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ALICE Status Report

Proton-Proton Physics with ALICE. ALICE Status Report. Jean-Pierre Revol CERN. Jean-Pierre Revol CERN. Fifth Workshop on High p T Physics at LHC Instituto de Ciencias Nucleares UNAM, Mexico September 27, 2010. ALICE. V0 T0 ZDC FMD PMD. Collaboration:

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ALICE Status Report

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  1. Proton-Proton Physics with ALICE ALICE Status Report Jean-Pierre Revol CERN Jean-Pierre Revol CERN Fifth Workshop on High pT Physics at LHC Instituto de CienciasNucleares UNAM, Mexico September 27, 2010

  2. jpr/Mexico/sept.2010

  3. ALICE V0 T0 ZDC FMD PMD Collaboration: > 1000 Members>100 Institutes > 30 countries Detector: Size: 16 x 26 meters Weight: 10,000 tons jpr/Mexico/sept.2010 3 3

  4. Installation next Dec. 7-Feb 4 break • – 6 EMCAL supermodules(complete EMCAL) • – 3 TRD modules (10 out of 18) [factor 2 increase in J/ψ trigger acceptance] • – TRD completed in 2012 • – PHOS 4th module in 2012 ALICE detector complete Except for: 4/10 EMCAL*(approved 2009) 7/18 TRD* (approved 2002) 3/5 PHOS (funding) 3/5 PHOS 7/18 TRD 18/18 TOF 7/7 HMPID 4/10 EMCAL 2x EMCAL 2x TOF 4 5 3 6 2 HMPID TRD 7 TPC 1 8 0 ITS 9 17 10 16 15 11 14 12 13 L3 Magnet 4 0 3 1 PHOS 2 jpr/Mexico/sept.2010

  5. Tight schedule implying working over Christmas 3/5 PHOS 10/18 TRD 18/18 TOF 7/7 HMPID 10/10 EMCAL ALICE configuration in 2011 2x 2x 2x 4 5 3 2x 6 2 7 1 2x 8 0 9 17 10 16 15 11 14 12 13 4 0 3 1 2 jpr/Mexico/sept.2010

  6. ALICE’ goals for 2010 μ = interactions/bunch crossing • Well within reach! * Overall goal at least a factor 10 over MB pp (150 nb-1) **Overall goal a few tens of thousand ϒ $≈ 50Hz and 106s jpr/Mexico/sept.2010

  7. Data taking with pp collisions • 18 detectors • Reduced luminosity since 1/7 • displaced beams (3.8σ) µ < 0.05 (low pileup) jpr/Mexico/sept.2010

  8. High Level Trigger • Present Hardware: • ~ 1500 CPU cores (60% of final) • Upgrade to 100% computing capacity by beginning of October (for HI) • HLT main tasks: • On-line Data Quality Monitoring • Calibration (TRD, etc.) • High pT single particle Trigger (under test (mode B), to be activated when needed) jpr/Mexico/sept.2010

  9. COMPUTING The ALICE GRID – 30,000 cores – 70 computer centres (1T0, 5T1, 64T2) – America, Europe, Africa and Asia – Stable and smooth operation 24 x 7 – Operated according to the Computing Model COMSATS/Pakistan and LBL/USA entered operation in the last three months – KISTIexperimenting T1 service – LLNL & Yerevan expected in operation soon jpr/Mexico/sept.2010

  10. Computing resources • Not all pledged resources are deployed (50-75%) • Centre’s efficiency to be improved • Since two months we are using > everything • Reconstruction, Analysis and Simulation 6%, 13% and 81% to be compared to Computing Model values are 15%, 30% and 55% • Reconstruction follows directly data taking • All reconstruction is done on the GRID, first pass@T0, the others @T1 as foreseen • Large simulation production:109 simulated events so far jpr/Mexico/sept.2010

  11. First Physics Results jpr/Mexico/sept.2010 • LHC is running well (Friday 56 bunches and 2x1031cm–2s–1) and a wealth of physics results have already been published, mostly on large cross-section phenomena! • ALICE published results (6 publications): • Multiplicity density and distributions of charged particles • 900 GeV: EPJC: Vol. 65 (2010) 111 • 900GeV, 2.36TeV: EPJC: Vol. 68 (2010) 89 • 7TeV: EPJC: Vol. 68 (2010) 345 • ratio (900GeV & 7TeV) PRL: Vol. 105 (2010) 072002 • momentumdistributions (900GeV) PL B: Vol. 693 (2010) 53 • Bose-Einstein correlations (900GeV) PRD: Vol. 82 (2010) 052001 • Many more in preparation (7 TeV)

