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

4

…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

5

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

6

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

7

The ElectroMagnetic CALorimeter The ElectroMagnetic CALorimeter (EMCAL)(EMCAL)

Acceptance = 1.4 = 100o

8

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

9

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%

10

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

11

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

12

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

13

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

14

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

15

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)

16

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

26

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