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The ALICE Experiment at LHC: Detector & Physics

The ALICE Experiment at LHC: Detector & Physics. V. Manzari INFN & University of Bari - Italy. XI Frascati Spring School “Bruno Touschek” LNF, May 15th – 19th, 2006. Contents. Nucleus-nucleus collisions at the LHC The Alice experiment Overview of Alice subsystems Physics Examples

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The ALICE Experiment at LHC: Detector & Physics

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  1. The ALICE Experiment at LHC:Detector & Physics V. Manzari INFN & University of Bari - Italy XI Frascati Spring School “Bruno Touschek” LNF, May 15th – 19th, 2006

  2. Contents • Nucleus-nucleus collisions at the LHC • The Alice experiment • Overview of Alice subsystems • Physics Examples • Jet quenching • Heavy flavours • Conclusions Frascati Spring School, May 15th -19th, 2006

  3. QCD tells us… • Ultimate goal: understanding of the QCD phase diagram - QCD prediction  the existence of a new state of matter at high temperature, the quark Gluon Plasma • Tc173 MeV, mq0, Nf=2,3 • Order of the transition? • c 0.3-1.3 GeV/fm3 • LHC will allow to go much deeper into a QGP phase and to study the QGP equation of state. Frascati Spring School, May 15th -19th, 2006

  4. Central collisions SPS RHIC LHC s1/2(GeV) 17 200 5500 dNch/dy 500 850 2–8 x 103 e (GeV/fm3) 2.5 4–5 15–40 Vf(fm3) 103 7x103 2x104 tQGP (fm/c) <1 1.5–4.0 4–10 t0 (fm/c) ~1 ~0.5 <0.2 SPS to RHIC to LHC • QGP is characterized by two qualitatives changes: deconfinement & chiral simmetry restoration • Both changes will certainly have consequences in the final state observed by the experimental apparatus  Energy per NN LHC ≈ 30 x RHIC  Initial energy density LHC ≈ 3  10 x RHIC  Volume LHC ≈ 3 x RHIC  QGP lifetime LHC ≈ 3 x RHIC  Formation time LHC ≈ 1/3 x RHIC • Initial condition at LHC different than at RHIC: “hotter – bigger – longer lived” Frascati Spring School, May 15th -19th, 2006

  5. Novel aspects… soft processes • The energy increase at LHC will make accessible a novel range of Bjorken-x - solid lines  relevant x-M2 ranges for particle production • Probe initial partonic state in a “new” Bjorken-x range (10-3- 10-5): - nuclear shadowing • high-density saturated gluon distribution (CGC) Energy increase  lower x   RHIC forward region  LHC mid rapidity (easier detection) Frascati Spring School, May 15th -19th, 2006

  6. Novel aspects… hard processes • Hard processes contribute significantly to total AA cross-section: (σhard/σtot = 98%) • Bulk properties dominated by hard processes • Hard probes abundantly produced • Hard processes are extremely useful tools: • Probe matter at very early times • Hard processes can be calculated by pQCD • Heavy quarks and Weakly interacting probes become accessible (Z0, W±) 5500 GeV Frascati Spring School, May 15th -19th, 2006

  7. 5.5 1027 70-50 106 ** 7.7 LHC as Ion Collider • Running conditions: • Expected Pb-Pb luminosity  rather low minimum-bias interaction rate (≈8kHz): - LHC detectors in heavy ion mode  lower rates & higher particle density • + other collision systems: pA, lighter ions (Sn, Kr, Ar, O) & energies (pp @ 5.5 TeV) √sNN (TeV) L0 (cm-2s-1) <L>/L0 (%) Run time (s/year) sgeom (b) Collision system pp 14.0 1034 * 107 0.07 PbPb *Lmax (ALICE) = 1031 ** Lint (ALICE) ~ 0.7 nb-1/year Frascati Spring School, May 15th -19th, 2006

  8. One dedicated HI experiment: ALICE Two pp experiments with HI program: ATLAS and CMS Frascati Spring School, May 15th -19th, 2006

