Abstract
The study of pion production in nuclei is important for signal and background determinations in current and future neutrino oscillation experiments. The first step, however, is to understand the pion production reactions at the free nucleon level. We present an exhaustive study of the charged-current and neutral-current neutrino and antineutrino pion production off nucleons, paying a special attention to the angular distributions of the outgoing pion. We show, using general arguments, that parity violation and time-reversal odd correlations in the weak differential cross sections are generated from the interference between different contributions to the hadronic current that are not relatively real. Next, we present a detailed comparison of three, state of the art, microscopic models for electroweak pion production off nucleons, and we also confront their predictions with polarized electron data, as a test of the vector content of these models. We also illustrate the importance of carrying out a comprehensive test at the level of outgoing pion angular distributions, going beyond comparisons done for partially integrated cross sections, where model differences cancel to a certain extent. Finally, we observe that all charged and neutral current distributions show sizable anisotropies, and identify channels for which parity violating effects are clearly visible. Based on the above results, we conclude that the use of isotropic distributions for the pions in the center of mass of the final pion-nucleon system, as assumed by some of the Monte Carlo event generators, needs to be improved by incorporating the findings of microscopic calculations.
Highlights
Knowledge of neutrino interaction cross sections is an important and necessary ingredient in any neutrino measurement, and it is crucial for reducing systematic errors affecting present and future neutrino oscillation experiments
We show, using general arguments, that parity violation and time-reversal odd correlations in the weak differential cross sections are generated from the interference between different contributions to the hadronic current that are not relatively real
We have carried out a careful analysis of the pion angular dependence of the charged current (CC) and neutral current (NC) neutrino and antineutrino pion production reaction off nucleons
Summary
Knowledge of neutrino interaction cross sections is an important and necessary ingredient in any neutrino measurement, and it is crucial for reducing systematic errors affecting present and future neutrino oscillation experiments. Though in this work we are mainly interested in neutrino-induced reactions, we shall dedicate a full section to pion electroproduction In this way, we can make a direct comparison of the vector part of the different models and data. With respect to the pion angular dependence of the weak cross sections, we will observe, first of all, that CC and NC distributions show clear anisotropies This means that using an isotropic distribution for the pions in the CM of the final pion-nucleon system, as assumed by some of the Monte Carlo event generators, is not supported by the results of the DCC and HNV models. The final expression, evaluated for massless leptons, is analogous to the corresponding one commonly used for pion electroproduction, which is rederived in Appendix D
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have