arXiv subjects

Rui-Xiang Shi

Publications and source records attributed to Rui-Xiang Shi.

16 recordsLinked to original sources

arXiv2026

$|\Delta I|=3/2$ non-leptonic hyperon decays in covariant baryon chiral perturbation theory

Inspired by the recent BESIII measurements of non-leptonic hyperon decays, we reexamine their $|\Delta I|=3/2$ amplitudes in covariant baryon chiral perturbation theory with the extended-on-mass-shell renormalization scheme. Using the same restricted set of diagrammatic topologies as in the early analyses in heavy baryon chiral perturbation theory, we assess the effects of relativistic corrections, explicit decuplet baryons, different spin-$3/2$ coupling schemes, and pion-loop contributions. Our results show that relativistic effects alone lead to only mild changes, while decuplet contributions, especially in the consistent-coupling scheme, significantly improve the fit quality. Pion-loop contributions further reduce the $\chi^2$ values. We highlight the importance of the consistent coupling scheme in the decuplet sector for describing the selected $|\Delta I|=3/2$ amplitudes.

hep-ph↗

arXiv2026

Radiative decays of the $\Lambda(1520)$ as a dynamically generated resonance

Inspired by the latest BESIII measurement of the $\Lambda(1520)\to\gamma\Sigma^0$ radiative decay, we systematically study the decays $\Lambda(1520)\to\gamma\Lambda(\Sigma^0)$ within the chiral unitary approach, where the $\Lambda(1520)$ is treated as a dynamically generated resonance from meson-baryon interactions. Compared with previous chiral unitary studies, we adopt dimensional regularization for $S$-wave loop integrals to preserve gauge invariance and, for the first time, include Feynman diagrams with photon coupling to intermediate baryons. Our calculated partial decay width $\Gamma(\Lambda(1520)\to\gamma\Sigma^0)$ agrees well with the new BESIII data, whereas the predicted $\Gamma(\Lambda(1520)\to\gamma\Lambda)$ is considerably smaller than the CLAS experimental result. By comparing our results with predictions from various quark models, we discuss the internal nature of the $\Lambda(1520)$ resonance, highlight its complex component structure, and stress the need for more refined theoretical frameworks and further experimental measurements.

hep-ph↗

arXiv2025

$J/\psi \Lambda $ femtoscopy and the nature of $P_{\psi s}^{\Lambda}(4338)$

Over the past two decades, numerous exotic hadron states have been discovered, yet their underlying nature remains unclear. It is widely acknowledged that understanding hadron-hadron interactions is essential to unraveling their properties. Hadron spectroscopy is a powerful tool for this endeavor, providing rich experimental data that can shed light on exotic systems. Recently, the LHCb experiment analyzed the process $B^{-} \rightarrow J/\psi \Lambda \bar{p}$ and observed a narrow peak in the $J/\psi \Lambda$ invariant mass spectrum, regarding it as a candidate for a pentaquark. In this work, we extract the coupled-channel $J / \psi \Lambda-\bar{D} \Xi_c-\bar{D}_s \Lambda_c$ potential based on the $J/\psi \Lambda$ invariant mass spectrum. Our results indicate the existence of a bound state below the $\bar{D} \Xi_c$ mass threshold, corresponding to the experimentally measured state $P_{cs}(4338)$. Furthermore, we predict the scattering lengths and momentum correlation functions for the $J/\psi \Lambda$ and $\bar{D}\Xi_c$ channels, which serve as theoretical references for future femtoscopy experiments.

hep-ph↗

arXiv2025

$V_{cb}$ puzzle in semi-leptonic $B\to D^*$ decays revisited

Inspired by the newly reported $B\to D^*(\to Dπ)\ell\barν_\ell$ differential decay rates by the Belle and Belle II Collaborations, we revisit the $V_{cb}$ puzzle in semi-leptonic $B\to D^*$ decays, considering the latest lattice QCD~(LQCD) simulations and light-cone sum rule~(LCSR) results. We examine the commonly used Caprini-Lellouch-Neubert~(CLN), Boyd-Grinstein-Lebed~(BGL), and heavy quark effective theory~(HQET) parameterizations. We demonstrate that these three parameterizations yield consistent results and reconfirm the $V_{cb}$ puzzle. Then, we use a state-of-the-art Bayesian method to estimate the impact of higher-order terms beyond the present HQET expansion on the uncertainty of $V_{cb}$. We show that higher-order effects cannot eliminate the deviation between the exclusive and inclusive determinations of $V_{cb}$. Finally, utilizing the best-fit results obtained in the HQET parameterization via fitting LQCD and LCSR data only as inputs, we predict the relevant observables, i.e., $R_{D^*}$, $F_L^{D^*}$, and $P_τ^{D^*}$, sensitive to new physics in the $B\to D^*\ell\barν_\ell$ decays. We conclude that lepton-flavour universality violations still exist in the $b\to cτν$.

