DDM, a focussed workshop on detector and data acquisition systems for muon spectroscopy was held 1-2 November, 2021 by Zoom. The meeting was very well attended, with over 40 participants joining to discuss the latest ideas in the field. Muon facilities currently in operation (ISIS (UK), J-PARC and MuSIC (Japan), PSI (Switzerland) and TRIUMF (Canada)) were well represented, while it was also good to welcome colleagues from sources at the CSNS (China) and SNS (USA) where muon facilities are in the planning.

The presentations gave an excellent overview of developments across the facilities, and the challenges each are facing as they design the next generation instruments. A common theme linking many talks was the continued development of silicon photo-multipliers (SiPMs), as a solid-state replacement for the traditional glass-vacuum PMT. There was an in-depth discussion of the J PARC/KEK system ‘Kalliope’, originally developed for the application of SiPMs at a pulsed muon beam. This system is now in use across all instruments at J PARC, including the new 3008 channel high field spectrometer (CYCLOPS). New firmware is now available, enabling the Kalliope system to run efficiently at continuous sources, such as MuSIC and TRIUMF. Real insight was given into the development process, along with the next steps: ‘Kalliope-2’. Both TRIUMF and ISIS highlighted new instrument developments, with SiPMs being used either to achieve fast timing on large area detectors (TRIUMF) or to create highly pixelated arrays to handle the very high data rates expected on the new ISIS instrument, SuperMuSR. ISIS also discussed the possibility of using DSP methods to gain an additional improvement in rate capability, with first tests complete and a prototype now in production. CSNS presented their completed detector array and data acquisition systems, now ready as a ‘day 1’ instrument, while considering future high density arrays to handle the very high rates expected at the source.

Transient µSR was introduced by J-PARC, highlighting the possibility of using event mode data acquisition in combination with intense beams to complete highly efficient studies of systems using continuously changing sample environment parameters. Finally, Prof Schöning (Heidelberg) was invited to give a presentation discussing the development of detector and DAQ systems for the Mu3e experiment at PSI. The unique demands of particle physics experiments drive detector development, and in this case the systems required for the Mu3e experiment point the way towards the possible development of future positron tracking systems for µSR measurements.

The discussion sessions covered topics such as performance metrics and diagnostics. Emphasis was on ‘lessons learnt’, the sharing of ideas and future ambitions. There were useful exchanges of ideas and experiences with SiPM detectors, comparing the different manufacturers and specifications. The community spent some time thinking about key issues in instrument design, including integration of diagnostic capability in both the instrument and beamline for commissioning, performance monitoring and fault finding.