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)支持加拿大最先进技术的开发；2)允许加拿大集团继续解决与在Nexo探测器内使用硅光电倍增器(SiPM)有关的关键问题。项目1)是NSERC推广3D集成技术(3D-SiPM)的独特机会，3D-SiPM由舍布鲁克大学(QC)推动，有望彻底改变高速光子探测。项目2)对于保持加拿大在Nexo光电探测器小组中的领导地位至关重要，并确保Nexo实验向美国能源部(DOE)提出一个全面的证据，证明预计将于2017年发生的精选无中微子双贝塔衰变。 这家加拿大集团在Nexo的合作中发挥着重要作用，D·辛克莱担任董事会主席，D·辛克莱和F·雷蒂埃尔担任执行委员会成员，K·格雷厄姆和F·雷蒂埃尔分别召集模拟小组和光探测器小组。光电探测器和高压系统的发展是下一步选择之前要解决的两个最优先的研发项目。Nexo光电探测器小组已经证明，使用Fondazione Bruno Kesler(FBK)制造的SiPM，在2456 MeV下可以达到1%或更高的能量分辨率。事实上，在斯坦福大学和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赫兹/mm^2，相关雪崩概率小于20%。阿拉巴马州大学的研究小组已经证明，SiPM的放射性含量与模拟小组定义的限值一致。在R.Gornea的领导下，高压小组还利用瑞士伯尔尼大学建立的装置在识别故障来源方面取得了进展，该装置现已转移到Carleton U。 Nexo合作的光电探测器开发工作正在从寻找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、在液体氙气中运行、读出、互连和机械组装。3D-SiPM技术最初是由U·舍布鲁克团队为正电子发射断层扫描技术开发的，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，让位从8x12 cm^2硅插入器的背面出来。这一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。在这笔赠款中，我们申请资金支持3D-SiPM的研发，升级TRIUMF测试装置，并调查SiPM在大电场中的运行，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.