arXiv subjects

Yan-Jun Sun

Publications and source records attributed to Yan-Jun Sun.

8 recordsLinked to original sources

arXiv2022

Family Non-universal $Z^\prime$ Effects on $B_{d,s} \to K^{0} {\overline K^{0}}$ Decays in Perturbative QCD Approach

The nonleptonic decays $B_{d,s} \to K^{*0} {\overline K^{*0}}$ are reanalyzed in perturbative QCD approach, which is based on the $k_{\rm T}$ factorization. In the standard model, the calculated branching fraction and longitudinal polarization fraction of $B_{d} \to K^{*0} {\overline K^{*0}}$ are in agreement with experimental measurements, while the predictions of $B_{s} \to K^{*0} {\overline K^{*0}}$ cannot agree with data simultaneously. The parameter that combines of longitudinal polarization fractions and branching fractions evaluated to be $L_{K^*\overline{K}^{*0}}^{\rm PQCD}= 12.7^{+5.6} _{-3.2}$, which is also larger than that abstracted from experimental measurements. We then study all observables by introducing a family non-universal $Z^{\prime}$ boson in $b\to s q\bar q$ transitions. In order to reduce the number of new parameters, we simplify the model as possible. It is found that with the fixed value $\omega_{B_s}=0.55$, these exists parameter space where all measurements, including the branching fraction, longitudinal polarization fraction and $L_{K^*\overline{K}^{*0}}$-parameter, could be accommodated simultaneously. All our results and the small parameter space could be further tested in the running LHC experiments, Belle-II and future high-energy colliders.

hep-ph↗

arXiv2021

Study of form factors and branching ratios for $D\rightarrow S,Al\bar{\nu_{l}}$ with light-cone sum rules

We systematically study the semileptonic decay process of $ D\rightarrow S,A l\bar{\nu_{l}}(l=e,\mu)$ by light-cone sum rules (LCSR) with chiral currents, calculate the form factors containing only the contribution of the leading twist light-cone distribution amplitudes (LCDAs). For scalar mesons $a_{0}(980)$ and $a_{0}(1450)$, we take them as $q\bar{q}$ states. For axial-vector meson, we study $a_{1}(1260)( 1^{3}p^{1})$ and $b_{1}(1235)( 1^{1}p^{1})$. Based on the results of these form factors, we further present the branching ratios of these semileptonic decay processes. The numerical results for $ D\rightarrow a_{0}(980), b_{1}(1235)l\bar{\nu_{l}} $ are in good agreement with experiments and that for $ D\rightarrow a_{0}(1450)l\bar{\nu_{l}}$ process are expected to be tested experimentally in the future.

hep-ph↗

arXiv2020

Masses of doubly heavy tetraquarks $QQ\bar{n}\bar{q}$ with $J^{P}=1^{+}$

We apply the method of QCD sum rules to study the doubly heavy tetraquark states $QQ\bar{q}\bar{n}$ with spin-parity $J^{P}=1^{+}$ and strangeness $S=0, -1$ using careful estimates of the Borel and threshold parameters involved. Masses of the doubly bottom and charmed tetraquarks with isospin $I=0,1/2, 1$ are computed precisely via taking into account multifarious condensates up to dimension $10$. Comparing with the two-heavy meson thresholds, we find that all nonstrange doubly-bottom tetraquarks and a doubly-charmed tetraquarks associted with $J_{3}$ with $J^{P}=1^{+}$ are stable against strong decay into two bottom mesons while a doubly-charmed tetraquarks associated with current $J_{2}$ is unstable against strong decay. By the way, weak decay widths of the doubly bottom tetraquarks are also given.

hep-ph↗

arXiv2019

Study of the radiative decay $J/\psi\rightarrow\eta_{c}+\gamma$ in light cone sum rules

