arXiv subjects

Kornelija Passek-Kumerički

Publications and source records attributed to Kornelija Passek-Kumerički.

8 recordsLinked to original sources

arXiv2023

Probing chiral-even and chiral-odd leading twist quark generalised parton distributions through the exclusive photoproduction of a $ γρ$ pair

We extend our studies of a new class of $2 \to 3$ exclusive processes using the collinear factorisation framework by considering the exclusive photoproduction of a $γ\,ρ$ pair, in the kinematics where the pair has a large invariant mass, {and the outgoing $ ρ$-meson has a sufficiently large transverse momentum to not resonate with the nucleon}. We cover the whole kinematical range from medium energies in fixed target experiments to very large energies of colliders, by considering the experimental conditions of JLab~12-GeV, COMPASS, future EIC and LHC (in ultra-peripheral collisions) cases. One of the main interest in studying the present process is that it provides access to both chiral-even and chiral-odd GPDs, depending on the polarisation of the outgoing $ρ$-meson, both at leading twist. Our analysis covers both neutral and charged $ ρ$-mesons. We find that the order of magnitude of the obtained cross sections are sufficiently large for a dedicated experimental analysis to be performed, especially at JLab, for both longitudinally and transversely polarised $ρ$. Furthermore, we compute the linear photon beam polarisation asymmetry {which is} sizeable for a longitudinally polarised meson. These predictions are obtained for both asymptotic distribution amplitude (DA) and the \textit{holographic} DA.

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arXiv2022

Accessing GPDs through the exclusive photoproduction of a photon-meson pair with a large invariant mass

We study the exclusive photoproduction of a photon-meson pair with a large invariant mass, working in the QCD factorisation framework. Explicitly, we consider a $ ρ$-meson or a charged $ π$ in the final state. This process gives access to chiral-even GPDs as well as chiral-odd GPDs. We focus here on the chiral-even sector. The computation is performed at leading order and leading twist. We discuss the prospects of measuring them in various experiments such as JLab 12-GeV, COMPASS, future EIC and LHC (in ultraperipheral collisions). In particular, the high centre of mass energies available at collider experiments can be used to probe GPDs at small skewness $ ξ$. We also compute the polarisation asymmetries with respect to the incoming photon. The results for an alternative distribution amplitude (`holographic' form) are also compared with the predictions obtained with an asymptotic distribution amplitude.

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arXiv2022

Accessing chiral-even quark generalised parton distributions in the exclusive photoproduction of a $ γπ^{\pm} $ pair with large invariant mass in both fixed-target and collider experiments

We compute the exclusive photoproduction of a $γ\,π^\pm$ pair using the collinear factorisation framework, in the kinematic regime where the pair has a large invariant mass. This exclusive channel presents a new avenue for the investigation of GPDs. It is particularly interesting as the high centre of mass energies available at future experiments will allow the study of GPDs at small skewness $ ξ$. We compute the scattering amplitude of the process, at leading twist and leading order in $α_s$, which is used to estimate its cross-section and linear polarisation asymmetries with respect to the incoming photon, for JLab~12-GeV, COMPASS, future EIC and LHC (in ultra-peripheral collisions) kinematics. We find that the order of magnitude of estimates are sufficiently large for a dedicated experimental analysis to be performed, especially at JLab. We also compare the results from an asymptotic distribution amplitude (DA) to those using a recently proposed \textit{holographic} DA.

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arXiv2022

Transition GPDs and exclusive electroproduction of $π-Δ(1232)$ final states

We investigate exclusive electroproduction of $π^-Δ^{++}$ within the handbag approach in which the helicity amplitudes factorize into generalized parton distributions (GPDs) and hard partonic subprocesses. We define the $p-Δ$ transversity GPDs while the helicity non-flip GPDs are taken from the literature. For the numerical estimates of observables we utilize large-$N_C$ results in order to relate a few of the $p-Δ$ GPDs to the proton-proton ones and neglect all other GPDs. In the calculation of the twist-2 and twist-3 subprocess amplitudes we take into account quark transverse momenta in combination with Sudakov suppressions. The partial cross sections for $γ^*p\to π^-Δ^{++}$ are predicted in the large-$N_C$ limit.

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arXiv2022

Accessing GPDs through the exclusive photoproduction of a $ γ$-meson pair

We consider the exclusive photo-production of a photon-meson pair with a large invariant mass, working in the QCD factorisation framework. Explicitly, we consider a $ ρ$-meson or a charged $ π$ in the final state. This process gives access both to chiral-even GPDs and chiral-odd GPDs, which are not well-known experimentally, especially the latter ones. The computation is performed at leading order and leading twist. We discuss the prospects of measuring them in experiments, focusing on the kinematics at the JLab 12-GeV experiment, and pPb ultra-peripheral collisions at LHC. In particular, the latter gives access to the small $ ξ$ regime of GPDs.

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arXiv2022

Wide-angle photo- and electroproduction of pions to twist-3 accuracy

We investigate wide-angle photo- and electroproduction of pions within the handbag mechanism in which the $γ^{(*)} N\to πN'$ amplitudes factorize into hard partonic subprocess amplitudes, $γ^{(*)} q\to πq'$, and form factors representing $1/x$-moments of generalized parton distributions (GPDs). The subprocess is calculated to twist-3 accuracy taking into account the 2- and 3-body Fock components of the pion. Both components are required for achieving gauge invariance in QED and QCD. The twist-2 and twist-3 distribution amplitudes (DAs) of the pion as well as the form factors are taken from our study of $π^0$ photoproduction. Extensive results on photoproduction of charged pions are presented and compared to experiment. Predictions on electroproduction of pions as well as on spin effects are also given. As a byproduct of our analysis we also obtain the complete twist-3 subprocess amplitudes contributing to deeply-virtual electroproduction of pions.

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arXiv2021

Wide-angle photoproduction of the $η'$-meson and its gluon content

We investigate wide-angle photoproduction of the $η'$ meson within the handbag approach to twist-3 accuracy. It turns out that, due to the gluon content of the $η'$, this process is dominated by twist-2 in contrast with pion and $η$ photoproduction. Using the presently available information on the twist-2 and twist-3 distribution amplitudes and on the $η- η'$ mixing, we provide prediction for the $η'$ cross section and helicity correlations. It is argued that $η'$ photoproduction is well suited to improve our knowledge of the two-gluon distribution amplitude.

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arXiv2019

On some implications of the BaBar data on the $γ^*η'$ transition form factor

At leading-twist accuracy the form factors for the transitions from a virtual photon to the $η$ or $η'$ can be expanded into a power series of the variable $ω$, being related to the difference of two photon virtualities. The series possess the remarkable feature that only the Gegenbauer coefficients of the meson distribution amplitudes of order $l\leq m$ contribute to the term $\sim ω^m$. Thus, for $ω\to 0$ only the asymptotic meson distribution amplitude contributes, allowing for a test of the mixing of the $η$ and $η'$ decay constants. Employing the Gegenbauer coefficients determined in analysis of the form factors in the real photon limit, we present predictions for the $γ^*η$ and $γ^*η'$ form factors and compare them to the BaBar data.

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