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.
  Mercoledì 13/09   09:00 - 13:00   Aula A208   I - Fisica nucleare e subnucleare
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.