hep-ph↗

arXiv2025

Status and prospect of weak radiative hyperon decays

Weak radiative hyperon decays represent a rich interplay between weak interactions and the internal structure of baryons, offering profound insights into Quantum Chromodynamics and weak interactions. Recent experimental observations, particularly from BESIII, have revealed deviations from theoretical predictions. These deviations could signal new physics or the need for refined theoretical models incorporating intermediate resonance effects. This review discusses recent theoretical advancements and key experimental findings, focusing on recent measurements from BESIII and their implications for strong interactions and baryon structure.

hep-ph↗

arXiv2024

Potential signature of new magicity from universal aspects of nuclear charge radii

Shell quenching phenomena in nuclear charge radii are typically observed at the well-established neutron magic numbers. However, the recent discovery of potential new magic numbers at the neutron numbers $N = 32$ and $N = 34$ has sparked renewed interest in this mass region. This work further inspects into the charge radii of nuclei around the $N = 28$ shell closure using the relativistic Hartree-Bogoliubov model. We incorporate meson exchange and point-coupling effective nucleon-nucleon interactions alongside the Bogoliubov transformation for pairing corrections. To accurately capture the odd-even staggering and shell closure effects observed in charge radii, neutron-proton correlations around Fermi surface are explicitly considered. The charge radii of Ca and Ni isotopes are used to test the theoretical model and show an improvement with neutron-proton pairing corrections, in particular for neutron-rich isotopes. Our calculations reveal a inverted parabolic-like trend in the charge radii along the $N = 28$ isotones for proton numbers $Z$ between 20 and 28. Additionally, the shell closure effect of $Z = 28$ persists across the $N = 28$, 30, 32, and 34 isotonic chains, albeit with a gradual weakening trend. Notably, the significantly abrupt changes in charge radii are observed across $Z = 22$ along both the $N = 32$ and $N = 34$ isotonic chains. This kink at $Z = 22$ comes from the sudden decrease of the neuron-proton correlation around Fermi surfaces across $Z = 22$ for $N = 30$, 32, and 34 isotones, and might provide a signature for identifying the emergence of neutron magic numbers $N = 32$ and 34. Furthermore, the calculated charge radii for these isotonic chains ($N = 28$, 30, 32, and 34) can serve as reliable guidelines for future experimental measurements.

nucl-th↗

arXiv2023

New Physics Searches at Kaon and Hyperon Factories

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

hep-ph↗

arXiv2023

Are we close to solving the puzzle of weak radiative hyperon decays?

The BESIII experiment at the Beijing Electron Positron collider, run as a ``hyperon factory'', recently reported the first measurement of the asymmetry parameter of the $Λ\to nγ$ decay and updated its branching fraction, which differs from the PDG average by 5.6 sigma. We highlight the impact of this new measurement on our understanding of the puzzle of weak radiative hyperon decays and pinpoint what needs to be done in the future.

hep-ph↗

arXiv2022

Weak radiative hyperon decays in covariant baryon chiral perturbation theory

Weak radiative hyperon decays, important to test the strong interaction and relevant in searches for beyond the standard model physics, have remained puzzling both experimentally and theoretically for a long time. The recently updated branching fraction and first measurement of the asymmetry parameter of $Λ\to nγ$ by the BESIII Collaboration further exacerbate the issue, as none of the existing predictions can describe the data. We show in this letter that the covariant baryon chiral perturbation theory, with constraints from the latest measurements of hyperon non-leptonic decays, can well describe the BESIII data. The predicted branching fraction and asymmetry parameter for $Ξ^-\toΣ^-γ$ are also in agreement with the experimental data. We note that a more precise measurement of the asymmetry parameter, which is related with that of $Σ^+\to pγ$, is crucial to test Hara's theorem. We further predict the branching fraction and asymmetry parameter of $Σ^0\to nγ$, whose future measurement can serve as a highly nontrivial check on our understanding of weak radiative hyperon decay and on the covariant baryon chiral perturbation theory.

