1 / 33

The ALICE Experiment Status and Results

The ALICE Experiment Status and Results. David Evans The University of Birmingham HEP Forum – 20 th September 2010. Outline of Talk. Brief introduction Detector status and performance Physics Analysis Plans for Pb-Pb collisions Summary. Physics Motivations. Study of QCD

djules
Télécharger la présentation

The ALICE Experiment Status and Results

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The ALICE ExperimentStatus and Results David Evans The University of Birmingham HEP Forum – 20th September 2010

  2. Outline of Talk • Brief introduction • Detector status and performance • Physics Analysis • Plans for Pb-Pb collisions • Summary

  3. Physics Motivations • Study of QCD • In particular QCD phase transition from hadronic matter to Quark-Gluon Plasma • Detector designed to cope with extreme environment of Pb-Pb collisions • Excellent tracking, particle ID etc • Play-off: limited interaction rate • pp for baseline – also ALICE is an excellent detector for studying global event properties of pp collisions, cross-sections etc. • No good for rare events – Higgs, SUSY etc.

  4. UK-built Central Trigger Processor (CTP) Delivers L0, L1 and L2 triggers Detector Overview • Optimised for PbPb collisions: • High granularity (dN/dy~8000) • Minimised material 4

  5. Detector Configuration 2010 • ITS, TPC, TOF, HMPID, MUON, V0, T0, FMD, PMD, ZDC (100%) • TRD (7/18) • EMCAL (4/12) • PHOS (3/5) • HLT (60%) full hadron and muon capabilities partial electron and photon Size: 16 x 26 metres Weight: 10,000 tons Collaboration: > 1000 members > 100 institutes > 30 countries 5

  6. TPC acceptance = 90% Momentum resolution ~ 5% @ 100 GeV ALICE Performance Low material budget low pt cut off

  7. Trigger and Data Samples • Minimum bias trigger: at least one charged particle in 8 units of  (all ALICE is read out) • SPD or V0A or V0C • Single-muon trigger (Muon chambers, SPD, V0, FMD, ZDC are read out). • Muon trigger in coincidence with “minimum bias” • Both above in coincidence with the beam pickup counters (BPTX) • A fraction of “bunch-crossing” triggers (just BPTX) • for control • to measure relative fractions of single- and double-diffractive events • High multiplicity trigger from SPD • study of very high multiplicity events (B’ham) February – March cosmic-ray data taking ~ 105 events pp run since 30th March 2010 0.9 TeV ~ 7 x 106 events 7 TeV ~ 600 x 106 events

  8. Detector Performance TPC only

  9. Physics Analysis First LHC physics paper First LHC high-energy physics paper • 5 papers published – accepted • Charged-particle density in 900 GeV pp collisions • K. Aamodt et al. (ALICE), Eur. Phys. J C 65 (2010) 111 • Charged-particle multiplicity in 0.9 and 2.36 pp collisions • arXiv:1004.3034[hep-ph] accepted in Eur. Phys. J C • Charged-particle multiplicity in 7 TeV pp collision – letter • arXiv:1004.3514[hep-ph] accepted in Eur. Phys. J C • Measurement of antiproton/proton ratio in pp at 0.9 and 7 TeV • Phys.Rev.Lett Vol 105, No 7 (2010) • Charged-particle transverse momentum spectra at 0.9 TeV • http://arxiv.org/abs/1007.0719, Phys. Lett. B • 1 paper submitted • Identical particle correlation in pp at 0.9 TeV • http://arxiv.org/abs/1007.0516, Phys. Rev. D • 2 papers in draft • Identified charged hadron spectra and yields in pp at 0.9 TeV • Strange particle production in pp at 0.9 TeV • Other analyses well underway • High multiplicity pp events, azimuthal correlations, event structure, p0 spectra, charm production,...

  10. Birmingham Analysis Focus • Trigger corrections • First pp physics (helped with first paper) • Diffractive physics • Study of very high multiplicity pp events at 7 TeV • High-pT correlations • Preparing for Pb-Pb

  11. dNch/dh versus √s Relative increase in dNch/dh Inelastic Nch ≥ 1 in |h|<1 dNch/dh versus√s ALICE CMS all Inelastic NonSingleDiffractive fits ~ s0.1 Results: - dNch/dh well described by power law (√s)0.2 • increase with energy significantly stronger in data than MC’s • Alice & CMS agree to within 1 s (< 3%) 11

  12. Multiplicity distribution ALICE CMS Multiplicity distribution 900 GeV Multiplicity distribution 7 TeV Results: • most of the ‘stronger increase’ is in the tail of Nch • ALICE & CMS still agree perfectly ! 12

  13. Momentum distribution 900 GeV Comparison to MC’s <pT>versus√s pT distribution Results: • Finally some (slight) difference ! • Spectrum seems to get harder towards midrapidity • MC’s have hard time to describe the full spectrum 13

  14. <pT> versus multiplicity <pT> vs Nch pT for different multiplicities arXiv:1007.0719 arXiv:1007.0719 Results: • Change concentrated at pt > 1 GeV (pQCD) • (surprisingly little change below ) • MC’s have hard time… •Perugia-0 (fails for multiplicity) describes well <pT>, but only for pT>500 MeV/c (ATLAS found agreement for pT > 500 MeV/c) 14

