arXiv subjects

Fu-Sheng Yu

Publications and source records attributed to Fu-Sheng Yu.

At least 19 recordsLinked to original sources

arXiv2026

Semileptonic Decay of $\Lambda_b \rightarrow N(1520)\ell^-\bar{\nu}_{\ell}$ from QCD Light-cone Sum Rules

We investigate the complete set of vector and axial-vector form factors for the charged-current transition $\Lambda_b^0\to N(1520)^+$ using QCD light-cone sum rules (LCSRs) based on the light-cone distribution amplitudes (LCDAs) of the $\Lambda_b$ baryon, with the hard-scattering kernels evaluated at tree level. In the hadronic representation of the correlation function, we include the pole contributions of both the negative-parity $N(1520)$, with $J^P=3/2^-$, and the positive-parity $N(1720)$, with $J^P=3/2^+$. By matching a selected set of Lorentz structures, we derive sum rules that separate the $N(1520)$ contribution from the $N(1720)$ contribution within the adopted two-pole hadronic ansatz. After extrapolating the large-recoil LCSR results over the physical $q^2$ region using a pole-improved $z$ expansion truncated at linear order, we predict the differential branching fractions, the lepton forward-backward asymmetry, the charged-lepton polarization, and the $N(1520)$ polarization in $\Lambda_b^0\to N(1520)^+\ell^-\bar{\nu}_{\ell}$ ($\ell=e,\mu,\tau$). The corresponding total branching fractions are $\mathcal{B}_{e,\mu,\tau} =(12.4\pm10.5,\,12.4\pm10.5,\,5.0\pm4.3)\times10^{-5}$. Within the stated approximations, these results may serve as theoretical benchmarks for future experimental studies of this channel.

hep-ph↗

arXiv2026

Revisiting Quark Confinement in the Proton through the Force on Quarks

Quark confinement, the fact that colored quarks are permanently bound inside color-neutral hadrons and have never been observed as isolated particles, remains one of the central issues of the Standard Model. Recently, Ji et al.\,\cite{Ji:2026lyj} proposed a framework to define and measure the force on quarks in the proton, obtaining strong evidence for a net confining force and thus opening a new perspective on the study of confinement. In this work, we improve this analysis by incorporating light-cone QCD sum rule results to supplement the limited experimental and lattice QCD information in the large-$|q^2|$ region. We further formulate the reconstruction of the quark force as a regularized inverse problem, thereby reducing the model dependence associated with the prescribed functional parametrizations used before. The resulting quark force provides a complementary, less parametrization-dependent determination and remains consistent with that implied by a linear QCD potential, which also supports the robustness of the framework proposed in Ref.\,\cite{Ji:2026lyj}. We also show that improved future inputs can substantially reduce the uncertainty in the reconstructed quark force.

hep-ph↗

arXiv2026

Exploring the neutron momentum distribution in nuclei through $\gamma n \to \pi^- p$ at an electron-positron collider

The neutron momentum distribution is essential both for reliably extracting fundamental free neutron observables from nuclear measurements and for probing the tensor force via the high-momentum neutron fraction, which is crucial to the theoretical understanding of short-range correlations (SRCs). In this work, we investigate this distribution by studying the $\gamma n \to \pi^- p$ process at an electron-positron collider, proposing to utilize the beryllium beam pipe at the Beijing Spectrometer III (BESIII). The cross sections for this process on both deuteron and beryllium targets are calculated within the impulse approximation framework. We also evaluate the effective luminosity of the photon flux from radiative Bhabha scattering, taking into account the distribution of target materials within the BESIII experimental setup. Our results show that tens of thousands of events can be generated at BESIII, offering the potential for precise measurements of the neutron momentum distribution. These findings suggest that electron-positron colliders could play a valuable role in elucidating nuclear structure and advancing our understanding of nonperturbative QCD, offering promising new avenues for both particle and nuclear physics.

hep-ph↗

arXiv2026

Final-state rescattering mechanism of doubly-charmed baryon decays: $\mathcal{B}_{cc}\to\mathcal{B}_{c}V$

