Magnetic Field Measurement and Analysis for the Muon g-2 Experiment at Fermilab

Abstract

The Fermi National Accelerator Laboratory (FNAL) Muon g −2 Experiment has measured the anomalous precession frequency a µ ≡ (g µ −2)/2 of the muon to a combined precision of 0.46 parts per million with data collected during its first physics run in 2018. This paper documents the measurement of the magnetic field in the muon storage ring. The magnetic field is monitored by nuclear magnetic resonance systems and calibrated in terms of the equivalent proton spin precession frequency in a spherical water sample at 34.7 °C. The measured field is weighted by the muon distribution resulting in ω p , the denominator in the ratio ω a /ω p that together with known fundamental constants yields a µ . The reported uncertainty on ω p for the Run-1 data set is 114 ppb consisting of uncertainty contributions from frequency extraction, calibration, mapping, tracking, and averaging of 56 ppb, and contributions from fast transient fields of 99 ppb.

Studying the b→sℓ+ℓ− anomalies and (g−2)μ<

“…The clues of LFU violation exist not only in B-meson decay processes, but also in other transitions, such as, the muon anomalous magnetic moment problem which has existed several decades. The measurement of a µ = (g −2) µ by Fermilab [79][80][81] just presents the 3.3σ deviation greater than the SM prediction [82] 1 , and agrees with the previous Brookhaven E821 experiment [92]. The combined average of the two experiments, ∆a µ = a exp µ −a SM µ = (2.51±0.59)×10 −9 shows the increased tension at the significant 4.2σ level and this is a growing motivation of NP.…”

Short-distance constraints for the longitudinal component of the hadronic light-by-light amplitude: an update

“…For simplicity, we concentrate here on the model presented by CCDGI in [44], which is equivalent to the HW2 model in [43], although the two groups make different choices for the parameters. 3 The representation of this model for the function G reads (in the notation of CCDGI)…”

“…The recent measurement of (g − 2) µ by the Fermilab Muon g − 2 collaboration [1][2][3][4] has made the discrepancy with the Standard-Model prediction more serious, by bringing it from the 3.7σ to the 4.2σ level when combined with the previous Brookhaven measurement [30]. The concrete perspective of additional reductions of the experimental uncertainty in the near future-mainly from subsequent Runs at Fermilab [31], but also the future J-PARC experiment [32] using a different technique-makes the need of further theoretical improvements more urgent.…”

Isospin-breaking effects in the two-pion contribution to hadronic vacuum polarization

“…Such new precision measurements are expected from CMD-3 [28], BaBar [29], BESIII [30], and Belle II [31] in the future. Improved understanding of the 2π channel has further become critical to address the emerging tension between lattice QCD [32][33][34][35] and e + e − data at least for the intermediate window quantity [36], with immediate consequences for the current 4.2σ discrepancy for the anomalous magnetic moment of the muon between experiment [37][38][39][40][41] and the prediction in the Standard Model [1][2][3][4][5][6][7][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] when the HVP contribution is derived from JHEP10(2022)032…”