Axial and pseudoscalar form factors from charged current quasielastic neutrino-nucleon scattering

Oleksandr Tomalak

doi:10.1103/physrevd.103.013006

Oleksandr Tomalak

Open Access

https://doi.org/10.1103/physrevd.103.013006

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Abstract

We study the scattering of neutrinos on polarized and unpolarized free nucleons, and also the polarization of recoil particles in these scatters. In contrast to electromagnetic processes, the parity-violating weak interaction gives rise to large spin asymmetries at leading order. Future polarization measurements could provide independent access to the proton axial structure and allow the first extraction of the pseudoscalar form factor from neutrino data without the conventional partially conserved axial current (PCAC) ansatz and assumptions about the pion-pole dominance. The pseudoscalar form factor can be accessed with precise measurements with muon (anti)neutrinos of a few hundreds $\mathrm{MeV}$ of energy or with tau (anti)neutrinos. The axial form factor can be extracted from scattering measurements using accelerator neutrinos of all energies.

Highlights

Neutrino physics is entering a precision era driven by new experiments and modern detector technology
An ambitious goal of percent level measurements calls for precise inputs from nuclear and hadronic physics [1,2,3]
The axial and pseudoscalar form factors require weak probes with neutrinos [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26] often accompanied with nuclear physics effects [27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44] or measurements of pion electroproduction [45,46,47,48,49,50,51]

Summary

INTRODUCTION

Neutrino physics is entering a precision era driven by new experiments and modern detector technology. We study the sensitivity of single-spin asymmetries in (anti)neutrino charged current quasielastic scattering on free nucleons to the axial and the pseudoscalar form factors. The matrix element of the quark current uγμPLd inside the nucleon in neutrino-neutron CCQE νln → l−p, can be expressed in terms of Sachs electric, GVE, and magnetic, GVM, isovector, axial, FA, and pseudoscalar, FP, form factors as [100]2. For (anti)neutrino scattering on the polarized nucleon target with the spin four-vector S, the asymmetry T is determined by the following structure-dependent factors AT, BT, and CT4: AT þGVM2rðF2GAVM−ηηGGVEVEÞð−pτ0Fþ·ASrþÞ2−2τ2FηGP ðVMkG· VESðÞk−0 ·. Up to lepton-mass-suppressed terms, the asymmetry Rl reaches maximum by an absolute value at backward angles when the momentum transfer is Q2þ For these kinematic boundaries, the longitudinal target single-spin asymmetry is given by. Flux normalization errors and detector systematics largely cancel in the asymmetry expression paving the way to clean probes of the nucleon axial and pseudoscalar form factors from polarization observables

POLARIZATION OBSERVABLES WITH MUON AND ELECTRON NEUTRINOS

AXIAL FORM FACTOR AT GEV ENERGIES

POLARIZATION OBSERVABLES WITH TAU NEUTRINOS

CONCLUSIONS