Delta-to-N-gamma Coulomb Quadrupole Amplitude in PQCD

Abstract

We present a leading-order pQCD calculation of the helicity-flip $\Delta \to N{\gamma }^{\ast }$ matrix element $G_0$ (Coulomb quadrupole amplitude $C2$), taking into account the transverse momenta of the quarks and the contribution from the gluons. In the large $Q^2$ limit, its scaling behavior acquires a double-logarithmic correction ${\log }^2(Q^2/{\Lambda }^2)$ compared with the standard scaling analysis, due to the contribution from the orbital motion of the small-$x$ partons. Based on this and on the latest JLab experimental results of the $C2-M1$ ratio $R_{SM}$ at $Q^2$ = 3 $\sim$ 4 GeV${}^2$, we make a phenomenological prediction for the latter at higher values of $Q^2$.

9 pages, two figures

References in corpus (10)

• $Q^2$ Dependence of Quadrupole Strength in the ${\gamma }^{\ast }p\to {\Delta }^{+}(1232)\to p{\pi }^0$ Transition
• Perturbative QCD Analysis of the Nucleon's Pauli Form Factor F_2(Q^2)
• Higher Twist Distribution Amplitudes of the Nucleon in QCD
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• Counting Rule for Hadronic Light-Cone Wave Functions
• Quadrupole Moments of N and Delta in the 1/N_c Expansion
• Delta --> N gamma in Large-Nc QCD
• The Singlet g_2 Structure Function in the Next-to-Leading Order
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Cited by in corpus (18)

• Electromagnetic excitation of the Delta(1232)-resonance
• Explanation and Prediction of Observables using Continuum Strong QCD
• Electroexcitation of nucleon resonances
• Nucleon and $\Delta$ elastic and transition form factors
• D-state effects in the electromagnetic N-Delta transition
• Elastic and transition form factors of the Δ(1232)
• Electromagnetic N->Delta transition and neutron form factors
• Nucleon to Delta electromagnetic transition in the Dyson-Schwinger approach
• Insights into the gamma* N -> Delta transition
• Electromagnetic Transition Form Factors of Baryon Resonances
• Transition form factors: ${\gamma }^{\ast }+p\to \Delta (1232)$, $\Delta (1600)$
• Study of nucleon resonances with electromagnetic interactions
• Improved empirical parametrizations of the ${\gamma }^{\ast }N\to \Delta (1232)$ and ${\gamma }^{\ast }N\to N(1520)$ helicity amplitudes and the Siegert's theorem
• Two-photon-exchange effects in the electro-excitation of the $\Delta$ resonance
• Electromagnetic multipole moments of baryons
• Gauge- and point-invariant vertices of nucleon-to-resonance interactions
• Low-Q^2 scaling behavior of the form-factor ratios for the NΔ(1232)-transition
• Zero-Mode Contribution in Nucleon-Delta Transition