Abstract
There is a long standing discrepancy between the Standard Model prediction for the muon g−2 and the value measured by the Brookhaven E821 Experiment. At present the discrepancy stands at about three standard deviations, with a comparable accuracy between experiment and theory. Two new proposals – at Fermilab and J-PARC – plan to improve the experimental uncertainty by a factor of 4, and it is expected that there will be a significant reduction in the uncertainty of the Standard Model prediction. I will review the status of the planned experiment at Fermilab, E989, which will analyse 21 times more muons than the BNL experiment and discuss how the systematic uncertainty will be reduced by a factor of 3 such that a precision of 0.14 ppm can be achieved.
Highlights
The muon anomaly aμ = (g − 2)/2 is a low-energy observable, which can be both measured and computed to high precision [1, 2]. It provides an important test of the Standard Model (SM) and it is a sensitive search for new physics [3]
Since the first precision measurement of aμ from the E821 experiment at BNL in 2001 [4], there has been a discrepancy between its experimental value and the SM prediction
A precise determination of the hadronic cross sections at the e+e− colliders (VEPP-2M, DAΦNE, BEPC, PEP-II and KEKB) has allowed a determination of aHμ LO with a fractional accuracy below 1%. These efforts have led to the development of dedicated high precision theoretical tools such as the addition of Radiative Corrections (RC) and the non-perturbative hadronic contribution to the running of α into the Monte Carlo (MC) programs used for the analysis of the experimental data [11];
Summary
A precise determination of the hadronic cross sections at the e+e− colliders (VEPP-2M, DAΦNE, BEPC, PEP-II and KEKB) has allowed a determination of aHμ LO with a fractional accuracy below 1% These efforts have led to the development of dedicated high precision theoretical tools such as the addition of Radiative Corrections (RC) and the non-perturbative hadronic contribution to the running of α (i.e. the vacuum polarisation, VP) into the Monte Carlo (MC) programs used for the analysis of the experimental data [11];. The lattice calculation has already reached a mature stage and has real prospects to match the experimental precision From both activities a further reduction of the error on aHμ LO can be expected and progress on aHμ LbL will be required. For the HLbL contribution there isn’t a direct connection with data, γ −γ measurements performed at e+e− colliders will help constrain the on-shell form factors [22, 23] and lattice calculations will help better determine the off shell contributions
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