<p>We explore the modifications of the 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 with the quark-meson coupling 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 falloff (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.</p>

Japan

Ahmad Jafar Arifi

South Korea

Parada T.P. Hutauruk

Brazil

Kazuo Tsushima

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

In this study, we investigate the properties of pseudoscalar and vector charmonia, bottomonia, and <math><msub><mi>B</mi><mi>c</mi></msub></math> mesons using the light-front quark model, focusing on the <math><mi>M</mi><mn>1</mn></math> radiative transition. For that purpose, we conduct a variational analysis with a quantum chromodynamics (QCD)-motivated effective Hamiltonian, employing a trial wave function expanded in the harmonic oscillator basis functions up to the <math><mn>3</mn><mi>S</mi></math> 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 <math><mi>M</mi><mn>1</mn></math> radiative transition, we consider both good (<math><mi>μ</mi><mo>=</mo><mo>+</mo></math>) and transverse (<math><mi>μ</mi><mo>=</mo><mo>⊥</mo></math>) current components with both longitudinal (<math><mrow><mi>h</mi><mo>=</mo><mn>0</mn></mrow></math>) and transverse <math><mo>(</mo><mi>h</mi><mo>=</mo><mo>±</mo><mn>1</mn><mo>)</mo></math> polarizations, demonstrating that the results from both components of currents and polarizations are identical. Self-consistency is achieved by substituting <math><mi>M</mi></math> with <math><msub><mi>M</mi><mn>0</mn></msub></math> 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 <math><msub><mi>B</mi><mi>c</mi></msub></math> mesons that can be tested in experiments.

Indonesia

Muhammad Ridwan

Terry Mart

Self-consistent <math><mi>M</mi><mn>1</mn></math> radiative transitions of excited <math><msub><mi>B</mi><mi>c</mi></msub></math> and heavy quarkonia with different polarizations in the light-front quark model

We investigate two-pion emission decays of singly charmed and bottom baryons, focusing on <math><mrow><msubsup><mrow><mi>Λ</mi></mrow><mrow><mi>Q</mi></mrow><mrow><mo>*</mo></mrow></msubsup><mo>(</mo><mn>1</mn><mi>P</mi><mo>)</mo></mrow></math> and <math><msubsup><mi>Ξ</mi><mi>Q</mi><mo>*</mo></msubsup><mo>(</mo><mn>1</mn><mi>P</mi><mo>)</mo></math> states with <math><msup><mi>J</mi><mi>P</mi></msup><mo>=</mo><mn>1</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></math> and <math><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></math>, which belong to the flavor triplet <math><msub><mover><mn>3</mn><mo>¯</mo></mover><mi>F</mi></msub></math>. Our study includes both sequential decays through intermediate states in the flavor sextet <math><msub><mn>6</mn><mi>F</mi></msub></math> and direct three-body decay, with coupling constants estimated using the chiral quark model and chiral-partner scheme. Examining recent Belle measurements for <math><msub><mi>Λ</mi><mi>c</mi></msub><mo>(</mo><mn>2625</mn><msup><mo>)</mo><mo>+</mo></msup></math>, we confirm its assignment as a <math><mi>λ</mi></math>-mode excitation with <math><msup><mi>J</mi><mi>P</mi></msup><mo>=</mo><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></math>. We then give predictions for other cases, including the <math><msubsup><mi>Ξ</mi><mi>Q</mi><mo>*</mo></msubsup></math> decays. The observed asymmetry in the <math><mi>π</mi><mi>π</mi></math> mass distribution highlights the role of the direct process, reflecting the chiral-partner structure. However, the direct process is less significant in three-body decays unless <math><mi>S</mi></math>-wave resonances are suppressed. Further experiments are needed to test our predictions and get more insights into the structure of heavy baryons.

