Electroproduction of single pions at low<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>ε</mml:mi></mml:math>and a measurement of the pion form factor up to<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>Q</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mo>=</mml:mo><mml:mn>10</mml:mn><mml:mn /></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inl

Bebek, C.; Brown, C. N.; Holmes, S.; Kline, R. V.; Pipkin, F. M.; Raither, S.; Sisterson, L. K.; Browman, A.; Hanson, K.; Larson, D.; Silverman, A.

doi:10.1103/physrevd.17.1693

Cited by 382 publications

(380 citation statements)

References 65 publications

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“…The neutron magnetic form factor and the pion form factor were taken from Refs. [58,59] and [60][61][62][63], respectively. The neutron electric form factor G E n (Q 2 ) is measured up to Q 2 = 1.45 GeV 2 [64], and Ref.…”

Section: N π ρ ω Contributionsmentioning

confidence: 99%

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Aznauryan¹,

Burkert²,

Biselli³

et al. 2009

Phys. Rev. C

252

380

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We present results on the electroexcitation of the low mass resonances (1232)P 33 , N (1440)P 11 , N (1520)D 13 , and N (1535)S 11 in a wide range of Q 2 . The results were obtained in the comprehensive analysis of data from the Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility (JLab) on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for π electroproduction off the proton. The data were analyzed using two conceptually different approaches-fixed-t dispersion relations and a unitary isobar model-allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the (1232)P 33 show the importance of a meson-cloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for Q 2 6 GeV 2 . For the Roper resonance, N (1440)P 11 , the data provide strong evidence that this state is a predominantly radial excitation of a three-quark (3q) ground state. Measured in pion electroproduction, the transverse helicity amplitude for the N (1535)S 11 allowed us to obtain the branching ratios of this state to the πN and ηN channels via comparison with the results extracted from η electroproduction. The extensive CLAS data also enabled the extraction of the γ * p → N (1520)D 13 and N (1535)S 11 longitudinal helicity amplitudes with good precision. For the N (1535)S 11 , these results became a challenge for quark models and may be indicative of large meson-cloud contributions or of representations of this state that differ from a 3q excitation. The transverse amplitudes for the N (1520)D 13 clearly show the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q 2 > 1 GeV 2 , confirming a long-standing prediction of the constituent quark model.

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Section: N π ρ ω Contributionsmentioning

confidence: 99%

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Aznauryan¹,

Burkert²,

Biselli³

et al. 2009

Phys. Rev. C

252

380

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show abstract

“…[14]. The resulting form factor is shown in fig.2 and compared with the experimental data of [18] at the space-like momentum transfers accessible within our approach 3 . The agreement is clearly satisfactory and at least as good as the one from the axial vector sum rule [6] (dashed line), which we show for comparison.…”

mentioning

confidence: 99%

The electromagnetic pion form factor and instantons

Forkel

Nielsen

1995

Physics Letters B

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We calculate the electromagnetic pion form factor at intermediate spacelike momentum transfer from the QCD sum rule for the correlation function of two pseudoscalar interpolating fields and the electromagnetic current. This correlator receives essential contributions from direct (i.e. small-scale) instantons, which we evaluate under the assumption of an instanton size distribution consistent with instanton liquid and lattice simulations. The resulting form factor is in good agreement both with the sum rule based on the axial-current correlator and with experiment. * Address after Nov. 1, 1994: European Centre for Theoretical Studies in Nuclear Physics and Related Areas, Villa Tambosi, Strada delle Tabarelle 286, I-38050 Villazzano, Italy † Permanent address: Instituto de Física, Universidade de São Paulo, 01498 -SP-Brazil. 1A central goal of strong-interaction physics is the understanding of hadrons on the basis of quantum chromodynamics (QCD). It is very unlikely that this goal can be reached without a thorough understanding of the QCD vacuum. At present, however, direct links between observed hadron properties and the vacuum structure are still rare and rely mostly on extensive numerical simulations. The aim of this letter is to study one such link -between direct instantons, i.e. small-scale topological vacuum fields, and electromagnetic pion propertiesanalytically in the framework of a QCD sum rule [1,2].Due to the Goldstone nature of the pion, sum rule calculations of pionic properties can be based on two in principle (but not in practice!) equally suitable sets of correlation functions, corresponding to the use of pseudoscalar or axial vector interpolating fields. The pion couples strongly to both of these source currents and thus contributes to the correlators in both channels.The pseudoscalar channel has some principal advantages for sum rule calculations. The accuracy of the standard pole-continuum parametrization for the corresponding spectral functions profits from the almost complete dominance of the pion in the low-mass region [3,4]. Furthermore, correlators involving the pseudoscalar interpolators have a simpler tensor structure. This simplifies in particular the calculation of three-point functions.All existing sum rule applications in the pion channel (with the exception of ref.[5], see below), however, are based on axial vector current correlators [1,2,6,7]. The use of the pseudoscalar interpolating field has been avoided, since it is known to receive essential contributions from direct instantons [3]. Like instanton contributions in general, they could initially not be estimated reliably, due to insufficient knowledge of the instanton size distribution in the vacuum. The attempt of an ab initio description in the dilute gas approximation[8], in particular, failed for all but the smallest instanton sizes due to infrared problems with large instantons. The same problems were encountered in the attempt to supplement the conventional operator product expansion (OPE) in QCD sum rules with di...

