Physical states are characterised uniquely by their pole positions and the corresponding residues. Accordingly, in those parameters also the nature of the states should be encoded. For bound states ...(poles on the real
s
-axis below the lowest threshold on the physical sheet) there is an established criterion formulated originally by Weinberg in the 1960s, which allows one to estimate the amount of compact and molecular components in a given state. We demonstrate in this paper that this criterion can be straightforwardly extended to shallow virtual states (poles on the real
s
-axis below the lowest threshold on the unphysical sheet) which should be classified as molecular. We argue that predominantly non-molecular or compact states exist either as bound states or as resonances (poles on the unphysical sheet off the real energy axis) but not as virtual states. We also discuss the limitations of the mentioned classification scheme.
The photoproduction of the
J
/
ψ
off the proton is believed to deepen our understanding of various physics issues. On the one hand, it is proposed to provide access to the origin of the proton mass, ...based on the QCD multipole expansion. On the other hand, it can be employed in a study of pentaquark states. The process is usually assumed to proceed through vector-meson dominance, that is the photon couples to a
J
/
ψ
which rescatters with the proton to give the
J
/
ψ
p
final state. In this paper, we provide a compelling hint for and propose measurements necessary to confirm a novel production mechanism via the
Λ
c
D
¯
(
∗
)
intermediate states. In particular, there must be cusp structures at the
Λ
c
D
¯
(
∗
)
thresholds in the energy dependence of the
J
/
ψ
photoproduction cross section. The same mechanism also implies the
J
/
ψ
-nucleon scattering lengths of order 1 mfm. Given this, one expects only a minor contribution of charm quarks to the nucleon mass.
Revisiting the nature of the Pc pentaquarks Du, Meng-Lin; Baru, Vadim; Guo, Feng-Kun ...
The journal of high energy physics,
27/8, Letnik:
2021, Številka:
8
Journal Article
Recenzirano
Odprti dostop
A
bstract
The nature of the three narrow hidden-charm pentaquark
P
c
states, i.e.,
P
c
(4312),
P
c
(4440) and
P
c
(4457), is under intense discussion since their discovery from the updated analysis ...of the process
Λ
b
0
→
J
/
ψ
pK
−
by LHCb. In this work we extend our previous coupled-channel approach Phys. Rev. Lett.
124
, 072001 (2020), in which the
P
c
states are treated as
Σ
c
∗
D
¯
∗
molecules, by including the
Λ
c
D
¯
∗
and
η
c
p
as explicit inelastic channels in addition to the
J/ψp
, as required by unitarity and heavy quark spin symmetry (HQSS), respectively. Since inelastic parameters are very badly constrained by the current data, three calculation schemes are considered: (a) scheme I with pure contact interactions between the elastic, i.e.,
Σ
c
∗
D
¯
∗
, and inelastic channels and without the
Λ
c
D
¯
∗
interactions, (b) scheme II, where the one-pion exchange (OPE) is added to scheme I, and (c) scheme III, where the
Λ
c
D
¯
∗
interactions are included in addition. It is shown that to obtain cutoff independent results, OPE in the multichannel system is to be supplemented with
S
-wave-to-
D
-wave mixing contact terms. As a result, in line with our previous analysis, we demonstrate that the experimental data for the
J/ψp
invariant mass distribution are consistent with the interpretation of the
P
c
(4312) and
P
c
(4440)/
P
c
(4457) as
Λ
c
D
¯
and
Σ
c
D
¯
∗
hadronic molecules, respectively, and that the data show clear evidence for a new narrow state,
P
c
(4380), identified as a
Σ
c
∗
D
¯
molecule, which should exist as a consequence of HQSS. While two statistically equally good solutions are found in scheme I, only one of these solutions with the quantum numbers of the
P
c
(4440) and
P
c
(4457) being
J
P
= 3/2
−
and 1/2
−
, respectively, survives the requirement of regulator independence once the OPE is included. Moreover, we predict the line shapes in the elastic and inelastic channels and demonstrate that those related to the
P
c
(4440) and the
P
c
(4457) in the
Σ
c
∗
D
¯
and
η
c
p
mass distributions from
Λ
b
0
→
Σ
c
∗
D
¯
K
−
and
Λ
b
0
→
η
c
pK
−
will shed light on the quantum numbers of those states, once the data are available. We also investigate possible pentaquark signals in the
Λ
c
D
¯
∗
final states.
We investigate in detail the role of heavy meson loops in the transition from JPC=1−− sources to candidates for QCD “exotics”, such as Zc(3900), Zb(10610) and Zb′(10650). We demonstrate that, if a ...vector state strongly couples to a heavy meson pair in an S-wave and this system decays to another heavy meson pair (e.g. via pion emission), again in an S-wave, the pertinent diagrams get enhanced significantly, if the intermediate states are (near) on-shell and have small relative momenta. In a limited kinematic range this mechanism generates “singularity regions” that lead to the creation of a large number of low-energy heavy meson pairs, providing an ideal environment for the formation of hadron–hadron bound states or resonances. For instance, we predict that the signals for Zb and Zb′ should be a lot stronger in ϒ(6S) decays due to this mechanism, if these states are indeed hadron–hadron resonances. The findings of this work should be valuable for deepening our understanding of the nature of the mentioned states.
