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Jet reconstruction with neutrals from full simulation

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New reader to mix HIJING and PYTHIA. Based on UA1 cone finder algorithm ... 2 algo comparison in JETAN. 100 GeV Gamma/Jets simulated. Jets in EMCal acceptance ... – PowerPoint PPT presentation

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Title: Jet reconstruction with neutrals from full simulation


1
Jet reconstruction with neutralsfrom full
simulation
Magali Estienne IPHC Strasbourg
EMCal Meeting - Frascati March 13. 2007
2
The actual jet finder package JETAN
More information on JETAN see M. L. Noriegas
talk in Bologna June 2006
READER
JETS
JET FINDER
  • ESDs (TPC/ITS)
  • Pythia events
  • New reader to mix HIJING and PYTHIA

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3
Role of EMCal in jet reconstruction
Case of a monochromatic 100 GeV jet generated by
PYTHIA Cone size for reconstruction Rc 0.4
In the EMCal acceptance
  • - Improves the resolution for jet reconstruction
  • Trigger jets

Monochromatic 100 GeV jets
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Physical information from EMCal
f
h
  • AIM merge TPC/ITS and EMCal information
  • In TPC/ITS information from particle tracks
    (px, py, pz, E)
  • gt Previously filled in a fMomentumArray
  • In EMCAL information from digits or clusters
    (eta, phi, Eintegrated)
  • gtTPC and EMCAL information filled in a SAME
    ARRAY fUnitArray

- Limited to EMCal acceptance - Extended to work
on all the TPC acceptance
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The jet finder in practice
  • Previously, the philosophy of the code was the
    following
  • for each new event in the system (ITS/TPC), a
    fMomentumArray TLorentzVector object was filled
    with px,py,pz and E
  • all the track information per event was then
    stored in a ?-? grid which was a Lego plot
    TH2D object
  • then, the information was dumped from the histo
    into cells. These cells were then given to the
    UA1 jet-finder
  • To merge the (ITS/TPC) and EMCal information,
    creation on a new TObject called fUnitArray which
    is directly filled with all the particle
    information per event. Should avoid
  • 1 to use an intermediate
    fMomentumArray
  • 2 to use an intermediate histogram
  • 3 (maybe) to loose information
    because of possible detector dead-zones
  • Given the particle ID in a Grid, ?, Dh, ?, Df, E,
    flags, px, py, pz can be stored for all
    particles in both TPC and EMCal per event
  • Main modifications/additions
  • In the reader
  • 1 new class to set the desired grids only one
    time at the beginning AliJetGrid
  • new classes of TTask type to read information
    from tracks or digits or clusters
  • AliJetFillUnitArrayTracks, AliJetFillUnitArrayEMC
    ALDigits, AliJetFillUnitArrayEMCALClusters
  • In the finder
  • Two technics kept
  • 1 class added to use Selector structure
    AliJetSelector Analysis framework

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Class relationships
AliJetHadronCorrection
AliJetUnitArray
AliJetGrid
AliJetSelector
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7
Set an initial grid
New/modified classes (I)
TPC - EMCal
  • AliJetGrid
  • 2 types of grid can be setted to deal with
    different binnings
  • extended to include detector dead-zones
  • Functions included

EMCal
// Getter Int_t GetMatrixIndex(Int_t iphi, Int_t
ieta) Int_t GetIndexIFromPhi(Double_t
phi) Int_t GetIndexJFromEta(Double_t eta) Int_t
GetIndex(Double_t phi, Double_t eta) Void
GetIJFromIndex(Int_t index,) Void
GetEtaPhiFromIndex(Int_t index, ) Int_t
GetNEntries() Int_t GetIndexFromEtaPhi() //
Setter
Binning given by the function
TowerIndexFromEtaPhi() or by an other grid
Binning given by the grid initially declared
  • In progress fill two full grids and then think
    how to merge them
  • Effect of different cell sizes on finder

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8
A fUnitArray object
New/modified classes (II)
  • AliJetUnitArray (AliJetFinderTypes)
  • - All the quantities stored from different
    detectors are in the same units
  • Its size number of EMCAL towers TPC bins
  • (gt Recently extended in order to work on
    all detectors)
  • The following quantities can be setted in or
    taken from the Array
  • - Digit(/Cluster)/Track h
  • - Digit(/Cluster)/Track f
  • - Digit(/Cluster)/Track Energy
  • - Digit/Cluster/Track ID
  • - Detector flag, Cut flag, In/Out jet flag
  • - Bin Size Dh, Df
  • - Track label
  • -
  • With the functions
  • SetUnitEta(), SetUnitPhi(), SetUnitEnergy(), etc.
  • GetUnitEta(), GetUnitPhi(), GetUnitEnergy(), etc.

