Transcript J/ψ関連の話

1
J/y production in
Au+Au and Cu+Cu
Collisions at RHIC
Taku Gunji
CNS, University of Tokyo
Heavy Ion Café 2007/2/10
2
Outline
Physics Motivation
 J/y in the medium
 J/y measurement at SPS
 J/y measurement at RHIC

d+Au collisions and cold matter effects
 Au+Au and Cu+Cu collisions

Comparison to the theoretical models
 Summary & Outlook

3
Physics Motivation
J/y suppression in QGP
due to the Debye Color Screening

T.Matsui & H. Satz PLB178 416 (1986)


Signature of de-confinement
Debye Color Screening
c
c
Color Screening
• Debye Radius < Rcc
No formation of c-cbar bound states

Suppression depends on temperature (density)
• Recent quenched lattice QCD calculations
• Melting temp. for J/y ~1.5-2.5Tc
• Melting temp. for cc,y’ ~1.1Tc
T. Hatsuda, M. Asakawa, PRL. 92 (2004) 012001
S. Datta, et al., PRD69 (2004) 094507
4
J/y = Thermometer of QGP

2 Key points
 Feed down contribution from y’ and cc
• All J/y = ~0.6 J/y (direct) + ~0.3cc + ~ 0.1y’
• Fraction is not well-understood experimentally

TJ/y ~ 2Tc and Tc, Ty’ ~ 1.1Tc
Expected J/y (All)
Suppression Pattern
“Sequential Melting”
Temperature can be
deduced from magnitude
of suppression.
温度
5
J/y 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
thermal gluons)
• cc coalescence
• Dissociation by
comovers
Cold Matter Effect
Final state Effect
6
J/y measurement at SPS

NA38([email protected] GeV)、NA50([email protected] GeV, [email protected])
e
 L 
abs
Nuclear Absorption
of J/y
L: effective path length of J/y
in nuclear target
Anomalous suppression
relative to nuclear Absorption
Pb+Pb
P
B
• Very promising to study J/y
production in A+A collisions at higher
collision energy.
• 10x √sNN at RHIC
• 2-3x gluon density at RHIC
7
PHENIX Experiment

PHENIX can measure J/y in wide rapidity range
Central Arms:
Hadrons, photons, electrons
J/y  e+e|h|<0.35
Pe > 0.2 GeV/c
Df = p (2 arms x p/2)
Muon Arms:
Muons at forward rapidity
J/y  m+m
1.2< |h| < 2.4
Pm > 2 GeV/c
Df = 2p
8
RHIC cold nuclear
matter effects (CNM)
9
J/y in d+Au collisions

Understand the cold matter effects




Gluon Shadowing
Nuclear absorption
Cronin effect (pT broadening)
rapidity y
Xd
J/y in
South
y<0
Xd
XAu
XAu
Coverage of XAu in d+Au at PHENIX
South muon arm (y < -1.2) :

J/y in
North
y>0
gluons in Pb / gluons in p
large XAu  0.090
Central arm (y  0) :

intermediate XAu  0.020
North muon arm (y > 1.2) :

Shadowing
Anti
Shadowing
small XAu  0.003
X
Eskola, et al., Nucl. Phys. A696 (2001) 729-746.
10
Results of RdAu vs. y

d+Au experiments at RHIC
RdAu vs. Rapidity
R AA =
RdAu
0 mb
3 mb
Low x2 ~ 0.003
(shadowing region)
( dN J /y / dy ) A + A
( dN J /y / dy ) p + p  < N col 
•Tendency is consistent with
the shadowing effects.
•Nuclear absorption cross
section : 0~3 mb.
• need more data to
quantify CNM effects.
11
J/y production in Au+Au and
Cu+Cu collisions at RHIC
12
RAA vs. Npart
RAA
1
Au+Au PHENIX Final
Cu+Cu PHENIX Preliminary
0
• Final results for Au+Au : nucl-ex/0611020 (submitted to PRL)
• Analysis for Cu+Cu will be finalized soon!
13
Observation 1
Different suppression
pattern between
mid-rapidity and
forward-rapidity
14
RAA vs. Npart in Au+Au
1

RAA
RAA vs. Npart.


0
Bar: uncorrelated error
Bracket : correlated error
1
0
S = RAA (1.2<|y|<2.2) /RAA (|y|<0.35)
|y|<0.35
1.2<|y|<2.2
• Different behavior in RAA
between mid-rapidity and
forward-rapidity.
• J/y suppression is larger
at forward-rapidity than
at mid-rapidity
• S ~ 0.6 for Npart>100
15
RAA and CNM effects
RAA
1

CNM effects
Gluon shadowing +
nuclear absorption
 J/y measurement in
d+Au collisions.

