Coherent pion production by neutrino scattering off nuclei

Abstract

The main part of coherent pion production by neutrinos on nuclei is essentially determined by PCAC, provided that the leptonic momentum transferred square Q 2 remains sufficiently small. We give the formulas for the charged and neutral current cross sections, including also the small non-PCAC transverse current contributions and taking into account the effect of the µ − -mass. Our results are compared with the experimental ones and other theoretical treatments. I. INTRODUCTIONCoherent production of pions by neutrinos has been studied by many experimental groups and measurements have been made for neutrino energies ranging from 2 to 80 GeV [1,2,3,4,5,6,7,8]. The main characteristics of such cross sections is that the energy of the recoiling nucleus and the invariant momentum transfer to it, always remain very small. A characteristic signature of these events is a sharp peak in the low |t| region. In addition to this, all experiments have observed that the momentum transfer from the leptonic sector Q 2 also remains very small, sharply peaking at Q 2 0.2 GeV 2 ; while the dependence of the cross section on the neutrino energy appears logarithmic at high energies.However, problems with the existence of the coherence phenomenon might appear at the lower energies used for the new oscillation experiments K2K, MiniBoone, MINOS etc. In particular, a new measurement by the K2K group at an average neutrino energy E 1 = 1.3 *

Comparison of Models of Neutrino-Nucleus Interactions

“…The Paschos-Schalla prescription [42,48] is very similar to the Berger-Sehgal model in both formulation and results. Since the pion-nucleus cross section is very forward-peaked, they fit the small angle region to an exponential.…”

“…Since the pion-nucleus cross section is very forward-peaked, they fit the small angle region to an exponential. The main improvement in the recent articles [44,42,48] comes from setting the minimum value of t from the value of Q^.…”

“…The PCAC models were designed to describe the early high energy data. PCAC [42] allows a connection between the coherent reaction and pion elastic scattering with a target nucleus. The reaction is generally modeled by combining PCAC with a specific description of pion-nucleus scattering.…”

Partially conserved axial vector current and coherent pion production by low energy neutrinos

“…Following the PCAC route we have tried to circumvent the uncertainties in modelling nuclear processes by direct appeal to data on pion nucleus elastic scattering, see also [16]. For Carbon targets this can be done easily because π + and π − data on differential and total cross sections exist for pion kinetic energies T π from 30 to 870 MeV.…”

Measurement of the ν_μ Charged Current π⁺ to Quasi-Elastic Cross Section Ratio on Mineral Oil in a 0.8 GeV Neutrino Beam

“…A variety of models exist for coherent pion production [35,36,37,38], but this interaction channel remains poorly understood and the models' predictions for the coherent pion production cross-sections vary by an order of magnitude. Recent results from K2K and SciBooNE [39,40] show no evidence for charged current coherent pion production; however, results from MiniBooNE and SciBooNE [41,42,43] do favor a coherent contribution to neutral current pion production, MiniBooNE obtaining a 19.5±3.6% coherent fraction and SciBooNE 17.9±4.1%.…”