arXiv subjects

Ahmad Jafar Arifi

Publications and source records attributed to Ahmad Jafar Arifi.

At least 19 recordsLinked to original sources

arXiv2026

Medium modification of pseudoscalar meson structure: Distribution amplitudes and parton distribution functions

In this work, we present a comprehensive investigation of the in-medium properties and internal structure of pseudoscalar mesons within the light-front quark model (LFQM), employing both Gaussian and power-law (PL) wave functions. We incorporate in-medium quark properties obtained from the quark-meson coupling (QMC) model into the LFQM, thereby providing a unified description in terms of quark degrees of freedom. We investigate the distribution amplitudes (DAs) and parton distribution functions (PDFs) of $π^{\pm}$, $K^{\pm}$, $D^{\pm}$, and $B^{\pm}$ mesons in symmetric nuclear matter. We find that the evolved in-medium pion DA and PDF are strongly suppressed at intermediate $x$, indicating substantial medium-induced modifications to the meson structure. The signs and magnitudes of the modified Gegenbauer coefficients $a_n'$, the parameter $ξ$, and the Mellin moments of the DAs and PDFs in nuclear matter are found to be consistent with other theoretical predictions. In particular, the second Gegenbauer coefficient of the pion DA, $a_2^π$, increases substantially with nuclear density, from $0.096$ ($0.057$) in vacuum to $0.232$ ($0.202$) at normal nuclear density for the Gaussian (PL) wave function, respectively. This increase indicates a broader pion DA and an enhanced second Gegenbauer moment in the nuclear medium. We further calculate the pion PDF ratio $R_{ρ/0}^π$ and find that its $x$ dependence exhibits a behavior qualitatively similar to the observed European Muon Collaboration (EMC) effect, highlighting the important role of QCD evolution in shaping the medium-modified partonic structure. Finally, we compare the calculated free-space $π^{\pm}$ and $K^{\pm}$ DAs with available free-space lattice QCD results and find reasonable agreement.

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arXiv2026

Electromagnetic structure of Bc and heavy quarkonia in the light-front quark model

We investigate the electromagnetic structure of heavy quarkonia and the $B_c$ meson within the light-front quark model (LFQM) to better understand the internal spatial charge distributions and QCD dynamics of heavy mesons. The light-front wave functions (LFWFs) are obtained using a variational approach with a few set of harmonic oscillator basis functions, providing a flexible yet tractable description of the bound-state dynamics. Using these LFWFs, we compute the electromagnetic form factors and compare our results with available lattice QCD data and other model calculations. Our results are roughly consistent with previous model predictions, showing that the electromagnetic radii of the $2S$ and $3S$ states are approximately 1.5 times and 1.9 times larger than those of their corresponding $1S$ states, reflecting the expected growth of spatial size in radial excitations.

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arXiv2026

Polarization-dependent mass modifications of $ϕ$ meson with finite momentum in nuclear matter

We investigate the in-medium properties of the $ϕ$ meson with finite momentum, going beyond the commonly studied case at rest. In a nuclear medium, Lorentz invariance is broken, leading to distinct longitudinal and transverse polarization modes that evolve differently with density and momentum. Within an effective Lagrangian approach, we calculate the polarization-dependent mass shifts and width modifications of the $ϕ$ meson arising from $K\bar{K}$ loops and mean-field interactions. The divergent loop integrals are regulated using two different schemes: a covariant form factor and dimensional regularization. Our results show that the mass shift of the transverse polarization is independent of the $ϕ$-meson momentum, whereas that of the longitudinal polarization decreases quadratically with momentum. This difference originates from the coupling of the longitudinal mode to the vector mean field and derivative-type interactions in the self-energy. These effects have direct implications for experimental observables, especially for upcoming measurements at J-PARC, and provide a new prediction for experiments studying hadron dynamics in dense matter.

