Paul Sorensen

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Highlights from RHIC lecture 2 The Opaque Medium
Paul Sorensen Brookhaven National Laboratory
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Expansion of the little bang
collision evolution
particle detectors
expansion and cooling
kinetic freeze-out
distributions and correlations of produced
particles
hadronization
lumpy initial energy density
QGP phase quark and gluon degrees of freedom
collision overlap zone
quantum fluctuations
? 1015 fm/c
? 10 fm/c
? 0 fm/c
?01 fm/c
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colliding nuclei sheets of CGC?
0 fm
Glasma?
time scale
1 fm 3x10-24 sec
growth of instabilities?
0.1 fm
transverse magnetic fields
turbulance?
QGP Phase
1 fm
hadronization hadronic
rescattering
freezeout
detectors
10 fm
1015 fm
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colliding nuclei sheets of CGC?
Glasma?
jets and heavy quarks form
0 fm
time scale
1 fm 3x10-24 sec
growth of instabilities?
jets are quenched, quarkonium screened, and flow
develops
0.1 fm
transverse magnetic fields
turbulance?
QGP Phase
1 fm
hadronization hadronic
rescattering
freezeout
detectors
10 fm
1015 fm
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Quarkonium as a Thermometer
Matsui and Satz Debye screening in deconfined
matter will melt Quarkonium states Karsch, Mehr,
and Satz Melting will be sequential
Screening confirmed in Lattice calculations of
Free Energy for QQ-bar at separation r
QGP Thermometer
lattice QCD O.Kaczmarek, hep-lat/0503017
Agnes Mocsy QM09
RBC-Bielefeld Coll. (2007)
Quarkonium dissociation when rDebye ltrQQbar
J/? melts at Tc
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Quarkonium Is Supressed
But its a challenge to tell what part of the
suppression is related to QGP formation or other
effects The energy (in)dependence is also
difficult to understand
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Quarkonium as a Thermometer
Still much more to come from RHIC With RHICII,
Upsilon data with good statistics will become
available
QGP Thermometer
Agnes Mocsy QM09
J/? melts at Tc
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Quarkonium Correlations
Mocsy and Petreczky

• Potential model shows correlations persist
• Heavy quark pairs may not diffuse away
• Recombination may occur (but not statistical)
• D and Dbar correlations should also be enhanced!

Young and Shuryak
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colliding nuclei sheets of CGC?
Glasma?
jets and heavy quarks form
0 fm
time scale
1 fm 3x10-24 sec
growth of instabilities?
jets are quenched, quarkonium screened, and flow
develops
0.1 fm
transverse magnetic fields
turbulance?
QGP Phase
1 fm
hadronization hadronic
rescattering
freezeout
detectors
10 fm
1015 fm
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Jet Quenching High pT Suppression
If jets lose energy in the QGP the number of
high momentum particles should be
suppressed photons serve as a reference
Transverse Momentum GeV
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Is it really jets being quenched?
pT,triggt4 GeV associatedgt2.5 GeV/c
Angular distribution of di-hadron pairs Data
indicate a surface bias caused by the opaque
plasma when you trigger on a high momentum
particle, it tends to come from a hard-scattered
parton near the surface unmodified but no
away-side
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Quick Diversion Soft-ish Correlations
The Picture that Emerges Surface bias ?
unmodified nearside High pT away-side quenched in
the medium Mach cones emitted on the away-side
from fast particles traversing matter
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Spectra of near- and away-side
The near- and away-side correlations have softer
spectra than pp The baryon to meson ratio is
like the bulk but not as expected from jets
jet
ridge
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How else can we think about the data?
Acoustic expansion and Initial State correlations
can give you a near-side Gaussian The Fourier
transform of the correlation function gives the
power spectrum in term of flow coefficients
vn2 This gives the harmonics vn2 for the flow
induced Gaussian. odd values do not have to be
zero (fluctuations)
Can azimuth correlations be described by flow
(vn) fluctuations with a few harmonics?
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Few parameter fit of azimuthal correlations
I can name that tune in 5 notes
4-5 harmonics give a good description of the data
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The data look like a modified gaussian
The difference between the Gaussian and Data is
the suppression of long wavelength modes!
See Also Discussions of Superhorizon fluctuations
in HIC, Ananta P. Mishra, Ranjita K. Mohapatra,
et al.
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Life is short
hadronization
lumpy initial energy density
Correct scale shows regions remain outside the
event horizon this has observable
consequences that involve non-trivial 2-particle
azimuthal correlations ESPECIALLY
correlations that could be mistaken for a Mach
Cone
QGP phase quark and gluon degrees of freedom
collision overlap zone
quantum fluctuations
? 10 fm/c
? 0 fm/c
?01 fm/c
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Multipole moments 2-particle correlations
See Also Discussions of Superhorizon fluctuations
in HIC, Ananta P. Mishra, Ranjita K. Mohapatra,
et al.
Short lifetime leads to incomplete
equilibration Similar to conclusion from v4/v22
(Ollitrault)
Valley is indicative of suppression of lower
harmonics
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Dijet Suppression
If you use high enough pT, the away-side returns
with the correct shape and its suppressed by a
factor of 5 No indication of mach cones etc
Direct observation of Dijets through dihadron
correlations Full jet-finding efforts are
underway but still a work in progress
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Is it really due to hot matter?
The reference sample indicates no suppression in
cold nuclear matter
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Heavy Quark Energy Loss
Electrons from decays of charm quarks are also
suppressed heavy quarks lose as much energy as
light quarks!
PRL 98, 172301 (2007)
Transverse Momentum GeV
This was not expected because of the dead-cone
effect
dead cone effect suppression of gluon
bremsstrahlung from massive charges at small
angles
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Viscosity from Heavy Quark Diffusion
PHENIX PRL 98 172301
Data on quenching and flow are compared to a
Langevin heavy quark transport calculation Small
relaxation time is inferred An upper limit on
the diffusion constant of the matter is obtained
Viscosity is estimated from diffusion
coefficient value comes out to 1 or 2 times 1/4p
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J/? suppression is at low pT not high
Open charm at high pT is suppressed like light
hadrons, but the J/? hadrons are not. Possible
explanations Production does not proceed
through a colored channel Screening of quarkonium
at finite momentum needs to be studied Recombinati
on of screened pairs?
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How Does the Suppression Depend on Hadron-type?
STAR Preliminary
The protons are not suppressed at intermediate
pT How would THAT fit into a jet-quenching
scenario!?
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Nquark scaling for the spectra
CENTRALITY DEPENDENCE OF THE SPECTRA
Quark number scaling also apparent in centrality
dependence of yields
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Baryon to meson ratios
A huge baryon excess at intermediate pT
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Color transparency for direct production

