1. Byungsik Hong (Korea University) For the CMS Collaboration Dihadron Correlations and Flow from CMS 10 December 20111HIM2011-12 Heavy-Ion Meeting (HIM2011-12) Yonsei University, Seoul, Korea, 10 December, 2011

2. Outline 1.Introduction –Physics motivation –LHC and the CMS detector 2.First experimental data from CMS –We concentrate only on the correlation and flow results in this presentation. –Correlations in pp at 7 TeV and PbPb at 2.76 TeV –Flow in PbPb at 2.76 TeV –Comparison to Hydro 3.Summary 10 December 20112HIM2011-12

3. Motivation  Correlation is a powerful tool to study –Hadron production mechanism –Jet-medium interactions in heavy-ion collisions –Bulk properties of the produced medium (sQGP)  Flow is a powerful tool to address –Equation-of-state –Viscosity of the medium –Fluctuations and initial conditions 10 December 2011HIM2011-123

4. 10 December 2011HIM2011-124 p+p at (√s) max = 14 TeV Designed L of pp: 10 34 cm -2 s -1 Pb+Pb at (√s NN ) max = 5.5 TeV p+p at (√s) max = 14 TeV Designed L of pp: 10 34 cm -2 s -1 Pb+Pb at (√s NN ) max = 5.5 TeV

5. CMS Detector Superconducting Coil (3.8 T) CALORIMETERS ECAL 76k scintillating PbWO 4 crystals HCAL Plastic scintillator/ Brass sandwich Steel YOKE Pixels (66M Ch.) Silicon Microstrips (9.6M Ch.) 220 m 2 of silicon sensors TRACKER Cathode Strip Chambers Resistive Plate Chambers MUON ENDCAPS MUON BARREL Drift Tube Chambers Resistive Plate Chambers 10 December 20115HIM2011-12 Weight: 12,500 tons Diameter: 15 m Length: 22 m HF Centrality in heavy-ion events for 2010 run Pixels (66M Ch.) Silicon microstrips (9.6M Ch.) 220 m 2 of silicon sensors TRACKER HF Centrality in heavy-ion events for 2010 run Very large coverage (|  | < 5.0)!

6. Summary of 2010 PbPb Run 10 December 2011HIM2011-126  A dedicated heavy-ion mode –Turn off zero suppression –Taking data at up to 220 Hz –12 MB event size  Triggering on minimum bias, jets, muons and photons –ALL rare probes written to tape –~half of minimum bias written  Recorded luminosity –PbPb @ √s NN = 2.76 TeV: 8.7  b -1  Reference pp data –pp @ √s = 2.76 TeV: 241 nb -1 –pp @ √s = 7 TeV: > 5 fb -1  Total volume of PbPb data –~0.89 PetaByte (Days since Nov. 1, 2010) Note: luminosities will be rescaled by few % after complete analysis of Van der Meer scans

7. Dihadron Correlation Technique 10 December 2011HIM2011-127 Event 1 Event 2 Same event pairsMixed event pairs 1: Trigger particle 2: Associated particle Associated hadron yield per trigger  =  assoc –  trig  =  assoc –  trig

8. High-Multiplicity pp Event 10 December 2011HIM2011-128

9. Ridge in High-Multiplicity pp 10 December 2011HIM2011-129 Striking “ridge-like” structure extending over  at  ~ 0 Intermediate p T : 1-3 GeV/c Minimum bias pp ( ~15) JHEP09, 091 (2010) 350K top multiplicity events out of 50 billion collisions High multiplicity pp (N  110)

10. p T Dependence in pp 10 December 2011HIM2011-1210 No ridge when correlating to high p T particles! 100 billion (1.78 pb -1 ) sampled minimum-bias events from high-multiplicity trigger 660K events

11. Differential Δφ Projection 10 December 2011HIM2011-1211 p T assoc p T trig CMS pp 7 TeV, N ≥ 110 2<|  |<4 CMS Preliminary

12. 10 December 2011HIM2011-1212 p T trig CMS pp 7 TeV, N ≥ 110 Ridge region (2<|  |<4) p T trig Jet region (|  |<1) Differential Δφ Projection

13. Near-Side Yields for N ≥ 110 10 December 2011HIM2011-1213 |  |<1 Zero-Yield-At-Minimum (ZYAM) 2<|  |<4

14. Near-Side Yields for N ≥ 110 10 December 2011HIM2011-1214  Jet yield in pp monotonically increases with N  Ridge in pp turns on around N~50-60 (4XMB) smoothly |  |<1 2<|  |<4