  12. Very First Collision at ALICE Historical moment√s = 900 GeV November 23, 2009 jpr/Mexico/sept.2010

  13. Very First ALICE Physics publication – Proof of existence for LHC and for ALICE – Results consistent with similar measurementsin proton-antiproton collisions at the same energy – A great stimulation for the Collaboration jpr/Mexico/sept.2010 First publication at LHC; prepared well in advance and submitted to EPJC only 5 days after data taking

  14. First surprise jpr/Mexico/sept.2010 • Charged-particle multiplicity measurement in proton-proton collisions at √s = 0.9 and 2.36 TeV (above Tevatron) with ALICE at LHC • More precise results at 0.9 TeVstill consistent with UA5 • Average multiplicities at the new energy not described by models • Relative increase between 0.9 TeV &7 TeV alsonot described by models

  15. First data at 7 TeV March 30th, First collisions at 7 TeV! jpr/Mexico/sept.2010 • Charged-particle multiplicity measurement in proton-proton collisions at √s = 7 TeV with ALICE at LHC • Trend seen between 0.9 TeVand 2.36 TeV confirmed by new data at higher energy

  16. Inelastic Nch ≥ 1 in |h|<1 Relative increase in dNch/dh ALICE CMS NonSingleDiffractive all Inelastic fits ~ s0.1 Particle production vs √s dNch/dh versus√s jpr/Mexico/sept.2010 Increase with energy significantly stronger in data than in MC’s ALICE & CMS agree to within 1 s (< 3%) dNch/dh increase with √s well described by a power law

  17. Particle production vs √s Martin Poghosyan Predicted correctly the CMS point at 7 TeV jpr/Mexico/sept.2010 • At high energy, simple Mueller-Kancheli: From which we obtain D = (αP -1) = 0.2 (was 0.12 before). • We have entered the realm of non-perturbative QCD and of Pomerons, important at LHC: • Particle production is dominated by soft mechanisms, even at LHC energies; • Global properties need proper account of non-perturbative processes (Diffractive processes, etc) (in many cases, main source of systematic uncertainties).

  18. LHC Parton overlap Partons prisoners of the proton (transverse size only increases as lns) Beyond HERA What is new at LHC is that this overlap could occur for relatively high pTpartons ~ 1 GeV/c (Kharzeev Qs2 ~ 0.7 GeV2) jpr/Mexico/sept.2010 As low x (~Q2/s) values are reached, both the parton density and the parton transverse sizes increase, there must be a scale (q2 < Qs2) where partons overlap. When this happens, the increase in the number of small-xpartons becomes limited by gluon fusion (ggg)

  19. Proton Proton Physics with ALICE Many reasons for ALICE to take pp collisions very seriously jpr/Mexico/sept.2010 What we do not know precisely is how parton overlap will manifest itself in pp collisionsstudy ALL aspects in a systematic way, especially extreme properties of pp collisions pp collisions always part of ALICE’s programme as they are needed to provide a comparison with future HI collisions The comparison goes also the other way: “is QGP produced in pp collisions” Unique features of ALICE (Low pT and PID capability)

  20. Multiplicity measurements Fiducial window = ΔθΔφ = 25mdar×80 mrad SPD2 SPD1 jpr/Mexico/sept.2010 Count Pixel tracklets in the two inermostlayers of the ITS (Pixel Detector) Correct for detector effects (acceptance, efficiency), using a detector response matrix obtained from MC simulations.(deconvolution method used to minimize dependence on model)

  21. Multiplicity Distributions Multiplicity Distribution 7 TeV Multiplicity Distribution 900 GeV PHOJET PYTHIA/ATLAS CSC tune For INEL > 0 events (at least one particle in |η| < 1.0) – no model describes correctly the data – most of the ‘stronger increase’ is in the tail of Nch – nice check that data integral gives same value dN/dη • The Inel > 0 sample is an accurate measurement but no data for comparison • useless for analytical models jpr/Mexico/sept.2010

  22. Comparison with other experiments NSD events ALICE CMS SD SD DD DD jpr/Mexico/sept.2010 • Excellent agreement with UA5 at 0.9 TeV,and with CMS at both 0.9 and 2.36 TeV • Comparison to other experimentsrequires the same event class definition! • How to go from INEL >0 to INEL, NSD? normalize to an eventclass used by other experiments, but • Model dependent and largest source of systematic uncertainty  must be measured! (cross-section and kinematics) • At 0.9 TeV and 1.8 TeV data from UA5 and E710 (ALICE used measured values) • At 7 TeV no data yet! Wait for TOTEM measurement, or measure it ourselves NSD INEL

