Exotic hadrons associated with $b$-quark

Abstract

Compared to charmonium-like states, exotic hadrons associated with $b$-quark offer distinct advantages for exploring the nature of multiquark phenomena and the dynamics of the strong interaction. Due to the heavier bottom quark mass, theoretical calculations, particularly those based on effective field theories and potential models, tend to be more reliable and under better control in the bottomonium sector. With its clean $e^+e^-$ collision environment and high luminosity, the Belle and Belle II experiments are ideally suited to explore these exotic hadrons associated with $b$-quark, including $Z_b$, $X_b$, and $Y_b$ states, and charmonium-like states in $B$ decays. Utilizing the large proton--proton collision dataset, the LHCb experiment has conducted extensive investigations of heavy-flavor multiquark states through $B$ and $Λ_b$ decay channels. The relevant phenomenological interpretations are also reviewed.

Figures (36)

• Figure 1: Belle detector from top review Belle-II:2010dhtAdachi:2018qme.
• Figure 2: At the LHC, heavy-flavor quark pairs are produced in the forward or backward direction (left). Layout of the upgraded LHCb detector (right) LHCb:2023hlw.
• Figure 3: Belle Collaboration data for the mass of the $\Upsilon\pi$ subsystem in the transitions from the $\Upsilon(10860)$ state to $\pi\pi\Upsilon(1S)$ (first plot), $\pi\pi\Upsilon(2S)$ (second plot), and $\pi\pi\Upsilon(3S)$ (third plot) Belle:2011aa.
• Figure 4: The distributions of $\Delta M^{\rm max}_{\pi}$ in $e^+e^-\to\pi^+\pi^-\Upsilon(1S,2S)$ at $\sqrt{s}$ = 10.746 GeV and 10.805 GeV Belle-II:2024mjm. Dots with error bars are from data, the green shaded histograms show the events in the $\Upsilon(10753)$ sideband region, red histograms show the phase space simulated events, and blue dashed histograms show the $Z_b(10610/10650)$ from simulations.
• Figure 5: Allowed transitions from the vector bottomonium $\Upsilon(10860)$ to lower lying states of bottomonium through the formation of the $Z_b$'s or their spin partners $W_{bJ}$ ($J=0,~1,~2$). To guide the eye, the relevant open-bottom $B^{(*)}\bar{B}^{(*)}$ thresholds are schematically shown on the right-hand side of the plot. See Ref. Voloshin:2011qa for further details.