arXiv subjects

Zhan Sun

Publications and source records attributed to Zhan Sun.

At least 19 recordsLinked to original sources

arXiv2026

Inclusive productions of $J/\psi+\eta_c$ in $e^{+}e^{-}$ annihilation at Belle

We study $e^{+}e^{-} \to J/\psi+\eta_c+X$ at next-to-leading order (NLO) in $\alpha_s$ within the nonrelativistic QCD (NRQCD) framework to assess the color-octet (CO) mechanism at low energies. QCD corrections significantly enhance both color-singlet (CS) and CO leading-order results, with non-negligible QED-diagram contributions to the CS channel. At $\Upsilon(4S)$, CO terms increase the inclusive cross section by $20\%$--$30\%$, and the enhancement grows rapidly with $\sqrt{s}$, yielding an energy dependence distinct from CS predictions and providing a sensitive test of NRQCD. Including $\psi(2S)$ feed-down further amplifies the NRQCD prediction by about $40\%$ at $\Upsilon(4S)$. With Belle's reconstruction of $J/\psi \to \mu^+\mu^-$ and six $\eta_c$ decay channels, the process shows promising potential for observation.

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arXiv2025

Next-to-leading order analysis of $J/\psi + \gamma$ production in photon-photon collisions at CEPC

We systematically investigate the production of $J/\psi + \gamma$ in $\gamma\gamma$ collisions within nonrelativistic QCD (NRQCD) factorization, with the direct-photon channel calculated specifically up to the next-to-leading order in $\alpha_s$. Calculations for CEPC energy region show the resolved photon contribution is negligible, while the direct photon process dominates, yielding substantial annual $J/\psi$ yields. Significant modifications to $J/\psi$ polarization parameters emerge from color-octet mechanisms, and different NRQCD long distance matrix elements (LDMEs) further yield distinct polarization patterns. Furthermore, the polarization predictions are highly sensitive to the $^3P_J^{[8]}$ LDME, while being insensitive to the $^1S_0^{[8]}$ and $^3S_1^{[8]}$ LDMEs. Leveraging the cleaner environment of $e^+e^-$ collisions versus hadronic processes, the production of $J/\psi$ associated with a photon in $\gamma\gamma$ collisions provides a high-precision platform to test LDMEs universality and resolve longstanding $J/\psi$ polarization puzzles.

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arXiv2024

Studies of $Z$ boson decay into double $\Upsilon$ mesons at the NLO QCD accuracy

In this paper, we employ the nonrelativistic QCD factorization to conduct a comprehensive examination of the $Z$ boson decay into a pair of $\Upsilon$ mesons, achieving accuracy at the next-to-leading-order (NLO) in $\alpha_s$. Our calculations demonstrate that the QED diagrams are indispensable in comparison to the pure QCD diagrams, and the implementation of QCD corrections markedly enhance the QCD results, whereas it substantially diminish the QED results. To ensure consistency with the experimental methodology, we have taken into account the feed-down transitions originating from higher excited states, which exhibit significant relevance. Combining all the contributions, we arrive at the NLO prediction of $\mathcal{B}_{Z \to \Upsilon(nS)+\Upsilon(mS)} \sim 10^{-11}$, which is notably lower than the upper limits set by CMS.

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arXiv2023

Analysis of double-$J/\psi$ production in $Z$ decay at next-to-leading-order QCD accuracy

In this article, we study in detail the double-$J/\psi$ yield through $Z$ decay at the next-to-leading-order (NLO) QCD accuracy within the nonrelativistic QCD factorization. At the tree level, the pure QCD diagrams predict a branching ratio of $\mathcal{B}_{Z \to J/\psi+J/\psi} \sim 10^{-12}$; however, the inclusion of the QED diagrams would augment this prediction by approximately 2-3 orders of magnitude. After incorporating the QCD corrections, the QCD results exhibit a considerable increase, whereas the QED results undergo a substantial reduction. Combining the QCD and QED contributions at NLO in $\alpha_s$, it is observed that the prediction of $\mathcal{B}_{Z \to J/\psi+J/\psi}=(1.110^{+0.334+0.054}_{-0.241-0.001})\times 10^{-10}$, which displays a fairly steady dependence on the renormalization scale, is significantly lower than the upper limits released by CMS.

