Activity report of

TG10

L. Pandola (LNGS) for the TG10 group

Gerda Collaboration Meeting, February 3-5, 2005

(simulations and background studies)

The Task Group 10Goals:

evaluation of the background index

Simulation of signal and backgrounds in the Gerda

detectorGeant4-based MaGe framework in collaboration with Majorana

Who: LNGS, Munich, Russian groups, MPIK

Validation and cross-check Pulse shape, segmentation, mirror charges, etc.With TG9: definition of data format

including

http://wwwgerda.mppmu.mpg.de/MC/monte_carlo.html

optimization of Gerda detector and data analysissensitivity to 02 signal

The MaGe frameworkMid-October 2004: Gerda & Majorana joint MC

workshopIdea: collaboration of the two MC groups for the development of a common framework based on

Geant4abstract set of interfaces: each experiment has its own concrete

implementationavoid the work duplication for the common parts (generators, physics, materials, management)provide the complete simulation chain

more extensive validation with experimental datarunnable by script; flexible for experiment-specific implementation of geometry and output;

suitable for the distributed development

The MaGe frameworkMajorana already had a working

framework, evaluated and found suitable for

Gerda needs and for joint development

Warning: To have a common framework simply means sharing the same generic interfaces.

No contraints to the Gerda side (geometry, physics, etc.) each component can be independently re-

written

(kindly supplied by the MC group)

Report: wwwgerda.mppmu.mpg.de/MC/gerda_monte_pic/gerda.pdf

Present situation:

Common CVS repository hosted at Munich

Discussion forum hosted at Berkeley

The MaGe structure

Generator, physics processes, material, management, etc.

mjgeometry mjio

gerdaiogerdageometry

Each group has its own geometry setup and corresponding output, everything else can be

shared.

To run a new simulation:write only your geometry and your output

register them in the management classes

Can be downloaded from the CVS repository in Munich

setup instructions at:

wwwgerda.mppmu.mpg.de/MC/monte_carlo_pic/setup.ps

Activity for the common part

Development of generic (not Gerda-specific) tools

Optimization and modularization of the frameworkInterface to the decay0 generator by V.I. Tretyak

Generator for cosmic ray muons

Random sampling of points uniformly from a specified (generic) volume

02 signal according to several theoretical models

All this work would have been duplicated ...

Access to the trajectories of all the secondaries

Activity for the Gerda-specific part

Description of the Gerda setup including shielding

(water tank, Cu tank, liquid Nitrogen), crystals array

and kapton cables

Gerda geometry

top -vetowater tank

lead shieldingcryo

vessel

neck

Ge array

New OO structure of geometry classes

Gerda MC Geometry

Flexible executable: set of commands to configure

geometry Number of columns and orientation,

segmentation of crystals, support structure/shielding on/off, etc.

Kevin Kröninger - MPI München

segmented crystals

(6x3)

10 columns

standard geometry

Output:Class to create a ROOT TTree with all the interesting information (energy deposition and position of hits in

Ge, Liquid N2, water, etc.)

Activity for the Gerda-specific part

Physics studies in progress:

background induced by cosmic ray muons and neutrons background in electronics and support

segmentation effect for background and 02 signal

ready to be interfaced with software for the simulation of pulse shape Munich

external background and shielding requirements

Generic AIDA interface for other analysis tools (e.g. HBOOK)

Two examples of macros/MG/geometry/detector GerdaArray

/MG/geometry/database false

/MG/geometry/detector/crystal/truecoaxial false

/MG/geometry/detector/general/numcol 3

/MG/geometry/detector/general/crypercol 3

/MG/geometry/detector/crystal/height 8.5 cm

/MG/generator/select cosmicrays

/MG/eventaction/rootschema GerdaArray

/MG/geometry/detector GerdaArray

/MG/geometry/database false

/MG/geometry/general/constructshield 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 3x3 array of non-coaxial

crystals in the Gerda shielding

Generates events uniformly in the volume of a Ge crystal

(without shielding). Kinematic read from a decay0 file

Geometry, tracking cuts, generator and output pattern selectable and tunable via macros

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

Cosmic ray muons (Phase I)

