arXiv subjects

Qin Chang

Publications and source records attributed to Qin Chang.

At least 37 records · Page 2Linked to original sources

arXiv2025

Studying the $B^{0} \to J/ψh_{1}$ decays with $h_{1}(1170)-h_{1}(1415)$ mixing in the perturbative QCD approach

In this paper, we study the $B^{0} \to J/ψh_{1}$ decays for the first time by using perturbative QCD approach up to the presently known next-to-leading order accuracy. The vertex corrections present significant contribution to the amplitude. In the calculation, the mixing between two light axial-vector mesons $h_{1}(1170)$ and $h_{1}(1415)$ are also studied in detail. The observables including the branching ratios, polarization fractions and $CP$ asymmetries are predicted and discussed explicitly. It is found that the $B^{0} \to J/ψh_{1}$ decays have relatively large branching fractions, which are generally at the order of ${\cal O}(10^{-6}\sim10^{-3})$, and thus are possible to be observed by the LHCb and Belle-II experiments in the near future. Moreover, they are very sensitive to the mixing angle $θ$ and can be used to test the values of $θ$. In addition, some ratios between the branching fractions of $B^{0} \to J/ψh_{1}$ decays can provide much stronger constraints on $θ$ due to their relatively small theoretical errors. The $B^{0} \to J/ψh_{1}$ decays are generally dominated by the longitudinal polarization contributions, specifically, $f_{L}(B^{0} \to J/ψh_{1})>80\%$, except for the case that $θ\sim 35^\circ$ and $-55^\circ$. Unfortunately, the direct $CP$ asymmetries of $B^{0} \to J/ψh_{1}$ decays are too small to be observed soon even if the effect of $θ$ is considered. The future precise measurements on $B^{0} \to J/ψh_{1}$ decays are expected for testing these theoretical findings and exploring the interesting nature of $h_{1}(1170)$ and $h_{1}(1415)$.

hep-ph↗

arXiv2025

Next-to-leading order QCD corrections to $B_c^*\to J/ψ$ form factors

Within the framework of Non-Relativistic Quantum Chromodynamics (NRQCD) factorization, we calculate the next-to-leading order (NLO) perturbative QCD corrections to the form factors for the semileptonic decays of $B_c^*$ into $J/ψ$ via (axial-)vector and (axial-)tensor currents. We obtain the complete analytical results for the form factors up to NLO, and provide their asymptotic expressions in the hierarchical heavy quark limit. The NLO corrections are found to be both significant and convergent in the relatively small squared transfer momentum ($q^2$) region, while also reducing the dependence on the renormalization scale $μ$. Finally, the theoretical predictions for $B_c^*\to J/ψ$ form factors over the full $q^2$ range are provided.

hep-ph↗

arXiv2024

Form factors of $Λ_b^0 \to Λ_c(2595)^+$ within light-cone QCD sum rules

In this work, we calculated the form factors of the weak decay process $Λ_b^0 \to Λ_c(2595)^+$, where the final charm baryon represents an excited state with spin-parity $\frac{1}{2}^-$. Utilizing the light-cone QCD sum rules approach, we incorporated the contributions of the lowest two charm baryon states: the ground state $Λ_c$ with $J^P=\frac{1}{2}^+$ and the excited state $Λ_c(2595)^+$ with $J^P=\frac{1}{2}^-$ in the hadronic representation of the $Λ_b \to Λ_c(2595)^+$ transition correlation function. This approach allows us to extract the form factors of the $Λ_b^0 \to Λ_c(2595)^+$ from $Λ_b^0 \to Λ_c^+$ transition. During the light-cone QCD sum rules procedure, we employed the light-cone distribution amplitudes (LCDAs) of the $Λ_b$ baryon. Furthermore, by combining these form factors with the helicity amplitudes of the bottom baryon transition matrix elements, we calculated the differential decay widths for the processes $Λ_b^0 \to Λ_c(2595)^+\ell^-\barν_\ell$ and provided the optimal choice of the interpolating current for $Λ_c$ in this process. Additionally, within the lifetime of $Λ_b^0$, we obtained the absolute branching fractions for the semileptonic decays $Λ_b^0 \to Λ_c(2595)^+ \ell^- \barν_\ell$. With the branching fractions of $Λ_b^0 \to Λ_c(2595)^+ \ell^- \barν_\ell$ calculated in this work, we also determined the parameter $R(Λ_c(2595)^+)$ which tests the lepton flavor universality. This parameter is defined as the ratio of branching fractions $Br(Λ_b^0 \to Λ_c(2595)^+τ^-\barν_τ)$ and $Br(Λ_b^0 \to Λ_c(2595)^+μ^-\barν_μ)$. Our results provide a valuable theoretical test for these decay channels and offer insights into the LCDAs of bottom baryons, paving the way for further in-depth investigations.

