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The ALICE e xperiment at LHC

The ALICE e xperiment at LHC. Domenico Di Bari Dipartimento Interateneo di Fisica INFN-Bari. P. Giubellino. HI @LHC: Constraints and Solutions. Extreme particle density : dN ch /d h ~ 2000 – 8000 x 500 compared to pp@LHC; x 30 compared to 32 S@SPS high granularity , 3D detectors

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The ALICE e xperiment at LHC

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  1. The ALICE experimentat LHC Domenico Di Bari Dipartimento Interateneo di Fisica INFN-Bari 4th Summer School on THE PHYSICS OF LHC 14-19 jun 2010 Martignano, GrecìaSalentina (Lecce, Italy)

  2. P. Giubellino

  3. HI @LHC: Constraints and Solutions • Extreme particle density : dNch/dh ~ 2000 – 8000 • x 500 compared to pp@LHC; x 30 compared to 32S@SPS • highgranularity, 3D detectors • Silicon pixels and drift detectors, TPC with low diffusion gas mixture (Ne-CO2) • conservative & redundant tracking • up to ~200 space points per track • large distance to vertex • e.g. emcal at 4.5 m (typical is 1-2 m !) • Large dynamic range in pt: from very soft (0.1 GeV) to fairly hard (100 GeV) • verythin detector, modest field0.5 T (low pt), • ALICE: ~ 10%X0 in r < 2.5 m (typical is 50-100%X0) • vertex detector works as ‘standalone low pt spectrometer’ (tracking & PID) • large lever arm+ good hit resolution (large pt) • B= 0.5T, tracking L ~ 3.5m, BL2 ~ like CMS !

  4. HI @LHC: Constraints and Solutions • Both partons & hadrons matter: fragmentation (i.e. hadrons) is part of the signal, not of the problem • partons (heavy quarks): secondary vertices, lepton ID • hadrons: use of essentially all known PID technologies • dE/dx, Cherenkov & transition rad., TOF, calorimeters, muon filter, topological • Modest Luminosity and interaction rates; short runs 10 kHZ (Pb-Pb), (< 1/10000 of pp@1034) ~ 1 month/year • allows slow detectors (TPC, SDD), moderate radiation hardness • moderate trigger selectivity, no pipelines (mostly ‘track & hold’ electronics) • large event size (~ 100 MB) + short runs => high throughput DAQ (> 1GB/s) • Single dedicated heavy ion experiment combine capabilities of a handful of more specialized HI expts at AGS/SPS/RHIC • 18 detector technologies, several smaller ‘special purpose’ detectors(HMPID, PHOS, PMD, FMD, ZDC..) • central barrel (~ STAR) + forward muon arm (~PHENIX)

  5. ALICE ACORDE V0 T0 ZDC FMD PMD Collaboration: > 1000 Members>100 Institutes > 30 countries Detector: Size: 16 x 26 meters Weight: 10,000 tons

  6. Are youasking me if QGP washere? I don’t know. Please, call the CSI experts…

  7. AHA, AHA, hereis the Higgs!!!

  8. ALICE Detector Installation mid 2009 Complete: ITS, TPC, TOF, HMPID, FMD, T0, V0, ZDC, Muon arm, Acorde PMD, PHOS(3/5), DAQ Partial installation: 7/18 TRD 4/10 EMCAL ~ 60% HLT ALICE Status New (‘post Chamonix’) LHC schedule: Likely configuration until end 2011

  9. Material budget distribution in ALICE X/X0<10% up to 250 cm from IP  Goodprecisionfor e/measurements Radialdistancefrombeamline

  10. Photonconvertionpointdistrib. @7TeV Actual agreement of data with MC < 8%

  11. some anxious minutes waiting for collisions.. ~ 16:35

  12. The first ‘event’ pops up in the ACR ~ 16:41

  13. Relief and jubilation.. Collisions in ALICE !! ~ 16:42 .. and some celebration..

  14. ‘First Physics’ in the making ~ 18:00 After years of looking at simulated data, there was no holding back: First physics results examined, ca 1 hour after data taking finished (284 events !)..

  15. TPC, TRD, TOF, HMPID ITS Muon Spectrometer A few days later… HMPID Cherenkov Ring TRD track TPC track On 6th December, ‘stable beams’ were declared & we could switch on all ALICE detectors for the first time..

  16. >15 Million interactions > 150 k Muon triggers Data Taking Summary Inter. rate ~ 30 – 90 Hz Integrated Data taking efficiency since 30.3 ~ 85%

  17. Beam spot at 2.36 TeV SPD Vertex resolution versus # tracks TPC pt spectrum Preliminary preliminary alignment ! Tracking works beautifully Plots as shown on 18 Dec ‘LHC’ jamboree

  18. pT = 1 – 1.5 GeV/c Impact parameter DCA before alignment after alignment s=181 mm alignment with cosmics only pT = 1 – 1.5 GeV/c Getting to know ALICE: Shape Data MC SPD Data MC cosmics + pp ( = 0 and π) 18

  19. ALICE - Work in Progress ALICE - Work in Progress K ® mn ALICE Work in Progress p ALICE - Work in Progress K0s ® pp K p PID (or 6 ways to measure Kaons) # 6: HMPID Cherenkov Results shown on 17 Febr LHCC

