Measuring the leading hadronic contribution to the muon g-2 via mu e scattering

G Abbiendi,O Nicrosini,F Piccinini,C M Carloni Calame,L Trentadue,C Matteuzzi,G Venanzoni,R Tenchini,M Passera,G Montagna,U Marconi

doi:10.1140/epjc/s10052-017-4633-z

Abstract

We propose a new experiment 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 through the elastic process mu , e rightarrow mu , e. The differential cross section of this process, measured as a function of the squared momentum transfer t=q^2<0, provides direct sensitivity to the leading-order hadronic contribution to the muon anomaly a^mathrm{{HLO}}_{mu }. By using a muon beam of 150 GeV, with an average rate of sim 1.3 times 10^7 muon/s, currently available at the CERN North Area, a statistical uncertainty of sim 0.3% can be achieved on a^mathrm{{HLO}}_{mu } after two years of data taking. The direct measurement of a^mathrm{{HLO}}_{mu } via mu e scattering will provide an independent determination, competitive with the time-like dispersive approach, 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.

Highlights

In searching for new physics, low-energy high-precision measurements are complementary to the LHC high-energy frontier
We propose a new experiment to measure the running of the electromagnetic coupling constant in the spacelike region by scattering high-energy muons on atomic electrons of a low-Z target through the elastic process μ e → μ e
We presented a novel approach to determine the running of α in the space-like region and aμHLO, 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

Summary

Introduction

In searching for new physics, low-energy high-precision measurements are complementary to the LHC high-energy frontier. The present error on aμHLO, ∼ 4 × 10−10, with a fractional accuracy of 0.6%, constitutes the main uncertainty of the SM prediction. An alternative evaluation of aμHLO can be obtained by lattice QCD calculations [6,7,8,9,10,11]. Even if current lattice QCD results are not yet competitive with those obtained with the dispersive approach via time-like data, their errors are expected to decrease significantly in the few years [12,13]. The O(α3) hadronic light-by-light contribution, aμHLbL, which has the second largest error in the theoretical evaluation, contributing with an uncertainty of (2.5–4) ×10−10, cannot at present be determined from data and its calculation relies on the use of specific models [14,15,16,17,18].

Theoretical framework

Experimental proposal

Preliminary considerations on the detector

Considerations on systematic uncertainties

Findings

Conclusions