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EMCal in ALICE

EMCal in ALICE . Norbert Novitzky. 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

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EMCal in ALICE

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  1. EMCal in ALICE Norbert Novitzky

  2. 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 • p0,photon,jets

  3. How does EMCAL work? The electro-magnetic calorimeter is constructed of layersof some material with highelectriccharge 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

  4. 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 Optical fiber collects light Scintillator generates light Two types of detector Led-Scintillator (PbSc) Led-Glass (PbGl) Incoming particles generate EM showers in the absorber, the showers generate flashes in the scintillating material. • better linearity in response • PHENIX PbSc/ALICE-EMCAL Pb absorber generates shower

  5. Energy Resolution PHENIX PbGl PbSc Phenix Focus

  6. EMCAL in LHC

  7. Physics with EMCal (motivation) p0 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.

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

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

  10. ALICE EMCal Comparing different electromagnetic calorimeters used in HI experiments

  11. 1.Resolution: Tracking vs calorimeter 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.

  12. 2.Advantages of Photon Trigger PHENIX AuAu From DongJo

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

  14. TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU TRU EMCaL Trigger CTP Vo LTU 5 trigger cables ethernet DDL to DAQ CR1 STU DDL to HLT CR2 Debug line Max 12 m Max 12 m 17 CAT7 cables 16 CAT7 cables One supermodule has 1152 towers, and this is read-out by 36 FEE cards. After simplification (2x2 sum), 3 TRUs process the data. SM5,0 SM5,1 TRU SM0,0 SM0,1

  15. EMCal Trigger – L0 level • TRU board: • 96 input channels – already 2x2 sum of the towers: • larger signal • less data to process 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. 1 Tower 2x2 2x2 = 1 TRU chan. 4x4 for trigger

  16. 32 TRU inputs 4 TRU inputs 4 TRU inputs V0 interface Trigger outputs DDL interface DCS interface L0 in TTCRq EMCal Trigger – L1 level • STU board: • L1 trigger signal: • Inputs from 32 TRUs (3072 data), need to be processed in less than 3ms. Jet trigger algorithm must fit in this small window. The jet trigger cannot be done in TRU, because it has too small acceptance region. • L1 signal trigger signal can be: • L1 photon signal (edge of the TRU regions) • L1 pi0 or L1 jet trigger can be calculated.

  17. Pi0 kinematics qL We are looking for p0->gg decays, when the invariant mass: Minv = The asymmetry of the two out coming photons: The opening angle of the photons depends on pT of p0: The photons start to merge.

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

  19. NLO Predictions for 10TeV hep-ph/9910252 http://lappweb.in2p3.fr/lapth/PHOX_FAMILY/readme_inc.html

  20. Expectation for first LHC run With 3 PHOS modules :

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