Transcript J/y measurement in Heavy Ion Collisions at RHIC

Workshop on “Frontiers in the physics of quark-gluon-plasma” 7/8/2006, RIKEN
J/y Measurement in
Heavy Ion Collisions at RHIC
Taku Gunji,
CNS, University of Tokyo
For the PHENIX Collaboration
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Outline
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Physics Motivation
Charmonium in the Medium
Cold Matter Effects
Results from d+Au Collisions
QGP Effects
 Color Screening and cc-bar coalescence
 Results from A+A Collisions
 Comparison to theoretical models
 Summary and Outlook
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Physics Motivation
 Heavy Quarks carry the information of the
early stage of collisions.
 Charm quarks are massive even at RHIC
 Creation takes place only at the begging of
collisions via the hard process.
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Sensitive to gluon PDF in nuclei.
Well calibrated by p+p collisions
Yields scale with Nbinary (without medium effect)
No Chemical equilibrium. Abundance will be frozen.
 Charmonium = “Probe of De-confinement”
 Color Screening Effect by QGP
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Charmonium in the Medium
 J/y production and evolution of the medium
 All stage of collisions modify the J/y yield.
Initial stage
Nuclear
medium
Hot and dense
medium
Mixed Phase
Freeze out
• Gluon
Shadowing
• CGC
• Nuclear
Absorption
• Cronin effect
• Color screening
• Dissociation by
gluons
• cc coalescence
• Dissociation by
secondary mesons
Cold Matter Effect
QGP Effect
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Charmonium in the Medium
 J/y production and evolution of the medium
 All stage of collisions modify the J/y yield.
Initial stage
Nuclear
medium
Hot and dense
medium
Mixed Phase
Freeze out
• Gluon
Shadowing
• CGC
• Nuclear
Absorption
• Cronin effect
• Color screening
• Dissociation by
gluons
• cc coalescence
• Dissociation by
secondary mesons
Cold Matter Effect
QGP Effect
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Cold Matter Effects
 Initial state effect:
Eskola et al. NPA696 (2001) 729
Gluon Shadowing
(or CGC gluon saturation)
 Depletion of Gluon PDF
in nuclei at small x.
 Final state effects:
gluons in Pb / gluons in p
Shadowing
Anti
Shadowing
x
Nuclear Absorption
 Break up interaction of J/y or
pre-resonance c-cbar state by spectators
Cronin effect
Converage of X in Au
By PHENIX
in d+Au experiments
 Initial state multiple scattering of partons
 d+Au collisions give the hints of these effects
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Results from d+Au Collisions
sdAu = spp (2x197)a
RdAu vs. Rapidity
RdAu
0 mb
Low x2 ~ 0.003
(shadowing region)
3 mb
(in gold)
= Xd - XAu
Small effect from gluon shadowing
 a>0.92, scale with XF not XAu
Small effect from nuclear absorption
 sabs = 0-3 mb, sabs = 4.2mb at SPS
Need more data to
quantify these effects.
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Color Glass Condensate
 At RHIC, coherent charm production in nuclear
color field at y>0 (Qs > mc) and dominant at
y>2.  Description by Color-Glass-Condensate
sdAu = spp (2x197)a
SPS
FNAL
RHIC
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Charmonium in the Medium
 J/y production and evolution of the medium
 All stage of collisions modify the J/y yield.
Initial stage
Nuclear
medium
Hot and dense
medium
Mixed Phase
Freeze out
• Gluon
Shadowing
• CGC
• Nuclear
Absorption
• Cronin effect
• Color screening
• Dissociation by
gluons
• cc coalescence
• Dissociation by
secondary mesons
Cold Matter Effect
QGP Effect
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J/y is “QGP thermometer”
 Color Screening by the QGP
 Suppression due to the Debye Screening.
 Tdiss (cc) ~ Tdiss (y’) < Tdiss (J/y)
 40% J/y come from y’ and cc.
J/y ~ 0.6 J/y + 0.3cc + 0.1y’
 HERA-B exp. Phys. Lett. B 561(2003)
 These effects result in the
sequential melting of J/y.
 J/y suppression
pattern may be able
to serve as a
“QGP thermometer”.
c
c
Color Screening
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Dissociation Temperature
 Recent Lattice Results
and Potential Analysis.
Question from experimentalists.
 How large the “systematic error”?
 J/y would survive at RHIC!?
 Same as SPS?
 J/y suppression at SPS can be
described by feed down effect.
 melting only cc and y’.
Datta & al, hep-lat/0409147
Alberico & al, hep-ph/0507084
Wong, hep-ph/0408020
Satz, hep-ph/0512217
M. Asakawa et al, PRL 92(2004)
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Coalescence of cc-bar pairs
New Scenario of J/y production in HIC at
RHIC! (negligible at SPS)
 First(?) discussion by T. Matsui
 Proceedings of the Second Workshop on
Experiments and Detectors for a Relativistic Heavy
Ion Collider (RHIC) at LBL, 1987.
