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  • Single top quark production with and without a Higgs boson
    Published: 2021-07-30, doi: 10.1088/1674-1137/ac0e8b
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    One method of probing new physics beyond the Standard Model is to check the correlation among higher-dimensional operators in the effective field theory. We examine the strong correlation between the processes $ pp\rightarrow tHq $ and $ pp\rightarrow tq $, which both depend on the same three operators. The correlation indicates that, according to the data of $ pp\rightarrow tq $, $ \sigma_{tHq} = \big[106.8 \pm 64.8\big]\; {\rm fb} $, which is significantly below the current upper limit $ \sigma_{tHq}\leqslant 900\; {\rm fb} $.
  • Core breaking and possible magnetic rotation in the semimagic nucleus 90Zr
    Published: 2021-07-30, doi: 10.1088/1674-1137/ac0fd2
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    The semimagic nucleus 90Zr, with Z = 40 and N = 50, is investigated in terms of large scale shell model calculations. A logical agreement is obtained between the available experimental data and predicted values. The calculated results indicate that the low-lying states are primarily dominated by the proton excitations from the fp orbitals across the Z = 38 or 40 subshell into the high-j $1g_{9/2}$ orbital. For the higher-spin states of 90Zr, the breaking of the N = 50 core plays a crucial role, and the contribution of different orbitals to each state are discussed in this article. The evolution from neutron core excitations to proton excitations is systematically studied along the neighboring N = 50 isotones. Furthermore, the strong $\Delta I$ = 1 sequence demonstrates an abrupt backbend attributed to the alignment of the valence nucleons in fp proton orbitals and is proposed to have a $\pi(fp)^{-2}(1g_{9/2})^{2} \otimes $$ \nu(1g_{9/2})^{-1}(2d_{5/2}/1g_{7/2})^{1}$ configuration before the backbend, based on the shell model calculations. The properties of this sequence before the backbend indicate a general agreement with the fingerprints of magnetic rotation; hence, the sequence with the $\pi(fp)^{-2}(1g_{9/2})^{2} \otimes \nu(1g_{9/2})^{-1}(2d_{5/2}/1g_{7/2})^{1}$ configuration is suggested as a magnetic rotational band arising from shears mechanism.
  • NLO effects for ΩQQQ baryons in QCD Sum Rules
    Published: 2021-07-30, doi: 10.1088/1674-1137/ac0b3c
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    We study the triply heavy baryons $\Omega_{QQQ}$ $(Q=c, b)$ in the QCD sum rules by performing the first calculation of the next-to-leading order (NLO) contribution to the perturbative QCD part of the correlation functions. Compared with the leading order (LO) result, the NLO contribution is found to be very important to the $\Omega_{QQQ}$. This is because the NLO not only results in a large correction but also reduces the parameter dependence, making the Borel platform more distinct, especially for the $\Omega_{bbb}$ in the $\overline{\rm{MS}}$ scheme, where the platform appears only at NLO but not at LO. Particularly, owing to the inclusion of the NLO contribution, the renormalization schemes ($\overline{\rm{MS}}$ and On-Shell) dependence and the scale dependence are significantly reduced. Consequently, after including the NLO contribution to the perturbative part in the QCD sum rules, the masses are estimated to be $4.53^{+0.26}_{-0.11}$ GeV for $\Omega_{ccc}$ and $14.27^{+0.33}_{-0.32}$ GeV for $\Omega_{bbb}$, where the results are obtained at $\mu=M_B$ with errors including those from the variation of the renormalization scale μ in the range $(0.8-1.2) M_B$. A careful study of the μ dependence in a wider range is further performed, which shows that the LO results are very sensitive to the choice of μ whereas the NLO results are considerably better. In addition to the $\mu=M_B$ result, a more stable value, (4.75-4.80) GeV, for the $\Omega_{ccc}$ mass is found in the range of $\mu=(1.2-2.0) M_B$, which should be viewed as a more relevant prediction in our NLO approach because of $ \mu $ dependence.