NuFIT

NuFIT
Name	NuFIT
Developer	Institute for Nuclear and Particle Physics collaborations
Released	2012
Latest release	ongoing
Programming language	Python, Fortran, C++
Operating system	Cross-platform
License	Open-source / academic

NuFIT is a collaborative global analysis framework producing best-fit values and confidence regions for neutrino oscillation parameters. It aggregates results from reactor, accelerator, solar, and atmospheric neutrino experiments to deliver standardized parameter estimates for the three-flavor neutrino mixing paradigm. NuFIT outputs are widely used by experimental collaborations, phenomenologists, and review committees to compare hypotheses involving neutrino masses, mixing angles, and CP violation.

Overview

NuFIT combines published results from experiments such as Super-Kamiokande, SNO (Sudbury Neutrino Observatory), Borexino, KamLAND, Daya Bay, RENO, Double Chooz, T2K, NOvA, MINOS, IceCube, ANTARES, K2K, SAGE (experiment), GALLEX, Homestake experiment, OPERA, MicroBooNE, MiniBooNE, CHOOZ, and KAMLAND-Zen to perform global fits. The project interfaces with theoretical inputs from groups and institutions such as Particle Data Group, Fermi National Accelerator Laboratory, CERN, Institut de Physique Théorique, Max Planck Institute for Physics, and ICTP. Its outputs are cited by review articles and working groups at venues including Neutrino 2020, Pontecorvo Lectures, International Workshop on Neutrino Telescopes, and policy white papers by agencies like DOE and ERC.

Data and Methodology

NuFIT ingests oscillation data sets, systematic error matrices, and likelihood surfaces released by collaborations including DUNE (experiment), Hyper-Kamiokande, JUNO, IceCube-Gen2, and others. The framework implements χ² minimization and Bayesian sampling techniques using tools influenced by software libraries such as ROOT (software), SciPy, PyStan, MultiNest, and BAT (Bayesian Analysis Toolkit). It adopts oscillation probabilities computed with matter effects following formalisms developed by Mikheyev–Smirnov–Wolfenstein, building on theoretical work from Bruno Pontecorvo, Ziro Maki, Masami Nakagawa, Shoichi Sakata, and later refinements by Wolfgang Pauli-era formalisms. Systematics treatment parallels methods used by NOvA and T2K, and flux modeling references predictions from Hahn-Meitner Institute-era reactor studies, solar models by Bahcall and neutrino cross-section inputs from GENIE (neutrino Monte Carlo generator) and NEUT.

Global Fit Results

NuFIT publishes best-fit values and allowed ranges for mixing angles θ12, θ13, θ23, mass-squared differences Δm21^2 and Δm31^2 (or Δm32^2), and the CP-violating phase δCP. Recent releases summarize tension and consistency among data from Daya Bay, RENO, T2K, NOvA, JUNO, and KamLAND. Results address the neutrino mass ordering question contrasting normal ordering favored by analyses incorporating JUNO sensitivity and accelerator data from T2K and NOvA against inverted ordering scenarios discussed in literature by Capozzi et al. and Gonzalez-Garcia. Confidence regions are presented in two-dimensional projections akin to plots used by Particle Data Group and by analysis teams at CERN workshops. NuFIT also quantifies marginalized likelihoods for parameters relevant to neutrinoless double-beta decay experiments like GERDA, CUORE, and KamLAND-Zen.

Impact on Neutrino Physics

NuFIT outputs serve as benchmarks for theoretical model-building at institutions such as Perimeter Institute, Institute for Advanced Study, Kavli Institute for Theoretical Physics, and university groups at MIT, University of Tokyo, Oxford University, University of California, Berkeley, and Princeton University. They inform experimental design studies for projects including DUNE (experiment), Hyper-Kamiokande, JUNO, IceCube-Gen2, KM3NeT, and prospective proposals at SNOLAB. The global fits influence global analyses of leptogenesis scenarios advanced by researchers at CERN and DESY, and feed into cosmological constraints from collaborations such as Planck (spacecraft), SDSS, and teams working on Euclid (spacecraft). NuFIT outputs are incorporated into phenomenological tests of sterile neutrino hypotheses tested by LSND, MiniBooNE, and future short-baseline programs like MicroBooNE and ICARUS.

History and Development

The NuFIT effort emerged from the consolidation of independent global-fit initiatives in the early 2010s, succeeding legacy analyses by groups led by researchers associated with Gonzalez-Garcia, Maltoni, Fogli, and the Valencia group. Milestones include the incorporation of high-precision reactor results from Daya Bay and accelerator appearance results from T2K and NOvA, updates following significant results presented at conferences like Neutrino 2018 and ICHEP, and regular versioned releases parallel to data releases by major collaborations. The project has evolved through contributions from researchers at Instituto de Física Corpuscular, IFIC, UNAM, Università di Torino, LAPTh, and national laboratories such as INR (Russian Academy of Sciences).

Software and Accessibility

NuFIT distributes tables, contour plots, and likelihood data files accessible to the community and is compatible with analysis toolchains used at Fermilab, CERN, and university groups. The code base leverages languages and ecosystems familiar to particle physicists, integrating with Python (programming language), Fortran, and C++ packages. Documentation and result summaries are prepared for working groups at meetings like Neutrino 2020 and for citation in review venues such as Reviews of Modern Physics and Annual Review of Nuclear and Particle Science. Researchers at JINA-CEE and collaborative networks use NuFIT results for cross-disciplinary studies spanning particle physics and astrophysics.

Category:Neutrino physics