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ALICE at the Eve of First Collisions Status and First Physics Plans

ALICE at the Eve of First Collisions Status and First Physics Plans. 50th RNM, Nov 2009, Heidelberg Jan Fiete Grosse-Oetringhaus for the ALICE collaboration CERN PH/ALICE. p+Si* collision * or other detector material. 11.09.08 run 58338. Content. First Measurements

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ALICE at the Eve of First Collisions Status and First Physics Plans

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  1. ALICE at the Eve of First CollisionsStatus and First Physics Plans 50th RNM, Nov 2009, Heidelberg Jan Fiete Grosse-Oetringhaus for the ALICE collaboration CERN PH/ALICE

  2. p+Si* collision * or other detector material 11.09.08 run 58338 Content • First Measurements • Historic data, models, predictions • Analysis procedures • Systematic uncertainties w.r.t first data • ALICE • Status • Commissioning of central systems and detectors • LHC • Incident, status and plans ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  3. Proton Physics at the LHC • ATLAS and CMS (general-purpose detectors for p+p) • Higgs boson search + physics beyond the Standard Model • LHCb • CP-symmetry violating processes in b-quark systems • ALarge Ion Collider Experiment (ALICE) • ALICE has special features also for p+p collisions • Low momentum cut-off and low material budget • Excellent particle identification (PID) • ALICE can give an important contribution to p+p physics • Rare signals need good description of underlying event (bulk is soft, no pQCD) • Tuning of MC generators will be done using measured distributions from all experiments (joint effort of all experiments, coordinated by CERN PH) • Reference for Pb+Pb ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  4. inv. yield dNch/dh h pT (GeV/c) P(Nch) <pT> (GeV/c) Skands, hep-ph/0905.3418 charged multiplicity Nch First Measurements • Pseudorapidity density dNch/dh • h = - ln tan q/2 • Multiplicity distribution • Momentum distribution dNch/dpT • Correlation <pT> vs. Nch ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  5. Charged-Particle Multiplicity • Simple observable in collisions of hadrons • Important ingredient for the understanding of multi-particle production • LHC will be an energy realm where multiple parton interactions are in the bulk of the events • Constrain, reject and improve models dNch/dh h P(Nch) Review article (K. Reygers, JFGO) Charged-Particle Multiplicity in Proton–Proton Collisions Journal of Physics G, to be published 30 GeV  1.8 TeV Nch ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  6. <Nch> NSD Ös (GeV) Feynman Scaling • Phenomenological arguments about the exchange of quantum numbers • Feynman-x: x = 2pz/Ös • Feynman scaling function f(pT, x) independent of cms energy (for large energies) Average Nch increases with ln s dNch/dh constant Clearlyviolated ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  7. KNO Scaling • Koba, Nielsen, Olesen (1972) • Based on Feynman scaling • Scaling variable z = Nch/<Nch> • Express P(Nch) as P(z) * <Nch> • Multiplicity distributions fall on one curve P(Nch) <Nch> P(z) UA1 Nch/<Nch> in |h| < 2.5 Nch in |h| < 2.5 • Successful for NSD events • up to 60 GeV for full phase space (ISR) • up to 900 GeV in central region (UA1, UA5) • remains only valid in |h| < 1 for soft events at 1.8 TeV (CDF) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  8. Negative Binomial Distributions • Bernoulli experiment • Probability for n failures and k success in any order, but the last trial is a success • Physical interpretation • Cascade production (clan model, Giovannini 86) • Ancestor particle are produced independently (Poisson) • Existing particle can produce additional one with some probability p ISR, 30 GeV • Successful for NSD events • up to 540 GeV in full phase space (ISR, UA5) • central intervals up to 1.8 TeV (UA5, CDF) UA5, 900 GeV ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  9. Combination of 2 NBDs representing soft and semihard part of the collision (w/ w/o minijets)(Giovannini 99) Two classes of events, not two production mechanisms in the same event Other data-driven approach identifies several KNO components (Alexopoulos 98) Two Component Approaches UA5, 900 GeV P(Nch) Normalized