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HIM2011-12 1
Byungsik Hong
(Korea University)
For the CMS Collaboration
Dihadron Correlations and Flow from CMS
10 December 2011
Heavy-Ion Meeting (HIM2011-12)Yonsei University, Seoul, Korea, 10 December, 2011
HIM2011-12 2
Outline
1. Introduction– Physics motivation– LHC and the CMS detector
2. First experimental data from CMS– We concentrate only on the correlation and flow re-
sults 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 2011
HIM2011-12 3
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 2011
10 December 2011 HIM2011-12 4
p+p at (√s)max = 14 TeV Designed L of pp: 1034 cm-2s-1
Pb+Pb at (√sNN )max = 5.5 TeV
p+p at (√s)max = 14 TeV Designed L of pp: 1034 cm-2s-1
Pb+Pb at (√sNN )max = 5.5 TeV
5
CMS DetectorSuperconducting Coil (3.8 T) CALORIMETERS
ECAL76k scintillating PbWO4 crystals
HCALPlastic scintillator/Brass sandwich
Steel YOKE
Pixels (66M Ch.)Silicon Microstrips (9.6M Ch.)220 m2 of silicon sensors
TRACKER
Cathode Strip ChambersResistive Plate Chambers
MUON ENDCAPS
MUON BARRELDrift Tube ChambersResistive Plate Chambers10 December 2011 HIM2011-12
Weight: 12,500 tonsDiameter: 15 mLength: 22 m
HFCentrality in heavy-ion eventsfor 2010 run
Pixels (66M Ch.)Silicon microstrips (9.6M Ch.)220 m2 of silicon sensors
TRACKER
HFCentrality in heavy-ion eventsfor 2010 run
Very large coverage (|| < 5.0)!
HIM2011-12 6
Summary of 2010 PbPb Run
10 December 2011
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– PbPb @ √sNN = 2.76 TeV: 8.7 mb-1
Reference pp data– pp @ √s = 2.76 TeV: 241 nb-1 – pp @ √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 completeanalysis of Van der Meer scans
HIM2011-12 7
Dihadron Correlation Technique
10 December 2011
Event 1
S(,) 1N trig
d 2N same
dd
B(,) 1N trig
d 2Nmix
dd
Event 2
Same event pairs Mixed event pairs1: Trigger particle
2: Associated particle
1
N trig
d 2Npair
ddB(0,0) S(,)
B(,)
Associated hadron yield per trigger
Dh = hassoc– htrig
Df = fassoc – ftrig
HIM2011-12 8
High-Multiplicity pp Event
10 December 2011
HIM2011-12 9
Ridge in High-Multiplicity pp
10 December 2011
Striking “ridge-like” structure
extending over at ~ 0
Intermediate pT: 1-3 GeV/c Minimum bias pp
(<N>~15)
JHEP09, 091 (2010) 350K top multiplicity events out of 50 billion collisions
R , N 1 S(,)
B(,) 1
N
High multiplicity pp (N 110)
HIM2011-12 10
pT Dependence in pp
10 December 2011
No ridge when correlating to high pT particles!
100 billion (1.78 pb-1) sampled minimum-bias events from high-multiplicity trigger
660K events
HIM2011-12 11
Differential Δφ Projection
10 December 2011
pTassoc
pTtrig
CM
S p
p 7
TeV
, N ≥ 11
02<||<4
CMS Preliminary
HIM2011-12 1210 December 2011
pTtrig
CMS pp 7 TeV, N ≥ 110
Ridge region (2<||<4)
pTtrig
Jet region (||<1)
Differential Δφ Projection
HIM2011-12 13
Near-Side Yields for N≥110
10 December 2011
||<1
Zero-Yield-At-Minimum (ZYAM)
2<||<4
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Near-Side Yields for N≥110
10 December 2011
Jet yield in pp monotonically increases with N Ridge in pp turns on around N~50-60 (4XMB) smoothly
||<1 2<||<4
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PbPb Event
10 December 2011
PbPb at = 2.76 TeV(14 X RHIC energy)
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Ridge in Heavy-Ion Collisions
10 December 2011
= 4 ~ 6 GeV/c = 2 ~ 4 GeV/c
pT
assoc
pT
trig
PbPb 0-5% most central
arXiv:1105.2438
PYTHIA8 simulation
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Differential Δφ Projection
10 December 2011
pTtrig
arXiv:1105.2438
Ridge region (2<||<4): Long-range correlations
(0-5% most central PbPb)Jet region (||<1): Short-range correlations pT
trig
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Integrated Associated Yield
10 December 2011
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 pT
ZYAM
v2 not subtracted: not significant in central collisions
(0-5% most central PbPb) arXiv:1105.2438
HIM2011-12 19
PbPb vs. pp
10 December 2011
Ridge Region
2 pT
assoc 4 GeV/c
CMS pp 7 TeV, N ≥ 110 CMS PbPb 2.76 TeV, 0-5%|| dependence || dependence
CMS L 3.1 b 1
Ridge Region
1 pT
assoc 2 GeV/c
x10
(X10
)
HIM2011-12 20
Centrality Dependence in PbPb
10 December 2011cos(2)
PbPb at 2.76 TeV
PbPb
Pb Pb
: 4 - 6 GeV/c
: 2 - 4 GeV/c
pT
assoc
pT
trig
HIM2011-12 21
v2-Subtracted Yields in PbPb
10 December 2011
Pb Pb PbPb
Ridge region (2<||<4)Jet minus ridge re-
gion
Jet region (||<1)
vs. RHIC
Similar trend in centrality to RHIC results!
