EMCal in ALICE

Norbert Novitzky

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Outline• How Electro-Magnetic Calorimeters works ?• Physics motivation

– What can we measure with Emcal ?– Advantages with Emcal ?

• ALICE Emcal general– Detector design– Physics performance or Data acquisition

• Emcal Trigger– What is trigger and why do we need it? – Trigger Region Unit and Summary Trigger Unit

• Physics with EMCal– 0,photon,jets

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How does EMCAL work?The electro-magnetic calorimeter is constructed of layers of some material with high electric charge nuclei interleaved with layers of silicon sealed in cells. Let's call the steel region the absorber material and the argon the collector region.

Principe of the calorimeter:The high-energy electron passes into the absorber material, where the high electric field inside the atoms causes the electron to change direction which causes it to emit a virtual photon. The virtual photon has sufficient energy and momentum that it produces a positron-electron pair. Now there are three high-energy charged particles sharing the energy of the initial electron, roughly parallel. Each of the electrons, positrons, photons produces further pairs in the material what is called “shower”.

The x0 is the radiation length: 0.5-3cm

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Two types of detector

Incoming particles generate EM showers in the absorber, the showers generate flashes in the scintillating material.

• better linearity in response• PHENIX PbSc/ALICE-EMCAL

The shower depth is a logarithmic function of particle energy.The number of Cherenkov photons is directly proportional to particle energy•better granularity•PHENIX PbGl/ALICE-PHOS

Pb absorbergenerates shower

Scintillatorgenerates

light

Optical fibercollects light

Led-Scintillator (PbSc)Led-Scintillator (PbSc) Led-Glass (PbGl)Led-Glass (PbGl)

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Febuary 12 2003 Phenix Focus 5

Energy Resolution

%.E

%.

EE 12

18

%.E

%.

EE 760

955

PbGl

PbSc

PHENIX

EMCAL in LHC

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Physics with EMCal (motivation)

0 can be measured in EMCal. In tracking detectors, the neutral particles cannot be detected. The missing energy of the jets can be measured in EMCal.

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RAA => Strong suppression of high PT hadrons in AA compared to pp with no corresponding suppression of Direct Photons

Physics with EMCal (motivation)

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Jet quenching:

Two particle correlation:

Phys.Rev.D74:072002,2006

Nuclear Modification Factor for various particles PHENIXNuclear Modification Factor for various particles PHENIX

ALICE EMCal

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Lead-scintillator sampling calorimeter||<0.7, =110o

Shashlik geometry, APD photosensorPHOS Readout electronics~13K towers (x~0.014x0.014)The EMCal is divided to Super-Modules (10+2/3)

ALICE EMCal

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PHENIX PHOS EMCAL

2x90 100 110

0.7 0.24 1.4

Acceptance 2.198 0.418 2.68

R_int 5m 4.6m 4.3m

Tower size 4x4cm (PbGl)5.52x5.52(PbSc)

2.2x2.2cm 6x6cm

Tower length 40cm(PbGl),33(PbSc)

18cm 24.6cm

Comparing different electromagnetic calorimeters used in HI experiments

1.Resolution: Tracking vs calorimeter

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Tracking detectors are better at low-pt, at higher pt the resolution get worst:(the plot is an illustration)Tracking detector at ALICE:ITSTPC

The EMCal was tested at PS and SPS energies. The plot shows the momentum dependence for the resolution. At higher pt, the resolution get better.

2.Advantages of Photon Trigger

PHENIX AuAu From DongJo

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TriggeringIn particle physics, a trigger is a system that uses simple criteria to rapidly decide which events in the detector to keep.

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Level Requirement

L0 <800ns

L1 <6.2s

L2 <80s

At ALICE there are 3 different trigger levels (L0->L2). All the subsystems (L0 and L1 trigger detectors) are sending the trigger signals to Central Trigger Processor where are processed.

EMCaL Trigger

STUMax 12 m

CTP

5 trigger cables

Vo LTU

16 CAT7 cables 17 CAT7 cables

ethernet

Max 12 m

DDL to DAQ CR1

DDL to HLT CR2Debug line

SM0,0 SM0,1

SM5,0 SM5,1

TRUTRU

TRU

TRUTRU

TRU

TRUTRU

TRUTRU

TRUTRU

TRUTRU

TRUTRU

TRUTRU

TRU

TRUTRU

TRU

TRUTRU

TRUTRU

TRUTRU

TRUTRU

TRUTRU

TRU

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One supermodule has 1152 towers, and this is read-out by 36 FEE cards. After simplification (2x2 sum), 3 TRUs process the data.

EMCal Trigger – L0 level

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TRU board:96 input channels – already 2x2 sum of the towers:• larger signal• less data to process

2x21 Tower

2x2 = 1 TRU chan.

4x4 for trigger

L0 trigger algorithm will trigger the photons at EMCal:In TRU is created 4x4 groups, and applying a digital threshold. The shower from photon must be in 4x4 region.

EMCal Trigger – L1 level

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STU board:L1 trigger signal:-Inputs from 32 TRUs (3072 data), need to be processed in less than 3s. Jet trigger algorithm must fit in this small window. The jet trigger cannot be done in TRU, because it has too small acceptance region.

DCS interface

TTCRq

V0 interface

DDL interface

L0 in

4 T

RU

in

puts

32 TRU inputs

4 T

RU

in

puts

Trig ge

r ou

tpu

ts

L1 signal trigger signal can be:

• L1 photon signal (edge of the TRU regions)

• L1 pi0 or L1 jet trigger can be calculated.

Pi0 kinematics

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We are looking for 0-> decays, when the invariant mass:Minv =

€

2E1E 2 1− cos θL( )( )L

The asymmetry of the two out coming photons:

The opening angle of the photons depends on pT of 0:

The photons start to merge.

pT PHOS(2.2x2.2)

EMCAL(6x6)

10GeV 12.8cm 11.5cm

20GeV 6.4cm 6cm

30GeV 4.2cm 4cm

Jet Reconstruction with EMcal

“TPC+EMCAL” Recovers large fraction of Jet Energy“TPC+EMCAL” Recovers large fraction of Jet Energy18

NLO Predictions for 10TeV

hep-ph/9910252 http://lappweb.in2p3.fr/lapth/PHOX_FAMILY/readme_inc.html 19

Expectation for first LHC run

With 3 PHOS modules :

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