The production of the hidden-charm pentaquarks P c via pion-induced reaction on a proton target is investigated within an effective Lagrangian approach. Three experimentally observed states, P c (4312), P c (4440), and P c (4457), are considered in the calculation, and the Reggeized t-channel meson exchange is considered as main background for the reaction π − p → J/ψn. The numerical results show that the experimental data of the total cross section of the reaction π − p → J/ψn at W ≃ 5 GeV can be well explained by contribution of the Reggeized t channel with reasonable cutoff. If the branching ratios Br[P c → J/ψN] ≃ 3% and Br[P c → πN] ≃ 0.05% are taken, the average value of the cross section from the P c (4312) contribution is about 1.2 nb/100 MeV, which is consistent with existing rude data at near-threshold energies. The results indicate that the branching ratios of the P c states to the J/ψN and πN should be small. The shape of differential cross sections shows that the Reggeized t-channel provides a sharp increase at extreme forward angles, while the differential cross sections from the P c states contributions are relatively flat. High-precision experimental measurements on the reaction π − p → J/ψn at near-threshold energies are suggested to confirm the LHCb hidden-charm pentaquarks as genuine states, and such experiments are also helpful to understand the origin of these resonance structures.
As the lightest physical states excited from the vacuum by the scalar gluon, ρ 0 photoproduction is considered to be a suitable way to extract proton mass radius and scattering lengths of ρ 0 and proton interaction. In this work, under the assumption of the scalar form factor of dipole form, the value of proton mass radius is calculated as 0.86 ± 0.08 fm by fitting the differential cross section of γp → ρ 0 p reaction at near-threshold energy W = 1.78 GeV. Moreover, the ρ 0 -proton scattering lengths α ρ 0 p = 0.24 ± 0.02 fm is obtained for the first time within the vector meson dominance model. Correspondingly, the binding energy of ρ 0 in nuclear matter is calculated to be 23.6 MeV. These results may provide useful theoretical information for an in-depth understanding of proton structure and its interaction with vector mesons.
The dynamic performance of ultra-precision cutting machine tools is an important factor for its machining accuracy. To improve the precision of the machine tool, a surface topography model is built in this paper and the tool path during the cutting process is achieved by dynamic finite element analysis (DFEA) of the air spindle in ANSYS, surface topography is obtained using MATLAB simulation by combing the model with the tool path, and an experiment is carried out for validation. Results show the simulation surface is highly consistent with the experimental result. Dynamic performance of the spindle is the main factor for texture generation, and optimization of spindle is investigated, DFEA of the optimized spindle shows better performance, and the connection mode between diamond tool and cutter head should be further studied.
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