arXiv subjects
Publications and source records attributed to Petr Bydžovský.
We study the process $γγ\toπ^0π^0$ involving the principle mechanisms, the structure of its cross section and the role of individual isoscalar-tensor resonances in the saturation of its energy spectrum.
We utilise an isobar model to investigate the $K^+ Σ^-$ photoproduction off a neutron in the resonance region. Except for the Born terms, we include high-spin (spin-3/2 and spin-5/2) nucleon resonances in the consistent formalism together with a few $Δ$ and kaon resonances to achieve an acceptable agreement with data. Interestingly, we reveal that no hyperon resonances are needed to achieve a reasonable description of data. On the other hand the $N(1720)3/2^+$ resonance was found to be very important for correct description of data. The free parameters of the model were fitted to experimental data from the LEPS and CLAS Collaborations on either differential cross sections or photon beam asymmetry. The novel feature of the fitting procedure is the use of a regularization method, the Least Absolute Shrinkage Selection Operator, and information criteria in order to choose the best fit.
Making use of the hybrid Regge-plus-resonance model, we investigate the process of kaon photoproduction off the proton target. We present a new model whose free parameters were adjusted to data in and above the resonance region and which provides an acceptable description of experimental data. The overwhelming majority of nucleon resonances selected in this analysis overlaps with those selected in our previous analyses and also with the Bayesian analysis with the Regge-plus-resonance model, which we deem to be dependable. A novel feature of our model consists in applying a different scheme for gauge-invariance restoration, which results in a need for implementing a contact current. As we further reveal, the choice of the gauge invariance restoration scheme as well as the choice of either pseudoscalar or pseudovector coupling in the strong vertex play a significant role for cross-section predictions at forward angles where data are scarce.
It is shown that the basic shape of dipion and $K\overline{K}$ mass spectra in decays $J/ψ\toϕ(ππ,K\overline{K})$, $ψ(2S)\to J/ψ\,ππ$, $Y(4260)\to J/ϕ~ππ$ and in the two-pion transitions of bottomonia states are explained by an unified mechanism based on the contribution of the $ππ$, $K\overline{K}$ and $ηη$ coupled channels including their interference. The role of the individual $f_0$ resonances in making up the shape of the dipion mass distributions in the charmonia and bottomonia decays is considered.