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Quark Matter 2011, Annecy, May 23-29 2011

Centrality and p T dependence of c harged p article R AA in PbPb collisions at √ s NN = 2.76 TeV. Andre S. Yoon for the CMS Collaboration. Quark Matter 2011, Annecy, May 23-29 2011. Nuclear Modification Factor. R AA > 1 (enhancement). “ QCD Medium ”.

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Quark Matter 2011, Annecy, May 23-29 2011

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  1. Centrality and pT dependence of charged particle RAA in PbPb collisions at √sNN = 2.76 TeV Andre S. Yoon for the CMS Collaboration Quark Matter 2011, Annecy, May 23-29 2011

  2. Nuclear Modification Factor RAA > 1 (enhancement) “QCD Medium” RAA = 1 (no medium effect) ~ “QCD Vacuum” RAA < 1 (suppression) arXiv:1102.1957 Tomographic access to medium properties via pQCD E-loss models Andre Yoon (MIT) Quark Matter 2011 2 2

  3. Current State of Knowledge • RAA is very sensitive to the details of the quenching parameters at high pT • CMS is capable of measuring single charged particle up to ~O(100) GeV/c ? Andre Yoon (MIT) Quark Matter 2011 3

  4. CMS Detector Muon Chambers Pixel and Silicon Strip Tracker ECAL + HCAL inside 3.8 T solenoid Beam Scintillator Counters (BSC) Hadronic Forward Calorimeter (HF) Andre Yoon (MIT) Quark Matter 2011 4

  5. Nuclear Modification Factor PbPb spectra (using minimum-bias and jet-triggers) pp reference spectrum (using minimum bias and jet-triggers) Andre Yoon (MIT) Quark Matter 2011 5

  6. Charged Particle Spectra in pp = 0.9 TeV = 7.0 TeV arXiv:1104.3547 Andre Yoon (MIT) Quark Matter 2011 6

  7. Reference pp Spectrum Low pT (1-10 GeV/c) High pT (10-100 GeV/c) xT = 2pT/ arXiv:1104.3547 Andre Yoon (MIT) Quark Matter 2011 7

  8. Reference pp Spectrum arXiv:1104.3547 • Bin-to-bin interpolation (pT<10 GeV/c) and NLO based xT scaling up to 100 GeV/c • Good agreement with PYTHIA8 (<10%) and NLO rescaled CMS 7 TeV measurement • Interpolation well constrained (7-13%) by measurements at different collision energies Andre Yoon (MIT) Quark Matter 2011 8

  9. Nuclear Modification Factor PbPb spectra (using minimum-bias and jet-triggers) pp reference spectrum (using minimum bias and jet-triggers) Andre Yoon (MIT) Quark Matter 2011 9

  10. Event selections Minimum Bias Trigger: - HF or BSC firing in coincidence on both sides JetTriggers: - Background subtracted uncorrected jet energies (35, 50 GeV) Pb Pb Pb Pb Pb Pb Event selection: - Beam halo veto - Primary vertex with at least 2 tracks - 3 towers (E>3 GeV) in each of HF± - Beam-scraping cleaning - Primary vertex |z|<15 cm Andre Yoon (MIT) Quark Matter 2011 10

  11. Inclusion Of Jet Triggers Jet energy distribution Charged particle distribution Jet triggers are used to enhance the pT reach and to have low fake Andre Yoon (MIT) Quark Matter 2011 11

  12. Tracking Performance in CMS • Efficiency ~65% and • fake < 3% up to 100 GeV/c • Momentum resolution below 5% (correction • <3 %) up to 100 GeV/c Andre Yoon (MIT) Quark Matter 2011 12

  13. Systematic Uncertainties for Spectra Andre Yoon (MIT) Quark Matter 2011 13

  14. Charged Particle Spectra in PbPb Andre Yoon (MIT) Quark Matter 2011 14

  15. Systematic Uncertainties for RAA Andre Yoon (MIT) Quark Matter 2011 15

  16. RAA(pT) for different centralities Andre Yoon (MIT) Quark Matter 2011 16

  17. RAA over two decades in pT! Andre Yoon (MIT) Quark Matter 2011 17

  18. Summary and Conclusions • With the pp reference spectrum constructed based on the CMS measurements, RAA is measured up to 100 GeV/c. • Unambiguous suppression of charged particles above a few GeV/c and a continued rise of RAA up to 0.5 (0-5%) are observed. • Put strong constraints on parton energy-loss models and allow an access to medium properties (dNg/dy and ) by comparison to pQCD predictions. Andre Yoon (MIT) Quark Matter 2011 18

  19. Backup Slides Andre Yoon (MIT) Quark Matter 2011 19

  20. Collision Centrality Pb Pb Pb Pb Pb Pb Events are classified according to the percentile of the Pb+Pb inelastic cross section based on total deposited HF energy Andre Yoon (MIT) Quark Matter 2011 20

  21. RCP(pT) for Different Centralities Andre Yoon (MIT) Quark Matter 2011 21

  22. Collision Centrality • Uncertainty on Ncoll value driven by two terms: • Trigger and event selection efficiency • Glauber parameters Andre Yoon (MIT) Quark Matter 2011 22

  23. Tracking efficiency in pp arXiv:1104.3547 Andre Yoon (MIT) Quark Matter 2011 2 23

  24. xT scaling interpolation • Small scaling violation due to running and the evolution of PDFs and FFs. • n = 5-6 NLO preferred • NLO residual corrections arXiv:1104.3547 Andre Yoon (MIT) Quark Matter 2011 2 24

  25. 2010 Heavy Ion Run at LHC 2010 has been a successful year at LHC After delivering 40 pb-1 of pp data, LHC delivered over 9 µb-1 of PbPb data ~ 7 µb-1used in this analysis Andre Yoon (MIT) Quark Matter 2011 25

  26. Inclusion Of Jet Triggers Jet energy distribution Charged particle distribution Jet triggers are used to enhance the pT reach and to have low fake Andre Yoon (MIT) Quark Matter 2011 26

  27. Comparison to ALICE RAA Andre Yoon (MIT) Quark Matter 2011 27

  28. RAA slope 0.00063 +/- 0.0014 Andre Yoon (MIT) Quark Matter 2011 28

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