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“…Experimental values of F have previously been determined at CEA and Cornell [4], DESY [5,6], and recently at Jefferson Lab [7]. Most of the high Q 2 data have come from experiments at Cornell covering a range of values in Q 2 between 0.28 and 9:77 GeV 2 .…”

mentioning

confidence: 99%

Determination of the Pion Charge Form Factor atQ2=1.60and2.45 (GeV/c)<

Horn¹,

Aniol²,

Arrington³

et al. 2006

Phys. Rev. Lett.

259

164

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The 1 H e; e 0 n cross section was measured at four-momentum transfers of Q 2 1:60 and 2:45 GeV 2 at an invariant mass of the photon nucleon system of W 2:22 GeV. The charged pion form factor (F ) was extracted from the data by comparing the separated longitudinal pion electroproduction cross section to a Regge model prediction in which F is a free parameter. The results indicate that the pion form factor deviates from the charge-radius constrained monopole form at these values of Q 2 by one sigma, but is still far from its perturbative quantum chromodynamics prediction. DOI: 10.1103/PhysRevLett.97.192001 PACS numbers: 14.40.Aq, 11.55.Jy, 13.40.Gp, 25.30.Rw A fundamental challenge in nuclear physics is the description of hadrons in terms of the constituents of the underlying theory of strong interactions, quarks, and gluons. Properties such as the total charge and magnetic moments are well described in a constituent quark framework, which effectively takes into account quark-gluon interactions. However, charge and current distributions, which are more sensitive to the underlying dynamic processes, are not well described.Hadronic form factors provide important information about hadronic structure. The coupling of a virtual photon to structureless particles is completely determined by their charge and magnetic moments. However, for composite particles one must account for the internal structure, which is accomplished by momentum transfer dependent functions. Examples of these functions are the electromagnetic form factors, which describe the distribution of charge and current.One of the simplest hadronic systems available for study is the pion, whose valence structure is a bound state of a quark and an antiquark. The electromagnetic structure of a spinless particle such as the pion is parametrized by a single form factor. Asymptotically, the pion charge form factor, F , is given in perturbative quantum chromodynamics (pQCD) [1]:

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Electroproduction of single pions at lowεand a measurement of the pion form factor up toQ2=10
C. Bebek
¹
,
C. N. Brown
²
,
S. Holmes
³

et al.

Cited by 382 publications

References 65 publications

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

The electromagnetic pion form factor and instantons

Determination of the Pion Charge Form Factor atQ2=1.60and2.45 (GeV/c)<

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Electroproduction of single pions at lowεand a measurement of the pion form factor up toQ2=10C. Bebek1, C. N. Brown2, S. Holmes3 et al.

Cited by 382 publications

References 65 publications

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

The electromagnetic pion form factor and instantons

Determination of the Pion Charge Form Factor atQ2=1.60and2.45 (GeV/c)<

Contact Info

Product

Resources

About

Electroproduction of single pions at lowεand a measurement of the pion form factor up toQ2=10
C. Bebek
¹
,
C. N. Brown
²
,
S. Holmes
³

et al.