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Christian Lippmann for the ALICE TRD Collaboration

Position Resolution, Electron Identification and Transition Radiation Spectra with Prototypes of the ALICE TRD. Christian Lippmann for the ALICE TRD Collaboration. Outline. The ALICE TRD Requirements Working Principle Test Beam Setup Results Summary and Outlook. The ALICE Experiment.

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Christian Lippmann for the ALICE TRD Collaboration

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  1. Position Resolution, Electron Identification and Transition Radiation Spectra with Prototypes of theALICE TRD Christian Lippmannfor the ALICE TRD Collaboration Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  2. Outline • The ALICE TRD • Requirements • Working Principle • Test Beam Setup • Results • Summary and Outlook Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  3. The ALICE Experiment HMPID PID (RICH) @ high pt PMD g multiplicity TPC Tracking, dEdx MUON m-pairs TOF PID TRD Electron ID PHOS g,p0 ITS Low pt tracking Vertexing Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  4. The TRD (Transition Radiation Detector) • 18 supermodules • 6 radial layers • 5 longitudinal stacks • 540 chambers • 750m2 active area • 28m3 of gas Each chamber: ≈ 1.45 x 1.20m2 ≈ 12cm thick (incl. Radiators and electronics) in total1.18 million read out channels Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  5. Requirements • The TRD should: • Provide electron identification. • Increase the tracking capability of the experiment. • Provide trigger on high-pt electrons. Pion rejection factor ≈ 100 required Angular resolution σα < 1° required Position Resolution σx < 400μm required • Same Requirements Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  6. Working Principle of the TRD • Drift chambers with FADC readout at 10MHz combined with a fiber/ foam sandwich radiator in front. • Transition Radiation (TR) photons (< 30keV, only for electrons) are absorbed by high-Z gas mixture (Xe,Co2)  large clusters Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  7. Testbeam Setup 1: • Testbeam at CERN PS in October 2002 • Momenta up to 4GeV/c • S1, S2: Scintillators as trigger • Cherenkov: Electron tagging • Si1: Track position • Dipole Magnet: Separate TR • He pipe: Minimize TR absorption Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  8. Results 1: TR Spectra • We have a quantitative understanding of TR production and absorption. [O.Busch, TRDs for the 3rd Millenium, Bari'03] Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  9. Testbeam Setup 2: • Testbeam at CERN PS in October 2002 • Momenta up to 6GeV/c • Added a calorimeter for better electron tagging • Stack of 4 small TRD prototypes • Si1, Si2 for position reference Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  10. Results 2: Average Signals • Pulse height vs. time bin for • pions, • electrons only dE/dx, • electrons dE/dx+TR. • We find for electrons: • larger dE/dx. • characteristic TR energy deposit on top. • Use differing energy deposit and TR signature to identify electrons! Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  11. Results 3: Pion Efficiency • The pion rejection has to be large to minimise number of pions misidentified as electrons. • The pion efficiency is the inverse of this value and has to be minimized. • Different radiator types were tested. • LQX = bidimensional likelihood.Uses: • deposited charge (dE/dx+TR) • position of largest cluster • We reach a rejection factor 100 • Can be increased by Neural Network (Poster HK12.42) Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  12. Results 4: Space Charge Effect (SCE) • We expect a space charge effect for perpendicular tracks from pileup of ions around same wire spot for given track. • Can influence pion rejection! gain Simulation with SCE: Ratio of Pulse Heights at 0° and 15° and comparison to simulations. Simulation without SCE: Pion rejection performance as function of angle should be constant [A.Andronic et al., NIM A in press] Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  13. Tracking: Example Event • The pulse height is sampled at 10MHz on eight pads. • For each time bin the position along the pad rows is reconstructed. • A straight line fit leads to the incident particles track. • Residuals define Position Resolution Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  14. Results 5: Position Resolution • Position Resolution = Sigma of Gauss-fit to Residuals Histogram • Here vs. signal-to-noise • Example at 15° • Larger Signals better resolution • σx= 300 - 400µm • When a radiator isused, the resolutionis worse for electrons Bremsstrahlung • Nice agreement with simulation! Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  15. Results 6: Position Resolution vs. Angle • Nominal gain (4000) • Requirementmet: σx 400µm • Resolution for electrons better due to larger S/N • Nice agreement with simulation Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  16. Results 7: Angular Resolution vs. Angle • Requirement met: σ < 1° • For electrons the agreement is not so goodmore investigations Christian Lippmann (ALICE TRD), DPG-Tagung Köln

  17. Summary and Outlook • We have tested prototypes of ALICE TRD chambers. • The requirements are met. We reach: • a position resolution of σx=200 - 400µm, • an angular resolution of σα=0.4 - 0.7° and • a pion rejection factor of 100. • Different systematic effects (Space charge effect, …) are well understood. • We have measured pure TR spectra for our specific Radiators. • Outlook: • Mass production starts (see talk HK45.9). • Testbeam with stack of 6 final fullsize TRD chambers in october at CERN. Christian Lippmann (ALICE TRD), DPG-Tagung Köln

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