hep-ph↗

arXiv2024

The QED nonfactorizable correction to the semileptonic charmed three-body $B$ decays

In this paper, the nonfactorizable photonic corrections to the effective four-fermion vertex for the $\overline{B}$ ${\to}$ $D^{({\ast})}$ $+$ ${\ell}^{-}$ $+$ $\barν_{\ell}$ decays are considered at the quark level within SM, where ${\ell}$ $=$ $e$, $μ$ and $τ$. It is found that the QED corrections are closely related with the mass of the charged lepton. The QED contributions will enhance branching ratios, which results in the slight reduction of ratios $R(D^{(\ast)})$ and the relationship $R(D^{(\ast)})_{e}$ $<$ $R(D^{(\ast)})_μ$.

hep-ph↗

arXiv2024

SKA Sensitivity to Potential Radio Emission from Dark Matter Annihilation in Ursa Major III

The recently discovered stellar system, Ursa Major III/UNIONS 1, may be the faintest and densest dwarf spheroidal satellite galaxy of the Milky Way. Owing to its close proximity and substantial dark matter (DM) component, Ursa Major III emerges as a highly promising target for DM indirect detection. It is known that electrons and positrons originating from DM annihilation can generate a broad radio spectrum through the processes of synchrotron radiation and inverse Compton scattering within galaxies. In this study, we investigate the potential of the Square Kilometre Array (SKA) in detecting radio signatures arising from DM annihilation in Ursa Major III over a 100 hour observation period. Our analysis indicates that the SKA has strong capabilities in detecting these signatures. For instance, the SKA sensitivity to the DM annihilation cross section is estimated to reach $\mathcal{O}(10^{-30})-\mathcal{O}(10^{-28})\; \rm cm^{3} s^{-1}$ in the DM mass range from several GeV to $\sim100$ GeV for the $e^+e^-$ and $μ^+μ^-$ annihilation channels. The precise results are significantly influenced by various astrophysical factors, such as the strength of magnetic field, the diffusion coefficient, and the DM density profile in the dwarf galaxy. We discuss the impact of the uncertainties associated with these factors, and find that the SKA sensitivities have the potential to surpass the current constraints, even when considering these uncertainties.

hep-ph↗

arXiv2024

Study of the $B^{+}\toπ^{+}\left(π^{+}π^{-}\right)$ decay in PQCD Approach

Based on the fitting results of the LHCb collaboration on the contributions of various intermediate resonances to the $B^{+}\toπ^{+}π^{+}π^{-}$ decay, we make systematically calculate the branching fractions and localized $CP$ asymmetries of the quasi-two-body $B^{+}\to π^{+} \left( ρ(770), ω(782), ρ(1450), f_{2}\left(1270\right)\to\right)π^{+}π^{-}$ decays within the perturbative QCD (PQCD) approach. Our theoretical predictions for the branching fractions agree well with the data within the errors. In order to further test the framework of the three-body $B$ decays in PQCD and the wave functions of $ππ$ pair, we also calculate the branching fractions of the corresponding two-body $B^{+}\toπ^{+}ρ(770)$, $B^{+}\toπ^{+}ω(782)$ and $B^{+}\toπ^{+}f_{2}\left(1270\right)$ decays under the narrow-width-approximation, which are in consistence with the experimental data. The direct $CP$ asymmetries of $B^{+}\toπ^{+}(ρ(770/1450)\to) π^{+}π^{-}$ decays are found to be very small because these decay modes are tree-dominated. However, due to the large penguin contributions from the chiral enhanced annihilation diagrams, $B^{+}\toπ^{+} (f_{2}\left(1270\right)\to )π^{+}π^{-}$ decay has a large direct $CP$ asymmetry, which is also discovered by LHCb collaboration. A relatively large $CP$ asymmetry is also expected in the $B^+\toπ^+ (ω\to)π^+π^-$ decay occurring via $ρ-ω$ mixing, which would be measured LHCb and Belle-II experiments in future.

