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Register a new userNext-to-leading-order QCD corrections to the decay of $Z$ boson into $chi_c(chi_b)$
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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 $chi_b$, $Z to bbar{b}[^3P_J^{[1]}]+g+g$ 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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The exclusive decay of the Higgs boson to a vector meson ($ J/psi $ or $ Upsilon(1S) $) and $ Z $ boson is studied in this work. The decay amplitudes are separated into two parts in a gauge invariant manner. The first part comes from the direct coupling of the Higgs boson to the charm (bottom) quark and the other from the $ HZZ^{*} $ or the loop-induced $ HZgamma^{*} $ vertexes in the standard model. While the branching ratios from the direct channel are much smaller than those of the indirect channel, their interference terms give nontrivial contributions. We further calculate the QCD radiative corrections to both channels, which reduce the total branching ratios by around 20% for both $ J/psi $ and $ Upsilon(1S) $ production. These results may help to check the SM predictions of the $ H cbar{c}(H bbar{b}) $ coupling and to seek for hints of new physics at the High Luminosity LHC or future hadron colliders.
We calculate the complete ${cal O}(alpha_s)$ corrections to the quark decay $bto ccs$ taking full account of the quark masses, but neglecting penguin contributions. For a c to the b quark mass ratio $m_c/m_b= 0.3$ and a strange quark mass of $0.2,$GeV, we find that the next-to-leading order (NLO) corrections increase $Gamma(bto ccs)$ by $(32pm 15)%$ with respect to the leading order expression, where the uncertainty is mostly due to scale- and scheme-dependences. Combining this result with the known NLO and non-perturbative corrections to other B meson decay channels we obtain an updated value for the semileptonic branching ratio of B mesons, $B_{SL}$, of $(12.0pm 1.4)% $ using pole quark masses and $(11.2pm 1.7)% $ using running $overline{mbox{MS}}$ masses.
We present the NLO QCD corrections for light Higgs pair production via vector boson fusion at the LHC within the CP conserving type II two higgs doublet model in the form of a fully flexible parton--level Monte Carlo program. Scale dependences on integrated cross sections and distributions are reduced with QCD K-factors of order unity.
In this paper, we calculate the total decay widths for the $W^+$-boson decays, $W^+ to B_c+b+bar{s}+X$ and $W^+ to B^*_c+b+bar{s}+X$, up to next-to-leading order (NLO) accuracy within the framework of the nonrelativistic QCD theory. Both the fixed-order and the fragmentation approaches are adopted to do the calculation. Differential decay widths $dGamma/dz$ and $dGamma/ds_1$ are also given. We find that the NLO corrections are significant in those two $W^+$ decay channels. Our numerical results show that at the LHC, there are about $7.03times 10^4$ $B_c$-meson events and $5.10times 10^4$ $B^*_c$-meson events to be produced via the $W^+$-boson decays per operation year.
D0 and CDF collaborations at the Fermilab Tevatron have searched for non-standard-model single top-quark production and set upper limits on the anomalous top quark flavor-changing neutral current (FCNC) couplings $kappa^g_{tc}/Lambda$ and $kappa^g_{tu}/Lambda$ using the measurement of total cross section calculated at the next-to-leading order (NLO) in QCD. In this Letter, we report on the effect of anomalous FCNC couplings to various decay branching ratios of the top quark, calculated at the NLO. This result is not only mandatory for a consistent treatment of both the top quark production and decay via FCNC couplings by D0 and CDF at the Tevatron but is also important for the study of ATLAS and CMS sensitivity to these anomalous couplings at the CERN LHC. We find that the NLO corrections to the partial decay widths of the three decay channels $ tto q + g$, $ tto q + gamma$ and $ tto q + Z$ are at the order of 10% in magnitude and modify their branching ratios by about 20%, 0.4% and 2%, respectively, as compared to their leading order predictions.
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