arXiv subjects

Shuang-Yi Li

Publications and source records attributed to Shuang-Yi Li.

4 recordsLinked to original sources

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↗

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↗

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↗