We study the non-leptonic weak decays of doubly charmed baryons (${\cal B}_{cc}$) into singly charmed baryons (${\cal B}_c$) and vector mesons ($V$), denoted as ${\cal B}_{cc}\to{\cal B}_{c}V$. The short-distance contributions are calculated within the naive factorization hypothesis, while the long-distance final-state interaction effects are modeled via hadronic triangle diagrams. Unlike previous approaches, which compute only the imaginary part using the Cutkosky cutting rule, we evaluate the complete loop integrals to obtain both the real and imaginary parts of the amplitudes. These provide the nontrivial strong phases essential for CP violation. The model parameters are determined using experimental data. With this improved calculation method, we predict the branching ratios and decay asymmetry parameters for various decay channels, as well as $CP$ violations for short-distance dominated and singly Cabibbo-suppressed channels. This strengthens our theoretical framework for future study of doubly charmed baryons. Certain decays, primarily driven by long-distance effects, have been calculated; their observation in future experiments could help clarify the role of final-state interactions in charm baryon decays. Therefore, our calculation of ${\cal B}_{cc}\to{\cal B}_{c}V$ provides crucial predictions for branching ratios, decay asymmetry parameters, and $CP$ violation, which are essential for guiding experimental study at LHCb.

hep-ph↗

arXiv2026

Final-state rescattering in $\bar{B}^{0}_{(s)}\to \Lambda^{+}_{c}\bar{\Lambda}^{-}_{c}$ decays

The LHCb Collaboration has recently reported the first observation of the decay $\bar B_s^0\to \Lambda_c^+\bar\Lambda_c^-$, along with measurements of the branching fractions for both $\bar B^0\to \Lambda_c^+\bar\Lambda_c^-$ and $\bar B_s^0\to \Lambda_c^+\bar\Lambda_c^-$. In this work, we investigate these two decays within the framework of final state re-scattering. Our results show that the predicted branching fractions are consistent with the experimental measurements, indicating the significant role of long-distance final-state interactions in such baryonic B decays. Furthermore, we present predictions for the direct CP asymmetries and the asymmetry parameters. Numerically, both decays exhibit nearly vanishing CP asymmetries, while $\bar B^0\to \Lambda_c^+\bar\Lambda_c^-$ displays a sizable longitudinal polarization, providing a sensitive observable for testing our theoretical framework in future experimental measurements.

hep-ph↗

arXiv2026

Probing direct $CP$ violation in $\Lambda_b^0 \to P_c^+ h^-$ $(h=\pi,K)$ with final-state rescattering

The LHCb Collaboration recently reported a measurement of the difference in direct CP asymmetries for the decays $\Lambda_b^0 \to J/\psi \, p \, h^-$ (with $h = K, \pi$), offering new experimental constraints on the decay dynamics of heavy baryons into charmonium final states. Inspired by these findings, we explore the branching ratios and direct CP violations for the decays $\Lambda_b^0 \to P_c^+(4312, 4440, 4457)\,h^-$ within the framework of final-state rescattering. Our analysis indicates that the branching fractions for $\Lambda_b^0 \to P_c^+ \pi^-$ lie around the $10^{-6}$ level, with the corresponding direct CP asymmetries approaching approximately $1\%$. In contrast, the direct CP violation for the decay $\Lambda_b^0 \to P_c^+ K^-$ is found to be very small, while its branching ratios show a strong dependence on the spin assignments of the $P_c$ states. These predictions may provide useful guidance for more precise CP measurements and amplitude analyses in the $P_c$ region in future experiments.

hep-ph↗

arXiv2026

Study of $CP$ violation in $\Lambda_b^0/\Xi^-_b\rightarrow \Lambda(1520)M$ decays with the final-state rescattering mechanism

