Matching between charged tracks and electromagnetic calorimeter (EMCAL) clusters in ALICE Alberto...
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Transcript of Matching between charged tracks and electromagnetic calorimeter (EMCAL) clusters in ALICE Alberto...
Matching between charged tracks and electromagnetic calorimeter (EMCAL) clusters in ALICE
Matching between charged tracks and electromagnetic calorimeter (EMCAL) clusters in ALICE
Alberto Pulvirenti
University & INFN Catania
ACAT 2007 Conference
Amsterdam, 24 April 2007
2
OutlookOutlook
The context› the ALICE experiment
› the EMCAL detector
› the computing framework
The algorithm ingredients› ALICE tracking
› EMCAL clusters
Description of the algorithm Tests and results Conclusions and perspectives
3
http://www.cern.ch
~9 km
LHC
SPS
CERN
The CERN Large Hadron Collider The CERN Large Hadron Collider & ALICE& ALICE
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…and “worst” expectation for
LHCLHC
“worst” actual case:
RHIC
Some numbers about LHCSome numbers about LHC
Pb-Pb collisions at 5.5 A TeV Expected charged
multiplicity› from RHIC data: (dNch / dy)y=0 = 3000
› design baseline: (dNch / dy)y=0 = 8000
Luminosity for Pb-Pb:› Lmax = 11027 cm-2s-1
Event rate: › 8000 minimum bias coll. / s
› ~109 events/year
› 1% collected
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The ALICE detectorThe ALICE detector
ITSlow pt trackingVertexing
ITSlow pt trackingVertexing
TPCTracking, dE/dx
TPCTracking, dE/dx
TRDElectron ID
TRDElectron ID
TOFPID
TOFPID
HMPIDPID at high pt
HMPIDPID at high pt
PHOS,0
PHOS,0
MUON-Arm -pairs
MUON-Arm -pairs
PMD multiplicity
PMD multiplicity
EMCALPhotons, jets
EMCALPhotons, jets
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AliROOT: the ALICE computing AliROOT: the ALICE computing frameworkframework
STEERBase classes, overal control
AliReconstruction ESDreconstruction
Event Summary DataEvent Summary Data
Particle generators
DPMJET
HIJING
HBTP
PYTHIA PDF
ISAJET
Particle transport
GEANT3 GEANT4 FLUKA
Analysis
HBT JET PWG0-4
Detectors
ZDCPHOS
EMCALHMPID
TOF
TRD
TPC
ITS
T0 V0PMDMUON
Response
Geometry Calibration
Alignment
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The ElectroMagnetic CALorimeter The ElectroMagnetic CALorimeter (EMCAL)(EMCAL)
Acceptance = 1.4 = 100o
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The ElectroMagnetic CALorimeter The ElectroMagnetic CALorimeter (EMCAL)(EMCAL)
12 supermodules› 24 strips in η
› 12 (or 6) modules in φ
› projective wr. to TPC/TRD sectors
12672 elementary sensors (towers)› 77 alternating layers of
1.44 mm Pb (1% Sb) 1.76 mm polystirene scintillator
› radiation length: ~20 X0
Acceptance:› φ : 80 190 degrees
› η : -0.7 0.7
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EMCAL primary objective: jet EMCAL primary objective: jet studystudy High energy partons fragmentation jets
Jets traveling through a dense color medium loose energy through gluon radiation “jet quenching”
EMCAL PROVIDES:EMCAL PROVIDES: Jet trigger Improved jet reconstruction up to 200 GeV jets
› background reduction› improved energy resolution (including neutrals)
Charged only
ChargeCharged + d +
NeutralNeutral
RMS [GeV] 21 1515
Econe/ET 0.50 0.770.77
Eff. 67% 80%80%
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PID with EMCAL (high momentum PID with EMCAL (high momentum particles)particles) discrimination ( measure of direct photons)
› invariant mass
› shower shape analysis
e discrimination› E (from EMCAL) / p (from tracking) ratio
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Tracking in ALICETracking in ALICE
TIME PROJECTION CHAMBER TIME PROJECTION CHAMBER (TPC)(TPC)
up to 180 pt / track [main contribution - seed]
INNER TRACKING SYSTEM (ITS)INNER TRACKING SYSTEM (ITS)up to 6 pt / track
[resolution improvement]
TRANSITION RADIATION TRANSITION RADIATION DETECTOR (TRD)DETECTOR (TRD)up to 6 pt / track
Tracking procedure based on Kalman Filter:1) Predict track intersection point at a layer of tracking device 2) Choose the cluster which determines the smalles ² increase3) Add a cluster adjust track parameters according to Kalman matrix
equations
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ITSITS TPCTPC TRDTRD
ALICE tracking work flowALICE tracking work flow
Seeding & inward track propagation through the
TPCInward track propagation
through the ITS
Outward track propagation through the
ITSOutward track
propagation through the TPC Outward track
propagation through the TRD
Final inward re-fit through all tracking devices, up to the beam Final inward re-fit through all tracking devices, up to the beam pipepipe
time
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Barrel to EMCAL track matchingBarrel to EMCAL track matching
Implementation in AliROOT framework› “tracker” class algorithm execution
› “track class” input data final information EMCAL clusters are not used to update the track state
vector
Target:› associating to each track the EMCAL cluster generated
by its particle (if any)
› cleaning the sample of cluster for photon analysis (jets)
› adding PID information from EMCAL to high momentum charged tracks
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Work-flow of the algorithmWork-flow of the algorithm
Search for EMC clusters close to the intersection
Create a list of “match candidates”
GeometricalCUTS
Quality parameter:Track-Cluster distance
Each cluster/track is used only in the “best” candidate
Save Save the “surviving” candidatesthe “surviving” candidates
as final information.as final information.