Recombination of J/y from
uncorrelated cc-bar pairs.
 statistical coalescence
 kinetic formation
 two component model
statistical hadronization model
hep-ph/0311048
(CERN yellow rpt)
Ncc = 28
Ncc = 19
Ncc = 12
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Let’s look at the data from
Au+Au and
Cu+Cu collisions.
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RAA as a function of Npart
1.2<|y|<2.4
|y|<0.35
• Factor of 3 suppression at most central (Au+Au/Cu+Cu)
• Beyond the cold matter effects extrapolated from d+Au results.
• Same suppression pattern at forward rapidity, but different
pattern at mid-rapidity between Au+Au and Cu+Cu.
• Pattern in Au+Au is different between mid-rapidity and
forward-rapidity.
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RAA as a function of pT
 Results from forward-rapidity.
Au+Au
Cu+Cu
Yield of low pT J/y is suppressed in both Au+Au and Cu+Cu.
• Tendency is same as SPS.
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Used NA50 Suppression
 Models describing NA50 suppression.
 extrapolation of T, gluon density from SPS.
SPS  RHIC :
~10x collision energy
~2-3x gluon energy density
Eur. Phys. J C42 (2005)
PRL 92 (2004) 212301
PRC 68 (2003) 041902
J/y suppression
at RHIC is
over-predicted
by the suppression
models that
described SPS
data successfully.
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Coalescence Models
 Models with recombination
 Dissociation + Recombination
Models with
recombination
– single charm quarks
combining in the
hadronization stages
to form J/y’s –
Statistic coalescence (PLB 571 (2003) 36)
Statistic coalescence (PRC 68 (2003) 041902)
HSD model (PRC 69 (2004) 054903)
Two component model (PRL 92 (2004) 212301)
match the observed
RHIC suppression
much better!
Need to look at other
observables.
(<pT2>, y-shape)
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2
<pT >
 At forward rapidity
(closed symbols)
<pT2> = 2.51 + 0.32 L
from pp & dA
p+p d+Au
Au+Au
<pT2> = 2.51 + 0.32 L
Open symbol: y ~ 0
Full & curves: y ~ 2
 Data points are consistent
with Cronin effect.
in between of direct
and recombination
 At mid rapidity
(open symbols)
Thews (Kinetic Model)
behavior in <pT2> is
Eur.Phys.J C43, 97 (2005)
different from forward-rapidity.
<pT2> does not increase with L in d-Au and Au-Au.
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Rapidity Shape
Thews (Kinetic Model)
Eur.Phys.J C43, 97 (2005)
• No significant
difference in
rapidity shape,
while
recombination
predicts narrower
rapidity shape.
• charm y-shape
and longitudinal
flow need to be
evaluated.
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Hydro + J/y transport
 QGP hydro (2+1D)
 Boltzman-type transport
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
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Dissociation by gluons in QGP
No thermalization of charm
No recombination
No interaction in HG
Cold matter effect (1mb)
QGP suppression
Only cold matter effect
Au+Au y~1.7 |y| ~ 0
The result fits reasonably well
the PHENIX data at y=1.7,
but not at y=0.
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Sequential Melting
 Survival probability vs. energy density (t0 ~ 1 fm/c)
 Assuming Successive Melting.
 Tdiss(cc,y’) ~ Tc (dissolved)
 Tdiss(J/y) ~ 2Tc (un-dissolved)
 S(J/y) = 0.6 + 0.4*S(y’)
 S(y’) from SPS data
 Interesting idea inferred from
Lattice QCD calculations.
 No dynamical dissociation
process.
 Need to be integrated with other
process.
 40% feed down is OK at RHIC?
Karsch, Kharzeev & Satz: PLB637(2006)75
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Summary
 PHENIX Measured J/y in p+p, d+Au, Au+Au and Cu+Cu
Collisions.
 Cold matter effects are weak at RHIC energy.
 Need more d+Au data to quantify these effects.
 Observed the suppression in A+A collisions.
 Suppression is beyond the Cold Matter Effects.
 Different behavior in RAA between Au+Au and Cu+Cu at mid-rapidity.
 Different behavior in RAA and <pT2> between Mid-Rapidity and
Forward-Rapidity.
 Weak suppression compared to “full” suppression
 Many works on the theoretical predictions.
 Suppression (dissociation by gluons) + recombination
 Static color screening + feed down
 QGP hydro + transport of J/y
 All describe better compared to “full” suppression models.
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Outlook
 We need to improve the current situation both
experimentally and theoretically.
 Experiment :
 More data : d+Au, A+A and p+p (reference)
 J/y v2 measurements : RP detector in PHENIX from 2007
 feed down effects : cc analysis in p+p is underway.
 Theoretical :
 Calculations with complete processes are needed.
Cold Matter Effects
• modified PDF, Cronin effect, Nuclear Absorption
Dissociation due to Debye screening (sequential melting;
feed-down effect) and dynamical effects in QGP and HG
• Medium Properties and effects on dissociation cross section, binding
energy, charm mass …
Recombination process
• Charm cross section, rapidity, pT, charm flow, jet quenching
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Charm Production at RHIC
Need to understand charm
production and its modification
in the medium.
Non-photonic e spectra
from PHENIX.
