Transcript "Correlation systematics versus RHIC/LHC theories"

Correlation systematics versus RHIC/LHC theories
Lanny Ray, The University of Texas at Austin
The Ridge Workshop
Institute of Nuclear Theory
May 7-11, 2012
INT Ridge Workshop - 5/10/2012
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Introduction and Outline
A-A collision theories must include (among other things):
 pQCD processes including minimum pt biased jets, and their evolution
in the dense, energetic collision system
 event-wise fluctuations in initial conditions, e.g. Npart and Nbinary
In this talk I will review and discuss:
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Experimental challenges for theory
Theoretical expectations for data
Initial state fluctuation model predictions
Jet + medium interaction model predictions
Ideas from pQCD
Conclusions
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Correlation data challenges for Theory
Two-particle angular and transverse momentum correlations
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Smooth evolution to the p-p collision limit
Coexistence of Glauber superposition of jet structure with large v2
Sharp transition in same-side peak and away-side ridge
1) increased yield beyond binary scaling
2) elongation on hD – “soft ridge”
3) reduced azimuth width
same-side
2D peak
h D  h1  h 2
D  1  2
Au-Au 62,200 GeV
STAR data
arXiv:1109.4380
dipole
quadrupole
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  2 N bin / N part
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Correlation data challenges for Theory
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 m  pt
yt  ln  t
 m
Transverse momentum structure peak at 1 – 1.5 GeV/c
1) persistence from p-p to central Au-Au
2) increased away-side width on ytD = yt1-yt2, “KT broadening”
3) evolution of same-side unlike-sign peak; from single to double peaks
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D
 ref , soft
( yt1, yt 2 )
away-side
unlike-sign
D
 ref , soft
STAR preliminary
( yt1, yt 2 )
same-side
unlike-sign
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From E. Oldag
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Correlation data challenges for Theory
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Transverse momentum content of “soft ridge” 1 – 1.5 GeV/c with
no softening at larger hD (within 2 units) or with increasing centrality
volume of
SS 2D peak
on (yt,yt)
STAR preliminary
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Correspondence between pt correlations and spectra (Tom Trainor’s analysis)
Charge-ordering (US > LS) along hD, D, and ytD
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From E. Oldag
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General expectations: jet + medium interaction
pQCD minijets are expected to
dissipate with increasing A-A
centrality. Surprisingly, jet-like
correlations follow Glauber linear
superposition (GLS) to mid
centrality.
Sarcevic, Ellis, Carruthers, PRD 40, 1446 (1989)
Kajantie, Landshoff, Lindfors, PRL 59, 2527 (1987)
Pang, Wang, X.-N. Wang, Xu, PRC 81, 031903 (2010)
Nayak, Dumitru, McLerran, Greiner,
NP A 687, 457 (2001)
Shin, Meuller, J. Phys. G 29, 2485 (2003)
D
 ref , soft ( yt1, yt 2 )
In transport/hydro models (strong
parton interactions) jet-related
correlation widths should increase,
amplitudes decrease, parton pt.
STAR preliminary
Hadronic corona + opaque core:
away-side dijet correlations
persist but fall off relative
to SS jet-related correlations.
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Theoretical ideas for the same-side hD elongation
Initial stage fluctuations plus hydro pressure driven radial flow:
 Beam jets – Voloshin, Shuryak
 Color-glass condensate flux tubes; glasma – many authors
 Initial Energy/momentum density fluctuations in hydro –
Gavin, Alver & Roland, Sorensen
Spherio (3+1 event-wise hydro; no jets)
Jet + medium interactions:
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Jet parton + thermal parton recombination – Chiu and Hwa
Momentum kick – C-Y Wong
AMPT – 2-to-2 parton cascade
HYDJET (CMS) – collisional and gluon radiation jet quenching
NexSpherio (3+1 hydro with NEXUS initial cond. & hard scattering)
pQCD preliminaries:
 Color coherence – 2-to-3 soft gluon radiation
 BFKL emission interference
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Initial fluctuations plus radial flow
ridge projection onto azimuth
 Voloshin, Nucl. Phys. A749, 287c (2005);
Shuryak, Phys. Rev. C76, 047901 (2007) –
beam jet fragments pushed out by strong radial flow;
ridge shaped by flow and path length attenuation.
Reduced
Labsorption
 S. Gavin, Phys. Rev. Lett. 97, 162302 (2006) –
initial state fluctuations with shear viscosity;
driven by hydrodynamic radial expansion
STAR pt angular correlation peak widths
 Alver & Roland, Phys. Rev. C 81, 054905 (2010) –
initial state fluctuations produce triangular flow and ridge
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CGC glasma predictions for the “ridge”
Dumitru et al., Nucl. Phys. A 810, 91 (2008)
Dumitru et al., Phys. Lett. B 697, 21 (2011)
Gavin et al., Phys. Rev. C 79, 051902(R) (2009)
Gavin, Moschelli, Nucl. Phys. A 854, 106 (2011);
ibid. 836, 43 (2010)
T. Lappi, Prog. Theor. Phys. Suppl. 187, 134 (2011);
arXiv:1011.0821
Lappi, Srednyak, Venugopalan, JHEP 01, 66(2010);
arXiv:0911.2068
Gelis et al., Ann. Rev. Nucl. Part Sci. 60, 463 (2010)
From Gavin & Moschelli:
radial
flow
 width determined by radial
flow blast-wave parameters
Same-side amplitude;
as-1(Qs) adjusted to fit
most-central data
STAR data: arXiv: 1109.4380 [nucl-ex]
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CGC glasma predictions for the “ridge”
Dumitru et al., Nucl. Phys. A 810, 91 (2008);
The correlation amplitude is predicted to
increase with centrality, however the
overall magnitude is adjusted to the data.
Daugherity (STAR-QM08), J.Phys.G 35,104090
azimuth
projection
vs radial boost
*See: STAR, arXiv:1109.4380
Predicted azimuth width is generally
too broad, requiring extreme radial
boost zB=2 (0.96c) to agree with data*
(0.7-1 rad).
Pseudorapidity widths are not predicted.
What about the pt
structure of the
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ridge?
Glasma two-gluon (pt,pt) correlations
T. Lappi, Prog. Theor. Phys. Suppl. 187, 134 (2011); arXiv:1011.0821
Lappi, Srednyak, Venugopalan, JHEP 01,66(2010); arXiv:0911.2068
extraneous
self-pairs
Away-side
No
radial
boost
Same-side
 d 2N
dN dN 