hep-ph↗

arXiv2024

Probing new physics with polarization components of the tau lepton in quasielastic $e^- p \to Λ_c τ^-$ scattering process

Kinematics restrict the ability of rare charm decays to explore the charged Lepton Flavor Violation processes mediated by the quark-level $c\to u \ell τ$ transition. To fill the gap, we propose exploring new physics (NP) through the quasielastic scattering process $e^-p\to τ^-Λ_c$ and the polarization of the $τ$ lepton. As analyzing modes for the $τ$ polarization, we consider the decays $τ^-\to π^-ν_τ$, $τ^-\to ρ^-ν_τ$, and $τ^- \to \ell^-\barν_{\ell}ν_τ$, and show that the $τ$ polarization components can be extracted from analyzing the kinematics of the $τ$ visible decay products. In the framework of a general low-energy effective Lagrangian, we then perform a detailed analysis of the polarization components in various aspects and scrutinize possible NP signals. With one upcoming experimental setup, we finally demonstrate promising event rate can be expected for the cascade process and, even in the worst-case scenario -- no signals is observed at all -- it can still provide a competitive potential for constraining the NP, compared with those from the high-$p_T$ dilepton invariant mass tails at high-energy colliders.

hep-ph↗

arXiv2023

Study of the nonleptonic charmless $B$ ${\to}$ $SS$ decays with the QCD factorization approach

Inspired by the brilliant prospects of the ongoing $B$ meson experiments, the hadronic charmless $B$ ${\to}$ $SS$ decays are studied by considering the next-to-leading (NLO) contributions with the QCD factorization approach, where $S$ denotes the scalar mesons $K_{0}^{\ast}(1430)$ and $a_{0}(1450)$. Branching ratios and $CP$ violating asymmetries are estimated with the updated values of hadronic parameters obtained from a covariant light-front quark model, for two scenarios where the scalar mesons are the $1^{3}P_{0}$ and $2^{3}P_{0}$ states. It is found that the NLO contributions are very important for the $B$ ${\to}$ $SS$ decays; For the $B$ ${\to}$ $a_{0}(1450)K_{0}^{\ast}(1430)$ and $B_{s}$ ${\to}$ $K_{0}^{\ast}(1430)\overline{K}_{0}^{\ast}(1430)$ decays, branching ratios can reach up to the order of ${\cal O}(10^{-5})$ by assuming that the scalar mesons are the $1P$ states, and should first be investigated in the future experiments.

hep-ph↗

arXiv2022

Possibility of experimental study on nonleptonic $B_{c}^{\ast}$ weak decays

The ground vector $B_{c}^{\ast}$ meson has not yet been experimentally discovered until now. Besides the dominant electromagnetic decays, nonleptonic weak decays provide another choice to search for the mysterious $B_{c}^{\ast}$ mesons. Inspired by the potential prospects of $B_{c}^{\ast}$ mesons in future high-luminosity colliders, nonleptonic $B_{c}^{\ast}$ weak decays induced by bottom and charm quark decays are studied within the SM by using a naive factorization approach. It is found that for $B_{c}^{\ast}$ ${\to}$ $B_{s,d}π$, $B_{s,d}^{\ast}π$, $B_{s,d}ρ$, $B_{s}K$, $B_{s}^{\ast}K$, $B_{s}K^{\ast}$, $η_{c}(1S,2S)π$, $η_{c}(1S,2S)ρ$ and $ψ(1S,2S)π$ decays, a few hundred and even thousand of events might be observable in CEPC, FCC-ee and LHCb@HL-LHC experiments.

