Determination of the longitudinal and the transverse part in π+ electroproduction

Ackermann, H.; Azemoon, T.; Gabriel, W.; Mertiens, H.D.; Reich, H.; Specht, G.; Janata, F.; Schmidt, D.

doi:10.1016/0550-3213(78)90523-0

Cited by 90 publications

(99 citation statements)

References 15 publications

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“…This means that there is a large gap to be filled in our understanding, extending to relatively high Q 2 values [17]. For Q 2 of a few GeV 2 an indirect experimental method must be used to determine F π with scattering of electrons from the pion cloud around a proton [18][19][20]. The most recent results from Jefferson Lab [21][22][23][24][25] have reached Q 2 = 2.45 GeV 2 but extension to 6 GeV 2 is foreseen [1], starting in 2018, as a key experiment (E12-06-101) for the 12 GeV upgrade.…”

Section: Introductionmentioning

confidence: 99%

Pseudoscalar meson electromagnetic form factor at high Q2 from full lattice QCD

et al. 2017

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We give an accurate determination of the vector (electromagnetic) form factor, F (Q 2 ), for a light pseudoscalar meson up to squared momentum transfer Q 2 values of 6 GeV 2 for the first time from full lattice QCD, including u, d, s and c quarks in the sea at multiple values of the lattice spacing. Our results show good control of lattice discretisation and sea quark mass effects. We study a pseudoscalar meson made of valence s quarks but the qualitative picture obtained applies also to the π meson, relevant to upcoming experiments at Jefferson Lab. We find that Q 2 F (Q 2 ) becomes flat in the region between Q 2 of 2 GeV 2 and 6 GeV 2 , with a value well above that of the asymptotic perturbative QCD expectation, but well below that of the vector-meson dominance pole form appropriate to low Q 2 values. Our calculations show that we can reach higher Q 2 values in future to shed further light on where the perturbative QCD result emerges.

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Section: Introductionmentioning

confidence: 99%

Pseudoscalar meson electromagnetic form factor at high Q2 from full lattice QCD

et al. 2017

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“…. The data Brauel et al [28] and that of Ackermann et al [29] have using the method of [2]. The Amendola data et al are from [30] The data point labeled PionCT is from [31].…”

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confidence: 99%

Singular charge density at the center of the pion?

Miller

2009

Phys. Rev. C

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We relate the three-dimensional infinite momentum frame spatial charge density of the pion to its electromagnetic form factor Fπ(Q 2 ). Diverse treatments of the measured form factor data including: phenomenological fits, non-relativistic quark models, the application of perturbative QCD, QCD sum rules, holographic QCD and the Nambu Jona-Lasinio (NJL) model all lead to the result that the charge density at the center of the pion has a logarithmic divergence. Relativistic constituent quark models do not display this singularity. Future measurements planned for larger values of Q 2 may determine whether or not a singularity actually occurs. Understanding the pion is a necessary step to learning how QCD describes the interaction and existence of elementary particles. As a nearly massless excitation of the QCD vacuum with pseudoscalar quantum numbers, the pion plays a central role in particle and nuclear physics as a harbinger of spontaneous symmetry breaking and as the carrier of the longest range force between nucleons.The importance of the pion has been recognized by a huge level of both experimental and theoretical activity aimed at measuring its properties and understanding its structure. New measurements of the pion electromagnetic form factor, F π (Q 2 ), have been performed [1, 2] and are planned [3]. Here we present the first phenomenological analysis of existing data to determine the charge density of the pion in a model independent manner.A proper determination of a charge density requires the measurement of a density operator. We shall show that measurements of the pion form factor directly involve the three-dimensional charge density of partons, in the infinite momentum frame,ρ ∞ (x − , b). In this frame [4], the electromagnetic charge density J 0 becomes J + and

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“…In Figure 6, besides the fitted data from NA7 and Fermilab, one has displayed the (unfitted) data from the DESY experiments [100,101] and the lowest photon virtuality data collected at Jefferson Lab by the F π Collaboration. The data points flagged by JLAB 2008 and DESY have been extracted from the latest -to our knowledge -publication of the F π Collaboration [99].…”

Section: The Pion Form Factor : the Model-dependent Datamentioning

confidence: 99%

$${\hbox {BHLS}}_2$$, a new breaking of the HLS model and its phenomenology

2020

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Previous studies have shown that the Hidden Local Symmetry (HLS) Model, supplied with appropriate symmetry breaking mechanisms, provides an Effective Lagrangian (BHLS) able to encompass a large number of processes within a unified framework. This allowed to design a global fit procedure which provides a fair simultaneous description of the e + e − annihilation into 6 final states (π + π − , π 0 γ, ηγ, π + π − π 0 , K + K − , K L K S ), the dipion spectrum in the τ decay and some more light meson decay partial widths. In this paper, additional breaking schemes are defined which improve the BHLS working and extend its scope so as to absorb spacelike processes within a new framework (BHLS 2 ). The phenomenology previously explored with BHLS is fully revisited in the BHLS 2 context with special emphasis on the φ mass region using all available data samples. It is shown that BHLS 2 addresses perfectly the close spacelike region covered by NA7 and Fermilab data; it is also shown that the recent Lattice QCD (LQCD) information on the pion form factor are accurately predicted by the BHLS 2 fit functions derived from fits to only annihilation data. The contribution to the muon anomalous magnetic moment a th 1 The e + e − → η ′ γ channel has been considered in [25,26] and found to contributes to a had µ at the 10 −12 level only and can thus be safely discarded.As clear in Equations (8), BKY breaks the symmetry of the HLS Model in the very definition of its Lagrangian. This is quite legitimate and strongly validated by its remarkable description of a considerable amount of data [25,26,27]. Nevertheless, it is of interest to explore other possibilities to improve the description of the data in some specific mass regions and, then, reduce or cancel out the additional systematic uncertainties reported in [27].Let us focus on Equation (4) which defines the original HLS covariant derivative :

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Determination of the longitudinal and the transverse part in π+ electroproduction

Cited by 90 publications

References 15 publications

Pseudoscalar meson electromagnetic form factor at high Q2 from full lattice QCD

Pseudoscalar meson electromagnetic form factor at high Q2 from full lattice QCD

Singular charge density at the center of the pion?

$${\hbox {BHLS}}_2$$, a new breaking of the HLS model and its phenomenology

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