 2 ( p , q )  Q S   2
 2
2
2
d
p
d
q
d
p
d
q



 

2
S
dN dN per-gluon pair
correlation
d 2 p d 2 q
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Comparing glasma (pt,pt) predictions to data
Assume LPHD
Glasma predictions, gluon-gluon correlations
# correlated pairs
# final pairs
T. Lappi, Prog. Theor. Phys.
Suppl. 187, 134 (2011)
Charged hadron
correlations in
p-p collisions*
Glasma
model
misses this
peak
associated
with the
ridge.
dN dN # correlated pairs # correlated pairs

dpt1 dpt 2
# final pairs
# final particles
This model has no radial flow. Radial
boost cannot reproduce the
correlations at larger pt.
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*See: Phys. Rev. C 84, 034906 (2011)
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AMPT
Essential aspects of the model [Lin, Ko, Zhang, Pal, Phys. Rev. C 72, 064901 (2005)]:
• HIJING production of F.S. hadrons (MC Glauber w. LUND & Pythia)
• In “string melting” mode all F.S. hadrons represented as q, anti-q at
space-time positions corresponding to MCG and assumed formation time.
• Parton cascade via pQCD 2-to-2 elastic scattering; adjustable cross section.
• Hadronization via coalescence – 3-momentum conservation, no E cons.
• Hadron cascade & chemistry using ART
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AMPT: Jets and parton cascade
LUND string fragmentation parameters (a = 0.5, b = 0.9 GeV-2); “string
melting,” w/out parton cascade and/or jets (> 2 GeV; no quenching)
200 GeV Au-Au 46-55% - jets, parton cascade on/off
No Jets, sparton = 0
With Jets, sparton = 0 (same as Hijing)
D
 ref
D
 ref
(hD ,D )
No Jets, sparton = 12 mb
( yt1, yt 2 )
(hD ,D )
( yt1, yt 2 )
With Jets, sparton = 12 mb
D
D
 ref
 ref
(hD ,D )
( yt1, yt 2 )
(hD ,D )
with hadron scattering
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From E. Oldag
( yt1, yt 2 )
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AMPT: Jets with varying parton cross section
LUND string fragmentation parameters (a = 0.5, b = 0.9 GeV-2); “string
melting,” with parton cascade and jets (> 2 GeV; no quenching)
200 GeV Au-Au 46-55% - vary sparton (using screening mass m)
D
D
D
 ref
 ref
(hD ,D )
0 mb
( yt1, yt 2 )
 ref
3 mb
STAR data
arXiv:1109.4380
6 mb
s gg
9as2
1