hep-ph↗

arXiv2022

Feasibility of searching for the Cabibbo-favored $D^{\ast}$ ${\to}$ $\bar{K}π^{+}$, $\bar{K}^{\ast}π^{+}$, $\bar{K}ρ^{+}$ decays

The current knowledge on the $D^{\ast}$ mesons are still inadequate. Encouraged by the positive development prospects of high-luminosity and high-precision experiments, the Cabibbo-favored nonleptonic $D^{\ast}$ ${\to}$ $\bar{K}π^{+}$, $\bar{K}^{\ast}π^{+}$, $\bar{K}ρ^{+}$ weak decays are studied with the naive factorization approach. It is found that branching ratios of these processes can reach up to ${\cal O}(10^{-10})$ or more, and can be accessible at STCF, CEPC, FCC-ee and LHCb@HL-LHC experiments in the future. It might even be possible to search for the $D^{{\ast}0}$ ${\to}$ $K^{{\ast}-}π^{+}$ and $K^{-}ρ^{+}$ decays at the running SuperKEKB experiments.

hep-ph↗

arXiv2022

Form factors of $P\to T$ transition within the light-front quark models

In this paper, we calculate the vector, axial-vector and tensor form factors of $P\to T$ transition within the standard light-front~(SLF) and covariant light-front~(CLF) quark models~(QMs). The self-consistency and Lorentz covariance of CLF QM with two types of correspondence schemes are investigated. The zero-mode effects and the spurious $ω$-dependent contributions to the form factors of $P\to T$ transition are analyzed. Employing a self-consistent CLF QM, we present our numerical predictions for the vector, axial-vector and tensor form factors of $c\to (q,s)$~($q=u,d$) induced $D \to (a_2,K^*_2)$, $D_s \to (K^*_2,f'_{2})$, $η_c(1S) \to (D^*_2,D^*_{s2})$, $ B_c \to (B^*_2,B^*_{s2})$ transitions and $b\to (q,s,c)$ induced $B \to (a_2,K^*_2,D^*_2)$, $B_s \to (K^*_2,f'_2,D^*_{s2})$, $B_c \to (D^*_2,D^*_{s2},χ_{c2}(1P))$, $η_b(1S) \to (B^*_2,B^*_{s2})$ transitions. Finally, in order to test the obtained form factors, the semileptonic $B\to \bar{D}_2^*(2460)\ell^+ν_\ell$~($\ell=e,μ$) and $\bar{D}_2^*(2460)τ^+ν_τ$ decays are studied. It is expected that our results for the form factors of $P\to T$ transition can be applied further to the relevant phenomenological studies of meson decays.

hep-ph↗

arXiv2022

An Adaptive Neuro-Fuzzy System with Integrated Feature Selection and Rule Extraction for High-Dimensional Classification Problems

A major limitation of fuzzy or neuro-fuzzy systems is their failure to deal with high-dimensional datasets. This happens primarily due to the use of T-norm, particularly, product or minimum (or a softer version of it). Thus, there are hardly any work dealing with datasets with dimensions more than hundred or so. Here, we propose a neuro-fuzzy framework that can handle datasets with dimensions even more than 7000! In this context, we propose an adaptive softmin (Ada-softmin) which effectively overcomes the drawbacks of ``numeric underflow" and ``fake minimum" that arise for existing fuzzy systems while dealing with high-dimensional problems. We call it an Adaptive Takagi-Sugeno-Kang (AdaTSK) fuzzy system. We then equip the AdaTSK system to perform feature selection and rule extraction in an integrated manner. In this context, a novel gate function is introduced and embedded only in the consequent parts, which can determine the useful features and rules, in two successive phases of learning. Unlike conventional fuzzy rule bases, we design an enhanced fuzzy rule base (En-FRB), which maintains adequate rules but does not grow the number of rules exponentially with dimension that typically happens for fuzzy neural networks. The integrated Feature Selection and Rule Extraction AdaTSK (FSRE-AdaTSK) system consists of three sequential phases: (i) feature selection, (ii) rule extraction, and (iii) fine tuning. The effectiveness of the FSRE-AdaTSK is demonstrated on 19 datasets of which five are in more than 2000 dimension including two with dimension greater than 7000. This may be the first time fuzzy systems are realized for classification involving more than 7000 input features.