  15. MC scoreboard Conclusion: • none of the tested MC’s (adjusted at lower energy) does really well • tuning one or two results is easy, getting everything right will require more effort • (and may, with some luck, actually teach us something on soft QCD rather than only turning knobs) 15 15

  16. pbar/p at mid-rapidity Baryon number transport by di-quark and/or a string junction Study pbar/p d u u u d u Traditional String junction • - Conventional approach: QGSM • pbar/p y asymmetry ~ 0 at LHC energies • (di-quark f.f. exponentially suppressed for large y • Different fragmentation functions • G.C. Rossi and G. Veneziano, Nucl Phys. B123(1997)507 • exponentially suppressed, intercept model dependent • Kopeliovich, Sov. J. Nucl. Phys. 45, 1078(1987) • Probability constant with rapidity u d J u

  17. pbar/p vs MCs Possible to check measurement compatibility with several models Monte-Carlo Scoreboard (part II) Green: MC ~ data Blue: MC << data

  18. Bose–Einstein correlations (HBT) QM enhancement of identical Bosons at small momentum difference enhancement of e.g. like-sign pions at low momentum difference qinv=|p1-p2|, as function of multiplicity and pair momentum kT = |pT1+pT2|/2 measure Space-Time evolution of the ‘dense matter’ system in heavy ions coll. interpretation in ‘small systems’ (pp, e+e-) is less obvious.. BE enhancement vs qINV BE enhancement vs qINV pp Pb+Au unlike sign p+p- high Nch, kT high multiplicity high momentum radius ~ 1/width (Phojet) baseline low multiplicity low momentum kT 18

  19. HBT @ 900 GeV Source Radius vs pair momentum Using different Baselines Source Radius vs Multiplicity • Results: • Radius increases with Nch, comparable to ISR, RHIC, TeV • rather constant vs <kT> ! • sign. systematic uncertainty from ‘baseline’ shape • dependence usually interpreted as sign of ‘flow’ in heavy ions • neglecting non-BE correlations (‘flat baseline’) can cause kT dependence (at high √ s)! Hot Matter-26/08/2010, ALICE physics, P. Kuijer, NIKHEF 19

  20. Charged: p, K, p at 900 GeV 20

  21. Decays: K0S, L, X, f at 900 GeV * X + X → L p L → p p K0S → pp • Preliminary results: • MC well below Data • more so at high pT • more so for L & X • f ~ ok (at least some MC) f → K K * 2009 Data (~300 k events) 21

  22. L/K0Sratio 900 GeV |h| < 1 • very good agreement between STAR (200 GeV) and ALICE (900 GeV) • very different from CDF (630/1800) and UA1 (630) for pT > 1.5 GeV • - UA1(630) and CDF(630) don’t agree either … • to be further investigated (different triggers, acceptance, feed-down correction ?) 22

  23. , , , *0, k*0, 0,  at 7 TeV *0 0 - EMCAL k*0 - 0 PHOS 0 &  K+K-

  24. Charm at 7 TeV D0→ K p p p Impact Parameter Resolution vs pT D+→ K p p D*→ D0 p 80 mm @ 1 GeV D0→ K p 24

  25. Charm at 7 TeV

  26. Charm at very low pT 2 GeV D0 cross section vs pT in |y| < 1 FONLL pQCD calculation • most of the cross section at low pT • shape at low pT very uncertain • 109 MB events => measure below 1 GeV • (PID important at low pT !) 26

  27. J/y @ 7 TeV e PID from TPC || < 0.9 TRD & EMCAL calibration ongoing J/  +- , -4 <  < -2.5

  28. J/y → m+m- <pT2> vs √ s <pT> vs √ s 28

  29. High pT and Jets Charged-track jets raw spectra at 0.9 and 7 TeV || < 0.5 4 jet algorithms compared uncorrected

  30. High pT particle correlations Trigger particle – highest pT particle in event Associated particle: all the others

  31. High Multiplicity Events • Activity started by B’ham • Highest multiplicity events in pp at 7 TeV similar to lighter ion-ion collisions at SPS • Could suggest high energy densities • Look for evidence of QGP in highest multiplicity events – or any other strange physics • Special high multiplicity trigger (developed by B’ham • Need to understand and reject pileup as this is significant at high mult. • Analysis ongoing High Multiplicity pp event at 7 TeV

  32. Planned quick PbPb analysis • Expect 2 weeks of Pb tuning • Followed by 2 weeks of Pb_Pb physics collisions • Can do a lot with just a few 100k events • Much high stats in 2011 – we hope. Wait until November for PbPb multiplicity v2 pT (RAA, RCP) HBT high pT correlations 32

  33. Summary • 2010 running very successful • All detector, online and offline systems working well • Alignment and calibration under control • About 600 million 7 TeV events collected • Physics analysis well underway • 6 papers published or submitted • others on the way • Preparations for Pb collisions this November well underway • ALICE has got off to a great start and we look forward to some new and interesting physics from the Pb data.

More Related