Resonance Transition Form Factors Research Articles

Mystery of Bloom-Gilman duality: A light-front holographic QCD perspective

Light-front wave functions motivated by holographic constructions are used to study Bloom-Gilman duality, a feature of deep inelastic scattering. Separate expressions for structure functions in terms of quark and hadronic degrees of freedom (involving transition form factors) are presented, with an ultimate goal of obtaining a relationship between the two expressions. A specific two-parton model is defined and resonance transition form factors are computed using previously derived light-front wave functions. A new form of global duality (integral over all values of $x$ between 0 and 1) is derived from the valence quark-number sum rule. Using a complete set of hadronic states is necessary for this new global duality to be achieved, and the previous original work does not provide such a set. This feature is remedied by amending the model to include a longitudinal confining potential, and the resulting complete set is sufficient to carry out the study of Bloom-Gilman duality. Specific expressions for transition form factors are obtained and all are shown to fall as $1/{Q}^{2}$, at asymptotically large values. This is because the Feynman mechanism dominates the asymptotic behavior of the model. These transition form factors are used to assess the validity of the global and local duality sum rules, with the result that both are not satisfied within the given model. Evaluations of the hadronic expression for $q(x,{Q}^{2})$ provide more details about this lack. This result is not a failure of the current model because it shows that the observed validity of both global and local forms of duality for deep inelastic scattering must be related to a feature of QCD that is deeper than completeness. Our simple present model suggests a prediction that Bloom-Gilman duality would not be observed if deep inelastic scattering experiments were to be made on the pion. The underlying origin of the duality phenomenon in deep inelastic scattering is deeply buried within the confinement aspects of QCD, and its origin remains a mystery.

Analytical investigation of electromagnetic transition form factors of nucleon resonances

In this paper, we investigated the transition form factors of nucleon resonances, in an analytical approach. Employing an improved hypercentral constituent quark model, we obtained analytical eigenfunctions which have been used to calculate the transverse and longitudinal helicity amplitudes for nucleon resonances. We compared the evaluated observables with experimental data and it has been shown that the present model provides a good description of the available data.

Measurement of New Observables from the $$\pi ^{+}\pi ^{-}p$$ Electroproduction Off the Proton

A key objective of the N* program is to measure the resonance transition form factors that contain information needed to explore the distance-dependence description of the interaction of a probe with the nucleon resulting in its excitation to one of its various resonance states. These resonance transition form factors are sensitive to the underlying degrees of freedom of the nucleon and their dynamics while being confined within the nucleon, and therefore serve to understand the emergent complexity of the Universe at the most fundamental level. Experimental observables from single- and double-charged electroproduction channels serve as dominant sources for the extraction of these form factors in the two dimensional landscape spanned by the variables $$Q^{2}$$ and W, which map out the space-time scale of the degrees of freedom and their dynamics during the interaction as well as the range of possible excitations of the nucleon, respectively. For the first time, observables in the double-charged channel that are sensitive to the polarization of the virtual photon are measured using the $$\pi ^{+}\pi ^{-}p$$ reaction channel. This article presents preliminary measurements for these new observables for $$2\;\mathrm{GeV^{2}}\;<\;Q^{2}\;<\;5\;\mathrm{GeV^{2}}$$ and $$1.400\;\mathrm{GeV}<\;W\;<\;2.125\;\mathrm{GeV}$$ using data collected at the experimental facility of Jefferson Laboratory, preceded by an introduction to these observables.

