arXiv subjects

Qin Qin

Publications and source records attributed to Qin Qin.

At least 19 recordsLinked to original sources

arXiv2026

Study of $\Lambda^0_b \to \Lambda D$ decays with the rescattering mechanism

We employ the final-state rescattering mechanism to systematically investigate the non-leptonic decays $\Lambda_b^0 \to \Lambda D$ (where $D = D^0$, $\overline{D}^0$, $D_+$, $D_-$), which can help improve the experimental precision of the $CP$-violating phase angle $\gamma$. The framework integrates short-distance factorizable amplitudes with long-distance non-factorizable contributions arising from hadronic triangle rescattering diagrams. We find that the final-state rescattering contributions are essential, not only because they provide the strong phases necessary for $CP$ violation, but also because they enhance the $\overline{D}^0 \Lambda$ branching fraction by two orders of magnitude. Numerically, we calculate the branching ratios of the channels with different partial waves, as well as the corresponding $CP$-violating observables. In particular, the direct $CP$ asymmetries $a_{CP}^{\mathrm{dir}}(D_+) = 0.28^{+0.07}_{-0.11}$ and $a_{CP}^{\mathrm{dir}}(D_-) = -0.14^{+0.06}_{-0.04}$ are found to be very significant. These results provide a reliable theoretical benchmark and can be tested against future measurements from the LHCb experiment.

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.

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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 $3σ$ is observed for $|V_{cd}|$ when compared to its exclusive world-average counterpart.

hep-ph↗

arXiv2025

Quantum Entanglement Autodistillation in Baryon Pair Decays

We study the spin-entangled mixed state of a spin-1/2 baryon-antibaryon pair produced in the process e+e- to J/psi, psi(2S) to BBbar. We demonstrate that the spin entanglement of the system can increase following the decays B to b + M and Bbar to bbar + Mbar, where b and bbar are spin-1/2 baryons and M, Mbar are spin-0 mesons. This phenomenon, known as entanglement autodistillation, represents a probabilistic amplification of entanglement during the decay process. We analyze the underlying mechanism and show that it depends only on the initial state of the BBbar system and the decay parameter alphaD, but not on the phase parameter phiD.

hep-ph↗

arXiv2025

Flavor Physics at the CEPC: a General Perspective

We discuss the landscape of flavor physics at the Circular Electron-Positron Collider (CEPC), based on the nominal luminosity outlined in its Technical Design Report. The CEPC is designed to operate in multiple modes to address a variety of tasks. At the $Z$ pole, the expected production of 4 Tera $Z$ bosons will provide unique and highly precise measurements of $Z$ boson couplings, while the substantial number of boosted heavy-flavored quarks and leptons produced in clean $Z$ decays will facilitate investigations into their flavor physics with unprecedented precision. We investigate the prospects of measuring various physics benchmarks and discuss their implications for particle theories and phenomenological models. Our studies indicate that, with its highlighted advantages and anticipated excellent detector performance, the CEPC can explore beauty and $τ$ physics in ways that are superior to or complementary with the Belle II and Large-Hadron-Collider-beauty experiments, potentially enabling the detection of new physics at energy scales of 10 TeV and above. This potential also extends to the observation of yet-to-be-discovered rare and exotic processes, as well as testing fundamental principles such as lepton flavor universality, lepton and baryon number conservation, etc., making the CEPC a vibrant platform for flavor physics research. The $WW$ threshold scan, Higgs-factory operation and top-pair productions of the CEPC further enhance its merits in this regard, especially for measuring the Cabibbo-Kobayashi-Maskawa matrix elements, and Flavor-Changing-Neutral-Current physics of Higgs boson and top quarks. We outline the requirements for detector performance and considerations for future development to achieve the anticipated scientific goals.

hep-ex↗

arXiv2025

Inclusive $\bar{B}\to X_s \ell^+\ell^-$ at the LHC: theory predictions and new-physics reach