  9. ALICE Detector • Large acceptance • Good tracking capabilities • Selective triggering • Excellent granularity • Wide momentum coverage • PID of hadrons and leptons • Good secondary vertex reconstruction • Photon detection Adopted a variety of experimental techiniques AA Physics Menu at LHC • Global properties • Multiplicities, η distributions, zero degree energy • Event history • HBT • Resonance decays • Fluctuations and critical behaviour • Event-by-event particle composition & spectroscopy • Neutral to charged ratio • Degrees of Freedom vs Temperature • Hadron ratios and spectra • Dilepton continuum • Direct photons • Collective effects • Elliptic flow • Deconfinement, chiral simmetry restoration • Charmonium, bottonium spectroscopy • (Multi-)strange particles • Partonic energy loss in QGP • Jet quenching, high pT spectra • Open charm and beauty Frascati Spring School, May 15th -19th, 2006

  10. ALICE: The dedicated HI experiment • ALICE is a general purpose experiment designed to study the physics of strongly interacting matter and the quark-gluon plasma in nucleus-nucleus collisions. • ALICE will meet the challenge to measure flavour content and phase-space distribution event-by-event at the highest particle multiplicities anticipated for Pb-Pb collisions: • Most (2p * 1.8 units h) of the hadrons (dE/dx + TOF), leptons (dE/dx, transition radiation, magnetic analysis) and photons (high resolution EM calorimetry). • Track and identify from very low pt (< 100 MeV/c; soft processes) up to very high pt (>100 GeV/c; hard processes). • Identify short lived particles (hyperons, D/B meson) through • secondary vertex detection. • Identify jets. Frascati Spring School, May 15th -19th, 2006

  11. Solenoid magnet 0.5 T Frascati Spring School, May 15th -19th, 2006

  12. Central Solenoid: from L3 (LEP) Frascati Spring School, May 15th -19th, 2006

  13. Central tracking & PID system: • ITS • TPC • TRD • TOF Frascati Spring School, May 15th -19th, 2006

  14. Central Tracking & PID |h|<0.9: B = 0.4 T TOF (3.7 – 4 m) TRD (2.9 - 3.7 m) TPC (85 - 250 cm) ITS (4 -45 cm) with: - Si pixel - Si drift - Si strip Frascati Spring School, May 15th -19th, 2006

  15. Combined momentum resolution at low momentum dominated by - ionization-loss fluctuations - multiple scattering at high momentum determined by - point measurement precision - alignment & calibration (assumed ideal here) resolution ~ 7% at 100 GeV/c excellent performance in hard region! Frascati Spring School, May 15th -19th, 2006

  16. Inner Tracking System (ITS) • longitudinal coverage: • |h| < 1 (tracking), |h|<2 (multiplicity) Frascati Spring School, May 15th -19th, 2006

  17. Picture of a solder bump bond (courtesy of VTT) bump-bonded assembly Sensor Chip bump-bonded assembly Sensor (200 µm thickness) Chip (150 µm thickness) ITS: Silicon Pixel Detector (SPD) • 2 layers, r = 3.9, 7.6 cm • sensitive length (in z): 28.6 cm (for both layers) • hybrid (bump-bonded) silicon pixel assemblies • Pb/Sn bumps • pixel size: 50 × 425 µm2 • binary r/o • module size: 12.8 × 69.6 mm2 • 240 modules • 9.8 M channels Frascati Spring School, May 15th -19th, 2006

  18. The Half Cylinders and their tooling Front view Half-Barrel final assembly ITS: Silicon Pixel Detector (SPD) • successful system beam test Oct. ’04 including full FEE and DAQ, DCS, ECS Combined with the other ITS detector systems • bump bonding at VTT (Finland) • series production started (e > 99%) • low-mass support/cooling sectors ready • assembly sites in Bari and Padova • Status • “ready for installation”: Nov ‘06 • viable schedule, but tight & little contingency Frascati Spring School, May 15th -19th, 2006

