Electron-positron annihilation intoϕf0(980)and clues for a new1--resonance

Abstract

We study the e e ÿ ! reaction for pions in an isoscalar s wave which is dominated by loop mechanisms. For kaon loops we start from the conventional R PT, but use the unitarized amplitude for K K ÿ scattering and the full kaon form factor instead of the lowest order terms. We study also effects of vector mesons using R PT supplemented with the conventional anomalous term for VVP interactions and taking into account the effects of heavy vector mesons in the K K transition form factor. We find a peak in m around the f 0 980 as in the experiment. Selecting the f 0 980 contribution as a function of the e e ÿ energy we also reproduce the experimental data except for a narrow peak, yielding support to the existence of a 1 ÿÿ resonance above the f 0 980 threshold, coupling strongly to this state.

Meson loops in the f0(980) and a0(980) radiative decays into ρ , ω

“…The procedure followed here to write the divergent part in terms of the meson-meson loop function is similar to what was done in ref. [40] in a different context. Therefore, gathering the convergent parts and keeping only the contributions to the d−term of Eq.…”

The three-body structure of the X(2175) and the Y(4260) states

“…1), thus, confirming the experimental findings. Using the results of [7], we implemented the final state interaction for the e + e − → φ f 0 (980) reaction in terms of our three-body amplitude and calculated the cross sections. This resulted into a peak in the cross section around 2175 MeV in accordance with the experimental cross sections obtained by different experimental groups [14].…”

“…In [7] the e + e − → φ f 0 (980) reaction, for which the data are available from BABAR [14], was studied using a loop mechanism involving pseudoscalar and vector meson loops. In the chiral models, the f 0 (980) resonance is dynamically generated in the KK interaction [18].…”

“…In [4] this resonance is seen as an enhancement in the K + K − K + K − cross section around 2150 MeV. A detailed theoretical study of the e + e − → φ f 0 (980) reaction was done in [7] by means of loop diagrams involving kaons and K * , using chiral amplitudes for the KK → ππ channel which contains the f 0 (980) pole generated dynamically by the theory. The study revealed that the loop mechanisms reproduced the background but failed to produce the peak around 2175 MeV, thus reinforcing the claims for a new resonance around this mass.…”

Photo- and electro-production of mesons on nucleons and nuclei

“…Hence, the t-matrices that we implement in the loops automatically generate this resonance which does not have to be introduced by hand. The details can be seen in [46]. The evaluation of the amplitude requires to work out the loop tensor T abc µν , such that the amplitude is T abc µν ǫ µ (γ)ǫ ν (φ).…”