arXiv subjects

Ji-Xin Yu

Publications and source records attributed to Ji-Xin Yu.

5 recordsLinked to original sources

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↗

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

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

$CP$ 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↗

arXiv2024

Establishing CP Violation in $b$-Baryon Decays

It is a long-standing puzzle why the {\it CP} violation (CPV) in the baryon system has not yet been definitively established as in the meson one. We demonstrate that individual partial-wave CPV in the $\Lambda_b\to p\pi^-$ and $pK^-$ decays can exceed $10\%$, but the destruction between the partial waves (the suppression by the small partial-wave weight) results in a small net direct CPV in the former (the latter) as measured currently. Our finding highlights the different dynamics responsible for CPVs in baryon and meson decays. We propose to probe the CPV observables associated with the angular distributions of the $\Lambda_b\to pa_1(1260)$, $pK_1(1270)$ decay products, which are large enough for being identified experimentally.

hep-ph↗