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

Abstract

We study the near-threshold $\Upsilon(1S)$ meson photoproduction from protons and nuclei by considering incoherent direct non-resonant (${\gamma}p \to {\Upsilon(1S)}p$, ${\gamma}n \to {\Upsilon(1S)}n$) and two-step resonant (${\gamma}p \to P^+_{bi} \to {\Upsilon(1S)}p$, ${\gamma}n \to P^0_{bi} \to {\Upsilon(1S)}n$, $i=1$, 2, 3; $P^{+,0}_{b1}=P^{+,0}_{b}(11080)$, $P^{+,0}_{b2}=P^{+,0}_{b}(11125)$, $P^{+,0}_{b3}=P^{+,0}_{b}(11130)$) bottomonium production processes with the main goal of clarifying the possibility to observe the non-strange hidden-bottom pentaquark states $P^{+,0}_{bi}$ 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 $\Upsilon(1S)$ 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 $P^{+,0}_{b}(11080)$, $P^{+,0}_{b}(11125)$ and $P^{+,0}_{b}(11130)$ 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 ${\Upsilon}(1S)p$ and ${\Upsilon}(1S)n$ 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.