NUFACT2014, XVIth International Workshop on Neutrino Factories and Future Neutrino Beam Facilities

Using electron scattering to constrain the axial-vector form factor

28 Aug 2014, 11:25

25m

Western Infirmary Lecture Theatre (University of Glasgow)

WG2: Neutrino Scattering Physics

Speaker

Dr Raúl González-Jiménez (Departamento de Física Atómica, Molecular y Nuclear, University of Seville)

Description

An important number of neutrino scattering experiments involve nuclei as targets. Many of these experiments are placed at the intermediate energy regime (from hundreds of MeV to a few GeV) where the quasi-elastic (QE) scattering process is one of the dominant channels in the reaction mechanism. Some examples are MiniBooNE, Miner$\nu$a, NOMAD and T2K experiments. We have analysed elastic electron-proton and QE electron-nucleus scattering reactions aiming to show how these processes can be used as tools to constrain the axial-vector form factor. This is a fundamental ingredient for the description of QE neutrino-nucleus cross sections. % From an experimental point of view, the use of electrons as projectiles, in comparison to neutrinos, has important advantages. For instance, it is possible to produce monochromatic beams with a better control of the kinematics that makes easier to determine the channels involved in the reaction. Although the electromagnetic (EM) interaction is dominant in electron-nucleon/nucleus scattering reactions, the electron feels also the weak neutral current (WNC) interaction. The parity violating asymmetry (${\cal A}^{PV}$) is defined as ${\cal A}^{PV}=(\sigma^+ - \sigma^-)/(\sigma^+ - \sigma^-)$, where $\sigma^{+/-}$ represents the electron-proton or electron-nucleus differential cross section with positive/negative helicity of the incident electron. This observable is different from zero due exclusively to the presence of the weak interaction. Thus, the PV asymmetry serves to study the different ingredients that enter in the nucleon weak neutral current, particularly, the WNC form factors. There exist an important number of PV electron-proton asymmetry data taken at different kinematics. By performing a statistical analysis of the full set of data we provide estimates on the electric and magnetic strange form factors ($G_{E,M}^s$) and on the axial-vector one ($G_A$). Additionally, we find that these three form factors ($G_{E,M}^s$ and $G_A$) are strongly correlated % (see refs. [1,2] for more details). We also present a brief discussion on the PV asymmetry linked to the QE electron-nucleus scattering process. This observable could provide information on the WNC nucleon form factors that complements the one obtained from the elastic reaction. In particular, it can help to constrain the isovector contribution in the axial-vector form factor [3]. [1] R. González-Jiménez, J. A. Caballero, T. W. Donnelly. arXiv:1403.5119 [nucl-th] (2014). [2] R. González-Jiménez, J. A. Caballero, T. W. Donnelly. Phys. Rep., 524, 1 (2013). [3] R. González-Jiménez, J. A. Caballero, T. W. Donnelly. In preparation.

Presentation materials

Slides

Raul_Gonzalez-Jimenez_NuFact_presentation.pdf