Highlights
• Study of C parity violating and strangeness changing J/ψPP weak decays
2021, 45(8): 083104. doi: 10.1088/1674-1137/ac06ac
Although $J/{\psi}$ weak decays are rare, they are possible within the standard model of elementary particles. Inspired by the potential prospects of the future intensity frontier, the C parity violating $J/{\psi}$ ${\to}$ ${\pi}{\eta}^{({\prime})}$, ${\eta}{\eta}^{\prime}$ decays and the strangeness changing $J/{\psi}$ ${\to}$ ${\pi}K$, $K{\eta}^{({\prime})}$ decays are studied via the perturbative QCD approach. It is determined that the $J/{\psi}$ ${\to}$ ${\eta}{\eta}^{\prime}$ decays have relatively large branching ratios, approximately on the order of $10^{-11}$, which might be within the measurement capability and sensitivity of the future STCF experiment.
• Search for dark matter production in association with the Z' boson at the LHC in pp collisions at ${{\sqrt{s}}}$ = 8 TeV using Monte Carlo simulations
2021, 45(8): 083001. doi: 10.1088/1674-1137/ac061c
This analysis evaluates the possibility of the search for Dark Matter (DM) particles using events with a Z$^{\prime}$ heavy gauge boson and a large missing transverse momentum at the Large Hadron Collider (LHC). We consider the muonic decay of Z$^{\prime}$. The analyzed Monte Carlo samples were the Open simulated files produced by the Compact Muon Solenoid (CMS) collaboration for proton-proton collisions, corresponding to an integrated luminosity of the LHC run-I with 19.7 fb $^{-1}$ at $\sqrt{s} =$ 8 TeV. Two scenarios, namely a simplified benchmark scenario, called Dark Higgs, and the effective field theory (EFT) formalism, were used for interpretations. Limits were set on Z$^{\prime}$, dark matter masses, and the cutoff scale of the EFT.
• Novel evidence for the σ-bond linear-chain molecular structure in 14C
2021, 45(8): 084002. doi: 10.1088/1674-1137/ac04a0
A multi-nucleon transfer and cluster decay experiment, $^7$Li($^{11}$B,$^{14}$C$^*\rightarrow\alpha$+$^{10}$Be)$\alpha$, is conducted at an incident beam energy of 55 MeV. This reaction channel has a significantly large Q-value, which favors populating the high lying resonant states in $^{14}$C. The decay paths, from these resonances to various states of the final nucleus $^{10}$Be, can be selected, owing to the experimentally achieved optimal resolution of the Q-value spectrum. A number of resonant states are reconstructed from the forward emitting $^{10}$Be + $\alpha$ fragments, and their major molecular structures can be detected according to the selective decay paths and relative decay widths. A state at 22.4(2) MeV validates the previously measured and theoretically predicted band head of the positive-parity $\sigma$-bond linear-chain molecular band. Two additional resonances at 22.9(2) and 24.2(2) MeV are identified and consistent with the predicted $2^+$ and $4^+$ members of the same molecular band, thus providing novel evidences for the existence of the exotic clustering chain structure in neutron-rich carbon isotopes. A few high energy resonances, which also indicate the presence of the $\sigma$-bond molecular structure, are observed; however, further studies are still required to clarify their ascription in band systematics.
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• Single top quark production with and without a Higgs boson
Published: 2021-07-30, doi: 10.1088/1674-1137/ac0e8b
Show Abstract
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.
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2021 Vol. 45, No. 8
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