Progress on Constraining the Strange Quark Contribution to the Proton Axial Form Factor

We report on a global fit of neutral-current elastic (NCE) neutrino-scattering data and parity-violating electron-scattering (PVES) data with the goal of determining the strange quark contribution to the vector and axial form factors of the proton. Previous fits [1,2] of this form included data from a variety of PVES experiments (PVA4, HAPPEx, G0, SAMPLE) and the NCE neutrino and anti-neutrino data from BNL E734. These fits did not constrain the strangeness form factor to the axial form factor G_A^s(Q²) at low Q² very well because there was no NCE data for Q² < 0.45 GeV². Our new fit includes for the first time MiniBooNE NCE data from both neutrino and anti-neutrino scattering; this experiment used a hydrocarbon target and so a model of the neutrino interaction with the carbon nucleus was required. Three different nuclear models have been employed; a relativistic Fermi gas model, the SuperScaling Approximation model, and a spectral function model [3]. We find a tremendous improvement in the constraint of G_A^s(Q²) at low Q² compared to previous work, although more data is needed from NCE measurements that focus on exclusive single-proton final states, for example from MicroBooNE [4].

[1] S.F. Pate, D. McKee, V. Papavassiliou, Phys. Rev. C78, 015207 (2008)

[2] S.F. Pate, D. Trujillo, EPJ Web of Conferences 66, 06018 (2014)

[3] C. Giusti and M.V. Ivanov, J. Phys. G: Nucl. Part. Phys. 47 024001 (2020)

[4] L. Ren, NuFact 2021, PoS, 402, 205 (2022), 10.22323/1.402.0205