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Yen-Jie Lee (CERN) for the CMS Collaboration MBUE working group CERN 3 rd Dec, 2012

Yen-Jie Lee (CERN) for the CMS Collaboration MBUE working group CERN 3 rd Dec, 2012. Two-particle correlations in pPb collisions from the CMS Collaboration. Introduction. Two-particle correlation: study of particle production mechanism. p. p. Introduction. Pb. Pb.

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Yen-Jie Lee (CERN) for the CMS Collaboration MBUE working group CERN 3 rd Dec, 2012

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  1. Yen-Jie Lee (CERN) for the CMS Collaboration MBUE working group CERN 3rd Dec, 2012 Two-particle correlations in pPb collisionsfrom the CMS Collaboration MBUE working group 2012

  2. Introduction MBUE working group 2012 Two-particle correlation: study of particle production mechanism p p

  3. Introduction MBUE working group 2012 Pb Pb Two-particle correlation: study of particle production mechanism and possible collective effects in high particle density environment created at the LHC energies p p

  4. Introduction MBUE working group 2012 p Pb Pb Pb Two-particle correlation: study of particle production mechanism and possible collective effects in high particle density environment created at the LHC energies p p ?

  5. Compact Muon Solenoid MBUE working group 2012 Pb |η|< 2.4 Muon |η|< 5.2 HCAL ECAL |η|< 3.0 Tracker |η|< 2.5 EMandHadroncalorimeters photons, jet Inner tracker: charged particles primary vertex solenoid proton Very large coverage for full tracking (|| up to 5.0)!

  6. High multiplicity events recorded by CMS MBUE working group 2012 pp PbPb pPb

  7. Defining two-particle correlation MBUE working group 2012 Signal pair distribution: Background pair distribution: Event 1 same event pairs mixed event pairs Δη = η1-η2 Δφ = φ1-φ2 Event 2

  8. Defining two-particle correlation MBUE working group 2012 Signal pair distribution: Background pair distribution: Event 1 same event pairs mixed event pairs Δη = η1-η2 Δφ = φ1-φ2 Event 2 Associated hadron yield per trigger: JHEP 09 (2010) 091

  9. Understanding the correlation function MBUE working group 2012 p p “Near-side” (,  ~ 0) correlations from single jets JHEP 09 (2010) 091

  10. Understanding the correlation function MBUE working group 2012 p p “Away-side” ( ~ ) back-to-back jet correlations “Near-side” (,  ~ 0) correlations from single jets Z axis adjusted to reveal the detail of the correlation function (peak truncated) JHEP 09 (2010) 091

  11. Understanding the correlation function MBUE working group 2012 p p Striking “ridge-like” structure extending over  at  ≈0 In high multiplicity events, N≥110 where: N ≡ number of offline tracks with pT>0.4 GeV/c JHEP 09 (2010) 091

  12. Understanding the correlation function MBUE working group 2012 Pb Pb Pb Pb 35-40% centrality CMS PbPb 2.76 TeV 35-40% CMS PbPb 2.76 TeV arXiv:1201.3158 EPJC 72 (2012) 2012 pTtrig: 4–6 GeV/c pTassoc: 2–4 GeV/c

  13. Understanding the correlation function MBUE working group 2012 Pb Pb Pb Pb 35-40% centrality CMS PbPb 2.76 TeV 35-40% CMS PbPb 2.76 TeV arXiv:1201.3158 EPJC 72 (2012) 2012 Particle azimuthal distributions: dN/d Σ vn cos(n()) pTtrig: 4–6 GeV/c pTassoc: 2–4 GeV/c

  14. Any guesses for pPb correlations? MBUE working group 2012 p Pb What do we expect to see in (high-multiplicity) pPb? N=235 event

  15. A ridge! MBUE working group 2012 p Pb What do we expect to see in (high-multiplicity) pPb? arXiv 1210.5482Accepted by PLB N ≡ number of offline tracks with pT>0.4 GeV/c

  16. A (relatively big) ridge! MBUE working group 2012 p Pb Physical origin still unclear pp 7 TeV arXiv 1210.5482Accepted by PLB JHEP 09 (2010) 091 N ≡ number of offline tracks with pT>0.4 GeV/c Much bigger than in pp!

