Calorimetry in
ALICE at LHC
Tatsuya Chujo
University of Tsukuba
for the ALICE Collaboration
International Conference on Technology andInstrumentation in Particle Physics (TIPP ’14)
Amsterdam, The Netherlands
June 2-6, 2014

Outline
1. Electromagnetic Calorimeters in ALICE• ALICE Experiment• PHOS• EMCal• Performance (2009-2013)
2. Upgrade during LHC long shutdown (2013-2014)• EMCal extension (DCal), PHOS upgrade• SRU readout upgrade (EMCal/DCal, PHOS)
3. Future plan
• Forward Calorimeter (FoCal)
4. Summary
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1. ElectromagneticCalorimeters in ALICE

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ALICE Physics Program and Hard Processes
Physics Goal of ALICE:
To study/ characterize the properties ofhot, dense, de-confined matter (“QuarkGluon Plasma”, QGP) as produced on a“macroscopic” scale in central Pb+Pb
collisions at the LHC.
• Initial temperature of matter:-Thermal γ radiation from QGP• Parton energy loss in QGP (jet quenching):– Probe the “stopping power” of the medium– dE/dx for partons in QGP➡ Requires EM calorimetry– Measure EM energy to provide total jet energy (or recoil γ)– Provide jet (or γ) trigger– Thermal γ, π0.
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4The ALICE Experiment

EMCal

PHOS
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5The ALICE Photon Spectrometer (PHOS)
Design goal: To measure π0’s and thermal photons (Initial T)•

3 of 5 Super-Modules installed (Run-1)

PHOS Super
Modules!

Support
Cradle!

PbWO4 crystals• APD Photosensor• Crystals at -25o C → ~triple LY• 10,752 crystals installed• At 4.6m from IR.
• Δη = 0.24, Δφ = 60o (100o)• Full-scale Energy: 100 GeV
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56x64 crystal array
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The ALICE Photon Spectrometer (PHOS)
Module: 2x8 crystals

100µm Stainlesssteel honeycomb
PbWO4 crystals 2.2 x 2.2 x 18 cm• 20 X0• APD + Preamp on crystal• Crystals at -25 oC• Δη = 0.24, Δφ = 60o (100o)High resolution, low occupancy,
but limited acceptance.
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56x64 crystal array
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The Electromagnetic Calorimeter (EMCal)
Large acceptance with moderate
resolution and occupancy.
••

A late addition to ALICE
Funding approval: Feb. 2008

Lead-Scintillator Sampling CalorimeterΔη = 1.4, Δφ =107o
Shashlik Geometry, APD Photosensor
12,288 Towers
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EMCal Assembly
•
•
•
•
•

3,072 identical modules, 2x2 towers
1.5o taper in ηTower granularity δη = δφ = 0.014
20.1 X077 layers Pb:Sc = 1.44 : 1.76 mm

12peruSrs peduleoM
leripModu24 St
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Modulesperstripmodule

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EMCal Readout
Preamplifier + APD

•
•
•••
•

4 x (6x6 cm2) towers/module
WLS fiber readout on 1cm grid
5x5 mm2 Hamamatsu and Perkin Elmer APDs
~4.5 photo-electrons/MeV at gain M=1
Operated at nominal gain M=30
Full-scale Energy = 250 GeV

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EMCal SM Readout Assembly and Readout•Signal Cables– 16 towers each

LED fibers(monitoring)
LED systemFEE cards
RCU+DCSGTL Bus•2 FEE crates per SM– 36 + 1 FEE cards + 3 TRU (Trigger Region Unit) per SM•

1 Readout+Detector Control Unit (RCU(Readout Control Unit) +DCS)
per FEE crate– Control via ethernet. Readout via fiber optic (ALICE DDL standard)– 2 GTL Readout/Control Bus per FEE crate

