

beam

Pencil beams

Selectable by macro

General-purpose samplersRandom sampling of the

primary position uniformly within an arbitrary volume or

surface (even of complex shape)


A MaGe/GERDA applications

Top muon veto

Neck

Cryostat

Water

Water tank

Detector array

GERDA geometry in MaGe

MaGe widely used for background and

sensitivity studies in GERDA, and for

design optimization

cosmic ray muons

maximum tolerable radioactivity for detector parts

efficiency of multiplicity cuts

neutrons

NIM A 570 (2007) 149

several GERDA notes

NIM A 570 (2007) 479

in preparation


MaGe/Geant4 validation for -rays - I

MaGe results compared with test-stand

experimental data

18-fold segmented n-type detector (Canberra-France)

mass: 1.6 kg

height: 70 mm

radii: 10 and 70

mm

6 segments in

3 segments in z

Max-Planck-Institut für Physik, Munich

Detector irradiated with

radioactive sources


MaGe/Geant4 validation for -rays - II

60Co source: data, MC, background

Core electrode energy spectrum Occupancy of each segment

substructure

average deviation ~5%

Substructure effect is reproduced in MaGe using an effective model for drift anisotropy. DAQ efficiency also

included nucl-ex/0701005v1


MaGe/Geant4 validation for -rays - III

SFL ratio between all events in a given peak and the single-

segment ones

only single-segment (=localized) events are

background for neutrinoless decay

Different -energy from radioactive

sources taken into account good agreement with

MaGe

nucl-ex/0701005v1


MaGe/Geant4 validation for -rays - IV137Cs : single line at 662

keV

w/o LAr veto

w/ LAr veto

Data taken at MPIK-

Heidelberg: Ge crystal

immersed in liquid argon

Very good agreement

with MaGe for 137Cs

(spectrum and absolute

rates)


Simulation of low-energy neutrons - I

AmBe source

neutron

Paraffin collimatorDetectorGERDA and

Majorana have irradiated test Ge

detectors with neutron sources. -rays produced by inelastic scattering

and radiative capture

Majorana setup

4.4 MeV from

Am-Be source

p(n,d)


Simulation of low-energy neutrons - II

The general spectral shape is reproduced fairly

well

Additional problem: proper description of

the primary AmBe spectrum (neutrons and

-rays)

DataMaGe + backgroundbackground

175 keV71mGe

140 keV75mGe

198 keV71mGe

The simulation has spurious and missing

peaks (mainly related to

metastable Ge states)

Data

MaGe


Radioactive contaminations - I

Cold Plate

1.1 kg Crystal

ThermalShroud

Vacuum jacket

Cold Finger

Bottom Closure

MaGe has been used for the finalization of the Majorana reference design: estimate of

background from different sources and radiopurity

requirements on detector components

Several radioactive isotopes and detector components have been

considered (2 TB of data produced)

Gross and Net Rates for Important Isotopes

Total Est. Background

(per t-y)

Background Source

Counts in ROI per t-y Counts in ROI 68Ge 60Co Germanium Gross 2.54 1.22 (100 day exp) Net 0.01 0.02 0.03

208Tl 214Bi 60Co Gross 0.12 0.03 0.26

Inner Mount Net 0.01 0.00 0.00 0.01

Gross 0.77 0.16 0.58 Cryostat

Net 0.22 0.04 0.00 0.26 Gross 2.28 0.30 0.02 Copper

Shield Net 0.64 0.06 0.00 0.70 Gross 0.18 0.04 0.34

Small Parts Net 0.02 0.01 0.00 0.03

muons cosmic activity

( ,n)

Gross 0.03 1.33 0.003

External Sources (6000 mwe)

Net 0.003 0.18 0.003 0.18

2 -decay < 0.01

TOTAL SUM 1.21


Radioactive contamination - II

Experiment

MaGe

Crystal1x84x8

Cou

nts

/ ke

V /

106

deca

ys

Different segmentation schemes tested for different radioactive

sources

Segmentation successfully rejects background. Good agreement data

vs. MC60Co


Surface contaminations

MaGe used to estimate background due to surface contamination in the crystals from natural

radioactivity

Example spectrum in Majorana Reference Design (222Rn to 206Pb)


Ongoing development: pulse shape

A (modular) software for the simulation of pulse shapes is under joint development. It can be used in conjunction with MaGe, providing the whole chain from event generation, propagation to pulse simulation

Advantages of running with MaGe is the flexibility and existing software

infrastructure (e.g. geometry, I/O). PS simulation can be

interfaced with any other MC. Different PS implementations

are possible

Gen

erat

or

MaGe

x, y

, z, t

, dE

Pulse shape

simulation

x, y, z, t, dEAny other MC

Common interface

defined (MGDO)


Conclusions

Two experiments, Majorana and GERDA, will look for 0 decay of 76Ge, with different designs

They have similar issues and requirements for MC simulation The MC groups are jointly developing since 2004 a

Geant4-based and OO Monte Carlo framework called MaGe Geant4 well established in physics, has flexible OO interfaces avoids duplication of work, easy to develop and mantain can be validated and tested more deeply and precisely includes general-purpose tools (generators, samplers) easy to use by macro (also for non-experts)

Used for several applications and background studies Simulation results compared with test stand data (

MaGe and Geant4 validation) -rays and low-energy neutrons

Interface with pulse shape generators in progress


Two examples of macros

/MG/geometry/detector MJRDBasicShield

/MG/geometry/idealCoax/setDefaults

/MG/geometry/idealCoax/deadLayerOn true

/MG/geometry/idealCoax/outerDeadLayer 1

micrometer

/MG/generator/select cosmicrays

/MG/eventaction/rootschema MCEvent

/MG/geometry/detector GerdaArray

/MG/geometry/database false

/MG/generator/select decay0

/MG/eventaction/rootschema GerdaArray

/MG/generator/confine volume

/MG/generator/volume Ge_det_0

/MG/generator/decay0/filename myfile.dat

Generates cosmic ray events in a single coaxial crystal in the Majorana setup. Crystal parameters are customized

Generates events uniformly in the volume of one Ge crystal in the GERDA array. Kinematics

read from an external file

Geometry, tracking cuts, generator and output pattern selectable and tunable via macros (same executable)

No need to recompile, easy to use for non-expert people

MaGe: a Monte Carlo framework for the GERDA and Majorana experiments Luciano Pandola INFN,...

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