Highlights
• Search for the doubly heavy baryons ${\boldsymbol \varOmega_{\boldsymbol{bc}}^{\bf 0}}$ and ${\boldsymbol\varXi_{\boldsymbol{bc}}^{\bf 0} }$ decaying to ${ \boldsymbol \varLambda_c^+\pi^- }$ and ${\boldsymbol\varXi_c^+\pi^- }$
2021, 45(9): 093002. doi: 10.1088/1674-1137/ac0c70
The first search for the doubly heavy ${{{{\varOmega}_{bc}^{0}}}}$ baryon and a search for the ${{{{\varXi}_{bc}^{0}}}}$ baryon are performed using $pp$ collision data collected via the ${\rm{LHCb}}$ experiment from 2016 to 2018 at a centre-of-mass energy of $13 \;{\rm{TeV}}$, corresponding to an integrated luminosity of 5.2$\;{\rm{f}}{{\rm{b}}^{ - 1}}$. The baryons are reconstructed via their decays to ${{{{\varLambda}^+_c}}} {{{{\pi}^-}}}$ and ${{{{\varXi}^+_c}}} {{{{\pi}^-}}}$. No significant excess is found for invariant masses between 6700 and 7300$\;{\rm{MeV}}/{c^2}$, in a rapidity range from 2.0 to 4.5 and a transverse momentum range from 2 to 20$\;{\rm{MeV}}/{c}$. Upper limits are set on the ratio of the ${{{{\varOmega}_{bc}^{0}}}}$ and ${{{{\varXi}_{bc}^{0}}}}$ production cross-section times the branching fraction to ${{{{\varLambda}^+_c}}}{{{{\pi}^-}}}$ (${{{{\varXi}^+_c}}}{{{{\pi}^-}}}$) relative to that of the ${{{{\varLambda}^0_b}}}$ (${{{{\varXi}_{b}^{0}}}}$) baryon, for different lifetime hypotheses, at 95% confidence level. The upper limits range from $0.5\times10^{-4}$ to $2.5\times10^{-4}$ for the ${{{{{{{{\varOmega}_{bc}^{0}}}}{{\rightarrow }}{{{{\varLambda}^+_c}}}{{{{\pi}^-}}}}}}}$ (${{{{{{{{\varXi}_{bc}^{0}}}}{{\rightarrow }}{{{{\varLambda}^+_c}}}{{{{\pi}^-}}}}}}}$) decay, and from $1.4\times10^{-3}$ to $6.9\times10^{-3}$ for the ${{{{{{{{\varOmega}_{bc}^{0}}}}{{\rightarrow }}{{{{\varXi}^+_c}}}{{{{\pi}^-}}}}}}}$ (${{{{{{{{\varXi}_{bc}^{0}}}}{{\rightarrow }}{{{{\varXi}^+_c}}}{{{{\pi}^-}}}}}}}$) decay, depending on the considered mass and lifetime of the ${{{{\varOmega}_{bc}^{0}}}}$ (${{{{\varXi}_{bc}^{0}}}}$) baryon.
• Probing top-philic new physics via four-top-quark production
2021, 45(9): 093107. doi: 10.1088/1674-1137/ac0c6f
We explore constraints on various new physics resonances from four top-quark production based on current experimental data. Both light and heavy resonances are studied in this work. A comparison of the full width effect and narrow width approximation is also presented.
• Color halo scenario of charmonium-like hybrids
2021, 45(9): 093111. doi: 10.1088/1674-1137/ac0ee2
The internal structures of $J^{PC} = 1^{--}, (0,1,2)^{-+}$ charmonium-like hybrids are investigated under lattice QCD in the quenched approximation. We define the Bethe-Salpeter wave function ($\Phi_n(r)$) in the Coulomb gauge as the matrix element of a spatially extended hybrid-like operator ($\bar{c}{c}g$) between the vacuum and n-th state for each $J^{PC}$, with r being the spatial separation between a localized $\bar{c}c$ component and the chromomagnetic strength tensor. These wave functions exhibit some similarities for states with the aforementioned different quantum numbers, and their r-behaviors (no node for the ground states and one node for the first excited states) imply that r can be a meaningful dynamical variable for these states. Additionally, the mass splittings of the ground states and first excited states of charmonium-like hybrids in these channels are obtained for the first time to be approximately 1.2-1.4 GeV. These results do not support the flux-tube description of heavy-quarkonium-like hybrids in the Born-Oppenheimer approximation. In contrast, a charmonium-like hybrid can be viewed as a “color halo” charmonium for which a relatively localized color octet $\bar{c}c$ is surrounded by gluonic degrees of freedom, which can readily decay into a charmonium state along with one or more light hadrons. The color halo picture is compatible with the decay properties of $Y(4260)$ and suggests LHCb and BelleII to search for $(0,1,2)^{-+}$ charmonium-like hybrids in $\chi_{c0,1,2}\eta$ and $J/\psi \omega (\phi)$ final states.