Recently, the LHCb collaboration reported the first observation of $CP$ violation in baryon decays, with a significance of more than $5\sigma$. This strongly motivates us to investigate the $CP$ violation in more baryon decay processes. In this work, we employ the final-state rescattering mechanism with introducing two model parameters, $\Lambda_{charm}$ and $\Lambda_{charmless}$, and calculate two-body non-leptonic baryon decays $\Lambda^0_b \rightarrow \Lambda(1520)\,\pi^0/\kappa(700)/f_0(500, 980)/\rho^0/K^{*0}/\phi$ and $\Xi^-_b \rightarrow \Lambda(1520)\,K^-$. Consequently, we evaluate the corresponding branching ratios, $CP$ asymmetries, and interference effects between different decay amplitudes. Our theoretical predictions for certain decay channels are in good agreement with current experimental measurements, while the remaining processes--particularly the remarkably large $CP$ violation observable revealed by the kinematic analysis are expected to be tested in future experiments.

hep-ph↗

arXiv2026

Study of $CP$ violation in $\Lambda_b^0\rightarrow N^*M$ decays with the final-state rescattering mechanism

In this work, we investigate the charmless non-leptonic two-body $\Lambda_b$ decays within the framework of final-state rescattering mechanism. In contrast to the Cutkosky cutting method, we compute both the absorptive and dispersive parts of the hadronic rescattering triangle diagrams. Based on the established formalism, we analyze the $\Lambda_b \to N^*(1535,1520)M$ decay processes with $M =K_S, K^*_0(700)$, $f_0(500,980), \rho(770), \bar{K}^{*0}$, $\phi$, and predict various physical observables, such as their branching ratios, direct and partial-wave $CP$ asymmetries, as well as decay asymmetry parameters. These two-body decay processes are expected to contribute primarily to the subsequent four-body decay channels, such as $\Lambda_b^0 \to p\,\pi^-\,\pi^+\,\pi^-$, whose $CP$ asymmetry measurements will be accessible at the LHCb experiment.

hep-ph↗

arXiv2025

Branching fraction of $\Xi_{bc}^+\to \Xi_{c}^+ J/\psi$ in the final-state-interaction approach

The process of $\Xi_{bc}^{+}\to \Xi_{c}^{+}J/\psi$ is among the most favored modes for searching for bottom-charm baryons. However, its branching fraction has never been studied in theory. In this work, we investigate the branching fraction of $\Xi_{bc}^{+}\to \Xi_{c}^{+}J/\psi$ in the final-state-interaction approach, as it is dominated by the color-suppressed non-factorizable contributions. A similar process, $\Lambda_{b}^{0}\to \Lambda^0 J/\psi$, is used as a control mode to fix the model parameter. Consequently, the branching fraction of $\Xi_{bc}^{+}\to \Xi_{c}^{+}J/\psi$ is predicted to be $(1.55_{-0.42}^{+0.50})\times10^{-4}$. With the production rate of bottom-charm baryons and the detection efficiencies of the final states, it is expected for considerable signal events to observe $\Xi_{bc}^+$ in the near future.

hep-ph↗

arXiv2025

Solving the Inverse Source Problem in Femtoscopy with a Toy Model

Hadron-hadron interactions, as a non-perturbative effect, play a significant role in understanding phenomenological problems in particle physics. Femtoscopy is a powerful tool in heavy-ion collision experiments, enabling the extraction of hadron-hadron interactions via momentum-correlation functions (CFs). These CFs are generally factorized into a convolution of source functions and hadron-hadron wave functions, with the latter encoding information about hadron-hadron interactions. However, source functions remain ambiguous and are commonly approximated by a Gaussian form. Reconstructing source functions from experimental correlation data constitutes an ``inverse problem." To address it, we propose a toy model based on the Tikhonov regularization. Employing a square potential well of four distinct potential strengths, we calculate the CFs for inputs of a Gaussian source function and its hybrid form. The obtained CFs are subsequently used to reconstruct the source functions via the Tikhonov regularization. Our results demonstrate that the Gaussian source function can be successfully reconstructed, indicating the potential of this approach for extracting realistic source functions of hadron pairs of interest in the future.

