First Measurements of the Parity-Violating and Beam-Normal Single-Spin Asymmetries in Elastic Electron-Aluminum Scattering
First Measurements of the Parity-Violating and Beam-Normal Single-Spin Asymmetries in Elastic Electron-Aluminum Scattering
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弹性电子铝散射中宇称破坏和束流法线单自旋不对称性的首次测量
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发表时间：
2018
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通讯作者：
K. Bartlett
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作者：
K. Bartlett
Qweak合作团队首次测量了Al 27核的弹性宇称违反和束正常单自旋不对称性。两者都是杰斐逊实验室Qweak实验期间进行的辅助测量的结果。实验的目的是通过测量违反弹性宇称的电子-质子散射不对称性来确定质子的弱电荷QpW。在实验过程中，辅助测量是在一个单独的铝合金靶上用不同的光束配置进行的，目的是直接测量来自实验的液氢靶单元的铝背景。本文讨论了三个主要结果：宇称违反Al 27不对称性分析用于校正铝靶背景在最终的Qweak分析，其扩展分析导致提取纯弹性宇称违反Al 27不对称性，和弹性束正常单自旋Al 27不对称性的测定。宇称破坏的结果也被用来作出半模型独立的测定铝27中子分布半径，一个重要的测试模型用来描述富中子物质。束法向单自旋不对称性可能揭示了理论与先前在Pb 208上进行的测量之间观察到的不一致，因为Al 27是下一个最高原子质量的原子核。在0.0236± 0.0001GeV处，Al 27的弹性宇称破坏非对称性为1.927± 0.173ppm.这种测量的宇称破坏不对称性意味着Al 27中子分布半径为3.024± 0.104 fm。计算该半径与Al 27质子分布半径之间的差，得到中子皮，其为0.092± 0.104 fm。这个趋肤值在其不确定性范围内与零一致，它证实了对像Al 27这样的轻核的天真期望。束流法向单自旋Al 27的不对称性在电子伏特Q = 0.154 GeV时为−16.322± 2.679 ppm。该值与先前观察到的从轻核测量的束正常单自旋不对称性的趋势一致，这激发了未来测量更高原子质量核的需要。
The Qweak collaboration has made the first measurements of the elastic parity-violating and beam-normal single-spin asymmetries from the Al 27 nucleus. Both are the result of ancillary measurements conducted during the Qweak experiment at Jefferson Lab. The goal of the experimental was to determine the proton’s weak charge, QpW , via a measurement of the elastic parity-violating electron-proton scattering asymmetry. During the experiment, ancillary measurements were made with different beam configurations on a separate aluminum alloy target, in an effort to directly measure the aluminum background coming from the experiment’s liquid hydrogen target cell. This dissertation discusses three primary results: the parity-violating Al 27 asymmetry analysis used to correct for the aluminum target background in the final Qweak analysis, its extended analysis leading to the extraction of the pure elastic parity-violating Al 27 asymmetry, and the determination of the elastic beam-normal single-spin Al 27 asymmetry. The parity-violating result was also used to make a semi model-independent determination of Al 27 neutron distribution radius, an important test for models used to describe neutron-rich matter. The beam-normal single-spin asymmetry stands to possibly shed light on an observed disagreement between theory and a previous measurement performed on Pb 208 , as Al 27 is the next highest atomic mass nucleus to have this observable measured. The elastic parity-violating Al 27 asymmetry was found to be 1.927± 0.173 ppm at 〈Q〉 = 0.0236± 0.0001GeV. This measured parity-violating asymmetry implies a Al 27 neutron distribution radius of 3.024± 0.104 fm. Calculating the difference between this radius and the Al 27 proton distribution radius yields the neutron skin, which was found to be 0.092± 0.104 fm. This skin value is consistent with zero, within its uncertainty, and it confirms the naive expectation for a light nucleus like Al 27 . The beam-normal single-spin Al 27 asymmetry was found to be −16.322± 2.679 ppm at 〈Q〉 = 0.154GeV. This value agrees with the previous observed trend of beam-normal single-spin asymmetries measured from light nuclei, which motivates the need for future measurements of higher atomic mass nuclei.