Probing the hidden-bottom pentaquark resonances in photonuclear bottomonium production near threshold: Differential observables

Abstract

We study the near-threshold $\Upsilon \left(1S\right)$ meson photoproduction from protons and nuclei by considering incoherent direct non-resonant ($\gamma p\to \Upsilon \left(1S\right)p$, $\gamma n\to \Upsilon \left(1S\right)n$) and two-step resonant ($\gamma p\to P_{bi}^{+}\to \Upsilon \left(1S\right)p$, $\gamma n\to P_{bi}^0\to \Upsilon \left(1S\right)n$, $i=1$, 2, 3; $P_{b1}^{+,0}=P_b^{+,0}\left(11080\right)$, $P_{b2}^{+,0}=P_b^{+,0}\left(11125\right)$, $P_{b3}^{+,0}=P_b^{+,0}\left(11130\right)$) bottomonium production processes with the main goal of clarifying the possibility to observe the non-strange hidden-bottom pentaquark states $P_{bi}^{+,0}$ in this production via differential observables. We calculate the absolute excitation functions, energy and momentum distributions for the non-resonant, resonant and for the combined (non-resonant plus resonant) production of $\Upsilon \left(1S\right)$ mesons on protons, on carbon and tungsten target nuclei at near-threshold incident photon beam energies by assuming the spin-parity assignments of the hypothetical hidden-bottom resonances $P_b^{+,0}\left(11080\right)$, $P_b^{+,0}\left(11125\right)$ and $P_b^{+,0}\left(11130\right)$ as $J^P={(1/2)}^{-}$, $J^P={(1/2)}^{-}$ and $J^P={(3/2)}^{-}$ within four different realistic choices for the branching ratios of their decays to the $\Upsilon \left(1S\right)p$ and $\Upsilon \left(1S\right)n$ modes (0.125, 0.25, 0.5 and 1%) as well as for two options for the background contribution. We demonstrate that the measurements of these combined observables on proton and nuclear targets in the near-threshold energy region in future experiments at the planned high-luminosity electron-ion colliders EIC and EicC in the US and China should provide evidence for the existence of the above hidden-bottom pentaquark resonances as well as clarify their decay rates.