Transcript Charmonium dissociation cross sections and J/ momentum

J/ nuclear modification factor
in nucleus-nucleus collisions
Xiao-Ming Xu
outline
• a brief review of J/ mechanisms in medium
• J/ nuclear modification factor in nucleusnucleus collisions
• summary
• J/ and the critical point
fundamental processes stimulated
by SPS
dissociation in QGP
T. Matsui, H. Satz, Phys. Lett. B178 (1986) 416
color screening
M.E. Peskin, Nucl. Phys. B156 (1979) 365
G. Bhanot, M.E. Peskin, Nucl. Phys. B156 (1979) 391
D. Kharzeev, H. Satz, Phys. Lett. B334 (1994) 155
g  J /  c  c
dissociation in hadronic matter
(1) constant cross sections
J/ + hadron  charmed mesons (charmed baryons)
Dissociation cross sections of J/ in collisions with
hadrons are assumed to be independent of the centerof-mass energy of J/ and hadron.
J. Ftacnik et al., Phys. Lett. B207 (1988) 194
S. Gavin et al., Phys. Lett. B207 (1988) 257
R. Vogt et al., Phys. Lett. B207 (1988) 263
C. Gerschel et al., Phys. Lett. B207 (1988) 253
dissociation in hadronic matter
(2) quark model calculations
J/ + hadron  charmed mesons (charmed baryons)
Barnes-Swanson quark-interchange model
The dissociation cross sections depend on the centerof-mass energy of J/ and hadron.
K. Martins et al., Phys. Rev. C51 (1995) 2723
C.-Y. Wong et al., Phys. Rev. C65 (2001) 014903
T. Barnes et al., Phys. Rev. C68 (2003) 014903
X.-M. Xu et al., Nucl. Phys. A713 (2003) 470
Prior form: gluon propagation before quark interchange
Post form: gluon propagation after quark interchange
dissociation in hadronic matter
(3) meson exchange model calculations
J/ + hadron  charmed mesons (charmed baryons)
hadronic effective Lagrangians
The dissociation cross sections depend on the center-ofmass energy of J/ and hadron.
S.G. Matinyan, B. Muller, Phys. Rev. C58 (1998) 2994
K .Haglin, Phys. Rev. C61 (2000) 031902
Z. Lin, C.M. Ko, Phys. Rev. C62 (2000) 034903
············
fundamental processes stimulated
by RHIC
recombination mechanism
c  c  J /  x
X.-M. Xu, Nucl. Phys. A658 (1999) 165
P. Braun-Munzinger, J. Stachel, Phys. Lett. B490 (2000) 196
R.L. Thews, M. Schroedter, J. Rafelski, Phys. Rev. C63
(2001) 054905

Spectral function analysis in quenched QCD
dissociation temperature of J / > 1.5Tc
dissociation temperature of c ~ 1.1Tc
M. Asakawa, T. Hatsuda, Phys. Rev. Lett. 92 (2004)
012001
Challenge:
Can we discover a new mechanism for J/
at LHC?
Model predictions on J/ produced in
nucleus-nucleus collisions
X.-M. Xu, Nucl. Phys. A697 (2002) 825
history of high-energy nucleus-nucleus collisions
AA
QGM (no T)
QGP
HM
1
2
3
5
history of high-energy nucleus-nucleus collisions
1. initial nucleon-nucleon collisions;
2. thermalization of quark-gluon matter;
3. evolution of quark-gluon plasma;
4. hadronization at a critical temperature;
5. evolution of hadronic matter until freeze-out.
production of cc
cc is a pointlike color singlet or a color octet pair from
2  2:
a  b  cc  x
2  1:
a  b  cc
cc is produced
in the initial nuclear collisions,
during the thermalization of quark-gluon matter,
in the evolution of quark-gluon plasma.
cc recombination
In quark-gluon matter probability for cc to form a bound
state J/ (cJ, ´) is proportional to the product of the
NRQCD nonperturbative matrix elements and a
medium modification factor.
NRQCD nonperturbative matrix elements
 Ο8H(3S1) = constant,
 Ο8H(3P0) = constant
 Ο8H(1S0) = constant,
Ο8H(3S1)=χ+σTa ψ · (a+HaH)ψ+σTaχ
Ο8H(1S0)=χ+Ta ψ (a+HaH) ψ+Taχ
1  i   a
i   a


