# The new versatile general purpose surface-muon instrument (GPS) based on silicon photomultipliers for ${\mu}$SR measurements on a continuous-wave beam

## TL;DR

This paper introduces a new versatile muon spectrometer using silicon photomultipliers, offering improved time resolution and a more compact design for muon-spin relaxation/rotation studies at PSI.

## Contribution

The paper presents a novel design of a general-purpose surface-muon instrument with SiPM-based detectors, enhancing performance and compactness over previous models.

## Key findings

- Achieved a time resolution of about 160 ps.
- Designed a compact instrument with increased solid angle coverage.
- Replaced traditional light guides with SiPM technology.

## Abstract

We report on the design and commissioning of a new spectrometer for muon-spin relaxation/rotation studies installed at the Swiss Muon Source (S$\mu$S) of the Paul Scherrer Institute (PSI, Switzerland). This new instrument is essentially a new design and replaces the old general-purpose surface-muon instrument (GPS) which has been for long the workhorse of the $\mu$SR user facility at PSI. By making use of muon and positron detectors made of plastic scintillators read out by silicon photomultipliers (SiPMs), a time resolution of the complete instrument of about 160 ps (standard deviation) could be achieved. In addition, the absence of light guides, which are needed in traditionally built $\mu$SR instrument to deliver the scintillation light to photomultiplier tubes located outside magnetic fields applied, allowed us to design a compact instrument with a detector set covering an increased solid angle compared to the old GPS.