Photon reconstruction Photon reconstruction and calorimeter softwareand calorimeter software

Mikhail ProkudinMikhail Prokudin

OutlineOutline

►Calorimeter software developmentCalorimeter software development photon reconstructionphoton reconstruction

►cluster findercluster finder►simple reconstructionsimple reconstruction

UrQMD eventsUrQMD events

matchingmatching Calorimeter drawing toolsCalorimeter drawing tools

►Cluster fittingCluster fitting requirementsrequirements

►ConclusionsConclusions►Next stepsNext steps

Photon reco. RequirementsPhoton reco. Requirements

►Robust reconstruction of single Robust reconstruction of single photonsphotons

►Two close photons case:Two close photons case: robust reconstruction of parameters in robust reconstruction of parameters in

case two separate maximumscase two separate maximums separation one/two photons in case of one separation one/two photons in case of one

maximummaximum

►Fast!Fast!

Cluster finderCluster finderCluster formationCluster formation

► Remove maximums near Remove maximums near charged trackscharged tracks real trackingreal tracking

► Precluster:Precluster: formed near local formed near local

maximummaximum► cut on maximum energycut on maximum energy

find maximum 2x2 matrix find maximum 2x2 matrix near maximumnear maximum

add a neighbor to local add a neighbor to local maximum cell with minimal maximum cell with minimal energy depositionenergy deposition► to add inromationto add inromation

check precluster energycheck precluster energy► >0.5GeV>0.5GeV

► Cluster: group of Cluster: group of preclusters with common preclusters with common cellscells

4870 Central UrQMD Au+Au 25GeV

CbmEcalClusterFinderV1. At SVN

RequirementsRequirements► Clusters should be largeClusters should be large

information for unfoldinginformation for unfolding► Clusters should be smallClusters should be small

hadrons backgroundhadrons background

Cluster finder performanceCluster finder performance

BenchmarkBenchmark► 2x1 GeV photons2x1 GeV photons► 3x3 cm cells3x3 cm cells

inner calorimeter inner calorimeter regionregion

► 2-102-10° angle° angle geometry of inner geometry of inner

calorimeter calorimeter regionregion

Simple reconstructionSimple reconstruction

► Energy:Energy: calibrationcalibration

►only energy in only energy in scintillator is visiblescintillator is visible

► Position:Position: S-curvesS-curves

► χχ22 calculation for calculation for reconstructed photonreconstructed photon

CbmEcalRecoSlow. At SVN

UrQMD events with simple UrQMD events with simple recoreco

Subtraction of mixed events is necessarily!

Invariant mass spectra

True

Mixed

Gamma spectra

Simple reconstructionSimple reconstruction

►Robust reconstruction of single Robust reconstruction of single photonsphotons

►Two close photons case:Two close photons case:►occupancyoccupancy

robust reconstruction of parameters in robust reconstruction of parameters in case two separate maximumscase two separate maximums

separation one/two photons in case of one separation one/two photons in case of one maximummaximum

►Fast!Fast!►Need more complex reconstruction!Need more complex reconstruction!

MatchingMatching

►Why?Why? check origin of clustercheck origin of cluster

►neutron clusters neutron clusters

physics processesphysics processes► ππ00 and and ηη decays decays►prompt photonsprompt photons►……

►Most simple method Most simple method at momentat moment

► Energy deposition in Energy deposition in the cluster > 70% of the cluster > 70% of cluster energycluster energy γγ/e is secondary also /e is secondary also

look for motherlook for mother►showers started before showers started before

the calorimeter treated the calorimeter treated correctlycorrectly

loss clusters with more loss clusters with more than one maximumsthan one maximums

CbmEcalMatching. At SVN

Matching. Usage exampleMatching. Usage example

π0

η

π0 born after IP (conversion)

Calorimeter drawing toolCalorimeter drawing tool

►DrawDraw calorimeter structurecalorimeter structure energy deposition in calorimeterenergy deposition in calorimeter reconstructed tracksreconstructed tracks

►and energiesand energies reconstructed photonsreconstructed photons

►energiesenergies►and matched MC particlesand matched MC particles

clustersclusters► found approximation qualityfound approximation quality►and and χχ2 2 of clusterof cluster

MC tracksMC tracks► type (photon, neutron …)type (photon, neutron …)►energyenergy

►……and all at one picture!and all at one picture!