RHIC CNM effects
(abs = 0, 1, 2mb at y=0, y=2)
R. Vogt et al., nucl-th/0507027
0
• Significant suppression relative to CNM effects.
• CNM effects predict larger suppression at mid-rapidity,
while data shows larger suppression at forward-rapidity.
Larger suppression by
CGC?
Heavy quark production is expected to be
suppressed due to “Color Glass Condensate”
at forward-rapidity. K. L. Tuchin hep-ph/0402298

Open charm yield
in Au+Au @ 200 GeV
h=0
h=2
• Larger suppression of J/y at forward-rapidity (Npart>100)
could be ascribed to Color Glass Condensate?
16
Larger suppression by
larger feed down?

Pythia calculation (done by S. X. Oda)
Red : 88 gg  c1cg  J/y
Green : 89 gg  c2cg  J/y
Blue : 105 gg  c2c  J/y
Magenta : MSEL 5 bbbar  J/y
Larger suppression
of J/y yield
at forward rapidity
might be partly
(~15%) due to the
broad distribution
of J/psi from chi_c.
17
18
Observation 2
J/y suppression
from final state effect
is stronger at RHIC
compared to SPS
19
Comparison of RAA to NA50
NA50 at SPS (0<y<1)
PHENIX at RHIC (|y|<0.35)
PHENIX at RHIC (1.2<|y|<2.2)

RAA vs. Npart

NA50 at SPS
• 0<y<1
 PHENIX at RHIC
• |y|<0.35
• 1.2<|y|<2.2
Bar: uncorrelated error
Bracket : correlated error
Global error = 12% and
Global error = 7% are not shown
• J/y Suppression (CNM
effects included) is similar
at RHIC (y=0) compared
to at SPS (0<y<1).
20
RAA and CNM
NA50 at SPS (0<y<1)
PHENIX at RHIC (|y|<0.35)
PHENIX at RHIC (1.2<|y|<2.2)

RAA at RHIC and SPS
RHIC CNM effects
(abs = 0, 1, 2mb at y=0, y=2)
R. Vogt et al., nucl-th/0507027
SPS CNM effects (abs = 4.18 mb)
NA50, Eur. Phys. J. C39 (2005):355
Bar: uncorrelated error
Bracket : correlated error
Global error = 12% and
Global error = 7% are not shown
21
RAA/CNM vs. Npart
NA50 at SPS (0<y<1)
PHENIX at RHIC (|y|<0.35)
PHENIX at RHIC (1.2<|y|<2.2)
Here, SPS data will
have sys. errors.

RAA/CNM at RHIC and SPS.
CNM:


abs = 4.18 mb for SPS
abs = 1 mb for RHIC
• Additional sys. error due to the
uncertainty of CNM (0-2mb) is
shown as box.
Bar: uncorrelated error
Bracket : correlated error
Global errors (12% and 7%)
are not shown here.
Box : uncertainty from CNM effect
• J/y suppression relative
to CNM effects is larger at
RHIC for the similar Npart.
(much larger
at forward rapidity)
22
RAA vs. pT


Suppression
trend is similar
for forward and
mid rapidity.
Suppression
consistent with
flat.
23
Exercise :
Comparison to
theoretical models
24
Dissociation by thermal
gluons
Dissociation by thermal gluons
• Successfully describe J/y suppression at SPS.
• Gluon density extrapolated to RHIC energy
R. Rapp et al., nucl-th/0608033
Nu Xu et al., nucl-th/0608010
Calculation for only y=0
• At mid-rapidity,
suppression is
weaker compared
to the dissociation
scenario in QGP.
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J/y
Recombination of J/y

c
c-bar
c
Coalescence of c-cbar


Abundant ccbar pairs at RHIC [10-30@central Au+Au]
Dissociation + Recombination of J/y
R.Rapp et al, EPJC43 (2005) 91
Kinetic formation model
N. Xu at al, nucl-th/0608010
Transport model
total
recombination
dissociation
total
dissociation
recombination
Magnitude of suppression matches better.
However, tendency can not be reproduced well.
26
<pT2> vs. centrality

