Physics Letters B 763 (2016) 358–364
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Heavy pentaquark states P
c
(4380) and P
c
(4450) in the J /ψ
production induced by pion beams off the nucleon
Sang-Ho Kim
a
, Hyun-Chul Kim
b,c,∗
, Atsushi Hosaka
d,e
a
Asia Pacific Center for Theoretical Physics (APCTP), Pohang, Gyeongbuk, 790-784, Republic of Korea
b
Department of Physics, Inha University, Incheon 402-751, Republic of Korea
c
School of Physics, Korea Institute for Advanced Study (KIAS), Seoul 130-722, Republic of Korea
d
Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki, Osaka, 567-0047, 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
10 May 2016
Received
in revised form 20 October 2016
Accepted
20 October 2016
Available
online 27 October 2016
Editor:
J.-P. Blaizot
In this study, we investigate the J/ψ production induced by pion beams off the nucleon, particularly the
heavy pentaquarks P
c
(4380) and P
c
(4450) in intermediate states, based on a hybridized Regge model.
The process involving ρ and π meson exchange in the t channel is considered as background, and the
heavy pentaquark exchange is included in the s channel. The coupling constants such as the ρ NN and
π NN vertices are taken from the NN potentials, whereas those for the J/ψρπ and J/ψππ vertices are
determined by using experimental data based on the branching ratios. In order to estimate the P
c
(4380)
and P
c
(4450) coupling constants, we use the experimental upper limit on the total cross section as a
guide for the π N → J /ψ N reaction. The background total cross section is the order of 10
−4
–10
−3
nb. In
the vicinity of the heavy pentaquark masses, the total cross section reaches about 1nb.
© 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
.
1. Introduction
Finding new exotic hadrons is one of the most important is-
sues
for hadron and particle physics. Recently, the LHCb Collab-
oration
announced the observation of two heavy pentaquarks in
b
→ J/ψ K
−
p decays [1], where the quark content is uudc
¯
c. The
significance of these pentaquarks is more than 9σ . The masses
and widths were reported as: M
P
c
= (4380 ± 8 ± 29) MeV and
P
c
= (205 ± 18 ± 86) MeV for the lower state, whereas M
P
c
=
(
4449.8 ± 1.7 ± 2.5) MeV and
P
c
= (39 ± 5 ± 19) MeV for the
higher state. Thus, it is very important to confirm these penta-
quark
states in other possible reactions. For example, the energy of
the pion beam at the Japan Proton Accelerator Research Complex
(J-PARC) facility is sufficient to observe them during the π N →
J /ψ N process. The photon beam at the Thomas Jefferson National
Accelerator Facility (Jefferson Lab) can also be used to measure the
P
c
states in J/ψ photoproduction [2–4].
In
fact, a recent theoretical study of the π
−
p → J/ψn reaction
with neutral charm pentaquarks P
0
c
[5] employed the effective La-
grangian
method. Lu et al. [5] assumed that the branching ratios
*
Corresponding author.
E-mail
addresses: sangho.kim@apctp.org (S.-H. Kim), hchkim@inha.ac.kr
(H.-Ch. Kim),
hosaka@rcnp.osaka-u.ac.jp (A. Hosaka).
of P
c
→ J/ψ N and P
c
→π N are about 10 % and 1%, respectively.
The background total cross section is in the order of 10–100 nb
and
the total cross section near the pentaquark masses increases
to around 1μb. This indicates that the magnitude of the total
cross section for J/ψ production in the vicinity of the pentaquark
masses is almost comparable to that of the π N →φN reaction.
In
the present study, we consider the contribution of penta-
quark
resonances to J /ψ production by using previous experimen-
tal
information on the upper limit of the π N → J /ψ N reaction
[6,7] and by employing a hybridized Regge model that incorpo-
rates
the heavy pentaquark states. To estimate the contribution of
the heavy pentaquarks to the π N → J/ψ N reaction, it is crucial
to know the background contribution. Recently, the open charm
production π
−
p → D
∗−
+
c
was analyzed based on a comparison
with the associated strangeness production π
−
p → K
∗0
[8–10]
(see
Fig. 1(a)), and thus the parameters for the π
−
p → D
∗−
+
c
reaction can be plausibly estimated. A similar approach was also
applied to various reactions such as
¯
pp →
¯
Y
c
Y
c
and
¯
pp →
¯
M
c
M
c
,
where Y
c
and M
c
denote
+
c
,
+
c
and D, D
∗
[11].
We
adopt the same strategy to study the hidden charm process
π
−
p → J /n together with the strangeness process π
−
p → φn
(see
Fig. 1(b)). However, the hidden charm (strangeness) reactions
are distinguished from the open charm (strangeness) reactions.
In the case of the open charm processes, the exchanged me-
http://dx.doi.org/10.1016/j.physletb.2016.10.061
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
.
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