Jet/Calorimeter Cluster Energy Corrections

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.

2
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)

3
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/(EH)
• Classification
• 0.95 lt f lt 1 EM particle
• 0.1 lt f lt 0.95 Interacting hadron
• 0 lt f lt 0.1 non-interacting (MIP)
  hadrion
• energy in ECAL HCAL and
• ECAL energy gt MIP interacting hadron also
  works

4
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 ETgt0.5 GeV
• Add neighboring (3x3) cells (dRlt 0.03 for ECAL,
  dRlt0.15 for HCAL)
• Mark out used cells
• Match ECAL and HCAL clusters (dR lt0.15)

5
EB cluster
pion proton photon
HB cluster
Jet
6
number of GenJets pT gt10GEV
GenJet h
h
Number of RecJets
RecJet h
7
jet energy in charged hadrons (p 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.

8
RecJet GenJet comparison
RecJet has 60 of the energy
Dijet mass form RecJet is 70 of from GenJet

9
ECAL/HCAL Cluster matching (DRlt0.15)
within a jet
outside the jets
10
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

11
Cluster Energy Correction

• estimate the energy correction from a simple fit
  to test beam data (for now)
• Use ECALHCAL energy of unique match clusters as
  particle energy

12
energy correction Jet energy
Correction 4.5 increase in jet energy
13
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 !
  

14

• ECAL thresholds are too high (ECAL noise 40 MeV)
• Significance of the improvement of resolution is
  less when ECAL thresholds are lowerd (100 MeV)

15
dR pion Jet axis
dR pi/photon
dR pi/photon
dR pi/photon
dR pion photons within Jet
16
Dijet mass from genJets
Z mass 3
17
DiJet mass after propagating Particles to ECAL
pT of pions within Jet
18
After rescaling pion energies by distribution in
page 11
Dijet mass from RecJets
19
Charged hadrons
photons
Neutral Hadrons (n, K_L)
Contribution to Jet Energy
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Df
Df
Dh
Dh
photon and ECAL cluster matching
Pion and ECAL cluster matching
21
Photon energy GeV
ECAL cluster energy/photon energy
There seems to be a non linearity in ECAL at
low energies
22
Most of photons in the jet are in this region

Cause under investigation seems to be in
digitization