SEMINARIO GRUPO FISICA DE ALTAS ENERGIAS

Abstract: In this talk we discuss production of goldstones (pions, kaons and eta) on the proton and nuclear targets. We consider several kinematic regimes.

For the proton target, we argue that the Adler relation (AR) for diffractive neutrinoproduction of goldstones is broken at high energies due to absorptive corrections. The dipole approach also confirms that in the black-disc limit, where the absorptive corrections aximize, the diffractive cross section ceases, on the contrary to the expectation based on PCAC.

In case of coherent pion production on nuclei, the process is controlled by the interplay of two length scales. One is related to the pion mass and is quite long (at low Q²), while the other, associated with heavy axial-vector states, is much shorter. The Adler relation is found to be broken at all energies, but especially strongly at nu > 10 GeV, where the cross section is suppressed by a factor A^-1/3. On the contrary, in a process where the recoil nucleus breaks up into fragments, the Adler relation turns out to be strongly broken at low energies, where the cross section is enhanced by a factor A^1/3, but has a reasonable accuracy at higher energies, where all the coherence length scales become long.