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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