  23. Systematics and results We now have huge statistics. Control of diffractive processes would allow high precision measurements Ultimately: TOTEM Now: ALICE jpr/Mexico/sept.2010

  24. Momentum Distribution at 900 GeV Comparison with MC’s pT Distribution – Spectrum seems to get harder for more central rapidity– MC’shave hard time to describe the full spectrum jpr/Mexico/sept.2010

  25. <pT> versus Multiplicity pT for different Multiplicities <pT> vsNch • – Change concentrated at pt > 1 GeV (pQCD) (surprisingly little change below ) • – MC’shave hard time… again! jpr/Mexico/sept.2010 Study pioneered by UA1

  26. Material budget • High precision reached in central region(crucial at low pT ( , etc.) • Expanding the charged particle multiplicity measurement to the forward region with the FMD MC and data agree within 5% in |η|<0.9 ITS material in simulation SSD Not fully corrected SDD SPD jpr/Mexico/sept.2010

  27. ITS Performance • SSD ventilation system improved and providing stable humidity; Common noise from power supplies to be cured in next long shutdown. Improved calibration. • Alignment of SSD and SPD essentially completed • Progress in SDD alignment and calibration Resolution along driftσSDD ~ 60 μm for both SDD3 and SDD4 On-going effort to reach the nominal resolution of 35 μm Drift speed vs. time (from dedicated injector runs) during p-p run in Dec. 2009  drift speed stability better than 0.15% for most SDD modules jpr/Mexico/sept.2010

  28. Impact parameter • Resolution well comparable to simulation and close to design value (CDF/running and STAR/upgrade for comparison) ALICE ITS CDF STAR Upgr. Essentially within specs! jpr/Mexico/sept.2010

  29. TPC field distortions go from 7% to 4% at 10 GeV/c (high pT!) From B=0 data Sensitive to ≤ 1mm effects on 5 m object! • Extracting Field distorsion maps from the data jpr/Mexico/sept.2010

  30. Electromagnetic Calorimeter • Latest addition to ALICE: 4/10 EMCal Super Modules installed and producing data • During the LHC 2010 pp run, measurement of the inclusive π0 and η spectra in the central rapidity region in ranges pT< 30 GeV/c at √s = 7 TeV and pT< 8 GeV/c at √s = 900 GeV. • L0 being commissioned (ready to run).  The L1 trigger needs the larger EMCal acceptance for jets. LED system: LED+photodiode for each strip π0 η • Reconstruction based on initial cosmic-ray calibration • Calibration based on pi-zero mass in progress jpr/Mexico/sept.2010

  31. TPC dE/dx s≈5-6% π K Cherenkov ring imaging HMPID P No vertex cut ! ALICE has excellent particle identification ALICE PID detectors Vertex detector pT(min)<100MeV TOF 150k channels! s ≈ 88 ps jpr/Mexico/sept.2010 PLC 20J. Schukraft 31

  32. KaonpT distributions stable & decays Identified Particle pT pKp K → m n K0S → pp ITS dE/dx TPC dE/dx TOF Identified particles jpr/Mexico/sept.2010 Many cross-checks for kaons (6 detectors)

  33. Charged π, K and p at √s = 900 GeV Spectrawithstatistical and systematicuncertainties Lévy functionfitsdescribe data well jpr/Mexico/sept.2010

  34. Neutral particles at √s = 900 GeV Very detailed study of identified particle production, useful for model tuning and for comparison with Heavy Ions jpr/Mexico/sept.2010

  35. Particle ratios vspT ALICE Preliminary ALICE Preliminary Poor agreement with models, but good agreement with other experiments … jpr/Mexico/sept.2010

  36. K/π ratio at √s = 900 GeV jpr/Mexico/sept.2010 Confirming slow rise vs √s7 TeV data analysis in preparation

  37. Λ/Ks0 ratio at √s = 900 GeV STAR and ALICE Feed down corrected (12-15% correction at ~ 2 GeV/c) 7 TeV data analysis (huge statistics) will tell us more jpr/Mexico/sept.2010 ALICE pp at 90 GeV similar to STAR at 200 GeV But different from CDF (630/1800) and UA1 (630) proton-antiproton data for pT > 1.5 GeV/c(under study: trigger, acceptance, feed down corrections, etc.)

