Measurement of Strange Quark Contributions to the Vector Form Factors of the Proton at Q**2=0.22 (GeV/c)**2

TL;DR

This study measures the parity-violating asymmetry in elastic electron-proton scattering to determine the strange quark contributions to the proton's vector form factors at a specific momentum transfer, providing new insights into proton structure.

Contribution

It presents the first disentanglement of strange electric and magnetic form factors at Q^2=0.22 (GeV/c)^2 using combined backward and forward scattering data.

Findings

Measured asymmetry A_LR = -17.23 ppm with uncertainties.

Determined strange electric form factor G_E^s(0.22) = 0.050 with uncertainties.

Determined strange magnetic form factor G_M^s(0.22) = -0.14 with uncertainties.

Abstract

A new measurement of the parity violating asymmetry in elastic electron scattering on hydrogen at backward angles and at a four momentum transfer of Q^2=0.22 (GeV/c)^2 is reported here. The measured asymmetry is A_LR=(-17.23 +- 0.82_stat +-0.89_syst) ppm. The Standard Model prediction assuming no strangeness is A_0=(-15.87 +- 1.22) ppm. In combination with previous results from measurements at forward angles, it it possible to disentangle for the first time the strange electric and magnetic form factors at this momentum transfer, G_E^s(0.22)=0.050 +- 0.038 +- 0.019 and G_M^s(0.22)=-0.14 +- 0.11 +- 0.11.