Calorimeter drawing toolsCalorimeter drawing tools► PhotonsPhotons

MCMC ReconstructedReconstructed

► **

► (Anti) neutrons(Anti) neutrons► Charged tracksCharged tracks

ReconstructedReconstructed► **

MCMC

► SecondarySecondary PhotonsPhotons ElectronsElectrons

CbmEcalQualityCheck. At SVN

Fitter requirementsFitter requirements

► Robust reconstruction Robust reconstruction of single photonsof single photons

► Two close photons Two close photons case:case: robust reconstruction of robust reconstruction of

parameters in case two parameters in case two separate maximumsseparate maximums

separation one/two separation one/two photons in case of one photons in case of one maximummaximum► χχ22 criteria criteria►all analyzed approaches all analyzed approaches

have failed to have failed to reconstruct photons reconstruct photons energy/position correctlyenergy/position correctly

► χχ22 shape should not shape should not depend on photon’s depend on photon’s energyenergy same value for same value for

efficiency cutefficiency cut► separation power of separation power of

one/two photons in one/two photons in case of one maximum case of one maximum as a criteriaas a criteria example: with 95% example: with 95%

efficiency for clusters efficiency for clusters formed by single formed by single photonphoton

Realization of fitterRealization of fitter► CbmEcalRecoSlow CbmEcalRecoSlow

►current version at SVNcurrent version at SVN

no so slow actually!no so slow actually!►40 sec per UrQMD event40 sec per UrQMD event

first approximationfirst approximation►CbmEcalRecoSimpleCbmEcalRecoSimple

χχ22 minimizationminimization

►minimizerminimizer TFitterMinuitTFitterMinuit

►shower shape (Eshower shape (Epredpred)) shower libshower lib

►σσ22 formula formula

cells cell

predcell

meascell EE

2

22 )(

Shower widthShower width

► Energy deposition in Energy deposition in cluster cells are not cluster cells are not independentindependent storing of RMS in shower storing of RMS in shower

library uselesslibrary useless► Analytical formulaAnalytical formula

with correlationwith correlation► ALICEALICE

σσ22=c=c00(E(Emeasmeas+c+c11))► no correlations!no correlations!

► PHENIXPHENIX σσ22=c=c00(E(Emeasmeas(1-E(1-Emeasmeas//

EEclustercluster))(1+k (1+k sin sin44θθEEclustercluster))+c+c11))► correlations are incorrelations are in

Angle dependenceAngle dependence► shower libraryshower library

h4 h5

h4

h5

σσ22 formula formula► σσ22 formula declared in formula declared in

configuration fileconfiguration file► … … and parameters tooand parameters too

for easy changefor easy change► without recompilationwithout recompilation

different formulas for different different formulas for different cell typescell types► … … to maintain commonnessto maintain commonness

► Sum of photon’s energies Sum of photon’s energies fixed to energy of clusterfixed to energy of cluster a switch in configuration filea switch in configuration file

► Parameters space is hugeParameters space is huge σσ22 formula formula

► best cbest cnn could be computed if could be computed if σσ22 formula is fixedformula is fixed

also parameters of cluster also parameters of cluster finderfinder

# Number of cells types for reconstruction# Number of cells types for reconstructiontypestypes=4=4## Number of constants for each typeNumber of constants for each typeconstsconsts=2=2# Use Ecluster, Emeas and Epred for measured cluster# Use Ecluster, Emeas and Epred for measured cluster e energy, nergy,

measuredmeasuredcell energy and predicted cellcell energy and predicted cell energy respectivelyenergy respectivelyc0_1c0_1=0.008=0.008c1_1c1_1=0.0016666=0.0016666c0_2c0_2=0.008=0.008c1_2c1_2=0.00345=0.00345c0_3c0_3=-1111=-1111c1_3c1_3=-1111=-1111c0_4c0_4=0.008=0.008c1_4c1_4=0.0043333=0.0043333sigma_1sigma_1=c1*(Emeas*(1-Emeas/Ecluster)+c0)=c1*(Emeas*(1-Emeas/Ecluster)+c0)sigma_2sigma_2=c1*(Emeas*(1-Emeas/Ecluster)+c0)=c1*(Emeas*(1-Emeas/Ecluster)+c0)sigma_3sigma_3=-1111=-1111sigma_4sigma_4=c1*(Emeas*(1-Emeas/Ecluster)+c0)=c1*(Emeas*(1-Emeas/Ecluster)+c0)# if chi2 for cluster is less than no fitting# if chi2 for cluster is less than no fittingchi2thchi2th=-1111=-1111# Max iterations in fitting process# Max iterations in fitting processmaxiterationsmaxiterations=1000=1000# Steps for calculation of gradients# Steps for calculation of gradientsestepestep=0.0001=0.0001cstepcstep=0.0005=0.0005# Fix sum of energies of cluster particles to energy of cluster# Fix sum of energies of cluster particles to energy of clusterfixclusterenergyfixclusterenergy=1=1# # Cluster finder stuff ## # Cluster finder stuff ## Maximums belong to charged tracks should excluded?# Maximums belong to charged tracks should excluded?removechargedremovecharged=1=1# Minimum precluster energy# Minimum precluster energyminclustereminclustere=0.3=0.3# Minimum energy of precluster maximum# Minimum energy of precluster maximumminmaxeminmaxe=0.2=0.2# An algorithm for preclustering: 0 --- default, 1 --- PHENIX like, # 2 # An algorithm for preclustering: 0 --- default, 1 --- PHENIX like, # 2