  19. Sector 0 (mixed bus) Sector 1 (full Al bus) SPD Frascati Spring School, May 15th -19th, 2006

  20. ITS: Silicon Drift Detector (SDD) • Hybrids : • 520 needed; production completed; done in industry • Modules: • 260 needed; assembly completed: June ‘06 • Ladders: • 36 needed; production ongoing assembly completed: July ‘07 • Mechanics • Components ready for assembly • Status: - ready for integration with SSD: Jul ‘06 View of modules with two hybrids; Was used in 2004 beam test Frascati Spring School, May 15th -19th, 2006

  21. ITS: Silicon Strip Detector (SSD) Ramping of component delivery and assembly • Production: • sensors from three vendors under production • FEE electronics: all chips in production • micro-cables & hybrids (Ukraine): • very advanced technology • Assembly: • shared between 4 ( later 5) sites (Finland, France, Italy); pre-production validated • Status: • Ready for integration with SDD: Jul ’06 • SDD+SSD ready for installation: Sep. ‘06 p-Hybrid Sensor n-Hybrid Frascati Spring School, May 15th -19th, 2006

  22. E E E E 88us 510 cm Time Projection Chamber (TPC) GAS VOLUME 88 m3 DRIFT GAS 90% Ne 10% CO2 Field cage finished FEE finished Read out chamber finished At present: pre-integration of field cage into experiment Readout plane segmentation 18 trapezoidal sectors each covering 20 degrees in azimuth Frascati Spring School, May 15th -19th, 2006

  23. TPC Mounting the TPC Central Electrode With 10-4 parallelism to readout chambers Completed Readout chamber installation Frascati Spring School, May 15th -19th, 2006

  24. Fully equipped TRD chamber Transition Radiation Detector (TRD) Pad chambers with a total of 1 200 000 channels Frascati Spring School, May 15th -19th, 2006

  25. Time-Of-Flight (TOF) • Multi-gap RPC • high performance: 50 ps resolution achieved! Frascati Spring School, May 15th -19th, 2006

  26. Testbeam Cosmic rays σ(TOF) ~ 60 ps TOF: performance and construction • Detector -Strip production: 20/week to increase to 40/week with 2nd automated assembly line -Finished : 11/06 -Module assembly : start 06/05; finish : 11/06 • Supermodules : installation test with mock-up done successfully • Start SuperModules installation July/August ‘06 Frascati Spring School, May 15th -19th, 2006

  27. ITS/TPC/TRD/TOF Pre-Integration Pre-Integration of ITS/TPC/TRD/ TOF/vacuum chamber April 2005 Frascati Spring School, May 15th -19th, 2006

  28. Specialized detectors: • HMPID • PHOS Frascati Spring School, May 15th -19th, 2006

  29. High Momentum Particle Identification (HMPID) - Detector production (7 modules) finished -CsI-cathode 35/42 ready and performance better than specified - Ready for Installation: July ‘06 Sensitivity of cathodes Required: >12 clusters Measured: >18 clusters for relativistic particles Cathode uniformity ~ 5 % Frascati Spring School, May 15th -19th, 2006

  30. single arm em calorimeter photons, g-jet tagging dense, high granularity (2x2x18cm3) crystals novel material: PbW04 ~18 k channels, ~ 8 m2 cooled to -25o PbW04 crystal Photon Spectrometer (PHOS) PbW04: Very dense: X0 < 0.9 cm Good energy resolution (after 6 years R&D): stochastic 2.7% / E1/2 noise 2.5% / E constant 1.3% Frascati Spring School, May 15th -19th, 2006

  31. MUON Spectrometer: • absorbers • tracking stations • trigger chambers • dipole Frascati Spring School, May 15th -19th, 2006

  32. Muon Magnet :world’s largest warm dipole Muon Filter Frascati Spring School, May 15th -19th, 2006

  33. Muon Tracking System • Advanced ‘Pad-chamber’ system with • 1.2* 106 readout channels • Sagitta resolution of < 50 μm for • Mass resolution of ~ 80 MeV at Upsilon • Production of chambers in • France, India, Italy, Russia • Scheduled to be finished end 2005 Frascati Spring School, May 15th -19th, 2006

