March 3, 2008E. Scapparone INSTR081 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.

March 3, 2008E. Scapparone INSTR0822 ALICE: A Large Ion Collider Experiment at CERN-LHC Size: 16 x 26 meters Weight: 10,000 tonnes p-p (L=10 31 cm -2 s -1 ), Pb-Pb (L= cm -2 s -1 )

March 3, 2008E. Scapparone INSTR083 Life in Pb-Pb interactions was never easy…. NA49 At RHIC became harder….. ALICE simulated central event !..also more RHIC STAR

March 3, 2008E. Scapparone INSTR084 6 layers, three technologies (keep occupancy at a few % for max multiplicity) SPD: silicon pixels (0.2 m 2, two layers, 9.8 M channels) SDD: silicon drift (1.3 m 2, two layers, 133 k channels) SSD: double-sided silicon strips (4.9 m 2, two layers, 2.6 M channels ) R out =43.6 cm SPD SSD SDD ITS(Inner Tracking System) L out =97.6 cm Material Budget: ≤ 1% X 0 per layer !

March 3, 2008E. Scapparone INSTR085 Challenge: track densities at r = 4 cm (1st layer): up to 100 / cm2 SPD (0.2 m 2 ) Cell size (r  z  : 50  m x 425 µm space resolution(r  ) : 12  m space resolution(z): 100  m ITS SDD (1.3 m 2 ) cell size (r ,z): 294 x 150  m2 space resolution (r , z) : 35  m space resolution(z): 23  m SSD (4.9 m 2 ) cell size (r ,z): 95 x 4200  m2 space resolution (r  ): 20  m space resolution (z); 830  m 40 m m 75 mm 42 mm 6 chips

March 3, 2008E. Scapparone INSTR0866 Inner Tracking System ~ 10 m 2 Si detectors, 6 layers Pixels, Drift, double sided Strips Strips SSD Drift SDD Pixels Inner Silicon Tracker Pixels SPD

March 3, 2008E. Scapparone INSTR087 TPC SSD/SDD SPD

March 3, 2008E. Scapparone INSTR0888 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% X 0 total material for perpendicular tracks novel digital electronics (ALTRO) highly integrated, digital shaping; tail cancellation;0-suppression; Baseline restoration Powerful laser calibration system TPC Drift gas:Ne (86) / CO 2 (9.5) / N 2 (4.5) σ(dE/dx) ≈ 5.5 to 6.5 %, depending on multiplicity (measurements and simulations)

March 3, 2008E. Scapparone INSTR0899 ALICE TPC: 5 years construction

March 3, 2008E. Scapparone INSTR0810 Cosmics recorded in Commissioning with Cosmics and Laser tracks Spatial resolution and Electronics noise in experiment according to specifications Status: installed and being commissioned

March 3, 2008E. Scapparone INSTR0811 e/  separation in central barrel p>1 GeV/c fast trigger for high momentum particles (hadrons, electrons)+ tracking 540 detectors ~ 760m 2 18 super modules length: 7m X/X 0 ~ 22 % 28 m 3 Xe/CO 2 (85/15) 1.2 million channels Transition Radiation Detector (TRD) Status: partially installed; being commissioned TRD

March 3, 2008E. Scapparone INSTR0812 TRD - Signal Generation & Processing Average pulse heigth (mV)  e-) = 90 %

March 3, 2008E. Scapparone INSTR0813 TRD Installation

March 3, 2008E. Scapparone INSTR0814 TOF requirements: Large array to cover the ALICE barrel (~150 m 2 ) 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 √

March 3, 2008E. Scapparone INSTR0815 TOF 2 crates /side pads, total sensitive area: ~150 m 2 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

March 3, 2008E. Scapparone INSTR0816 Cross section of a double-stack MRPC strip 2 rows of 48 readout pads (3.5 x 2.5 cm 2 ) Active strip length = 120 cm Differential signal to FEA card 10 gaps 250  m

March 3, 2008E. Scapparone INSTR0817 Test beam of single strips Efficiency Time resolution( ps) ε > 99.9 % average ~ 50 ps Gas mixture: C 2 F 4 H 2 (90%) – SF 6 (5%) – C 4 H 10 (5%) Similar results obtained when strips are inserted inside the modules

March 3, 2008E. Scapparone INSTR0818 M = p ((t2 c2 /L2 )-1)1/2 σ TOF = 80 ps ; B = 0.5 T

March 3, 2008E. Scapparone INSTR SMs installed ; next 4 SMs to be installed next week; being commissioned

