Ridge correlation structure in high multiplicity pp collisions with CMS

Ridge correlation structure in high multiplicity pp collisions with CMS Dragos Velicanu for the CMS Collaboration MBUEWG CERN, Geneva, June 17 2011

Results from High Multiplicity pp Dragos Velicanu (MIT) pp Ridge for MBUEWG June 2011 2

Trigger on High Multiplicity pp Total integrated luminosity: 980nb -1 JHEP 1009:091, 2010 Two HLT thresholds: N online > 70 N online > 85 N online > 85 trigger un-prescaled for full 980nb -1 data set ~350K top multiplicity events (N>110) out of 50 billion collisions 3

Angular Correlation Technique 4 Event 1 Background distribution: d d N d N S same trig 2 1 ), ( d d N d N B mix trig 2 1 ), ( Signal distribution: Event 2 ), ( ), ( 0,0 1 2 N N pair trig B S B d d N d N Divide signal by background trig assoc trig assoc same event pairs mixed event pairs

Correlations in High Multiplicity pp Intermediate p T : 1-3 GeV/c High multiplicity pp (N>110) 5

Correlations in High Multiplicity pp Intermediate p T : 1-3 GeV/c Away-side ( ~ ) back-to-back jet correlations High multiplicity pp (N>110) Near-side (, ~ 0) correlations from single jets 6

Correlations in High Multiplicity pp Intermediate p T : 1-3 GeV/c Striking ridge-like structure extending over at ~ 0 High multiplicity pp (N>110) 7

Correlations in High Multiplicity pp Intermediate p T : 1-3 GeV/c Striking ridge-like structure extending over at ~ 0 (not observed before in hadron collisions or MC models) High multiplicity MC High multiplicity pp (N>110) Minbias pp 8

Correlations in High Multiplicity pp Intermediate p T : 1-3 GeV/c Striking ridge-like structure extending over at ~ 0 High multiplicity pp (N>110) 9

Correlations in High Multiplicity pp Intermediate p T : 1-3 GeV/c Striking ridge-like structure extending over at ~ 0 (Similarity to Heavy Ion) arxiv:1105.2438 CMS PbPb 2.76 TeV High multiplicity pp (N>110) 10

Ridge in high multiplicity pp CMS pp 7 TeV, N 110? CMS PbPb 2.76 TeV, 0-5% Interpretations: Multi-jet correlations Jet-Jet color connections Jet-proton remnant color connections Glasma tube Hydrodynamic flow z Reaction plane y x EPOS model: pp 59 citations (link to SPIRES) Jet Color Glass Condensate Phys. Lett. B697:21-25, 2011 Quark Gluon Plasma K. Werner, WWND2011 11

New Results 2x as much data Δη dependence p T dependence Multiplicity dependence 12

New Results 2x as much data Δη dependence p T dependence Multiplicity dependence Ridge goes away at high p T 13

dependence of the ridge Zero-Yield-At-Minimum (ZYAM) Ridge is mostly flat in 14

p T trig projections in various p T ranges CMS Preliminary 2< <4 CMS pp 7 TeV, N 110 p T assoc 15

projections in bins of p T CMS pp 7 TeV, N 110 Jet region ( <1) p T Ridge region (2< <4) p T 16

p T dependence of the ridge Jet region ( <1) Ridge region (2< <4) 17

x10 Ridge in pp and PbPb CMS pp 7 TeV, N 110 CMS PbPb 2.76 TeV, 0-5% dependence dependence CMS L 3.1 b 1 Ridge Region 1 p T assoc 2 GeV/c Ridge Region 2 p T assoc 4 GeV/c x10 18

Near-side yield vs p T Jet region ( <1) N Ridge region (2< <4) N Ridge first increases with p T, and then drops at high p T 19

Near-side yield vs p T MinBias-like HighMult-like Ridge region (2< <4) N Ridge first increases with p T, and then drops at high p T 20

