Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1305.3847

Proton Compton scattering in a unified proton-Delta Model

Yun Zhang·Konstantin Savvidy
View original source ↗Read source document ↗Export metadata ↓

Abstract

We develop a field-theoretic model for the description of proton Compton scattering in which the proton and its excited state, the Δ+ resonance, are described as part of one multiplet with a single Rarita-Schwinger wavefunction. In order to describe the phenomena observed, it is necessary to incorporate both minimal and non-minimal couplings. The minimal coupling reflects the fact that the Δ+ is a charged particle, and in this model the minimal coupling contributes also to the M1 magnetic transition via the γNΔvertex. The non-minimal couplings consist of five electromagnetic form-factors, which are accessed at fixed and vanishing momentum-transfer squared with real photons in Compton scattering experiments, therefore it is possible to extract a rather well-determined set of optimal parameters which reasonably well fit the data in the resonance region 140-450 MeV. The crucial parameter which determines the γNΔtransition amplitude and therefore the height of the resonance peak is equal to 3.66 +- 0.03, in units of μ_N. We find that this parameter also primarily determines the contributions to magnetic polarizability in this model. In the low-energy region up to 140 MeV, we separately fit the electric and magnetic polarizabilities, while keeping the other parameters fixed and obtain values in line with previous approaches. The basic model is then extended by incorporating the sigma-meson channel with the currently favored parameters, and the pion vertex corrections.

Explore related subjects

hep-phnucl-th

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Yun Zhang, Konstantin Savvidy. 2013-05-16. Proton Compton scattering in a unified proton-Delta Model. https://doi.org/10.1103/physrevc.88.064614

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Exploring new physics in the angular distribution of $\bar B\rightarrow D^*(\rightarrow Dπ)τ^-(\rightarrow V^-ν_τ)\barν_τ$

The decays $\bar{B}\rightarrow D^*τ^{-}\barν_τ$ provide sensitive probes of new physics in the $b\rightarrow cτν$ transition. We discuss the effects of new physics in the decay chain $\bar{B}\rightarrow D^*(\rightarrow Dπ)τ^{-}(\rightarrow V^-ν_τ)\barν_τ$ where $V$ is a vector meson. We first present a comprehensive analysis of the five-dimensional angular distribution for the full decay chain $\bar{B}\rightarrow D^*(\rightarrow Dπ)τ^{-}(\rightarrow ρ^-ν_τ)\barν_τ$, exploiting the hadronic $τ$ decay to $ρ^-ν_τ$ to circumvent the experimental challenge of direct $τ$ reconstruction. The differential decay rate is expressed in terms of measurable kinematic variables $θ^*$, $E_ρ$, $θ_ρ$, $χ_ρ$, and $q^2$ -- with complete coefficient functions provided for scalar, pseudoscalar, vector, axialvector, and tensor new-physics interactions. From this distribution we construct a set of integrated observables, including the $D^*$ polarization fractions and lepton-side forward-backward and azimuthal asymmetries, which isolate distinct combinations of helicity amplitudes. We also show that by decomposing the vector-meson energy spectrum into its longitudinal ($L$) and transverse ($T$) helicity sectors, two additional analyzing powers ($α_L$ and $α_T$) related to the measurement of $τ$ polarization $P_τ^{D^*}(q^2)$ are obtained. Without information on the polarization of meson $V$, the spin analyzing power of $ρ$ is much larger than that of $a_1$ with $α_ρ=0.45$ and $α_{a_1}=0.02$. We further perform a numerical analysis using current experimental data on $R_{D^*}$ and the $D^*$ longitudinal polarization fraction $\langle F_L^{D^*}\rangle$ to constrain the complex new-physics couplings $g_L$, $g_R$, $g_P$, and $g_T$, revealing the correlations among them.

hep-ph↗
arXiv2026

Inclusive diffraction in eA at small x with the Sartre event generator

We present an extension of the Sar\emph{t}re event generator that implements inclusive diffractive deep inelastic scattering for both proton and nuclear targets at small $x$. The calculation is performed in the colour-dipole picture using the IPsat and IPnonsat dipole amplitudes that Sar\emph{t}re also employs for exclusive processes, and includes the transverse and longitudinal $q\bar q$ contributions together with the $q\bar qg$ Fock state that dominates at large $M_X$. The partonic diffractive system is hadronised with \pythia, giving fully exclusive hadronic final states. We compare to the combined H1 and ZEUS inclusive diffractive measurements and to diffractive $D^*$ production, and present predictions for the Electron-Ion Collider. This makes Sar\emph{t}re the only event generator providing inclusive diffractive DIS in small-$x$ for both $ep$ and $eA$ collisions.

hep-ph↗
arXiv2026

Resummation of threshold double logarithms in gluon fragmentation into $^1S_0^{[1,8]}$ quarkonia

I investigate the threshold double logarithmic behavior of the fragmentation function of a gluon into $^1S_0^{[1,8]}$ quarkonia, which is suppressed by $1/N$ in Mellin space. While threshold double logarithms have been resummed to all orders in the strong coupling for gluon fragmentation functions for quarkonia at leading power in $1/N$, it has not been known how to resum them for channels suppressed by powers of $1/N$. Threshold resummation can be important for the $^1S_0^{[1,8]}$ channels, as the tree-level gluon fragmentation functions have finite yet nonzero values at the kinematical threshold. I derive a formalism for resumming the threshold double logarithms for these channels at the leading double logarithmic level and discuss the phenomenological impact.

hep-ph↗