Beam dynamics corrections to the Run-1 measurement of the muon anomalous magnetic moment at Fermilab

With the long-standing tension between experiment and Standard-Model (SM) prediction in the anomalous magnetic moment of the muon aμ recently reaffirmed by the Fermilab experiment, the crucial question becomes which other observables could be sensitive to the underlying physics beyond the SM to which aμ may be pointing. While from the effective field theory (EFT) point of view no direct correlations exist, this changes in specific new physics models. In particular, in the case of explanations involving heavy new particles above the electroweak (EW) scale with chiral enhancement, which are preferred to evade exclusion limits from direct searches, correlations with other observables sensitive to EW symmetry breaking are expected. Such scenarios can be classified according to the SU(2)L representations and the hypercharges of the new particles. We match the resulting class of models with heavy new scalars and fermions onto SMEFT and study the resulting correlations with h → μμ and Z → μμ decays, where, via SU(2)L symmetry, the latter process is related to Z → νν and modified W-μ-ν couplings.

Section: Introductionsupporting

confidence: 71%

Consequences of chirally enhanced explanations of (g − 2)μ for h → μμ and Z → μμ

Crivellin

Hoferichter

2021

“…They can thus lead to relevant quantum corrections to leptonic precision observables and generate lepton flavour violating decays of leptons that are extremely suppressed in the SM since they vanish in the limit of massless neutrinos. The (g − 2) µ discrepancy [17,18], recently reinforced by the g − 2 experiment at Fermilab [19][20][21][22], with a tension of 4.2 σ compared to the SM prediction [23], can be explained with a Z boson heavier than the electroweak (EW) scale if it couples flavour violatingly to the second and third lepton generation [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43].…”

Section: Jhep06(2021)068mentioning

confidence: 99%

“…∆a µ is extracted from the measurement of refs. [17,18] and from the recent results from the Fermilab Muon g − 2 experiment [19][20][21][22]. The theory consensus is taken from ref.…”

Section: Anomalous Magnetic Moments and Electric Dipole Momentsmentioning

confidence: 99%

Global analysis of leptophilic Z′ bosons

Buras

Crivellin

Kirk

et al. 2021

New neutral heavy gauge bosons (Z′) are predicted within many extensions of the Standard Model. While in case they couple to quarks the LHC bounds are very stringent, leptophilic Z′ bosons (even with sizable couplings) can be much lighter and therefore lead to interesting quantum effects in precision observables (like (g − 2)μ) and generate flavour violating decays of charged leptons. In particular, $$ \mathrm{\ell}\to \mathrm{\ell}^{\prime }v\overline{v} $$ ℓ → ℓ ′ v v ¯ decays, anomalous magnetic moments of charged leptons, ℓ → ℓ′γ and ℓ → 3ℓ′ decays place stringent limits on leptophilic Z′ bosons. Furthermore, in case of mixing Z′ with the SM Z, Z pole observables are affected. In light of these many observables we perform a global fit to leptophilic Z′ models with the main goal of finding the bounds for the Z′ couplings to leptons. To this end we consider a number of scenarios for these couplings. While in generic scenarios correlations are weak, this changes once additional constraints on the couplings are imposed. In particular, if one considers an Lμ− Lτ symmetry broken only by left-handed rotations, or considers the case of τ − μ couplings only. In the latter setup, on can explain the (g − 2)μ anomaly and the hint for lepton flavour universality violation in $$ \tau \to \mu v\overline{v}/\tau \to ev\overline{v} $$ τ → μv v ¯ / τ → ev v ¯ without violating bounds from electroweak precision observables.

“…Recently, renewed interest in the electromagnetic properties of axial-vector resonances has been triggered by hadronic corrections to the anomalous magnetic moment of the muon, with the current Standard-Model prediction , differing from experiment [34][35][36][37][38], a exp µ = 116 592 061(41) × 10 −11 , (1.2) by 4.2σ. While at present the uncertainty is dominated by hadronic vacuum polarization, with an emerging tension between the determination from e + e − data [9,[14][15][16][17][18][19][20] and lattice QCD [9,[39][40][41][42][43][44][45][46][47][48], see refs.…”

Section: Introductionmentioning

confidence: 99%

On the transition form factors of the axial-vector resonance f1(1285) and its decay into e+e−

Zanke¹,

Hoferichter

Kubis³

2021

Estimating the contribution from axial-vector intermediate states to hadronic light-by-light scattering requires input on their transition form factors (TFFs). Due to the Landau–Yang theorem, any experiment sensitive to these TFFs needs to involve at least one virtual photon, which complicates their measurement. Phenomenologically, the situation is best for the f1(1285) resonance, for which information is available from e+e− → e+e−f1, f1 → 4π, f1 → ργ, f1 → ϕγ, and f1 → e+e−. We provide a comprehensive analysis of the f1 TFFs in the framework of vector meson dominance, including short-distance constraints, to determine to which extent the three independent TFFs can be constrained from the available experimental input — a prerequisite for improved calculations of the axial-vector contribution to hadronic light-by-light scattering. In particular, we focus on the process f1 → e+e−, evidence for which has been reported recently by SND for the first time, and discuss the impact that future improved measurements will have on the determination of the f1 TFFs.