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For hadron correction
New/modified classes (III)
  • In order to avoid double counting between TPC
    tracks selected and EMCAL digits or clusters gt a
    hadron correction has to be applied.
  • The following classes have been added
  • AliJetHadronCorrection, AliJetHadronCorrectionv0
    and AliJetHadronCorrectionv1

Study with simulations in progress -
Simulation of p/- and p/p in precise (eta,phi)
locations - Eta/Energy mapping and
parametrisation of the detector phase space -
After track matching, extract correction factor
to be applied - Can be improved with PID
- Try other technics
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10
Fill charged neutral information
New/modified classes (IV)
AliJetESDReader
  • Flag added to choose the detector configuration
  • 2 alternatives
  • switch in the function FillMomentumArray() which
    calls the functions FillUnitArray directly
    included in the class AliJetESDReader
  • switch in the function FillMomentumArray() which
    calls objects of TTask type where the object
    fUnitArray is filled



// Fill information from TPC tracks from
ESDs void FillMomentumArray(Int_t event) //
Fill information from TPC and EMCAL from
ESDs void FillUnitArrayFromTPCTracks(Int_t
event) void FillUnitArrayFromEMCALHits(Int_t
event) void FillUnitArrayFromEMCALDigits(Int_t
event) void FillUnitArrayFromEMCALClusters(Int_t
event) void InitUnitArray() // Correction of
hadronic energy virtual void SetHadronCorrection(I
nt_t flag) virtual void SetHadronCorrector(AliEMC
ALHadronCorrectionv1 corr) // For EMCAL digit
calibration Virtual Float_t Calibrate(Int_t amp,
Int_t cellId) Void Exec(Option_t option)
New classes
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11
Other comments
New/modified classes (V)
AliUA1JetFinder
// Find jets functions void FindJetsTPC() //
Previous FindJets() which is using the
fMomentumArray //
filled to fill then dump a fLego plot.
// It has to be called when
looking for jets in TPC/ITS
// acceptance void FindJets() // New
function which is directly using a fUnitArray to
give // the jet finder
code the desired values
other minor changes in classes
  • For the moment, fMomentumArray kept but I will
    not use it anymore to fill the fUnitArray object
    to gain time
  • fUnitArray technics takes more time than
    fMomentumArray but in PbPb it should diminish
  • fUnitArray more convenient to store information
    flags, eta, phi, P, E, in/out jet
  • AliJetSelector structure implemented as well as
    the Andreis Analysis framework.

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12
2 algo comparison in JETAN
100 GeV Gamma/Jets simulated Jets in EMCal
acceptance Pythia pp evts _at_ 5.5TeV Jet finder
parameters Pt cut 2. GeV R 0.4 MinCellEt
0. Et seed 4. GeV MinJetEt 14 GeV Fake jets
removed
Good agreement
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W/o and W EMCal
- Gamma-jet simulation - Jets in EMCal
acceptance - Fake jets removed
TPC TPCEMCal
Mean energy increases compared to TPC alone BUT
RMS increases !!!
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Resolution still too bad
Entries
Entries
Energy (GeV)
Energy (GeV)
Emean 64.2/-0.6 Resolution 47
Emean 67.8/-1.1 Resolution 42
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15
Reasons for bad resolution and mean energy
I am trying to identify possible sources of
problem
  • Related to my code and the way I fill the
    fUnitArray
  • Step by step check of the code from the digit in
    Reco to the ESDs
  • Related to the way digits are stored in ESDs
    there was a problem (digit ID higher than the
    number of digits in EMCal). Aleksei has worked on
    it.
  • AliRoot HEAD installed and production of 10000
    Gamma-Jets (100GeV) events and 10000 100 GeV jets
    events.
  • Bug fixed but worth resolution than before !!!
  • Related to hadron correction
  • Should have minor effect
  • Related to the physics itself ?
  • Strategy start to understand what is going on
    on simple cases
  • gt Simulation of 100 GeV p0 in EMCal acceptance
  • gt Simulation of 100 GeV g in EMCal acceptance

