Enhancing the direct search for dark matter in the XENON nT experiment with a water Cerenkov neutron detector

在2022财年，实现了三个主要的中子否决里程碑。)钆水净化系统（GdWPS）首次在闭环循环（CLC）中使用纯水，与含有中子否决权的700吨水屏蔽分离。这样我们就验证了它所有部件的基本功能。在整个700吨XENONnT水屏蔽（包括探测器的介子和中子否决权）中保持水质，我们的GdWPS证明它提高了屏蔽纯水的质量。在返回CLC操作后，我们最终向闭环中的~3吨水中加入了硫酸钆（GdS），使其在1月份达到了硫酸钆的最终目标浓度0.5%。对全水盾中溶解GdS的中子否决操作参数进行了优化。这三个里程碑意味着现在中子否决系统已经准备好装载GdS，从而达到我们设计的中子标记效率。不幸的是，实验的其余部分还没有达到我们现在可以进行的状态，但我们已经准备好了，我们所有的系统都已显示出预期的效果。我们可以随时溶解GdS，只要GdS均匀分布在700吨的水盾中，就可以达到充分的效率。

Three major neutron veto milestones were reached in FY2022:1.) The gadolinium water purification system (GdWPS) was first commissioned with pure water in closed loop circulation (CLC), separate from the 700 tonne water shield that contains also the neutron veto. We thus verified the basic functions of all its components.2.) Maintaining water quality in the full 700 tonne XENONnT water shield - which comprises the detector's muon and neutron veto - our GdWPS proved that it improved the quality of the shields pure water.3.) After returning to CLC operation we finally added gadolinium sulfate (GdS) to the ~3 tons of water in the closed loop, bringing it up to the ultimate target concentration of 0.5 % of gadolinium sulfate in January. We optimize operating parameters for coming neutron veto operation with GdS dissolved in the whole water shield.Together these three milestones mean that now the neutron veto systems are all ready to be loaded with GdS and thus reach our design neutron tagging efficiency. Unfortunately the rest of the experiment is not yet in a state that we can proceed at this point in time, but we are ready and all our systems have been shown to work as expected. We can dissolve GdS at any time and reach full efficiency as soon as the GdS is evenly distributed in the 700 tonne water shield.