Neutrino Energy Reconstruction Methods Using Electron Scattering Data

The precise measurement of neutrino properties is among the highest priorities in fundamental particle physics, involving many experiments worldwide. Since the experiments rely on the interactions of neutrinos with bound nucleons inside atomic nuclei, the planned advances in the scope and precision of these experiments requires a commensurate effort in the understanding and modeling of the hadronic and nuclear physics of these interactions, which is incorporated as a nuclear model in neutrino event generators. This model is essential to every phase of experimental analyses and its theoretical uncertainties play an important role in interpreting every result.Any nuclear model used to describe neutrino-nucleus scattering should first be validated against these data. Since the vector part of the weak response is related to the electro-magnetic response through CVC, such a test is necessary, but not sufficient, to ensure the validity of a model for given kinematics, namely given values of the transferred energy ω(= ν for neutrinos) and momentum q. The main challenges in connecting electron and neutrino reactions:• matching models used to predict neutrino-nucleus observables to electron scattering data.• expanding theory to include more semi-inclusive predictions.• provide semi-inclusive neutron, proton and pion data sets with broad angular range.The cross section for neutrino scattering from nuclei is sensitive to the same underlying structure determined by QCD, and as probed with pure electromagnetic processes, such as charged lepton scattering from nucleons and nuclei. As such, there are a number of ways that electron scattering data inform ν - A cross section modeling, as well as providing a test-bed for model validation. In contrast to past and current neutrino beams, charged lepton scattering has the distinct advantage of nearly monochromatic beams with well determined energies, allowing for a significantly cleaner kinematic separation of the various production mechanisms in inclusive scattering, such as reso- nance production and nucleon elastic scattering. In addition to providing important experimental input such as nucleon isovector elastic form factors and resonance transition form factors, electron scattering data provide critical information on the distributions of initial state momentum and energy for nucleons in nuclei, the importance of 2-body currents and final state interaction effects. In this analysis, we will give a brief overview of the experimental input provided by electron scattering data.

Resonances from lattice QCD

The spectrum of hadron is mainly composed as shortly-lived states (resonance) that decay onto two or more hadrons. These resonances play an important role in a variety of phenomenologically significant processes. In this talk, I give an overview on the present status of a rigorous program for studying of resonances and their properties using lattice QCD. I explain the formalism needed for extracting resonant amplitudes from the finite-volume spectra. From these one can extract the masses and widths of resonances. I present some recent examples that illustrate the power of these ideas. I then explain similar formalism that allows for the determination of resonant electroweak amplitudes from finite-volume matrix elements. I use the recent calculation of the πγ* → ππ amplitude as an example illustrating the power of this formalism. From such amplitudes one can determine transition form factors of resonances. I close by reviewing on-going efforts to generalize these ideas to increasingly complex reactions and I then give a outlook of the field.

Flavour decomposition of electromagnetic transition form factors of nucleon resonances

In Poincar\'e-covariant continuum treatments of the three valence-quark bound-state problem, the force behind dynamical chiral symmetry breaking also generates nonpointlike, interacting diquark correlations in the nucleon and its resonances. We detail the impact of these correlations on the nucleon's elastic and nucleon-to-Roper transition electromagnetic form factors, providing flavour-separation versions that can be tested at modern facilities.

Pion Electroproduction and Siegert’s Theorem

Nucleon to Resonance transition form factors are discussed within the MAID model for pion electroproduction on the nucleon. For low \(Q^2\) the consequences of Siegert’s theorem are presented and medium to large violations of the Long Wavelength Limit at the pseudo-threshold are observed for the phenomenological parametrizations of the longitudinal transition form factors of different nucleon resonances.

Formula omitted] program at CLAS

The Nlow asterisk program is one of the major goals of CLAS experiments in Jefferson Lab and many outstanding results have been carried out. In this note, I will present some highlight recent measurements of nucleon resonance transition form factors from electro-production as the second resonances. The new pion electro-production data resolve a longstanding puzzle of the nature of the Roper resonance, and confirm the assertion of the symmetric constituent quark model of the Roper as the first radial excitation of the nucleon. The single pion electro-production data for high Q2 confirms the slow fall off of the S11(1535) transition form factor with Q2, and better constrain the branching ratios βNπ:βNη=0.50:0.45. For the first time, the longitudinal transition amplitude to the S11(1535) was extracted from the nπ+ data. Also, new results on the transition amplitudes for the D13(1520) resonance are presented showing a rapid transition from helicity 3/2 dominance seen at the real photon point to helicity 1/2 dominance at higher Q2.

