arXiv subjects

N. Hammoud

Publications and source records attributed to N. Hammoud.

7 recordsLinked to original sources

arXiv2026

Frascati 22 GeV Workshop Summary

This document summarizes the outcomes of the "Science at the Luminosity Frontier: Jefferson Lab at 22 GeV" workshop, held at the INFN Laboratori Nazionali di Frascati in December 2024. The primary goal of the workshop was to critically assess and refine the scientific case for a proposed energy upgrade of the Continuous Electron Beam Accelerator Facility (CEBAF) to 22 GeV. This document intends to capture the progress on developing the scientific case since the publication of a lengthy "White Paper" in summer 2024 signed by about 450 authors.

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arXiv2025

$ϕ\to 3π$ and $ϕπ^{0}$ transition form factor from Khuri-Treiman equations

This work studies the $ϕ\to 3π$ decay and the $ϕ\to π^0 γ^\ast$ transition form factor, utilizing the Khuri-Treiman formalism to account for analyticity, crossing, and unitarity. Using once-subtracted dispersion relations, we perform a simultaneous fit to the $ϕ\to 3π$ Dalitz plot distribution and the $ϕ\to π^0 γ^\ast$ measurements from the KLOE collaboration, finding good agreement with these experimental data. These results reaffirm the applicability of the Khuri-Treiman approach in the analysis of three-body decays. An interesting result is that the subtraction constant appearing in the equations is similar to a sum rule expectation, in contrast to analogous studies of $ω\to 3π$ decays and $ω\to π^0 γ^\ast$, which shows significant deviations. Our results also provide a reasonable description of the trend of the transition form factor data from BaBar in the $e^{+}e^{-}\toϕπ^{0}$ scattering region. These intriguing theoretical differences between the decays of $ϕ$ and $ω$ could encourage further experimental measurements to assess the discrepancies and refine the theoretical predictions.

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arXiv2024

XYZ spectroscopy at electron-hadron facilities III: Semi-inclusive processes with vector exchanges

Inclusive production processes will be important for the first observations of $XYZ$ states at new generation electron-hadron colliders, as they generally benefit from larger cross sections than their exclusive counterparts. We make predictions of semi-inclusive photoproduction of the $χ_{c1}(1P)$ and $X(3872)$, whose peripheral production is assumed to be dominated by vector exchanges. We validate the applicability of Vector Meson Dominance in the axial-vector charmonium sector and calculate production rates at center-of-mass energies relevant for future experimental facilities. We find the semi-inclusive cross sections near threshold to be enhanced by a factor of $\sim 2-3$ compared to the exclusive reaction and well suited for a first observation in photoproduction.

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arXiv2023

Dynamics in near-threshold $J/ψ$ photoproduction

The study of $J/ψ$ photoproduction at low energies has consequences for the understanding of multiple aspects of nonperturbative QCD, ranging from mechanical properties of the proton, to the binding inside nuclei, and the existence of hidden-charm pentaquarks. Factorization of the photon-$c \bar c$ and nucleon dynamics or Vector Meson Dominance are often invoked to justify these studies. Alternatively, open charm intermediate states have been proposed as the dominant mechanism underlying $J/ψ$ photoproduction. As the latter violates this factorization, it is important to estimate the relevance of such contributions. We analyse the latest differential and integrated photoproduction cross sections from the GlueX and $J/ψ$-007 experiments. We show that the data can be adequately described by a small number of partial waves, which we parameterize with generic models enforcing low-energy unitarity. The results suggest a nonnegligible contribution from open charm intermediate states. Furthermore, most of the models present an elastic scattering length incompatible with previous extractions based on Vector Meson Dominance, and thus call into question its applicability to heavy mesons. Our results indicate a wide array of physics possibilities that are compatible with present data and need to be disentangled.

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arXiv2023

Ambiguities in Partial Wave Analysis of Two Spinless Meson Photoproduction

We describe the formalism to analyze the mathematical ambiguities arising in partial-wave analysis of two spinless mesons produced with a linearly polarized photon beam. We show that partial waves are uniquely defined when all accessible observables are considered, for a wave set which includes $S$ and $D$ waves. The inclusion of higher partial waves does not affect our results, and we conclude that there are no mathematical ambiguities in partial-wave analysis of two mesons produced with a linearly polarized photon beam. We present Monte Carlo simulations to illustrate our results.

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arXiv2023

Khuri-Treiman analysis of $J/ψ\toπ^{+}π^{-}π^{0}$

We study the decay $J/ψ\toπ^{+}π^{-}π^{0}$ within the framework of the Khuri-Treiman equations. We find that the BESIII experimental di-pion mass distribution in the $ρ(770)$-region is well reproduced with a once-subtracted $P$-wave amplitude. Furthermore, we show that $F$-wave contributions to the amplitude improve the description of the data in the $ππ$ mass region around 1.5 GeV. We also present predictions for the $J/ψ\toπ^{0}γ^{*}$ transition form factor.

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arXiv2020

Strong evidence of $ρ(1250)$ from a unitary multichannel reanalysis of elastic scattering data with crossing-symmetry constraints

An analysis is presented of elastic $P$-wave $ππ$ phase shifts and inelasticities up to 2 GeV, aimed at identifying the corresponding $J^{PC}=1^{--}$ excited $ρ$ resonances and focusing on the $ρ(1250)$ vs. $ρ(1450)$ controversy. The approach employs an improved parametrization in terms of a manifestly unitary and analytic three-channel $S$-matrix with its complex-energy pole positions. The included channels are $ππ$, $\rho2π$, and $ρρ$, the latter two being effective in the sense that they mimic several experimentally observed decay modes with nearby thresholds. In an alternative fit, the $\rho2π$ mode is replaced by $ωπ$, which is also an experimentally relevant channel. The improvement with respect to prior work amounts to the enforcement of maximum crossing symmetry through once-subtracted dispersion relations called GKPY equations. A separate analysis concerns the pion electromagnetic form factor, which again demonstrates the enormous importance of guaranteeing unitarity and analyticity when dealing with very broad and highly inelastic resonances. In the case of $ρ(1250)$ vs. $ρ(1450)$, the failure to do so is shown to give rise to an error in the predicted mass of about 170 MeV. A clear picture emerges from these analyses, identifying five vector $ρ$ states below 2 GeV, viz. $ρ(770)$, $ρ(1250)$, $ρ(1450)$, $ρ(1600)$, and $ρ(1800)$, with $ρ(1250)$ being indisputably the most important excited $ρ$ resonance. The stability of the fits as well as the imposition of unitarity, analyticity, and approximate crossing symmetry in the analyses lend very strong support to these assignments. The possibly far-reaching consequences for meson spectroscopy are discussed.

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