The PRad windowless gas flow target

We report on a windowless, high-density, gas-flow target at Jefferson Lab that was used to measure r(p), the root-mean-square charge radius of the proton. The target achieved its design goal of an areal density of 2 x 10(18) atoms/cm(2), with the gas uniformly distributed over the 4 cm length of the cell and less than 1% residual gas outside the cell. This design eliminated scattering from the end caps of the target cell, a problem endemic to previous measurements of the proton charge radius in electron scattering experiments, and permitted a precise, model-independent extraction of r(p) by reaching unprecedentedly low values of Q(2), the square of the electron's transfer of four-momentum to the proton.

Automated summary

The study presents a windowless, high-density, gas-flow target at Jefferson Lab, successfully achieving its design goal to accurately measure the root-mean-square charge radius of the proton. By eliminating scattering from the end caps of the target cell, the study permits a precise extraction of the proton charge radius.