\section{Detector development within the Canadian nuclear physics community}

%GH: text from Retiere
Detector technology is a key to discoveries in nuclear physics. There are two types of technological challenges in general, 1) the implementation of a new detector concepts based on an existing technology, and 2) the development of a new technology that leads to a new detector concept. The line between 1) and 2) is blurry, however, because even a solution that has been demonstrated to be effective by a separate group may be hard to replicate. But, in general, 1) is lower risk than 2). Both activities should be supported within the Canadian Subatomic Physics community.

Detector technologies used in the nuclear physics community are very broad, including gas detector and silicon detector for positioning/tracking, germanium, silicon and scintillating detectors for calorimetry ($\gamma$ and also stopping particles), scintillator for fast timing or for neutron detection. Nevertheless, the implementation of all these technologies requires a combination of precision manufacturing capabilities, and cutting edge expertise in mechanical engineering, electronics engineering and data acquisition system (real-time computing), in addition to specific expertise in detector technology. Support for this exists in Canada from TRIUMF, through the NSERC supported MRS program, and within universities. Enhanced coordination is desirable in order to improve efficiency and capabilities by allowing increased specialization of individuals and sharing work across institutes. As it stands, expertise tends to be broad, but not always very specialized at each institute in order to offer capabilities to tackle any project. TRIUMF, having a bigger group has the most diverse offering of expertise.  However, the preferred mode of operation is for TRIUMF to establish synergies with universities. In the next decade, the TRIUMF science technology department is expected to continue supporting the construction of detectors for nuclear physics.

Research and development of a new detection technology is driven by the needs of future experiment. In some cases, the goals an experiment cannot be achieved with the existing technology and new solutions must be developed. For example the nEXO experiment required the development of a new solution for the detection of 175~nm photons, as the solution used in EXO-200 could not be scaled up to the photo-detection area required by nEXO. Such R\&D is however very time consuming, because it involves significant risk. In Canada, detector R\&D can only be for a few technologies that are sufficiently compelling from the need and interest point of view, to generate critical mass and ensure that Canada can have a competitive edge. Furthermore, technologies with applications outside subatomic physics should be preferred, as they widen the funding sources and strengthen the ``benefit to Canadians'' claim. 

\subsection{Future Technologies}

The list below highlights technologies that appear compelling, with Canada having the possibility of playing a leading role, coupled to a need for future experiments within the Canadian Subatomic community.

\begin{enumerate}
\item{{\bf Integrated detectors.} The trend of integrating more and more detector and electronics has been on-going for more than 20 years, but it is not having the same successes as monolithic silicon detectors for tracking minimum ionizing particles. This has been mostly driven by the need to minimize materials along the particle path, but it is also relevant when the radioactivity of material may generate background. Canada has some competitive edge with the Teledyne--DALSA facility in Bromont, Quebec that enables the construction of 3D integrated silicon devices. However, the associated silicon level electronics design capabilities are only available at U. Sherbrooke. Nevertheless, it remains compelling in general.}
\item{{\bf Solid state detectors.} This covers a wide range of detectors, from germanium used for $\gamma$ detection, to silicon detectors used for tracking particles. Both technologies are used in nuclear physics. While they are quite different, design tools (sensor level design) and characterization overlap significantly and could be pooled together.}
\item{{\bf Photo-detectors.} A sub-set of photo-detector is the avalanche diode that also falls in the solid-state category. There is clearly a need for compact and fast ($<$100~ps timing resolution for single photons) photo-detectors, which cannot be easily achieved by PMTs and has led in part to the rise of the SiPM technology. Nevertheless, PMTs are still the leading application where low dark noise is required. There is a very strong need for enhanced photo-detectors in Canada from $\mu$SR to nEXO to SNO+, to Hyper-Kamiokande. Canada has also a competitive edge with Teledyne-DALSA that manufactures state of the art CCDs and is starting to produce 3D integrated Single Photon AValanche Diodes, also called Photon to Digital Converter. Canada has already made substantial investment in the development this solution.}
\item{{\bf Quantum sensors.} 
%GH: additional text from Makoto
As quantum computing and communication is booming, new technologies are being developed, mostly cryogenic. Some of these technologies appear compelling for nuclear physics, for example for the detection of low energy phenomena in electron capture process. 
Other examples are in the area of precision symmetry studies with
the use of atomic fountain, atom interferometry, and atomic/molecular clock technologies.
Canada is investing very significant money in quantum technology, therefore it is an opportunity for SAP contribute to a field where Canada is trying to build a competitive edge.}
\item{{\bf Machine learning technologies.}
% suggestion from Makoto
Nearly a decade ago, ALPHA-Canada pioneered the use of a Machine Learning (ML) technique in antimatter physics, in the
analysis of the first-ever spectroscopy measurement on antihydrogen [Nature 483, 439 (2012)].
The technique is becoming central to many physics analyses, as evident by the recent workshop on Machine Learning held jointly between GlueX and PANDA (Sept 2020) as well as the Artificial Intelligence/Machine Learning Town Hall Meeting at Jefferson Lab (Aug 2020) where 26 ML projects were presented, ranging from FPGA use for fast triggering to unsupervised cauterization in calorimetry.  We expect even more widespread
application of ML across the nuclear physics community, including theory.}

\end{enumerate}

This list of technologies is not exhaustive, and so far the development effort in Canada has not been coordinated. Furthermore, the Canadian funding system does not lend itself well to funding significant R\&D effort. In general, grant applications are for solving technological issues pertaining to a specific project. Some exceptions exist. The Photon to Digital Converter development was funded, in part, for the development of next generation liquid argon and liquid xenon experiments that are separate projects, albeit using related technologies. Cross-project funding appears critical for driving the development of potentially ground breaking but expensive technology. In general, this calls for more coordination at the Canadian level. Establishing a technical board bridging both CINP and IPP within the SAP community should be considered. Its role should be to assess technical opportunities and foster collaborations. In addition, the technical board should provide some oversight regarding the technical resources and capabilities available. 

As discussed above, resources and capabilities are critical to the success of experiments, even when using demonstrated technologies. Specialization of resources allows the tackling of harder problems, but it comes at the expense of versatility, particularly when the resources are managed at the institutional level rather than the national level. A possible solution would be to have the technical board foster work sharing between the various institution offering technical resources.  In parallel, specific R\&D efforts could be fostered mostly by breaking down the barriers between projects.

\subsection{Applications}

Some noteworthy broader applications:
TRIUMF is working on a Single Photon Air Analyser for particulate detection in forest fires or for air quality monitoring that is expected to lead to a patent.
Two patents are in progress from U.Sherbrooke for the Photon to Digital Converter (PDC). More innovations are foreseen with the development of a new generation of PDC. This PDC should have significant sensitivity in the near infra-red, which would make it compelling for quantum communication and LIDAR applications. 

\subsection{Conclusions}

%GH: text from 2015 brief
It is important to sustain and enhance the capabilities for detector development
and construction in the Canadian SAP community. This requires increased
coordination and communication within the community, not only on the level of
the scientists but also on the level of engineers and technical staff.  To
enhance this coordination, TRIUMF proposes to initiate a series of topical
workshops related to precision machining, detector design, simulations, and
integration, as well as readout electronics and data acquisition systems. Such
workshops would enable the sharing of technical expertise and would build
strong working level connections between institutions at the technical level.

In any funding scenario, the NSERC subatomic physics envelope needs to continue
to allow for such long-term directed research and development for the next
generation of nuclear and particle physics experiments.