Muon Spectrometers

Abstract

The detection of muons and the measurement of their momenta is an important task both in astroparticle physics and in elementary particle physics. In cosmic ray physics, the need for muon detectors is obvious since atmospheric showers consist mainly of muons when reaching the surface of the earth. In accelerator-based experiments, the muon plays a special role as a long-lived particle with only electromagnetic interactions; it can easily be identified, and muons provide in many theoretical models a characteristic signature for new physics. A muon spectrometer consists of a position-sensitive detector that records tracks of charged particles, and a magnetic field so that charge and momentum can be deduced from the track curvature. The identification of muons often relies on the large amount of absorber material in front of the muon detector, which allows only muons (and neutrinos) to pass. We first describe the general detector layout and discuss the related uncertainties. Then we present several examples of muon spectrometers that were or are successfully operated in accelerator physics or in cosmic ray physics. We include also muon detectors without a magnetic field. Finally, we report on the application of muon detectors outside particle and astroparticle physics.