夸克胶子等离子体中的热法和charm法生产
169 浏览量
2020-04-04
06:38:34
上传
评论
收藏 357KB PDF 举报
Physics Letters B 758 (2016) 434–439
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Thermal charm and charmonium production in quark gluon plasma
Kai Zhou
a,b,c
, Zhengyu Chen
a
, Carsten Greiner
b
, Pengfei Zhuang
a,∗
a
Physics Department, Tsinghua University, Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
b
Institute for Theoretical Physics, Johann Wolfgang Goethe-University Frankfurt, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany
c
Frankfurt Institute for Advanced Studies, Ruth-Moufang-Str. 1, 60438 Frankfurt am Main, Germany
a r t i c l e i n f o a b s t r a c t
Article history:
Received
17 February 2016
Received
in revised form 22 April 2016
Accepted
17 May 2016
Available
online 19 May 2016
Editor:
W. Haxton
We study the effect of thermal charm production on charmonium regeneration in high energy nuclear
collisions. By solving the kinetic equations for charm quark and charmonium distributions in Pb+Pb
collisions, we calculate the global and differential nuclear modification factors R
AA
(N
part
) and R
AA
(p
t
)
for J/ψ s. Due to the thermal charm production in hot medium, the charmonium production source
changes from the initially created charm quarks at SPS, RHIC and LHC to the thermally produced charm
quarks at Future Circular Collider (FCC), and the J /ψ suppression (R
AA
< 1) observed so far will be
replaced by a strong enhancement (R
AA
> 1) at FCC at low transverse momentum.
© 2016 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
Statistical Quantum Chromodynamics (QCD) predicts that, a
strongly interacting matter will undergo a deconfinement phase
transition from hadron matter to quark matter at finite temper-
ature
and density. It is expected that, this new state of matter,
the so-called quark gluon plasma (QGP), can be created by liberat-
ing
quarks and gluons from hadrons through high energy nuclear
collisions. Since the QGP can only exist in the initial period and
cannot be directly observed in the final state of the collisions,
one needs sensitive probes to demonstrate the formation of this
new state. J /ψ suppression has long been considered as such a
probe since the original work of Matsui and Satz [1], and many
progresses have been achieved both experimentally and theoret-
ically,
see for instance the recent review paper [2,3]. While the
charmonium production mechanism changes from initial produc-
tion
at SPS energy [4–6] to initial production plus regeneration at
RHIC and LHC energies [7–14], the charm quarks are all from the
initial production.
Recently, the Future Circular Collider (FCC) at CERN is pro-
posed
to push the energy frontier beyond LHC, which includes
the plan of Pb+Pb collision at
√
s
NN
= 39 TeV [15]. What would
we expect about the charmonium production at this new energy
regime? Since a much more hot medium will emerge at FCC,
gluons and light quarks inside the medium would be more en-
ergetic
and denser. Therefore, the thermal production of charm
quarks via gluon fusion and quark and anti-quark annihilation may
*
Corresponding author.
E-mail
addresses: zhou@th.physik.uni-frankfurt.de (K. Zhou),
zhuangpf@mail.tsinghua.edu.cn (P. Zhuang).
have a sizeable effect on charmonium regeneration. For the in-
medium
charm quark production, there are already many studies,
by considering leading order [16–18] and including next to lead-
ing
order [19] QCD processes. Taking into account the quadratic
dependence of the charmonium regeneration on charm quark den-
sity,
we expect that, the extra increase of charm quark pairs via
the thermal production in QGP will obviously enhance the charmo-
nium
yield at FCC. Since the very hot medium can eat up almost
all the initially produced charmonia, the regeneration becomes the
only source of the finally observed soft charmonia. This makes J /ψ
more effective to probe the medium properties. In this paper, we
focus on the effect of thermal charm production on charmonium
production in heavy ion collisions at LHC and FCC energies.
The
full information of charm quarks in medium is contained in
their distribution function f
c
(t, x, p) in phase space, its momentum
integration is the number density n
c
(t, x) =
d
3
p/(2π)
3
f
c
(t, x, p).
When charm quarks approach kinetic equilibrium with the medium
significantly fast in high energy nuclear collisions, only the evo-
lution
of the chemical abundance needs to be considered. By
integrating out the charm quark momentum assuming thermal
distribution, the Boltzmann equation for f
c
becomes the rate equa-
tion
for n
c
,
∂
μ
n
μ
c
=r
gain
−r
loss
, (1)
where n
μ
c
=n
c
(1, v) is the charm current with medium velocity v,
and the gain and loss terms r
gain
and r
loss
on the right hand side
are respectively the charm quark production and annihilation rates
inside QGP. The rates can be calculated through perturbative QCD.
http://dx.doi.org/10.1016/j.physletb.2016.05.051
0370-2693/
© 2016 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.
资源评论