Propagate track to the EMCAL surface
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Performance testsPerformance testsTest on single-track events
Data:• 1 track / event (fixed type)• fixed momentum
• 1, 5, 10, 25, 50, 75, 100 GeV• fixed direction
Objective:• evaluate / shift between track hit and
reconstructed cluster• evaluate typical cluster size (# towers)
Test on “box” eventsData:• <N> (fixed) track / event
• photons, pions, electrons• Random momentum in a fixed range (1-10 GeV)• Random direction in a fixed window (EMCAL
acceptance)
Objective:• evaluate efficiency
and contamination in a simple multi-track scenario
Test on “physical” simulations
Proton-Proton collision: PYTHIA
Pb-Pb collisions: HIJING parameterized
Objective:• evaluate efficiency and contamination in a “physical” sample with a realistic
momentum distribution and signals from neutral particles (as a perturbation factor)
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Phi and Eta shift between hits and Phi and Eta shift between hits and clustersclusters
ELECTRONS
PHOTONS
PIONS
17
Average #digits per particle Average #digits per particle
amp > 1% of total
amp > 2% of total
amp > 5% of total
amp > 10% of total
Cluster/Particle energy Cluster/Particle energy comparisoncomparison
electrons & photons:
~100% of total
pions:
~20% of total
19
Track matching evaluationTrack matching evaluation
Efficiency
true
correctfound
N
N
Contamination
found
fakefound
N
Nc
fakefound
correctfoundfound NNN
Geometrical cuts tuned on pion events
and used for all tests without changes
20
Efficiency evaluation: “box” of Efficiency evaluation: “box” of electronselectrons
10 primaries / event
50 primaries / event
100 primaries / event
150 primaries / event
21
Efficiency evaluation: “box” of Efficiency evaluation: “box” of pionspions
10 primaries / event
50 primaries / event
100 primaries / event
150 primaries / event
22
Efficiency evaluation: PYTHIA Efficiency evaluation: PYTHIA simulation of minimum bias p-p simulation of minimum bias p-p collisions at 14 TeVcollisions at 14 TeV
23
Efficiency evaluation: Efficiency evaluation: HIJING parameterized HIJING parameterized (preliminary)(preliminary)
dN/dη = 4000
24
Conclusions & perspectivesConclusions & perspectives
Track matching code preliminary version implemented within ALICE reconstruction framework› based on Kalman Filter-style track propagation
Efficiency results:› box: good
not negligible contamination for high multiplicity (150)
› PYTHIA: good
› HIJING: good only for very high momenta investigate performances at this track density
Future perspectives:› improve results for high mutiplicity events
cluster pattern study
25
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Work-flow of the algorithm:Work-flow of the algorithm:STEP 1 STEP 1 propagation propagation
Seed: outer “snapshot” of the reconstructed track Propagate tracks to the EMCAL surface
XY plane (transverse to beam)
Cluster positions
Track intersections with EMCAL
27
Track propagation planeTrack propagation plane(in track local coords.)(in track local coords.)
not all clusters lie in the same plane
(Δy,Δz)LOCAL cuts (Δφ,Δη)GLOBAL cuts
X
Track local reference system:
rotation of detector plane around Z axis, in order to put it in a plane orthogonal to X axis
X = distance of detector plane from origin
Z
Y
28
Insertion of track matching into Insertion of track matching into global barrel reconstruction work-global barrel reconstruction work-flowflow
ITS (in – I)
TPC (in - I)
ITS (out)
TPC (out)
TRD (out)
TOF (matching)
ITS (refit)
TPC (refit)
TRD (refit)
Entry point
EMCAL (matching)
29
Energy distribution in clustersEnergy distribution in clusters
Portion (%) of total cluster energy per hit tower.
LOG
sca
le!!
!
e (25 GeV) (25 GeV)
30
ALICE objectivesALICE objectives
Heavy ion collisions in a new energy range
Properties of nuclear matter at high temperature and energy density
Formation and study of Quark-Gluon Plasma (QGP)
10 –6 s 10 –4 s 3 m ~1010 yrs
Big
B
an
g
QGPQGP Nucleons Nuclei Atoms Today