--- --- ALICE like, 3 --- default, but remove low energy cellsALICE like, 3 --- default, but remove low energy cellspreclusteralgopreclusteralgo=0=0# Minimum cell energy# Minimum cell energymincellemincelle=0.020=0.020# Minimum size of precluster# Minimum size of preclusterminsizeminsize=4=4# Attach to cluster nearby cells with Edep>fMinCellE# Attach to cluster nearby cells with Edep>fMinCellEattachcellsattachcells=0.1 =0.1

Example of configuration file

Photon reconstruction. Merged Photon reconstruction. Merged photonsphotons

Simple reconstruction

Cluster fitting

Fitting of clusters with two maximums allows us disentangle photons! σ2 formula and parameters does not require much tuning!

Fitter requirementsFitter requirements

► Robust reconstruction Robust reconstruction of single photonsof single photons

► Two close photons Two close photons case:case: robust reconstruction of robust reconstruction of

parameters in case two parameters in case two separate maximumsseparate maximums

separation one/two separation one/two photons in case of one photons in case of one maximummaximum► χχ22 criteria criteria►all analyzed approaches all analyzed approaches

have failed to have failed to reconstruct photons reconstruct photons energy/position correctlyenergy/position correctly

► χχ22 shape should not shape should not depend on photon’s depend on photon’s energyenergy same value for same value for

efficiency cutefficiency cut► separation power of separation power of

one/two photons in one/two photons in case of one maximum case of one maximum as a criteriaas a criteria example: with 95% example: with 95%

efficiency for clusters efficiency for clusters formed by single formed by single photonphoton

χχ22 distributions. Single distributions. Single photonsphotons

95%

1 G

eV

95%

4 G

eV

σ2=c0(Emeas(1-Emeas/Ecluster)+c1)

c1=0.0005

95%

1 G

eV

95%

4 G

eV

σ2=c0(Emeas+c1)

Shape of χ2 for each energy looks Ok, but cut with 95% efficiency has different value!

Need a different σ2 formula!

Rejection power. Inner regionRejection power. Inner region

σ2=c0(Emeas(1-Emeas/Ecluster)+c1)σ2=c0(Emeas+c1)

Rejection power. Outer Rejection power. Outer regionregion

σ2=c0(Emeas(1-Emeas/Ecluster)+c1)σ2=c0(Emeas+c1)

Reconstruction in outer region is most sensible to σ2 formula!

ConclusionsConclusions

►Calorimeter software development in Calorimeter software development in progressprogress Cluster finder: CbmEcalClusterFinderV1Cluster finder: CbmEcalClusterFinderV1 Reconstruction: CbmEcalRecoSimpleReconstruction: CbmEcalRecoSimple

►and CbmEcalRecoSlowand CbmEcalRecoSlow

Matching: CbmEcalMatchingMatching: CbmEcalMatching Quality check: CbmEcalQualityCheckQuality check: CbmEcalQualityCheck

ConclusionsConclusions

► Photons reconstructionPhotons reconstruction simple procedures are ready to usesimple procedures are ready to use more complicated proceduresmore complicated procedures

►not too slownot too slow►fit clusters with more than one maximumfit clusters with more than one maximum►still have limited usabilitystill have limited usability

σσ22 formula formula► bad cluster rejectionbad cluster rejection► not trivialnot trivial

► All presented calculations done using 2 All presented calculations done using 2 computerscomputers

UrQMD transport, reconstruction, etc.UrQMD transport, reconstruction, etc.►3.0 GHz Core 2 Duo3.0 GHz Core 2 Duo►2.0 GHz Core 2 Duo (My laptop)2.0 GHz Core 2 Duo (My laptop)

Next stepsNext steps►Reconstruction tuningReconstruction tuning►Detector optimizationDetector optimization

geometrygeometry segmentationsegmentation

►Detailed sensitivity studies for process Detailed sensitivity studies for process with photonswith photons ππ00, , ηη,, χχc …c …

►e/e/ππ separation with real tracking separation with real tracking►Detailed detector geometryDetailed detector geometry

construction detailsconstruction details light collection efficiencylight collection efficiency