  34. Cosmic rays trigger • Forward detectors: • PMD • FMD, T0, V0, ZDC Frascati Spring School, May 15th -19th, 2006

  35. Trigger Counters T0/V0/FMD/Accorde Accorde: large area Scintillator + PM trigger on Cosmic rays V0: Scintillator + PM FMD: Si m-strips T0: Quartz-C + PM Frascati Spring School, May 15th -19th, 2006

  36. Physics Examples: • Jet Quenching • Heavy Flavours Frascati Spring School, May 15th -19th, 2006

  37. Jets in QCD: - Cascades of consecutive emissions of partons initiated by partons from an initial hard scattering; - Parton fragmentation  showering and hadronization. In-medium effects  modifications of the jet structure: Reduction of single inclusive high pt particles: - Parton specific (stronger for gluons than quarks) - Flavour specific (stronger for light quarks)  Measure identified hadrons (p, K, p, Λ, etc.) + heavy partons (charm, beauty) at high pT Change of fragmentation function for hard jets (pt>>10 GeV/c) - Transverse and longitudinal fragmentation functions of jets - Jet broadening  reduction of jet energy, dijets, g-jet pairs - Suppression of mini-jets: same-side/away-side correlations Jet quenching Frascati Spring School, May 15th -19th, 2006

  38. Experimentally • Highest sensitivity to the medium properties: - modifications of the reconstructed jets - partonic energy loss  decrease particles carrying a high fraction of the jet energy and appearance of radiated energy via an increase of low-energy particles - broadening of the distribution of jet-particle momenta • Measurement of Jet Energy: • In present configuration Alice measures only charged particles ( and electromagnetic energy in PHOS) • The large EM Calorimeter will improve the jet energy resolution, increase the selection efficiency and further reduce the bias on the jet fragmentation + jet trigger capabilities needed to increase the statistics at high Et. • Measurement of Jet Structure very important: • Requires good momentum analysis from ~ 1 GeV/c to ~ 100 GeV/c • Alice excels in this domain • pp and pA measurements essential as reference! Frascati Spring School, May 15th -19th, 2006

  39. Energy domains for jet reconstruction 2 GeV20 GeV 100 GeV 200 GeV Mini-Jets 100/event 1/event 100k/month • Event structure and properties • at p > 2 GeV/c • Correlation studies • Limit is given by underlying event • Reconstructed Jets • Event-by-event well • distinguishable objects Example : 100 GeV jet + underlying event Frascati Spring School, May 15th -19th, 2006

  40. e.g.: for 100 GeV jet Reduced cone size... • Large underlaying hadron background  reduced cone size R • Central PbPb at √s=5.5 TeV • dNch/dy = 2000-8000 • dET/dh ~ 1.5-6 TeV • Energy in R < 0.7: 0.4 -1.5 TeV • Problems • Identification... • Energy resolution: background fluctuations comparable to jet energy • use smaller cone size, R ~ 0.3 Frascati Spring School, May 15th -19th, 2006

  41. Jet quenching? • Excellent jet reconstruction… but challenging to measure global medium modification … • Et=100 GeV (reduced average jet energy fraction inside R): • Radiated energy ~20% • R=0.3 : dE/E=3% • Most of radiated energy stays within cone •  • Jet quenching rather means a medium-induced redistribution of the jet energy inside the jet cone Jet shape: average fraction of energy in a sub-cone of radius R Frascati Spring School, May 15th -19th, 2006

  42. Low-pT tracking essential... Simple quenching model: The energy loss of a 100 GeV jet is simulated by reducing the energy of the jet by 20% and replacing the missing energy by: 1 x 20 GeV gluon 2 x 10 GeV gluons 4 x 5 GeV gluons (Jets simulated with Pythia) Summary: • ALICE combines low-pt tracking and PID  study of the jet-structure over a wide range of momenta and particle species. • Jet reconstruction restricted to relatively high-energy jets (Et>30-40 GeV) while leading particle correlation studies play an important role in the low-Et region. Frascati Spring School, May 15th -19th, 2006