  20. … National Geographic was sort of correct.. K0s ® pp PDG: 497.6 MeV PDG: 1115.7 MeV L ® pp L ® pp PDG: 1019.5 MeV F ® K+K- PDG: 1115.7 MeV The Particle Zoo Revisited: Plots as shown on 18 Dec ‘LHC’ jamboree

  21. Work in progress K* ® Kp February 2010 April 2010 X(ssd) ® Lp ® pp p April 2010 W(sss) ® LK ® pp K More Particle Appearances h ® gg ®e+e- e+e-

  22. PHOS (9 m2) p0 ® gg ® e+e- e+e- p0 ® gg 1 < pt < 1.5 GeV X ® Lp ® pp p More Particles.. Plots as shown on 18 Dec ‘LHC’ jamboree

  23.  Reconstruction from conversion

  24. .. ‘lots’ of data.. ITS No vertex cut ! all plots: preliminary calibration & alignment ! TPC TOF TRD Protons Electrons Kaons Pions Pions velocity v/c ‘Good pp interactions’: (rate few Hz) - 300 k : √s = 900 GeV - 30 k : √s = 2.36 TeV ALICE special: Particle Identification (very important for heavy ion physics later in 2010) Plots as shown on 18 Dec ‘LHC’ jamboree 15/2/2006 LHCC Status Report J. Schukraft

  25. (Anti)Nuclei

  26. P. Giubellino

  27. Event Classes s = 0.9 and 2.36 TeV • Inelastic (INEL) = Single-diffractive (SD) + Double-diffractive (DD) + Non-diffractive (ND); • Non-single diffractive (NSD) = ND+DD • Use measured cross sections for diffractive processes • Change MC generator fractions (SD/INEL, DD/INEL) such that they match these fractions • s = 7 TeV • Diffraction is quite unknown • Hadron-level def. of evts to minimize model dependence • All events that have at least one charged primary particle in |η| < 1: “INEL>0”

  28. »p This is the first (and easiest) of many numbers we need to (re)measure to get confidence in our detectors, tune the simulations, study background, .... Phase 2 is still a long way to go.. last time measured at the ISR for pp Physics exploitation of ALICE has started for good ! Phase 1: rediscovering the standard model (QCD in the case of ALICE) submitted to EPJC 28 Nov 2009 The average number of charged particles created perpendicular to the beam in pp collisions at 900 GeV is: dN/dh = 3.10 ± 0.13 (stat) ± 0.22 (syst) Physics exploitation of ALICE has started for good ! National Geographic News (4 Dec.) ‘….a machine called ALICE.... found that a (!) proton-proton collision recorded on November 23 created the precise ratio of matter and antimatter particles predicted from theory..’

  29. dN/d: comparison to exp.

  30. Multiplicitydistributions @ 0.9,2.36,7 TeV • 0.9 TeV: consistentwith UA5 • Fitwith NBD (Negative BinomialDistrib.) ok in a limited-regions • 7 TeV: NBD fitslightly deviate at highestmultiplicities

  31. Tail grows faster ! Life starts getting interesting.. Larger increase of multiplicity at mid-rapidity than in MC generators Good news for the Heavy Ion program: More charged particles will create a denser and hotter system !

  32. Physics Analysis • Papers published • ‘First Physics’, EPJC 65 (2010) 111 • Papers submitted • Detailed analysis of charged particle multiplicity (0.9 & 2.36 TeV) EPJC, 18.4 • First look at multiplicity at 7 TeV • Papers almost ready (900 GeV Data) • Charged particle pT • Identified particles pT (π, K, p) • Strangeness production (K0, Λ, Ξ,Φ) • Baryon-antibaryon asymmetry • Bose-Einstein correlations • Other ongoing Analysis • π0 spectra, event structure, azimuthal correlations, -φ correlations, high multiplicity events, ………

  33. P. Giubellino

  34. P. Giubellino

  35. P. Giubellino

  36. CharmedMesons

  37. + -invariant mass asmeasuredby the MuonSpectrometer 2.5 <  < 4

  38. Femtoscopy (HBT correlation) By correlating two (or more) particles (i.e. Bose-Einstein enhancement for pairs of pions at low pT), the ALICE experiment will probe the space-time substructure of the dynamic matter at the femtometer (10 -15 m) scale. 0-9 TeV These measurements are of great interest both for heavy ion and for proton-proton collisions. Indeed, the space-time substructure of the "system" created in proton collisions is not well understood, and may reveal information on the confinement process inaccessible through momentum-space probes alone

  39. In 1956, Robert Hanbury Brown and Richard Q. Twiss published A test of a new type of stellar interferometer on Sirius, in which two photomultiplier tubes (PMTs), separated by about 6 meters, were aimed at the star Sirius. Light was collected into the PMTs using mirrors from searchlights. An interference effect was observed between the two intensities, revealing a positive correlation between the two signals, despite the fact that no phase information was collected. Hanbury Brown and Twiss used the interference signal to determine the apparent angular size of Sirius, claiming excellent resolution.

  40. P. Giubellino

  41. Thanksforyourpatience…

  42. Backup slides

  43. DoublePomeronExch. (DPE) Single Diffraction (SD) DoubleDiffraction (DD) Rapidity Rapidity Rapidity

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