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arXiv2026

Quarkonium spectra with magnetically induced anisotropic confinement

Strong magnetic fields modify the force that confines quarks inside hadrons and make it direction-dependent. Using quark-antiquark potentials obtained from lattice simulations as inputs to a quark potential model, we investigate how the anisotropic confinement affects the mass spectrum of quarkonium. In the strong-field regime, we find downward mass shifts induced by a softening of the confining potential along the field direction. In particular, the mass shifts of radially excited states are more significant than that of the ground state. For the longitudinal spin eigenstates, the excited-state spectrum strongly depends on the magnetic-field strength, in contrast to the spectrum with conventional isotropic confinement, which is insensitive to the field strength. This provides a clean probe of magnetically induced confinement anisotropy that can be confirmed in future lattice simulations.

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arXiv2026

Hadronic exceptional points

Exceptional points, where eigenvalues and eigenvectors coalesce, are a defining feature of non-Hermitian systems and have been extensively observed in photonic, atomic, and condensed matter systems. However, they have received little attention in quantum chromodynamics (QCD), which is the fundamental theory of quarks, gluons, and hadrons. We propose that imaginary magnetic fields provide a simple realization of non-Hermitian dynamics in hadronic systems. Based on two theoretical approaches, a hadronic effective Lagrangian and a constituent quark model, we compute mass spectra of neutral mesons and find exceptional points separating the real-spectrum and complex-eigenvalue regimes. In small fields, the real spectrum exhibits level attraction between hadronic states, whereas in larger fields, hadrons are deconfined, which is a signature of a field-induced inverted potential. Our findings open a new avenue for studying QCD dynamics in non-Hermitian environments.

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arXiv2026

Landau-Zener-Stückelberg-Majorana dynamics of magnetized quarkonia

The mass spectrum of hadrons in magnetic fields features avoided level-crossing structures arising from the mixing of spin eigenstates. In this work, we investigate the impact of level-crossing dynamics of charmonia subjected to time-dependent magnetic fields, where we particularly focus on the occupation probabilities of two or more states as they undergo transitions at avoided crossings. Using a static spectrum of charmonia in magnetic fields, we construct a multi-channel Landau-Zener Hamiltonian. Within this framework, we analyze the time evolution under several representative magnetic-field profiles, including linear ramps and Gaussian decays corresponding to single-passage dynamics, as well as Gaussian pulses realizing double-passage dynamics, and compute the occupation probabilities over a wide range of sweep rates and initial conditions. Our results show that nonadiabatic dynamics, including Landau-Zener transitions and Stückelberg interference, strongly influences the occupation probabilities of charmonia. These findings provide new insights into the real-time dynamics of magnetized hadrons and offer useful guidance for future lattice simulation studies.

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arXiv2026

Kaon T-even transverse-momentum-dependent distributions and form factors in a self-consistent light-front quark model

We present a self-consistent light-front quark model (LFQM) for the kaon based on the Bakamjian--Thomas (BT) construction and apply it to the electromagnetic and scalar form factors, as well as the full set of unpolarized T-even transverse-momentum-dependent distributions (TMDs) and their collinear parton distribution functions (PDFs). A uniform implementation of the invariant mass $M_0$ in both the hadronic matrix elements and the associated Lorentz structures enforces four-momentum conservation at the meson--quark vertex and yields current-component--independent observables by consistently incorporating the light-front zero-mode structure required by covariance. The electromagnetic form factor $F_{K^+}(Q^2)$ is demonstrated to be unique by explicit computation from all available current components ($γ^+$, $γ^\perp$, and $γ^-$). In the scalar channel, we compare the direct $f_S(Q^2)$ and mass-factored $F_S(Q^2)$ definitions and show that they are not interchangeable within the BT-based LFQM, since the replacement $M\!\to\!M_0(x,\bm{k}_\perp)$ must be implemented at the integrand level. Using a Gaussian light-front wave function, the twist-2 TMD $f_1^q$ exhibits an exact Gaussian dependence in $\bm{k}_\perp$, while higher-twist TMDs ($f^{\perp q}$, $e^q$, $f_4^q$) display systematic twist and flavor hierarchies. We further analyze the perturbative QCD evolution of the valence PDFs for the pion and kaon and report their Mellin moments at representative scales, enabling direct comparison with phenomenology.