The N* physics program at Jefferson Lab

Recent measurements of nucleon resonance transition form factors with CLAS at Jefferson Lab are discussed. The new data confirm the assertion of the symmetric constituent quark model of the Roper as the first radial excitation of the nucleon. The data on high Q2 nπ+ production better constrain the branching ratios βNπ and βNη. For the first time, the longitudinal transition amplitude to the S11(1535) was extracted from the nπ+ data. Also, new results on the transition amplitudes for the D13(1520) resonance are presented showing a rapid transition from helicity 3/2 dominance seen at the real photon point to helicty 1/2 dominance at higher Q2. I also discuss the status of the search for new excited nucleon states.

Hadron Spectroscopy at CLAS and the Evolution of Strong Degrees of Freedom

Understanding the strong force constitutes one of the biggest challenges in fundamental science that we can and have to tackle now as the needed experimental and theoretical tools become available. Perturbative Quantum ChromoDynamics (pQCD) at small distances, which is governed by quark and gluon fields, and Chiral Perturbation Theory (ChPT) at larger distances, which is governed by pion fields, are both already experimentally validated. However, strong fields at intermediate distances, where they generate about 98% of the total mass of nucleons and therefore of all normal matter, are not understood on similarly firm grounds. Electron scattering in particular serves as an ideal tool to investigate this intermediate region by measuring the resonance transition form factors of three-quark systems with varying momentum transfer and spatial resolution of the probe. The status of the research program at Jefferson Lab to study baryon transition form factors and the evolution of the underlying effective degrees of freedom, or the origin of mass, will be exemplified by recent results in single and double-pion production obtained with CLAS by the Hall B collaborations. These results demonstrate that the separation of resonance and background contributions and therefore the extraction of the electro-coupling amplitudes of resonances become easier and cleaner at higher four-momentum transfers (Q2). Furthermore, the double-pion in comparison to the single-pion channel shows a higher sensitivity to energetically higher lying resonances and a distinctly different dependence on the contributing background amplitudes. The combined analysis of the single- and double-pion data thus reduces model dependent uncertainties significantly, which allows us to extract the resonant electro-coupling amplitudes in an unprecedented quality.

Electromagnetic properties of baryons in a relativistic quark model

Results on electromagnetic form factors of the nucleon and photon transition form factors of non-strange baryon resonances calculated in a relativistically covariant quark model based on the Bethe-Salpeter equation are presented. The relevance of the instanton-induced quark interaction on these properties is discussed.

Electroweak form factors of non-strange baryons

We compute electroweak form factors of the nucleon and photon transition form factors of non-strange baryon resonances up to the third resonance region in a model with instanton-induced interaction. The calculation is based on the Bethe-Salpeter equation for three light constituent quarks and is fully relativistic (U. Löring et al., Eur. Phys. J. A 10, 309 (2001)). Static nucleon properties and photon resonance couplings are in good agreement with experiment and the Q2 behaviour of the experimentally known form factors up to large momentum transfer is accounted for.

HADES, the new electron-pair spectrometer at GSI

The High Acceptance DiElectron Spectrometer HADES is presently set up at GSI, Darmstadt, for the systematic study of hadron properties inside nuclear matter. Resonance widths and effective masses of vector mesons as well as electromagnetic transition formfactors of neutral mesons and baryon resonances will be investigated in the low in variant mass region M inv ≤ 1 GeV/c 2 with a resolution Δ M inv /M inv ≅ 1% (σ).

Electromagnetic transition form factors of negative parity nucleon resonances

We have calculated the transition form factors for electromagnetic excitation of the negative parity resonances of the nucleon using different models previously proposed, and we discuss their results and limits by comparison with experimental data.