hep-ph↗

arXiv2022

New physics in $s\to d$ semileptonic transitions: rare hyperon vs. kaon decays

We investigate the potential of rare hyperon decays to probe the short distance structure in the $s\to dν\barν$ and $s\to d\ell^+\ell^-$ transitions. Hyperon decays into neutrinos ($B_1\to B_2ν\barν$) can be reliably predicted by using form factors determined in baryon chiral perturbation theory. Their decay rates are sensitive to different short-distance operators, as compared to their kaon counterparts, and the corresponding branching fractions are in the range of $10^{-14}\sim10^{-13}$ in the standard model. In the context of the low-energy effective theory, we find that the anticipated BESIII measurements of the $B_1\to B_2ν\barν$ decays would lead to constraints on new physics in the purely axial vector $\bar d γ_μγ_5 s$ current that are stronger than the present limits from their kaon siblings $K\to ππν\barν$. On the other hand, although hyperon decays into charged leptons are dominated by long-distance hadronic contributions, angular observable such as the leptonic forward-backward asymmetry is sensitive to the interference between long- and short-distance contributions. We discuss the sensitivity to new physics of a potential measurement of this observable in comparison with observables in the kaon decays $K_L\toμ^+μ^-$ and $K^+\toπ^+μ^+μ^-$. We conclude that the current kaon bounds are a few orders of magnitude better than those that could be obtained from $Σ^+\to pμ^+μ^-$ except for two scenarios with new physics in the $(\bar d γ^μs)(\bar\ellγ_μγ_5\ell)$ and $(\bar d γ^μγ_5s)(\bar\ellγ_μ\ell)$ currents. Finally, we point out that the loop effects from renormalization group evolution are important in this context, when relating the low-energy effective field theory to new physics models in the UV.

hep-ph↗

arXiv2021

Discriminating 1D new physics solutions in $b\to s\ell\ell$ decays

The recent measurements of $R_{K^+}$, $R_{K_S^0}$, $R_{K^{*+}}$, $B_s\toμ^+μ^-$, a set of CP-averaged angular observables for the $B^0\to K^{*0}μ^+μ^-$ decay, and its isospin partner $B^+\to K^{*+}μ^+μ^-$ by the LHCb Collaboration, consistently hint at lepton universality violation in the $b\to s\ell\ell$ transitions. In this work, we first perform global fits to the $b\to s\ell\ell$ data and show that five one-dimensional scenarios, i.e, $δC_9^μ$, $δC_{10}^μ$, $δC_L^μ$, $δC_9^μ=C_{10}^{μ\prime}$, and $δC_9^μ=-C_9^{μ\prime}$ can best explain the so-called B anamolies. Furthermore, we explore how these scenarios can be distinguished from each other. For this purpose, we first study the combinations of four angular asymmetries $A_i$~$(i=3,4,5,9)$ and find that they cannot distinguish the five new physics scenarios. We then show that a newly constructed ratio $R_{S}$ can uniquely discriminate the five new physics scenarios in proper intervals of $q^2$ if it can be measured with a percent level precision.

hep-ph↗

arXiv2021

Implications of new evidence for lepton-universality violation in $b\to s\ell^+\ell^-$ decays

Motivated by renewed evidence for new physics in $b \to s\ell\ell$ transitions in the form of LHCb's new measurements of theoretically clean lepton-universality ratios and the purely leptonic $B_s\toμ^+μ^-$ decay, we quantify the combined level of discrepancy with the Standard Model and fit values of short-distance Wilson coefficients. A combination of the clean observables $R_K$, $R_{K^*}$, and $B_s\to μμ$ alone results in a discrepancy with the Standard Model at $4.0σ$, up from $3.5σ$ in 2017. One-parameter scenarios with purely left-handed or with purely axial coupling to muons fit the data well and result in a $\sim 5 σ$ pull from the Standard Model. In a two-parameter fit of %$C_9$ and $C_{10}$, new-physics contributions with both vector and axial-vector couplings to muons the allowed region is much more restricted than in 2017, principally due to the much more precise result on $B_s \to μ^+ μ^-$, which probes the axial coupling to muons.Including angular observables data restricts the allowed region further.A by-product of our analysis is an updated average of $\text{BR}(B_s \to μ^+ μ^-) = (2.8\pm 0.3) \times 10^{-9}$.

hep-ph↗

arXiv2021

Understanding $P_{cs}(4459)$ as a hadronic molecule in the $Ξ_b^-\to J/ψΛK^-$ decay

Recently, the LHCb Collaboration reported on the evidence for a hidden charm pentaquark state with strangeness, i.e., $P_{cs}(4459)$, in the $J/ψΛ$ invariant mass distribution of the $Ξ_b^-\to J/ψΛK^-$ decay. In this work, assuming that $P_{cs}(4459)$ is a $\bar{D}^*Ξ_c$ molecular state, we study this decay via triangle diagrams $Ξ_b\rightarrow \bar{D}_s^{(*)}Ξ_c\to (\bar{D}^{(*)}\bar{K})Ξ_c\to P_{cs} \bar{K}\to (J/ψΛ) \bar{K}$. Our study shows that the production yield of a spin 3/2 $\bar{D}^*Ξ_c$ state is approximately one order of magnitude larger than that of a spin $1/2$ state due to the interference of $\bar{D}_sΞ_c$ and $\bar{D}_s^*Ξ_c$ intermediate states. We obtain a model independent constraint on the product of couplings $g_{P_{cs}\bar{D}^*Ξ_c}$ and $g_{P_{cs}J/ψΛ}$. With the predictions of two particular molecular models as inputs, we calculate the branching ratio of $Ξ_b^-\to (P_{cs}\to)J/ψΛK^- $ and compare it with the experimental measurement. We further predict the lineshape of this decay which could be useful to future experimental studies.

