Beam-Line FIG. 3. Implementation of detectors in the πM1 area in a Geant4 [10] simulation. The beam strikes the thin scintillator beam hodoscope and three GEM chambers, passes through a hole in the annular veto scintillator, enters the cryotarget vacuum chamber and strikes one of the targets, then exits the vacuum chamber and goes through the beam monitor. Scattered particles are detected by two symmetric spectrometers, each with two straw chambers wrapped in RF shielding and two planes of scintillator paddles.

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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/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.

Axion-Like Particles (ALPs) are a generic, calculable, and well motivated extension of the Standard Model with far reaching phenomenology. ALPs that couple only to hypercharge represent one subset of such models, coupling the ALP to both photons and the Z boson. We examine the current constraints on this class of models with an ALP mass in the 100 MeV to 100 GeV range, paying particular attention to the region between 100 MeV to 10 GeV, a portion of parameter space which is ill constrained by current experiments. We show that the more than 109Z bosons produced in the Giga-Z mode of the future ILC experiment, combined with the highly granular nature of its detectors, will allow for ALPs coupled to hypercharge to be discovered with couplings down to nearly 10−5 GeV−1 over a range of masses from 0.4 to 50 GeV.

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