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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EB cluster

HB cluster+ pion + proton + photon

Jet

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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 from genJetsZ’ mass 3

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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

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Most of photons in the jet are in this region

Cause under investigation: seems to be in digitization