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Register a new userFurther studies on the exclusive productions of $J/psi+chi_{cJ}$ ($J=0,1,2$) via $e^+e^-$ annihilation at the $B$ factories
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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 $mathcal O (alpha^3alpha_s)$-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 $mathcal O (alpha^3alpha_s^2)$, we perform the QCD corrections to these $mathcal O (alpha^3alpha_s)$-order terms for the first time, which are found to be able to significantly influence the $mathcal O (alpha^3alpha_s)$-order results. In particular, in the case of $chi_{c1}$ and $chi_{c2}$, the newly calculated $mathcal O (alpha^3alpha_s^2)$-order terms can to a large extent counteract the $mathcal O (alpha^3alpha_s)$ 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.
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Using $4.479 times 10^{8}$ $psi(3686)$ events collected with the BESIII detector, we search for the decays $psi(3686) rightarrow e^{+}e^{-}chi_{c0,1,2}$ and $chi_{c0,1,2} rightarrow e^{+}e^{-}J/psi$. The decays $psi(3686) rightarrow e^{+}e^{-}chi_{c0,1,2}$ and $chi_{c0,1,2} rightarrow e^{+}e^{-}J/psi$ are observed for the first time. The measured branching fractions are $mathcal{B}(psi(3686) rightarrow e^{+}e^{-}chi_{c0,1,2}) = (11.7 pm 2.5 pm 1.0)times10^{-4}$, $(8.6 pm 0.3 pm 0.6)times10^{-4}$, $(6.9 pm 0.5 pm 0.6)times10^{-4}$, and $mathcal{B}(chi_{c0,1,2} rightarrow e^{+}e^{-}J/psi) = (1.51 pm 0.30 pm 0.13)times10^{-4}$, $(3.73 pm 0.09 pm 0.25)times10^{-3}$, $(2.48 pm 0.08 pm 0.16)times10^{-3}$. The ratios of the branching fractions $frac{mathcal{B}(psi(3686) rightarrow e^{+}e^{-}chi_{c0,1,2})}{mathcal{B}(psi(3686) rightarrow gammachi_{c0,1,2})}$ and $frac{mathcal{B}(chi_{c0,1,2} rightarrow e^{+}e^{-}J/psi)}{mathcal{B}(chi_{c0,1,2} rightarrow gamma J/psi)}$ are also reported.
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., $frac{dsigma}{dcostheta}=A+Bcos^2theta$, 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.
We make a detailed study on the typical production channel of double charmoniums, $e^+e^-to J/psi+eta_c$, at the center-of-mass collision energy $sqrt{s}=10.58$ GeV. The key component of the process is the form factor $F_{rm VP}(q^2)$, which has been calculated within the QCD light-cone sum rules (LCSR). To improve the accuracy of the derived LCSR, we keep the $J/psi$ light-cone distribution amplitude up to twist-4 accuracy. Total cross sections for $e^+e^-to J/psi+eta_c$ at three typical factorization scales are $sigma|_{mu_s} = 22.53^{+3.46}_{-3.49}~{rm fb}$, $sigma|_{mu_k} = 21.98^{+3.35}_{-3.38}~{rm fb}$ and $sigma|_{mu_0} = 21.74^{+3.29}_{-3.33}~{rm fb}$, respectively. The factorization scale dependence is small, and those predictions are consistent with the BABAR and Belle measurements within errors.
The products of the electron width of the J/psi meson and the branching fraction of its decays to the lepton pairs were measured using data from the KEDR experiment at the VEPP-4M electron-positron collider. The results are Gamma_{ee}(J/psi)*Br(J/psi->e^+e^-)=(0.3323pm0.0064pm0.0048) keV, Gamma_{ee}(J/psi)*Br(J/psi->mu^+mu^-)=(0.3318pm0.0052pm0.0063) keV. Their combinations Gamma_{ee}times(Gamma_{ee}+Gamma_{mumu})/Gamma=(0.6641pm0.0082pm0.0100) keV, Gamma_{ee}/Gamma_{mumu}=1.002pm0.021pm0.013 can be used to improve theaccuracy of the leptonic and full widths and test leptonic universality. Assuming emu universality and using the world average value of the lepton branching fraction, we also determine the leptonic Gamma_{ll}=5.59pm0.12 keV and total Gamma=94.1pm2.7 keV widths of the J/psi meson.
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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