No Arabic abstract
The two-channel photoproductions of $gamma p to K^{*+} Sigma^{0}$ and $gamma p to K^{*0} Sigma^{+}$ are investigated based on an effective Lagrangian approach at the tree-level Born approximation. In addition to the $t$-channel $K$, $kappa$, $K^*$ exchanges, the $s$-channel nucleon ($N$) and $Delta$ exchanges, the $u$-channel $Lambda$, $Sigma$, $Sigma^*$ exchanges, and the generalized contact term, we try to take into account the minimum number of baryon resonances in constructing the reaction amplitudes to describe the experimental data. It is found that by including the $Delta(1905)5/2^+$ resonance with its mass, width, and helicity amplitudes taken from the Review of Particle Physics [Particle Data Group, C. Patrignani {it et al.}, Chin. Phys. C {bf 40}, 100001 (2016)], the calculated differential and total cross sections for these two reactions are in good agreement with the experimental data. An analysis of the reaction mechanisms shows that the cross sections of $gamma p to K^{*+}Sigma^{0}$ are dominated by the $s$-channel $Delta(1905)5/2^+$ exchange at low energies and $t$-channel $K^*$ exchange at high energies, with the $s$-channel $Delta$ exchange providing significant contributions in the near-threshold region. For $gamma p to K^{*0}Sigma^{+}$, the angular dependences are dominated by the $t$-channel $K$ exchange at forward angles and the $u$-channel $Sigma^*$ exchange at backward angles, with the $s$-channel $Delta$ and $Delta(1905)5/2^+$ exchanges making considerable contributions at low energies. Predictions are given for the beam, target, and recoil asymmetries for both reactions.
The few available data for the reactions $gamma p rightarrow K^{0} Sigma^{+}$ and $gamma n rightarrow K^{+} Sigma^{-}$ are compared to models developed for the processes $gamma p rightarrow K^{+} Sigma^{0}$ and $gamma p rightarrow K^{+} Lambda$. It is found that some of these phenomenological models overpredict the measurements by up to a factor of 100. Fitting the data for all of these reactions leads to drastically reduced Born coupling constants.
We investigate the photoproduction of $K^*$ vector meson for the study of the $Lambda(1405)$ resonance. The invariant mass distribution of $piSigma$ shows a different shape from the nominal one, peaking at 1420 MeV. This is considered as a consequence of the double pole structure of $Lambda(1405)$, predicted in the chiral unitary model. Combined with other reactions, such as $pi^- p to K^0 piSigma$, experimental confirmation of this fact will reveal a novel structure of the $Lambda(1405)$ state.
The photo-induced $K^*$ vector meson production is investigated for the study of the $Lambda(1405)$ resonance. This reaction is particularly suited to the isolation of the second pole in the $Lambda(1405)$ region which couples dominantly to the $bar K N$ channel. We obtain the mass distribution of the $Lambda(1405)$ which peaks at 1420 MeV, and differs from the nominal one. Combined with several other reactions, like the $pi^- p to K^0 pi Sigma$ which favours the first pole, this detailed study will reveal a novel structure of the $Lambda(1405)$ state.
We compute dilepton invariant mass spectra from the decays of rho mesons produced by photon reactions off nuclei. Our calculations employ a realistic model for the rho photoproduction amplitude on the nucleon which provides fair agreement with measured cross sections. Medium effects are implemented via an earlier constructed rho propagator based on hadronic many-body theory. At incoming photon energies of 1.5 -3 GeV as used by the CLAS experiment at JLAB, the average density probed for iron targets is estimated at about half saturation density. At the pertinent rho-meson 3-momenta the predicted medium effects on the rho propagator are rather moderate. The resulting dilepton spectra approximately agree with recent CLAS data.
The quantum chromodynamics (QCD) sum rules for the Delta baryons are analyzed by taking into account the finite-width effects, through explicit utilization of the Breit-Wigner shape. We apply a Monte-Carlo based analysis to the traditional and the parity-projected sum rules. The first Delta excitation state is also considered as a sub-continuum resonance and the widths are calculated using the mass values as input.