Mixing of pseudoscalar mesons and M1 radiative decays

We discuss the mixing of pseudoscalar mesons, in particular SU(3) breaking effects, based on ideas abstracted from QCD. The admixtures of η and η′ in η_c are calculated and utilized to estimate the M1 radiative decays ψ → ηγ, η′γ. A reasonably consistent picture emerges for these decays as well as others involving only the light quarks.     

Quark loop model of radiative meson decays

Radiative meson decays are computed from quark loop anomalies, taking into account the SU(3) splitting of the quark masses. Predicted rates for ?→ηγ,K ^*→Kγ, and η→ππγ are brought into satisfactory agreement with experiment. Formulas are given for the radiative decay rates of charmed las are given for the radiative decay rates of charmed mesons, and a mechanism suggested for suppression of the radiative decays of mesons containing a charmed quark.     

Low energy effective Lagrangian description of η and η′ decays

A chiral Lagrangian incorporating a resolution of theU(1) problem is used to study some aspects of the η?η′ system. Mass relations, mixing angle predictions, and the 3π decay modes of η and η?η′ are obtained to be of the correct order of magnitude. Supplementing this Lagrangian with certain four derivative terms gives a rate for η?η′→ηππ which is nonvanishing in the chiral limit and in reasonable agreement with experiment. Some of the radiative decays of η and η′ are also discussed.     

The radial excitations of η−η′ mesons

The possibility of identification of a number of the recently discoveredJ ^PC=0^?+ isosinglet resonances (the ζ(1275), ι(1460) and others) as radial excitations of the η(549)- and η′(958)-mesons is investigated within the earlier developed phenomenological approach to analyse radial excitations of light mesons. The widths of the electromagnetic and strong decays of these mesons and the branching ratios of their production in the radiativeJ/ψ decay, as well as in the π^- p charge exchange reaction, are estimated. It is pointed out that the abundant production of the ι-meson in theJ/ψ-decays and the small width of the ι→2γ decay put forward repeatedly as an evidence for the glueball nature of this meson, can qualitatively be obtained in one of the considered schemes of the radial excitations of the η?η′-system.     

Photon production in heavy-ion collisions at SPS energies

Single photon spectra in heavy-ion collisions at SPS energies are studied in the relativistic transport model that incorporates self-consistently the change of hadron masses in dense matter. We separate the total photon spectrum into “background” arising from the radiative decays of π⁰ and η mesons, and the “thermal” one from other sources. For the latter we include contributions from radiative decays of ρ, ω, η′, and a₁, radiative decays of baryon resonances, as well as two-body processes such as ππ → ργ and πρ → πγ. It is found that more than 95% of all photons come from the decays of π⁰ and η mesons, while the thermal photons account for less than 5% of the total photon yield. The thermal photon spectra in our calculations with either free or in-medium meson masses do not exceed the upper bound set by the experimental measurement of the WA80 Collaboration.     

Looking for new gauge bosons in radiative decays of pseudoscalar mesons

We perform the model independent analysis of possibilities of looking for new gauge bosons in radiative decays of π⁰, η, η′ mesons. For this purpose we consider various experimental constraints on properties of light gauge bosons. It is shown that the branching ratios of these decays can be as large as: BR(π⁰→γ+X)?10^?3, BR(η→γ+X)?10^?4, BR(η′→γ+X)?10^?6, what is highly interesting from the experimental point of view.     

Two schemes ofη−η′-mixing

Proceeding from the expansion of composite operators in interpolating hadronic fields, the width of the decays η(η′)→γγ andJ/ψ→η(η′)γ have been calculated. Two mechanisms of pseudoscalar field mixing (“mass-mixing” and “current-mixing”) are considered. In the given schemes, the values of η?η′-mixing angle θ _p are, respectively, (?15.0±1.8)^o and (?19.7±2.2)^o.     

(η−η′−ι)-mixing,decay and production mechanisms

We present a phenomenological model for meson-glueball mixing and apply it to the mixing of the pseudoscalar mesons η and η′ with the ι(1440)-particle as the prime candidate for a 0^?+-glueball. Using the MIT bag model framework, our model incorporates, among other elements, configuration mixing effects due to virtually excited states, as well as mixing of quark and gluon components. We evaluate the portions of quark antiquark and two-gluon admixtures in η,η′ and ι. The results are used to study various decay and production processes involving these particles. In particular, we calculate the radiative and the 2γ-decay widths of the light mesons and make predictions for the widths of the ι in these channels. Furthermore, production mechanisms of the light mesons in electromagnetic and hadronicJ/ψ-decays are used to evaluate the branching ratios for the production of the ι in variousJ/ψ-transitions. Our results are generally in reasonable agreement with experimental data. Especially we predict a rather large width for the decay ι→ργ and a sizable production rate for the ι in the transitionJ/ψ→ωι.     

