Study of resonant processes for multi-pion production in pˉ+p→ℓ++ℓ−+nππ\bar p +p\to\ell ^++\ell^- +n_\pi \pi annihilation

In frame of a phenomenological approach based on Compton-like Feynman amplitudes, we study multi-pion production in antiproton nucleon collisions. The main interest of this reaction is related to the possibility to study the properties of the presumable $\bar N N$ atom and of its resonances. For the case of formation of a scalar or pseudoscalar resonant state, with $I^G(J^{P})=1^-(0^{\pm}),~0^+(0^-)$ numerical results are obtained. The differential cross section in an experimental set-up where the pions invariant mass is measured, is given with explicit dependence on the lepton pair and pions invariant mass.Comment: 9 pages, 4 figure

Testing axial and electromagnetic nucleon form factors in time-like regions in the processes pˉ+n→π−+ℓ−+ℓ+\bar p + n\to \pi^- +\ell^-+\ell^+ and pˉ+p→π0+ℓ−+ℓ+\bar p+ p\to \pi^0 +\ell^- + \ell^+, ℓ=e\ell=e, μ\mu

In frame of a phenomenological approach based on Compton-like Feynman amplitudes, we study the annihilation channel in antiproton nucleon collisions with production of a single charged or neutral pion and a lepton-antilepton pair. These reactions allow to access nucleon and axial electromagnetic form factors in time-like region and offer a unique possibility to study the kinematical region below two nucleon threshold. The differential cross section in an experimental set-up where the pion is fully detected is given with explicit dependence on the relevant nucleon form factors. The possibility to measure heavy charged pion in the annihilation channel is also discussed.Comment: 23 pages, 9 figure

Antiproton-nucleus electromagnetic annihilation as a way to access the proton timelike form factors

Contrary to the reaction pbar + p --> e+ e- with a high momentum incident antiproton on a free target proton at rest, in which the invariant mass M of the (e+ e-) pair is necessarily much larger than the (pbar p) mass, in the reaction pbar + d --> n e+ e- the value of M can take values near or below the (pbar p) mass. In the antiproton-deuteron electromagnetic annihilation, this allows to access the proton electromagnetic form factors in the time-like region of q^2 near the (pbar p) threshold. We estimate the cross section dsigma(pbar +d --> e+ e- n)/dM for an antiproton beam momentum of 1.5 GeV/c. We find that near the (pbar p) threshold this cross section is about 1 pb/MeV. The case of heavy nuclei target is also discussed. Elements of experimental feasibility are presented for the process pbar + d --> n e+ e- in the context of the Panda project.Comment: 14 pages, 11 figures. submitted to EPJ

Annihilation of pˉ+p→e++e−+π0\bar p+p\to e^++e^-+ \pi^0 and pˉ+p→γ+π0\bar p+p\to \gamma + \pi^0 through ω\omega-meson intermediate state

The s-channel annihilation of proton and antiproton into a neutral pion and a real or virtual photon followed by lepton pair emission is studied. Such mechanism is expected to play a role at moderate values of the total energy $\sqrt{s}$, when the pion is emitted around $90^{\circ}$ in the center of mass. A fair comparison with the existing data is obtained taking into account scattering and annihilation channels. The cross section is calculated and numerical results are given in the kinematical range accessible in the PANDA experiment at FAIR.Comment: 22 pages, 9 figures- Given more details on the model- final version accepted for publicatio

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.Comment: 9 pages, 6 figure