16 research outputs found
Study of resonant processes for multi-pion production in 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 atom and of its resonances. For the
case of formation of a scalar or pseudoscalar resonant state, with
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 and , ,
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 and through -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
, when the pion is emitted around 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