hep-ph↗

arXiv2025

Tomography of high-twist proton structure through $ep$ elastic scattering

We present the first high-twist study of the proton form factors $F_{1,2}(Q^2)$ in $ep$ elastic scattering based on the perturbative QCD $k_T$ factorization, $Q^2$ being momentum transfer squared. It is motivated by unexpectedly large higher-power contributions from subleading-twist light-cone distribution amplitudes (LCDAs), which are attributed to the enhancement in endpoint regions of parton momentum fractions. We highlight that the endpoint enhancement, tamed by the $k_T$ resummation effect, is crucial for accommodating the approximate scaling behavior of the $Q^4F_1(Q^2)$ data at intermediate $Q^2\sim {\cal O}(10)$ GeV$^2$. The proton LCDAs up to twist 6 are then extracted, and verified by the charge-parity asymmetries observed in hadronic heavy baryon decays. Our work provides new insights into the proton three-dimensional structure and manifests the precision requirement for reliable perturbative analyses of baryonic exclusive processes.

hep-ph↗

arXiv2025

First determination of $V_{cs,cd}$ from inclusive $D$ meson decays

We report the first determination of the Cabibbo-Kobayashi-Maskawa matrix elements $|V_{cs}|$ and $|V_{cd}|$ from a global fit to data from inclusive and sum-of-exclusive charm decays. Simultaneously, the heavy quark expansion parameters are determined, and they are in good agreement with results from the literature, validating the robustness of this work. With the current precision, our determined value for $|V_{cs}|$ is consistent with the world-average value extracted from exclusive charm decay processes, while a tension of approximately $3\sigma$ is observed for $|V_{cd}|$ when compared to its exclusive world-average counterpart.

hep-ph↗

arXiv2025

The $\Lambda_{b} \to \Lambda$ transition form factors in perturbative QCD approach

In this work, we investigate the $\Lambda_b \to \Lambda$ transition form factors in the perturbative QCD (PQCD) approach, incorporating higher-twist light-cone distribution amplitudes (LCDAs). The resulted form factors show that higher-twist LCDAs are dominant numerically. By combining our PQCD predictions at low-$q^2$ with lattice QCD results at high-$q^2$, $z$-series expansion fits are performed to parametrize the form factors over the full kinematic range. We also provide the prediction for physical observables in the rare decay $\Lambda_b \to \Lambda \mu^+ \mu^-$, including the differential branching fraction, dilepton longitudinal polarization fraction, and forward-backward asymmetries (lepton-side, hadron-side, and combined lepton-hadron). Our obtained form factors are consistent with those in other theoretical methods within the uncertainties.

hep-ph↗

arXiv2025

An analysis of nuclear parton distribution function based on relative entropy

In this work, we propose a method to quantify the difference between nuclear parton distribution functions in different nuclei and parton distribution functions in free nucleons using the relative entropy (also known as Kullback-Leibler divergence), a measure widely employed in quantum information theory. By introducing certain constraints and the ``minimum relative entropy" hypothesis, we can determine the shape of the structure function in the intermediate-$x$ region, which is intimately connected with the renowned EMC effect. For quark structure functions, our results align with the latest global fits to experimental data. This agreement suggests that the relative entropy-based methodology may provide novel insight into the structure of nucleons, particularly in cases where experimental data and theoretical QCD constraints are limited, such as those pertinent to gluon nPDFs. Therefore, we applied this methodology to gluon nPDFs, analyzing the results from two commonly used global fitting groups, EPPS21 and nNNPDF3.0. Our analysis suggests that the central values of EPPS21 align more closely with the ``minimum relative entropy" hypothesis. This finding underscores the utility of the proposed method and provides a valuable reference for future global fitting of nPDFs.

hep-ph↗

arXiv2025

Ill-Posedness in Limited Discrete Fourier Inversion and Regularization for Quasi Distributions in LaMET

We systematically investigated the limited inverse discrete Fourier transform of the quasi distributions from the perspective of inverse problem theory. This transformation satisfies two of Hadamard's well-posedness criteria, existence and uniqueness of solutions, but critically violates the stability requirement, exhibiting exponential sensitivity to input perturbations. To address this instability, we implemented Tikhonov regularization with L-curve optimized parameters, demonstrating its validity for controlled toy model studies and real lattice QCD results of quasi distribution amplitudes. The reconstructed solutions is consistent with the physics-driven $\lambda$-extrapolation method. Our analysis demonstrates that the inverse Fourier problem within the large-momentum effective theory (LaMET) framework belongs to a class of moderately tractable ill-posed problems, characterized by distinct spectral properties that differ from those of more severely unstable inverse problems encountered in other lattice QCD applications. Tikhonov regularization establishes a rigorous mathematical framework for addressing the underlying instability, enabling first-principles uncertainty quantification without relying on ansatz-based assumptions.

