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Measurement of Parity Violation in np Capture: the NPDGamma Experiment

机译:np捕获中奇偶校验违规的测量:NPDGamma实验

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The NPDGamma experiment will measure the parity-violating directional gamma ray asymmetry A_(gamma) in the reaction n-vector + p -> d + gamma. Ultimately, this will constitute the first measurement in the neutron-proton system that is sensitive enough to challenge modern theories of nuclear parity violation, providing a theoretically clean determination of the weak pion-nucleon coupling. A new beamline at the Los Alamos Neutron Science Center (LANSCE) delivers pulsed cold neutrons to the apparatus, where they are polarized by transmission through a large volume polarized ~(3)He spin filter and captured in a liquid para-hydrogen target. The 2.2 MeV gamma rays from the capture reaction are detected in an array of CsI(Tl) scintillators read out by vacuum photodiodes operated in current mode. We will complete commissioning of the apparatus and carry out a first measurement at LANSCE in 2004-05, which would provide a statistics-limited result for A_(gamma) accurate to a standard uncertainty of +-5 X 10~(-8) level or better, improving on existing measurements in the neutron-proton system by a factor of 4. Plans to move the experiment to a reactor facility, where the greater flux would enable us to make a measurement with a standard uncertainty of +-1 X 10~(-8), are actively being pursued for the longer term.
机译:NPDGamma实验将测量反应n-向量+ p-> d +γ中违反奇偶性的方向伽马射线不对称性A_(γ)。最终,这将构成中子-质子系统中的第一个测量,该测量足够灵敏以挑战现代违反核对等的理论,从而为弱的π-核子耦合提供理论上明确的确定。洛斯阿拉莫斯中子科学中心(LANSCE)的一条新射束线将脉冲冷中子传递至该装置,在其中通过通过大体积极化〜(3)He自旋滤光片传输而被极化,并被捕获在液态对氢目标中。在一系列以当前模式操作的真空光电二极管读出的CsI(T1)闪烁体阵列中检测到来自捕获反应的2.2 MeV伽马射线。我们将完成该设备的调试,并于2004-05年在LANSCE进行首次测量,这将为A_(γ)提供统计量受限的结果,其准确度可达到+ -5 X 10〜(-8)的标准不确定度或更好,将中子-质子系统中的现有测量值提高4倍。计划将实验移至反应堆设施,在该设施中,更大的通量将使我们能够进行标准不确定度为+ -1 X 10的测量〜(-8)是长期的积极追求。

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