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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