In recent years data have been accumulated at various experiments about states in the heavy quarkonium mass range that seem to be inconsistent with the most simple variants of the quark model. In ...this contribution it is demonstrated that most of those data are consistent with a dominant molecular nature of those states. It is also discussed which kind of observables are sensitive to the molecular component and which are not.
Abstract The nature of the three narrow hidden-charm pentaquark P c states, i.e., P c (4312), P c (4440) and P c (4457), is under intense discussion since their discovery from the updated analysis of ...the process Λ b 0 → J / ψ pK − $$ {\Lambda}_b^0\to J/\psi {pK}^{-} $$ by LHCb. In this work we extend our previous coupled-channel approach Phys. Rev. Lett. 124, 072001 (2020), in which the P c states are treated as Σ c ∗ D ¯ ∗ $$ {\Sigma}_c^{\left(\ast \right)}{\overline{D}}^{\left(\ast \right)} $$ molecules, by including the Λ c D ¯ ∗ $$ {\Lambda}_c{\overline{D}}^{\left(\ast \right)} $$ and η c p as explicit inelastic channels in addition to the J/ψp, as required by unitarity and heavy quark spin symmetry (HQSS), respectively. Since inelastic parameters are very badly constrained by the current data, three calculation schemes are considered: (a) scheme I with pure contact interactions between the elastic, i.e., Σ c ∗ D ¯ ∗ $$ {\Sigma}_c^{\left(\ast \right)}{\overline{D}}^{\left(\ast \right)} $$ , and inelastic channels and without the Λ c D ¯ ∗ $$ {\Lambda}_c{\overline{D}}^{\left(\ast \right)} $$ interactions, (b) scheme II, where the one-pion exchange (OPE) is added to scheme I, and (c) scheme III, where the Λ c D ¯ ∗ $$ {\Lambda}_c{\overline{D}}^{\left(\ast \right)} $$ interactions are included in addition. It is shown that to obtain cutoff independent results, OPE in the multichannel system is to be supplemented with S-wave-to-D-wave mixing contact terms. As a result, in line with our previous analysis, we demonstrate that the experimental data for the J/ψp invariant mass distribution are consistent with the interpretation of the P c (4312) and P c (4440)/P c (4457) as Λ c D ¯ $$ {\Lambda}_c\overline{D} $$ and Σ c D ¯ ∗ $$ {\Sigma}_c{\overline{D}}^{\ast } $$ hadronic molecules, respectively, and that the data show clear evidence for a new narrow state, P c (4380), identified as a Σ c ∗ D ¯ $$ {\Sigma}_c^{\ast}\overline{D} $$ molecule, which should exist as a consequence of HQSS. While two statistically equally good solutions are found in scheme I, only one of these solutions with the quantum numbers of the P c (4440) and P c (4457) being J P = 3/2 − and 1/2 − , respectively, survives the requirement of regulator independence once the OPE is included. Moreover, we predict the line shapes in the elastic and inelastic channels and demonstrate that those related to the P c (4440) and the P c (4457) in the Σ c ∗ D ¯ $$ {\Sigma}_c^{\left(\ast \right)}\overline{D} $$ and η c p mass distributions from Λ b 0 → Σ c ∗ D ¯ K − $$ {\Lambda}_b^0\to {\Sigma}_c^{\left(\ast \right)}\overline{D}{K}^{-} $$ and Λ b 0 → η c pK − $$ {\Lambda}_b^0\to {\eta}_c{pK}^{-} $$ will shed light on the quantum numbers of those states, once the data are available. We also investigate possible pentaquark signals in the Λ c D ¯ ∗ $$ {\Lambda}_c{\overline{D}}^{\left(\ast \right)} $$ final states.
We discuss some general features of the effective range expansion, the content of its parameters with respect to the nature of the pertinent near-threshold states and the necessary modifications in ...the presence of coupled channels, isospin violations and unstable constituents. As illustrative examples, we analyse the properties of the χc1(3872) and Tcc+ states supporting the claim that these exotic states have a predominantly molecular nature.
We study the inclusive and exclusive cross sections of
e
+
e
-
→
hadrons
for center-of-mass energies between 3.70 and
3.83
GeV
to infer the mass, width, and couplings of the
ψ
(
3770
)
resonance. By ...using a coupled-channel
K
-matrix approach, we setup our analysis to respect unitarity and the analyticity properties of the underlying scattering amplitudes. We fit several models to the full dataset and identify our nominal results through a statistical model comparison. We find that, accounting for the interplay between the
ψ
(
2
S
)
and the
ψ
(
3770
)
, no further pole is required to describe the
ψ
(
3770
)
line shape. In particular we derive from the pole location
M
ψ
(
3770
)
=
3778.8
±
0.3
MeV
and
Γ
ψ
(
3770
)
=
25.0
±
0.5
MeV
. Moreover, we find the decay to
D
+
D
-
and
D
0
D
¯
0
to be consistent with isospin symmetry and derive an upper bound on the branching ratio
B
(
ψ
(
3770
)
→
non-
D
D
¯
)
<
6
%
at
90
%
probability.
A formalism is discussed that allows for a straightforward treatment of the relativistic three-body problem while keeping the correct analytic structure. In particular it is demonstrated that ...sacrificing covariance for analyticity can be justified by the hierarchy of different contributions in the spirit of an effective field theory. For definiteness the formalism is applied to the
K
K
K
¯
system allowing for the emergence of the
a
0
(
980
)
and the
f
0
(
980
)
as hadronic molecules. For simplicity all inelastic channels are switched off.
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