  17. A (relatively big) ridge! MBUE working group 2012 p Pb Initial-state geometry + collective expansion arXiv 1210.5482Accepted by PLB N ≡ number of offline tracks with pT>0.4 GeV/c

  18. Multiplicity Evolution MBUE working group 2012 p Pb Low multiplicity Low transverse density Divide into 4 multiplicity bins: arXiv 1210.5482Accepted by PLB N ≡ number of offline tracks with pT>0.4 GeV/c

  19. Multiplicity Evolution MBUE working group 2012 p Pb Increasing multiplicity Increasing transverse density Divide into 4 multiplicity bins: arXiv 1210.5482Accepted by PLB N ≡ number of offline tracks with pT>0.4 GeV/c

  20. Multiplicity Evolution MBUE working group 2012 p Pb Increasing multiplicity High transverse density Divide into 4 multiplicity bins: arXiv 1210.5482Accepted by PLB N ≡ number of offline tracks with pT>0.4 GeV/c

  21. Multiplicity Evolution MBUE working group 2012 p Pb Increasing multiplicity Highest transverse density Divide into 4 multiplicity bins: arXiv 1210.5482Accepted by PLB N ≡ number of offline tracks with pT>0.4 GeV/c

  22. Quantitative evolution of ridge effect MBUE working group 2012 Want to use the same approach as in pp ridge paper for “apples-apples” comparison

  23. Quantitative evolution of ridge effect MBUE working group 2012 Want to use the same approach as in pp ridge paper for “apples-apples” comparison Average over ridge region (2<|Δη|<4)

  24. Quantitative evolution of ridge effect MBUE working group 2012 Want to use the same approach as in pp ridge paper for “apples-apples” comparison Average over ridge region (2<|Δη|<4)

  25. Multiplicity and pT dependence MBUE working group 2012 0 – 1 1 – 2 2 – 3 3 – 4 pT (GeV/c) Multiplicity N<35 35≦N<90 90 ≦ N<110 N≧110 N ≡ number of offline tracks with pT>0.4 GeV/c

  26. Multiplicity and pT dependence MBUE working group 2012 0 – 1 1 – 2 2 – 3 3 – 4 pT (GeV/c) Multiplicity N<35 35≦N<90 90 ≦ N<110 N≧110 N ≡ number of offline tracks with pT>0.4 GeV/c

  27. Multiplicity and pT dependence MBUE working group 2012 0 – 1 1 – 2 2 – 3 3 – 4 pT (GeV/c) Multiplicity N<35 35≦N<90 90 ≦ N<110 N≧110 N ≡ number of offline tracks with pT>0.4 GeV/c

  28. No ridge in pPb MC MBUE working group 2012 Compare to AMPT and HIJING pPb Generator-level HIJING pPb, N>=120 AMPT pPb, N>=100 No ridge in these pPb MCs!

  29. Ridge Associated Yield MBUE working group 2012 ZYAM example arXiv 1210.5482Accepted by PLB N ≡ number of offline tracks with pT>0.4 GeV/c

  30. Ridge Associated Yield MBUE working group 2012 In the signal (N>110) region, the strength of the effect rises and falls with pT ZYAM example arXiv 1210.5482Accepted by PLB N ≡ number of offline tracks with pT>0.4 GeV/c

  31. Ridge Associated Yield MBUE working group 2012 In the pT range where the yield is the strongest, the ridge turns on at N≈50 In the signal (N>110) region, the strength of the effect rises and falls with pT ZYAM example arXiv 1210.5482Accepted by PLB N ≡ number of offline tracks with pT>0.4 GeV/c

  32. Summary and Conclusions MBUE working group 2012 A significant ridge is observed in high multiplicity (central) pPb collisions at 5 TeV strong mechanism to produce particles in a plane much larger than in pp Correlations from back to back jets Correlations from planar particle production Correlations from planar particle production

  33. Summary and Conclusions MBUE working group 2012 A significant ridge is observed in high multiplicity (central) pPb collisions at 5 TeV strong mechanism to produce particles in a plane much larger than in pp Effect turns on slightly above average minimum bias multiplicity Effect rises and falls with pT similar trend as observed in both PbPb and pp ridge before

  34. Outlook MBUE working group 2012 All this came from a few hours of LHC pPb test running, only one fill! Thank you LHC! Several questions to be asked: What is the physics origin of the ridge? Collective effect? Modification of jet structure? Have we created a medium in pPb collision? Elliptic flow measurement (vn) ? Jet quenching ? Hope for more surprises from the full pPb run coming up in January!

  35. Backup MBUE working group 2012

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