Abstract
The precision measurement of the anomalous magnetic moment g − 2 of the muon at present exhibits a 3.5 σ deviation between theory and experiments. In the next few years it will be measured to higher precisions at Fermilab and J-PARC. The theoretical prediction can be improved by reducing the uncertainty on the leading hadronic correction $ a_\mu ^{HLO} $ to the g − 2. Here we present a new approach to determine $ a_\mu ^{HLO} $ with space-like data, by means of a precise measurement of the hadronic contribution to the effective electromagnetic coupling α, exploiting the elastic scattering of 150 GeV muons (currently available at CERN North area) on atomic electrons of a low-Z target. The direct measurement of $ a_\mu ^{HLO} $ in the space-like region will provide a new independent determination and will consolidate the theoretical prediction of the muon g − 2 in the Standard Model. It will allow therefore a firmer interpretation of the measurements of the future muon g − 2 experiments at Fermilab and J-PARC.
Highlights
The discrepancy between the experimental value of the muon anomalous magnetic moment aμ = (g − 2)/2 and the Standard Model (SM) prediction, ∆aμ ∼ (28 ± 8) × 10−10 is a long standing issue in particle physics [1, 2]
We propose to use Eq (1) to determine aHμ LO by measuring the running of α using the CERN muon beam of energy Eμ = 150 GeV, colliding on electron at rest of a fixed target
The experiment MUonE presented to determine the leading hadronic contribution to the muon g-2, by scattering high-energy muons on atomic electrons of a low-Z target through the process μe → μe, is primarily based on a precise measurement of the scattering angles of the two outgoing particles as the q2 of the muon-electron interaction can be directly determined by the electron scattering angle
Summary
The proposal described here is to determine aHμ LO from a measurement of the effective electromagnetic coupling α in the space-like region, where the vacuum polarization is expectd to be a smooth function of the squared momentum transfer In this approach the hadronic contribution to the running of α can be measured by means of the t-channel μ − e elastic scattering process, from which aHμ LO can be determined directly [12] 1. We propose to use Eq (1) to determine aHμ LO by measuring the running of α using the CERN muon beam of energy Eμ = 150 GeV, colliding on electron at rest of a fixed target This technique is similar to the one used for the measurement of the pion form factor, as described in [19]. Such a beam is available at the CERN North Area
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