measured by the CMS experiment in pp and PbPb collisions Wei Li - PowerPoint PPT Presentation

Correlations and fluctuations measured by the CMS experiment in pp and PbPb collisions Wei Li for the CMS Collaboration Quark Matter 2011, Annecy, May 23-29 2011

Introduction Jet quenching Correlation measurements are powerful tools to:  Study the mechanism of hadron production  Probe the jet-medium interactions in AA  Explore the bulk properties of the medium Intriguing ridge structure at RHIC Ridge in pp at LHC! STAR Au+Au 0-10% PHOBOS Au+Au 0-30% CMS pp 7 TeV PRL 104, 062301 (2010) PRC 80 (2009) 64912 JHEP 09 (2010) 091 Wei Li (MIT) Quark Matter 2011, Annecy 2

Introduction Jet quenching Correlation measurements are powerful tools to:  Study the mechanism of hadron production  Probe the jet-medium interactions in AA  Explore the bulk properties of the medium Ridge in pp at LHC! Outline: CMS pp 7 TeV  Correlations in high multiplicity pp at 7 TeV  Correlations in PbPb at 2.76 TeV JHEP 09 (2010) 091 Wei Li (MIT) Quark Matter 2011, Annecy 3

CMS experiment Hadron Calorimeter (HCAL) EM Calorimeter (ECAL) Beam Scintillator Counters (BSC) Forward Calorimeter (HF) TRACKER (Pixels and Strips) η=0 y x  η=2.5  Muon System Z Very large coverage (|  | < 5.0)! Wei Li (MIT) Quark Matter 2011, Annecy 4

Dihadron correlation technique in CMS Particle 1: trigger Signal distribution: Background distribution: Particle 2: associated 1 d 2 N same 1 d 2 N mix S(   ,   )  B(   ,   )  Event 1 d   d   d   d   N trig N trig ฀ ฀ Event 2 same event pairs mixed event pairs Associated hadron yield per trigger:  =  assoc –  trig d   d    B(0,0)  S(   ,   ) 1 d 2 N pair  =  assoc –  trig B(   ,   ) N trig Wei Li (MIT) Quark Matter 2011, Annecy 5 ฀

High multiplicity pp collisions Wei Li (MIT) Quark Matter 2011, Annecy

High multiplicity pp collisions Very high particle density regime See talk by Dragos Velicanu (05/23, 3:00pm) Is there anything interesting happening? Dedicated triggers on high multiplicity events from a single collisions (not pileup!) N online > 85 trigger un-prescaled for full 980nb -1 data set JHEP 09 (2010) 091 ~350K top multiplicity events (N>110) out of 50 billion collisions! Wei Li (MIT) Quark Matter 2011, Annecy 7

Ridge in high multiplicity pp Intermediate p T : 1-3 GeV/c 350K events High multiplicity pp (N  110) Minimum Bias pp (<N> ~ 15)    S(   ,   )     R   ,   N  1 B(   ,   )  1     peak truncated N JHEP 09 (2010) 091 ฀ Striking “ ridge-like ” structure extending over  at  ~ 0 (not observed before in hadron collisions or MC models) Wei Li (MIT) Quark Matter 2011, Annecy 8

Ridge in high multiplicity pp Interpretations: 48 citations CMS pp 7 TeV, N ≥ 110 Multi-jet correlations Jet-Jet color connections Jet Jet-proton remnant color connections Glasma tube Color Glass Condensate ? PHOBOS AuAu 200 GeV 0-30% Phys. Lett. B697:21-25, 2011 Hydrodynamic flow Quark z Gluon Reaction Plasma plane EPOS model: pp y x … K. Werner, WWND2011 Wei Li (MIT) Quark Matter 2011, Annecy 9

Ridge in high multiplicity pp Updated new results: Associated hadron yield per trigger:  ~ 2 x statistics of previous results d   d    B(0,0)  S(   ,   ) 1 d 2 N pair  Extend multiplicity reach B(   ,   ) N trig  Detailed ( , ) dependence p T trig assoc p T 100 billion (1.78 pb -1 ) sampled minimum bias events from high-multiplicity trigger ฀ ฀ ฀ 660K events Wei Li (MIT) Quark Matter 2011, Annecy 10

Ridge in high multiplicity pp Updated new results: Associated hadron yield per trigger:  ~ 2 x statistics of previous results d   d    B(0,0)  S(   ,   ) 1 d 2 N pair  Extend multiplicity reach B(   ,   ) N trig  Detailed ( , ) dependence p T trig assoc p T 100 billion (1.78 pb -1 ) sampled minimum bias events from high-multiplicity trigger ฀ ฀ ฀ 660K events No ridge when correlating to high p T particles! Wei Li (MIT) Quark Matter 2011, Annecy 11

 projections in various p T ranges trig p T CMS Preliminary 2<|  |<4 CMS pp 7 TeV, N ≥ 110 assoc p T Wei Li (MIT) Quark Matter 2011, Annecy 12

 projections in various p T ranges CMS pp 7 TeV, N ≥ 110 p T Jet region (|  |<1) Wei Li (MIT) Quark Matter 2011, Annecy 13

 projections in various p T ranges CMS pp 7 TeV, N ≥ 110 p T Jet region (|  |<1) p T Ridge region (2<|  |<4) Wei Li (MIT) Quark Matter 2011, Annecy 14

