A High-Resolution Muon Spectrometer Using Multi-Layer Gas Cherenkov Radiators*

Having a high-resolution momentum measurement capability is of outmost importance in high-energy physics and neutrino research. Typically, when it comes to hadrons and electrons, calorimeters are sufficient to provide accurate measurement of their momenta. However, calorimeters are not ideal for muons because muons can easily escape the active volume without any appreciable interactions. To address this shortcoming, a magnetic field and trackers are often used to measure muon momentum by reconstructing the curvature of muon trajectories. Alternatively, time-of-flight or multiple Coulomb scattering methods are used to estimate muon momentum, however, the resolution is much lower (~20% in the muon momentum range of 0.5–4.5 GeV/c). Here, we propose a different paradigm for muon momentum measurement that utilizes multi-layer pressurized gas Cherenkov radiators. Since the muon Cherenkov threshold momentum level for gas radiators depends on pressure, the muon momentum can be accurately measured by carefully varying the pressure to provide sequential threshold momentum levels. Our new concept offers a feasible solution to flexible muon spectrometers that significantly improve resolution (<10%) and extend the measurable momentum range to 0.2–10 GeV/c without relying on bulky magnets.