BHLS₂ Upgrade : τ spectra, muon HVP and the [π⁰,~η,~η^′] System

2021/05/31 by M. Benayoun, Maurice Benayoun, L. DelBuono +3 · 12 citations
Physics and Astronomy · #Algorithm #Computer science #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Physics #Quantum Chromodynamics and Particle Interactions #hep-ex #hep-ph

paper · pdf · open access · doi:10.1140/epjc/s10052-022-10096-4

published in The European Physical Journal C 82(2), 184 (Springer Science+Business Media) · Version accepted for publication in EPJ C

openalex publication_date 2022/02/01 · arxiv created 2022/02/09 · arxiv updated 2022/03/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

The generic Hidden Local Symmetry (HLS) model has given rise to the BHLS₂ variant which introduces symmetry breaking in the vector meson sector; the central mechanism is a modification of the covariant derivative at the root of the HLS approach. However, the description of the Belle τ dipion spectra is not satisfactory whereas the dealing with its annihilation sector (e⁺ e^- → π⁺ π^-/π⁺ π^-π⁰/ π⁰ γ/ηγ/K⁺ K^-/K_L K_S) is optimum. This issue is solved by an additional breaking term allowing to include the [π⁰,η,η^′] system. This extension of the usual 't~Hooft determinant term only affects the BHLS₂ kinetic energy term. One obtains a fair account for the τ dipion spectra as well as for the annihilation channels. The Belle dipion spectrum provides evidence for a violation of CVC in the τ lepton decay; this evidence is strengthened by imposing the conditions <0|J_μ^q |[q^′ q^′](p)>=ip_μf_q δ_{q q^′} , \ [q q], q=u,d,s\ on BHLS₂ axial current matrix elements. BHLS₂ is found to recover the usual (completed) formulae for the [π⁰,~η,~η^′] mixing parameters and the global fits return mixing parameter values in agreement with expectations and better uncertainties. Updating the muon HVP, one argues that the strong tension between the KLOE and BaBar pion form factors imposes to provide two solutions : a_μ^HVP-LO(\rm KLOE)=687.31 ± 2.93 and a_μ^HVP-LO(\rm BaBar)=692.36 ± 2.95, in units of 10^-10, rather than some combination of these. Taking into account common systematics, their differences with the experimental BNL-FNAL average value exhibit significances > 5.4σ (KLOE) and > 4.1σ (BaBar) with fit probabilities favoring the former.

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