• Brodsky and Sickles PLB 668 111 (2008)
• Proton directly produced in hard scattering
• Proton size decreases with pT so that the proton
  is less quenched

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Color Transparency? Large Baryon v2
If the matter is transparent to baryons, why is
baryon v2 so large?
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Complimentary Observables
Can Energy Loss or Tranparency Explain the
Observed v2?
Less energy loss for baryons can explain RCP, but
would predict smaller baryon v2, not
larger! Data suggest alternative explanations at
intermediate pT Color tranparency could explain
higher pT
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Recombination Models for B/M
Coalescence models provide a ready explanation
for both v2 and RAA but any model that predicts
larger baryon production where density is larger
will do
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My Favorite Puzzle
Why is the Lambda/Kshort ratio in 630 GeV pp
collisions as large as in the RHIC AuAu
collisions!?
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My Favorite Puzzle
The evolution of the B/M ratio in pp collisions,
from low multiplicity to high Perhaps indicative
of an effect common to both systems to the
reaction plane AuAu is telling us something
about pp!
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B/M in the Ridge
The Baryon/Meson ratio is enhanced in the ridge
similar to inclusives
jet
ridge
large B/M in the reaction plane, in the ridge, in
AuAu and as we increase snn in pp What ties all
these together?
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Basic Inferences

• Jet Quenching calculations and data indicate
• Matter density is large 30-50 times cold nuclear
  matter
• dN/dy of gluons is 1400

A high temperature, high density medium, thats
opaque to fast probes is created AuAu
collisions Heavy quarks also feel the drag of
the medium diffusion constant estimates also
consistent with low viscosity At intermediate
pT, baryons are not suppressed but they do have
large v2
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Topologically Induced Parity Violation
metastable domains where vacuum excitations break
P and CP violation could be created in Heavy Ion
Collisions A fundamental aspect of QCD Chiral
Magnetic Effect may lead to observable
consequences
The topological charge density Animation by Derek
Leinweber
T.D. Lee, PRD 8 1226 (1973) Morley, Schmidt,
Z.Phys. C26, 627 (1985) Kharzeev, Pisarski,
Tytgat, PRL81512(1998) Kharzeev, Pisarski,
PRD61111901(2000) Voloshin, PRC62044901(2000) Kh
arzeev, Krasnitz, Venugopalan, PLB545298(2002) Fi
nch, Chikanian, Longacre, Sandweiss, Thomas,
PRC65 (2002)
2.4 by 2.4 by 3.6 fm.
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Observable Consequences
Kharzeev, PLB 633 260 (2006) hep-ph/0406125 Kha
rzeev, Zhitnitsky, NPA 797 67 (2007) Kharzeev,
McLerran, Warringa, NPA 803 227 (2008) Fukushima,
Kharzeev, Waringa, PRD 78, 074033
Passing nuclei cause a huge magnetic field If
parity violating regions exist, charge separation
can occur
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D. Kharzeev
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Observable Consequences
direction of the charge seperation changes
event-to-event an event average is zero signal
is too small to see in 1 event requires a
correlation measurement becomes parity even,
complicating the interpretation of the signal
a and ß indices are for different charges
a,ß opposite sign

a,ß same sign
- -
central
peripheral
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Observable Consequences
direction of the charge seperation changes
event-to-event an event average is zero signal
is too small to see in 1 event requires a
correlation measurement becomes parity even,
complicating the interpretation of the signal
a,ß opposite sign
a,ß same sign
central
peripheral
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Possible Evidence for Parity Violation
Kharzeev, PLB 633 260 (2006) hep-ph/0406125 Kha
rzeev, Zhitnitsky, NPA 797 67 (2007) Kharzeev,
McLerran, Warringa, NPA 803 227 (2008) Fukushima,
Kharzeev, Waringa, PRD 78, 074033
Not the initially predicted signal opaque medium
interference proposed as an explanation
consistent with data Non-PV models dont produce
the effect. PV is being considered as a leading
explanation
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Possible Evidence for Parity Violation
A parity even observable, sensitive to PV has
been studied the challenge is to eliminate all
other reasonable scenarios The data will be
submitted for publication next week we welcome
new input and ideas