Near-side yield vs p T in pp (N≥110) Zero-Yield-At-Minimum (ZYAM) Ridge region (2<|  |<4) Jet region (|  |<1) Wei Li (MIT) Quark Matter 2011, Annecy 15

Near-side yield vs p T in pp Ridge region (2<|  |<4) N Significant ridge effect for N ≥ 90 in pp Ridge first rises with p T , and then drops at high p T Wei Li (MIT) Quark Matter 2011, Annecy 16

Near-side yield vs multiplicity in pp Jet region (|  |<1) Ridge region (2<|  |<4)  Jet yield in pp monotonically increases with N  Ridge in pp turns on around N ~ 50 – 60 (4 x MinBias) smoothly (<N> ~ 15 in MinBias pp events) Wei Li (MIT) Quark Matter 2011, Annecy 17

PbPb collisions at the LHC PbPb at 2.76 TeV (14 x RHIC energy) Wei Li (MIT) Quark Matter 2011, Annecy 18

Heavy- ion “ridge” at LHC 0-5% most central Pb Pb arXiv:1105.2438 p T trig : 4 ~ 6 GeV/c p T assoc : 2 ~ 4 GeV/c Associated hadron yield per trigger: d   d    B(0,0)  S(   ,   ) 2 N pair 1 d See talk by Jeremy Callner B(   ,   ) N trig ฀ (05/24, 3:20pm) ฀ Wei Li (MIT) Quark Matter 2011, Annecy 19 ฀

Ridge vs p T in PbPb Ridge region (2<|  |<4) arXiv:1105.2438 p T Wei Li (MIT) Quark Matter 2011, Annecy 20

Ridge vs p T in PbPb Ridge region (2<|  |<4) arXiv:1105.2438 p T ZYAM v 2 not subtracted Ridge in PbPb collisions tends to diminish at high p T Wei Li (MIT) Quark Matter 2011, Annecy 21

Ridge in pp and PbPb CMS pp 7 TeV, N ≥ 110 CMS PbPb 2.76 TeV, 0-5% |  | dependence |  | dependence   3.1  b  1 CMS L x10 Ridge Region Ridge Region assoc  2 GeV/c assoc  4 GeV/c 1  p T 2  p T ฀ x10 ฀ ฀ Wei Li (MIT) Quark Matter 2011, Annecy 22

Centrality dependence in PbPb p T trig PbPb 2.76 TeV : 4 - 6 GeV/c assoc p T : 2 - 4 GeV/c ฀ ฀ Pb Pb Pb Pb cos(2  ) Wei Li (MIT) Quark Matter 2011, Annecy 23

v 2 -subtracted associated yield in PbPb Jet region (|  |<1) Wei Li (MIT) Quark Matter 2011, Annecy 24

v 2 -subtracted associated yield in PbPb Jet region (|  |<1) Ridge region (2<|  |<4) Jet minus ridge region Pb Pb Pb Pb Qualitatively, similar trend in centrality to RHIC results Wei Li (MIT) Quark Matter 2011, Annecy 25

Alternative approach: Fourier analysis It was recently realized that the ridge may be induced just by higher order flow terms (v 2 , v 3 , v 4 , v 5 , …) Elliptic flow (v 2 ) Triangular flow (v 3 ) from event-by-event fluctuation z Reaction Reaction y plane plane x y x Phys. Rev. C81:054905, 2010 Add V 2 and V 3 “Shoulder”? Δ  Δ  Δ  Δ  ~ V 2 cos(2Δ  ) ~ V 3 cos(3Δ  ) Δ  “Ridge”? Δ  Wei Li (MIT) Quark Matter 2011, Annecy 26

Fourier analysis of  correlations pair 1 dN d    N assoc  f cos(n   ) 2  (1  2 Fourier decomposition: V ) n N trig n  1 2<|  |<4 2<|  |<4 Flow driven correlations: f  v n f (p T f (p T trig )  v n assoc ) V f V 2 ฀ n f V 4 f V 5 (f: Fourier analysis of long- f V 1 range dihadron correlations) f V 3 ฀ Short-range non-flow effects excluded Complementary to standard flow methods (EP, cumulants, LYZ) See talks by: Julia Velkovska (05/24, 11:05am) Victoria Zhukova (05/23, 5:50pm) Wei Li (MIT) Quark Matter 2011, Annecy 27