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16
100 GeV g in EMCal acceptance
Too high energy Counted twice ?
TPCEMCal
Simulation of 2500 events with 1 g emitted inside
the EMCal acceptance Reconstruction of 2370 gs
No more double counts
EMCal only
Tracks responsible for double energy count
TPC only
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TPCEMCal EMCal
Small differences !
Charged electron from double decay or conversion
? Double count of electrons ?
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Remove (true) matches
  • True match if track label cluster primary
    index
  • Remove matches by looking at true matches
  • It removes high pt  jets  reconstructed

All particles
Matches removed
  • How to proceed in true life ?
  • 1 Do track matching
  • Test of Alberto's track matching code
  • 2 Identify electron with p/E cut g
    invariant mass ?
  • 3 Remove their double energy contribution

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My to Do list !
  • Questions to be solved
  • Improve the resolution and the mean jet energy
    reconstructed
  • - Check the code step by step
  • - Identify problems with simple event cases
  • - Cut on electrons
  • Hadron correction to be correctly done with
    the new EMCAL geometry
  • gt in progress but need to obtain first good
    resolution
  • Make the code independent on AliEMCALGeometry
  • gt class AliJetGeoDummy will be implemented if
    possible using TGeoManager.
  • Run on the coming Jet-Jet, Gamma-Jet productions

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Backup
20
21
The cone algorithm
F
1. Estimate ETbkgd per cell from all cells 2.
Sort cells in decreasing ET 3. Until change in
Ebkgd between 2 iterations is smaller than a set
threshold - Clear the jet list and flag
cells outside a jet - jet-finding loop for
each cell, from the highest cell energy. If
Ei-Ebkgd gt Eseed and if the cell is not flagged
as being inside a jet
From Mercedes Lopez-Noriega
  • Set the jet-cone centroid to be the center of
    the jet seed cell
  • Using cells with ?(hi-h)2(fi-f)2 lt Rc of the
    initial centroid, calculate the energy weighted
    centroid
  • Repeat until difference between iterations
    shifts less than one cell.
  • Store centroid as jet candidate.
  • Recalculate background energy using information
    from cells outside jets.

?
  • Parameters
  • - Mininum pT for tracks or energy for digits
  • - cone radius Rc, Eminseed for the seed, Eminjet
    for a jet
  • Input list of cells in an h-f grid sorted in
    decreasing cell energy Ei

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22
Background estimation methods in the cone
algorithm
F
Statistical method an average background energy
is obtained from N jet-free events Cone method
the energy in all grid cells outside the jet cone
is added and scaled with the inside/outside cone
area ratio Ratio method ratio of the average
energy in the grid with a pT-cut to the one
without a pT-cut. Event by event, the background
energy is estimated by multiplying the average
background energy of the event without pT-cut
with the calculated ratio
Cone area
Background area
?
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Compare with the ALICE PPR II
Fake jets removed
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Simulation in full TPC Acceptance
Simulation in f2p and hlt0.5
TPC TPCEMCal
Simulation in f2p and hlt0.5 BUT jets
reconstruction in the EMCal acceptance
TPC TPCEMCal
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Compare fMomentumArray/fUnitArray with TPC/ITS
only
In order to compare algorithms with a
fMomentumArray filled and a fUnitArray filled, a
cut on h (hlt0.5) and f has been introduced
before the candidate track selection to compare
quantities in the EMCal acceptance.
-gt 400 evts simulated -gt Only TPC -gt 104-125 GeV
Jet multiplicity
No lego
fUnitArray
EMCAL acceptance in h
EMCAL acceptance in f
Jet energy
Need to generate more events for better comparison
26
M.E. 03/13/2007 EMCAL Meeting - Frascati
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