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arXiv2025

Structure of heavy quarkonia in a strong magnetic field

We investigate the structural modifications of heavy quarkonia in the presence of strong magnetic fields using a constituent quark model. By incorporating the effects of spin mixing and quark Landau levels, we employ a nonrelativistic Hamiltonian that captures the essential features of quark dynamics in a magnetic field. The two-body Schrödinger equation is solved using the cylindrical Gaussian expansion method, which respects the cylindrical symmetry induced by a magnetic field. We extract the corresponding light-front wave function (LFWF) densities and analyze their transverse and longitudinal structures, revealing characteristic features such as transverse momentum broadening. While the longitudinal structure is only slightly modified within the nonrelativistic Hamiltonian, we discuss some corrections that can significantly affect its longitudinal structure. Furthermore, we discuss the structure modifications of excited states and find notable changes in the LFWF densities, and state reshuffling near avoided crossings. These results demonstrate the sensitivity of hadron structure to external magnetic fields and help bridge our understanding to relativistic approaches.

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arXiv2025

A Brief History and Outlook of Hadronic Physics in Indonesia

Hadronic physics has gradually emerged as one of the growing research frontiers in Indonesia, driven by efforts to better understand the properties of the strong interaction and the internal structure of hadrons from the fundamental principles of Quantum Chromodynamics. In the last few decades, Indonesian researchers have made significant contributions to developing various theoretical and phenomenological aspects of hadrons. In addition, on the experimental side, Indonesian scientists have participated in hadron experiment facilities overseas, such as the ALICE collaboration at CERN, which has strengthened the scientific activities and networks and has supported the training of young Indonesian researchers. In the present paper, we review Indonesian scientists' contributions to hadronic physics, highlight ongoing research directions in both experimental and theoretical, and outline strategies for future development toward integration into the international hadronic physics community.

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arXiv2025

Heavy Quarkonia in the Light-Front Quark Model

We present recent progress in constructing heavy quarkonia light-front wave functions from the light-front quark model, a relativistic framework well-suited for describing partonic structure and hadronic form factors. In this proceeding, we discuss the recent application of the model to the $M1$ radiative transition such as $J/ψ\to η_c γ$ among other transitions. Additionally, we compare our results on the transition form factor with available lattice QCD data. These show our efforts to deepen our understanding of the structure of heavy quarkonia from light-front model perspective.

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arXiv2025

Beyond leading twist: $ρ$ meson decay constants and distribution amplitudes in a self-consistent light-front quark model

In this study, we present a comprehensive analysis of decay constants and chiral-even and chiral-odd distribution amplitudes (DAs) up to twist 4 for the $ρ$ meson in the standard light-front quark model (LFQM) based on the Bakamjian-Thomas (BT) construction. For the $ρ$ meson, which possesses both longitudinal $(h=0)$ and transverse $(h=\pm 1)$ polarizations, two types of decay constants, $f_ρ^{\parallel}$ and $f_ρ^{\perp}$, arises accordingly. We demonstrate that these decay constants can be self-consistently extracted from both local ($z^μ=0$) and nonlocal ($z^μ\neq 0$) matrix elements $\langle 0 | \bar{q}(z)\, Γ\, q(-z) | ρ(P,h) \rangle$, with $Γ= (γ^μ, σ^{μν}, γ^μγ_5, \mathbf{1})$, in a manner independent of current components, polarizations, and reference frames. In particular, we emphasize the role of nonlocal matrix elements involving axial-vector and scalar currents, where mixing between $f_ρ^{\parallel}$ and $f_ρ^{\perp}$ occurs. We show that this mixing is consistently resolved through the BT construction, ensuring the proper extraction of these decay constants. Additionally, we investigate the structure of chiral-even DAs ($ϕ_{2;\mathrm{V}}^\parallel, ϕ_{3;\mathrm{V}}^\parallel, ψ_{3;\mathrm{A}}^\perp, ϕ_{4;\mathrm{V}}^\parallel$) and chiral-odd DAs ($ϕ_{2;\mathrm{T}}^\perp, ϕ_{3;\mathrm{T}}^\perp, ψ_{3;\mathrm{S}}^\parallel, ϕ_{4;\mathrm{T}}^\perp$) beyond leading twists, and present their corresponding $ξ$-moments and Gegenbauer moments. These results provide deeper insight into the nonperturbative structure of vector mesons and demonstrate the robustness and self-consistency of the LFQM based on the BT framework.

