Measurement of the Charged Pion Electromagnetic Form Factor

Volmer, J.; Abbott, D.; Anklin, H.; Armstrong, Christopher; Arrington, J.; Assamagan, K.; Avery, S.; Baker, O. K.; Blok, H. P.; Bochna, C.; Brash, E. J.; Breuer, H.; Chant, N. S.; Dunne, J.; Eden, T.; Ent, R.; Gaskell, D.; Gilman, R.; Gustafsson, K.; Hinton, W.; Huber, G. M.; Jackson, H. E.; Jones, M.; Keppel, C.; Kim, P. H.; Kim, W.; Klein, A.; Koltenuk, D.; Liang, M.; Lolos, G. J.; Lung, A.; Mack, D.; McKee, D.; Meekins, D.; Mitchell, J.; Mkrtchyan, H.; Mueller, B.; Niculescu, G.; Niculescu, I.; Pitz, D.; Potterveld, D. H.; Qin, L. M.; Reinhold, J.; Shin, I. K.; Stepanyan, S.; Tadevosyan, V.; Tang, L.; Meer, R. L. J. van der; Vansyoc, K.; Westrum, Derek van; Vulcan, W.; Wood, S. A.; Yan, Chao; Wenheng, Zhao; Zihlmann, B.

doi:10.1103/physrevlett.86.1713

Cited by 281 publications

(152 citation statements)

References 16 publications

(21 reference statements)

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“…In summary, we verified that the new data for the pion electromagnetic form factor [21] is satisfactory described by our symmetric ansatz of the vertex function when the experimental value of f exp π is fitted and the constituent quark mass is chosen in the range between 0.2 and 0.3 GeV. We performed a detailed analysis of the contribution of the lightfront pair-term to the form factor for different momentum transfer directions in the Breit frame.…”

Section: Numerical Results and Summarymentioning

confidence: 93%

Frame dependence of the pair contribution to the pion electromagnetic form factor in a light-front approach

Melo¹,

Frederico²,

Pace³

et al. 2003

Braz. J. Phys.

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The frame dependence of the pair-term contribution to the electromagnetic form factor of the pion is studied within the Light Front approach. A symmetric ansatz for the pion Bethe-Salpeter amplitude with a pseudo scalar coupling of the constituent to the pion field is used. In this model, the pair term vanishes for the DrellYan condition, while it is dominant for momentum transfer along the light-front direction. I IntroductionWithin the Front Form dynamics [1], where the state of the system is defined at x + = t + z = 0, if one uses the impulse approximation of the plus component of the electromagnetic current (j + ) in the Drell-Yan frame to calculate the form factors, the pair production from the incoming photon (pair-term contribution) is in general suppressed by lightfront momentum conservation (see, e.g., [2]). This was seen in schematic covariant models for spin-zero composite systems [3,4,5]. However, even in the Drell-Yan frame the pair term is present in j + for spin-one systems and is necessary to keep the rotational properties of the matrix element of the current [6,7].To avoid the difficulties associated with the rotational properties of the impulse approximation some physically motivated schemes to extract form factors from the current were used [8,9,10]. In another approach, free of these ambiguities [11], the plus component of the momentum transfer is non zero while the transverse momentum transfer vanishes in the Breit frame. This can be achieved by departing from the Drell-Yan condition by rotating the system around the y-direction, i.e, a non-kinematical transformation, and thus changing the direction of the momentum transfer in the z − x plane.However, by relaxing the Drell-Yan condition, a lightfront pair term can contribute to the plus component of the current, which can be studied in the pion example, as a prototype of a relativistic system of bound constituents. In this work, the composite system of a constituent quark and antiquark, is described by an ansatz for the Bethe-Salpeter amplitude which is nonconstant and symmetric with a pseudo scalar coupling of the constituent to the pion field. Our aim here is to discuss, within that model, the magnitude of the pair contribution to the pion electromagnetic form factor for momentum transfers in the z − x plane in the Breit-frame, as has been done in Ref. [5].The work is organized as follows. In Sec. II, we present the model of the pion Bethe-Salpeter amplitude and its eletromagnetic current in impulse approximation. In Sec. III, we discuss the numerical results for the pion electromagnetic form factor where the separate contribution of the pair term is given. We also present our summary in Sec. III. II Pion Model and Electromagnetic CurrentThe electromagnetic current of the pion is calculated in impulse approximation, using a pseudoscalar coupling between pion and quark fields, given by the effective Lagrangian (see, e.g.[12]):where g = m/f π is the coupling constant from the Goldberg-Treiman relation at the quark level, and m is the

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Section: Numerical Results and Summarymentioning

confidence: 93%

Frame dependence of the pair contribution to the pion electromagnetic form factor in a light-front approach

Melo¹,

Frederico²,

Pace³

et al. 2003

Braz. J. Phys.

