The Muon (g-2) experiment has succeeded in improving the BNL measurement of a_mu by completing the analysis of its 2018-2020 sample with four times the BNL statistics. Both statistical and systematic errors on a_mu were improved by a factor ~2, increasing to more than 5 sigma’s the discrepancy between this measurement and its Standard Model (SM) evaluation based on e+e- data. This exciting result motivated an intense work on the theory side to discriminate between BSM scenarios or independent SM evaluation carried out with lattice calculations. The existing tension in this sector is really puzzling and the experiment, including the aMUSE team, is working hard to complete both the analysis of the full data set (×20 BNL), aiming to a further factor two reduction on the errors and a test of concurring BSM scenarios with very light new particles, motivated by g-2 and dark matter open questions. The theory group is using these new developments to obtain more accurate predictions for cLFV observables that can be tested with the Mu2e experiment. In this respect, aMUSE aims to complete the construction and commissioning phase of the experiment and to start the first physics run with beam. Collecting 1/10 of the total number of Protons on Target (10^19), this first data taking period will allow to improve the cLFV sensitivity by a factor 1000, exploring mass scales not achievable with current, next-generation or even larger energy colliders.
The connection and synergy between the Muon Campus activity and its future upgrades (Mu2e-II and AMF) are focused on the development of a new generation of detectors to overcome the challenges foreseen for the next-generation cLFV experiments. For Mu2e-II, ongoing studies on innovative gas mixtures that could improve tolerance to very high energy deposits over time while preserving a very low material budget are a pre-requisite for the design of extremely light tracking systems, able to sustain a rate capability up to 10^8 tracks/sec on the detector. The ×10 increase in radiation level and ×3 increase in hit occupancy for calorimetry ask for a dramatic technology change with much faster crystals than CsI. The primary solution exploits the 280 nm fast component (0.9 ns) of BaF2 crystals while minimizing its long (600 ns) component above 350 nm. This is achieved by both Yttrium doping of crystals and coupling them to newly developed Solar-Blind SiPMs. The BaF2 emission is so fast and bright that application on TOF-PET can be also explored for the medical field. Moreover, the ten-fold increase in muon beam intensity gave rise to a completely different design of the pion production target, involving active cooling. Developments in the conceptual design of the AMF, with muons transported through a fixed-field alternating gradient storage ring, have triggered the conceptual design for muon surface beam detectors. Simulations and hardware tests have been performed, orienting toward a design consisting of a silicon-pixel positron tracker and a photon pair-conversion detector. Thanks also to aMUSE, the Muon Collider has become a priority in US, recognised in the P5 report.
In order to achieve our goals and build bridges towards other fields of excellence and applications for society, collaboration and connections with industries are also exploited. Partnerships arising from the synergies of our work on High Precision Crystals and Silicon Photomultipliers finds applications for mine clearance, medical physics and laser-plasma characterization.