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arXiv2025

$M1$ Radiative Transition of Light Mesons in the Light-Front Quark Model

We investigate the $M1$ radiative transitions between light vector $\mathcal{V}$ and pseudoscalar $\mathcal{P}$ mesons in the 1S and 2S states in the light-front quark model. To this end, we use the light-front wave functions (LFWFs) obtained from the QCD-motivated effective Hamiltonian that includes smeared spin-spin interactions, where a few harmonic oscillator basis functions were employed as trial wave functions. The results, including their couplings and widths, obtained from LFWFs with different trial wave functions are compared with the available experimental data and other theoretical predictions.

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arXiv2025

In-medium electromagnetic form factors of pseudoscalar mesons from the quark model

We explore the modifications of hadron structure in a nuclear medium, focusing on the spacelike electromagnetic form factors (EMFFs) of light and heavy-light pseudoscalar mesons. By combining the light-front quark model (LFQM) with the quark-meson coupling (QMC) model, which reasonably reproduces EMFFs in free space and the saturation properties of nuclear matter, respectively, we systematically analyze the in-medium EMFFs and charge radii of mesons with various quark flavors. Our findings show that the EMFFs of charged (neutral) mesons exhibit a faster fall-off (increase) with increasing four-momentum transfer squared and nuclear density. Consequently, the absolute value of the charge radii of mesons increases with nuclear density, where the rate of increase depends on their quark flavor contents. We observe that the EMFFs of pions and kaons undergo significant modifications in the nuclear medium, while heavy-light mesons are only slightly modified. By decomposing the quark flavor contributions to EMFFs, we show that the medium effects primarily impact the light-quark sector, leaving the heavy-quark sector nearly unaffected. The results of this study further suggest the importance of the medium effects at the quark level.

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arXiv2025

Self-consistent $M1$ radiative transitions of excited $B_c$ and heavy quarkonia with different polarizations in the light-front quark model

In this study, we investigate the properties of pseudoscalar and vector charmonia, bottomonia, and $B_c$ mesons using the light-front quark model, focusing on the $M1$ radiative transition. For that purpose, we conduct a variational analysis with a QCD-motivated effective Hamiltonian, employing a trial wave function expanded in the harmonic oscillator basis functions up to the $3S$ state. We fit the model parameters to mass spectra and decay constants, obtaining reasonable agreement with experimental data and correctly reflecting the hierarchy of mass spectra and decay constants. In analyzing the $M1$ radiative transition, we consider both good ($μ=+$) and transverse ($μ={\perp}$) current components with both longitudinal $(h=0)$ and transverse $(h=\pm1)$ polarizations, demonstrating that the results from both components of currents and polarizations are identical. Self-consistency is achieved by substituting $M$ with $M_0$ when computing the operators for decay constants and radiative transitions. We also find that the difference between longitudinal and transverse polarizations of the observables may quantify the anisotropy of the model wave function. Our results on radiative transitions align reasonably well with experimental data, lattice QCD, and theoretical predictions. Furthermore, we also provide predictions for $B_c$ mesons that can be tested in experiments.

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arXiv2024

Heavy-Quark Spin Symmetry Violation effects in Charmed Baryon Production

In this work, we investigate the Heavy-Quark Spin Symmetry (HQSS) exhibited in the effective Lagrangians governing the three-point interactions of $D$ mesons, charmed baryons, and nucleons. We first construct the effective Lagrangians, and there are 12 distinct terms. As a result, we observe that the invariant Lagrangian under HQSS manifests exclusively in the pseudoscalar $D$ mesons coupling to nucleons and $Λ_c$ baryons, whereas nucleons and $Σ_c$ ($Σ_c^*$) baryons only couple with vector $D$ mesons. By taking into account the violated heavy-quark spin transformation, one can recover all interactions from the effective Lagrangians. Furthermore, we compute the differential cross-sections of the $p\bar p \to Y_c\bar{Y}_c'$ scatterings, where $Y_c,\bar{Y_c}' = Λ_c,~Σ_c,~Σ_c^*$, to reveal the residue of the violating HQSS (VHQSS) on charmed baryon production. Ultimately, by accounting for VHQSS, we aim for precise predictions of production rates, which are essential for the High-Energy Storage Ring (HESR) experiments at the Facility for Antiproton and Ion Research (FAIR).