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arXiv2022

$X(3860)$ production in association with $J/\psi$ via $e^{+}e^{-}$ annihilation at Belle

In this paper, we study the $X(3860)$ production associated with $J/\psi$ via $e^{+}e^{-}$ annihilation at the next-to-leading-order (NLO) QCD accuracy, within the nonrelativistic QCD (NRQCD) framework. Under the hypothesis of $J^{PC}_{X(3860)}=0^{++}$, the predicted total cross sections agree well with the Belle's measurements at $\sqrt{s}=\Upsilon(4S,5S)$, while the theoretical results given by the $2^{++}$ hypothesis significantly undershoot the data. This is consistent with the Belle's conclusion that the $0^{++}$ hypothesis is favored over the $2^{++}$ hypothesis for $X(3860)$. Despite the agreement of the total cross sections, the NRQCD predictions seem to be incompatible with the Belle-measured $J/\psi$ angular distributions. We also perform the NLO calculations of $\sigma_{e^{+}e^{-} \to J/\psi+X(3940)}$ on the assumption of $J^{PC}_{X(3940)}=0^{-+}$, discovering that the NRQCD predictions that coincide with the light-cone results are in good agreement with the experiment.

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arXiv2022

Doubly-charmed baryon production in $Z$ boson decay

In this paper, we carry out a detailed study of doubly-charmed baryon production in $Z$ boson decay, on the basis of the nonrelativistic QCD factorization. With the inclusion of the di-quark states $(cc)[^3S_1]_{\bar{\textbf{3}}}$ and $(cc)[^1S_0]_{{\textbf{6}}}$, the branching ratio of $\mathcal{B}_{Z \to \Xi_{cc}+X}$ is predicted to be of the $10^{-5}$ order, indicating its experimental measurability. By comparing to the $\Lambda^{+}_{c}$ yield in $Z$ decay, we predict $\mathcal{R}_{\Xi_{cc}^{+}}(=\frac{\Gamma(Z \to \Xi^{+}_{cc}) \times \mathcal{B}(\Xi^{+}_{cc} \to \Lambda_c^{+}K^{-}\pi^{+})}{\Gamma(Z \to \Lambda_c^{+})})=(0.85^{+0.10}_{-0.07}) \times 10^{-4}$ and $\mathcal{R}_{\Xi_{cc}^{++}}(=\frac{\Gamma(Z \to \Xi^{++}_{cc}) \times \mathcal{B}(\Xi^{++}_{cc} \to \Lambda_c^{+}K^{-}\pi^{+}\pi^{+})}{\Gamma(Z \to \Lambda_c^{+})})=(1.70^{+0.20}_{-0.14}) \times 10^{-4}$, which are at clear variance with the SELEX measurements but comparable with the values given by the LHCb and Belle collaborations.

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arXiv2022

A Survey of Video-based Action Quality Assessment

Human action recognition and analysis have great demand and important application significance in video surveillance, video retrieval, and human-computer interaction. The task of human action quality evaluation requires the intelligent system to automatically and objectively evaluate the action completed by the human. The action quality assessment model can reduce the human and material resources spent in action evaluation and reduce subjectivity. In this paper, we provide a comprehensive survey of existing papers on video-based action quality assessment. Different from human action recognition, the application scenario of action quality assessment is relatively narrow. Most of the existing work focuses on sports and medical care. We first introduce the definition and challenges of human action quality assessment. Then we present the existing datasets and evaluation metrics. In addition, we summarized the methods of sports and medical care according to the model categories and publishing institutions according to the characteristics of the two fields. At the end, combined with recent work, the promising development direction in action quality assessment is discussed.

cs.CV↗

arXiv2021

Impact of $Z \to \eta_{c,b}+g+g$ on the inclusive $\eta_{c,b}$ meson yield in $Z$-boson decay