We present theoretical predictions for observables in inclusive $\bar{B}\to X_s \ell^+\ell^-$ suitable for measurements at hadron colliders through a sum-over-exclusive approach. At low $q^2$ we calculate the branching ratio and three angular observables. At high $q^2$ we provide the branching ratio and the ratio of the $\bar B \to X_s \ell^+\ell^-$ rate with respect to the inclusive $\bar B \to X_u \ell \barν$ rate with the same phase-space cut. We compare our predictions to the $B$ factory measurements and also to an extraction of the experimental rate through a sum-over-exclusive method using branching ratios of the exclusive $\bar B \to K^{(*)}μ^+μ^-$ modes measured at LHCb. We find a consistent picture comparing Standard Model theory and experiment. As such, our analysis does not support a recent claim about a deficit in the inclusive branching ratio in the high-$q^2$ region. Finally, we present current model-independent bounds on new physics and emphasize the potential of complementary analyses of $\bar{B}\to X_s \ell^+\ell^-$ at Belle II and the LHC.

hep-ph↗

arXiv2025

CP violation analysis of $D^0\to M^0 K \to M^0(π^\pm \ell^\mp ν)$

CP violation in the charm sector is highly sensitive to new physics due to its small predicted value within the standard model. By this work, we investigated the CP violation in the cascade decay process $D^0(t_1) \to π^0 K(t_2) \to π^0(π^\pm \ell^\mp ν)$. Our results indicate that the CP violation induced by the interference of unmixed $D$-meson decay amplitudes dominates, with a peak value reaching $5 \times 10^{-3}$. This is one order of magnitude larger than the sub-leading contribution, namely the double-mixing CP violation. Furthermore, the CP violation in the decay channel with the semileptonic final state $π^- \ell^+ ν_\ell$ is one to two orders of magnitude larger than that in the channel with $ π^+ \ell^- \barν_\ell$. We propose that the CP asymmetry of the combined two decay channels can be measured experimentally. The resulting value is approximately half of the CP violation observed in the $π^- \ell^+ ν_\ell$ channel, with the dominant contribution still reaching the order of $10^{-3}$. This approach offers the advantage of eliminating the need for flavor tagging of the initial $D$ meson, thereby avoiding associated efficiency losses.

hep-ph↗

arXiv2025

Double-mixing CP violation in $B$ decays

We study a long-overlooked CP violation observable, termed double-mixing CP violation, which arises from the interference between two neutral meson oscillating paths involved in a decay chain. The double-mixing CP violation is beneficial for the precise test of the Standard Model CKM mechanism, as it offers the potential to extract weak phases without pollution from strong dynamics. To provide a comprehensive understanding of the double-mixing CP violation, we perform phenomenological analyses on the cascade decays of the $B^0_d$ and $B^0_s$ mesons. Our results show that the double-mixing CP violation can be very significant in certain decay channels, such as $B^0_s \to ρ^0 K \to ρ^0(π^-\ell^+ν_\ell)$. In addition, we employ the decay process $B^0_d \to D^0 K \to (K^-π^+)(π\ellν)$ to demonstrate that the involved strong and weak phases can be directly determined from the experimental data without any theoretical inputs.

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 ($τ$) 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 $τ$ 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↗

arXiv2025

Data determination of HQET parameters in inclusive charm decays

This work delves into the phenomenology of electronic inclusive decays of $D$ mesons, encompassing $D^0, D^+, D^+_s\to Xe^{+}ν$. The theoretical formulas for the decay widths and electron energy moments of these decays are presented as expansions with powers of $α_s$ and $Λ_{\rm QCD}/m_c$. Remarkably, the expansion exhibits excellent convergence properties when we choose the 1S mass scheme for charm. The formulas are subsequently fitted to experimental data, and the $D$ meson matrix elements of operators in the heavy quark effective theory are hence determined by data for the first time, including \begin{align} μ^2_π(D^{0,+}) &= (0.09\pm 0.05) \mathrm{GeV}^2, \qquad \qquad μ^2_π(D^{+}_s) = (0.11\pm 0.05) \mathrm{GeV}^2, \nonumber \\ μ^2_G(D^{0,+}) &= (0.32\pm 0.02) \mathrm{GeV}^2, \qquad \qquad μ^2_G(D^{+}_s) = (0.43\pm 0.02) \mathrm{GeV}^2, \nonumber \\ ρ_D^3(D^{0,+}) &= (-0.003\pm 0.002) \mathrm{GeV}^3, \qquad\ ρ_D^3(D^{+}_s) = (-0.004\pm 0.002) \mathrm{GeV}^3, \nonumber \\ ρ_{LS}^3(D^{0,+}) &= (0.004\pm 0.002) \mathrm{GeV}^3, \qquad \ \ \ ρ_{LS}^3(D^{+}_s) = (0.005\pm 0.002) \mathrm{GeV}^3 . \nonumber \end{align} These determined parameters will play a crucial role as inputs in various physical quantities, including $D$ meson lifetimes.