Results from DASP one + e − annihilation between 3.1 and 5.2 GeV

This paper summarizes the measurements one ⁺ e ^? annihilation performed by the DASP Collaboration in the energy range between 3.1 and 5.2 GeV. The following topics are covered: total cross section, production and two body decays of the narrow resonances, radiative decays of theJ/ψ and ψ′ resonances and evidence for theX(2.82), ψ′ cascade decays, inclusive η production and evidence for theF meson, semileptonic decays of charmed mesons and properties of the heavy lepton.     

Radiative decays of the Jψ and evidence for a new heavy resonance

The three photon final state produced in e⁺e^? collisions has been measured at the mass of the $\text{J}\text{ψ}$ resonance using the nonmagnetic part of the double arm spectrometer DASP. The decays $\text{J}\text{ψ}\text{→ ηγ, η'γ}$ and π^oγ were observed and their branching ratios are given. A four standard deviation signal was observed in the γγ mass spectrum at a mass of (2.83 ± 0.03) GeV. An upper limit is given for the direct decay $\text{J}\text{ψ}\text{→ 3γ}$.     

Production and decay of toponiumP-states

Energy levels, production and decay rates of toponiumP-states are calculated and their dependence on different assumptions on the short distance part of the potential is studied. The branching ratio for radiative decays to lower lyingS-states will be very large. Weak decays ofP-states will play an important role for quark masses above 25 GeV. Experimental consequences of our results are discussed.     

Partial wave analysis for p̄ p and e+ e− annihilation processes

A new highly modular and generic Partial Wave Analysis (PWA) software package including a general framework for future hadron spectroscopy experiments like PANDA is currently under development. The aims and present status of the software package are summarized and the first PWA results obtained with the already existing tools are presented. These analyses are mainly focused on important aspects of antiproton proton annihilation processes with relevance for the PANDA experiment. For this purpose Crystal Barrel LEAR data are currently under investigation in order to gain a deeper insight to the production mechanisms of vector mesons. In addition analyses for the identification of resonances in radiative J / ψ decays from BESIII data are summarized.     

Radiative decays J/ψ → η(')γ in perturbative QCD

With the recent investigations of the g^*g^*-η^(') transition form factor and η-η^' mixing scheme, we present an updated study of the radiative decays J/ψ → η^(')γ in perturbative QCD. The decays are taken as a test ground for the g^*g^*-η^(') transition form factors and the η-η^' mixing scheme. The form factors are found to be working for glunic η^' production and the mixing angle is constrained to be φ=35.1°±0.8°.     

Radiative decays of radially excited pseudoscalar mesons in the extended Nambu-Jona-Lasinio model

In the extended NJL model the radiative decay widths of the radially excited states of the pseudo-scalar π, η, and η′ mesons are calculated. The predictions for the decay widths of the processes π(1300) → (ρ⁰, ω)γ, η(1295) → (ρ⁰, ω, φ)γ, and η(1475) → (ρ⁰, ω, φ)γ are given. Nowadays, there are no solid experimental data for these processes. The comparison of the results obtained in the framework of the standard and the extended NJL models for decays of the ground states of mesons is given. It is shown that these calculations correspond to each other and are also in satisfactory agreement with experimental data. This allows one to expect that the extended NJL can give reliable predictions for the excited states of mesons.     

Search for the radiative capture reaction d+d → 4He+γ from the ddμ muonic molecule state

A search for the muon-catalyzed fusion (MCF) reaction d+d → ⁴He+γ in the ddμ muonic molecule was performed using the experimental MCF installation TRITON and NaI(Tl) detectors for γ quanta. A high-pressure target filled with deuterium was exposed to the negative muon beam of the JINR phasotron to detect γ quanta with an energy of 23.8 MeV. The first experimental estimation for the yield of radiative deuteron capture from the ddμ state J=1 was obtained at a level of η_γ≤2×10^?5 per one fusion.     

Production of pseudoscalar glueballs in J/ψ radiative decays

Using a previously developed framework for relativistic bound states we calculate the production of pseudoscalar glueballs in J/ψ radiative decays. The results favour the interpretation of ι(1460) as a fairly pure glueball state. Radiative production of ι(1460) in ϒ and toponium decays should be suppressed.     

In search of the ηc

We argue that the X(2.88) detected in π^?p → γγ + n at 40 GeV/c cannot be the η_c. We discuss the possibility that a qq?cc? state is produced there, probably the same state discovered in radiative decay of the J/ψ. Only at much higher energies is the η_c expected to dominate over qq?cc? in the π^?p interaction. We also discuss coherent photoproduction and find that four quark state production would dominate over η_c.