Di-hadron correlations measurements from CMS

Dragos Velicanu

Workshop on P- and CP-odd Effects in Hot and Dense Matter (2012)

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 1

Understanding Initial Conditions

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 2

Goal: To understand initial conditions of PbPb and pp collisions through long range correlations of produced charged particles

Two views of possible PbPb initial conditions Probe the initial condition of proton structure

Understanding Initial Conditions

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 3

Goal: To understand initial conditions of PbPb and pp collisions through long range correlations of produced charged particles

CMS Detector

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 4

TRACKER (Pixels and Strips)

Very large coverage for tracking (|| up to 5.0)!

EM Calorimeter (ECAL) Hadron Calorimeter (HCAL)

Beam Scintillator Counters (BSC)

Forward Calorimeter

(HF)

Muon System

PbPb and pp collisions at the LHC

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 5

Correlations of charged tracks

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 6

Event 1

Event 2

same event pairs

mixed event pairs

Signal pair distribution: Background pair distribution:

Correlations of charged tracks

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 7

Event 1

Event 2

same event pairs

mixed event pairs

Signal pair distribution: Background pair distribution:

Divide Signal by Background Associated hadron yield per trigger:

Correlation function

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 8

Event 1

Event 2

same event pairs

mixed event pairs

Signal pair distribution: Background pair distribution:

JHEP 09 (2010) 091

High multiplicity pp (N>110) 𝑠 = 7 𝑇𝑒𝑉

Associated hadron yield per trigger:

Understanding the pp correlations

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 9

“Near-side” (, ~ 0) correlations from single jets

“Away-side” ( ~ )

back-to-back jet correlations

High multiplicity pp: more than 8 times more particles are produced from a single collision than average, 7e-5 selection

Understanding the pp correlations

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 10

Minbias pp

High multiplicity MC

Striking “ridge-like” structure extending over

at ~ 0 Not seen before in

high multiplicity MC

nor MinBias pp!

Quantitative ridge Measurements

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 11

Zero-Yield-At-Minimum (ZYAM)

Ridge region: 2<||<4

Jet region: || < 1

Ridge || and multiplicity dependence

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 12

Zero-Yield-At-Minimum (ZYAM)

Ridge region: 2<||<4

Ridge is flat in ||

pT dependence of the pp ridge

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 13

Jet region ||<1 Ridge region: 2<||<4

PbPb correlations

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 14

pTtrig: 4–6 GeV/c

pTassoc: 2–4 GeV/c

CMS PbPb 2.76 TeV 35-40%

Pb Pb 35-40% centrality

arXiv:1201.3158

CMS PbPb 2.76 TeV

EPJC 72 (2012) 2012

PbPb correlations: Geometry

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 15

pTtrig: 4–6 GeV/c

pTassoc: 2–4 GeV/c

CMS PbPb 2.76 TeV 35-40%

Pb Pb 35-40% centrality

arXiv:1201.3158

CMS PbPb 2.76 TeV

EPJC 72 (2012) 2012

𝑉2Δ cos(2 Δϕ)

PbPb correlations: Geometry

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 16

Pb Pb

Pb Pb

EPJC 72 (2012) 2012

PbPb correlations: Geometry?

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 17

pTtrig: 4–6 GeV/c

pTassoc: 2–4 GeV/c

CMS PbPb 2.76 TeV 35-40%

Pb Pb 35-40% centrality

arXiv:1201.3158

CMS PbPb 2.76 TeV

EPJC 72 (2012) 2012

Pb Pb 0-5% centrality

CMS PbPb 2.76 TeV

elliptic flow cos(2Δϕ) term not prominent

JHEP 07 (2011) 076

Ridge Region (2<|Δη|<4)

2 < pT

assoc < 4 GeV/c

PbPb correlations: Ridge Yield

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 18

CMS PbPb 2.76 TeV

arXiv:1201.3158

CMS PbPb 2.76 TeV

elliptic flow cos(2Δϕ) term not prominent

JHEP 07 (2011) 076

Ridge yield goes down at high pT

JHEP 07 (2011) 076

Associated yield

Ridge is flat in Δη

Ridge Region (2<|Δη|<4)

2 < pT

assoc < 4 GeV/c

Comparison of ridge in pp and PbPb

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 19

Ridge is flat in Δη

Ridge yield goes down at high pT

JHEP 07 (2011) 076

Ridge is flat in Δη

Ridge yield goes down at high pT

pp

pp

PbPb

PbPb

Qualitatively similar properties but not quantitatively

PbPb correlations: Geometry?