In this paper, we carry out the next-to-leading-order QCD corrections to $Z \to \eta_Q+g+g~(Q=c,b)$ (labeled as $gg$) through the color-singlet (CS) state of $Q\bar{Q}[^1S_0^{[1]}]$, with the aim of assessing the impact of this process on $Z$ bosons decaying into inclusive $\eta_Q$. We find that the QCD corrections to the $gg$ process can notably enhance its leading-order results, especially for the $\eta_c$ case, which would then greatly increase the existing predictions of $\Gamma_{Z \to \eta_Q+X}$ given by the CS-dominant process $Z \to \eta_{Q}[^1S_0^{[1]}]+Q+\bar{Q}$. Moreover, with these significant QCD corrections, the $gg$ process would exert crucial influence on the CS-predicted $\eta_Q$ energy distributions. In conclusion, in the CS studies of $Z \to \eta_Q+X$, besides $Z \to \eta_{Q}[^1S_0^{[1]}]+Q+\bar{Q}$, $Z \to \eta_Q[^1S_0^{[1]}]+g+g$ can provide phenomenologically indispensable contributions as well.

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arXiv2021

Next-to-leading-order study of $J/\psi$ angular distributions in $e^{+}e^{-} \to J/\psi+\eta_c,\chi_{cJ}$ at $\sqrt{s} \approx 10.6$ GeV

In this paper, we present a detailed next-to-leading-order (NLO) study of $J/\psi$ angular distributions in $e^{+}e^{-} \to J/\psi+\eta_c,\chi_{cJ}$ ($J=0,1,2$) within the nonrelativistic QCD factorization (NRQCD). The numerical NLO expressions for total and differential cross sections, i.e., $\frac{d\sigma}{d\cos\theta}=A+B\cos^2\theta$, are both derived. With the inclusion of the newly-calculated QCD corrections to $A$ and $B$, the $\alpha_{\theta}(= B/A)$ parameters in $J/\psi+\chi_{c0}$ and $J/\psi+\chi_{c1}$ are moderately enhanced, while the magnitude of ${\alpha_\theta}_{J/\psi+\chi_{c2}}$ is significantly reduced; regarding the production of $J/\psi+\eta_c$, the $\alpha_\theta$ value remains unchanged. By comparing with experiment, we find the predicted ${\alpha_\theta}_{J/\psi+\eta_c}$ is in good agreement with the $\textrm{B}\scriptsize{\textrm{ELLE}}$ measurement; however, ${\alpha_\theta}_{J/\psi+\chi_{c0}}$ is still totally incompatible with the experimental result, and this discrepancy seems to hardly be cured by proper choices of the charm-quark mass, the renormalization scale, and the NRQCD matrix elements.

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arXiv2021

Comprehensive studies of $\Upsilon$ inclusive production in $Z$ boson decay

In this paper, we present a comprehensive study of $\Upsilon$ inclusive production in $Z$ boson decay, including the first complete next-to-leading-order calculations of the color-octet (CO) contributions. With the inclusion of the newly-calculated remarkable QCD corrections, the CO processes exhibit crucially phenomenological influence on the existing predictions built on the color-singlet mechanism. We also include the exhaustive evaluations of the feed-down contributions, which remained ignored in the literature, and find them to be considerable. Summing up all the contributions, the $\mathcal{B}_{Z \to \Upsilon(nS)+X}$ still notably undershoot the data released by the L3 Collaboration.

hep-ph↗

arXiv2020

$\Upsilon$ electroproduction at HERA, EIC, and LHeC within the nonrelativistic QCD framework