HIM2011-12 22
Possible Origin of Ridge
10 December 2011
The ridge & Mach-cone like emission may be induced by higher or-der flow terms!
~ V3 cos(3Δ)
ΔΔ Ridge ΔΔ
Mach-cone like
~ V2 cos(2Δ)
ΔΔ
V2 + V3
x
y
Triangular flow (v3) from event-by-event fluctuation
PRC81, 054905 (2010)
Reaction plane
x
z
y
Elliptic flow (v2)
Reactionplane
G. Qin, H. PetersonS. Bass, B. Müller
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Fourier Decomposition
10 December 2011
Fourier analysis of long-range dihadron correlation− Short-range non-flow effects are excluded.− Complementary to standard flow analysis methods (EP, cumulants, LYZ)
V3fV1
f
V2f
V4f
V5f
2<||<42<||<4
])ncos(V21[2
N
d
dN
N
1
1n
fn
assocpair
trig
HIM2011-12 24
Fourier Decomposition
10 December 2011
arXiv:1105.2438
n=2 n=3 n=4 n=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
(
)
Large
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v2 from Long-Range Correlations
10 December 2011
70-80%
0-5%
)p(v)p(vV assocT
fn
trigT
fn
fn )flow(v (Fourier)V f
nfn ZPC70, 665 (1996)
PRC81, 054905 (2010)
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v2f
v2{2}v2{4}
v2 from Long-Range Correlations
10 December 2011
)p(v)p(vV assocT
fn
trigT
fn
fn )flow(v (Fourier)V f
nfn ZPC70, 665 (1996)
PRC81, 054905 (2010)
0-5%
for small fluctuation
Borghini, Dhin, OllitraultPRC64, 054901 (2001)
70-80%
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v3 from Long-Range Correlations
10 December 2011
70-80%
0-5%
)p(v)p(vV assocT
fn
trigT
fn
fn )flow(v (Fourier)V f
nfn ZPC70, 665 (1996)
PRC81, 054905 (2010)
HIM2011-12 28
v3 from Long-Range Correlations
10 December 2011
)p(v)p(vV assocT
fn
trigT
fn
fn )flow(v (Fourier)V f
nfn ZPC70, 665 (1996)
PRC81, 054905 (2010)
0-5%
for small fluctuation
Borghini, Dhin, OllitraultPRC64, 054901 (2001)
v3f
v3{2}
70-80%
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vfn vs. Centrality
10 December 2011
Powerful constraints on the viscosity of the medium Sensitive to the initial conditions
PbPbPb Pb
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More on v2
10 December 2011
LHC vs. RHIC ()
PHENIX > CMS at high pT for centrality > 30%
CMS vs. ALICE ()
CMS and ALICE agree in general except in most peripheral events
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Systematics on v2
10 December 2011
scaling
Scaling with transverse density across systems &
Constraint on
Smooth increase from RHIC to LHC by 15-20%
Excitation function at mid
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v4 and v6
10 December 2011
Different methods for ()
Signals are sizable, reaching ~7%
Compatible and
vs. () from LYZ
signal is small, but finite,reaching ~2% at mid-cent.
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v5
10 December 2011
increases quadratically with pT
in contrast with other flow harmonics.
Alver et al., PRC82, 034913 (2010)Prediction for RHIC, 0-5% centrality
HIM2011-12 34
Full Harmonic Spectra
10 December 2011
vs Npart shows different trends: − Even orders decrease and diminish with increasing Npart.− depends weakly on centrality & finite for central collisions.
HIM2011-12 35
Comparisons to Hydro
10 December 2011
and together have better sensitivities on . The centrality dependence adds further constraints.
For Glauber initial conditions
HIM2011-12 36
Initial Conditions & η/s
10 December 2011
Different initial conditions add another parameter space
Quantitative comparison re-quires further tuning
Yet to be determined which set of parameters works best
HIM2011-12 37
Summary
10 December 2011
1. Long-range ridge correlations observed in high-multiplicity pp– Ridge yield increases in low pT and vanished at high pT
2. Systematic study of dihadron correlations in PbPb– In central events, the ridge yield significantly drops at high pT
– Extracted flow parameters are consistent with other results done by the cumulant and LYZ methods
3. Flow parameters− is compatible with RHIC data− is sizable and weakly depends on the centrality− is higher than at RHIC)– and are finite– Important basis for the initial conditions and of sQGP
