arXiv subjects

Rinaldo Baldini Ferroli

Publications and source records attributed to Rinaldo Baldini Ferroli.

7 recordsLinked to original sources

arXiv2025

$G$-parity violating amplitudes in the $J/ψ\to π^+ π^-$ decay

The decays of the negative $G$-parity meson $J/ψ$ into even numbers of pions violate $G$-parity. Such decays, as well as other $G$-parity decays into hadrons, can be parametrized in terms of three main intermediate virtual states: one photon, one photon plus two gluons, and three gluons. Since the electromagnetic interaction does not conserve $G$-parity, $J/ψ$ decays into positive $G$-parity final states should be dominantly electromagnetic. Nevertheless, the one-photon contribution to $J/ψ\to π^+ π^-$, that can be estimated by exploiting the cross section $σ(e^+e^-\to π^+ π^-)$, differs from the observed decay probability for {more than} 4.5 standard deviations. We present a computation of the $ggγ$ amplitude based on a phenomenological description of the decay mechanism in terms of dominant intermediate states $ηγ$, $η'γ$ and $f_1(1285)γ$. The obtained value is of the order of the electromagnetic contribution.

hep-ph↗

arXiv2021

Probing the internal structure of baryons

Electromagnetic form factors are fundamental observables that describe the electric and magnetic structure of hadrons and provide keys to understand the strong interaction. At the Beijing Spectrometer (BESIII), form factors have been measured for different baryons in the time-like region for the first time or with the best precision. The results are presented with examples focus on but not limited to the proton/neutron, the $Λ$, with a strange quark, and the $Λ_c$, with a charm quark.

hep-ex↗

arXiv2021

A possible simultaneous fit to the available $e^+e^- \rightarrow Λ^+_c \barΛ^-_c$ cross section data nearby $ψ(4660)$ by means of a strong correction to the Coulomb enhancement factor

There are two available set of data on the $e^+e^- \rightarrow Λ^+_c \barΛ_c^-$ cross section above threshold. The BELLE measurement, with ISR return, is compatible with the presence of a resonant state, called $ψ(4660)$ (formerly known as $Y(4660)$), observed also in other final states. The BESIII dataset has shown a different trend, with a flat cross section. We propose a new solution to fit both datasets by means of a strong correction to the Coulomb enhancement factor. Mass and width of the resonant state is extracted.

hep-ph↗

arXiv2020

The cross section of $e^+e^- \to Λ\overline Σ^0+{\rm c.c.}$ as a litmus test of isospin violation in the decays of vector charmonia into $Λ\overline Σ^0+{\rm c.c.}$

Under the aegis of isospin conservation, the amplitudes in Born approximation, i.e., considering the only one-photon-exchange mechanism, of the decay $ψ\to Λ\overline Σ^0+{\rm c.c.}$, where $ψ$ is a vector charmonium, and of the reaction $e^+e^- \to Λ\overline Σ^0+{\rm c.c.}$ at the $ψ$ mass, are parametrized by the same electromagnetic coupling. It follows that, the modulus of such a coupling can be extracted the data on the two observables: the decay branching fraction and the annihilation cross section. By considering the first two vector charmonia, $J/ψ$ and $ψ(2S)$, it is found that, especially in the case of $ψ(2S)$, there is a substantial discrepancy between the values of the modulus of the same electromagnetic coupling extracted from the branching ratio and the cross section. We propose, as a possible explanation for such a disagreement, the presence in the decay amplitude of an isospin-violating contribution driven by a mechanism based on physical (on-shell) intermediate states, that, due to their own nature, should be more effective in the $ψ(2S)$ decay than in that of the $J/ψ$.

hep-ph↗

arXiv2020

Amplitudes separation and strong-electromagnetic relative phase in the $ψ(2S)$ decays into baryons

The strong, electromagnetic and mixed strong-electromagnetic amplitudes of the $ψ(2S)$ decays into baryon-anti-baryon pairs have been obtained by exploiting all available data sets in the framework of an effective Lagrangian model. We observed that at the $ψ(2S)$ mass the QCD regime is not completely perturbative, as can be inferred by the relative strength of the strong and the mixed strong-electromagnetic amplitudes. Recently a similar conclusion has been reached also for the $J/ψ$ decays. The relative phase between the strong and the electromagnetic amplitudes is $φ= (58\pm 8)^\circ$, to be compared with $φ= (73\pm 8)^\circ$ obtained for the $J/ψ$. On the other hand, in the case of the $ψ(2S)$ meson, different values of the ratio between strong and mixed strong-electromagnetic amplitudes are phenomenologically required, while for the $J/ψ$ meson only one ratio was enough to describe the data. Finally, we also observed a peculiar behavior of the mixed strong-electromagnetic amplitudes of the decays $ψ(2S)\toΣ^+ \overline Σ^-$ and $ψ(2S)\toΣ^- \overline Σ^+$.

hep-ph↗

arXiv2019

Strong and electromagnetic amplitudes of the $J/ψ$ decays into baryons and their relative phase

The Feynman amplitude for the decay of the $J/ψ$ meson into baryon-antibaryon can be written as a sum of three sub-amplitudes: a purely strong, a purely electromagnetic and a mixed strong-electromagnetic. Assuming that the strong and mixed strong-electromagnetic sub-amplitudes have the same phase, the branching ratio of the decay contains an interference term that depends on the relative phase $φ$ between strong and electromagnetic sub-amplitudes. In this work we calculate this phase, by using an effective strong Lagrangian density and considering, as final states, pairs of baryons, $\mathcal{B}\overline{\mathcal{B}}$, belonging to the spin-1/2 SU(3) octet. Moreover, we obtain the purely strong, purely electromagnetic and mixed strong-electromagnetic contributions to the total branching ratio and hence the moduli of the corresponding sub-amplitudes, for each pair of baryons. Of particular interest is the mixed strong-electromagnetic contribution that, not only is determined for the first time, but it is proven to be crucial, in the framework of our model, for the correct description of the decay mechanism. Finally we use the purely electromagnetic branching ratio to calculate the Born non-resonant cross section of the annihilation processes $e^+ e^- \to \mathcal{B}\overline{\mathcal{B}}$ at the $J/ψ$ mass. By taking advantage from all available data, we obtain the relative phase between strong and electromagnetic sub-amplitudes: $φ= (73\pm 8)^\circ$.

hep-ph↗

arXiv2010

No Sommerfeld resummation factor in e+e- -> ppbar ?

The Sommerfeld rescattering formula is compared to the e+e- -> ppbar BaBar data at threshold and above. While there is the expected Coulomb enhancement at threshold, two unexpected outcomes have been found: |G^p (4M_p^2)|= 1, like for a pointlike fermion, and moreover data show that the resummation factor in the Sommerfeld formula is not needed. Other e+e- -> baryon-antibaryon cross sections show a similar behavior near threshold.

hep-ph↗