Flux at Gran Sasso: 1.1/m2 h (270 GeV)

Small flux, small Ge volume:

59 events/kg y

Further reduced by anti-coincidence with other Ge-crystals and with top (or Cerenkov)-veto

Input energy spectrum

from Lipari and Stanev, Phys. Rev. D 44 (1991) 3543

Energy (keV)

Input angular spectrum

uniform in

cos

1 in

first approximatio

n

~ 60 – 70 events/kg y in H-M

Cosmic ray muons (Phase I)9 Ge crystals for a total mass of 19 kg; threshold: 50 keV

Energy (MeV)

3.93 yearsSum

spectrum

Energy (MeV)

Number of hit

detectorsmulti-hit: 35.2%

149 counts in 1500 2500 keV

21 counts in 2000 2100 keV

(1.5 2.5 MeV): 2·10-3 counts/keV kg y

annihilation peak

below threshold

single-Ge(~4·10-3 counts/keV kg y in H-M simul.)

C. Doerr, NIM A 513 (2003) 5961.5 MeV 2.5 MeV

Cosmic ray muons (Phase I)

Threshold for plastic scintillator (top -

veto): 1 MeV

3.93 years

Sum spectrum

Ge anti-coincidence

Energy (MeV)

Energy (MeV)

(suppression factor: ~2)

Ge and top -veto anti-coincidence

(suppression factor: ~20)

~ 4 events/kg y

Cosmic ray muons (Phase I)Counts in 1.52.5

MeV (3.93 years)

Counts in 2.02.1 MeV(3.93 years)

Background index

(cts/keV kg y)

No cuts 149 21 (H-M=34) ~ 2-3 · 10-3

Ge anti-coincidence 46 6 ~ 6 · 10-4

Ge anti-coincidenceTop -veto (100% eff.)

6 1 < 1.6 · 10-4

(95% CL)

Ge anti-coincidenceTop -veto (98% eff.)

8 1 < 1.9 · 10-4

(95% CL)

Ge anti-coincidenceTop -veto (95% eff.)

9 1 < 2.1 · 10-4

(95% CL)

Cerenkov -veto(thr = 5 MeV, 100% eff.)

0 0 < 0.4 · 10-4

(95% CL)

Instrumentation of water as a Cerenkov -veto is an open issue for the Collaboration (

redundancy)

Background substantially lower than previously estimated

Cosmic ray muons (Phase I)

Cross-check of isotope production with independent codes (e.g. FLUKA) would be very

welcome

Correlated issue: production of short-lived radioactive isotopes induced by the muon

showersdelayed energy deposition

Most dangerous isotopes ( above Q):

Isotope Life time Gammas where rate15C 2.44 s 5.2 MeV Water 1.8 c/year13B 17.4 ms 3.68 MeV Water 0.6 c/year16N 7.13 s 6.1, 7.1

MeVWater 3.5 c/day

14O 70.6 s 2.31 MeV Water 6.1 c/y

Production in dangerous isotopes in nitrogen is much smaller

Background index not evaluated yet probably negligible

Neutrons (Phase I)

To do next: validation of the simulation with data and cross-check with independent codes

Cosmogenic neutrons (muon interaction in the rock)small flux (200 n/m2y), hard energy spectrum (up to tens of

GeV)Energy and angular spectrum from H. Wulandari et al. hep-ex/0401032

Negligible in Gerda: < 3.8 · 10-5 cts/keV kg y (95% CL)with Ge-anticoincidence Neutrons from fission and (,n)

soft energy spectrum (up to 8 MeV), higher flux (20 n/m2 h) Work in progress. Difficult to simulate because CPU-

intensive

0.05% of the events deposit energy the nitrogen volume 90 ev/m2 y

Probably not an issue. from n+p shielded by LN2In H-M: 3 · 10-3 cts/keV kg y (without water

shielding) !