hep-ph↗

arXiv2024

CP violation observables in baryon decays

The era of baryon physics is on the horizon with the accumulation of increasing data by collaborations such as LHCb, Belle II, and BESIII. Despite the wealth of data, one of the critical issues in flavor physics, namely CP violation in baryon decays, still awaits experimental confirmation. It is evident that the development of formulas and phenomenological analyses will play a pivotal role in advancing theoretical investigations and experimental measurements in this domain. In this work, we discuss the fundamental definitions and properties of polarization, asymmetry parameters and their associated CP violating observables that may arise in baryon decays. Additionally, we provide a detailed analysis of b-baryon quasi-two and -three body decays based on angular distributions. We highlight the significance of CP asymmetries defined by spin and momentum correlations, as non-trivial spin distributions are expected in baryon decays due to their non-zero polarization in productions and decays. Of particular importance is a complementary relation can be establised for two different types of observables, that are $\mathcal{T}$-even and -odd CP asymmetries respectively. The complementarity indicates that one observable exhibits the sine dependence on strong phase $Δδ$, while another exhibits as cosine. This gives us an distinctive opportunity to avoid the potential large suppression to CP asymmetries from small phase $Δδ$. Two points (\textbf{i}) the exact proof of strong phase dependence behaviour, and (\textbf{ii}) the criterion for complementary observables are clarified. Based on these arguments from theoretical aside, some brief discussions and suggestions on experimental measurements are offered in the final discussions. Lastly, we present a pedagogical introduction to angular distribution techniques based on helicity descriptions for both two and three body decays.

hep-ph↗

arXiv2024

Complementary $CP$ violation induced by $T$-odd and $T$-even correlations

In this letter, we propose a novel approach to concurrently measure the complementary $CP$ violation observables induced by $T$-odd correlations and their corresponding $T$-even counterparts, where $T$ represents time reversal. Our analysis demonstrates that $T$-odd and -even correlations, when satisfying specific conditions, result in cosine and sine strong phase dependencies of the corresponding $CP$ violation, respectively. Additionally, we identify pairs of these $CP$ violation observables in hadron decays depend on precisely the same strong phases within the helicity amplitude scheme. This complementarity effectively reduces the strong phase reliance in the study of $CP$ violation, while also mitigating the risk of suppressed $CP$ violation due to exceptionally small strong phases. Furthermore, our proposal holds potential for uncovering $CP$ violation in baryon decays that have not yet been observed in experiments.

hep-ph↗

arXiv2023

Possible large CP violation in charmed $Λ_b$ decays

We propose that the cascade decay $Λ_b \to D(\to K^+π^-) N(\to pπ^-)$ may serve as the discovery channel for baryonic CP violation. This decay chain is contributed by, dominantly, the amplitudes with the intermediate $D$ state as $D^0$ or $\bar{D}^0$. The large weak phase between the two kinds of amplitudes suggests the possibility of significant CP violation. While the presence of undetermined strong phases may complicate the dependence of CP asymmetry, our phenomenological analysis demonstrates that CP violation remains prominent across a broad range of strong phases. The mechanism also applies to similar decay modes such as $Λ_b \rightarrow D(\rightarrow K^+ K^-) Λ$. Considering the anticipated luminosity of LHCb, we conclude that these decay channels offer a promising opportunity to uncover CP violation in the baryon sector.