Another test for recombination
No recombination
Recombination
(pQCD charm )
Recombination
(thermal charm)
27
Kinetic formation model.
Dissociation + recombination model (R. Rapp and so on)
N cc =
dir
1
2
I 1 ( c N oc )
th
 c N op
th
I 0 ( c N oc )
th
+  c N cc
2
th
Charm cross section (binary scaling)
• NLO pQCD calc, PHENIX, STAR
c ~ 10 at RHIC, ~30 at LHC
¼ c+g
X.N.Wang PLB540 (2002) 62
J/y+g
Gluon thermal dist.
(T=0.35 GeV)
k[GeV]
28
Transport model
Dissociation + recombination model (Nu Xu et al.)
ccbar  J/y +g
J/y +g ccbar
R. L. Thews Eur. Phys. J C43, 97 (2005)
29
Sequential Melting

RAA/CNM vs. Bjorken
energy density
 Bj =
Here, SPS data will
have sys. errors .

1
dE T
t 0 A dy
y=0
t0 = 1 fm/c. Be careful!
• Not clear t0 at SPS
• Crossing time ~ 1.6 fm/c
F. Karsch et al., PLB, 637 (2006) 75
• J/y suppression at SPS
can be understood
from the melting of y’
and cc.
30
Sequential Melting

Here, SPS data will
have sys. errors.
Bar: uncorrelated error
Bracket : correlated error
Global error = 12% is not shown here.
Box : uncertainty from CNM effects
F. Karsch et al., PLB, 637 (2006) 75
dET/dy : PHENIX, PRC 71, 034908 (2005)
RAA/CNM vs. Bjorken
energy density
 Bj =

1
dE T
t 0 A dy
y=0
t0 = 1 fm/c. Be careful!
• Not clear t0 at SPS
and RHIC.
• t0 < 1 fm/c at RHIC
• Nucl. Phys. A757, 2005
31
Sequential Melting

Here, SPS data will
have sys. errors.
RAA/CNM vs. Bjorken
energy density
 Bj =

1
dE T
t 0 A dy
y=0
t0 = 1 fm/c Be careful!
• t0 < 1 fm/c at RHIC
Bar: uncorrelated error
Bracket : correlated error
Global error = 12% and 7%
are not shown here.
Box : uncertainty from CNM effects
• Direct J/y melting at RHIC?
• Error is large and need better
CNM measurements at RHIC.
• Need to measure feed-down
contribution at RHIC energy.
32
Threshold Model

All J/y is suppressed above a threshold density.
A. K. Chaudhuri, nucl-th/0610031
Calculation for only y=0.
nc = threshold participant density
• Fate of J/y depends on the
local energy density
( participants density, n)
 Similar model to the sequential
melting and associated to “onset
of J/y suppression”.
 nc = 4.0 fm-2 matches to our
mid-rapidity data.
(cf. n~4.32 fm-2 in most central
Au+Au collisions)
• Describes well midrapidity data.
• How about forwardrapidity?
33
Summary
First high statistic data of J/y in Au+Au and Cu+Cu collisions
at mid-rapidity and forward-rapidity are available.
 Suppression is larger at forward-rapidity than at
mid-rapidity for Npart>100.
 Suggesting initial state effect such as Color Glass Condensate?
 More feed down contribution at forward-rapidity?
 RAA/CNM seems to be lower at RHIC compared to at SPS
 However, suppression at mid-rapidity isn’t so strong as
expected by the models (destruction by thermal gluons)
extrapolated from SPS to RHIC.
 Suppression + Recombination models match better.
 Not consistent with the picture of only y’ and cc melting at
RHIC. Suppression of directly produced J/y?

Backup slides
Regeneration should cause narrowing of pT – does it?
Mean pT2 pretty flat
• as expected in regeneration picture of Thews
• Yan picture almost flat to start with, gives
slight fall-off with centrality
Caution - <pT2> from fits often unreliable for AA
(stable when restricted to pT<5 GeV/c here)
Better for theoretical comparisons to look at RAA(pT)?
nucl-ex/0611020
First cc observation


From run5 p+p central arms
Further analysis is on going.
FG
Mixed event BG
cc1 cc2
Mee-Mee [GeV]
Mee-Mee [GeV]
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
dAu = pp (2x197)a
SPS
FNAL
RHIC
XAu, XF dependence of a
Shadowing is weak.
 Not scaling with X2
but scaling with XF.
 Coincidence?

dAu = pp (2x197)a
• 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
SPS J/y suppression

Dissociation by gluons
NA60 In-In 158 GeV
preliminary
Pb-Pb @ 158 GeV
Dissociation by gluons

