  Reactions induced by high energy antiprotons on proton on nuclei are
accompanied with large probability by the emission of a few mesons. Interesting
phenomena can be observed and QCD tests can be performed, through the detection
of one or more mesons. The collinear emission from high energy (anti)proton
beams of a hard pion or vector meson, can be calculated similarly to the
emission of a hard photon from an electron \cite{Kuraev:2013izz}. This is a
well known process in QED, and it is called the "Quasi-Real Electron method",
where the incident particle is an electron and a hard photon is emitted leaving
an 'almost on shell' electron impinging on the target \cite{Baier:1973ms}. Such
process is well known as Initial State Emission (ISR) method of scanning over
incident energy, and can be used, in the hadron case, to produce different kind
of particles in similar kinematical conditions. In case of emission of a
charged light meson, $\pi$ or $\rho$-meson, in proton-proton(anti-proton)
collisions, the meson can be deviated in a magnetic field and detected. The
collinear emission (along the beam direction) of a charged meson may be used to
produce high energy (anti)neutron beams. This can be very useful to measure the
difference of the cross sections of (anti)proton and (anti)neutron scattering
from the target and may open the way for checking sum rules with antiparticles.
Hard meson emission allows also to enhance the cross section when the energy
loss from one of the incident particles lowers the total energy up to the mass
of a resonance. The cross section can be calculated, on the basis of factorized
formulas, where the probability of emission of the light mesons multiplies the
cross section of the sub-process. Multiplicity distributions for neutral and
charged meson production are also given.
