We revisit the bottomonium spectrum motivated by the recently exciting experimental progress in the observation of new bottomonium states, both conventional and unconventional. Our framework is a nonrelativistic constituent quark model which has been applied to a wide range of hadronic observables from the light to the heavy quark sector, and thus the model parameters are completely constrained. Beyond the spectrum, we provide a large number of electromagnetic, strong and hadronic decays in order to discuss the quark content of the bottomonium states and give more insights about a better way to determine their properties experimentally.

The LHCb Collaboration has recently observed four $J/\psi \varphi$ structures called $X(4140)$, $X(4274)$, $X(4500)$, and $X(4700)$ in the $B^{+}\to J/\psi \varphi K^{+}$ decays. We study them herein using a nonrelativistic constituent quark model in which the degrees of freedom are quark-antiquark and meson-meson components. The $X(4140)$ resonance appears as a cusp in the $J/\psi \varphi$ channel due to the near coincidence of the $D_s^{\pm }{D}_s^{*\pm }$ and $J/\psi \varphi$ mass thresholds. The remaining three [$X(4274)$, $X(4500)$, and $X(4700)$] appear as conventional charmonium states with quantum numbers $3{{}^{3}P}_1$, $4{{}^{3}P}_0$, and $5{{}^{3}P}_0$, respectively, and their masses and widths are slightly modified due to their coupling with the corresponding closest meson-meson thresholds. A particular feature of our quark model is a lattice-based screened linear confining interaction that has been constrained in the light-quark sector and usually produces higher excited heavy-quark states with lower masses than standard quark model predictions.

The bottom-charmed ( $$B_c$$Bc ) mesons are more stable than their charmonium ( $$c{{\bar{c}}}$$cc¯ ) and bottomium ( $$b{{\bar{b}}}$$bb¯ ) partners because they cannot annihilate into gluons. However, the low production cross-sections and signal-to-background ratios avoided until now their clear identification. The recent experimental results reported by CMS and LHCb at CERN open the possibility of having a $$B_c$$Bc spectrum as complete as the ones of charmonium and bottomonium. Motivated by this expectation, we compute bottom-charmed meson masses in the region energies in which decay meson–meson thresholds are opened, looking for the analogs to the X(3872) in the $$B_c$$Bc spectroscopy. We use a constituent quark model in which quark–antiquark degrees of freedom are complemented by four-body Fock states configurations. The model has been applied to a wide range of hadronic observables, in particular to the X(3872), and thus the model parameters are completely constrained. No extra states are found in the $$J^P=0^+$$JP=0+ and $$J^P=1^+$$JP=1+ sectors. However, in the $$J^P=2^+$$JP=2+ sector we found an additional state very close to the $$D^*B^*$$D∗B∗ threshold which could be experimentally detected.

The LHCb Collaboration has recently reported the observation for the first time of a spin-3 resonance in the heavy quark sector. They have shown that the ${\overline{D}}^0{K}^{-}$ structure seen in the $B_s^0\to {\overline{D}}^0{K}^{-}{\pi }^{+}$ reaction and with invariant mass 2.86 GeV is an admixture of a spin-1 and a spin-3 resonance. Motivated by the good agreement between our theoretical predictions some time ago and the properties extracted from the experiment of the $D_{s1}^{*}(2860)$ and $D_{s3}^{*}(2860)$ states, we perform an extension of the study of the strong decay properties of the $D_{sJ}^{*}(2860)$ and present the same analysis for the $D_{s1}^{*}(2700)$ and $D_{sJ}(3040)$ mesons. This provides a unified and simultaneous description of the three higher excited charmed-strange resonances observed until now. For completeness, we present theoretical results for masses and strong decays of the low-lying charmed-strange mesons and those experimental missing states which belong to the spin multiplets of the discovered $D_{s1}^{*}(2700)$, $D_{sJ}^{*}(2860)$ and $D_{sJ}(3040)$ resonances. The theoretical framework used is a constituent quark model which successfully describes hadron phenomenology from light to heavy quark sectors.

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Using a nonrelativistic constituent quark model in which the degrees of freedom are quark-antiquark and meson-meson components, we have recently shown that the $D^{(*)}K$ thresholds play an important role in lowering the mass of the $c\overline{s}$ states associated with the physical $D_{s0}^{*}(2317)$ and $D_{s1}(2460)$ mesons. This observation is also supported by other theoretical approaches such as lattice-regularized QCD or chiral unitary theory in coupled channels. Herein, we extend our computation to the lowest $P$-wave $B_s$ mesons, taking into account the corresponding $J^P=0^{+}$, $1^{+}$ and $2^{+}$ bottom-strange states predicted by the naive quark model and the $BK$ and $B^{*}K$ thresholds. We assume that mixing with $B_s^{(*)}\eta$ and isospin-violating decays to $B_s^{(*)}\pi$ are negligible. This computation is important because there is no experimental data in the $b\overline{s}$ sector for the equivalent $j_q^P=1/2^{+}$ ($D_{s0}^{*}(2317)$, $D_{s1}(2460)$) heavy-quark multiplet and, as it has been seen in the $c\overline{s}$ sector, the naive theoretical result can be wrong by more than 100 MeV. Our calculation allows us to introduce the coupling with the $D$-wave $B^{*}K$ channel and to compute the probabilities associated with the different Fock components of the physical state.