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EMCal/PHOS Performance
PHOS

EMCal

σ 2.8%
=
⊕1%
EE

σx =
••

3.2⊕ 0.7mm
E

σ 10.5%=⊕1.9%EE

σx =5.3⊕1.5mmEBoth calorimeters have had extensive beam tests at the CERN PS
Important for detailed response description in Monte Carlo simulation

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L0 and L1 Trigger efficiencies
TTMBMB(1/N ) dN /dp

PHOS
pp

(1/Npp) dN π0PHOS
π0/dp

TEMCalR = 583 ± 5 at p >4 GeV/c104103

102

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ALICE performance
pp @ s=7 TeVPHOS
02.04.201151015

L1 shower trigger

PHOS
20253035p , GeV/cT•Calorimeter triggers have been inoperation during LHC 2011 p+p 7 TeVrun period with rejection factors of~x3000

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L1 jet trigger
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E/p response (EMCal)
EMCal• Seen clear E/p peak (p-Pb, 5.02 TeV), and demonstrated
clear discrimination between hadrons and electrons.
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Invariant mass spectra in p+p: π0
EMCal

PHOS

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Invariant mass spectra in Pb+Pb (central): π0EMCal

PHOS

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Mean and width of π0 mass peak (p+p)

PHOS

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EMCal

Good agreementTIPP
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2. Upgrade during LHC
long shutdown (2013-2014)

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EMCal Extension/Upgrade (DCal)
EMCal
Δφ=107o

DCal (Di-jet Calorimeter):June 2,2014

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Same modules as the EMCAL,
shorter SuperModules in η.
Including PHOS, acceptance isΔη=1.4, Δφ=67º
Enhance di-jet yield (w/ jet trigger)
To be completed installation in2013-2014 shutdown.
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DCal installation (2013 - 2014)
DCal SM in ALICE surface before
installation (Sep. 2013 @ CERN, P2)

DCal C-side installation(2013 fall)• 3 sectors of full DCal SMs, and 1 sector of 1/3 SMs• C-side sectors installed in fall 2013, A-side to be installed in fall 2014
• L0 and L1 trigger geometry reconfiguration in on-going.
• DCal + PHOS common jet trigger is also under development.

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PHOS new module and CPV for Run-2

CPV for PHOS
• Added new PHOS 1SM (50% coverage of 1 SM = 1,792 crystals).
• For Run2, PHOS will have 3½ modules with azimuthal coverage Δφ=70˚.
• Charged Particle Veto (CPV) will be installed in front of one PHOS SM.
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FEE Upgrade: RCU/GTL bus

point-to-point SRU• Replace 2 (RCU+DCS+SIU) + 4 GTL Bus with single SRU mod.
– Developed by CERN-RD51.
– Replace serial readout of 10 cards/GTL bus with parallel readout of all
FEE boards• Minimum readout speed ~30µs (set by ALTROs in FEE)

– FEE-SRU communication via DTC LVDS serial link
– SRU-LDC communication via ALICE DDL protocol (or Gigabit ethernet)•• Compatible with existing DDL readout – fibers/RORC
Results: SRU readout allowed to achieve 20-50 times shorter readout time withrespect to RCU readout in Run-1.
– e.g.) PHOS readout time was 900 us (Run-1) -> up to 25 us by SRU.

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Current status of SRU in PHOS/EMCal/DCal
PHOS FEE card
DTC CARDSRU••

PHOS:–upgraded all FEE boards (~430).

–New SRU and FEE F/W is now beingcommissioned together w/ EMCal/DCal.

