Update of the e + e − → π+π− cross section measured by the spherical neutral detector in the energy region 400 &lt; √s &lt; 1000 MeV

Ачасов, М. Н.; Beloborodov, K.; Berdyugin, A. V.; Богданчиков, А. Г.; Bozhenok, A. V.; Bukin, A. D.; Bukin, D.A.; Dimova, T.; Дружинин, В. П.; Голубев, В. Б.; Korol, A. A.; Koshuba, S. V.; Пахтусова, Е. В.; Serednyakov, S. I.; Shatunov, Yu. M.; Sidorov, V.; Силагадзе, З. К.; Skrinsky, A.N.; Tikhonov, Yu. A.; Vasiljev, A. V.

doi:10.1134/s106377610609007x

Cited by 203 publications

(186 citation statements)

References 10 publications

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“…Since about 95% of the final pion-box (g − 2) µ integral originate from virtualities below 1 GeV, it is most critical that the low-energy properties be correctly reproduced. Experimentally, the available constraints derive from e + e − → π + π − data, which determine the time-like form factor [74][75][76][77][78][79], and space-like measurements by scattering pions off an electron target [80,81]. We have also checked that our representation is consistent with extractions of the space-like form factor from e − p → e − π + n data [82][83][84][85], although due to the remaining model dependence of extrapolating to the pion pole we do not use these data in our fits.…”

Section: Evaluation Of the Full Pion Boxmentioning

confidence: 99%

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Dispersion relation for hadronic light-by-light scattering: two-pion contributions

Colangelo

Hoferichter

Procura

et al. 2017

J. High Energ. Phys.

374

257

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In this third paper of a series dedicated to a dispersive treatment of the hadronic light-by-light (HLbL) tensor, we derive a partial-wave formulation for two-pion intermediate states in the HLbL contribution to the anomalous magnetic moment of the muon (g − 2) µ , including a detailed discussion of the unitarity relation for arbitrary partial waves. We show that obtaining a final expression free from unphysical helicity partial waves is a subtle issue, which we thoroughly clarify. As a by-product, we obtain a set of sum rules that could be used to constrain future calculations of γ * γ * → ππ. We validate the formalism extensively using the pion-box contribution, defined by two-pion intermediate states with a pion-pole left-hand cut, and demonstrate how the full known result is reproduced when resumming the partial waves. Using dispersive fits to high-statistics data for the pion vector form factor, we provide an evaluation of the full pion box, a π-box µ = −15.9(2)×10 −11 . As an application of the partial-wave formalism, we present a first calculation of ππ-rescattering effects in HLbL scattering, with γ * γ * → ππ helicity partial waves constructed dispersively using ππ phase shifts derived from the inverse-amplitude method. In this way, the isospin-0 part of our calculation can be interpreted as the contribution of the f 0 (500) to HLbL scattering in (g − 2) µ . We argue that the contribution due to charged-pion rescattering implements corrections related to the corresponding pion polarizability and show that these are moderate. Our final result for the sum of pion-box contribution and its S-wave rescattering corrections reads a π-box µ + a ππ,π-pole LHC µ,J=0 = −24(1) × 10 −11 .

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Section: Evaluation Of the Full Pion Boxmentioning

confidence: 99%

“…We fit this representation simultaneously to the space-like data from [81] as well as one of the time-like data sets [74][75][76][77][78][79] (restricted to data points below 1 GeV). Moreover, we varied s 1 , p = 1, 2, and constructed an error band for the uncertainties in δ 1 1 apart from the phase shifts at s m and s A .…”

Section: Jhep04(2017)161mentioning

confidence: 99%

Dispersion relation for hadronic light-by-light scattering: two-pion contributions

Colangelo

Hoferichter

Procura

et al. 2017

J. High Energ. Phys.

374

257

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“…The need for keeping under control accurately radiative corrections to QED processes has been recently reinforced by the update of the e + e − → π + π − cross section by SND collaboration at VEPP-2M. This reanalysis [25], which leads to a decrease of the measured cross section by two systematic errors in average with respect to the previous one, became necessary due to a flaw in the Monte Carlo generators previously used in data analysis to compute radiative corrections to e + e − → π + π − and e + e − → µ + µ − .…”

Section: Introductionmentioning

confidence: 99%

Matching perturbative and parton shower corrections to Bhabha process at flavour factories

et al. 2006

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We report on a high-precision calculation of the Bhabha process in Quantum Electrodynamics, of interest for precise luminosity determination of electron-positron colliders involved in R measurements in the region of hadronic resonances. The calculation is based on the matching of exact next-to-leading order corrections with a Parton Shower algorithm. The accuracy of the approach is demonstrated in comparison with existing independent calculations and through a detailed analysis of the main components of theoretical uncertainty, including two-loop corrections, hadronic vacuum polarization and light pair contributions. The calculation is implemented in an improved version of the event generator BABAYAGA with a theoretical accuracy of the order of 0.1%. The generator is now available for high-precision simulations of the Bhabha process at flavour factories.

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“…Working with the τ data also allows us to avoid having to deal with the discrepancies between the determinations of the π + π − electroproduction cross-sections obtained by different experiments [17][18][19][20]. 2 We should add that, though a model is needed for the part of the I = 1 spectral function beyond s = m 2 τ , for the low Q 2 values relevant to a HLO µ , the vacuum polarization we construct is very insensitive to the parametrization used in this region.…”

Section: Introductionmentioning

confidence: 99%

Tests of hadronic vacuum polarization fits for the muon anomalous magnetic moment

2013

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Using experimental spectral data for hadronic τ decays from the OPAL experiment, supplemented by a phenomenologically successful parameterization for the high-s region not covered by the data, we construct a physically constrained model of the isospin-one vector-channel polarization function. Having such a model as a function of Euclidean momentum Q 2 allows us to explore the systematic error associated with fits to the Q 2 dependence of lattice data for the hadronic electromagnetic current polarization function which have been used in attempts to compute the leading order hadronic contribution, a HLO µ , to the muon anomalous magnetic moment. In contrast to recent claims made in the literature, we find that a final error in this quantity of the order of a few percent does not appear possible with current lattice data, given the present lack of precision in the determination of the vacuum polarization at low Q 2 . We also find that fits to the vacuum polarization using fit functions based on Vector Meson Dominance are unreliable, in that the fit error on a HLO µ is typically much smaller than the difference between the value obtained from the fit and the exact model value. The use of a sequence of Padé approximants known to converge to the true vacuum polarization appears to represent a more promising approach.

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Update of the e + e − → π+π− cross section measured by the spherical neutral detector in the energy region 400 < √s < 1000 MeV

Cited by 203 publications

References 10 publications

Dispersion relation for hadronic light-by-light scattering: two-pion contributions

Dispersion relation for hadronic light-by-light scattering: two-pion contributions

Matching perturbative and parton shower corrections to Bhabha process at flavour factories

Tests of hadronic vacuum polarization fits for the muon anomalous magnetic moment

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