Cross section : g+J/y  c + c-bar

LO calculation
2
2 p  32   m Q
 Diss ( k ) =
  
3  3   0

Diss




1/ 2
1 ( k /  0  1)
2
mQ
(k /  0 )
Decay width
5
k[GeV]
 =< v ref  Diss   g
 d kv ref  Diss ( k ) f ( k ; T )
3
< v ref  Diss =
3/2
'
 d kf ( k ; T )
3
f ( k ; T ) = (exp( k / T )  1)
T = 350 MeV,  = 0.8 fm/c
0
1
0
Dissociation by gluons
Cross sectionはLO計算。正しいのか？
• Binding Energyの小さいy’やccに適応可能か？
5
Successful models (1)

Dissociation by thermal gluons

Based on LO pQCD cross section between J/y (cc) and g
R. Rapp PLB92 (2004) 212301
X.N.Wang PLB540 (2002) 62
Pb-Pb @ 158 GeV
20 40
100
ET [GeV]
PHENIX – p+p J/ψ – new run6 data
• Forward rapidity falloff steeper than 3gluon pQCD model - black curve [Khoze et al. , Eur.
Phys. J. C39, 163-171 (2005)]
• Slightly favors flatter shape at mid-rapidity
than most models
PHENIX - hep-ex/0611020
• BR•tot = 178 ± 3 ± 53 ± 18 nb
• Harder pT than lower energy & softer at
forward rapidity
<pT2> = 3.59±0.06
±0.16
<pT2> = 4.14±0.18
+0.30-0.20
Statistical Model (1)

Statistical Hadronization

元々のMotivationはSPSで<J/y>/<h>が中心衝突度に
依存しない事。Hadron生成量は統計Modelで記述できる。
Hadronの生成量

もうひとつのパラメター：u,d,s,c (Fugacity)

• u,d,s,c quarkがどれほど化学平衡に達しているかという指標
• 実際のYield =  x ni
Statistical Model (2)

RHICではs ~ 1 (SPSでは、s<0.7)


Charm quarkは重い。殆どがHiggs Mass



衝突初期にしか出来ない。
ＱＧＰ中での熱的生成量(exp-(2mc/Tc)) ~ 10-7
なのに、平衡状態を仮定して、J/yのＹｉｅｌｄを計算

N cc =
dir
Strange quarkがようやく平衡状態
cが平衡状態からのずれを担う。
1
2
I 1 ( c N oc )
th
 c N op
th
I 0 ( c N oc )
th
+  c N cc
2
th
cc-bar cross section
(experiment, FONLL)
Model Input: Nccdir, T, m, Volume
このModelはp+p, Au+AuにおけるCharm Productionに大きく依存する。
Statistical Model (3)


Charm Production Cross sectionによる大きな不確定
性がある。
NNLO pQCD計算
d/dy = 63.7+95.6-42.3 mb
d/dy = 123 mb (PHENIX)
•2倍程度、大きい。
•CDFが測定したCharm Cross
SectionもNNLOより
1.5倍程度大きい。
NNLO pQCD計算のCharm Cross
Sectionでは、よく合っているが、
PHENIXの実験結果では不一致。
Recombination – In medium Formation

Medium中でもJ/y生成。

Kinetic Formation Model
N cc =
dir
dN J /y
dt
=< v  F  c N c  < v  D   g N J /y

Transport Model
1
2
I 1 ( c N oc )
th
 c N op
th
I 0 ( c N oc )
th
+  c N cc
2
th
Recombination – In medium Formation

問題点と疑問点
• Charm Cross Sectionの大きな不確定性
• p+p, Au+AuにおけるCharm y, pT分布?
• QGP中ではCharmはDiffusiveに動いているが、理由はまだ分かっていない。
• J/y+gccbar のCross Sectionが正しいか？
 ccやy’に対するRecombinationは考えられていない。
• Ncの与え方。どのモデルもNcは時間に対して一定。正しい？
• Charmの熱的生成はない、Charm数は保存。
• DメソンへのRecombinationも考慮すべき。NcNc(t)、tと共に減少するはず。
ただ、DメソンとJ/yではFreezeout時間が異なるか？
• J/yの方が圧倒的に早く生成されるなら、正しいかも。
• Naïveには、ccが空間的に近くにないといけない。ccがCoupleするよりも、
u,dとCoupleする方が多いはず。
dN J /y
dt
=< v  F  c N c  < v  D   g N J /y
dN J /y
dt
Au+AuにおけるCharm, D, J/y生成
を理解しなければならない。
=< v  F   c (t ) N c (t )  < v  D   g N J /y ,
dN c
dt
=  < v c   D   u ,d ,s N c
24
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 p,
K, p