hep-lat↗

arXiv2025

$CP$ violation in two-body hadronic $\Lambda_b$ decays in the PQCD approach

We systematically investigate the $CP$-averaged branching ratios and $CP$ violations (CPVs) for the two-body hadronic decays $\Lambda_b\to ph$, where $h$ runs through the mesons $\pi^-$, $\rho^-$, $a_1^-(1260)$, $K^-$, $K^{\ast -}$, $K_1^-(1270)$ and $K_1^-(1400)$, in the perturbative QCD approach to order $\alpha_s^2$ in the strong coupling. Various topological amplitudes are obtained by incorporating subleading-twist hadron distribution amplitudes, which exhibit reasonable hierarchical patterns, sizable strong phases, and non-negligible higher-power corrections. The predicted direct CPVs in $\Lambda_b\to p\pi^-,pK^-$, different from those in similar $B$ meson decays, are as small as the current data. The low CPV in $\Lambda_b\to p\pi^-$ results from the cancellation between the $S$- and $P$-wave CPVs, while the one in $\Lambda_b\to pK^-$ is determined by the tiny $S$-wave CPV. However, individual partial-wave CPVs can exceed $10\%$, consistent with direct CPVs in $B$ meson decays. The CPVs in the $\Lambda_b\to pK_1^-(1270),pK_1^-(1400)$ channels are relatively larger. In particular, CPVs above $20\%$ appear in the up-down asymmetries associated with the final-state angular distributions of $\Lambda_b\to pK_1^-(1270),pK_1^-(1400)$, followed by the secondary $K_1\to K\pi\pi$ decays. These observables offer promising prospects for firmly establishing baryon CPVs. The decay asymmetry parameters of $\Lambda_b\to ph$ are also predicted for future experimental confrontations.

hep-ph↗

arXiv2025

New horizon in particle physics: first observation of CP violation in baryon decays

Recently, the LHCb Collaboration achieved the observation of CP violation (CPV) in baryon decays through the process of $\Lambda_b^0\to pK^-\pi^+\pi^-$, reporting an asymmetry of $(2.45\pm0.46\pm0.10)\%$ with a significance of 5.2$\sigma$. This marks a breakthrough and a milestone in particle physics, six decades after the first observation of CPV in mesons. It will be helpful to understand the matter-antimatter asymmetry in the universe. In addition to the global CPV, local CPV is also observed by LHCb in the low mass region of $m_{p\pi^+\pi^-}<2.7$GeV as $(5.4\pm0.9\pm0.1)\%$ with a significance of 6.0$\sigma$. Intriguingly, this measurement aligns well with a theoretical prediction of $(5.6-5.9)\%$ based on a CPV dynamics using the data of $N\pi\to p\pi^+\pi^-$ scatterings. Since baryons contain one more quark than mesons, the dynamics of baryon decays are significantly different from those of mesons. Therefore, the first observation of baryon CPV by LHCb opens a new horizon in the studies of dynamics of the strong interaction.

hep-ph↗

arXiv2025

CP violation studies at Super Tau-Charm Facility

Charge-parity ($C\!P$) violation in the tau-charm energy region is a promising area for sensitive tests of Standard Model (SM) predictions and searches for new, beyond the SM physics. A future Tau-Charm Facility that operates at center-of-mass energies between 2.0 and 7.0 GeV, with a peak luminosity of $0.5\times10^{35}$~cm$^{-2}$s$^{-1}$, would provide huge numbers of hadrons and tau ($\tau$) leptons that are produced in low-background environments and with well understood kinematic properties. In this report, prospects for unique studies of $C\!P$ violation in the decay of charmed hadrons, and in the production and decay of hyperons and $\tau$ leptons at a next-generation tau-charm facility are discussed. In addition, opportunities for improved tests of $CPT$ invariance test in $K^{0}-\bar{K}^{0}$ mixing are presented.

hep-ex↗