Transcript Document

The long-range pseudo-rapidity
correlations in high-energy collisions
王福强
Purdue University
The Big Bang and the Little Bang
Quark Gluon Plasma (QGP)
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Proton, neutron, meson (hadron)
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Nuclear Phase Diagram
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Heavy-Ion Collisions simulation
Hadron cascade
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STAR
CMS
ALICE
PHENIX
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Relativistic Heavy-Ion Collider (RHIC) at
Brookhaven National Laboratory (BNL)
STAR and PHENIX experiments
New York
7/1/2013
BNL－RHIC
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Two types of discoveries
• Theoretically predicted, and experimentally
verified, e.g.
– J/Y
– W, Z bosons
• Surprises, e.g.
– Parity violation
– Microwave background radiation
Long-range pseudo-rapidity correlations
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Variables, observables
y
STAR: Solenoidal Tracker
At RHIC
g = 100
f
x
13 fm
p
pT

1 p  pz
  ln
2 p  pz


  ln  tan 
2

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pz
z
Hydrodynamic bulk collectivity, elliptic flow
py
f = atan
py
px
px
y
z
e=
x
coordinate space anisotropy
y2 - x2
px2 + py2
momentum space anisotropy
p
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v2 =
y2 + x2
px2 - py2
0
p
fparticleFR.P. (rad)
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Collective expansion of QGP
- elliptic (2nd order) and higher order event
anisotropic collectivity and its Nquark scaling
- hydro-dynamic properties of QGP
PHENIX Preliminary, QM12
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Elliptic expansion during the partonic (quark-gluon) phase
Hadron formation via quark recombination / coalescence
Hadron
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Energy loss (jet quenching) in QGP
jet
p
Au
p
q
Au
Phys. Rev. Lett. 91, 072304 (2003)
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g
central Au+Au
arXiv: 1208.2254
PRL109, 152302 (2012)
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Novel phenomena in heavy-ions
•
•
•
•
•
Double-peak away-side correlations
Odd harmonics
Long-range ridge correlations
Ridge in small systems
…
Au+Au
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ridge
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Jet Correlations
Jet event in ee collision
STAR Au+Au collision
trigger particle
pT > 3 GeV/c
Df
associated
particle
Jet produces high pT particles  Select a high pT particle to trigger on jet.
NB:
trigger = off-line trigger
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Dihadron correlations
STAR, PRL91 (2003)
STAR, PRL 95 (2005); PRC82 (2010)
pTtrig=4-6 GeV/c
assoc
pT
=0.15-4 GeV/c
•
•
•
•
Clear evidence of jet-quenching, and it’s a
final-state effect
Low pT enhancement and broadening
Away-side double peak; Large-D small-Df
ridge correlation
v2 subtracted but not higher harmonics
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trigger
jet
Away-side
-1
0
1
p
Df
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Relative to the Event Plane
Associated
Df
fS
STAR, arXiv:1010.0690v1
Todoroki (PHENIX) 1304.2852
EP
|D| > 0.7
v2max {2,gap=0.7}
• Ep-dep correl
v2max{2,gap=0.7}, v3{2,gap=0.7}
• Evolution of structure seems to remain from in-plan to out-of-plane.
• Single away-side peak in-plane, double-peak out-of-plane.
• Jet interactions with QGP medium. Physics mechanisms?
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Three-particle correlations
Trigger
Δf1
Δf2
• v2 and v4 subtracted.
• Does v3 remove all of the off-diag.
peak strength? Need further study.
• Deflected jets contributions (to diag.
peaks) must be present.
• Need to be followed up with v3
subtraction.
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The longitudinal ridge
~0
~1
trigger particle
pT > 3 GeV/c
D
Df
d+Au
|Df|<0.7
trigger particle
pT > 3 GeV/c
assoc. particle
pT =1-3 GeV/c
Au+Au
ridge
assoc. particle
pT =1-2 GeV/c
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Ridge vs trigger angle
v2max {2,gap=0.7}
v2max{2,gap=0.7}, v3{2,gap=0.7}
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Ridge yield vs trigger angle
v2max {2,gap=0.7}
v2max{2,gap=0.7}, v3{2,gap=0.7}
Subtract
v3
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Ridge in small systems
usual p-p collision
high multiplicity p-p collision
LHC-CMS
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• Why wasn’t it discovered long ago by HEP?
