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Lead glass simulations. Collaboration Meeting XXI. Eliane Epple, TU Munich Kirill Lapidus, INR Moscow. March 2010 GSI. Outline. Cherenkov light tracing Lookup table Physical application. HADES EMC. Hardware: Cherenkov light EM calorimeter 142 * 6 lead glass blocks Physics: - PowerPoint PPT Presentation
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Lead glass simulations
Eliane Epple, TU MunichKirill Lapidus, INR Moscow
Collaboration Meeting XXI
March 2010GSI
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1. Cherenkov light tracing
2. Lookup table
3. Physical application
Outline
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HADES EMC
Hardware:
Cherenkov light EM calorimeter
142 * 6 lead glass blocks
Physics:
e/h separation at high momentum
π0, η reconstruction
Sesimbra meeting status:
EMC is implemented in HGeant
First simulations were started
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The challenge
Realistic studies require simulation of the electron/gamma and
hadron response Hadron response is complex and can’t be simulated simply via
energy deposit in the module Need for proper Cherenkov light tracing Previously obtained results are not satisfactory:
8.7% / sqrt(E)~5% / sqrt(E)
γ in simulation: γ in reality:
old simulationsOpal results
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The solution
Use the Light Transport code written by Mikhail Prokudin, ITEP
(CBM ECal)
Standalone program outside HGeant
Tuning of the parameters
Light attenuation length in the lead glass
PMT geometry and quantum efficiency
Reflective properties of the lead glass wrapping
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Tuning results
γ 580 MeV cosmics
Experimental reference for the tuning
Energy resolution for γ
Same response shown by γ 580 MeV and cosmics
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Single lead glass module response to different particle species
eγπpn
Cherenkov
thresholds
Pπ = 98 MeV/c
Pp = 700 MeV/c
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e/pi separation
at 95% electron efficiency
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Making things faster:Lookup table instead of the light tracing
• Light tracing is very slow: 1.2 s/event for 1 GeV γ
• Prepare a lookup table for the probability of the p. e. production
• 4D lookup table: t = (x2 + y2)1/2, z, θ, energy
• Make use of THnSparse class as a container
• Binning: 30 * 30 * 180 * 30 = 5·106, populated by 3·109 trial photons
• 2D projections: (z, t) and (energy, z)
glass pmt
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Testing the approach: Full tracing vs Lookup table
Tracing
Lookup table
pion, p = 0.3 GeV/c neutron, p = 2 GeV/c
gamma, p = 0.1 GeV/c gamma, p = 1 GeV/c
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Testing the approach: Full tracing vs Lookup table
Tracing
Lookup table
gamma, p = 0.1 GeV/c gamma, p = 1 GeV/c
In general Lookup table works well
A bit more effort is needed for correct gamma width
Increase the bin numbers/statistics in the table
4%
4.5%
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What is the profit from the Lookup table?
γ 1 GeV CC 8 AGeV AuAu 1.25 AGeV
no EMC — 0.2 0.7
Tracing 1.2 4.9 10.2
Lookup < 0.1 0.6 1.7
Computational time, seconds per event
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Application:light system at high energies
Pluto cocktail for C + C at 8 AGeV
Mp = Mn = 8.9
Mπ+ = Mπ– = Mπ0 = 1.86
Mη = 0.093
Full HADES geometry in front of EMC
Simple reconstruction software was written
Digitization Clustering Pair makingRPC matching
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Diphoton invariant mass in CC at 8 AGeV
Employ only calorimeter data
Overwhelming background
from hadron misidentification
CC 8 AGeV
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Diphoton invariant mass in CC at 8 AGeV
Cluster matching with RPC hits to reject charged hadrons
Significant background suppression
Clear π0-peak
η is not visible, more statistics is mandatory
CC 8 AGeV
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Diphoton invariant mass in CC at 8 AGeV
Cluster matching with RPC hits to reject charged hadrons
Significant background suppression
Clear π0-peak
η is not visible, more statistics is mandatory
CC 8 AGeV
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Summary
1. New approach to Cherenkov light tracing
2. Reasonable response both to gamma and hadrons
3. Working Lookup table
4. Simulation software is complete
5. First realistic diphoton spectra for the light system
at high energies (π0 reconstruction is shown)
Outlook:
— Further development of the reconstruction software
— η reconstruction
— Attack heavy systems
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Additional slides
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Integral Lookup table test
TracingLookup table
Reconstructed diphoton invariant mass for
CC 8 AGeV 10k events
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Calibrations and corrections for the simulation(to be done)
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Correlation of energy deposition and Cherenkov photon yield
N_pe = 1785 * (E/GeV)
OPAL paper NIM A290 76-94N_pe = 1800 * (E/GeV)
~ 10K Cherenkov photons tracked in each module
Limited energy range was investigated due to extreme hit multiplicities
Dep
osi
ted
en
erg
y in
mo
du
le, M
eV
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Study of response to single photons:energy deposition in EMC
— whole EMC— 3x3 cluster
▼ whole EMC▼ 3x3 cluster
Deposited energy for 1 GeV photon Energy dependence
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EMI 9903B quantum efficiency
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Lead glassinteraction lengths
Lead glass
Quantity Value Units Value Units
<Z/A> 0.42101
Density 6.22 g cm-3
Nuclear collision length 95.9 g cm-2 15.42 cm
Nuclear interaction length 158.0 g cm-2 25.40 cm
Pion collision length 122.2 g cm-2 19.64 cm
Pion interaction length 190.0 g cm-2 30.55 cm
Radiation length 7.87 g cm-2 1.265 cm
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EMC geometry
Top view of one sector
142 identical modules
Technical drawing by Polish group
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Position as present Shower
phi (0, 2pi) theta (18, 45)L = 240 cm
d x d = 9.2 x 9.2 cm2
sigma_theta = d/L/sqrt(12)sigma_phi = sigma_theta
sigma_E/E = 5% / sqrt(E/GeV)
EMC geometry
C+C @ 8 AGeV10M events
Pluto
Multiplicities (min. bias)M_pi0 = 1.86M_eta = 0.093
Diphoton decays only
Simple simulation:geometry and Pluto input
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S/B = 10%S/B = 11%
sigma_eta = 25 MeVsigma_eta = 25 MeV
pγ > 300 MeV pγ > 500 MeV
Diphoton invariant mass
EMC acceptance spatial & energy smearing of photon
M, GeV M, GeV