Modeling neutrino-nucleus interactions for neutrino oscillation experiments
We present our recent progress on the relativistic modeling of neutrino-nucleus reactions for their implementation in MonteCarlo event generators (GENIE, NEUT) employed in neutrino oscillation experiments. We compare charged-current neutrino () and antineutrino () cross sections obtained within the SuSAv2 model, which is based on the Relativistic Mean Field theory and on the analysis of the superscaling behavior exhibited by () data. We also evaluate and discuss the impact of multi-nucleon excitations arising from 2p-2h states excited by the action of weak forces in a fully relativistic framework, showing for the first time their implementation in GENIE and their comparison with recent T2K data.
Current efforts in long-baseline experiments are aimed at improving knowledge of oscillations, where the development and implementation of realistic -nucleus interaction models are essential to constrain experimental uncertainties. The current state of the art for experimental systematics is in the region of 5-10 Abe2016 () and are mostly related to flux and cross section predictions (3-4). A decrease of 2-3 on these uncertainties would allow to shorten running time and experimental costs (reducing by half either the experimental exposure or the detector volume) while increasing the sensitivity to determine mass hierarchy or CP violation in the neutrino sector. Such a reduction of systematics will therefore represent an essential step toward understanding the matter-antimatter asymmetry in the Universe, whilst also aiding in other areas of fundamental physics, such as the analysis of supernovae explosions and the search for both sterile and proton decay. Accordingly, an accurate understanding of interaction physics is essential for current and upcoming experiments. Thus, the SuSAv2-MEC approach Megias:2016ee (); Megias:2016nu (); Ivanov14 () is applied to the analysis of data from oscillation experiments with the aim of shedding light on the systematics arising from nuclear effects in both initial and final states. For practical purposes, the SuSAv2 model and the 2p-2h MEC contributions can be described in a simple way for different kinematics and nuclei MegiasOxygen (); MegiasMinerva (); ARFG (); nppairs (); density (), translating sophisticated and demanding microscopic calculations into a relatively straightforward formalism hence easing its implementation in event generators. In Fig. 1, we show the comparison of the SuSAv2-MEC model, which is based on relativistic, microscopic calculations simomec (); megiasmec (), with T2K CC0Np data cc0pinp (); dolan () for 0 protons above 500 MeV/c (left panel). The 1p1h channel corresponds to RMF-based calculations and the effect of emission followed by re-absorption in the nuclear medium is provided by the GENIE -nucleus event generator genie (). The 2p2h channel is generated for the first time by new implementation of the SuSAv2-MEC model within GENIE. The accurate modeling of 2p2h microscopic calculations (thick dot-dashed lines) within GENIE (solid maroon line) can be observed in the right panel, where a comparison of the full SuSAv2-MEC model with CC0 data cc0pi () is also shown. Its capability to describe data in a wide energy range and its ease to be implemented in event generators makes the SuSAv2-MEC model a promising candidate to reduce experimental systematics in current and future experiments.
Acknowledgements.This work was partially supported by the Spanish Ministerio de Economia y Competitividad and ERDF (European Regional Development Fund) under contracts FIS2017-88410-P, and by the Junta de Andalucia (grant No. FQM160). GDM acknowledges support from a Junta de Andalucia fellowship (FQM7632, Proyectos de Excelencia 2011). We acknowledge the support of CEA, CNRS/IN2P3 and P2IO, France; and the MSCA-RISE project JENNIFER, funded by EU grant n.644294, for supporting the EU-Japan researchersâ mobility.
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