lpc jet/met meeting 1/12/2006l. perera1 jet/calorimeter cluster energy corrections – status goal:...
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LPC Jet/Met meeting 1/12/2006 L. Perera 1
Jet/Calorimeter Cluster Energy Corrections – Status
Goal: To improve the individual jet energy determination based on measured cluster structure.
• Response of the ECAL is different for EM particles (photons/ electrons) and hadrons.
• Energy determination will improve if we can separate EM particles and hadrons and apply separate corrections.
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Classification
– EM particles: Energy in ECAL should be okay as it is calibrated for electrons.
– Non-interaction hadrons: All energy (except MIP), in HCAL and it is calibrated for hadrons (charged pions).
– Interacting hadrons: deposit some energy in ECAL- needs to be corrected.
• Challenge: Overlapping particles (many particles going through the same cell)
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Procedure
• Cluster cells in the ECAL and HCAL
• Match ECAL and HCAL clusters and find the fraction of ECAL energy ( f ) in the matched clusters :
f= E/(E+H)• Classification:
• 0.95 < f < 1 EM particle
• 0.1 < f < 0.95 Interacting hadron
• 0 < f < 0.1 non-interacting (MIP) hadrion
• energy in ECAL+ HCAL and
ECAL energy > MIP interacting hadron also works
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Analysis
• Using a 120 GeV Z´ q q (u,d,s) MC sample ( no noise or pile-up)
• Analysis done in ExRootAnalys
• Currently considering ECAL /HCAL barrel
• A simple algorithm to cluster ECAL and HCAL cells separately in eta-phi:
– Seed cell ET>0.5 GeV
– Add neighboring (3x3) cells (dR< 0.03 for ECAL, dR<0.15 for HCAL)
– Mark out used cells
• Match ECAL and HCAL clusters (dR <0.15)
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number of GenJets pT >10GEV GenJet
Number of RecJets RecJet
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jet energy in charged hadrons (K p)
1 2
Energy in all charged hadrons within a cone of 0.5 around GEnJet axis (as a fraction of GenJet energy)
• At the IP• After propagating them to HCAL in 4T.
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RecJet GenJet comparison
RecJet has 60% of the energy Dijet mass form RecJet is
70% of from GenJet
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ECAL/HCAL Cluster matching (R<0.15)
within a jet
outside the jets
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Energy distribution in clusters
• 35% of jet energy is in uniquely matched clusters • One ECAL cluster matching one HCAL cluster• Easier to do energy correction
• 30 of jet energy is in clusters which have multiple matches• Energy correction is not straightforward
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Cluster Energy Correction
• estimate the energy correction from a simple fit to test beam data (for now)
• Use ECAL+HCAL energy of unique match clusters as particle energy
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energy correction
Jet energy
Correction: 4.5 % increase in jet energy
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Improvement in DiJet mass
• Mean of dijet mass increased by 4.5%
• Width of the dijet mass decreased by 6.5%
• Small but in the right direction !
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• ECAL thresholds are too high (ECAL noise 40 MeV)
• Significance of the improvement of resolution is less when ECAL thresholds are lowerd (100 MeV)
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dR pion photons within Jet
dR pi/photon dR pion Jet axisdR pi/photondR pi/photon
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DiJet mass after propagating
Particles to ECALpT of pions within Jet
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After rescaling pion energies
by distribution in page 11Dijet mass from RecJets
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Charged hadronsphotons
Neutral
Hadrons (n, K_L) Contribution to Jet Energy
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Pion and ECAL cluster
matching
photon and ECAL cluster
matching
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There seems to be a non linearity in ECAL at low energies
ECAL cluster energy/photon energyPhoton energy GeV