Based on the nonrelativistic QCD framework, we study the $\Upsilon$ production in semi-inclusive deep inelastic electron-proton scattering (SIDIS) at HERA, EIC, and LHeC, with the main aim of assessing the viability of observing $\Upsilon$ electroproduction at the three colliders. The color-octet (CO) contributions are found to have a crucial effect on both the integrated and differential cross sections, serving to further establish the significance of the CO mechanism. By setting the kinematic cuts to $p_{t,\Upsilon}^{\star 2}>1~\textrm{GeV}^{2}$, $W>50$ GeV, $2<Q^2<100~\textrm{GeV}^2$, and $0.3<z<0.9$, only a few electroproduced $\Upsilon$ events can be generated at HERA, partially accounting for its lack of measured $\Upsilon$ electroproduction. However, under the same cut conditions, the EIC and LHeC can accumulate about $8.7\times10^{2}$ and $3.7\times10^{4}$ reconstructed $\Upsilon$ events in one operation year, respectively, which manifestly indicates the prospect of detecting the $\Upsilon$-related SIDIS processes at the two forthcoming $ep(eA)$ colliders.

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arXiv2020

The production of the doubly charmed baryon in deeply inelastic $ep$ scattering at the Large Hadron Electron Collider

In this paper, we carry out a detailed study on the production of the doubly charmed baryon in deeply inelastic $ep$ scattering (DIS) for $Q^2\in[2, 100]~\textrm{GeV}^2$, at the Large Hadron Electron Collider (LHeC) with $E_e=60(140)$ GeV and $E_p=7000$ GeV. To exclude the contributions from the diffractive productions and the $b$ hadron decays, we impose the kinematic cuts $0.3 1~\textrm{GeV}^2$ in the center-of-mass (CM) frame of $\gamma^{*}p$. Based on the designed LHeC luminosity, by detecting the decay channel $\Xi^{+}_{cc}(\Xi^{++}_{cc}) \to \Lambda_c^{+}$ with the subsequent decay $\Lambda_c^{+} \to pK^{-}\pi^{+}$, we predict that about 1880 (2700) $\Xi^{+}_{cc}$ events and 3750 (5400) $\Xi^{++}_{cc}$ events can be accumulated per year, which signifies the prospect of observing them via the DIS at the forthcoming LHeC. In addition, we also predict the distributions of a rich variety of physical observables in the laboratory frame and the $\gamma^{*}p$ CM frame, including $Q^2$, $p_t^{2}$, $Y$(rapidity), $p_t^{\star2}$, $Y^{\star}$, $W$, and $z$ distributions, respectively, which can provide helpful references for studying the doubly charmed baryon. In conclusion, we think that in addition to the LHC, the LHeC is also a helpful platform for studying the properties of the doubly charmed baryon.

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arXiv2020

The studies on $Z \to \Upsilon(1S)+g+g$ at the next-to-leading-order QCD accuracy

In this paper, we carry out the next-to-leading-order (NLO) studies on $Z \to \Upsilon(1S)+g+g$ via the color-singlet (CS) $b\bar{b}$ state. We find the newly calculated NLO QCD corrections to this process can significantly influence its leading-order (LO) results, and greatly improve the dependence on the renormalization scale. By including the considerable feeddown contributions, the branching ratio $\mathcal{B}_{Z \to \Upsilon(1S)+g+g}$ is predicted to be $(0.56 \sim 0.95)\times 10^{-6}$, which can reach up to $19\% \sim 31\%$ of the LO predictions given by the CS dominant process $Z \to \Upsilon(1S)+b+\bar{b}$. Moreover, $Z \to \Upsilon(1S)+g+g$ also seriously affect the CS predictions on the $\Upsilon(1S)$ energy distributions, especially when $z$ is relatively small. In summary, for the inclusive $\Upsilon(1S)$ productions in $Z$ decay, besides $Z \to \Upsilon(1S)+b+\bar{b}$, the gluon radiation process $Z \to \Upsilon(1S)+g+g$ can provide indispensable contributions as well.

hep-ph↗

arXiv2019

Inclusive productions of $\Upsilon(1S,2S,3S)$ and $\chi_b(1P,2P,3P)$ via the Higgs boson decay

