Measurement of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>γ</mml:mi><mml:msup><mml:mi>γ</mml:mi><mml:mo>*</mml:mo></mml:msup><mml:mo>→</mml:mo><mml:mi>η</mml:mi></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>γ</mml:mi><mml:msup><mml:mi>γ</mml:mi><mml:mo>*</mml:mo></mml:msup><mml:mo>→</mml:mo><mml:msup><mml:mi>η</mml:mi><mml:mo>′</mml:mo></mml:msup></mml:math>transition form factors

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doi:10.1103/physrevd.84.052001

Cited by 103 publications

(52 citation statements)

References 39 publications

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“…A recent result from BABAR on the and 0 transition form factors is also in agreement with QCD [2]. In light of this, the BABAR result on the pion form factor increasing well above Brodsky-Lepage asymptotics and showing no sign of Q 2 F ðQ 2 Þ ''flattening,'' definitely looks puzzling.…”

Section: Pion Form Factor In Qcd and In Quark Modelssupporting

confidence: 56%

“…e þ e À 0 , with one lepton scattered at a small angle and emitting a quasireal photon, and the other lepton scattering through a large angle, thus emitting a deeply virtual Ã . No sign of convergence towards perturbative QCD asymptotics [5] is seen in the BABAR data for the 0 [1], while the and 0 form factors [2] appear to be consistent with prior theory expectations. The probed momentum transfers, Q 2 $ 40 GeV 2 , extend far beyond any nonperturbative energy scale relevant for low-energy QCD-Q 2 ) m 2 ; Ã 2 QCD ; m 2 ð 0 Þ ; ð4f Þ 2 .…”

Section: Introductionmentioning

confidence: 52%

“…With the advent of QCD came the impetus to study the off-shell form factors of 0 , , and 0 as a way of testing QCD in exclusive processes. The most recent experimental advance in this direction has been achieved by the BABAR collaboration [1,2] that measured the form factors of pseudoscalar mesons in the region of momentum transfer extending to jQ 2 j4 & 100 GeV 2 , significantly increasing the experimental Q 2 range over previous measurements by CLEO [3] and CELLO [4]. The pion transition form factor measurement is based on the process e þ e À !…”

Section: Introductionmentioning

confidence: 99%

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Pion-photon transition form factor and new physics in theτsector

McKeen¹,

Pospelov²,

Roney³

2012

Phys. Rev. D

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Recent measurement of the Ã form factor of the neutral pion in the high Q 2 region disagrees with a priori predictions of QCD-based calculations. We comment on existing explanations, and analyze a possibility that this discrepancy is not due to poorly understood QCD effects, but is a result of some new physics beyond the standard model (SM). We show that such physics would necessarily involve a new neutral light state with mass close to the mass of 0 , and with stronger than 0 couplings to heavier SM flavors such as c, , and b. It is found that only the coupling to the lepton can survive the existing constraints and lead to the observed rise of the pion form factor relative to Q À2 at high Q 2 . We perform numerical fits to data and determine the allowed range of masses and couplings for such new particles. This range of masses and couplings could also reduce or eliminate the tension between the e þ e À and decay determinations of the hadronic vacuum polarization. Dedicated experimental analysis of pair production in association with such new states should provide a conclusive test of the new physics hypothesis as an explanation of the pion form factor rise. We also comment on the calculations of the pion form factor in the chiral quark model, and point out a possible dynamical origin of the quark mass scale inferred from the form factor measurement.

show abstract

Section: Pion Form Factor In Qcd and In Quark Modelssupporting

confidence: 56%

Section: Introductionmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Pion-photon transition form factor and new physics in theτsector

McKeen¹,

Pospelov²,

Roney³

2012

Phys. Rev. D

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“…The Gegenbauer moments of the LCDAs can be extracted using fits to data for the γ * γ → η ( ) transition form factors at different Q 2 reported by the CLEO [37] and BaBar [38] collaborations. The authors of [31] have assumed SU(3) flavor symmetry and have chosen the first few Gegenbauer moments of the quark LCDAs φ q and φ s according to some popular QCD sum-rule calculations for the pion LCDA.…”

Section: Hadronic Input Parametersmentioning

confidence: 99%

Exclusive radiative Z-boson decays to mesons with flavor-singlet components

Alte

König

Neubert

2016

J. High Energ. Phys.

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We present a detailed study of the exclusive radiative decays Z → η ( ) γ employing the QCD factorization approach. We derive a factorization formula for the decay amplitudes valid at leading power in an expansion in (Λ QCD /m Z ) 2 , which includes convolutions of calculable hard-scattering kernels with the leading-twist quark and gluon light-cone distribution amplitudes of the mesons. Large logarithms arising in the evolution from the high scale m Z down to hadronic scales are resummed using the renormalization group, carefully accounting for the effects of the heavy bottom and charm quarks. Our results for the branching ratios are very sensitive to hadronic input parameters, such as the decay constants and mixing angle characterizing the η −η system. Using the most recent estimates of these parameters, we obtain the branching ratios Br(Z → ηγ) ∼ 1.6 · 10 −10 and Br(Z → η γ) ∼ 4.7 · 10 −9 . A measurement of these processes at a future high-luminosity Z factory could provide interesting information on the gluon distribution amplitude.

show abstract

“…, 0 , for which the transition from factors (TFFs), F ðQ 2 Þ and F 0 ðQ 2 Þ, with Q 2 being the virtuality of the off-mass-shell photon, are defined. The usual procedure [7] using the TFFs to evaluate the -0 mixing angle is to calculate the Q 2 dependence of these transition form factors and compare with the experimental data, which are given at a certain range of Q 2 [8][9][10]. However, theoretical calculations for the TFFs at finite Q 2 suffer sizable corrections and are sensitive to the nonperturbative model used for the distribution amplitude of the mesons, which results in large uncertainties in determining the mixing angle.…”

mentioning

confidence: 99%