Physics Letters B 764 (2017) 254–259
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
The hidden charm pentaquarks are the hidden color-octet uud
baryons?
Sachiko Takeuchi
a,c,d,∗
, Makoto Takizawa
b,d,e
a
Japan College of Social Work, Kiyose, Tokyo 204-8555, Japan
b
Showa Pharmaceutical University, Machida, Tokyo 194-8543, Japan
c
Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki, Osaka, 567-0047, Japan
d
Theoretical Research Division, Nishina Center, RIKEN, Hirosawa, Wako, Saitama 351-0198, Japan
e
J-PARC Branch, KEK Theory Center, Institute of Particle and Nuclear Studies, KEK, Tokai, Ibaraki, 319-1106, Japan
a r t i c l e i n f o a b s t r a c t
Article history:
Received
22 August 2016
Received
in revised form 31 October 2016
Accepted
20 November 2016
Available
online 23 November 2016
Editor:
J.-P. Blaizot
Keywords:
Hidden-charm
pentaquark
Color-octet
baryon
Exotic
hadron
Multiquark
hadron
Baryon–meson
scattering
The I( J
P
) =
1
2
(
1
2
−
),
1
2
(
3
2
−
), and
1
2
(
5
2
−
) uudcc pentaquarks are investigated by the quark cluster model.
This model, which reproduces the mass spectra of the color-singlet S-wave q
3
baryons and qq mesons,
also enables us to evaluate the quark interaction in the color-octet uud configurations. It is shown
that the color-octet isospin-
1
2
spin-
3
2
uud configuration gains an attraction. The uudcc states with this
configuration have structures around the
(∗)
c
D
(∗)
thresholds: one bound state, two resonances, and one
large cusp are found. We argue that the negative parity pentaquark found by the LHCb experiments may
be given by these structures.
© 2016 The Authors. 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
.
1. Introduction
In 2015, LHCb collaboration reported that two candidates of the
new exotic baryons, P
c
(4380) and P
c
(4450), had been observed in
the
0
b
→ J /ψ pK
−
decay. The mass of the higher peak, P
c
(4450),
is 4449.8 ± 1.7 ± 2.5MeVwith a width of 39 ± 5 ± 19 MeV,
while the lower and broader peak, P
c
(4380), has a mass of 4380 ±
8 ± 29 MeV and a width of 205 ± 18 ± 86 MeV. The most favor -
able
set of the spin parity for the lower and the higher peaks is
J
P
= (
3
2
−
,
5
2
+
), though (
3
2
+
,
5
2
−
) or (
5
2
+
,
3
2
−
) are also acceptable
[1]. Also, because the J /ψ contribution is necessary to describe
the decay data [2], it is almost certain the peaks have the cc pair
and are considered as the isospin-
1
2
uudcc pentaquarks.
Beside of the predicting work [3], the LHCb observation of
P
c
(4380) and P
c
(4450) has evoked many theoretical studies: the
hadronic molecule with the meson exchange interaction, the chi-
ral
unitary approach with the hidden local gauge symmetry, the
QCD sum rule, the chiral quark model, the diquark/triquark model
as well as that of the kinematical effects [4]. At present, the theo-
retical
and experimental knowledge is not enough and one cannot
draw a definite picture of these peaks.
*
Corresponding author.
E-mail
address: s.takeuchi@jcsw.ac.jp (S. Takeuchi).
Here, we concentrate our attention on the short range part
of the hidden-charm pentaquark structure, which is governed by
the quark and gluon dynamics. For this purpose, we employ the
quark cluster model, which successfully explained the short range
part of the baryon–baryon interaction [5] and the structure of the
light flavored pentaquark (1405) [6]. It is also shown that the
baryon–baryon interaction derived from the lattice QCD is found
to be similar to that of the quark cluster model [7]. Since we
are interested in the short range region, we have investigated the
S-wave five-quark systems as a first step. They correspond to the
negative-parity pentaquarks. In order to discuss the positive-parity
pentaquark state, which has also been observed by the LHCb ex-
periments,
one has to investigate the P -wave five-quark systems,
which is beyond the scope of the present paper.
Let us first discuss possible configurations of uud quarks in the
uudcc systems. Since the whole system is the color-singlet and the
cc pair is color-singlet or octet, the remaining three light quarks
are also color-singlet or color-octet. So, when the orbital configu-
ration
is totally symmetric, the uud configuration in the uudcc sys-
tems
is totally symmetric (56-plet) or mixed symmetric (70-plet)
in the flavor-spin SU
f σ
(6) space. They are classified as:
56
f σ
= 8
f
×2
σ
+10
f
×4
σ
(1)
70
f σ
= 1
f
×2
σ
+8
f
×2
σ
+8
f
×4
σ
+10
f
×2
σ
. (2)
http://dx.doi.org/10.1016/j.physletb.2016.11.034
0370-2693/
© 2016 The Authors. 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
.
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