The theoretical predictions for the study of the $a_0(980)$ and $f_0(980)$ mesons in the $ϕ$ radiative decays
The potentialities of the production of the $a_0(980)$ and $f_0(980)$ mesons in the $ϕ$ radiative decays are considered.
hep-ph↗
arXiv subjects
N. N. Achasov
Publications and source records attributed to N. N. Achasov.
Exclusive hadron production in e^+e^- collisions up to the J/psi energy
The predictions are presented for the diagonal and transition form factors of light hadrons in the time-like region up to the production threshold of an open charm quantum number. The comparison with existing data on the decays of J/psi and psi(2S) mesons into such hadrons shows that some new resonance structures may be present in the mass range between 2 GeV and the J/psi mass. Searching them may help in a better understanding of the mass spectrum in quark models, and in revealing the details of the three-gluon mechanism of the OZI rule breaking.
hep-ph↗
Two-Photon Production of Four-Quark States Up to the $J/ψ$ Energy
Evidence for an explicitly exotic state with isospin 2 and spin-parity 2^+ near the $ρρ$ threshold and nontrivial complementary indications of the unusual quark composition of the $f_0(980)$ and $a_0(980)$ states obtained from the reactions of two-photon formation of neutral meson resonances are discussed, together with puzzling phenomena in the channels $γγ\toρ^0ϕ$ and $γγ\toρ^0ρ^0$ at high energies.
hep-ph↗
On the Nature of the Scalar a_0(980) and f_0(980)-Mesons
It is presented a critical consideration of all unusual properties of the scalar $a_0(980)$ and $f_0(980)$-mesons in the four-quark, two-quark and molecular models. The arguments are adduced that the four-quark model is more preferable. It is discussed the complex of experiments that could finally resolve this issue.
hep-ph↗
The $ρ^{\pm}-ρ^0$ Mass Splitting Problem
It is discussed the problem of the $ρ^\pm-ρ^0$ mass splitting. It is suggested to use the $ϕ\toρπ\to 3π$ decay to measure the $ρ^{\pm}-ρ^0$ mass splitting.
hep-ph↗
Nature of the scalar $a_0(980)$ and $f_0(980)$-mesons
It is presented a critical consideration of all unusual properties of the scalar $a_0(980)$ and $f_0(980)$-mesons in the four-quark, two-quark and molecular models. The arguments are adduced that the four-quark model is more preferable. It is discussed the complex of experiments that could finally resolve this issue.
hep-ph↗
New explanation of the GAMS results on the $f_0(980)$ production in the reaction $π^-p\to π^0π^0n$
The observed alteration of the S-wave $π^0π^0$ mass spectrum in the reaction $π^-p\toπ^0π^0n$ with increasing $-t$, i.e., the disappearance of a dip and the appearance of a peak in the region of the $f_0(980)$ resonance as $-t$ increases, is explained by the contribution of the $π^-p\to f_0(980)n$ reaction amplitude with the quantum numbers of the $a_1$ Regge pole in the $t$ channel. It is very interesting that nontrivial evidence for the $a_1$ exchange mechanism in the reaction $π^-p\to π^0π^0n$ follows for the first time from the experiment on an unpolarized target. The explanation of the GAMS results suggested by us is compared with that reported previously. Two ways of experimentally testing these explanations are pointed out.
hep-ph↗
Electromagnetic form factors in the J/ψmass region: The case in favor of additional resonances
Using the results of our recent analysis of e^+e^- annihilation, we plot the curves for the diagonal and transition form factors of light hadrons in the time-like region up to the production threshold of an open charm quantum number. The comparison with existing data on the decays of J/ψinto such hadrons shows that some new resonance structures may be present in the mass range between 2 GeVand the J/ψmass. Searching them may help in a better understanding of the mass spectrum in both the simple and a more sophisticated quark models, and in revealing the details of the three-gluon mechanism of the OZI rule breaking in K\bar K channel.
