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Particle identification in ALICE

Particle identification in ALICE. E. Scapparone(INFN/CERN) on behalf of the ALICE Collaboration INSTR08, March 3, 2008. Outline - Experimental layout and status of the main subdetectors; - Detector performance; - Example of ALICE phsycs potential.

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Particle identification in ALICE

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  1. Particle identification in ALICE E. Scapparone(INFN/CERN) on behalf of the ALICE Collaboration INSTR08, March 3, 2008 Outline - Experimental layout and status of the main subdetectors; - Detector performance; - Example of ALICE phsycs potential. E. Scapparone INSTR08

  2. ALICE: A Large Ion Collider Experiment at CERN-LHC p-p (L=1031 cm-2 s-1), Pb-Pb (L= 1027 cm-2 s-1) Size: 16 x 26 meters Weight: 10,000 tonnes E. Scapparone INSTR08 2

  3. ..also more difficult @ RHIC At RHIC became harder….. Life in Pb-Pb interactions was never easy…. NA49 STAR ALICE simulated central event ! E. Scapparone INSTR08

  4. ITS(Inner Tracking System) Material Budget: ≤ 1% X0 per layer ! SSD • 6 layers, three technologies (keep occupancy at a few %for max multiplicity) • SPD: silicon pixels (0.2 m2, two layers, 9.8 M channels) • SDD: silicon drift (1.3 m2, two layers, 133 k channels) • SSD: double-sided silicon strips (4.9 m2, two layers, 2.6 M channels) SDD SPD Lout=97.6 cm Rout=43.6 cm E. Scapparone INSTR08

  5. ITS 40 mm 42 mm 6 chips 75 mm Challenge: track densities at r = 4 cm (1st layer): up to 100 / cm2 SPD (0.2 m2) Cell size (rf,z) : 50 mm x 425 µm space resolution(r) : 12 mm space resolution(z): 100 mm SDD (1.3 m2) cell size (r,z): 294 x 150 mm2 space resolution (r, z) : 35 mm space resolution(z):23 mm SSD (4.9 m2) cell size (r,z): 95 x 4200 mm2 space resolution (r): 20 mm space resolution (z); 830 mm E. Scapparone INSTR08

  6. Inner Silicon Tracker Inner Tracking System ~ 10 m2 Si detectors, 6 layers Pixels, Drift, double sided Strips Pixels SPD Pixels Drift SDD Strips SSD E. Scapparone INSTR08 6

  7. TPC SPD SSD/SDD E. Scapparone INSTR08

  8. TPC Drift gas:Ne (86) / CO2 (9.5) / N2 (4.5) • Optimized for dN/dη ≈ 8000 • l = 5 m, Ø = 5.6m, 88 m3, 570,000 channels x 500 time bins, • up to 80 Mbytes/event (after 0 suppression) • Features: • lightweight: 3% X0 total material for perpendicular tracks • novel digital electronics (ALTRO) • highly integrated, digital shaping; tail cancellation;0-suppression; Baseline restoration • Powerful laser calibration system σ(dE/dx) ≈ 5.5 to 6.5 %, depending on multiplicity (measurements and simulations) E. Scapparone INSTR08 8

  9. ALICE TPC: 5 years construction E. Scapparone INSTR08 9

  10. Cosmics recorded in TPC@ALICE Commissioning with Cosmics and Laser tracks Spatial resolution and Electronics noise in experiment according to specifications Status: installed and being commissioned E. Scapparone INSTR08 10

  11. TRD Transition Radiation Detector (TRD) • e/p separation in central barrel p>1 GeV/c • fast trigger for high momentum particles (hadrons, electrons)+ tracking • 540 detectors ~ 760m2 • 18 super modules • length: 7m • X/X0 ~ 22 % • 28 m3 Xe/CO2 (85/15) • 1.2 million channels Status: partially installed; being commissioned E. Scapparone INSTR08 11

  12. TRD - Signal Generation & Processing Average pulse heigth (mV) e(e-) = 90 % E. Scapparone INSTR08

  13. TRD Installation E. Scapparone INSTR08 13

  14. TOF requirements: • Large array to cover the ALICE barrel (~150 m2) • Time resolution σ < 100 ps • High efficiency, ε > 95% • High segmentation: few thousands of particles per unit of rapidity expected in Pb-Pb collision at s = 5.5 TeV/nucleon pair √ ALICE choice: a detector based on MRPC, segmented in ~157,000 channels, (3.5 x 2.5) cm2 area E. Scapparone INSTR08

  15. 157248 pads, total sensitive area: ~150 m2 TOF 18 Supermodules, each made of 5 modules: 2 external(19 strips), 2 intermediate (19 strips), 1 central(15 strips) 7.4 m Readout performed by two VME Crates/Side 2 crates /side E. Scapparone INSTR08

  16. Cross section of a double-stack MRPC strip 10 gaps 250 mm Differential signal to FEA card 2 rows of 48 readout pads (3.5 x 2.5 cm2) Active strip length = 120 cm E. Scapparone INSTR08

  17. Test beam of single strips Gas mixture: C2F4H2(90%) – SF6 (5%) – C4H10(5%) ε > 99.9 % average ~ 50 ps Efficiency Time resolution( ps) Similar results obtained when strips are inserted inside the modules E. Scapparone INSTR08

  18. M = p ((t2 c2 /L2 )-1)1/2 σTOF = 80 ps ; B = 0.5 T E. Scapparone INSTR08

  19. 10 SMs installed ; next 4 SMs to be installed next week; being commissioned E. Scapparone INSTR08 19