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 20

CMS PbPb 2.76 TeV

arXiv:1201.3158

Pb Pb 0-5% centrality

CMS PbPb 2.76 TeV

elliptic flow cos(2Δϕ) term not prominent

JHEP 07 (2011) 076

PbPb correlations: Fluctuations

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 21

CMS PbPb 2.76 TeV

arXiv:1201.3158

CMS PbPb 2.76 TeV

elliptic flow cos(2Δϕ) term not prominent

JHEP 07 (2011) 076

Triangular flow

Elliptic flow

Triangular flow Elliptic flow

+ + + n=2 n=3 n=4 n=5

Two-particle correlation

Pb Pb 0-5% centrality

PbPb correlations: Fluctuations

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 22

CMS PbPb 2.76 TeV

arXiv:1201.3158

CMS PbPb 2.76 TeV

elliptic flow cos(2Δϕ) term not prominent

JHEP 07 (2011) 076

Pb Pb 0-5% centrality

PbPb correlations: Fourier Analysis

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 23

CMS PbPb 2.76 TeV

arXiv:1201.3158

Pb Pb 0-5% centrality

CMS PbPb 2.76 TeV

elliptic flow cos(2Δϕ) term not prominent

JHEP 07 (2011) 076

Fourier decomposition:

PbPb correlations: Fourier Analysis

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 24

Fourier decomposition: EPJC 72 (2012) 2012

For flow driven correlations:

However,

• pT dependent flow fluctuation could break the factorization

• Non-flow could also factorize

factorization

“Factorization” seems to work

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 25

v2(pT) from correlation method derived using fixed pTassoc

of 1-1.5 GeV/c agrees well with EP method

Dihadron correlation

o HF Event plane

0-5% 15-20% 35-40%

Pb Pb Pb Pb Pb Pb

PbPb 2.76 TeV

v2

pT (GeV/c)

0-5% 15-20% 35-40%

More Constraints from Higher vn

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 26

v2

v3

Schenke et. al., arXiv:1109.6289

Pb Pb

Measure all vn to over-constrain the hydro calculations

η/s

Initial conditions (Glauber vs CGC)

More Constraints from Higher vn

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 27

v2

v3

Schenke et. al., arXiv:1109.6289

Pb Pb

Measure all vn to over-constrain the hydro calculations

η/s

Initial conditions (Glauber vs CGC)

v4 v5

Summary

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 28

• pp-ridge extends out to at least || ≈ 4 , tends to flat in - long range correlation

• pp-ridge first appears at 3-4× average multiplicity and seems to saturate at 8-10×

• pp-ridge yield peaks at intermediate pTtrig ≈ 3

GeV/c and decreases at high pTtrig

• PbPb also exhibits long range correlations that rise and fall with pT

trig and centrality

• Precise measurements of higher vn will better nail down the PbPb initial conditions and /s

Backup

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 29

Factorization of Fourier Harmonics

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 30

Test of factorization:

VnΔ(1,1) VnΔ(1,2) VnΔ(1,3) VnΔ(1,m)

VnΔ(2,1)

VnΔ(3,1)

VnΔ(2,2) VnΔ(2,3) VnΔ(2,m)

VnΔ(3,2) VnΔ(3,3) VnΔ(3,m)

VnΔ(m,1) VnΔ(m,2) VnΔ(m,3) VnΔ(m,m)

…

…

…

…

…

…

…

…

pTtrig

pTassoc

Assuming factorization

Take low reference pT bin (1-1.5 GeV/c)

Check if vn(pT) can derive rest of matrix:

?

Factorization of Fourier Harmonics

6/23/2012 Dragos Velicanu Workshop on P- and CP-odd Effects in Hot

and Dense Matter (2012) 31

Check if vn(pT) can derive rest of matrix:

Take low reference pT bin (1-1.5 GeV/c)

?

EPJC 72 (2012) 2012

Like-Sign vs Unlike-Sign pp ridge

32

No dependence on relative charge sign