Speaker
Description
There has been a long-standing discrepancy between theoretical predictions and experimental measurements in the evaluation of the muon anomalous magnetic moment a_μ. The leading order hadronic contribution to a_μ, a_μ^HLO , represents the dominant source of uncertainty in the Standard Model evaluation. The MUonE experiment aims to determine a_μ^HLO with high precision using a novel experimental approach. MUonE will take place in CERN’s north area, using the M2 beamline that produces 160GeV muons that will be scattered on a low Z target. The experiment has a modular structure composed of multiple 1m long tracking stations that have individual targets. a_μ^HLO can be evaluated by the extraction of the effective electromagnetic coupling from the shape of the differential cross section of the µ - e elastic scattering. Upstream of the tracking stations there are the beam momentum spectrometer (BMS) stations. The role of the BMS is to measure the momentum of individual incoming muons to a few per mille accuracy. For the 2025 test run dedicated stations were designed for the BMS stations with a new support structure made out of a carbon fibre composite called M55J, and were equipped with silicon strip sensors (2S modules) that were developed for the CMS phase 2 upgrade. The development of the new support structure and preliminary results on the performance of the BMS from the 2025 test run will be presented.