hep-ph↗
Analysis of preliminary data on $e^+e^-\toϕ\toγf_0(980)\toγπ^0π^0$ reaction
We perform the analysis of the preliminary data on $e^+e^-\toϕ\toγf_0(980)\toγπ^0π^0$ reaction simultaneously with the data on $ππ$ scattering and reactions $J/ψ\toϕπ^+π^-$ and $K^-p\toπ^+π^-(Λ,Σ)$. It is found that the $f_0(980)$ meson mass $m_{f_0}=950$ MeV and $B(ϕ\toγf_0\toγπ^0π^0)\simeq1\cdot10^{-4}$.
hep-ph↗
Isoscalar resonances with J^{PC}=1^{--} in e^+e^-annihilation
The analysis of the vector isoscalar excitations in the energy range between 1 and 2 GeV of the $e^+e^-$ annihilation is presented for the final states $π^+π^-π^0$, $ωπ^+π^-$, $K^+K^-$, $K^0_SK^\pmπ^\mp$ and $K^{\ast0}K^-π^++ c.c$. The effects of both the resonance mixing and the successive opening of multiparticle channels, with the energy dependent partial widths, are taken into account. The work extends our previous analysis hep-ph/9609216 of the vector isovector excitations and is aimed to compare the existing data with the predictions of the $q\bar q$ model. It is shown that this hypothesis does not contradict the data.
hep-ph↗
Mechanisms of the Reaction $π^-p\to a^0_0(980)n\toπ^0ηn$ at High Energies
Over the last twenty years, it was assumed that the reaction $π^-p\to a^0_0(980)n\toπ^0ηn$ at high energies is dominated by $b_1$ Regge pole exchange. We show that the new Brookhaven and Serpukhov data on the $t$ distributions for this reaction can be explained within the framework of the Regge pole model only if the $ρ_2$ Regge pole exchange conspiring with its daughter plays a crucial role. The tentative estimates of the absolute $π^-p\to a^0_0(980)n\toπ^0ηn$ reaction cross section are obtained. The contributions of the one-pion exchange mechanism and the Regge cuts are also estimated.
hep-ph↗
Search for the scalar a_0 and f_0 mesons in the ϕradiative decays
The potentialities of the production of the $a_0$ and $f_0$ mesons in the $ϕ$ radiative decays are considered based on a new two-channel analysis of the $ππ$ scattering in a energy region near 1 GeV. We predict $BR(ϕ\toγf_0(980))\sim10^{-5}-10^{-4}$ that is a great value for the decay forbidden by the Okubo-Zweig-Iizuka rule. We discuss the four-quark, $K\bar K$-molecule and two-quark scenarios for the $a_0$ and $f_0$ mesons. It is presented arguments that the $e^+e^-$-colliders and especially the $ϕ$ factories give the possibility to choose a single one out of them.
hep-ph↗
Search for the scalar $a_0$ and $f_0$ mesons in the reactions $e^+e^-\toγπ^0π^0(η)$
It is shown that the reactions $e^+e^-\toγπ^0π^0(η)$ give a good chance for observing scalar $a_0$ and $f_0$ mesons. In the photon energy region less then 100 MeV the vector meson contributions $e^+e^-\to V^0\toπ^0 V'^0\toγπ^0π^0(η)$ are negligible in comparison with the scalar mesons $e^+e^-\toϕ\toγf_0(a_0)\toγπ^0π^0(η)$ for $BR(ϕ\toγf_0(a_0)\toγπ^0π^0(η))$ greater than $5\cdot10^{-6}(10^{-5})$. Using two-channel treatment of the $ππ$ scattering the predictions for $BR(ϕ\toγ(f_0+σ)\toγππ)$ are derived. The four quark model, the model of $K\bar K$ molecule and the$s\bar s$ model of scalar $f_0$ and $a_0$ mesons are discussed.
