Excited and exotic bottomonium spectroscopy from lattice QCD

We explore the spectrum of excited and exotic bottomonia using lattice QCD. Highly excited states are identified with masses up to 11,000 MeV, many of which can be grouped into supermultiplets matching those of the quark model while exotic spin-parity-charge-conjugation quantum numbers JPC = 0+−, 1−+, 2+− that cannot be formed from $$ \overline{q}q $$ q ¯ q alone are also identified. Single-meson operator constructions are used that have good JPC in the continuum, these are found to overlap well onto heavy quark states up to J ≤ 4. A continuum JPC is assigned to each level, based on the distribution amongst lattice irreps and dominant operator overlaps. States with a dominant gluonic component are identified and form a hybrid supermultiplet with JPC = (0, 1, 2)−+, 1−−, approximately 1500 MeV above the ground-state ηb, similar to previous computations with light, strange and charm quark systems.

Triangle singularity as the origin of $$X_0(2900)$$ and $$X_1(2900)$$ observed in $$B^+\rightarrow D^+ D^- K^+$$

The LHCb collaboration recently reported the observation of a narrow peak in the $$D^- K^+$$ D - K + invariant mass distributions from the $$B^+\rightarrow D^+ D^- K^+$$ B + → D + D - K + decay. The peak is parameterized in terms of two resonances $$X_0(2900)$$ X 0 ( 2900 ) and $$X_1(2900)$$ X 1 ( 2900 ) with the quark contents $${\bar{c}}{\bar{s}}ud$$ c ¯ s ¯ u d , and their spin-parity quantum numbers are $$0^+$$ 0 + and $$1^-$$ 1 - , respectively. We investigate the rescattering processes which may contribute to the $$B^+\rightarrow D^+ D^- K^+$$ B + → D + D - K + decays. It is shown that the $$D^{*-}K^{*+}$$ D ∗ - K ∗ + rescattering via the $$\chi _{c1}K^{*+}D^{*-}$$ χ c 1 K ∗ + D ∗ - loop and the $${\bar{D}}_{1}^{0}K^{0}$$ D ¯ 1 0 K 0 rescattering via the $$D_{sJ}^{+}{\bar{D}}_{1}^{0}K^{0}$$ D sJ + D ¯ 1 0 K 0 loop can simulate the $$X_0(2900)$$ X 0 ( 2900 ) and $$X_1(2900)$$ X 1 ( 2900 ) with consistent quantum numbers. Such phenomena are due to the analytical property of the scattering amplitudes with the triangle singularities located to the vicinity of the physical boundary.

Hidden-bottom molecular states from $$\varSigma ^{(*)}_bB^{(*)}-\varLambda _bB^{(*)}$$ interaction

In this work, we study possible hidden-bottom molecular pentaquarks $$P_b$$ P b from coupled-channel $$\varSigma ^{(*)}_bB^{(*)}-\varLambda _bB^{(*)}$$ Σ b ( ∗ ) B ( ∗ ) - Λ b B ( ∗ ) interaction in the quasipotential Bethe-Salpeter equation approach. In isodoublet sector with $$I=1/2$$ I = 1 / 2 , with the same reasonable parameters the interaction produces seven molecular states, a state near $$ \varSigma _bB$$ Σ b B threshold with spin parity $$J^P=1/2^-$$ J P = 1 / 2 - , a state near $$\varSigma ^*_bB$$ Σ b ∗ B threshold with $$3/2^-$$ 3 / 2 - , two states near $$\varSigma _bB^*$$ Σ b B ∗ threshold with $$1/2^-$$ 1 / 2 - and $$3/2^-$$ 3 / 2 - , and three states near $$\varSigma _b^*B^*$$ Σ b ∗ B ∗ threshold with $$1/2^-$$ 1 / 2 - , $$3/2^-$$ 3 / 2 - , and $$5/2^-$$ 5 / 2 - . The results suggest that three states near $$\varSigma _b^* B^*$$ Σ b ∗ B ∗ threshold and two states near $$\varSigma _b B^*$$ Σ b B ∗ threshold are very close, respectively, which may be difficult to distinguish in experiment without partial wave analysis. Compared with the hidden-charm pentaquark, the $$P_b$$ P b states are relatively narrow with widths at an order of magnitude of 1 MeV or smaller. The importance of each channel considered is also discussed, and it is found that the $$\varLambda _b B^*$$ Λ b B ∗ channel provides important contribution for the widths of those states. In isoquartet sector with $$I=3/2$$ I = 3 / 2 , cutoff should be considerably enlarged to achieve bound states from the interaction, which makes the existence of such states unreliable. The results in the current work are helpful for searching for hidden-bottom molecular pentaquarks in future experiments, such as the COMPASS, J-PARC, and the Electron Ion Collider in China (EicC).

Analysis of the X0(2900) as the scalar tetraquark state via the QCD sum rules

In this article, we study the axialvector-diquark–axialvector-antidiquark (AA)-type and scalar-diquark–scalar-antidiquark (SS) type fully open flavor [Formula: see text] tetraquark states with the spin-parity [Formula: see text] via the QCD sum rules. The predicted masses [Formula: see text] GeV and [Formula: see text] GeV support assigning the [Formula: see text] to be the AA-type scalar [Formula: see text] tetraquark state.

Strong decays of the $$\varXi (1620)^0$$ as a $$\varLambda {\bar{K}}$$ and $$\varSigma {\bar{K}}$$ molecule

In this work, we study the strong decays of the newly observed $$\varXi (1620)^0$$ Ξ ( 1620 ) 0 assuming that it is a meson-baryon molecular state of $$\varLambda {\bar{K}}$$ Λ K ¯ and $$\varSigma {\bar{K}}$$ Σ K ¯ . We consider four possible spin-parity assignments $$J^P=1/2^{\pm }$$ J P = 1 / 2 ± and $$3/2^{\pm }$$ 3 / 2 ± for the $$\varXi (1620)^0$$ Ξ ( 1620 ) 0 , and evaluate its partial decay width into $$\varXi \pi $$ Ξ π and $$\varXi \pi \pi $$ Ξ π π via hadronic loops with the help of effective Lagrangians. In comparison with the Belle data, the calculated decay width favors the spin-party assignment $$1/2^-$$ 1 / 2 - while the other spin-parity assignments do not yield a decay width consistent with data in the molecule picture. We find that about 52–68% of the total width comes from the $${\bar{K}}\varLambda $$ K ¯ Λ channel, while the rest is provided by the $${\bar{K}}\varSigma $$ K ¯ Σ channel. As a result, both channels are important in explaining the strong decay of the $$\varXi (1620)^0$$ Ξ ( 1620 ) 0 . In addition, the transition $$\varXi (1620)^0\rightarrow \pi \varXi $$ Ξ ( 1620 ) 0 → π Ξ is the main decay channel in the $$J^{P}=1/2^{-}$$ J P = 1 / 2 - case, which almost saturates the total width. These information are helpful to further understand the nature of the $$\varXi (1620)^0$$ Ξ ( 1620 ) 0 .