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“…An advantage of this approach is that it also utilizes the existing data on the pion EM FF in the spacelike region. [20][21][22] As a result, the errors of the determined masses and widths are thereby remarkably reduced. In Sec.…”

Section: Introductionmentioning

confidence: 88%

The mass and width differences of the neutral and charged ρ(770), ρ(1450) and ρ(1700) mesons from e+e−→ π+π− and τ−→ ντπ−π0 processes

Bartoš

Dubnička

Dubničková

et al. 2017

Int. J. Mod. Phys. A

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Unlike the Review of Particle Physics, the clear nonzero values of the mass and width differences of the neutral and charged [Formula: see text] mesons are determined by an application of the Unitary & Analytic model of the pion electromagnetic and the pion weak form factor in a description of the data on [Formula: see text] and [Formula: see text] processes, respectively. Also the mass and the width differences of the neutral and charged [Formula: see text] and [Formula: see text] mesons are determined for the first time, however, they are masked by large evaluated errors. Therefore, in order to come to a definite conclusion, more precise data on [Formula: see text] and [Formula: see text] in the region of [Formula: see text] and [Formula: see text] mesons are desirable.

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“…Particularly, as the fundamental part of the theory, topics of investigating the binding and confinement of quarks and gluons inside hadrons have been actively pursued, and prominent examples include the charged pion form factor experiments [2,3] and GlueX experiment [4].…”

Section: Dynamical Properties Of Hadronsmentioning

confidence: 99%

“…The actual target thicknesses Target Target length (cm) Target thickness (g/cm 2 ) LH 2 3.918 ± 0.01 0.283 ± 0.002 Table 3.1: Cryotarget thicknesses not corrected for beam offset. The target length is given by L = 2 R 2 − dx 2 , and the target cell radius R is corrected for thermal contraction, and dx is the beam offset from the target center.…”

Section: Target Thicknessmentioning

confidence: 99%

Exclusive Backward-Angle Omega Meson Electroproduction

Li¹

2017

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Exclusive meson electroproduction at different squared four-momenta of the exchanged virtual photon, Q 2 , and at different four-momentum transfers, t and u, can be used to probe QCD's transition from hadronic degrees of freedom at the long distance scale to quark-gluon degrees of freedom at the short distance scale. Backward-angle meson electroproduction was previously ignored, but is anticipated to offer complimentary information to conventional forward-angle meson electroproduction studies on nucleon structure.This work is a pioneering study of backward-angle ω cross sections through the exclusive 1 H(e, e ′ p)ω reaction using the missing mass reconstruction technique. The extracted cross sections are separated into the transverse (T), longitudinal (L), and LT, TT interference terms.The analyzed data were part of experiment E01-004 (F π -2), which used 2.6-5.2 GeV electron beams and HMS+SOS spectrometers in Jefferson Lab Hall C. The primary objective was to detect coincidence π in the forward-angle, where the backward-angle ω events were fortuitously detected. The experiment has central Q 2 values of 1.60 and 2.45 GeV 2 , at W = 2.21 GeV. There was significant coverage in φ and ǫ, which allowed separation of σ T,L,LT,TT . The data set has a unique u coverage of −u ∼ 0, which corresponds to −t > 4 GeV 2 .The separated σ T result suggest a flat ∼ 1/Q 1.33±1.21 dependence, whereas σ L seems to holdat the ∼90% confidence level.After translating the results into the −t space of the published CLAS data, our data show evidence of a backward-angle ω electroproduction peak at both Q 2 settings. Previously, this phenomenon showing both forward and backward-angle peaks was only observed in the meson photoproduction data.Through comparison of our σ T data with the prediction of the Transition Distribution Amplitude (TDA) model, and signs of σ T dominance, promising indications of the applicability of the TDA factorization are demonstrated at a much lower Q 2 value than its preferred range of Q 2 > 10 GeV 2 .These studies have opened a new means to study the transition of the nucleon wavefunction through backward-angle experimental observables. Acknowledgements

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Measurement of the Charged Pion Electromagnetic Form Factor

Cited by 281 publications

References 16 publications

Frame dependence of the pair contribution to the pion electromagnetic form factor in a light-front approach

Frame dependence of the pair contribution to the pion electromagnetic form factor in a light-front approach

The mass and width differences of the neutral and charged ρ(770), ρ(1450) and ρ(1700) mesons from e+e−→ π+π− and τ−→ ντπ−π0 processes

Exclusive Backward-Angle Omega Meson Electroproduction

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