15. PbPb Event 10 December 2011HIM2011-1215

16. Ridge in Heavy-Ion Collisions 10 December 2011HIM2011-1216 = 4 ~ 6 GeV/c = 2 ~ 4 GeV/c PbPb 0-5% most central arXiv:1105.2438 PYTHIA8 simulation

17. Differential Δφ Projection 10 December 2011HIM2011-1217 p T trig arXiv:1105.2438 Ridge region (2<|  |<4): Long-range correlations (0-5% most central PbPb) Jet region (|  |<1): Short-range correlations p T trig

18. Integrated Associated Yield 10 December 2011HIM2011-1218  Ridge-region yield: integration of the near-side enhancement  Jet-region yield: sum of the near-side short- & long-range yields  Ridge in PbPb diminishes at high p T ZYAM v 2 not subtracted: not significant in central collisions (0-5% most central PbPb) arXiv:1105.2438

19. PbPb vs. pp 10 December 2011HIM2011-1219 Ridge Region CMS pp 7 TeV, N ≥ 110 CMS PbPb 2.76 TeV, 0-5% |  | dependence Ridge Region x10 (X10)

20. Centrality Dependence in PbPb 10 December 2011HIM2011-1220 cos(2  ) PbPb at 2.76 TeV PbPb PbPb : 4 - 6 GeV/c : 2 - 4 GeV/c : 4 - 6 GeV/c : 2 - 4 GeV/c

21. v 2 -Subtracted Yields in PbPb 10 December 2011HIM2011-1221 PbPb PbPb Ridge region (2<|  |<4) Jet minus ridge region Jet region (|  |<1) Jet region (|  |<1) vs. RHIC Similar trend in centrality to RHIC results!

22. Possible Origin of Ridge 10 December 2011HIM2011-1222 The ridge & Mach-cone like emission may be induced by higher order flow terms! ~ V 3 cos(3Δ  ) ΔΔ ΔΔ Ridge ΔΔ ΔΔ Mach-cone like ~ V 2 cos(2Δ  ) ΔΔ ΔΔ V 2 + V 3 x y Triangular flow (v 3 ) from event-by-event fluctuation PRC81, 054905 (2010) Reaction plane x z y Elliptic flow (v 2 ) Reaction plane G. Qin, H. Peterson S. Bass, B. M ü ller

23. Fourier Decomposition 10 December 2011HIM2011-1223  Fourier analysis of long-range dihadron correlation − Short-range non-flow effects are excluded. − Complementary to standard flow analysis methods (EP, cumulants, LYZ) V3fV3f V1fV1f V2fV2f V4fV4f V5fV5f 2<|  |<4

24. Fourier Decomposition 10 December 2011HIM2011-1224 arXiv:1105.2438 n=2n=3n=4n=5 (0-5% most central PbPb) Ridge region (2<|  |<4): Long-range correlations Dotted lines: Sum of five terms(n=1~5) in the Fourier series ( )

25. v 2 from Long-Range Correlations 10 December 2011HIM2011-1225 70-80% 0-5% ZPC70, 665 (1996) PRC81, 054905 (2010)

26. v2fv2f v 2 {2} v 2 {4} v 2 from Long-Range Correlations 10 December 2011HIM2011-1226 ZPC70, 665 (1996) PRC81, 054905 (2010) 0-5% 70-80%

27. v 3 from Long-Range Correlations 10 December 2011HIM2011-1227 70-80% 0-5% ZPC70, 665 (1996) PRC81, 054905 (2010)

28. v 3 from Long-Range Correlations 10 December 2011HIM2011-1228 ZPC70, 665 (1996) PRC81, 054905 (2010) 0-5% v3fv3f v 3 {2} 70-80%

29. v f n vs. Centrality 10 December 2011HIM2011-1229  Powerful constraints on the viscosity of the medium  Sensitive to the initial conditions PbPb PbPb

30. More on v 2 10 December 2011HIM2011-1230 PHENIX > CMS at high p T for centrality > 30% CMS and ALICE agree in general except in most peripheral events

31. Systematics on v 2 10 December 2011HIM2011-1231 Smooth increase from RHIC to LHC by 15-20%

32. v 4 and v 6 10 December 2011HIM2011-1232

33. v5v5 10 December 2011HIM2011-1233 Alver et al., PRC82, 034913 (2010) Prediction for RHIC, 0-5% centrality

34. Full Harmonic Spectra 10 December 2011HIM2011-1234

35. Comparisons to Hydro 10 December 2011HIM2011-1235 For Glauber initial conditions

36. Initial Conditions & η/s 10 December 2011HIM2011-1236  Different initial conditions add another parameter space  Quantitative comparison requires further tuning  Yet to be determined which set of parameters works best

37. Summary 10 December 2011HIM2011-1237