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

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 20112HIM

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 2011HIM

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

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 20115HIM 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)!

Summary of 2010 PbPb Run 10 December 2011HIM  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 √s NN = 2.76 TeV: 8.7  b -1  Reference pp data √s = 2.76 TeV: 241 nb -1 √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

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

High-Multiplicity pp Event 10 December 2011HIM

Ridge in High-Multiplicity pp 10 December 2011HIM 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)

p T Dependence in pp 10 December 2011HIM 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

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

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

Near-Side Yields for N ≥ December 2011HIM |  |<1 Zero-Yield-At-Minimum (ZYAM) 2<|  |<4

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

PbPb Event 10 December 2011HIM

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

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

Integrated Associated Yield 10 December 2011HIM  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:

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

Centrality Dependence in PbPb 10 December 2011HIM cos(2  ) PbPb at 2.76 TeV PbPb PbPb : GeV/c : GeV/c : GeV/c : GeV/c

v 2 -Subtracted Yields in PbPb 10 December 2011HIM 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!

Possible Origin of Ridge 10 December 2011HIM 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, (2010) Reaction plane x z y Elliptic flow (v 2 ) Reaction plane G. Qin, H. Peterson S. Bass, B. M ü ller

Fourier Decomposition 10 December 2011HIM  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

Fourier Decomposition 10 December 2011HIM arXiv: 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 ( )

v 2 from Long-Range Correlations 10 December 2011HIM % 0-5% ZPC70, 665 (1996) PRC81, (2010)

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

v 3 from Long-Range Correlations 10 December 2011HIM % 0-5% ZPC70, 665 (1996) PRC81, (2010)

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

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

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

Systematics on v 2 10 December 2011HIM Smooth increase from RHIC to LHC by 15-20%

v 4 and v 6 10 December 2011HIM

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

Full Harmonic Spectra 10 December 2011HIM

Comparisons to Hydro 10 December 2011HIM For Glauber initial conditions

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

Summary 10 December 2011HIM