A Liquid Hydrogen Target for the MUSE Experiment at PSI
Abstract
A 280 ml liquid hydrogen target has been constructed and tested for the MUSE experiment at PSI to investigate the proton charge radius via simultaneous measurement of elastic muon-proton and elastic electron-proton scattering. To control systematic uncertainties at a sub-percent level, strong constraints were put on the amount of material surrounding the target and on its temperature stability. The target cell wall is made of 120\,μm-thick Kapton, while the beam entrance and exit windows are made of 125\,μm-thick aluminized Kapton. The side exit windows are made of Mylar laminated on aramid fabric with an areal density of 368\,g/m2. The target system was successfully operated during a commissioning run at PSI at the end of 2018. The target temperature was stable at the 0.01 K level. This suggests a density stability at the 0.02\,% level, which is about a factor of ten better than required.