Post on 14-Dec-2015
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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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.
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