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arXiv2024

The Properties of Radially Excited Charmonia in The Light Front Quark Model

Investigating the properties of excited charmonia is important to clarify its internal structure. In this paper, we present the mass spectra (MS) and decay constants (DC) for charmonia up to 3S states calculated by means of the light-front quark model based on a variational approach. In particular, we consider the QCD-motivated effective Hamiltonian, which includes both confinement (linear and screened) and Coulomb-like potentials. Furthermore, since the existence of the nature of heavy quark symmetry, we treat hyperfine interactions perturbatively. We developed the harmonic oscillator expansion method to approximate the wave function (WF) for excited states. We found that the results of our theoretical calculations, using screened potentials rather than linear ones, are in good agreement with experimental data. By looking at the mass and decay constant result, we found that our result on the ψ(3S) state matched the properties of the ψ(4040) resonance.

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arXiv2024

Two-pion emission decays of negative parity singly heavy baryons

We investigate two-pion emission decays of singly charmed and bottom baryons, focusing on $Λ_Q^*(1P)$ and $Ξ_Q^*(1P)$ with $Q=c$ (charm) or $b$ (bottom) quarks and $J^P=1/2^-,3/2^-$, belonging to antisymmetric flavor triplet $\bar{\boldsymbol{3}}_F$. Our analysis encompasses both sequential processes, involving intermediate states belonging to symmetric flavor sextet $\boldsymbol{6}_F$ such as $Σ_Q(1S)$ and $Ξ_Q^\prime(1S)$ respectively with $J^P=1/2^+,3/2^+$, derived from the chiral quark model, and direct process crucial for comparison with experimental data, whose coupling constants estimated using the chiral-partner scheme. We also incorporate the convolution of the parent particle's mass for the Dalitz plot, enabling a more realistic comparison with experimental data. We scrutinize the Dalitz plots of these negative parity states in light of recent Belle measurements for $Λ_c(2625)^+$. Our findings support the assignment of $Λ_c(2625)^+$ as the $λ$-mode excitation with $J^P=3/2^-$ in the quark model, deduced from the the ${Λ_cπ}$ invariant mass distribution, and we then give predictions for other cases, including the $Ξ_Q^*$ decays. The observed asymmetry in the ${ππ}$ invariant mass distribution underscores the important role of the direct process, reflecting the chiral-partner structure in the heavy baryon sector. It is evident that the presence of the direct process is not significant in the three-body decays unless the $S$-wave resonance contribution is suppressed. We suggest further experimental verification to test our predictions and get more insights into the structure of heavy baryons.

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arXiv2024

Structure of Heavy Mesons in the Light-Front Quark Model

We investigate the structure of ground-state heavy mesons within the light-front quark model, utilizing wave functions derived from the Single Gaussian Ansatz (SGA) and the Gaussian Expansion Method (GEM). By performing a $χ^2$ fit to static properties such as mass spectra and decay constants, we determine the model parameters for each approach. We then compare the impacts of both methods on the light-front wave functions and structural observables. Our analysis reveals significant differences in the distribution amplitudes (DAs) $ϕ_{2;M}(x)$ near the endpoints, with GEM showing enhanced amplitudes and correct asymptotic behavior $ϕ_{2;M}(x \to 1) \propto (1-x)$, consistent with perturbative QCD. This endpoint behavior is linked to the short-range (high-momentum) wave function governed by color Coulomb interaction and relativistic kinematics. GEM accurately reproduces a power-law damping $ψ_0(k \to \infty) \propto 1/k_\perp^2$, aligning with perturbative QCD predictions. Furthermore, the electromagnetic form factors of pseudoscalar mesons in the low-$Q^2$ region fall off faster with GEM than with SGA. Overall, while both methods adequately describe static properties, GEM provides a more accurate description of structural properties, being more sensitive to details and asymptotic behaviors.

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