EMCal/DCal:–

SRU switching over done (2013, spring)–

SRUs for all of EMCal + installed part of DCal (Cside)

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EMCal SRU+FEE(spring, 2013)
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3. Future upgrade plan:
Direct photon measurements atforward rapidity region at LHC

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Physics of photon measurements at forward η @ LHC%Ini(al%condi(on,%CGC,%%early%thermaliza(on%Color%Glass%
Collision%
Condensate%(CGC)

sQGP%produc<on,%thermal%
dynamics%QGP

“Glasma”

strongly%coupled%%
Quark%Gluon%Plasma%% Hadron%gas
(sQGP)

t%=%@1%fm%%%%%%%%%%%%%%%%%%t%=%0%fm%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%t=%0.6%fm/c%%%%%%%%%%%%%%%%%%%%t=%20%fm/c%
Time• Results from d-Au (RHIC), p-Pb (LHC) collisions, there are some indications ofColor Glass Condensate (CGC) formation, but not conclusive.
• Main observables so far by hadrons, which include final state interaction.
• Experimental challenge: essential to make a measurement at forward
direction by a cleaner probe, such as direct photons.
➡ Larger kinematic reach in saturation region at LHC.
➡ CGC vs. Glauber initial condition→ key to understand the early thermalization of QGP.
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Forward Calorimeter (FoCal) in ALICE•Electromagnetic calorimeterfor γ and π0 measurement,with Hadron Calorimeter.
• At z ≈ 8m (outside magnet)
3.3 < η < 5.3

Main challenge: separate γ/π0 at high energy• Need small Molière radius, high-granularity read-out• Si-W calorimeter, granularity ≈ 1mm2
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FoCal-E Strawman Design• Si/W sandwich calorimeter layer structure:- W absorbers (thickness 1X0)+ Si sensors• Longitudinal segmentation:- 4 segments low granularity (LG)
- 2 segments high granularity (HG)
• LG segments- 4 (or 5) layers- Si-pad with analog readout- cell size 1 x 1 cm2- longitudinally summed• HG segments- single layer- CMOS-pixel (MAPS*)- pixel size ≈ 25 x 25 μm2- digitally summed in 1mm2 cells*MAPS = Monolithic Active Pixel Sensor (cm)June 2,2014

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Detector Performance•

Reasonable energy resolution, extremely good two-shower separation
with HG segments•→ efficient pion rejection (e.g. via shower shape analysis)

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High Granularity (HG) Prototype, MAPS
MAPS prototype• 4x4 cm2 cross section, 28 X0 depth• 24 layers: W absorber + 4 MAPS each
• MIMOSA PHASE 2 chip (IPHC Strasbourg)- 30 μm pixels- 640 μs integration time(needs upgrade – too slow for experiment)• 39 M pixels total• Test with beams at DESY, CERN PS, SPS

Event Display:measurement (DESY) of
pile-up of two 5.4 GeV
electrons, demonstrates
two-shower separation
capabilities
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Low Granularity (LG) Prototype, PAD•First	  LG	  (PAD)	  prototype	  (ORNL).
- Si-pad with analog readout.
- cell size 1x1 cm2- longitudinally summed•

4	  tungsten	  plates	  are	  interleaved	  with	  silicon	  pad	  sensor	  layers.	  
– ORNL	  ASICs	  are	  located	  on	  summing	  board	  on	  side	  of	  module.
– Readout	  by	  RD-­‐51	  readout	  system• APV25	  hybrid/	  Beetle	  hybrid

PLAN

June 2,2014•

The integrated system of FoCal-E (HG + LG) will
be tested at PS (Sep. 2014) and SPS (Nov. 2014).

•LoI is under preparation, will be submitted insummer 2014 to ALICE.

Beetle hybrid

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4. Summary• Complimentary EM Calorimeters in ALICE:– PHOS: high resolution, low occupancy, limited acceptance,with emphasis to measure low pT π0’s and thermal photons– EMCal: Moderate resolution and occupancy, large
acceptance with emphasis to measure Jets
– Run-1 performance:• PHOS and EMCal have been working as design.
• Upgrades during LS1 (2013-2014):– DCal, PHOS upgrades, SRU readout upgrade• Future upgrade in Forward region:– FoCal: direct direct photons to determine the initialcondition of QGP, crucial to understand QGP properties.
FoCalJune 2,2014

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