美国罗彻斯特大学K. S. McFarland和T. Cai团队在研究中取得进展。他们的最新研究提出了从反中微子质子散射测量轴向矢量形式因子。该研究于2023年2月1日发表于国际一流学术期刊《自然》杂志上。

该团队报告了他们所知的第一次高统计量测量νˉ_μp→μ⁺n的氢原子截面，利用MINERvA11实验的塑料闪烁靶，从自由质子靶中提取F_A，并测量核子轴向电荷半径r_A为0.73±0.17 fm。这里提出的反中微子-氢散射可以在不需要核理论修正的情况下获得轴向形式因子，并能够与日益精确的晶格量子色动力学计算直接比较。

最后，为这一分析而开发的工具和所呈现的结果在理解弱扇区中核子结构的能力方面取得了实质性的进步，也有助于当前和未来的中微子振荡实验更好地约束中微子相互作用模型。

据了解，从核子中散射高能粒子探测它们的结构，就像在使用电子束建立质子非零大小的实验中所做的那样。使用带电轻子作为散射探针可以测量电荷的分布，这被编码在核子的矢量形式因子中。散射弱相互作用的中微子提供了测量核子矢量和轴向矢量形式因子的机会，从而提供了对其结构的额外的、互补的探针。核子跃迁轴向形式因子F_A可以通过中微子散射自由核子ν_μn→μ⁻p和ν¯_μp→μ⁺n来测量，作为负四动量传递平方(Q²)的函数。到目前为止，F_A(Q²)已从中微子-氘散射中束缚核子中提取，这需要不确定的核修正。

附：英文原文

Title: Measurement of the axial vector form factor from antineutrino–proton scattering

Author: Cai, T., Moore, M. L., Olivier, A., Akhter, S., Dar, Z. Ahmad, Ansari, V., Ascencio, M. V., Bashyal, A., Bercellie, A., Betancourt, M., Bodek, A., Bonilla, J. L., Bravar, A., Budd, H., Caceres, G., Carneiro, M. F., Daz, G. A., da Motta, H., Felix, J., Fields, L., Filkins, A., Fine, R., Gago, A. M., Gallagher, H., Gilligan, S. M., Gran, R., Granados, E., Harris, D. A., Henry, S., Jena, D., Jena, S., Kleykamp, J., Klustov, A., Kordosky, M., Last, D., Le, T., Lozano, A., Lu, X.-G., Maher, E., Manly, S., Mann, W. A., Mauger, C., McFarland, K. S., Messerly, B., Miller, J., Moreno, O., Morfn, J. G., Naples, D., Nelson, J. K., Nguyen, C., Paolone, V., Perdue, G. N., Plows, K.-J., Ramrez, M. A., Ransome, R. D., Ray, H., Ruterbories, D., Schellman, H., Salinas, C. J. Solano, Su, H., Sultana, M., Syrotenko, V. S., Valencia, E., Vaughan, N. H., Waldron, A. V., Wascko, M. O.

Issue&Volume: 2023-02-01

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 beams1. 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 nucleon2. 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, FA, can be measured from neutrino scattering from free nucleons, νμn→μp and νˉμp→μ+n

, as a function of the negative four-momentum transfer squared (Q2). Up to now, FA(Q2) has been extracted from the bound nucleons in neutrino–deuterium scattering3,4,5,6,7,8,9, which requires uncertain nuclear corrections10. Here we report the first high-statistics measurement, to our knowledge, of the νˉμp→μ+n

cross-section from the hydrogen atom, using the plastic scintillator target of the MINERvA11 experiment, extracting FA from free proton targets and measuring the nucleon axial charge radius, rA, to be 0.73±0.17fm. 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 computations12,13,14,15. 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 experiments16,17,18,19,20 to better constrain neutrino interaction models.

DOI: 10.1038/s41586-022-05478-3

Source: https://www.nature.com/articles/s41586-022-05478-3