hep-ph↗

arXiv2023

Super-resolution Reconstruction of Single Image for Latent features

Single-image super-resolution (SISR) typically focuses on restoring various degraded low-resolution (LR) images to a single high-resolution (HR) image. However, during SISR tasks, it is often challenging for models to simultaneously maintain high quality and rapid sampling while preserving diversity in details and texture features. This challenge can lead to issues such as model collapse, lack of rich details and texture features in the reconstructed HR images, and excessive time consumption for model sampling. To address these problems, this paper proposes a Latent Feature-oriented Diffusion Probability Model (LDDPM). First, we designed a conditional encoder capable of effectively encoding LR images, reducing the solution space for model image reconstruction and thereby improving the quality of the reconstructed images. We then employed a normalized flow and multimodal adversarial training, learning from complex multimodal distributions, to model the denoising distribution. Doing so boosts the generative modeling capabilities within a minimal number of sampling steps. Experimental comparisons of our proposed model with existing SISR methods on mainstream datasets demonstrate that our model reconstructs more realistic HR images and achieves better performance on multiple evaluation metrics, providing a fresh perspective for tackling SISR tasks.

eess.IV↗

arXiv2023

CP violation induced by neutral meson mixing interference

We propose a new kind of CP violation effect -- the double-mixing CP asymmetry -- in a type of cascade decays that involves at least two mixing neutral mesons in the decay chain. It is induced by the interference between different oscillation paths of the neutral mesons in the decay process. The double-mixing CP asymmetry is of critical importance for phenomenology, providing opportunities for clean determination of CKM phase angles free of uncertainties induced by the strong dynamics. To illustrate this point, we perform a phenomenological analysis on two examples: $B^0_s \to ρ^0 K \to ρ^0 (π^-\ell^+ν_\ell)$ and $B^0 \to D^0 {K} \to D^0 (π^+\ell^-\barν_\ell)$. Our results demonstrate that the double-mixing CP asymmetry can be numerically significant in the absence of strong phases, as shown by the former example. Additionally, the latter example showcases the direct extraction of weak and strong phases from data, without the need for theoretical inputs.

hep-ph↗

arXiv2023

Diagrammatic analysis of hidden- and open-charm tetraquark production in $B$ decays

Discoveries of tetraquarks not only enrich the hadronic spectrum but also provide more platforms to understand quantum chromodynamics. We study the production processes of hidden-charm and open-charm tetraquarks in $B$ decays by analyzing their topological amplitudes. Relations between different channels are found, which confront tests by experiments to probe the nature of the tetraquarks. Furthermore, promising channels to find more tetraquarks are proposed.

hep-ph↗

arXiv2022

Inclusive weak-annihilation decays and lifetimes of beauty-charmed baryons

Imbalanced beauty-charmed baryons $ Ξ_{bc}^{+,0} $ are of great significance to the development of heavy flavor physics. In this work, we study the inclusive weak-annihilation decays of $Ξ_{bc}^{+,0}$ and their contributions to the $Ξ_{bc}^{+,0}$ lifetimes. For the calculation of the inclusive $Ξ_{bc}^{+,0}\to X_{cs}$ decay width where $X_{cs}$ stands for the sum of the final states with charm number +1 and strange number -1, we work in the heavy diquark effective theory which provides us with a convenient technical tool to construct the operator product expansion. The $Ξ_{bc}^{+,0}$ is considered to be a superposition of two states with one containing a spin-0 $bc$ diquark and the other one containing a spin-1 $bc$ diquark. It is found that both the $Ξ_{bc}^{+,0}$ lifetimes and the $Ξ_{bc}^{+,0}\to X_{cs}$ branching ratios are very sensitive to the $bc$ spin in $Ξ_{bc}^{+,0}$. The $Ξ_{bc}^{+,0}\to X_{cd}$ results are also presented. As $Ξ_{bc}^+$ has a longer lifetime than $Ξ_{bc}^{0}$ and bigger branching ratios of similar decay channels, the exclusive decays $Ξ_{bc}^+\to D^{(*)+}Λ$, $Ξ_{bc}^+\to Λ_c^+\bar{K}^{(*)0}$, $Ξ_{bc}^+\to D^{(*)+}K^-p$, and $Ξ_{bc}^+\to D^{0}\bar{K}^{(*)0}p$ are more promising for experimental searches of $Ξ_{bc}^{+,0}$ at the LHC comparing with exclusive decay $Ξ_{b c} ^{0} \to D^0pK^-$.

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