nEXO photo-detector development

该提案的目的是通过以下方式支持nEXO实验光电探测器的开发：1）促进加拿大最先进技术的发展; 2）允许加拿大小组继续解决与在nEXO探测器中使用硅光电倍增器（SiPM）有关的关键问题。项目1）是NSERC推广由舍布鲁克大学（QC）推动的三维集成技术（3D-SiPM）的独特机会，预计将彻底改变高速光子探测。项目2）对于保持加拿大在nEXO光电探测器组中的领导地位至关重要，并确保nEXO实验向美国能源部（DOE）提供了一个充分的证据，以证明预计将在2017年发生的中微子较少的双β衰变选择。 加拿大小组在nEXO合作中发挥着重要作用，D.Sinclair担任董事会主席，D.Sinclair和F.Retière担任执行理事会成员，K.Graham和F.Retière分别召集模拟和光电探测器小组。光电探测器和高压系统的发展是两个最高优先级的R&D项目之前，要解决的向下选择。nEXO光电探测器小组已经表明，使用布鲁诺·凯斯勒基金会（FBK）制造的SiPM，可以在2456 MeV下实现1%或更好的能量分辨率。实际上，斯坦福大学和TRIUMF的测量表明FBK SiPM满足所有规格：光子探测效率大于15%，暗噪声率小于50 Hz/mm ^2，相关雪崩概率小于20%。美国亚拉巴马小组已经表明，SiPM放射性含量与模拟小组定义的限值一致。在R.Gornea的领导下，高压组在确定击穿源方面也取得了进展，该小组使用了在伯尔尼大学（瑞士）建立的装置，该装置现已转移到卡尔顿大学。 nEXO合作中的光电探测器开发工作正在从确定合适的光电探测器转向优化性能和解决集成问题：高压兼容性，液体氙中的操作，读出，互连和机械组装。最初由U.Sherbrooke小组为正电子发射断层扫描技术开发的3D-SiPM技术有望解决所有的集成问题，基本上是通过让光子进入SiPM的正面，而位从8x12cm^2硅中介层的背面出来。该解决方案是加拿大最先进的解决方案，需要大量的研发，但有希望获得出色的回报。在这项资助中，我们申请资助支持3D-SiPM的研发，升级TRIUMF测试装置，并研究SiPM在大电场中的操作，这是当前nEXO设计的主要问题之一。

The aim of this proposal is to support the development of photo-detectors for the nEXO experiments by 1) enabling the development of a state of the art Canadian technology and 2) allowing the Canadian group to continue addressing critical issues pertaining to the use of silicon photo-multipliers (SiPMs) within the nEXO detector. Item 1) is a unique opportunity for NSERC to promote the 3 dimensional integration technology (3D-SiPM) that is driven by the université de Sherbrooke (QC) and is expected to revolutionize high speed photon detection. Item 2) is critical to maintain the Canadian leadership within the nEXO photo-detector group, and to ensure that the nEXO experiment presents a full-proof case to the US Department of Energy (DOE) for the neutrino-less double beta decay down select expected to happen in 2017. The Canadian group is playing a major role within the nEXO collaboration with D.Sinclair being chair of the board, D.Sinclair and F.Retière being member of the executive council, and K.Graham and F.Retière convening the simulation and photo-detector groups respectively. The developments of photo-detectors and of the high voltage system are the two highest priority R&D items to be addressed before the down select. The nEXO photo-detector group has shown that 1% or better energy resolution can be achieved at 2456 MeV using SiPMs manufactured by the Fondazione Bruno Kesler (FBK). Indeed measurements at Stanford and TRIUMF show that the FBK SiPMs meet all specifications: photon detection efficiency larger than 15%, dark noise rate less than 50Hz/mm^2, and correlated avalanche probability less than 20%. The U.Alabama group has shown that the SiPM radioactive content is consistent with the limits defined by the simulation group. The high voltage group has also made progress in identifying sources of breakdown under the leadership of R.Gornea using a setup built at the University of Bern (Switzerland) that has now been moved to Carleton U. The photo-detector development effort within the nEXO collaboration is shifting from identifying suitable photo-detectors to optimizing performances and addressing integration issues: high voltage compatibility, operation in liquid Xenon, readout, interconnection and mechanical assembly. The 3D-SiPM technology originally developed by the U.Sherbrooke group for Positron Emission Tomography promises to solve all the integration issues, essentially by having photons entering the front face of the SiPM and bits coming out of the back side of a 8x12cm^2 silicon interposer. This solution is a state of the art Canadian solution requiring significant R&D but promising outstanding rewards. In this grant we request funding for supporting the R&D on 3D-SiPM, upgrading the TRIUMF test setup and investigating operation of SiPMs within a large electric field which is one of the major issues of the current nEXO design.