Residuals Successful for all regions up to 1.8 TeV Physical interpretation unclear Nch ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  10. Predictions for LHC Energies • Extrapolations of trends at lower Ös • Just for average multiplicities • For the multiplicity distribution • Gluon saturation models (Armesto et al, Kharzeev et al) • Dual Parton Model / Quark-Gluon String Model • Monte Carlo generators • Pythia (pQCD + soft phenomenology) with all its tunes • Phojet (based on DPM/QGSM) • Epos dNch/dh predictions range from 4.8 to 7.8 (systematic uncertainties ~ 9%) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  11. Predictions for Ös = 14 TeV Multiplicity distributions differ by a factor 2 up to an order of magnitude (systematic uncertainties < 18%) More details in the mentioned review full phase space full phase space |h| < 1 |h| < 1 ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  12. full full EMCAL γ, π0, jets L3 Magnet T0/V0 Trigger ACORDE Cosmic trigger 36% 39% full HMPID PID (RICH) @ high pT TRD Electron ID (TR) TOF PID full full PMD γ multiplicity full TPC Tracking, PID (dE/dx) full full ITS Low pT tracking PID + Vertexing MUON μ-pairs full 60% FMD Charged multiplicity PHOS γ, π0, jets ALarge Ion Collider Experiment Dipole Not shown: ZDC (at ±116m) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  13. Proton-Proton Cross-section • Many experiments triggered on and published non single-diffractive events (NSD=ND+DD) • ALICE will measure inelastic (INEL) and NSD insensitive inelastic, ALICE trigger ND SD DD dN/dy dN/dy dN/dy Pythia, 900 GeV Rapidity y y y ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  14. Detector Acceptance h Minimum-Bias Trigger • Hit in central region (SPD) or in forward region V0 (either side) • Beam-gas background may motivate the use of different MB triggers • SPD and V0 (either side) • SPD and V0 (both sides) Efficiencies using Pythia/full detector simulation, 10 TeV ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  15. all events all events all events no trigger no trigger no trigger no trigger no vertex no vertex no vertex no vertex no vertex dNch/dh Measurement • Basically if the detector was perfect • But… there is • Detector acceptance, tracking efficiency • Decay, energy loss, stopping • Vertex reconstruction efficiency/bias, trigger efficiency/bias • Low momentum cut-off • Three corrections needed • Track-to-particle correction • pT cut-off (only TPC) • Vertex reconstruction correction • Trigger bias correction Primary Particles = charged particles produced in the collision and their decay products excluding weak decays from strange particles ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  16. Correction on Track Level Acceptance and tracking inefficiency Reconstructed tracks Secondary particles Track-to-particle correction Cuts 23% (171%)‏ 15% (138%)‏ 1% (25%)‏ 17% (5%)‏ Corrected primary particles Primary particles – (17%)‏ SPD (TPC) 3% (18%)‏ 20% (9%)‏ 1% (3%)‏ pT cut-off correction Cuts Acceptance and tracking inefficiency Decay and material Values for SPD (TPC) Percentages relative to initial number of primary particles ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  17. Corrections • Track-to-particle correction • Acceptance of the SPD clearly visible • Average factor ~ 1.3 (central region) • Function of h, z-position of event vertex (vtx-z), pT (only TPC) • Trigger-bias correction • Corrects towards • Inelastic events • NSD events • Event and track level • Evt level: fct of multiplicity, vtx-z h vtx-z (cm) correction factor Event level towards NSD multiplicity ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  18. Method Verification dNch/dh • Method test • Use reconstructed values • 20,000 events • Under certain assumptions exact reproduction of MC • Use MC vertex • Use MC truth (h, vtx-z) of each reconstructed track Ratio 900 GeV - inelastic h dNch/dh Ratio 900 GeV – inelastic h ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  19. Systematic Uncertainties ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  20. dNch/dh h Analysis Result SPD Pythia, 10 TeV Analysis sample: 50,000 simulated events Correction sample: 200,000 simulatedevents More details CERN-THESIS-2009-033 (on CDS) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  21. |h| < 1 measured