A measurement of the ?0, ? and ?? electromagnetic form factors

Behrend, H. J.; Criegee, L.; Field, J. H.; Franke, G.; Jung, H.; Meyer, J.; Podobrin, O.; Schröder, V.; Winter, G. G.; Bussey, P.; Campbell, A. J.; Hendry, D.; Lumsdon, S.; Skillicorn, I. O.; Ahme, J.; Blobel, V.; Feindt, M.; Fenner, H.; Harjes, J.; Köhne, J. H.; Peters, J.; Spitzer, H.; Weihrich, T.; Apel, W. D.; Engler, J.; Flügge, G.; Fries, D. C.; Fuster, J.; Gamerdinger, K.; Grosse‐Wiesmann, P.; Küster, H.; Müller, H.; Ranitzsch, K. H.; Schneider, H.; Boer, W. De; Buschhorn, G.; Grindhammer, G.; Gunderson, B.; Kiesling, C.; Kotthaus, R.; Kroha, H.; Lüers, D.; Oberlack, H.; Schacht, P.; Scholz, Stephan; Wiedenmann, W.; Davier, M.; Grivaz, J.-F.; Haïssinski, J.; Journé, V.; Diberder, F. Le; Veillet, J. J.; Blohm, K.; George, R.; Goldberg, M.; Hamon, O.; Kapusta, F.; Poggioli, L.; Rivoal, M.; D’Agostini, G.; Ferrarotto, F.; Iacovacci, M.; Shooshtari, G.; Stella, B.; Cozzika, G.; Ducros, Y.; Alexander, G.; Beck, A.; Bella, G.; Grunhaus, J.; Klatchko, A.; Levy, A.; Milstène, C.

doi:10.1007/bf01549692

Cited by 374 publications

(121 citation statements)

References 23 publications

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“…2 Here and below we denote by 1 ellipse (ellipsoid) a confidence region in the ða 2 ; a 4 Þ plane that represents a coverage probability equal to 68.27%. predicted by perturbative QCD, from below, while at low momenta it also yields reasonable agreement with the CELLO data [5]. 3 Therefore, it came as a surprise that the data on Ã !…”

Section: Status Of Experimental Datamentioning

confidence: 77%

“…Experimental information is mostly available for an asymmetric configuration in which one of the photons is quasi-on-mass-shell with q 2 ! 0 [5][6][7]. In that case, perturbative QCD cannot be directly applied at a consolidated level because the real photon is emitted at large distances and has, therefore, a hadronic content that demands the application of nonperturbative techniques.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Pion-photon transition: The new QCD frontier

Bakulev¹,

Михайлов²,

Pimikov³

et al. 2011

Phys. Rev. D

132

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We perform a detailed analysis of all existing data (CELLO, CLEO, BABAR) on the pion-photon transition form factor by means of light-cone sum rules in which we include the next-to-leading order QCD radiative corrections and the twist-four contributions. The next-to-next-to-leading order radiative correction together with the twist-six contribution are also taken into account in terms of theoretical uncertainties. Keeping only the first two Gegenbauer coefficients a 2 and a 4 , we show that the 1 error ellipse of all data up to 9 GeV 2 greatly overlaps with the set of pion distribution amplitudes obtained from nonlocal QCD sum rules-within the range of uncertainties due to twist-four. This remains valid also for the projection of the 1 error ellipsoid on the ða 2 ; a 4 Þ plane when including a 6 . We argue that it is not possible to accommodate the high-Q 2 tail of the BABAR data with the same accuracy, despite opposite claims by other authors, and conclude that the BABAR data still pose a challenge to QCD.

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Section: Status Of Experimental Datamentioning

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Pion-photon transition: The new QCD frontier

Bakulev¹,

Михайлов²,

Pimikov³

et al. 2011

Phys. Rev. D

132

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“…The slope of the TFF corresponds to ð1.60 AE 0.17ðstatÞ AE 0.08ðsysÞÞ GeV −2 and agrees within errors with the VMD model predictions. The uncertainty of the η 0 transition form-factor slope matches the best determination in the spacelike region from the CELLO Collaboration b η 0 ¼ ð1.60 AE 0.16Þ GeV −2 [30], and improves the previous determination of the slope in the timelike region b η 0 ¼ ð1.7 AE 0.4Þ GeV −2 [1,8]. The η 0 form factor is determined by both universal π þ π − rescattering and a reaction specific part, with the latter contributing about 20% to the form-factor slope [14].…”

Section: Fig 7 (Color Online)mentioning

confidence: 67%

Observation of the Dalitz decayη′→γe+e−

Ablikim¹,

Ачасов²,

Ai³

et al. 2015

Phys. Rev. D

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We report the first observation of the Dalitz decay η 0 → γe þ e − , based on a data sample of 1.31 billion J=ψ events collected with the BESIII detector. The η 0 mesons are produced via the J=ψ → γη 0 decay process. The ratio Γðη 0 → γe þ e − Þ=Γðη 0 → γγÞ is measured to be ð2.13 AE 0.09ðstatÞ AE 0.07ðsysÞÞ × 10 −2 . This corresponds to a branching fraction Bðη 0 → γe þ e − Þ ¼ ð4.69 AE 0.20ðstatÞ AE 0.23ðsysÞÞ × 10 −4 . The transition form factor is extracted and different expressions are compared to the measured dependence on the e þ e − invariant mass. The results are consistent with the prediction of the vector meson dominance model.

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“…The transition form factor, F (q 2 1 , q 2 2 ), is equal to one for real photons and is usually parametrized in the form F (q inspired by the Vector Dominance Model [17]. The parameter b for the η meson has been measured at high q 2 values in γγ experiments with single-tagging [18][19][20] and in the η leptonic radiative decays η → ℓ + ℓ − γ [21][22][23] at low q 2 values, closer to those of this measurement. The results do not show appreciable dependence on q 2 and the value assumed in this analysis, b η = (1.94 ± 0.15) GeV −2 , was obtained as an average of the measurements at low q 2 .…”

Section: Signal and Background Modelmentioning

confidence: 99%

Measurement of η meson production in γγ interactions and Γ(η → γγ) with the KLOE detector

Babusci¹,

Badoni²,

Balwierz-Pytko³

et al. 2013

J. High Energ. Phys.

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We present a measurement of η meson production in photon-photon interactions produced by electron-positron beams colliding with √ s = 1 GeV. The measurement is done with the KLOE detector at the φ-factory DAΦNE with an integrated luminosity of 0.24 fb −1 . The e + e − → e + e − η cross section is measured without detecting the outgoing electron and positron, selecting the decays η → π + π − π 0 and η → π 0 π 0 π 0 . The most relevant background is due to e + e − → ηγ when the monochromatic photon escapes detection. The cross section for this process is measured as σ(e + e − → ηγ) = (856 ± 8 stat ± 16 syst ) pb. The combined result for the e + e − → e + e − η cross section is σ(e + e − → e + e − η) = (32.72 ± 1.27 stat ± 0.70 syst ) pb. From this we derive the partial width Γ(η → γγ) = (520 ± 20 stat ± 13 syst ) eV. This is in agreement with the world average and is the most precise measurement to date.

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A measurement of the ?0, ? and ?? electromagnetic form factors

Cited by 374 publications

References 23 publications

Pion-photon transition: The new QCD frontier

Pion-photon transition: The new QCD frontier

Observation of the Dalitz decayη′→γe+e−

Measurement of η meson production in γγ interactions and Γ(η → γγ) with the KLOE detector

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