The muong−2: a brief overview of hadronic crosssection data

Abstract

The hadronic vacuum polarisation contributions to the anomalous magnetic moment of the muon, a had,VP µ are evaluated dispersively via a combination of experimentally measured e + e − → hadrons cross section data. Many experiments have dedicated programmes to precisely measure these final states, meaning that a vast amount of data is now available and that, in some cases, overall precision has reached the sub-percent level. However, data tensions are evident between measurements of the same hadronic channels from different experiments, which reduces the overall quality of the data combinations used to determine a had, VP µ . The inclusion of these data in the KNT18 analysis results in a had, LO VP µ = (693.26 ± 2.46) × 10 −10 and a had, NLO VP µ = (−9.82 ± 0.04) × 10 −10 . The corresponding new estimate for the Standard Model prediction is found to be a SM µ = (11 659 182.04 ± 3.56) × 10 −10 , which is 3.7σ below the current experimental measurement.

MUON SPIN PRECESSION FREQUENCY EXTRACTION AND DECAY POSITRON TRACK FITTING IN RUN 1 OF THE FERMILAB MUON \MakeLowercase{$g-2$\xspace} EXPERIMENT

“…For the HighKick and 9d datasets with n values of 0.120, the CBO frequencies were found to be 2.559 and 2.615 rad/µs respectively, corresponding to approximately 0.415 MHz. These frequencies correspond to the expected frequencies as described in Section 2.6, with some slight deviations due to statistics, bad resistors, and the reduced sensitivity in the Ratio Method 16 . The CBO lifetimes between the different datasets are relatively consistent, barring the HighKick dataset for which a smaller CBO lifetime was measured, attributed to the changing behavior of the bad resistors in that dataset.…”

“…The average R value for fits to 50 different random seeds are provided in Section 5.4.4. 16 The VW frequencies, though time-randomized out in the analysis presented here, were found to be approximately 2.30 and 2.04 MHz for the datasets with n = 0.108 and n = 0.120 respectively.…”

“…The cross-section data for Equation 1.9 has been measured in different energy ranges by various experiments; a brief overview is given by A. Keshavarzi [16]. There are two approaches to measuring this cross-section data.…”

Anomalous gauge couplings vis-$\grave{a}$-vis $(g-2)_μ$ and flavor observables

“…The traditional method has been to use dispersion relations alongwith experimental results and if this is adopted, the experimental result would imply a discrepancy ∆a DISP µ = 251(59)×10 −11 , a 4.2σ deviation from the the SM [37,38]. On the other hand, the adoption of the Lattice QCD results from Budapest-Marseille-Wuppertal (BMW) collaboration [39] for the same significantly reduces the deviation down to ∆a BMW µ = 107(69) × 10 −11 or an agreement at the 2σ level (see ref [40][41][42] for reviews).…”