Thailand

Nongnapat Ponkhuha

Daris Samart

Two-pion emission decays of negative parity singly heavy baryons

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 <math><msup><mi>χ</mi><mn>2</mn></msup></math> 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 <math><msub><mi>ϕ</mi><mrow><mn>2</mn><mo>;</mo><mi>M</mi></mrow></msub><mo>(</mo><mi>x</mi><mo>)</mo></math> near the end points, with GEM showing enhanced amplitudes and correct asymptotic behavior <math><mrow><msub><mrow><mi>ϕ</mi></mrow><mrow><mn>2</mn><mo>;</mo><mi>M</mi></mrow></msub><mo>(</mo><mi>x</mi><mo>→</mo><mn>1</mn><mo>)</mo><mo>∝</mo><mo>(</mo><mn>1</mn><mo>−</mo><mi>x</mi><mo>)</mo></mrow></math>, consistent with perturbative QCD. This end point 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 <math><mrow><msub><mrow><mi>ψ</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>(</mo><mi>k</mi><mo>→</mo><mi>∞</mi><mo>)</mo><mo>∝</mo><mn>1</mn><mo>/</mo><msubsup><mrow><mi>k</mi></mrow><mrow><mo>⊥</mo></mrow><mrow><mn>2</mn></mrow></msubsup></mrow></math>, aligning with perturbative QCD predictions. Furthermore, the electromagnetic form factors of pseudoscalar mesons in the low-<math><msup><mi>Q</mi><mn>2</mn></msup></math> 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.

Lucas Happ

Shuhei Ohno

Makoto Oka

Structure of heavy mesons in the light-front quark model

In the light-front quark model (LFQM) amenable to the simultaneous study of both the mass spectroscopy and the wave function related observables, we examine the decay constants and distribution amplitudes (DAs) up to the twist-4. The analysis of the heavy pseudoscalar mesons is carried out both in the <math><mn>1</mn><mi>S</mi></math> and <math><mn>2</mn><mi>S</mi></math> states. This investigation involves calculating the local and nonlocal matrix elements <math><mo>⟨</mo><mn>0</mn><mo>|</mo><mover><mi>q</mi><mo>¯</mo></mover><mi>Γ</mi><mi>q</mi><mo>|</mo><mi>P</mi><mo>⟩</mo></math> using three distinct current operators <math><mi>Γ</mi><mo>=</mo><mo>(</mo><msup><mi>γ</mi><mi>μ</mi></msup><msub><mi>γ</mi><mn>5</mn></msub><mo>,</mo><mi>i</mi><msub><mi>γ</mi><mn>5</mn></msub><mo>,</mo><msup><mi>σ</mi><mrow><mi>μ</mi><mi>ν</mi></mrow></msup><msub><mi>γ</mi><mn>5</mn></msub><mo>)</mo></math>. Considering a general reference frame where <math><msub><mi>P</mi><mo>⊥</mo></msub><mo>≠</mo><mn>0</mn></math> and investigating all available current components, we examine not only the frame independence but also the component independence of the decay constants. The explicit findings from our study provide the evidence for the equality of the three pseudoscalar meson decay constants obtained from the three distinct current operators <math><mi>Γ</mi></math>. The notable agreement in decay constants is attained by imposing the Bakamjian-Thomas construction of the LFQM, namely, the meson state is constructed by the noninteracting quark and antiquark representations while the interaction is added to the mass operator, which provides the self-consistency condition replacing the physical mass <math><mi>M</mi></math> with the invariant mass <math><msub><mi>M</mi><mn>0</mn></msub></math> for the noninteracting quark-antiquark representation of the meson state. In addition to obtaining the process-independent pseudoscalar meson decay constant, regardless of the choice of current operators <math><mi>Γ</mi></math>, we further demonstrate its explicit Lorentz and rotation invariance. In particular, we present the analysis conducted on the twist-4 DA derived from the minus component of the axial-vector current. Finally, we discuss the various twist DAs and their <math><mi>ξ</mi></math>-moments associated with the <math><mn>1</mn><mi>S</mi></math> and <math><mn>2</mn><mi>S</mi></math> heavy pseudoscalar mesons.

Ho-Meoyng Choi

United States

Chueng-Ryong Ji

Pseudoscalar meson decay constants and distribution amplitudes up to the twist-4 in the light-front quark model

