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 × 10¹⁸ 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.

我们报告了杰斐逊实验室用于测量的无窗，高密度气流目标 ${\mathrm{[R}}_p$，质子的均方根电荷半径。该目标实现了2×10 ^18个原子/ cm的面密度的设计目标${}^{\mathrm{2个}}$，气体均匀分布在电池的4厘米长，电池外部的残留气体少于1％。这种设计消除了靶细胞端盖的散射，这是以前在电子散射实验中测量质子电荷半径所特有的问题，并允许精确，独立于模型的提取${\mathrm{[R}}_p$ 通过达到前所未有的低价值 ${问}^{\mathrm{2个}}$，是电子将四动量传递到质子的平方。