In this paper, we carry out the complete $\mathcal O(\alpha\alpha_s^{2})$-order study on the inclusive productions of $\Upsilon(nS)$ and $\chi_b(nP)$ ($n=1,2,3$) via the Standard Model Higgs boson decay, within the framework of nonrelativistic QCD. The feeddown effects via the higher excited states are found to be substantial. The color-octet $^3S_1^{[8]}$ state related processes consisting of $H^0 \to b\bar{b}[^3S_1^{[8]}]+g$ and $H^0 \to b\bar{b}[^3S_1^{[8]}]+Q+\bar{Q}$ ($Q=c,b$) play a vital role in the predictions on the decay widths. Moreover, our newly calculated next-to-leading order QCD corrections to $H^0 \to b\bar{b}[^3S_1^{[8]}]+g$ can enhance its leading-order result by 3-4 times, subsequently magnifying the total $^3S_1^{[8]}$ contributions by about $40\%$. Such a remarkable enhancement will to a large extent influence the phenomenological conclusions. For the color-singlet $^3P_J^{[1]}$ state, in addition to $H^{0} \to b\bar{b}[^3P_J^{[1]}]+b+\bar{b}$, the newly introduced light hadrons associated process, $H^{0} \to b\bar{b}[^3P_J^{[1]}]+g+g$, can also provide non-negligible contributions, especially for $^3P_2^{[1]}$. Summing up all the contributions, we have $\mathcal B_{H^0 \to \chi_b(nP)+X} \sim 10^{-6}-10^{-5}$ and $\mathcal B_{H^0 \to \Upsilon(nS)+X} \sim 10^{-5}-10^{-4}$, which meets marginally nowadays LHC experimental data and can help in understanding the heavy quarkonium production mechanism as well as the Yukawa couplings.

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arXiv2018

Further studies on the exclusive productions of $J/\psi+\chi_{cJ}$ ($J=0,1,2$) via $e^+e^-$ annihilation at the $B$ factories

By including the interference effect between the QCD and the QED diagrams, we carry out a complete analysis on the exclusive productions of $e^+e^- \to J/\psi+\chi_{cJ}$ ($J=0,1,2$) at the $B$ factories with $\sqrt{s}=10.6$ GeV at the next-to-leading-order (NLO) level in $\alpha_s$, within the nonrelativistic QCD framework. It is found that the $\mathcal O (\alpha^3\alpha_s)$-order terms that represent the tree-level interference are comparable with the usual NLO QCD corrections, especially for the $\chi_{c1}$ and $\chi_{c2}$ cases. To explore the effect of the higher-order terms, namely $\mathcal O (\alpha^3\alpha_s^2)$, we perform the QCD corrections to these $\mathcal O (\alpha^3\alpha_s)$-order terms for the first time, which are found to be able to significantly influence the $\mathcal O (\alpha^3\alpha_s)$-order results. In particular, in the case of $\chi_{c1}$ and $\chi_{c2}$, the newly calculated $\mathcal O (\alpha^3\alpha_s^2)$-order terms can to a large extent counteract the $\mathcal O (\alpha^3\alpha_s)$ contributions, evidently indicating the indispensability of the corrections. In addition, we find that, as the collision energy rises, the percentage of the interference effect in the total cross section will increase rapidly, especially for the $\chi_{c1}$ case.

hep-ph↗

arXiv2018

Next-to-leading-order QCD corrections to the decay of $Z$ boson into $\chi_c(\chi_b)$

