Measurement of a Lepton Lepton Electroweak Reaction (MOLLER): An Ultraprecise Measurement of the Weak Mixing Angle using Moller Scattering at Jefferson Laboratory

欧洲核子研究中心希格斯玻色子的发现是对标准模型的期待已久的验证，该模型总结了我们目前对基本粒子及其相互作用的理解。四种基本力是引力、电磁力、弱核力和强核力。普通物质由原子核中以质子和中子形式结合在一起的基本粒子、电子和上下夸克的子集组成。电磁力和弱力已经成功地统一成了量子电弱理论，而将其他两种力统一起来也是亚原子理论家的目标。尽管标准模型取得了成功，但它并不完整。宇宙中大约97%的物质和能量都是未知的；这种“暗”物质和能量是从天体物理观测中解释星系自转速度所需要的，但还不包括在标准模型中。此外，对于弱力的中介体Z玻色子质量处的弱混合角的两个最精确的测量彼此不一致，也不符合希格斯的测量质量。*Moller合作将测量极化电子-电子(Moller)散射中的宇称破坏不对称性，以便超精确地测量弱混合角。这是一个在标准模型中有明确预测的量，由于测量的精确度，任何与预测值的偏差都是新物理的标志。这种不对称性是由于通过光子(电磁力的中介体)和Z玻色子的散射的干涉而产生的。这种不对称性预计在十亿分之三十五(Ppb)的数量级上，合作伙伴将测量到0.73 ppb以内，分数精度约为2%。这项测量将在杰斐逊实验室A厅进行，使用11 GeV纵向极化电子入射到1.5米长的液氢靶上。阿环面光谱仪将被用来分离莫勒电子和氢中质子的散射电子，并将它们聚焦在目标下游28米的探测器平面上。散射电子的积分产额将由224个石英切伦科夫探测器阵列测量。穆勒实验将与对撞机上进行的两种最精确的弱混合角测量中的任何一种一样好，并将有助于解决与希格斯质量的差异。它是对在高能对撞机上直接寻找新物理的补充。由于其精确度，穆勒在接触相互作用尺度远远超过10TeV的标准模型之外具有发现物理的潜力，这一灵敏度水平将在未来十年内即使在对撞机上也无法获得。

The discovery of the Higgs boson at CERN was the long-awaited validation of the Standard Model, which summarizes our current understanding of fundamental particles and their interactions. The four fundamental forces are the gravitational, electromagnetic, weak and strong nuclear forces. Ordinary matter consists of a subset of the fundamental particles, electrons and up- and down- quarks bound together as protons and neutrons in the nucleus. The electromagnetic and weak forces have been successfully unified into a quantum electroweak theory, and it is a goal of subatomic theorists to unify the other two forces as well. Despite the success of the Standard Model, it is not complete. Approximately 97% of the matter and energy in the universe is unknown; this "dark" matter and energy is needed to explain the rotation rates of galaxies from astrophysical observations, but is not yet included in the Standard Model. In addition, the two most precise measurements of the weak mixing angle at the mass of the Z boson, which is the mediator of the weak force, do not agree with each other or the measured mass of the Higgs.******The MOLLER collaboration will measure the parity-violating asymmetry in polarized electron-electron (Moller) scattering in order to make an ultra-precise measurement of the weak mixing angle. This is a quantity with a definite prediction in the Standard Model and due to the precision of the measurement any deviation from the predicted value is a sign of new physics. The asymmetry arises due to the interference of scattering via a photon (mediator of the electromagnetic force) and a Z boson. This asymmetry is expected to be on the order of 35 parts per billion (ppb), and the collaboration will measure it to within 0.73 ppb, a fractional accuracy of about 2%. The measurement will be carried out in Hall A of Jefferson Lab, using 11 GeV longitudinally polarized electrons incident on a 1.5 m liquid hydrogen target. Atoroidal spectrometer will be used to separate the Moller electrons from those which scatter from the protons in the hydrogen, and focus them at the detector plane 28 m downstream of the target. The integrated yield of the scattered electrons will be measured by an array of 224 quartz Cherenkov detectors.******The MOLLER experiment will be as good as either of the two most precise measurements of the weak mixing angle made at colliders, and will help to resolve the discrepancy with the Higgs mass. It serves as a complement to direct searches for new physics at high energy colliders. Due to its precision MOLLER has discovery potential for physics beyond the Standard Model with contact interaction scales well over 10 TeV, a level of sensitivity which will not be accessible, even at colliders, for the next decade.