In Press
More >
• Chromomagnetic and chromoelectric dipole moments of quarks in the reduced 331 model
Published: 2021-09-14, doi: 10.1088/1674-1137/ac1b9a
Show Abstract
The one-loop contributions to the chromomagnetic dipole moment $\hat\mu_t(q^2)$ and electric dipole moment $\hat d_t(q^2)$ of the top quark are calculated within the reduced 331 model (RM331) for non-zero $q^2$. It is argued that the results are gauge independent and thus represent valid observable quantities. In the RM331, $\hat \mu_t(q^2)$ receives new contributions from two heavy gauge bosons, namely $Z'$ and $V^\pm$, and one neutral scalar boson $h_2$, along with a new contribution from the standard model's Higgs boson via flavor changing neutral currents. The latter, which is also mediated by the $Z'$ gauge boson and the scalar boson $h_2$, can provide a non-vanishing $\hat d_t(q^2)$ if there is a $CP$-violating phase. The analytical results are presented in terms of both Feynman parameter integrals and Passarino-Veltman scalar functions, which are useful to cross-check the numerical results. Both $\hat\mu_t(q^2)$ and $\hat d_t(q^2)$ are numerically evaluated for parameter values still allowed by the constraints from experimental data. It is found that the new one-loop contributions of the RM331 to the real (imaginary) part of $\hat \mu_t(q^2)$ are of the order of $10^{-5}$ ($10^{-6}$), which means at least three orders of magnitude smaller than the standard model prediction but larger than the predictions of other models of new physics. In the RM331, the dominant contribution arises from the $V^\pm$ gauge boson for $\|q\|$ in the 30-1000 GeV interval and a mass $m_{V}$ of the order of a few hundreds of GeV. As for $\hat d_t(q^2)$, it receives its largest contribution from $h_2$ exchange and can reach values of the order of $10^{-19}$, i.e., smaller than the contributions predicted by other standard model extensions.
• Cosmological implications of a BL charged hidden scalar: leptogenesis and gravitational waves
Published: 2021-09-14, doi: 10.1088/1674-1137/ac1e09
Show Abstract
In this study, we investigated the cosmological implications of a complex singlet scalar ${\cal{S}}$ with non-trivial $B-L$ charges in the conformal $U(1)_{B-L}$ theory. It was found that, in a sizable region of parameter space, ${\cal{S}}$ may disturb the resonant leptogenesis mechanism, which is used to generate baryon asymmetry, and affect the symmetry breaking dynamics in the strong first order phase transition. The stochastic gravitational waves (GWs) produced at the phase transition can be probed in future GW experiments. The GW searches prefer a relatively light ${\cal{S}}$ at the TeV-scale; however, this is difficult to detect directly at future high-energy colliders.
• Description of elastic scattering induced by the unstable nuclei 9,10,11,13,14C
Published: 2021-09-14, doi: 10.1088/1674-1137/ac1fe1
Show Abstract
The elastic-scattering angular distributions and total reaction cross sections of $^{9,10,11,13,14}{\rm{C}}$ projectiles were predicted using the obtained $^{12}{\rm{C}}$ and $^{9}{\rm{Be}}$ global optical model potentials, respectively. The predictions were analyzed in detail by comparison with the available experimental data. The results indicate that the $^{12}{\rm{C}}$ and $^{9}{\rm{Be}}$ global optical model potentials provide a satisfactory description of the elastic scattering data for the reactions induced by the $^{9,10,11,13}{\rm{C}}$. For the neutron-rich carbon isotope $^{14}{\rm{C}}$, the elastic scattering can be well described by changing the real part radius parameter of the $^{12}{\rm{C}}$ global optical model potential. Possible physical explanations for the observed differences are further discussed.
Current Issued
2021 Vol. 45, No. 10
Published:
Archive