hep-ph↗
Interference in the reaction $e^+e^-\toγπ^+π^-$ and the final state interaction
We describe the interference between amplitudes $e^ + e^-\toρ\toγπ^+π^-$ and $e^ + e^-\toϕ\toγ(f_0 + σ) \toγπ^ + π^-$, with regard to the phase of the elastic $ππ$ scattering background and mixing of the $f_0$ and $σ$ mesons. It is shown that the Fermi-Watson theorem for the final state interaction in the reaction $e^ + e^-\toρ\toγπ^ + π^-$ is not valid in the case of soft photons, $ω< 100$ MeV, in the $ϕ$ meson region. The interference patterns in the spectrum of the photon energy differential cross-section and in the full cross-section as a function of the beam energy are obtained.
hep-ph↗
Isobar Electroproduction as a Background from Interaction of Beams with Residual Gas at $ϕ$-Factories
It is shown that when beams interact with a residual gas at $ϕ$-factories the reaction of the electroproduction of the $Δ(1232)$ isobar proceeds vigorously. The isobar decay gives $\sim 10^7$ pions during an effective year of $10^7$ s per meter of a residual gas. These pions are emitted largely across the beam axis and have a resonance energy distribution with a peak nearby 265 MeV of a width close to 120 MeV in the isobar rest system. There are presented formulae for the distributions of the four-momentum transfer square, the angles, the energies and the momentum of the decay products, that is all required for the simulation of the process under consideration.
hep-ph↗
Mechanisms of the reaction pi^-p --> a^0_0(980)n --> p-^0 eta n at high energies
The main dynamical mechanisms of the reaction $π^-p \rightarrow a^0_0 (980)n \rightarrow π^0ηn$ at high energies, currently investigated at Serpukhov and Brookhaven, are considered in detail. It is shown that the observed forward peak in its differential cross section can be explained within the framework of the Regge pole model only by the conspiring $ρ_2$ Regge pole exchange. The tentative estimates of the absolute $π^-p \rightarrow a^0_0(980)n \rightarrow π^0ηn$ reaction cross section at $P_{lab}^{π^-} = 18$ GeV/c are obtained: $σ\approx200$ nb and, in the forward direction, $dσ/dt\approx940$ nb/GeV$^2$. The contribution of the one pion exchange, which is forbidden by $G$-parity and which can rise owing to the $f^0_0(980)-a^0_0(980)$ mixing, is also estimate. A role of the Regge cuts in the non-flip helicity amplitude is briefly examined and a conclusion is made that the contributions of the cuts have to be inessential in comparison with the conspiring $ρ_2$ Regge pole exchange.
hep-ph↗
The interference in the reaction $e^+e^-\toγπ^+π^-$ and the search for the decay $ϕ\toγf_0\toγπ^+π^-$
We describe the interference between amplitudes $e^+e^- \to ρ\to γπ^+π^-$ and $e^+e^- \to ϕ\to γf_0 \to γπ^+π^-$, where $f_0$ meson is considered in the frameworks of the four-quark model and the model of the scalar $K\bar K$ molecule. The general expressions for the differential cross section with the radiative corrections and two angle cuts are given. The interference patterns are obtained in the spectrum of the differential cross section by the energy of the photon and in the full cross section by the energy of the beams.
hep-ph↗
Rho primes in analyzing e+e- annihilation, MARK III, LASS and ARGUS data
The results of an analysis are presented of some recent data on the reactions $e^+e^-\toπ^+π^-π^+π^-$, $e^+e^-\toπ^+π^-π^0π^0$ with the subtracted $ωπ^0$ events, $e^+e^-\toωπ^0$, $e^+e^-\toηπ^+π^-$, $e^+e^-\toπ^+π^-$, $K^-p\toπ^+π^-Λ$, the decays $J/ψ\toπ^+π^-π^0$, $tau^-\toν_tauπ^+π^-π^-π^0$ $tau^-\toν_τωπ^-$, upon taking into account both the strong energy dependence of the partial widths on energy and the previously neglected mixing of the $ρ$ type resonances. The above effects are shown to exert an essential influence on the specific values of masses and coupling constants of heavy resonances and hence are necessary to be accounted for in establishing their true nature.
hep-ph↗