2m 2 1  m 2 / s
Model fit parameters
s(mb) quad
0
0
3
0.064
6
0.115
12
0.153
Data 0.136(2)
A2DG
shD
sD
0.116 1.01
0.99
0.247 1.98
0.76
0.309 2.27
0.66
0.373 2.30
0.59
0.207(7) 0.83(5) 0.66(2)
Why doesn’t the (yt,yt) peak move down?
Why does the azimuth width decrease?
12 mb Increasing s enough to reproduce v2
grossly overestimates the SS 2D peak
amplitude and hD width
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AMPT: centrality dependence
LUND string fragmentation parameters (a = 0.5, b = 0.9 GeV-2); “string
melting,” with parton cascade (12 mb) and jets (> 2 GeV; no quenching)
200 GeV Au-Au – centrality dependence @ fixed s=12 mb
D
D
 ref
 ref
(hD ,D )
84-93%
( yt1, yt 2 )
46-55%
STAR arXiv:1109.4380
18-28%
The data approximately follow GLS up
to ~3; AMPT with s ~ 0 follows GLS
but produces no quadrupole (v2).
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AMPT: parton correlations
The preceding results are counter-intuitive. We therefore studied the predicted parton
correlations as a function of parton cross section (0,1.5,3,6,9,12 mb) with no coalescence
200 GeV Au-Au 46-55% - parton correlations
0 mb
1.5 mb
3 mb
D
D
0 mb
1.5 mb
3 mb
9 mb
12 mb
 ref
 ref
(hD ,D )
6 mb
9 mb
12 mb
(hD ,D )
( yt1, yt 2 )
6 mb
( yt1, yt 2 )
angular (hD,D) correlations
SS peak: amplitude and widths (h,) increase
Quadrupole: increases to exp. value at ~6mb
(yt,yt) correlations
Jet peak: strong dissipation as
expected. What is coalescence doing?
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AMPT: parton correlations
LUND string fragmentation parameters (a = 0.5, b = 0.9 GeV-2); “string
melting,” with parton cascade and jets (> 2 GeV; no quenching)
200 GeV Au-Au 46-55% - vary sparton
Final-state hadrons: coalescence
Model fit parameters
s(mb) quad
0
0
1.5
0.024
3
0.064
6
0.115
12
0.153
Data 0.136(2)
A2DG
shD
sD
0.116 1.01
0.99
0.234 1.85
0.86
0.247 1.98
0.76
0.309 2.27
0.66
0.373 2.30
0.59
0.207(7) 0.83(5) 0.66(2)
Partons at end of cascade
Model fit parameters
s(mb)
0
1.5
3
6
12
quad
0.003
0.055
0.116
0.197
0.259
A2DG
0.063
0.146
0.234
0.343
0.541
shD
0.44
1.01
1.28
1.65
2.48
sD
0.44
0.69
0.66
0.59
0.57
STAR arXiv:1109.4380
Quadrupole increases smoothly with sparton in both cases.
The SS 2D peak evolves very rapidly in both cases.
Initial width increase, then
a decrease. Is the latter
due to radial flow in the
parton cascade?
The parton SS peak azimuth width increases when parton’s scatter.
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Monte Carlo Models: NexSPHERIO
Number correlations
Sharma et al., PRC 84,
054915 (2011)
Au-Au 200 GeV
hD width for same-side
pt correlations
STAR data
pt correlations
nexspherio
Jet-like peak predicted;
hD width increase not predicted
No away-side double ridge
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Color coherence – pQCD soft gluons
Rick Field – ISMD, ECT* 2010
p-p at 7 TeV, N > 110
1 < pt < 3 GeV/c
h extended
jet correlations
CMS Collaboration,
JHEP 1009,091(2010).
x-axis
Proton
Proton
z-axis
Initial or FinalState Radiation
Leading Jet
y-axis
Higher order 2→3 or 2→4 matrix elements.
Soft gluon – jet angular correlations
(LR) Phys. Rev. D 84, 034020 (2011)
Color coherent soft gluon radiation:
k
p1
p2
coherent 2  3 processes
pi  p j
Wij  g 2
pi  k k  p j
Psoft gluon  i  j Wij
Ellis, Nucl.Phys. B286, 643 (1987)
With varied
IR, collinear
cut-offs
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BFKL emission and interference
E. Levin and A. H. Rezaeian, Phys. Rev. D 84, 034031 (2011)
Two-Pomeron exchange
with two-gluon emission
interference
Angular correlation – hD independent
peak at D = 0, but also away-side!
azimuth quadrupole
See also: Kopeliovich, Rezaeian, Schmidt
Phys. Rev. D 78, 114009 (2008).
INT Ridge Workshop - 5/10/2012
See Amir
Rezaeian’s
talk tomorrow
morning!
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Summary and Conclusions
Observed correlation structure on relative angles and (yt,yt) pose strict
challenges for theoretical models:
centrality evolution of the ridge
(yt,yt) composition of the same-side ridge
(yt,yt) correlation peak – persistent position and increasing amplitude
General expectations for strong jet + medium interaction, with possible
thermalization, disagree with data trends.
Initial state fluctuation + radial flow (e.g. Glasma) produce SS hD elongation
but does not produce sufficient (yt,yt) structure at pt ~ 1 – 2 GeV/c.
Jet + medium interaction models (e.g. AMPT, NexSpherio) can produce SS
hD elongation. But can they account for the azimuth narrowing and (yt,yt)
peak’s persistence?
pQCD models for the quadrupole are appearing in the literature which do not
require hydro. Perhaps the same will be developed for the ridge.
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