Near-side yield vs Multiplicity Jet region ( <1) Ridge region (2< <4) Ridge in pp turns on around N ~ 50-60 (4x MinBias) smoothly (<N> ~ 15 in MinBias pp events) 21

Near-side yield vs Multiplicity <N> Ridge starts to turn on Ridge region (2< <4) Ridge in pp turns on around N ~ 50-60 (4x MinBias) smoothly (<N> ~ 15 in MinBias pp events) 22

Summary Surprising new effect in pp pt, Δη, multiplicity dependence New testing ground for high density QCD physics Outlook CMS pp 7 TeV, N 110 pt distribution, global properties, PID correlations Check more HI observables (jet quenching, dijet asymetry, low pt PID spectra ) 23

Backups 24

Understanding the Correlation Structure What was used in PHOBOS, ISR, UA5 R(,) (N 1) S N (,) B N (,) 1 N p T inclusive CMS 7TeV pp minimum bias 25

Understanding the Correlation Structure Away-side (~ ) jet correlations: Correlation of particles between backto-back jets Momentum conservation: ~ -cos() p T inclusive CMS 7TeV pp minimum bias Bose-Einstein correlations:,) ~ (0,0) Near-side (~ 0) jet peak: Correlation of particles within a single jet Short-range correlations ( < 2): Resonances, string fragmentation, clusters 26

Comparing to various MC PYTHIA8, v8.135 27

More MC models PYTHIA D6T MinBias, N>70 PYTHIA D6T, Dijet 80-120GeV HERWIG++, N>110 Madgraph, Dijet 100-250GeV, N>90 28

Cross Check: Event Pileup Compare different run periods Change in pileup fraction by factor 4-5 has almost no effect on ridge signal 29

Cross Check: Event Pileup Correlate tracks from high multiplicity vertex with tracks from different collision (vertex) in same bunch crossing N>110 1.0GeV/c<p T <3.0GeV/c 2.0< <4.8 No background or noise effects seen in cross-collision correlations 30

Cross Check: Analysis Code Standard analysis Control analysis II Control analysis I N>110 1<p T <3GeV/c >2 Independent code Same definition of R Same input file (skim) Independent code Different definition of R Different input file (skim) Ridge is seen with three independent analysis codes 31

Cross Check: Trigger Min-bias trigger vs high mult trigger HLT 70 vs HLT 85 for N > 110 Min bias trigger 1<p T <2GeV/c >2 N>110 1<p T <2 GeV/c >2 Ridge is seen using min bias trigger + offline selection No trigger bias seen from comparison of trigger paths 32

Cross Check: ECAL photons Use ECAL photon signal Mostly single photons from 0 s No efficiency, and p T, smearing corrections N>110 1<p T <3GeV/c CMS preliminary N>110 1<p T <3GeV/c >2 Track-photon correlations Note: photons reconstructed using particle flow event reconstruction technique 33

Cross Check: ECAL photons Use ECAL photon signal Mostly single photons from 0 s No efficiency, and p T, smearing corrections N>110 1<p T <3GeV/c CMS preliminary N>110 1<p T <3GeV/c >2 Photon-photon correlations Qualitative confirmation Independent detector, independent reconstruction 34

Particle density in high Mult pp Similar particle densities in these pp collisions as were seen in CuCu at RHIC CMS pp 7TeV, N>100 PHOBOS CuCu 62.4GeV 35

CMS Experiment EM Calorimeter (ECAL) Hadron Calorimeter (HCAL) Beam Scintillator Counters (BSC) Forward Calorimeter (HF) Tracker (Pixels and Strips) Large coverage ( η <5.0) 50 μm vertex resolution Muon system 36

Trigger on High Multiplicity pp CMS trigger and DAQ Level-1: E T > 60 GeV in calorimeters High-Level trigger: number of tracks with p T >0.4 GeV/c, <2 from a single vertex 37