Abstract
The goal of the MUonE experiment is to determine the leading-order hadronic vacuum polarization $a_\mu^{\text{HVP-LO}}$, the dominant contribution to the overall uncertainty of the muon magnetic anomaly, \(a_{\mu}=(g-2)/2\), through a precise measurement of the space-like process of elastic \(\mu e\) scattering. This will be accomplished using the CERN SPS muon beam on a low-\(Z\) target. The MUonE detector system combines silicon tracking stations with a downstream electromagnetic calorimeter (ECAL) comprising PbWO$_4$ crystals with APD readout, followed by a muon filter.
This study focuses on the MUonE ECAL and its role in the 2025 Run--1 data-taking campaign, a reduced but representative configuration of the final experiment. The work covered here includes simulation, detector refurbishment, calibration, synchronization with the tracker, and energy reconstruction in the regime of limited time sampling and significant pile-up incidence. Simulation studies are used to quantify shower leakage, derive position-dependent corrections relevant for gain matching, and establish expectations for the calorimeter energy and spatial resolution. The experimental data, acquired with muon and electron beams, were used to characterize the wavedorm baseline (ADC pedestal) behavior, noise stability, beam-intensity effects, and inter-channel correlations. All of these were studied to develop and validate a common-mode baseline-reconstruction technique that optimizes the consistency between predicted and reconstructed energy.
Using the Run--1 dataset, this work presents the commissioning and performance of the ECAL detector both on its own and within the integrated MUonE apparatus. The calorimeter is synchronized with the tracker, its spatial matching performance is measured and compared with simulation, and its response is calibrated through hardware and software gain-matching procedures supplemented by simulation-based leakage corrections. Stability, linearity, and energy-resolution studies show that the detector response is reproducible and physically understood at the percent level.
Building on this detector-level characterization, this work presents the first ECAL-assisted particle-identification study using the MUonE Run--1 data. Calorimetric observables improve the separation between electrons and muons in the small-angle scattering region, where tracker-only information is intrinsically limited. The first joint tracker--ECAL kinematic distributions are shown to be consistent with elastic \(\mu e\) scattering. In a complementary study, this work develops an ECAL-assisted, data-driven strategy toward the leptonic contribution to the running of the electromagnetic coupling, \(\Delta\alpha_{\mathrm{lep}}(Q^{2})\), through studies of event selection, efficiency, and stability. Overall, the results establish the MUonE ECAL as a quantitatively characterized and experimentally validated detector starting point for a future full-precision phase of the MUonE experiment.
