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1. Nucleon binding energy and transverse momentum imbalance in neutrino-nucleus reactions

   T. Cai, et al. ( April 2020 , Physical review)

   We have measured new observables based on the final state kinematic imbalances in the mesonless production of ν μ + A → μ − + p + X in the MINERνA tracker. Components of the muon-proton momentum imbalances parallel ( δ p Ty ) and perpendicular ( δ p Tx ) to the momentum transfer in the transverse plane are found to be sensitive to the nuclear effects such as Fermi motion, binding energy, and non-quasielastic (QE) contributions. The QE peak location in δ p Ty is particularly sensitive to the binding energy. Differential cross sections are compared to predictions from different neutrino interaction models. The Fermi gas models presented in this study cannot simultaneously describe features such as QE peak location, width, and the non-QE events contributing to the signal process. Correcting the genie’s binding energy implementation according to theory causes better agreement with data. Hints of proton left-right asymmetry are observed in δpTx. Better modeling of the binding energy can reduce the bias in neutrino energy reconstruction, and these observables can be applied in current and future experiments to better constrain nuclear effects. 

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2. Nucleon binding energy and transverse momentum imbalance in neutrino-nucleus reactions

   Cai, T. ; Lu, X.-G. ; Harewood, L. A. ; Wret, C. ; Akbar, F. ; Andrade, D. A. ; Ascencio, M. V. ; Bellantoni, L. ; Bercellie, A. ; Betancourt, M. ; et al ( May 2020 , Physical review)

   We have measured new observables based on the final state kinematic imbalances in the mesonless production of νμ + A → μ− + p + X in the MINERνA tracker. Components of the muon-proton momentum imbalances parallel (δpTy) and perpendicular (δpTx) to the momentum transfer in the transverse plane are found to be sensitive to the nuclear effects such as Fermi motion, binding energy, and non-quasielastic (QE) contributions. The QE peak location in δpTy is particularly sensitive to the binding energy. Differential cross sections are compared to predictions from different neutrino interaction models. The Fermi gas models presented in this study cannot simultaneously describe features such as QE peak location, width, and the non-QE events contributing to the signal process. Correcting the genie’s binding energy implementation according to theory causes better agreement with data. Hints of proton left-right asymmetry are observed in δpTx. Better modeling of the binding energy can reduce the bias in neutrino energy reconstruction, and these observables can be applied in current and future experiments to better constrain nuclear effects. 

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3. Nucleon binding energy and transverse momentum imbalance in neutrino-nucleus reactions

   https://doi.org/10.1103/PhysRevD.101.092001  

   Cai, T. ; Lu, X.-G. ( May 2020 , Physical review)

   null (Ed.)

   We have measured new observables based on the final state kinematic imbalances in the mesonless production of ν μ + A → μ − + p + X in the MINERνA tracker. Components of the muon-proton momentum imbalances parallel ( δ p Ty ) and perpendicular ( δ p Tx ) to the momentum transfer in the transverse plane are found to be sensitive to the nuclear effects such as Fermi motion, binding energy, and non-quasielastic (QE) contributions. The QE peak location in δ p Ty is particularly sensitive to the binding energy. Differential cross sections are compared to predictions from different neutrino interaction models. The Fermi gas models presented in this study cannot simultaneously describe features such as QE peak location, width, and the non-QE events contributing to the signal process. Correcting the genie’s binding energy implementation according to theory causes better agreement with data. Hints of proton left-right asymmetry are observed in δ p Tx . Better modeling of the binding energy can reduce the bias in neutrino energy reconstruction, and these observables can be applied in current and future experiments to better constrain nuclear effects. 

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4. Measurement of final-state correlations in neutrino muon-proton mesonless production on hydrocarbon at $langle E_nurangle=3$ GeV

   Lu, X. G. ( July 2019 , Physical review letters)

   Final-state kinematic imbalances are measured in mesonless production of νμ+A→μ−+p+X in the MINERvA tracker. Initial- and final-state nuclear effects are probed using the direction of the μ−−p transverse momentum imbalance and the initial-state momentum of the struck neutron. Differential cross sections are compared to predictions based on current approaches to medium modeling. These models underpredict the cross section at intermediate intranuclear momentum transfers that generally exceed the Fermi momenta. As neutrino interaction models need to correctly incorporate the effect of the nucleus in order to predict neutrino energy resolution in oscillation experiments, this result points to a region of phase space where additional cross section strength is needed in current models, and demonstrates a new technique that would be suitable for use in fine-grained liquid argon detectors where the effect of the nucleus may be even larger. 

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5. Measurement of the axial vector form factor from antineutrino–proton scattering

   https://doi.org/10.1038/s41586-022-05478-3  

   Cai, T. ; Moore, M. L. ; Olivier, A. ; Akhter, S. ; Dar, Z. Ahmad ; Ansari, V. ; Ascencio, M. V. ; Bashyal, A. ; Bercellie, A. ; Betancourt, M. ; et al ( February 2023 , Nature)

   Abstract Scattering of high energy particles from nucleons probes their structure, as was done in the experiments that established the non-zero size of the proton using electron beams 1 . The use of charged leptons as scattering probes enables measuring the distribution of electric charges, which is encoded in the vector form factors of the nucleon 2 . Scattering weakly interacting neutrinos gives the opportunity to measure both vector and axial vector form factors of the nucleon, providing an additional, complementary probe of their structure. The nucleon transition axial form factor, F A , can be measured from neutrino scattering from free nucleons, ν μ n  →  μ − p and $${\bar{\nu }}_{\mu }p\to {\mu }^{+}n$$ ν ¯ μ p → μ + n , as a function of the negative four-momentum transfer squared ( Q 2 ). Up to now, F A ( Q 2 ) has been extracted from the bound nucleons in neutrino–deuterium scattering 3–9 , which requires uncertain nuclear corrections 10 . Here we report the first high-statistics measurement, to our knowledge, of the $${\bar{\nu }}_{\mu }\,p\to {\mu }^{+}n$$ ν ¯ μ p → μ + n cross-section from the hydrogen atom, using the plastic scintillator target of the MINERvA 11 experiment, extracting F A from free proton targets and measuring the nucleon axial charge radius, r A , to be 0.73 ± 0.17 fm. The antineutrino–hydrogen scattering presented here can access the axial form factor without the need for nuclear theory corrections, and enables direct comparisons with the increasingly precise lattice quantum chromodynamics computations 12–15 . Finally, the tools developed for this analysis and the result presented are substantial advancements in our capabilities to understand the nucleon structure in the weak sector, and also help the current and future neutrino oscillation experiments 16–20 to better constrain neutrino interaction models. 

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