cs.LG↗

arXiv2021

Study of $ B_{u,d,s} \to K_0^(1430) P $ and $K_0^(1430) V$ decays within QCD factorization

We study the nonleptonic charmless $B_{u,d,s} \to K_0^*(1430)P$ $(P=K\,, π)$ and $ K_0^*(1430)V$ $ (V=K^*\,, ρ\,, ω\,, ϕ)$ decays. The amplitudes are calculated within the QCD factorization, and the non-perturbative quantities are evaluated by using a covariant light-front approach. The branching fractions and CP asymmetries of theses decay modes are calculated, some decay modes are first predicted, and some useful relations based on $SU(3)$ flavor symmetry are discussed. Comparing the theoretical results with the current available experimental data, it is found that $K_0^*(1430)$ can be described as the lowest-lying p-wave $(s,u/d)$ state rather than the first excited one.

hep-ph↗

arXiv2020

Tensor form factors of $P\to P,\,S,\,V$ and $A$ transitions within the standard and the covariant light-front approaches

In this paper, we investigate the tensor form factors of $P\to P,\,S,\,V$ and $A$ transitions within the standard light-front (SLF) and the covariant light-front (CLF) quark models (QMs). The self-consistency and Lorentz covariance of CLF QM are analyzed via these quantities, and the effects of zero-mode are discussed. For the $P\to V$ and $A$ transitions, besides the inconsistence between the results extracted via longitudinal and transverse polarization states, which is caused by the residual $ω$-dependent spurious contributions, we find and analyze a "new" self-consistence problem of the traditional CLF QM, which is caused by the different strategies for dealing deal with the trace term in CLF matrix element. A possible solution to the problems of traditional CLF QM is discussed and confirmed numerically. Finally, the theoretical predictions for the tensor form factors of some $c\to q,\,s$ and $b\to q,\,s\,,c$ ($q=u,d$) induced $P\to P,\,S,\,V$ and $A$ transitions are updated within the CLF QM with a self-consistent scheme.

hep-ph↗

arXiv2020

Study of $b\to c$ induced $\bar{B}^* \to V \ell \barν_\ell$ decays

In this paper, we investigate the tree-dominated $\bar{B}^*_{u,d,s,c} \to V \ell^- \barν_\ell$ ($V=D^*_{u,d}\,,D^*_s\,,J/ψ$ and $\ell=e\,,μ\,,τ$) decays in the Standard Model with the relevant form factors obtained in the light-front quark model. These decays involve much more helicity states relative to the corresponding $\bar{B}^* \to P \ell^- \barν_\ell$ and $\bar{B} \to V \ell^- \barν_\ell$ decays, and moreover, the contribution of longitudinal polarization mode ($V$ meson) is relatively small, $\sim 30\%$, compared with the corresponding $B$ meson decays. We have also computed the branching fraction, lepton spin asymmetry, forward-backward asymmetry and ratio $R_V^{\ast(L)}\equiv \frac{\mathcal{B}(\bar{B}^*\to Vτ^- \barν_τ)}{\mathcal{B}(\bar{B}^*\to V \ell^{\prime-} \barν_{\ell^{\prime}})}$ ($\ell'=e\,,μ$). Numerically, the branching fractions of $\bar{B}^* \to V \ell^{\prime-} \barν_{\ell^{\prime}}$ decays are at the level of ${\cal O}(10^{-7})$, and are hopeful to be observed by LHC and Belle-II experiments. The ratios $R_{D^*\,,D^*_s\,,J/ψ}^{\ast(L)}$ have relatively small theoretical uncertainties and are close to each other, $R^{*(L)}_{D^*}\simeq R^{*(L)}_{D^*_s}\simeq R^{*(L)}_{J/ψ} \simeq [0.26,0.27]~([0.27,0.29])$, which are a bit different from the predictions in some previous works. The future measurements are expected to make tests on these predictions.

