Measuring the leading-order hadronic contribution to the muon g-2 in the space-like region

Abstract

Abstract.A new experiment is proposed to measure the running of the electromagnetic coupling constant in the space-like region by scattering high-energy muons on atomic electrons of a low-Z target. The differential cross section of the elastic process μe → μe provides direct sensitivity to the leading-order hadronic contribution to the muon anomaly a HLO μ . It is argued that by using the 150-GeV muon beam available at the CERN North Area, with an average rate of ∼ 1.3 × 10 7 muon/s, a statistical uncertainty of ∼ 0.3% can be achieved on a HLO μ after two years of data taking. The direct measurement of a HLO μ via μe scattering will provide an independent determination and consolidate the theoretical prediction for 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.

Lepton anomalous magnetic moments in Lattice QCD+QED

“…In the case of the electron and the tau we adopt directly the findings of Ref. [26], namely [28] Notice that the uncertainty of our result (3.4) is almost coinciding with the statistical uncertainty (∼ 2 • 10 −10 ) expected in the MUonE experiment for the measured contribution [a HVP µ − a HVP MUonE ] after two years of data taking at the CERN North Area [24]. Before closing this Section we take advantage of the well known fact that a HVP e is proportional to the slope Π 1 of the leading HVP function at vanishing photon virtuality, namely a HVP e = (4/3)α 2 em m 2 e Π 1 with Π 1 ≡ (1/12) ∞ 0 dt t 4 V (t).…”

“…Before closing this section we mention that the MUonE experiment [24] aims at determining a HVP µ by measuring the running of α em (q 2 ) for space-like values of the squared four-momentum transfer q 2 using a muon beam on a fixed electron target. There is, however, a kinematical region not covered by the MUonE experiment and the corresponding contribution to a HVP µ needs to be estimated using either e + e − data or lattice QCD simulations.…”

Light-quark contribution to the leading hadronic vacuum polarization term of the muon g−2 from twisted-mass fermions

“…The quantity ∆α HVP em (q 2 ) can be extracted from the q 2 -dependence of the µe → µe cross section data after the subtraction of the leptonic and weak contributions [51,52]. For the proposed MUonE experiment exploiting the muon beam at the CERN North Area [79] the region x ∈ [0.93, 1] in Eq. ( 58) cannot be reached and, therefore, the corresponding contribution…”