Activity report of TG10

1
Activity report of TG10
(simulations and background studies)
L. Pandola (LNGS) for the TG10 group
Gerda Collaboration Meeting, February 3-5, 2005
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The Task Group 10
Goals
evaluation of the background index
optimization of Gerda detector and data analysis
sensitivity to 0n2b signal
Simulation of signal and backgrounds in the Gerda
detector
Geant4-based MaGe framework in collaboration with
Majorana
Validation and cross-check Pulse shape,
segmentation, mirror charges, etc. With TG9
definition of data format
including
Who LNGS, Munich, Russian groups, MPIK
http//wwwgerda.mppmu.mpg.de/MC/monte_carlo.html
3
The MaGe framework
Mid-October 2004 Gerda Majorana joint MC
workshop
Idea collaboration of the two MC groups for the
development of a common framework based on Geant4
abstract set of interfaces each experiment has
its own concrete implementation
avoid the work duplication for the common parts
(generators, physics, materials, management)
?
?
provide the complete simulation chain
more extensive validation with experimental data
?
runnable by script flexible for
experiment-specific implementation of geometry
and output
?
?
suitable for the distributed development
4
The MaGe framework
Majorana already had a working framework,
(kindly supplied by the MC group)
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
Present situation
Common CVS repository hosted at Munich
Discussion forum hosted at Berkeley
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The MaGe structure
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/mo
nte_carlo_pic/setup.ps
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Activity for the common part
Development of generic (not Gerda-specific) tools
?
Optimization and modularization of the framework
Interface to the decay0 generator by V.I. Tretyak
?
0n2b signal according to several theoretical
models
Random sampling of points uniformly from a
specified (generic) volume
?
Generator for cosmic ray muons
?
?
Access to the trajectories of all the secondaries
All this work would have been duplicated ...
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Activity for the Gerda-specific part
Gerda geometry
top m-veto
water tank
neck
lead shielding
cryo vessel
Description of the Gerda setup including
shielding (water tank, Cu tank, liquid Nitrogen),
crystals array and kapton cables
Ge array
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Gerda MC Geometry
New OO structure of geometry classes
Flexible executable set of commands to configure
geometry Number of columns and orientation,
segmentation of crystals, support
structure/shielding on/off, etc.
10 columns
segmented crystals (6x3)
standard geometry
Kevin Kröninger - MPI München
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Activity for the Gerda-specific part
Output
Class to create a ROOT TTree with all the
interesting information (energy deposition and
position of hits in Ge, Liquid N2, water, etc.)
ready to be interfaced with software for the
simulation of pulse shape ? Munich
Generic AIDA interface for other analysis tools
(e.g. HBOOK)
Physics studies in progress
background induced by cosmic ray muons and
neutrons
g background in electronics and support
segmentation effect for background and 0n2b signal
external g background and shielding requirements
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Two examples of macros
/MG/geometry/detector GerdaArray /MG/geometry/data
base false /MG/geometry/detector/crystal/truecoaxi
al 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/data
base 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
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Cosmic ray muons (Phase I)
Flux at Gran Sasso 1.1 m/m2 h (270 GeV)
60 70 events/kg y in H-M
Further reduced by anti-coincidence with other
Ge-crystals and with top (or Cerenkov) m-veto
Input energy spectrum
from Lipari and Stanev, Phys. Rev. D 44 (1991)
3543
Input angular spectrum
uniform in ?
first approximation
in ?
Energy (keV)
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Cosmic ray muons (Phase I)
9 Ge crystals for a total mass of 19 kg
threshold 50 keV
Sum spectrum
annihilation peak
3.93 years
149 counts in 1500 ? 2500 keV
21 counts in 2000 ? 2100 keV
Energy (MeV)
(1.5 ? 2.5 MeV) 210-3 counts/keV kg y
single-Ge
(410-3 counts/keV kg y in H-M simul.)
