Nuclear Effects in Neutrino Induced Coherent Pion Production at K2K and MiniBooNE

Abstract

The coherent pion production induced by neutrinos in nuclei is studied using a delta hole model in local density approximation taking into account the renormalization of ∆ properties in a nuclear medium. The pion absorption effects have been included in an eikonal approximation. These effects give a large reduction in the total cross section. The numerical results for the total cross section are found to be consistent with recent experimental results from K2K and MiniBooNE collaborations and other older experiments in the intermediate energy region.PACS numbers: 13.15.+g, 23.40.Bw, 25.30.Pt The present experiments at K2K and MiniBooNE are designed to search for ν-oscillations in ν µ disappearance and ν e appearance channels. In these experiments, the ν µ -spectrum is determined by the observed energy spectrum of muons which are predominantly produced in forward direction through the charged current quasielastic reactions induced by ν µ . In this kinematic region the major background to these events come from the non quasielastic events in which pions are produced through coherent and incoherent processes induced by charged and neutral weak currents in ν-nucleus interactions. The neutral current induced π 0 production is of particular importance as it constitutes a major background to the electron signal in ν e appearance channel. The analysis of ν-oscillation experiments, therefore, requires a better understanding of pion production processes in ν-nucleus interaction and many experiments are being done to study ν-induced coherent and incoherent production of pions from nuclei [1].The coherent production of charged pions from 12 C has been recently studied by the K2K collaboration [2]. The coherent production of neutral pions has been studied by the K2K collaboration for 16 O [3] and by the MiniBooNE collaboration for 12 C [4]. Many experimental groups have earlier studied the coherent production of pions induced by neutrinos from other nuclei at higher energies [5]- [7]. Theoretically various authors [8]-[9] have used Adler's PCAC theorem to predict the total cross sections for neutrino reactions, which overestimate the experimental cross sections at low energies. In these calculations the nuclear medium effects are included only through the final state interaction of the outgoing pions with the nucleus using a model of pion nucleus scattering. A theoretical framework for treating the nuclear medium effects in the neutrino production of coherent pions using some model of nuclear structure has been recently discussed by some groups [10] but no definite predictions are made for the kinematics of the neutrino oscillation experiments of present interest.We present in this letter a calculation of the neutrino induced production of coherent pions from nuclei at intermediate neutrino energies. The nuclear medium effects are taken into account in the weak production process as well as in the final state interaction of the outgoing pions with the nucleus. The calculation uses the local density approximation to the de...

Theoretical study of neutrino-induced coherent pion production off nuclei at T2K and MiniBooNE energies

“…[33] and the fact that the coherent pion production reaction in nuclei is mostly driven by the axial part of the interaction, allows us to conclude that most of the previous theoretical studies [9,12,27,30,31] of the pion coherent channel might be overestimating the cross section roughly by a factor of two. This can be easily understood as follows.…”

“…So far the formalism has used the bound wave functions of the nucleus, which appear via the proton and neutron densities, and has considered only a plane wave for the pion. Pion distortion effects are important, specially for | k π | < 0.5 GeV [29,30,31,32], and are considered here by replacing in Eq. (5)…”

“…The model of Ref. [30] uses similar medium corrections and improves on the description of the elementary reaction. On the other hand the final pion distortion is treated in the eikonal approximation which is known to fail at low pion energies.…”

“…[31,32] the authors follow the Kelkar et al calculation in the treatment of the final pion distortion while using, as in Ref. [30], a more complete and fully relativistic elementary amplitude.…”

Coherent pion production off nuclei at T2K and MiniBooNE energies revisited

“…There are other approaches to coherent production that do not rely on PCAC but on microscopic models for pion production at the nucleon level [3,[5][6][7][8][9][10][11][12][13]. The dominant contribution to the elementary amplitude at low energies is given by the ∆-pole mechanism (∆ excitation and its subsequent decay into πN ).…”