activity report of tg10
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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
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