hep-ph↗

arXiv2019

Contributions from $Φ_{B2}$ to the $B$ ${\to}$ $PP$ decays within the QCD factorization

With the potential for the improvements of measurement precision,the refinement of theoretical calculation on hadronic $B$ weak decays is necessary. In this paper, we study the contributions of $B$ mesonic distribution amplitude $Φ_{B2}$ within the QCD factorization approach, and find that $Φ_{B2}$ contributes to only the nonfactorizable annihilation amplitudes for the $B$ ${\to}$ $PP$ decays ($P$ denotes the ground $SU(3)$ pseudoscalar mesons). Although small, the $Φ_{B2}$ contributions might be helpful for improving the performance of the QCD factorization approach, especially for the pure annihilation $B_{d}$ ${\to}$ $K^{+}K^{-}$ and $B_{s}$ ${\to}$ $π^{+}π^{-}$ decays.

hep-ph↗

arXiv2019

Form factors of $V'\to V''$ transition within the light-front quark models

In this paper, we calculate the matrix element and form factors of vector-to-vector ($V'\to V'$) transition within the standard light-front~(SLF) and covariant light-front~(CLF) quark models~(QMs), and investigate the self-consistency and Lorentz covariance of the CLF QM within two types of correspondences between the manifest covariant Bethe-Salpeter approach and the LF approach. The zero-mode and valence contributions to the form factors of $V'\to V'$ transition in the CLF QM and their relation to the SLF results are analyzed, and the main conclusions obtained via the decay constants of vector and axial-vector mesons and form factors of $P\to V$ transition in the previous works are confirmed again. Furthermore, we present our numerical predictions for the form factors of $c\to (q,s)$ ($q=u,d$) induced $D^*\to (K^*\,,ρ)$, $D^*_s\to (ϕ\,,K^*)$, $J/Ψ\to (D^*_s\,,D^*)$, $B^*_c\to (B^*_s\,,B^*)$ transitions and $b\to (q,s,c)$ induced $B^*\to (D^*\,,K^*\,,ρ)$, $B^*_s\to (D^*_s\,,ϕ\,,K^*)$, $B^*_c\to (J/Ψ\,,D^*_s\,,D^*)$, $Υ(1S)\to (B_c^*\,,B_s^*\,,B^*)$ transitions, which can be applied further to the relevant phenomenological studies of meson decays.

hep-ph↗

arXiv2019

Study of $\bar{B}_{u,d,s}^* \to D_{u,d,s}^* V\,(V=D_{d,s}^{-}\,,K^{-}\,,ρ^-)$ weak decays

Motivated by the rapid development of heavy flavor physics experiment, we study the tree-dominated nonleptonic $\bar{B}_{u,d,s}^* \to D_{u,d,s}^*V$~($V=D^{*-},D_s^{*-},K^{*-},ρ^-$) decays within the factorization approach. The relevant transition form factors are calculated by employing the covariant light-front quark model. The helicity amplitudes are calculated and analyzed in detail, and a very clear hierarchy structure $ |H_{-0}| \approx 2|H_{00}| > |H_{0-}|\approx|H_{--}|>|H_{0+}|\approx|H_{++}|$ is presented. The branching fractions are computed and discussed. Numerically, the CKM-favored $\bar{B}^*_q\to D^*_q ρ^{-}$ and $D^*_q D_s^{*-}$ decays have relatively large branching fractions, $\gtrsim {\cal O}(10^{-8})$, and are hopeful to be observed by LHC and Belle-II experiments in the future.

hep-ph↗