GMINUS2

Local Manager: Giuseppe Di Sciascio; PI: Giovanni Cantatore (TS).

The Muon g-2 experiment, located at Fermilab (Illinois – 60 km from Chicago), is a particle physics experiment built to measure the muon’s anomalous magnetic moment with the record precision of 0.14 parts per million (ppm). The muon anomalous magnetic moment, a_\mu = \frac{g-2}{2}​, is a low-energy observable which can be both measured and computed to high precision, making it a sensitive test of the Standard Model and a probe for new physics. The current measurement of a_\mu ​ has reached a precision of 0.2 ppm, while the last datasets are under analysis to achieve the final accuracy goal. 

The experiment is based on the precise measurement of the anomalous spin precession frequency, extracted from the arrival time distribution of high-energy positrons produced in the muons decay. The positrons are detected by 24 electromagnetic calorimeters positioned around a 14 m diameter magnetic storage ring. The calorimeters are made of Lead Fluoride crystals coupled to Silicon Photomultipliers. The magnetic field of the storage ring, uniform at the ppm level in the storage region, is monitored with Nuclear Magnetic Resonance probes. 

The first result of the experiment, based on the 2018 data-taking campaign, was published in 2021 and confirmed the previous result obtained at Brookhaven National Laboratory in 2006, showing a discrepancy of 4.2 standard deviations with the Standard Model prediction. A second result, based on the 2019 and 2020 datasets was published in 2023, with an improved statistical accuracy and reduced systematic uncertainties. The last dataset, still under analysis, will provide a further reduction in the statistical and systematic uncertainties achieving the final goal of 0.14 ppm on the a_\mu experimental value. 

References: 

  1. D. P. Aguillard et al. (Muon g-2 Collaboration) – Measurement of the Positive Muon Anomalous Magnetic Moment to 0.20 ppm – Phys. Rev. Lett. 131, 161802 https://doi.org/10.1103/PhysRevLett.131.161802 
  1. B. Abi et al. (Muon g-2 Collaboration) – Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm - Phys. Rev. Lett. 126, 141801 https://doi.org/10.1103/PhysRevLett.126.141801