Based on the framework of nonrelativistic Quantum Chromodynamics (NRQCD), we carry out next-to-leading order (NLO) QCD corrections to the decay of $Z$ boson into $\chi_c$ and $\chi_b$, respectively. The branching ratio of $Z \to \chi_{c}(\chi_b)+X$ is about $10^{-5}(10^{-6})$. It is found that, for $Z \to \chi_c(\chi_b)+X$, the single gluon fragmentation diagrams of $^3S_1^{[8]}$, which first appear at the NLO level, can provide significant contributions, leading to a great enhancement on the leading-order results. Consequently the contributions from the color octet (CO) channels will account for a large proportion of the total decay widths. Moreover, the introduction of the CO processes will thoroughly change the color singlet (CS) predictions on the ratios of $\Gamma_{\chi_{c1}}/\Gamma_{\chi_{c0}}$, $\Gamma_{\chi_{c2}}/\Gamma_{\chi_{c0}}$, $\Gamma_{\chi_{b1}}/\Gamma_{\chi_{b0}}$ and $\Gamma_{\chi_{b2}}/\Gamma_{\chi_{b0}}$, which can be regarded as an outstanding probe to distinguish the CO and CS mechanism. With regard to the CS ($^3P_J^{[1]}$) channels, the heavy quark pair associated processes serve as the leading role, however, in the case of $\chi_b$, $Z \to b\bar{b}[^3P_J^{[1]}]+g+g$ can also contribute significantly. Summing over all the feeddown contributions from $\chi_{cJ}$ and $\chi_{bJ}$, respectively, we find $\Gamma(Z \to J/\psi+X)|_{\chi_c-\textrm{feeddown}}=(0.28 - 2.4) \times 10^{-5}$ and $\Gamma(Z \to \Upsilon(1S)+X)|_{\chi_b-\textrm{feeddown}}=(0.15 - 0.49) \times 10^{-6}$.

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arXiv2018

Exclusive production of $J/\psi+\eta_c$ at the $B$ factories Belle and Babar using the principle of maximum conformality

We predict the rate for exclusive double-charmonium production in electron-positron annihilation $e^+ e^- \to J/\psi+\eta_c$ using perturbative quantum chromodynamics and the NRQCD framework for hard, heavy-quarkonium exclusive processes. The cross sections measured at the $B$-factories Belle and Babar at $\sqrt{s}=10.6$ GeV disagree with the pQCD leading-order predictions by an order of magnitude. The predictions at next-to-leading order are, however, very sensitive to the choice of the renormalization scale, resulting in an apparent discrepancy between the theoretical prediction and the data. We show that this discrepancy can in fact be eliminated by applying the Principle of Maximum Conformality (PMC) to set the renormalization scale. ... By carefully applying the PMC to different topologies of the annihilation process, one achieves precise pQCD predictions, together with improved perturbative convergence. We also observe that the single-photon-fragmentation QED correction is important, an effect which increases the total cross-section by about $10\%$. The scale-fixed, scheme-independent cross-section predicted by the PMC is $\sigma_{\rm tot}|_{\rm PMC}=20.35 ^{+3.5}_{-3.8}$ fb, where the uncertainties come from the squared average of the errors due to the value of the charm mass and the uncertainty from the quarkonium wavefunctions at the origin. We find that the typical momentum flow of the process is $2.30$ GeV, which explains the guessed choice of $2-3$ GeV using conventional scale-setting. The scale-fixed $e^+ e^- \to J/\psi+\eta_c$ cross-section predicted by the PMC shows excellent agreement with the Belle and Babar measurements, emphasizing the importance of a rigorous renormalization scale-setting procedure.

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arXiv2018

The asymmetries of the $B \to K^* \mu^+ \mu^-$ decay and the search of new physics beyond the Standard Model

In this paper, we compute the forward-backward asymmetry and the isospin asymmetry of the $B \to K^* \mu^+ \mu^-$ decay. The $B \to K^*$ transition form factors (TFFs) are key components of the decay. To achieve a more accurate QCD prediction, we adopt a chiral correlator for calculating the QCD light-cone sum rules for those TFFs with the purpose of suppressing the uncertain high-twist distribution amplitudes. Our predictions show that the asymmetries under the Standard Model and the Minimal Supersymmetric Standard Model with minimal flavor violation are close in shape for $q^2 \ge 6~{\rm GeV}^2$ and are consistent with the Belle, LHCb and CDF data within errors. When $q^2 < 2~{\rm GeV}^2$, their predictions behave quite differently. Thus a careful study on the $B \to K^* \mu^+ \mu^-$ decay within small $q^2$-region could be helpful for searching new physics beyond the Standard Model. As a further application, we also apply the $B \to K^*$ TFFs to the branching ratio and longitudinal polarization fraction of the $B\to K^*\nu\bar\nu$ decay within different models.

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