multiplicity true multiplicity Multiplicity Measurement • Efficiency, acceptance • Resolution vs. bin size  bin flow • Correction by unfolding • Detector response • Probability that a collision with the true multiplicity t is measured as an event with the multiplicity m • Vertex reconstruction, trigger bias correction • Like for dNch/dh, but in unfolded variables (true multiplicity) because it is applied after unfolding ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  22. Challenges with Unfolding • Example with a simple quadratic response matrix R • True distribution (Gaussian is assumed) converted to measured distribution using R • 10,000 measurements generated • R is inverted and used to infer the 'true' distribution large statistical fluctuations "inverted" "measured" ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  23. Unfolding using c2-Minimization • One free parameters per bin for unfolded spectrum Ut • Regularization • Prefer constant • Least curvature • Reduced cross-entropy (MRX)(optional: a-priori distribution e)(Nucl.Instrum.Meth. A340:400-412,1994) Regularizations ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  24. Unfolding using Bayesian Method Bayesian method (based on Bayes’ theorem) (e.g. Nucl.Instrum.Meth.A362:487-498,1995) Response matrix Smearing matrix Prior distribution (guess) Measured distribution Unfolded distribution Weight parameter (optional) • Iterative method: • Choose prior distribution Pt • Calculate • Replace Pt by ; go to 2. Limited number of iterations provides implicit regularization (V. Blobel, hep-ex/0208022) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  25. Example of Unfolding using Bayesian Method Events Ratio Nch Nch already close to input distribution after 1 (!) iteration ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  26. Systematic Uncertainties • Uncertainty does not shift whole spectrum • By definition spectrum is normalized • Spectrum gets distorted • Uncertainty a function of multiplicity  depends on the true spectrum • Data is unfolded with modified response matrices that consider changes in cross-sections, particle composition, spectra, material budget, misalignment Ratio change/normal Efficiency change Nch Uncertainty (%) Nch ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  27. Systematic Uncertainties (2) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  28. Analysis Result P(Nch) Nch Pythia, 10 TeV Analysis sample: 90,000 simulated events Correction sample: 380,000 simulatedevents More details CERN-THESIS-2009-033 (on CDS) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  29. Momentum Distribution • Loose quality criteria for tracks • Track-vertex DCA matching ~ 2 - 3 cm • Bin-by-bin corrections similar to dNch/dh analysis • Second analysis using unfolding being investigated • pT resolution ~ 7 % @ 10 GeV/c (cosmics) Plot from J. Otwinowski 2x104 pp @ 900 GeV pT (GeV/c) pT resolution from cosmics spT / pT Plot from M. Ivanov pT (GeV/c) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  30. Commissioning October data-taking 100M events • ALICE has been operating 24/7 • Aug - Oct 2008: 1200 h of data-taking • since Aug 2009: 2000 h of data-taking • Cosmics • 468M TOF triggered • 160M with HLT filtering  at least one track per event • 50k SPD triggered • 475k MUON triggered • 740k TOF-TRD triggered • Calibration & Alignment • LHC Injection Tests • Trigger alignment • "Early Physics Running" • Test detectors at high rates with artificial triggers ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  31. Inner Tracking System • Silicon Pixel Detector • 106 out of 120 modules stably running ~ 88% • Dead/noisy pixels < 0.15% • Improvements in cooling 2009 • Silicon Drift Detector • 247 out of 260 modules ~ 95% • Fraction of bad anodes ≈ 2% • Silicon Strip Detector • 1477 out of 1698 modules ~ 87% • Fraction of bad strips ≈ 1.5 % SPD - double cluster in same track not realigned realigned A. Dainese  sspatial=14 mm (MC ideal geometry: sspatial=11 mm) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  32. Time Projection Chamber • About 0.15% non-active channels • Temperature stable within 0.1 K • Very low noise of 0.7 ADC counts (700 e) • Direct energy calibration using Krypton gas cosmic event DTRMS=53 mK Dtmin/max= 206 mK Gain map Krypton calibration A