O ( P0 )  χ ( D   )T ψ(a H a H )ψ ( D   )T χ
3
2
2
H 3
8
ψ the field that annihilates a heavy quark.
χ the field that creates a heavy antiquark.
medium modification factors
S-wave color-octet state
 min
exp   d ' ng  v rel gcc [ S ( 8 ) ]   (d  VT t )
  0

P-wave color-octet state
 min
exp   d ' ng  v rel gcc [ P ( 8 ) ]   (d  VT t )
  0

medium: quark-gluon matter (no T and T)
2 S 1 (8)
cross section 
g  cc[n LJ ]  c  c
(8) :
gcc [ L
]
cc dissociation
penetrates through deconfined matter and hadronic matter,
interacts with partons in deconfined matter
g  cc[n
2 S 1 (1)
J
L ]  c  c,
interacts with hadrons in hadronic matter
qq  cc[n
2 S 1 (1)
J
L ]  qc  cq
two definitions
• Charmonium is prompt if the point at which the
charmonium state is produced and the collision point of
the colliding beams cannot be resolved using a vertex
detector.
A charmonium coming from the decay of b-hadrons is not prompt.
• Charmonium is direct if the charmonium is prompt but
does not come from the decay of a higher charmonium
state.
The prompt J/ includes direct J/ as well as the radiative feeddown from
direct cJ and direct .
dN
dyd 2 p
= short-distance production 
recombination  dissociation
charmonium from initial nuclear collisions
22
dNini
(Sa / A  1)
2
dyd p
charmonium from prethermal stage
21
dN pre
2 2
dN pre
dyd 2 p
dyd 2 p
charmonium from thermal stage
21
dNthe
dyd 2 p
2 2
dNthe
dyd 2 p
pT- and y- spectra
Momentum distribution of J/:
21
22
22
21
22
dN pre
dN pre
dNini
dNthe
dNthe
dN

(Sa / A  1) 



2
2
2
2
2
dyd p dyd p
dyd p dyd p dyd p dyd2 p
cc produced via recombination during the thermalization of
quark-gluon matter and in the evolution of quark-gluon
plasma cause enhancement of J/ in some momentum
region.
dN
AdN
ratio:
RAA 
2
2
dyd p
AA
dyd p
NN
The ratio is the J/ nuclear modification factor.
left: pT distribution  J/  right: rapidity distribution
ratio versus pT at y=0, central Au-Au collisions, 200GeV
ratio versus rapidity at pT=4 GeV/c, central Au-Au collisions, 200GeV
nuclear modification factors for high-pT J/ in
Cu-Cu collisions --- from Hugo Pereira Da Costa’s talk
PHENIX Minimum Bias
STAR + PHENIX Central collisions
nuclear modification factors for high-pT J/
in Au-Au collisions --- from Duncan Prindle’ talk
Star preliminary
Au+Au: 0-80%
SUMMARY
(1) Mechanisms: dissociation and recombination.
(2) Has the study of J/ at both SPS and RHIC
accomplished the discovery of mechanisms for
J/ in nucleus-nucleus collisions?
(3) Competition between charmonium dissociation
and charmonium formed from charm quarks and
antiquarks in deconfined matter.
(4) J/ enhancement in some momentum region
Suggest J/ as a probe of the critical point
Reason:
On one side of the critical point, confined matter,
no recombination of charm quark and charm antiquark.
On the other side of the critical point, deconfined matter,
recombination of charm quark and charm antiquark.
The nuclear modification factor of J/ is affected by the
recombination.
Method:
1. system size dependence of RAA
2. beam energy dependence of RAA
Find a critical point in Fig. 5 of Phys. Rev. Lett. 98, 232301 (2007)
Azimuthal Asymmetry of J/ Production
X.-N. Wang, F. Yuan, Phys. Lett. B540 (2002) 62
J/ is affected only by g  J /  c  c
v2 ( pT=3 GeV, NP=130 )  0.022
at RHIC
Z.W. Lin, D. Molnar, Phys. Rev. C68 (2003) 044901
V. Greco, C.M. Ko, R. Rapp, Phys. Lett. B595 (2004) 202
L. Yan, P. Zhuang, N. Xu, Phys. Rev. Lett. 97 (2006) 232301
g  J /  c  c
J/ is affected by dissociation
and recombination
c  c  J /  g