arXiv subjects
Publications and source records attributed to Miroslav Nagy.
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.
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.
We present a unified analysis of the decays of bottomonia Upsilon(mS) -> Upsilon(nS) pi pi (m>n, m=2,3,4,5, n=1,2,3), charmonia J/psi -> phi (pi pi, K antiK), psi(2S) -> J/psi pi pi and the isoscalar S-wave processes pi pi -> pi pi, K antiK, eta eta. In this analysis we extend our recent study of low-lying (m=2,3) radial excitations of bottomonia to modes involving higher (m=4,5) excited states. Similarly as for the data on lower radial excitations, we confirm that the data for higher radially excited states from the BaBar and Belle collaborations can be described under conditions that the final bottomonium is a spectator and the multichannel pi pi scattering is considered in a model-independent approach based on analyticity, unitarity and the uniformization procedure. Indeed we show that the dipion mass distributions in the two-pion transitions of both charmonia and bottomonia states are explained by a unified mechanism based on the contribution of the pi pi and K antiK coupled channels including their interference (final-state interactions). Therefore, our main result is that the lower and higher radially excited states of charmonia and bottomonia have no specific features in mutual comparison and can be understood in a unified picture, e.g. proposed by our approach.
The effect of isoscalar S-wave multichannel pi pi -> pi pi, K antiK, eta eta scattering is considered in the analysis of decay data of the Upsilon-mesons. We show that when allowing for the final state interaction contribution to the decays Upsilon(mS) -> Upsilon(nS) pi pi (m>n, m=2,3, n=1,2) in our model-independent approach, we can explain the two-pion energetic spectra of these Upsilon transitions including the two-humped shape of the di-pion mass distribution in Upsilon(3S) -> Upsilon(1S) pi pi as the coupled-channel effect. It is shown also that the considered bottomia decay data do not offer new insights into the nature of the f0 mesons, which were not already deduced in our previous analyses of pseudoscalar meson scattering data.
Peculiarities of obtaining parameters for broad multi-channel resonances from data are discussed analyzing the experimental data on processes $ππ\toππ,K\bar{K}$ in the $I^GJ^{PC}=0^+0^{++}$ channel in a model-independent approach based on analyticity and unitarity and using an uniformization procedure. We show that it is possible to obtain a good description of the $ππ$ scattering data from the threshold to 1.89 GeV with parameters of resonances cited in the PDG tables as preferred. However, in this case, first, representation of the $ππ$ background is unsatisfactory; second, the data on the coupled process $ππ\to K\bar{K}$ are not well described even qualitatively above 1.15 GeV when using the resonance parameters from the only $ππ$ scattering analysis. The combined analysis of these coupled processes is needed, which is carried out satisfactorily. Then both above-indicated flaws, related to the analysis of solely the $ππ$-scattering, are cured. The most remarkable change of parameters with respect to the values of only $ππ$ scattering analysis appears for the mass of the $f_0 (600)$ which is now in some accordance with the Weinberg prediction on the basis of mended symmetry and with an analysis using the large-$N_c$ consistency conditions between the unitarization and resonance saturation. The obtained $ππ$-scattering length $a_0^0$ in case when we restrict to the analysis of the $ππ$ scattering or consider so-called A-solution (with a lower mass and width of $f_0(600)$ meson) agrees well with prediction of chiral perturbation theory (ChPT) and with data extracted at CERN by the NA48/2 Collaboration from the analysis of the $K_{e4}$ decay and by the DIRAC Collaboration from the measurement of the $π^+π^-$ lifetime.
The $f_0$ mesons are studied in a combined analysis of data on the isoscalar S-wave processes $ππ\toππ,K\overline{K},ηη$ and on decays $J/ψ\toϕ(ππ, K\overline{K})$, $ψ(2S)\to J/ψ(ππ)$, and $Υ(2S)\toΥ(1S)ππ$ from the Argus, Crystal Ball, CLEO, CUSB, DM2, Mark II, Mark III, and BES II collaborations. The method of analysis, based on analyticity and unitarity and using an uniformization procedure, is set forth with some details. Some spectroscopic implications from results of the analysis are discussed.
After describing the SU(2) linear sigma model (L$σ$M), we dynamically generate it using the B.W. Lee null tadpole sum (characterizing the true vacuum) together with the dimensional regularization lemma. Next we generate the chiral-limiting (CL) nonstrange and strange constituent quark masses ${\hat m}=325.7$ MeV; $m_s=486$ MeV away from the CL. Finally, we study vector meson dominance (VMD) and the pion, kaon charge radii and the loop-order $ρ\toπγ$, $π^0\toγγ$ amplitudes in the quark model. Lastly, we verify this procedure using tree-order VMD graphs.
We start by studying the Goldberger-Treiman discrepancy (GTd) $Δ= (2.259\pm 0.591)%$. Then we look at the $πN$ $σ$ term, with the dimensionless ratio $σ_N/2m_N=3.35%$. Finally we return to predicting (via the quark model) the $πN$ coupling constant, with GTd $Δ\to 0$ as $m_q\to m_N/3$.