We investigate the in-medium properties of pseudoscalar and vector mesons with the light-light and heavy-light quarks in a light-front quark model, using the in-medium quark properties computed by the quark-meson coupling model. Both models are constructed on an equal footing with the constituent quark degree of freedom. Here, we particularly focus on the weak decay constants and distribution amplitudes (DAs) of the mesons in symmetric nuclear matter. We find that the weak decay constants decrease as nuclear density increases for <math><mi>π</mi></math>, <math><mi>K</mi></math>, <math><mi>D</mi></math>, and <math><mi>B</mi></math> pseudoscalar as well as <math><mi>ρ</mi></math>, <math><msup><mi>K</mi><mo>*</mo></msup></math>, <math><msup><mi>D</mi><mo>*</mo></msup></math>, and <math><msup><mi>B</mi><mo>*</mo></msup></math> vector mesons, where their properties in free space have good agreement with the available experimental and lattice QCD data. A larger reduction is found for the light-light quark pseudoscalar mesons, while a smaller reduction is found for the heavy-light quark vector mesons, in particular, with the bottom quark. We discuss the effect of the vector potential on the weak decay constants, and present our predictions for the in-medium modifications of DAs. Also, a comparison with the free space lattice QCD data is made.

Parada. T. P. Hutauruk

In-medium properties of the light and heavy-light mesons in a light-front quark model

The issue of resulting in the same physical observables with different current components, in particular from the minus current, has been challenging in the light-front quark model (LFQM) even for the computation of the two-point functions such as meson decay constants. At the level of one-body current matrix element computation, we show the uniqueness of pseudoscalar and vector meson decay constants using all available components including the minus component of the current in the LFQM consistent with the Bakamjian-Thomas construction. Regardless of the current components, the polarization vectors, and the reference frames, the meson decay constants are uniquely determined in the noninteracting constituent quark and antiquark basis while the interactions of the constituents are added to the meson mass operator in the LFQM.

Yongseok Oh

Independence of current components, polarization vectors, and reference frames in the light-front quark model analysis of meson decay constants

The mass spectra and wave functions of both <math><mn>1</mn><mi>S</mi></math> and <math><mn>2</mn><mi>S</mi></math> state heavy pseudoscalar (<math><mi>P</mi></math>) and vector (<math><mi>V</mi></math>) mesons are analyzed within the light-front quark model. Important empirical constraints employed in our analysis of the mass spectra and wave functions are the experimental mass-gap relation, <math><mi>Δ</mi><msub><mi>M</mi><mi>P</mi></msub><mo>&gt;</mo><mi>Δ</mi><msub><mi>M</mi><mi>V</mi></msub></math>, where <math><mi>Δ</mi><msub><mi>M</mi><mrow><mi>P</mi><mo>(</mo><mi>V</mi><mo>)</mo></mrow></msub><mo>=</mo><msubsup><mi>M</mi><mrow><mi>P</mi><mo>(</mo><mi>V</mi><mo>)</mo></mrow><mrow><mn>2</mn><mi>S</mi></mrow></msubsup><mo>−</mo><msubsup><mi>M</mi><mrow><mi>P</mi><mo>(</mo><mi>V</mi><mo>)</mo></mrow><mrow><mn>1</mn><mi>S</mi></mrow></msubsup></math> and the hierarchy of the decay constants, <math><msub><mi>f</mi><mrow><mn>1</mn><mi>S</mi></mrow></msub><mo>&gt;</mo><msub><mi>f</mi><mrow><mn>2</mn><mi>S</mi></mrow></msub></math>, between <math><mn>1</mn><mi>S</mi></math> and <math><mn>2</mn><mi>S</mi></math> meson states. We maintain the orthogonality of the trial wave functions of the <math><mn>1</mn><mi>S</mi></math> and <math><mn>2</mn><mi>S</mi></math> states in our variational calculation of the Hamiltonian with the Coulomb plus confining potentials and treat the hyperfine interaction perturbatively for the heavy-heavy and heavy-light <math><mi>P</mi></math> and <math><mi>V</mi></math> mesons due to the nature of the heavy quark symmetry. Realizing that the empirical constraints cannot be satisfied without mixing of the <math><mn>1</mn><mi>S</mi></math> and <math><mn>2</mn><mi>S</mi></math> states, we find the lower bound of the mixing angle <math><mi>θ</mi></math> between <math><mn>1</mn><mi>S</mi></math> and <math><mn>2</mn><mi>S</mi></math> states as <math><msub><mi>θ</mi><mi>c</mi></msub><mo>=</mo><msup><mi>cot</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup><mo>(</mo><mn>2</mn><msqrt><mn>6</mn></msqrt><mo>)</mo><mo>/</mo><mn>2</mn><mo>≃</mo><mn>6</mn><mi>°</mi></math> and obtain the optimum value of the mixing angle around 12° to cover both the charm and bottom flavors of the heavy quark. The mixing effects are found to be more significant to the <math><mn>2</mn><mi>S</mi></math> state mesons than to the <math><mn>1</mn><mi>S</mi></math> state mesons. The properties of <math><mn>1</mn><mi>S</mi></math> and <math><mn>2</mn><mi>S</mi></math> state mesons including the mass spectra, decay constants, twist-2 distribution amplitudes, and electromagnetic form factors are computed. Our results are found to be in a good agreement with the available data and lattice simulations. In particular, the <math><mn>2</mn><mi>S</mi></math> state pseudoscalar <math><msub><mi>D</mi><mi>s</mi></msub></math> meson is predicted to have a mass of 2600 MeV, which is very close to the mass of the newly discovered <math><msub><mi>D</mi><mrow><mi>s</mi><mn>0</mn></mrow></msub><mo>(</mo><mn>2590</mn><msup><mo>)</mo><mo>+</mo></msup></math> meson by the LHCb Collaboration. This supports the interpretation of the observed state as a radial excitation of the <math><msubsup><mi>D</mi><mi>s</mi><mo>+</mo></msubsup></math> meson.