  38. K*→ K p X → L p W → L K < 2% of statistics at 7 TeV Much more to come: strange particles S*→ L p We want high statistics studies (pT, multiplicity dependence, etc.) jpr/Mexico/sept.2010

  39. p0 and h from  conversion • e± identification in TPC (TRD soon) ALICE performance jpr/Mexico/sept.2010

  40. Charmed particles D0→ K ppp D+→ K pp D*→ D0 p √s = 7TeV:– new signals– more decay modes – pT distributions D0→ K–p+ Goal: total cross section statistics limited at low pT 109evts to measure below 1 GeV/c Ds+→ Φπ+→ K+K–p+ jpr/Mexico/sept.2010 Lowest pT reach for ALICE

  41. J/y → m+m-, y = 2.5–4.1 J/ψ at √s = 7 TeV J/y → e+e- |y| < 1 – Hard to measure J/y with our current low luminosity (also 1st year Pb–Pb luminosity will be verylowpriority to MB in pp) – ‘proof of performance’ higher luminosity later this year (μμ) and next year Acceptance and efficiency corrected distributions Compared to MC generator (CDF parameterization) Two η ranges jpr/Mexico/sept.2010

  42. 900 GeV: |y|<0.5 7 TeV; |y|<0.5 0.9 TeV: p/p = 0.957±0.006(stat) ±0.014(syst) 7 TeV: p/p = 0.990±0.006(stat) ±0.014(syst) Proton-antiproton ratio Related to probability to transport baryon number from η= 8.9 to 0 Measurement suggested by B. Kopeliovich αSJ = 0.5, and αP = 1.2, C ~ 9 (Red curve) – Most precise ratio measurements so far – For the first time, compatible with no asymmetry, in central region jpr/Mexico/sept.2010

  43. Multiplicity dependence of pp properties jpr/Mexico/sept.2010 • Dependence on multiplicity (<pT>, size of interaction region, topology, strangeness and charm contents, correlations, , etc.) is interesting in itself • Is it described by models? • Are there similarities with Heavy Ion collisions? • Study done so far with our 109 minimum bias triggers • To be extended using high multiplicity triggers, in the spirit of studying extreme events to search for new phenomena: is QCD describing all high multiplicity events?

  44. Source Radius vs Multiplicity (Phojet) Bose Einstein Correlations Multiplicity overlap between pp and HI. Scaling with M similar to STAR but different from HI pp sizes smaller than HI at same multiplicities jpr/Mexico/sept.2010 • Quantum Mechanical enhancement of identical Bosons at small momentum difference • enhancement of like-sign pions at low momentum differenceqinv=|p1-p2|, as function of multiplicity and pair momentumkT = |pT1+pT2|/2

  45. S┴ vs Multiplicity 900 GeV S┴ vs Multiplicity 7 TeV Event shape analysis small S┴: large S┴: Transversesphericity S┴,defined as a function of eigenvaluesof the momentum tensor Sxy ALICE performance Guy Paic & Antonio Ortiz HM events more spherical than models jpr/Mexico/sept.2010

  46. Df (w.r.t. Leading Particle) Df (w.r.t. Leading Particle) Underlying Event Studies Uncorrected Data 7 TeV 900 GeV • Less back-to-back-ishthan MC • Is it related to the effect seen in shape analysis • (seeJason Ulery) jpr/Mexico/sept.2010

  47. High Multiplicity triggers First data A unique trigger at LHC: L0 from Pixels Simulation SPD Layer 1 (|h| < 2) 10 timesmean multiplicity 1031 cm-2 s-1 105 s – 15M events so far.– ALICE’s goal: get at least 10 times the equivalent of our 109 event MB sample! (~150M) – Requires careful handling of event overlap μ ≤ 0.05 Jan-Fiete Grosse-Oetringhaus (2007) jpr/Mexico/sept.2010

  48. Conclusion jpr/Mexico/sept.2010 • ALICE physics programme started with very first data • Many signs that pp collisions are not yet well understood • Global event properties (Multiplicity, pT spectra, etc.) • Identified particle production • √s dependence of multiplicity • Particle correlations • All current MC generators need tuning • We have already learned a lot with our first ~ 10 nb–1 • ALICE is ready the much awaited first Heavy Ion collisions on November 11 (see Paolo Giubellino on HI) • The future can only be bright for ALICE and the other experiments at LHC

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