Evidence for theϕ-Meson Contribution to Vacuum Polarization Obtained with the Orsaye+e−C

Abstract

The absolute cross section for the <? + e"-*/-i + /x" reaction was measured in a 12~MeV total cm. energy range centered at the mass of the </ ? meson 0 We observe a deviation from the s" 1 dependence of the cross section predicted by quantum electrodynamics when hadronic modifications are neglected. A good fit to the data requires that one take into account y~* <P~* y virtual transitions. Direct evidence for such a vacuum-polarization effect is thus established with a confidence level higher than 0.99.Cabibbo and Gatto 1 have stressed that e + e~ colliding beams offer a unique possibility of studying experimentally the K&llen-Lehmann representation of the complete photon propagator da Imll(«)

Hadron Contribution to Vacuum Polarisation

“…3. The precision of the τ -based evaluation for ∆α (5) had (M 2 Z ), however, was comparable with the e + e − -based one. This is due to different QED kernels in the two evaluations with the former one giving a much larger weight to the low energy data.…”

“…The use of tau data of semi-leptonic τ decays in the evaluation of a had µ and ∆α (5) had (M 2 Z ) was originally proposed in Ref. 26 based on the fact that hadronic spectral functions (or normalised invariant mass-squared distributions) from τ decays are directly related to the isovector vacuum polarisation currents when isospin invariance, or the conserved vector current (CVC), and unitarity hold.…”

New results in $\rho^0$ meson physics

“…Ideally we would obtain the low energy corrections to the photon propagator experimentally, and be able to use QCD perturbatively for higher energies (though the threshold above which we can ignore non-perturbative effects is difficult to determine [16]). The φ meson has already been seen in e + e − → µ + µ − [1,4]. It is only noticeable around the pole region where, due to its small width (4.4 MeV), it produces a sharp peak easily seen in the available data.…”

“…To do this we shall look at two related processes, e + e − → π + π − and e + e − → µ + µ − . The effect of the strong interaction is obvious in the first reaction and provides a large enhancement to the production of pions in the vector meson resonance region [1][2][3][4]. This enhancement, relative to what would be expected for a structureless, pointlike pion, is reflected in the deviation of the pion form factor, F π (q 2 ), from 1, and is primarily associated with the ρ meson (where q µ is the four momentum of the virtual photon).…”

Hadronic vacuum polarization and e+e− → μ+μ− cross section: Reanalysis with new precise data for σh with 4π final states included

“…The last precise measurement of a µ , together with the last decades data for electro-hadron production, leads to an evidence of tension between Standard Theory and experiments [1,2]. Similar confrontation of the theoretical technique with the experimental accuracy is offered by long time known [3,4] interference effect between leptonic and hadronic vacuum polarization functions in close vicinity of narrow resonances: ω and φ as well as heavier quarkonia the J/Ψ, Ψ and Υ's. There, the hadronic vacuum polarization is enhanced several orders of magnitude above remaining hadronic background.…”