4,406 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.
Bottom Baryons
Recently CDF and D0 collaborations observed several bottom baryons. In this
work we perform a systematic study of the masses of bottom baryons up to
in the framework of heavy quark effective field theory (HQET) using the
QCD sum rule approach. The extracted chromo-magnetic splitting between the
bottom baryon heavy doublet agrees well with the experimental data.Comment: 8 pages, 5 figures, 3 tables. More discussions and references adde
A review of the open charm and open bottom systems
Since the discovery of the first charmed meson in 1976, many open-charm and
open-bottom hadrons were observed. In 2003 two narrow charm-strange states
and were discovered by the BaBar and CLEO
Collaborations, respectively. After that, more excited heavy hadrons were
reported. In this work, we review the experimental and theoretical progress in
this field.Comment: Review accepted by Reports on Progress in Physics, 161 pages, 53
figures, 23 tables, more references added and review on heavy baryons adde
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