March 3, 2008E. Scapparone INSTR0820 December 2007 cosmic run Event display of a muon crossing the TOF detector

March 3, 2008E. Scapparone INSTR0821 Proximity Focused RICH 11 m 2 active detector area 7 modules - 0.6< η < 0.6; Δφ = 58 deg CsI Photocathode read by pads Threshold momentum = 1.21* (Particle Mass) PID optimization for 1 GeV < p < 6 GeV High Momentum Particle Identifier: HMPID

March 3, 2008E. Scapparone INSTR0822 HMPID (Sept ’06) HMPID: Installed; being commissioned

March 3, 2008E. Scapparone INSTR0823 Example of a high multiplicity event as seen by the HMPID dN/d  =6000

March 3, 2008E. Scapparone INSTR stations of high granularity pad tracking chambers, over 1 million channels Complex absorber/small angle shield system (~10 I ) to minimize background (90 cm from vertex) RPC Trigger Chambers MUON spectrometer set-up  0.7 T, bending power 3 Tm  4 MW power, 800 tons  World’s largest warm dipole Trigger pt cut on single  : ~1 GeV/c

March 3, 2008E. Scapparone INSTR0825 Lepton Acceptance ATLAS & CMS present a large lepton acceptance |  |<2.4 ALICE combines muonic and electronic channels - covers the low p T region (quarkonia) - covers the forward region 2.5<  <4.0

March 3, 2008E. Scapparone INSTR0826 Charged Particle Identification ITS kaons pions protons dE/dx (MIP units) TPC All known PID techniques used in ALICE  dE/dx = 6.8% at dN/dy=8000 (5.5% for isolated tracks) HADRON-ID  3  separation power P(GeV/c) dE/dx (MIP units)

March 3, 2008E. Scapparone INSTR0827 Combined PID Performance Efficiency/Contamination Kaon PID (the most difficult case...) ITS TPC TOF(*) (120 ps) p (GeV/c) (C  : C K : C p = 0.75 : 0.15 : 0.1) Higher efficiency & Lower contamination wrt individual detectors p (GeV/c) Combined PID ITS & TPC & TOF (*) very conservative

March 3, 2008E. Scapparone INSTR0828 Extension of PID to higher momenta combining the dE/dX of TRD and TPC Combine TPC and TRD dE/dx capabilities (similar number of samples/track) to get statistical ID in the relativistic rise region 8<p<10 GeV/c

March 3, 2008E. Scapparone INSTR0829 Open Charm Detection in Hadronic Decays Mass GeV/c 2 c  =124  m ~0.55 D 0  K -  + accepted/event important also for J/  normalization

March 3, 2008E. Scapparone INSTR0830 Spectra

March 3, 2008E. Scapparone INSTR0831 Finally … ALICE is becoming reality after almost 15 years in the making 2 nd 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.

March 3, 2008E. Scapparone INSTR0832 RISERVE

March 3, 2008E. Scapparone INSTR0833 GIF results No ageing effect measured at PS Working voltage = 13 kV

March 3, 2008E. Scapparone INSTR0834 GIF results: No current increase Source on Source off Source on Source off I (  A) Flow = 1.4 cm 3 /s The gas going to the chamber 2 was bubbled through water for some time of the exposure

March 3, 2008E. Scapparone INSTR0835 Ageing study: Total charge = 14 mC/cm 2 Charge/event = 2 pC 7 *10 9 events /cm 50 Hz/cm 2 T= sec = 1620 days Pb-Pb run Time(min) two MRPC strips irradiated at GIF

March 3, 2008E. Scapparone INSTR0836 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… Conclusion

March 3, 2008E. Scapparone INSTR0837 PHOton Spectrometer: PHOS PbO 4 W- crystal calorimeter for Photons, neutral mesons, 1 to > 100GeV Crystals: 2.2*2.2 cm 2, 20 X 0, APD R/O Operated at – 25 deg; 5 pe / MeV σ(E) ≈ 3%; σ(x,y) ≈ 4 mm; σ(t) ≈ 1 ns; at 1GeV < 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 3 rd module during 2008; Ultimately 5 modules with crystals expected by 2010

March 3, 2008E. Scapparone INSTR0838 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 projective towers in ‘Shashlik’ geometry with APD R/O L0 trigger in < 900 ns for high-p T jets, photons, electrons Status: project approved in Dec of 12 supermodules early 2009

March 3, 2008E. Scapparone INSTR0839 Partial view of Muon chambers

March 3, 2008E. Scapparone INSTR0840 TOF Standalone PID (80 ps res. as in the PPR)