Measurement of the slope of the π0 electromagnetic form factor

Farzanpay, F.; Gumplinger, P.; Stetz, A.W.; Poutissou, J. M.; Blevis, I.; Hasinoff, M.; Virtue, C. J.; Waltham, Chris; Robertson, B.C.; Mulera, T.; Shor, A.; Lowe, J.; Chew, S.H.

doi:10.1016/0370-2693(92)90577-q

Cited by 37 publications

(37 citation statements)

References 39 publications

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“…[32]). This number is not very far from the central values of two last experiments, a π = 0.026 ± 0.024 ± 0.0048 [39], a π = 0.025 ± 0.014 ± 0.026 [40], but the experimental errors are rather large. An earlier experiment [41] produced a π = −0.11 ± 0.03 ± 0.08, a result whose central value has opposite sign and much larger absolute magnitude.…”

Section: B Anomalous Form Factormentioning

confidence: 65%

Pion in the holographic model with 5D Yang-Mills fields

Grigoryan

Radyushkin

2008

Phys. Rev. D

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We study pion in the holographic model of Hirn and Sanz which contains two Yang-Mills fields defined in the background of the sliced AdS space. The infrared boundary conditions imposed on these fields generate the spontaneous breaking of the chiral symmetry down to its vector subgroup. Within the framework of this model, we get an analytic expression for the pion form factor and a compact result for its radius. We also extend the holographic model to include Chern-Simons term which is required to reproduce the appropriate axial anomaly of QCD. As a result, we calculate the anomalous form factor of the pion and predict its Q 2 -slope for the kinematics when one of the photons is almost on-shell. We also observe that the anomalous form factor with one real and one virtual photon is given by the same analytic expression as the electromagnetic form factor of a charged pion. One of the advantages of the present model is that it does not require an infrared boundary counterterm to correctly reproduce the anomaly of QCD.

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Section: B Anomalous Form Factormentioning

confidence: 65%

Pion in the holographic model with 5D Yang-Mills fields

Grigoryan

Radyushkin

2008

Phys. Rev. D

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“…The Dalitz decay of the TT° has been well studied experimentally [8] as well as theoretically [9]. For KDQ\ decays and other decay modes under investigation, i.e., K ee , K + -• 7r + 7r°, n° -> e + e~e + e~ (i^DDai), and direct K+ -• 7r + e+e~ (Knee), the observed final state charged particles are the same.…”

mentioning

confidence: 83%

Determination of the branching ratio of the decayπ0→e+
Deshpande
¹
,
Alliegro
²
,
Chaloupka
³

et al. 1993
Phys. Rev. Lett.
14
2
7
0
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Employing the decay chain K + -> 7r + 7r°, 7r° -• e + e~ we have observed the decay TT° -• e + e~. With a signal sample of ?^21 events we measure the branching ratio for n° -> e + e~ to be (6.9 ±2.3 ± 0.6) x 10~8, normalized to the decay K + -> TT+IT 0 , 7r° -* e + e~/y. This result is consistent with the unitarity lower bound and the published 90% confidence level upper limit of 13xl0~8.

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“…The π 0 γ * γ * form factor has been studied previously in the decay π 0 → e + e − γ [9,10,11], where the quantity of interest has been the slope parameter a of the first-order Taylor expansion f (x, 0) = 1+ax, with x ≡ m 2 e + e − /M 2 π 0 . Here we use a form factor parametrizaton based on the model of D'Ambrosio, Isidori, and Portolés (DIP) [12], but with an additional constraint that ensures the coupling vanishes at large momenta [13].…”

Section: Arxiv:08022064v2 [Hep-ex] 11 May 2008mentioning

confidence: 99%

Determination of the Parity of the Neutral Pion via Its Four-Electron Decay

et al. 2008

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We present a new determination of the parity of the neutral pion via the double Dalitz decay π 0 → e + e − e + e − . Our sample, which consists of 30 511 candidate decays, was collected from KL → π 0 π 0 π 0 decays in flight at the KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the negative π 0 parity, and place a limit on scalar contributions to the π 0 → e + e − e + e − decay amplitude of less than 3.3% assuming CPT conservation. The π 0 γ * γ * form factor is well described by a momentum-dependent model with a slope parameter fit to the final state phase space distribution. Additionally, we have measured the branching ratio of this mode to be B(π 0 → e + e − e + e − ) = (3.26 ± 0.18) × 10 −5 .PACS numbers: 14.40.Aq, 13.40.GpThe parity of the neutral pion has been determined indirectly by studying negative pions captured on deuterium [1,2]. The observed reactions imply that the π − is a pseudoscalar and that the parities of the π − and the π 0 are the same. It has long been known that the decay π 0 → γγ in principle offers a direct means of determining the π 0 parity through the polarizations of the photons [3,4]. Given that there are no available methods for measuring the polarization of a high-energy photon, this measurement has never been performed. However, it was soon noted that the double Dalitz decay π 0 → e + e − e + e − , which proceeds through an intermediate state with two virtual photons (see Fig. 1), is sensitive to the parity of the pion since the plane of a Dalitz pair is correlated with the polarization of the virtual photon [5,6]. This process was studied in a 1962 hydrogen bubble chamber experiment using stopping negative pion capture (π − p → nπ 0 ). That group observed 206 π 0 → e + e − e + e − events and reported that the observed distribution of the e + e − planes was consistent with a pseudoscalar pion and disfavored a scalar pion at the level of 3.6 standard deviations [7]; this experiment also produced a measurement of the branching ratio of this decay, which remains the most precise result to date. Using a sample of more than 30 000 π 0 → e + e − e + e − decays, we report new precise measurements of the properties of this decay. Our modeling of the decay includes for the first time a proper treatment of the exchange contribution to the matrix element, and consideration

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Measurement of the slope of the π0 electromagnetic form factor

Cited by 37 publications

References 39 publications

Pion in the holographic model with 5D Yang-Mills fields

Pion in the holographic model with 5D Yang-Mills fields

Determination of the branching ratio of the decayπ0→e+
Deshpande
¹
,
Alliegro
²
,
Chaloupka
³

et al. 1993
Phys. Rev. Lett.
14
2
7
0
View full text Add to dashboard Cite

Determination of the Parity of the Neutral Pion via Its Four-Electron Decay

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Measurement of the slope of the π0 electromagnetic form factor

Cited by 37 publications

References 39 publications

Pion in the holographic model with 5D Yang-Mills fields

Pion in the holographic model with 5D Yang-Mills fields

Determination of the branching ratio of the decayπ0→e+Deshpande1, Alliegro2, Chaloupka3 et al. 1993Phys. Rev. Lett.14270View full textAdd to dashboardCite

Determination of the Parity of the Neutral Pion via Its Four-Electron Decay

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Determination of the branching ratio of the decayπ0→e+
Deshpande
¹
,
Alliegro
²
,
Chaloupka
³

et al. 1993
Phys. Rev. Lett.
14
2
7
0
View full text Add to dashboard Cite