Implication of charm
Energy loss
Yield vs. pT for two
rapidity ranges
in p+p collisions.
Charm vs. y
Non-photonic e v2
from PHENIX.
Thermalization of
Charm.
BW fit of D-meson spectra
From STAR.
Freeze out and collective
Behavior of charm.
AuAu Central charm
hadron
AuAu Central ,
K, p
Back Up Slides
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PHENIX Experiment
 J/y measurement at wide y coverage.
Central Arms:
Hadrons, photons, electrons
J/y  e+e|h|<0.35
Pe > 0.2 GeV/c
Df =  (2 arms x /2)
Muon Arms:
Muons at forward rapidity
J/y  m+m1.2< |h| < 2.4
Pm > 2 GeV/c
Df = 2
XAu, XF dependence of a
 Shadowing is weak.
 Not scaling with X2
but scaling with XF.
sdAu = spp (2x197)a
Coincidence?
Shadowing
Gluon energy loss
Nuclear Absorption
Sudakov Suppression?
Energy conservation
hep-ph/0501260
Gluon Saturation?
hep-ph/0510358
(in gold)
= Xd - XAu
E866, PRL 84, (2000) 3256
NA3, ZP C20, (1983) 101
PHENIX, PRL96 (2006) 012304
Cronin Effect
a vs. pT for 3 xAu region
Comparison to lower
energy results.
High x2
~ 0.09
E866 at s = 39 GeV.
Trend of pT broadening
at RHIC is consistent
With lower energy results
Low x2
~ 0.003
J/y measurements at SPS
 Suppression in S+A
 turned out to be similar to p+A
 Anomalous suppression in Pb+Pb
J/y Suppression as a function of pT (Pb+Pb)
Comover Interaction
 In HG, survived J/y’s interact with secondary
hadrons: J/y + h  DD.
 Crucial parameter : J/y-hadron inelastic cross-section,
(syhinel) a very uncertain parameter !
Theoretical estimates : syhinel ~0.1-1 mb
 Dual Parton Model
 Ncom = C1*Npart+C2*Ncol
 syhinel ~ 0.46 mb
A.Capella,D.Sousa,
nucl-th/0303055
Azimuthal anisotropy of J/y
 Key to differentiate recombination and transport
model.
Zhu et al. PLB 607, 107 (2005)
 Recombination :
 10% v2 @ 2GeV/c
• If charm quark v2 is
same as light quark v2.
 Transport model:
 0.5% v2 @ 2GeV/c
• More suppression of low pT
J/y in the out-of-plane.
(“Geometry only”)
 Need more statistics
and good RP resolution.
 RP detector at Run7
coalescence of
thermalized charm
X 0.1
(Rapp)
J/y Polarization
 Sensitive to Production Mechanism
J/y production models predict different polarization.
CEM and CSM: no polarization
COM: transverse at high PT
Ioffe and Kharzeev, hep-ph/0306176: transverse
(~0.35-0.40) at low PT if QGP is formed
Khoze, Martin, Ryskin, and Stirling, hep-ph/0410020:
longitudinal polarization at high PT
Run3 d+Au
Results consistent with no
polarization, large error bars
due to low statistics.
PHENIX Preliminary
J/y in Ultra-Pheriperal Collisions
 Photo-production gpJ/yp :
Sensitive to Gluon distribution at small x.
J. Nystrand, NPA 752 (2005) 470c
QM05
dsJ/y/dy|y=0 = 44 ± 16 (stat) ± 18 (syst) mb
First U measurements
 Preliminary results from run5 p+p muon arms
First cc observation
 From run5 p+p central arms
 Further analysis is on going.
FG
Mixed event BG
cc1 cc2
Meeg-Mee [GeV]
Meeg-Mee [GeV]
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Color Screening by the QGP
 Probe of the “de-confinement”
 T. Matsui and H. Satz (1986)
 Suppression due to the Debye
Screening in the de-confined phase
 Screening Radius rD(T)
decreases with temperature T.
 when rD(T) falls below the
binding radius ri of QQ-bar
state i , state i cannot exist.
 Tdiss (cc) ~ Tdiss (y’) < Tdiss (J/y)
c
c
Color Screening
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Various Coalescence Models
 Statistical Hadronization (A. Andronic et al.)
 All Charmonium dissolved in the QGP
 Charm equilibrium in the QGP
 Open and Closed charm form at the freeze-out.
 Kinetic Formation (Thews et al.)
 Continuous formation/dissociation of J/y in the QGP
 Used vacuum binding energy of J/y
 2 Component Model (R. Rapp et al.)




In-medium binding energies of J/y inferred from Lattice.
formation/dissociation of J/y in the QGP and HG
statistical coalescence at the freeze-out
rate equation in the thermal fireball model.
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Coalescence Models
 Models with recombination
Models with
recombination
– single charm quarks
combining in the
hadronization stages
to form J/y’s –
Thews (Kinetic Model)
Eur.Phys.J C43, 97 (2005)
Rapp et al. (2-Component)
PRL 92, 212301 (2004)
match the observed
RHIC suppression
much better!
Need to look at other
observables.
(<pT2>, y-shape)