Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data
Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data
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DOI：
10.1103/physrevlett.114.062003
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发表时间：
2015-02-10
影响因子：
8.6
通讯作者：
Zonta, I.
中科院分区：
文献类型：
--
作者：
Adikaram, D.;Rimal, D.;Zonta, I.
使用非极化和极化电子散射提取的质子电形状因子G（E）（p）的值之间存在显著差异。计算预测，小的双光子交换（TPE）贡献可以显著影响G（E）（p）的提取。从非极化的电子-质子截面。我们确定了TPE的贡献，通过测量正电子-质子的比例，电子-质子的弹性散射截面使用同时，第三电子-正电子束入射到液氢目标和检测散射粒子在杰斐逊实验室CLAS检测器。这种新的技术使我们能够同时覆盖虚拟光子偏振（λ）和动量传递（Q（2））的宽范围，以及消除与亮度相关的系统误差。在Q（2）= 1.45 GeV ~ 2时，截面比随电子能量的减小而增大。这一测量结果与Q（2）处的形状因子差异的大小一致，约为1.75 GeV 2，并且与包括核子和Delta中间态的强子计算一致，这些计算已被证明可以解决高达2-3 GeV 2的差异。
There is a significant discrepancy between the values of the proton electric form factor, G(E)(p), extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of G(E)(p). from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (epsilon) and momentum transfer (Q(2)) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing epsilon at Q(2) = 1.45 GeV2. This measurement is consistent with the size of the form factor discrepancy at Q(2) approximate to 1.75 GeV2 and with hadronic calculations including nucleon and Delta intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV2.