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 $120\hat{I}¼$m-thick Kapton, while the beam entrance and exit windows are made of $125\hat{I}¼$m-thick aluminized Kapton. The side exit windows are made of Mylar laminated on aramid fabric with an areal density of $368$g/m${}^2$. 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.

7 pages, 10 figures