Mixing effects on <math><mrow><mn>1</mn><mi>S</mi></mrow></math> and <math><mn>2</mn><mi>S</mi></math> state heavy mesons in the light-front quark model

Decay properties of multistrangeness <math><mi>Ξ</mi></math> and <math><mi>Ω</mi></math> baryon resonances are investigated within the constituent quark model by including relativistic corrections. The strong decay widths of various <math><mi>Ξ</mi></math> and <math><mi>Ω</mi></math> resonances are computed and tested for internal quark configurations to pin down their spin-parity (<math><msup><mi>J</mi><mi>P</mi></msup></math>) quantum numbers and internal structures. We found that the Roper-like resonances in the multistrangeness sector have large decay widths bearing resemblances to their siblings in light and heavy baryon sectors. In addition, we obtained the decay ratio for the <math><mi>Ω</mi><mo>(</mo><mn>2012</mn><mo>)</mo></math> as <math><mi>Γ</mi><mrow><mo>(</mo><mi>Ω</mi><mo>→</mo><mi>Ξ</mi><mover><mi>K</mi><mo>¯</mo></mover><mi>π</mi><mo>)</mo></mrow><mo>/</mo><mi>Γ</mi><mrow><mo>(</mo><mi>Ω</mi><mo>→</mo><mi>Ξ</mi><mover><mi>K</mi><mo>¯</mo></mover><mo>)</mo></mrow><mo>=</mo><mn>4.5</mn><mo>%</mo></math>, which is consistent with the experimental data when <math><msup><mi>J</mi><mi>P</mi></msup><mo>=</mo><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></math> is assigned. This observation holds the possibility that the <math><mi>Ω</mi><mo>(</mo><mn>2012</mn><mo>)</mo></math> could naturally be explained as a three-quark state in the quark model. The decays of other low-lying <math><mi>Ξ</mi></math> and <math><mi>Ω</mi></math> resonances are systematically analyzed, which would be useful to unveil the structure of these resonances in future experiments.

Daiki Suenaga

Atsushi Hosaka

Strong decays of multistrangeness baryon resonances in the quark model

We investigate relativistic corrections of an order <math><mn>1</mn><mo>/</mo><msup><mi>m</mi><mn>2</mn></msup></math>, where <math><mi>m</mi></math> is the constituent quark mass, to heavy baryon decays by emitting one pseudoscalar meson in the quark model. This work is motivated by shortcomings in the previous studies in the nonrelativistic quark model for decays of the Roper-like states, such as <math><msub><mi>Λ</mi><mi>c</mi></msub><mo>(</mo><mn>2765</mn><mo>)</mo></math>. We find that the relativistic corrections due to the internal motion of quarks are essential ingredients in improving their decay properties, such that the decay widths are significantly increased. In addition, such corrections can explain a phenomenological suppression of the quark axial-vector coupling constant <math><msubsup><mi>g</mi><mi>A</mi><mi>q</mi></msubsup></math> for the <math><msub><mi>Σ</mi><mi>c</mi></msub><mo>(</mo><mn>2455</mn><mo>)</mo></math> and <math><msub><mi>Σ</mi><mi>c</mi></msub><mo>(</mo><mn>2520</mn><mo>)</mo></math> decays.