Measurement of the leading hadronic contribution to the muon g-2 via space-like data.
Abbiendi G., Carloni Calame C., Incagli M., Marconi U., Matteuzzi C., Montagna G., Nicrosini O., Passera M., Piccinini F., Tenchini R., Trentadue L., Venanzoni G.
The precision measurement of the anomalous magnetic moment of the muon presently exhibits a $3.5\sigma$ discrepancy with the Standard Model (SM) prediction. In the next few years this measurement will reach an even higher precision at Fermilab and J-PARC. While the QED and electroweak contributions to the muon g-2 can be determined very precisely, the leading hadronic (HLO) correction is affected by a large uncertainty which dominates the error of the SM prediction. We propose a novel approach to determine the HLO contribution to the muon g-2 based on the measurement of the effective electromagnetic coupling in the space-like region at low-momentum transfer. We will discuss the possibility of performing this measurement at CERN, by means of a very precise determination of the muon-electron elastic differential cross-section, exploiting the scattering of 150 GeV muons (currently available at CERN's North area) on atomic electrons of a $low-Z$ target. We will describe the experimental challenges posed by this measurement and by a detector able to keep the systematic effects at the required level of 10 ppm. This measurement will provide an independent determination of the HLO contribution to the muon g-2 competitive with the time-like dispersive approach, thus consolidating the SM prediction. It will therefore allow a firmer interpretation of the measurements of the future muon g-2 experiments at Fermilab and J-PARC.