EMCal in ALICE Norbert Novitzky 1

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 2

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 x 0 is the radiation length: 0.5-3cm 3

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 absorber generates shower Scintillator generates light Optical fiber collects light Led-Scintillator (PbSc) Led-Glass (PbGl) 4

Febuary Phenix Focus5 Energy Resolution PbGl PbSc PHENIX

EMCAL in LHC 6

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. 7

R AA => Strong suppression of high P T hadrons in AA compared to pp with no corresponding suppression of Direct Photons Physics with EMCal (motivation) 8 Jet quenching: Two particle correlation: Phys.Rev.D74:072002,2006 Nuclear Modification Factor for various particles PHENIX

ALICE EMCal 9 Lead-scintillator sampling calorimeter |  |<0.7,  =110 o Shashlik geometry, APD photosensor PHOS Readout electronics ~13K towers (  x  ~0.014x0.014) The EMCal is divided to Super-Modules (10+2/3)

ALICE EMCal 10 PHENIXPHOSEMCAL  2x  Acceptance R_int5m4.6m4.3m Tower size4x4cm (PbGl) 5.52x5.52(PbSc) 2.2x2.2cm6x6cm Tower length40cm(PbGl), 33(PbSc) 18cm24.6cm Comparing different electromagnetic calorimeters used in HI experiments

1.Resolution: Tracking vs calorimeter 11 Tracking detectors are better at low-pt, at higher pt the resolution get worst: (the plot is an illustration) Tracking detector at ALICE: ITS TPC 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 12

Triggering In particle physics, a trigger is a system that uses simple criteria to rapidly decide which events in the detector to keep. 13 LevelRequirement L0<800ns L1 <6.2  s L2 <80  s 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 STU Max 12 m CTP 5 trigger cables VoLTU 16 CAT7 cables 17 CAT7 cables ethernet Max 12 m DDL to DAQ CR1 DDL to HLT CR2 Debug line SM0,0 SM0,1 SM5,0 SM5,1 TRU 14 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 15 TRU board: 96 input channels – already 2x2 sum of the towers: larger signal less data to process 2x2 1 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 16 STU board: L1 trigger signal: -Inputs from 32 TRUs (3072 data), need to be processed in less than 3  s. 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 TT CR q V0 interface DDL interface L0 in 4 TRU inputs 32 TRU inputs 4 TRU inputs Trig ger out put s 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 17 We are looking for  0 ->  decays, when the invariant mass: M inv = L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. pTPHOS (2.2x2.2) EMCAL (6x6) 10GeV12.8cm11.5cm 20GeV6.4cm6cm 30GeV4.2cm4cm

Jet Reconstruction with EMcal “TPC+EMCAL” Recovers large fraction of Jet Energy 18

NLO Predictions for 10TeV hep-ph/

Expectation for first LHC run With 3 PHOS modules : 20