At present, there are many experimental and theoretical results for $J/\psi\rightarrow\eta_{c}+\gamma$ process, while the results are inconsistent based on different methods and considerations. In this paper, the light cone sum rules method is used in studying the radiative decay $J/\psi\rightarrow\eta_{c}+\gamma$. We give the transition form factor of this process based on the leading twist distribution amplitude of $\eta_{c}$ meson, with this form factor further obtain the decay width. Our result is consistent with those of other sum rules. A comparison of our result with others' about the decay width is also presented.

hep-ph↗

arXiv2019

The Excited Charmonium Production in $e^{+}e^{-}$ Annihilation

We calculate the form factor and cross section of the excited charmonium production process $e^{+}+e^{-}\rightarrow ψ\left ( 2S \right )+η_{c}$ by light-cone sum rules. In our method, the form factor depends on the distribution amplitude of $η_{c}$ meson. Experimentally, the energy scale of $e^{+}+e^{-}\rightarrow ψ\left ( 2S \right )+η_{c}$ process is much larger than the initial energy scale of $η_{c}$ meson in our BHL model. Therefore, we further consider the evolution of the distribution amplitude with the energy scale, and select the distribution amplitude as our input parameter when the final effective energy scale is $μ=5.00\ GeV$. This treatment means that we have chosen the relativistic distribution amplitude. The results show that the relativistic effect contributes greatly to the form factor and cross section. Our results are consistent with Belle experimental data.

hep-ph↗

arXiv2011

$B \to A$ transitions in the light-cone QCD sum rules with the chiral current

In this article, we calculate the form-factors of the transitions $B \to a_1(1260)$, $b_1(1235) $ in the leading-order approximation using the light-cone QCD sum rules. In calculations, we choose the chiral current to interpolate the $B$-meson, which has outstanding advantage that the twist-3 light-cone distribution amplitudes of the axial-vector mesons have no contributions, and the resulting sum rules for the form-factors suffer from much less uncertainties. Then we study the semi-leptonic decays $B \to a_1(1260) l\barν_l$, $b_1(1235) l\barν_l$ $(l=e,μ,τ)$, and make predictions for the differential decay widths and decay widths, which can be confronted with the experimental data in the coming future.

hep-ph↗

arXiv2011

$B_{(s)}\to S$ transitions in the light cone sum rules with the chiral current

$B_{(s)}$ semi-leptonic decays to the light scalar meson, $B_{(s)}\to S l\barν_l, S l \bar{l}\,\,(l=e,μ,τ)$, are investigated in the QCD light-cone sum rules (LCSR) with chiral current correlator. Having little knowledge of ingredients of the scalar mesons, we confine ourself to the two quark picture for them and work with the two possible Scenarios. The resulting sum rules for the form factors receive no contributions from the twist-3 distribution amplitudes (DA's), in comparison with the calculation of the conventional LCSR approach where the twist-3 parts play usually an important role. We specify the range of the squared momentum transfer $q^2$, in which the operator product expansion (OPE) for the correlators remains valid approximately. It is found that the form factors satisfy a relation consistent with the prediction of soft collinear effective theory (SCET). In the effective range we investigate behaviors of the form factors and differential decay widthes and compare our calculations with the observations from other approaches. The present findings can be beneficial to experimentally identify physical properties of the scalar mesons.

hep-ph↗

arXiv2011

The cross section of the process $e^{+}+e^{-}\to J/ψ+η_c$ within the QCD light-cone sum rules

We calculate the cross section of the exclusive process $e^{+} +e^{-}\to J/ψ+η_c$ at the leading order approximation within the QCD light-cone sum rules (LCSR) approach. It is found that the form factor $F_{VP}(V=J/ψ,P=η_c)$ depends mainly on the behavior of the twist-2 distribution amplitude of the $η_c$-meson at the scale of this process. Thus in order to obtain a reliable estimation of the cross section, it is important to have a realistic distribution amplitude of the $η_c$ meson, and to deal with the evolution of the distribution amplitude to the effective energy scale of the process. Our results show that one can obtain a compatible prediction with the Belle and BarBar experimental data.

hep-ph↗