C. Doerr, NIM A 513 (2003) 596

CNGS muons Flux at Gran Sasso: 0.86 /m2 d (<E> ~ 15

GeV)

30 times smaller than cosmic ray flux and softer spectrum

LVD Collaboration, hep-ex/0304018

Top -veto uneffective: only Ge-anticoin. and water -veto Not evaluated yet in detail

Rough estimate (15-GeV ):

LVD Collaboration,

hep-ex/0304018

No cuts: < 1.2· 10-4 cts/keV kg y (95%) Ge-anticoincidence:

< 8 · 10-5 cts/keV kg y (95%) Ge and Cerenkov -veto:

< 4 · 10-5 cts/keV kg y (95%)

Not a critical issue

Signal and background studies

Photons carry energy to more

than one crystal/segment (multiple-site)

Example: 60Co

Hit crystals Hit segments

~19% ~6%

Cut on the number of hit

crystals or segments

reduces 60Co events to 19%

(6%)

Kevin Kröninger - MPI München

Signal and background studiesBackground suppression efficiency:

Segmentation: 6 (phi) x 3 (z) Threshold: 10 keV; Energy window: Q± 5 keVPulse shape analysis and pattern recognition not included

Source 1 crystal 1 crystal AND signal

window

1 segment 1 segment AND signal

window

Number of events

Signal 0.96 0.92 0.89 0.86 100k60Co (crystal) 0.19 3.0 · 10-4 0.06 2.6 · 10-5 1 M60Co (cable) 0.28 1.7 · 10-4 0.14 9.6 · 10-6 1 M

208Tl (crystal) 0.18 2.4 · 10-4 0.06 5 · 10-5 1 M208Tl (cable) 0.24 2.2 · 10-4 0.12 8 · 10-5 1 M

68Ge (crystal) 0.22 9.8 · 10-4 0.05 1.2 · 10-4 1 M210Pb (crystal) 1 0 9.9 · 10-3 0 10k

Kevin Kröninger - MPI München

MPI Munich MC activities

Pulse shape analysis (incl. MC)

Test facility for Ge-crystals (incl. MC)

Future tasks:

Maintenance of a common CVS server for MaGe

Update of geometry: crystals and support structure

Background and signal studies/background suppressionSegmentation

studies

Kevin Kröninger - MPI München

Other background calculations

Background from inner tank envelope:direct simulation of transportation

signal window: 1800 2300 keVCu: 25 · 10-6 Bq/kg of 232ThFe: 20 · 10-3 Bq/kg of 232Th

(c/keV kg y) Cu Fe (neck)

Center 10-4 1.1 · 10-4

50 cm below center

1.2 · 10-4 2 · 10-5

10-3 c/kg keV y guaranteed

With 50-cm-below position, Fe negligible

Background from external gammas:detector placed 50 cm below center

intensity of 2.6 MeV: 0.0625 cm-2s-

1

Water shielding: 300 cm in the cylindrical part 200 cm above and

below

6.6 · 10-6 c/keV kg y

1-2 · 10-4 c/keV kg y

A. Klimenko – INR, ITEP, Dubna, MPIK

Cts/keV kg y

Cylindrical part 6.6 · 10-6

Upper spherical part

1.1 · 10-4

Bottom flat part 2.0 · 10-4

Open neck 1.1 · 10-2

Neck with 10cm Pb 1.1 · 10-4

Neck with 15cm Pb 1.1 · 10-5

upper partcylindrical partlower part

To go lower than 10-5 c/keV kg y: bottom part: 7 cm of

Pb

cylindrical part: no further shielding neededneck: 15 cm of Pb

upper part: 6 cm of Pb

Cu tank: LAr is requiredA. Klimenko – INR, ITEP,

Dubna, MPIK

Other background calculations

ConclusionsMC package MaGe ready for Gerda & Majorana groups Downloadable from CVS, flexible and runnable by

macroStructure complete and ready for physics studies

Backgrounds, segmentation, pulse shape (via interface) Precise description of Gerda setup and shielding

First results of signal and bck in crystals & cables

3-month activity and still a lot of work to do in the future......Well begun is half done !

Preliminary results of -induced and n backgroundTop -veto enough for background of a few ·10-4 c/kg

keV yNeutrons, CNGS and isotopes production presumably not critical

Estimation of external background and shielding

10-4 c/kg keV achievable with present shielding, 10-5 needs LAr