hep-ph↗

arXiv2021

Magnetic moments of the spin-$\frac{3}{2}$ doubly charmed baryons in covariant baryon chiral perturbation theory

Inspired by the discovery of the spin-$\frac{1}{2}$ doubly charmed baryon $Ξ_{cc}^{++}$ and the subsequent theoretical studies of its magnetic moments, we study the magnetic moments of its spin-$\frac{3}{2}$ heavy quark spin symmetry counterparts, up to the next-to-leading order in covariant baryon chiral perturbation theory (BChPT) with the extended-on-mass-shell renormalization (EOMS) scheme. With the tree-level contributions fixed by the quark model while the two low energy constants (LECs) $C$ and $H$ controlling the loop contributions determined in two ways: the quark model (case 1) and lattice QCD simulations together with the quark model (case 2), we study the quark mass dependence of the magnetic moments and compare them with the predictions of the heavy baryon chiral perturbation theory (HB ChPT). It is shown that the difference is sizable in case 1, but not in case 2 due to the smaller LECs $C$ and $H$, similar to the case of spin-$\frac{1}{2}$ doubly charmed baryons. Second, we predict the magnetic moments of the spin-$\frac{3}{2}$ doubly charmed baryons and compare them with those of other approaches. The predicted magnetic moments in case 2 for the spin-$\frac{3}{2}$ doubly charmed baryons are closer to those of other approaches. In addition, the large differences in case 1 and case 2 for the predicted magnetic moments may indicate the inconsistency between the quark model and the lattice QCD simulations, which should be checked by future experimental or more lattice QCD data.

hep-ph↗

arXiv2020

Towards the discovery of new physics with lepton-universality ratios of $b\to s\ell\ell$ decays

Tests of lepton-universality as rate ratios in $b\to s \ell\ell$ transitions can be predicted very accurately in the Standard Model. The deficits with respect to expectations reported by the LHCb experiment in muon-to-electron ratios of the $B\to K^{(*)}\ell\ell$ decay rates thus point to genuine manifestations of lepton non-universal new physics. In this paper, we analyse these measurements in the context of effective field theory. First, we discuss the interplay of the different operators in $R_K$ and $R_{K^*}$ and provide predictions for $R_{K^*}$ in the Standard Model and in new-physics scenarios that can explain $R_K$. We also provide approximate numerical formulas for these observables in bins of interest as functions of the relevant Wilson coefficients. Secondly, we perform frequentist fits to $R_{K}$ and $R_{K^*}$. The SM disagrees with these measurements at $3.7σ$ significance. We find excellent fits in scenarios with combinations of $\mathcal O_{9(10)}^\ell=\bar sγ^μb_L~\ellγ_μ(γ_5) \ell$ operators, with pulls relative to the Standard Model in the region of $4σ$. An important conclusion of our analysis is that a lepton-specific contribution to $\mathcal O_{10}$ is essential to understand the data. Under the hypothesis that new-physics couples selectively to the muons, we also present fits to other $b\to sμμ$ data with a conservative error assessment, and comment on more general scenarios. Finally, we discuss new lepton universality ratios that, if new physics is the origin of the observed discrepancy, should contribute to the statistically significant discovery of new physics in the near future.

hep-ph↗

arXiv2019

Revisiting the new-physics interpretation of the $b\to cτν$ data

We revisit the status of the new-physics interpretations of the anomalies in semileptonic $B$ decays in light of the new data reported by Belle on the lepton-universality ratios $R_{D^{(*)}}$ using the semileptonic tag and on the longitudinal polarization of the $D^*$ in $B\to D^*τν$, $F_L^{D^*}$. The preferred solutions involve new left-handed currents or tensor contributions. Interpretations with pure right-handed currents are disfavored by the LHC data, while pure scalar models are disfavored by the upper limits derived either from the LHC or from the $B_c$ lifetime. The observable $F_L^{D^*}$ also gives an important constraint leading to the exclusion of large regions of parameter space. Finally, we investigate the sensitivity of different observables to the various scenarios and conclude that a measurement of the tau polarization in the decay mode $B\to Dτν$ would effectively discriminate among them.

hep-ph↗