In the past decade many charmonium-like states were observed experimentally. Especially those charged charmoniumlike Z c states and bottomonium-like Z b states can not be accommodated within the naive quark model. These charged Z c 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.

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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 [Formula: see text] and D (2460) 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.

China is the largest contributor to global atmospheric mercury (Hg), and accurate emission inventories in China are needed to reduce large gaps existing in global Hg mass balance estimates and assess Hg effects on various ecosystems. The China Atmospheric Mercury Emission (CAME) model was developed in this study using probabilistic emission factors generated from abundant on-site measurements and literature data. Using this model, total anthropogenic Hg emissions were estimated to be continuously increasing from 356 t in 2000 to 538 t in 2010 with an average annual increase rate of 4.2%. Industrial coal combustion, coal-fired power plants, nonferrous metal smelting, and cement production were identified to be the dominant Hg emission sources in China. The ten largest contributing provinces accounted for nearly 60% of the total Hg emissions in 2010. Speciated Hg emission inventory was developed over China with a grid-resolution of 36 × 36 km, providing needed emission fields for Hg transport models. In this new inventory, the sectoral Hg speciation profiles were significantly improved based on the latest data from field measurements and more detailed technology categorization. The overall uncertainties of the newly developed inventory were estimated to be in the range of -20% to +23%.

We investigate the newly observed X (4500) and X (4700) based on the diquark-antidiquark configuration within the framework of QCD sum rules. Both of them may be interpreted as the D-wave cscs tetraquark states of J P = 0 + , but with opposite color structures, which is remarkably similar to the result obtained in Chen and Zhu (Phys Rev D 83:034010, 2011) that X (4140) and X (4274) can be both interpreted as the S-wave cscs tetraquark states of J P = 1 + , also with opposite color structures. However, the extracted masses and these suggested assignments to these X states do depend on these running quark masses where m s (2 GeV) = 95 ± 5 MeV and m c (m c ) = 1.23 ± 0.09 GeV. As a byproduct, the masses of the hidden-bottom partner states of X (4500) and X (4700) are extracted to be both around 10.64 GeV, which can be searched for in the ϒφ invariant mass distribution.

Inspired by P(c)(4380) and P(c)(4450) recently observed by LHCb, a QCD sum rule investigation is performed, by which they can be identified as exotic hidden-charm pentaquarks composed of an anticharmed meson and a charmed baryon. Our results suggest that P(c)(4380) and P(c)(4450) have quantum numbers J(P)=3/2(-) and 5/2(+), respectively. Furthermore, two extra hidden-charm pentaqurks with configurations D̅Σ(c)(*) and D̅(*)Σ(c)(*) are predicted, which have spin-parity quantum numbers J(P)=3/2(-) and J(P)=5/2(+), respectively. As an important extension, the mass predictions of hidden-bottom pentaquarks are also given. Searches for these partners of P(c)(4380) and P(c)(4450) are especially accessible at future experiments like LHCb and BelleII.

In the simple color-magnetic interaction model, we investigate possible ground cscs tetraquark states in the diquark-antidiquark basis. We use several methods to estimate the mass spectrum and discuss possible assignment for the X states observed in the J/ψφ channel. We find that assigning the Belle X(4350) as a 0 ++ tetraquark is consistent with the tetraquark interpretation for the X(4140) and X(4270) while the interpretation of the X(4500) and X(4700) needs orbital or radial excitation. There probably exist several tetraquarks around 4.3 GeV that decay into J/ψφ or ηcφ.

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