  43. Heavy Flavours • LHC is the first machine where heavy quarks will be produced abundantly in heavy-ion collisions. • Heavy flavour production in pp and AA collisions to pt ≈0: - open charm and open beauty: - mechanism of heavy-quark production, propagation and hadronisation (in-medium quenching compared to massless partons) - cross sections as a reference for quarkonia production  excellent impact parameter resolution (secondary vertex) and PID capability  wide pt range - quarkonia: - yields and pt spectra of J/Y, Y’, , ’ and ’:  e+e- in central region and m+m- in forward region Frascati Spring School, May 15th -19th, 2006

  44. Heavy flavour energy loss? • Energy loss for heavy flavours is expected to be reduced  • harder pt spectra for heavy- wrt light-flavour mesons: i) Casimir factor • light hadrons originate predominantly from gluon jets, heavy flavoured hadrons originate from heavy quark jets • CR is 4/3 for quarks, 3 for gluons ii) dead-cone effect • gluon radiation expected to be suppressed for q < MQ/EQ (heavy quarks with momenta < 20-30 GeV/c  v << c) [Dokshitzer & Karzeev,Phys. Lett. B519 (2001) 199] [Armesto et al., Phys. Rev. D69 (2004) 114003] average energy loss Casimir coupling factor distance travelled in the medium transport coefficient of the medium ( gluon density  probe the medium)  R.Baier et al., Nucl. Phys. B483 (1997) 291 (“BDMPS”) Frascati Spring School, May 15th -19th, 2006

  45. RAA(D) in ALICE • The dead cone effect can be studied in the pt-dependence of the nuclear modification factor RAA ‘High’ pT (6–15 GeV/c) Energy loss can be studied (it is the only expected effect) Low pT (< 6–7 GeV/c) Nuclear shadowing Nuclear modification factor: production yield in AA collisions normalized to elementary pp collisions, scaled with the number of binary collisions  good sensitivity for measurement of c quenching Frascati Spring School, May 15th -19th, 2006

  46. expected d0 resolution (s) Detection strategy for D0 K-p+ • Weak decay with mean proper length ct = 124 μm • Track Impact Parameter (distance of closest approach of a track to the primary vertex) of the decay products d0 ~ 100 μm • STRATEGY: invariant mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices - Measurement of Impact Parameters - Measurement of Momenta - Particle identification to tag the two decay products Frascati Spring School, May 15th -19th, 2006

  47. statistical. systematic. D0 K-p+ • expected ALICE performance • S/B ≈ 10 % • S/(S+B) ≈ 40 (1 month Pb-Pb running)  similar performance in pp (wider primary vertex spread) pT - differential Frascati Spring School, May 15th -19th, 2006

  48. Proposed ALICE EMCAL • To improve the capabilities in triggering and measurement of high energy jets • EM Sampling Calorimeter (STAR Design) • Pb-scintillator linear response • -0.7 < h < 0.7 • p/3 < F < p (opposite to PHOS) • Energy resolution ~15%/√E • Rails already installed • Support structure funded by DoE, • to be installed this summer • 10 +1/2+1/2 Supermodules (SM) • 1 SM = 24x12 modules • 1 module = 4 channels : • 1.2 x 104 total channels (granularity) Frascati Spring School, May 15th -19th, 2006

  49. EMCAL • Single detector : 6x6x25 cm3 shashlik 1.44mm Pb/1.76mm scintillator sampling • 77 layers = 20 Xo • WLS fiber+APD readout • Front End Electronics mainly developed for TPC and PHOS • First SM to be ready for 2008 run • Full Calorimeter to be completed for 2010 run EMCAL Project: Italy (LNF, Ct) + France + US Frascati Spring School, May 15th -19th, 2006

  50. Conclusions • LHC • the next jump in heavy-ion physics “it is dangerous to make predictions, especially about the future” • significant extension of reach at both soft and hard frontiers • ALICE • dedicated heavy-ion experiment • address most relevant observables, from very soft to very hard • novel technologies! • production well under way • Busy months ahead  working detector well on track for the start-up of LHC (summer 2007) • Study collisions of lower-mass ions (varying energy density) and protons (pp and pA) as reference • pp data will also allow for a number of genuine pp physics studies we are looking forward towards exciting times! Frascati Spring School, May 15th -19th, 2006

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