Neutrino production of single pions: Dipole description

Abstract

The light-cone distribution amplitudes for the axial current are derived within the instanton vacuum model (IVM), which incorporates nonperturbative effects including spontaneous chiral symmetry breaking. This allows to extend applicability of the dipole approach, usually used in the perturbative domain, down to Q 2 → 0, where partially conserved axial current (PCAC) imposes a relation between the neutrino-production cross section and the one induced by pions. A dramatic breakdown of the Adler relation (AR) for diffractive neutrino-production of pions, caused by absorptive corrections, was revealed recently in [1]. Indeed, comparing with the cross section predicted by the dipole phenomenology at Q 2 → 0 on a proton target we confirmed the sizable deviation from the value given by the AR, as was estimated in [1] within a simplified two-channel model. The dipole approach also confirms that in the black-disc limit, where the absorptive corrections maximize, the diffractive cross section ceases, on the contrary to the expectation based on PCAC.

Diffractive neutrino production of pions on nuclei: Adler relation within the color-dipole description

“…Here we extend the results obtained for neutrino-proton interactions in [40] to the nuclei using the Glauber-Gribov approach [8,9]. While in the high-energy (''frozen'') regime the shadowing corrections are given by the trivial exponential attenuation factor, we use an approach that is also valid at intermediate energies, where the dipole size fluctuates during propagation through the nucleus.…”

“…Also, the color-dipole model has been applied to the description of the neutrino physics in [32][33][34][35][36][37][38][39]. Single-pion production by neutrinos on a proton target has been studied recently within the colordipole approach in [40].…”

Incurable Adler relation for soft neutrino interactions

“…Within the two-channel approximation, the two time scales Eqs. (16) are well defined, and all events within the certain energy range (see Fig. 3) belong to the regime II, where the AR is valid.…”

“…In this case pion production can be described as νp → l( qq)p → lπp, i.e. neutrino fluctuates into a qq dipole, which interacts elastically with the target and then is projected to the pion wave function [16]. This process is illustrated in the graph in the left panel of Fig.…”

“…This amplitude is pretty well known from phenomenology, since it has been fitted to photoproduction and DIS data. The light-cone qq distribution amplitudes Ψ A µ and Ψ π are calculated in the instanton vacuum model [18,19,20] (see details in [16,21]). The results for nuclear effects are shown by solid curves in the right panel of Fig.…”