side Images from R. Schmidt, A. Matyja ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  33. Transition Radiation Detector • 7 out of 18 modules installed • Completion of full TRD: expected early-2011 • 2% non-active channels • Cosmics data-taking with TOF pre-trigger and TRD L1 selection • Purity above 90% for at least one TRD track • Gain calibration with Krypton • Final gas mixture with Xe/CO2 for e-p separation Cluster-track residuals Plot from E. Sicking - GSI report ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  34. integrated over run 79774 Time of Flight • ~ 6% non-active channels • Cosmics • Relative time alignment • Present time resolution ~ 130 ps (no channel-by-channel calibration yet due to too low statistics) picture from D.De Gruttola Injection test 25 ns ~ 7.5 m detector length picture from R. Preghenella ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  35. Bad electrical contact between wedge and U-profile with the bus on at least 1 side of the joint Bad contact at joint with the U-profile and the wedge Resistive joint of about 200 nΩ LHC – Incident • As you know we should have had first collisions in Sep/Oct 2008… • On the 19th Sep 2008, during 5 TeV commissioning (no beam) of Sector 34 an incident occurred • A splice between two magnets opened and an electric arc developed Drawing from F. Bertinelli ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  36. LHC – Incident Temperatures LHC Sector 34 Friday 19.09.08 • 46% of the 595 MJ stored inductive energy missing, consumed in electrical arcs • Enough to heat and melt 375 kg of copper • Vacuum and pressure levels in cryostat subsectors: peak of 8 bar in cryostats, designed for 1.5 bar collateral damage • 2t of Helium (of 15t in the sector) rapidly released in tunnel (followed by further 4t at lower rates) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  37. LHC – Consolidation & Repairs • Main damage over ~700 metres • 39 out of 154 dipoles, • 14 out of 47 quadrupole short straight sections • All magnets repaired or replaced • New pressure relief valves to prevent collateral damage in similar incident • Improved Quench Protection System • 250 km of additional cabling (doubling previous amount present) • Last interconnect closed on 17th June 2009 2nW Splice resistance measurement LHC is cold Sep 1st Oct 1st ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  38. LHC Planning • 900 GeV collisions in December • Ramp to 2.2 TeV (if if if) • Shutdown over Christmas • Commissioning of nQPS in Jan 2010 • 7 TeV collisions over the whole year • Ion beam setup in Oct 2010 • 1 month of ion collisions in 2010 TODAY 2010 2010 IONS Planning from Mike Lamont, LHC team ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  39. 900 GeV Collisions • Assumed scenario • 2 on 2 bunches • For each orbit (and for each experiment) • 1 bunch-bunch encounter (bb) • 1 bunch-empty encounter (be) • 1 empty-bunch encounter (eb) • Initial detectors • At least SPD, TPC, V0, FMD, ZDC • Plus all other detectors that are ready and run stable • ALICE will initially trigger on bunch-crossings • A few 1010 protons per bunch, β* = 10 m, µ ~ 1% • Empty-bunch / empty-empty for beam-gas / background / halo • Most events will be empty (offline selection) • Move to minimum-bias trigger when background levels are understood delayed by 75ns ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  40. p+Si* collision * or other detector material 11.09.08 run 58338 Summary • ALICE is commissioned • Calibration and alignment is very advanced • ALICE's first analyses are fully prepared • LHC seems to be at the eve of collisions… • ALICE can measure with a few days of data basic properties of p+p collisions from 900 GeV to 14 TeV • This provides the reference and paves the way for a rich heavy-ion program that will study the QGP in detail Thank you for your attention! ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

  41. References • JFGO, K. Reygers, review on Charged-Particle Multiplicity in Proton–Proton Collisions, Journal of Physics G, to be published • JFGO, Measurement of the Charged-Particle Multiplicity in Proton-Proton Collisions with the ALICE Detector, CERN-THESIS-2009-033 (on CDS) ALICE at the Eve of First Collisions - Jan Fiete Grosse-Oetringhaus

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