C. Doerr, NIM A 513 (2003) 596
Number of hit detectors
1.5 MeV
2.5 MeV
multi-hit 35.2
below threshold
Energy (MeV)
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Cosmic ray muons (Phase I)
Sum spectrum Ge anti-coincidence
(suppression factor 2)
3.93 years
Energy (MeV)
Threshold for plastic scintillator (top m-veto)
1 MeV
4 events/kg y
Energy (MeV)
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Cosmic ray muons (Phase I)
Counts in 1.5?2.5 MeV (3.93 years) Counts in 2.0?2.1 MeV (3.93 years) Background index (cts/keV kg y)
No cuts 149 21 (H-M34) 2-3 10-3
Ge anti-coincidence 46 6 6 10-4
Ge anti-coincidence Top m-veto (100 eff.) 6 1 lt 1.6 10-4 (95 CL)
Ge anti-coincidence Top m-veto (98 eff.) 8 1 lt 1.9 10-4 (95 CL)
Ge anti-coincidence Top m-veto (95 eff.) 9 1 lt 2.1 10-4 (95 CL)
Cerenkov m-veto (thr 5 MeV, 100 eff.) 0 0 lt 0.4 10-4 (95 CL)
Background substantially lower than previously
estimated
Instrumentation of water as a Cerenkov m-veto is
an open issue for the Collaboration (?
redundancy)
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Cosmic ray muons (Phase I)
Correlated issue production of short-lived
radioactive isotopes induced by the muon showers
delayed energy deposition
Most dangerous isotopes (g above Qbb)
Isotope Life time Gammas where rate
15C 2.44 s 5.2 MeV Water 1.8 c/year
13B 17.4 ms 3.68 MeV Water 0.6 c/year
16N 7.13 s 6.1, 7.1 MeV Water 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
Cross-check of isotope production with
independent codes (e.g. FLUKA) would be very
welcome
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Neutrons (Phase I)
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. g from np shielded by LN2
In H-M 3 10-3 cts/keV kg y (without water
shielding) !
C. Doerr, NIM A 513 (2003) 596
To do next validation of the simulation with
data and cross-check with independent codes
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CNGS muons
Flux at Gran Sasso 0.86 m/m2 d (ltEgt 15 GeV)
LVD Collaboration, hep-ex/0304018
30 times smaller than cosmic ray flux and softer
spectrum
Top m-veto uneffective only Ge-anticoin. and
water m-veto
Not evaluated yet in detail
Rough estimate (15-GeV m)
LVD Collaboration, hep-ex/0304018
Not a critical issue
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Signal and background studies
Example 60Co
Photons carry energy to more than one
crystal/segment (multiple-site)
Cut on the number of hit crystals or segments
reduces 60Co events to 19 (6)
19
6
Kevin Kröninger - MPI München
Hit crystals
Hit segments
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Signal and background studies
Background suppression efficiency
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 100k
60Co (crystal) 0.19 3.0 10-4 0.06 2.6 10-5 1 M
60Co (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 M
208Tl (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 M
210Pb (crystal) 1 0 9.9 10-3 0 10k
Segmentation 6 (phi) x 3 (z) Threshold 10 keV
Energy window Qbb 5 keV Pulse shape
analysis and pattern recognition not included
Kevin Kröninger - MPI München
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MPI Munich MC activities
Kevin Kröninger - MPI München
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Other background calculations
Background from inner tank envelope
Cu 25 10-6 Bq/kg of 232Th
Fe 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
A. Klimenko INR, ITEP, Dubna, MPIK
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Other background calculations
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
To go lower than 10-5 c/keV kg y
A. Klimenko INR, ITEP, Dubna, MPIK
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Conclusions
MC package MaGe ready for Gerda Majorana groups
?
Downloadable from CVS, flexible and runnable by
macro
Structure complete and ready for physics studies
?
Preliminary results of m-induced and n background
?
Top m-veto enough for background of a few 10-4
c/kg keV y
Neutrons, CNGS and isotopes production presumably
not critical
10-4 c/kg keV achievable with present shielding,
10-5 needs LAr
3-month activity and still a lot of work to do in
the future...
...Well begun is half done !