2,244 research outputs found
The hidden-charm pentaquark and tetraquark states
In the past decade many charmonium-like states were observed experimentally.
Especially those charged charmonium-like states and bottomonium-like
states can not be accommodated within the naive quark model. These
charged states are good candidates of either the hidden-charm tetraquark
states or molecules composed of a pair of charmed mesons. Recently, the LHCb
Collaboration discovered two hidden-charm pentaquark states, which are also
beyond the quark model. In this work, we review the current experimental
progress and investigate various theoretical interpretations of these
candidates of the multiquark states. We list the puzzles and theoretical
challenges of these models when confronted with the experimental data. We also
discuss possible future measurements which may distinguish the theoretical
schemes on the underlying structures of the hidden-charm multiquark states.Comment: Review accepted by Physics Reports, 152 pages, 66 figures, and 29
table
The Y(2175) State in the QCD Sum Rule
We study the mass of the state Y(2175) of J^{PC} = 1^{--} in the QCD sum
rule. We construct both the diquark-antidiquark currents (ss)(s_bar s_bar) and
the meson-meson currents (s_bar s)(s_bar s). We find that there are two
independent currents for both cases, and derive the relations between them. The
OPE convergence of these two currents is sufficiently fast, which enables us to
perform good sum rule analysis. Both the SVZ sum rule and the finite energy sum
rule lead to a mass around 2.3+-0.4 GeV, which is consistent with the observed
mass within the uncertainties of the present QCD sum rule. The coupling of the
four-quark currents to lower lying states such as \phi(1020) turns out to be
rather small. We also discuss possible decay properties of Y(2175) if it is a
tetraquark state.Comment: 10 pages, 6 figures, revised version to appear in Phys. Rev.
Establishing low-lying doubly charmed baryons
We systematically study the -wave doubly charmed baryons using the method
of QCD sum rules. Our results suggest that the recently
observed by LHCb can be well identified as the -wave state of
. We study its relevant state, whose mass is
predicted to be around 3.7 GeV. We also systematically study the -wave
doubly charmed baryons, whose masses are predicted to be around 4.1 GeV.
Especially, there can be several excited doubly charmed baryons in this energy
region, and we suggest to search for them in order to study the fine structure
of the strong interaction.Comment: 6 pages, 2 figures, 1 table; A mistake was found when evaluating
decay constants of the S-wave charmed baryons. The conclusion is not change
Doubly hidden-charm/bottom tetraquark states
We study the mass spectra for the and
tetraquark states by developing a moment sum rule method. Our results show that
the tetraquarks lie below the threshold of
. They are probably stable and very narrow. The masses
for the doubly hidden-charm states are higher than the
spontaneous dissociation thresholds of two charmonium mesons. We suggest to
search for such states in the and
channels.Comment: 8 pages, 2 figures. More references added. Conference proceedings for
6th International Conference on New Frontiers in Physics (ICNFP 2017), Crete,
Greece, 17-29 Aug, 201
Open-flavor charmed/bottom and tetraquark states
We provide comprehensive investigations for the mass spectrum of exotic
open-flavor charmed/bottom , , , tetraquark states with various spin-parity assignments
and in the framework of QCD sum rules. In the
diquark configuration, we construct the diquark-antidiquark interpolating
tetraquark currents using the color-antisymmetric scalar and axial-vector
diquark fields. The stable mass sum rules are established in reasonable
parameter working ranges, which are used to give reliable mass predictions for
these tetraquark states. We obtain the mass spectra for the open-flavor
charmed/bottom , , , tetraquark states with various spin-parity quantum numbers. In
addition, we suggest searching for exotic doubly-charged tetraquarks, such as
in future experiments at facilities
such as BESIII, BelleII, PANDA, LHCb and CMS, etc.Comment: 19 pages, 4 figures, 5 tables, accepted by Phys. Rev. D (in press
Residues Responsible for the Selectivity of α-Conotoxins for Ac-AChBP or nAChRs
Nicotinic acetylcholine receptors (nAChRs) are targets for developing new drugs to treat severe pain, nicotine addiction, Alzheimer disease, epilepsy, etc. α-Conotoxins are biologically and chemically diverse. With 12–19 residues and two disulfides, they can be specifically selected for different nAChRs. Acetylcholine-binding proteins from Aplysia californica (Ac-AChBP) are homologous to the ligand-binding domains of nAChRs and pharmacologically similar. X-ray structures of the α-conotoxin in complex with Ac-AChBP in addition to computer modeling have helped to determine the binding site of the important residues of α-conotoxin and its affinity for nAChR subtypes. Here, we present the various α-conotoxin residues that are selective for Ac-AChBP or nAChRs by comparing the structures of α-conotoxins in complex with Ac-AChBP and by modeling α-conotoxins in complex with nAChRs. The knowledge of these binding sites will assist in the discovery and design of more potent and selective α-conotoxins as drug leads
F-wave heavy-light meson spectroscopy in QCD sum rules and heavy quark effective theory
We study the F-wave c_bar s heavy meson doublets (2+,3+) and (3+,4+). They
have large orbital excitations L=3, and may be good challenges (tests) for
theoretical studies. To study them we use the method of QCD sum rule in the
framework of heavy quark effective theory. Their masses are predicted to be
m_{(2+,3+)} = (3.45 \pm 0.25, 3.50 \pm 0.26) GeV and m_{(3+,4+)} = (3.20 \pm
0.22, 3.26 \pm 0.23) GeV, with mass splittings Delta m_{(2+,3+)} = m_{3+} -
m_{2+} = 0.046 \pm 0.030 GeV and Delta m_{(3+,4+)} = 0.053 \pm 0.044 GeV,
respectively. We note that this is a pioneering work and these results are
provisional.Comment: 10 pages, 8 figures, 3 tables, accepted by PR
Hunting for exotic doubly hidden-charm/bottom tetraquark states
We develop a moment QCD sum rule method augmented by fundamental inequalities
to study the existence of exotic doubly hidden-charm/bottom tetraquark states
made of four heavy quarks. Using the compact diquark-antidiquark configuration,
we calculate the mass spectra of these tetraquark states. There are 18
hidden-charm tetraquark currents with ,
, , , , , , and . We
use them to perform QCD sum rule analyses, and the obtained masses are all
higher than the spontaneous dissociation thresholds of two charmonium mesons,
which are thus their dominant decay modes. The masses of the corresponding
hidden-bottom tetraquarks are all below or very close to the
thresholds of the and , except
one current of . Hence, we suggest to search for the doubly
hidden-charm states in the and channels.Comment: 5 pages, 3 figures and 2 tables. published in PL
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