• Two types of discoveries:
– Theoretically predicted, and experimentally verified
– Surprises
• HEP moved on to more exclusive processes
• There may be still important physics that were missed in last
half century.
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p-Pb collision (high Mul.)
p-p collision (high Mul.)
Physical origin unclear
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CGC/Glasma
Dusling & Venugopalan 1211.3701
Dusling and Venugopalan, arXiv:1302.7018
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Another explanation: Hydro flow
• In heavy-ions, large D small Df correlations:
subtract v2  non-zero finite correlation (ridge)
• In pp, pA, dA systems, large D small Df correlations:
subtract flat pedestal  non-zero finite correlation (ridge)
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d+Au ridge?
PHENIX, arXiv:1303.1794
Bozek, PRC85 (2012)
1.25-1.5 GeV/c
PHENIX
acceptance
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•
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Jet contribution within PHENIX acceptance
LHC+RHIC more stringent test on theoretical models.
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Df projections in different D
(TPC mult. ||<1 as centrality)
0.15 < pTtrig < 3 GeV/c, 1 < pTassoc < 2 GeV/c
ZYAM-ed
ZYAM-ed
ZYAM-ed
Straight difference
No ZYAM involved
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• ZYAM syst. error from different sizes of Df region for ZYAM.
• Efficiency corrected: 85 ± 5% .
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D projections in different Df
(TPC mult. ||<1 as centrality)
0.15 < pTtrig < 3 GeV/c
1 < pTassoc < 2 GeV/c
ZYAM-ed
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ZYAM-ed
• ZYAM syst. error from different sizes of Df region for ZYAM.
• Efficiency corrected: 85 ± 5% .
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Central – Peripheral
0.15 < pTtrig < 3 GeV/c, 1 < pTassoc < 2 GeV/c
FTPC 0-20% - 40-100%
TPC 0-20% - 50-80%
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TPC 0-20% - 50-80%
Minimal
ridge
TPC 0-20% - 50-80%
• ZYAM syst. error from different sizes of Df region for ZYAM.
• Efficiency corrected: 85 ± 5% .
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Very forward correlations
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TPC-FTPC correlations
D triangle acceptance
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Sanity check
All charged hadrons
TPC-TPC
PHOBOS, PRC 72 (2005) 031901(R)
3
4D  2p
2(acc.)  2
2
3D  2p
2(acc.)  1
0.5 
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 20
3D  2p
2(acc.)  1
 20
TPC-FTPC
5
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ZYAM’ed D Correlations
(TPC mult. as centrality)
Raw correl.
Discontinuity because it’s D not  distribution.
At D=2, TPC-TPC and TPC-FTPC pairs come form different ’s.
ZYAM’ed
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Fourier fit results
TPC-TPC Au-side
TPC-FTPC Au-side
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TPC-TPC d-side
TPC-FTPC d-side
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Fourier fit results (replot of previous slide)
Au-side
d-side
Summary
• Correlations have v1 and v2 components
• v1 appears ~1/N. v2 ~constant over multiplicity
• Even at very forward d-side, v2 component is large (maybe even larger
than Au-side).
• Not sure what the data mean.
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Conclusions
• Particle correlations in heavy-ions
– Novel phenomenon of v3
– After v3 subtraction, features of jet-medium
interactions remain
• Ridge in small systems
– Intriguing
– May contain important physics
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The question of v1
• In the pt=1-2 GeV/c region, directed flow fluctuation effect
may be negligible.
Pandit (STAR), arXiv:1211.7162
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Have to rethink about inclusive dihadron
•
•
•
We have used so far <vt{2}*va{2}>=<vt{2}>*<va{2}>. This is OK because fluctuations
are already included in v{2}.
However, if v{2} depends on slice, then <vt{2}slice*va{2}slice>≠<vt{2}slice>*<va{2}slice>.
<vt{2}slice*va{2} slice> = (vt{2}1*va{2}1 + vt{2}6*va{2}6)/2
= (vt{2}1*va{2}1 + vt{2}6*va{2}1 - vt{2}6*va{2}1 + vt{2}6*va{2}6)/2
= <vt{2}>*va{2}1 - vt{2}6* (va{2}1 - va{2}6)/2
> <vt{2}>*va{2}1 which is the maximum.
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ZYAM’ed D Correlations
(ZDC as centrality)
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