  20. December 2007 cosmic run Event display of a muon crossing the TOF detector E. Scapparone INSTR08

  21. High Momentum Particle Identifier: HMPID • Proximity Focused RICH • 11 m2 active detector area • 7 modules • - 0.6< η < 0.6; Δφ = 58 deg • CsI Photocathode read by 16100 pads • Threshold momentum = 1.21* (Particle Mass) • PID optimization for • 1 GeV < p < 6 GeV E. Scapparone INSTR08 21

  22. HMPID: Installed; being commissioned HMPID (Sept ’06) E. Scapparone INSTR08 22

  23. Example of a high multiplicity event as seen by the HMPID dN/dh=6000 E. Scapparone INSTR08

  24. 0.7 T, bending power 3 Tm • 4 MW power, 800 tons • World’s largest warm dipole MUON spectrometer set-up Complex absorber/small angle shield system (~10 lI) to minimize background (90 cm from vertex) RPC Trigger Chambers 5 stations of high granularity pad tracking chambers, over 1 million channels Trigger pt cut on single m: ~1 GeV/c E. Scapparone INSTR08

  25. Lepton Acceptance ATLAS & CMS present a large lepton acceptance |h|<2.4 ALICE combines muonic and electronic channels - covers the low pT region (quarkonia) - covers the forward region 2.5<h<4.0 E. Scapparone INSTR08

  26. Charged Particle Identification HADRON-ID 3 s separation power All known PID techniques used in ALICE ITS sdE/dx = 6.8% at dN/dy=8000 (5.5% for isolated tracks) TPC protons kaons dE/dx (MIP units) dE/dx (MIP units) pions E. Scapparone INSTR08 P(GeV/c) P(GeV/c)

  27. Combined PID Performance Kaon PID (the most difficult case...) (Cp : CK : Cp= 0.75 : 0.15 : 0.1) Efficiency/Contamination TPC ITS TOF(*) (120 ps) p (GeV/c) p (GeV/c) p (GeV/c) Higher efficiency & Lower contamination wrt individual detectors Combined PID ITS & TPC & TOF (*) very conservative p (GeV/c) E. Scapparone INSTR08

  28. Extension of PID to higher momenta combining the dE/dX of TRD and TPC 8<p<10 GeV/c Combine TPC and TRD dE/dx capabilities (similar number of samples/track) to get statistical ID in the relativistic rise region E. Scapparone INSTR08

  29. Open Charm Detection in Hadronic Decays Mass 1.864 GeV/c2 c=124 m ~0.55 D0K-+ accepted/event important also for J/ normalization E. Scapparone INSTR08

  30. Spectra E. Scapparone INSTR08

  31. Finally … • ALICE is becoming reality after almost 15 years in the making • 2nd Commissioning run is going on this week. • Further commissioning running until first beams, scheduled for summer 2008 • All systems on track for taking first pp collisions • ALICE is the general purpose Heavy Ion experiment, designed to address the very rich, expected physics program: particle id will play a central role in this challenging physics. E. Scapparone INSTR08 31

  32. RISERVE E. Scapparone INSTR08

  33. GIF results Working voltage = 13 kV No ageing effect measured at PS E. Scapparone INSTR08

  34. GIF results: No current increase I (mA) Flow = 1.4 cm3/s Source on Source on The gas going to the chamber 2 was bubbled through water for some time of the exposure Source off Source off E. Scapparone INSTR08

  35. Ageing study: two MRPC strips irradiated at GIF Time(min) Total charge = 14 mC/cm2 Charge/event = 2 pC 7 *109 events /cm2 @ 50 Hz/cm2 T=1.4 108 sec = 1620 days Pb-Pb run E. Scapparone INSTR08

  36. Conclusion ALICE is taking shape All large structures are installed and integration of detector subsystems will start in August The ALICE Collaboration looks forward to first operation of LHC for the expected and the unexpected… E. Scapparone INSTR08

  37. PHOton Spectrometer: PHOS • PbO4W- crystal calorimeter for Photons, neutral mesons, 1 to > 100GeV • Crystals: 2.2*2.2 cm2 , 20 X0, APD R/O Operated at – 25 deg; 5 pe / MeV • σ(E) ≈ 3%; σ(x,y) ≈ 4 mm; σ(t) ≈ 1 ns; at 1GeV • - 0.12 < η < 0.12; Δφ = 100 deg; at R = 460 cm • L0 trigger available at < 900 ns • Module tested, calibrated in test beam; 1 or 2 modules to be installed in 04/08 • 3rd module during 2008; • Ultimately 5 modules with 18 000 crystals expected by 2010 E. Scapparone INSTR08 37

  38. ElectroMagnetic Calorimeter: EMCAL • Pb-Scintillator em calorimeter for • Jet physics in conjunction with tracking and PID • Approximately opposite to PHOS • -0.7 <η < 0.7; Δφ = 107 deg • EM resolution σ(E) < 0.1/√E • 13 000 projective towers in ‘Shashlik’ geometry with APD R/O • L0 trigger in < 900 ns for high-pT jets, photons, electrons Status: project approved in Dec 2007 2 of 12 supermodules early 2009 E. Scapparone INSTR08 38

  39. Partial view of Muon chambers E. Scapparone INSTR08 39

  40. TOF Standalone PID (80 ps res. as in the PPR) E. Scapparone INSTR08

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