2020 Vol. 44, No. 1

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2020, 44(1): 013001. doi: 10.1088/1674-1137/44/1/013001
Abstract:
The high-precision measurement of Higgs boson properties is one of the primary goals of the Circular Electron Positron Collider (CEPC). The measurements of \begin{document}$H \to b\bar b/c\bar c/gg$\end{document} decay branching fraction in the CEPC experiment is presented, considering a scenario of analysing 5000 fb-1 \begin{document}$e^+e^-$\end{document} collision data with the center-of-mass energy of 250 GeV. In this study the Higgs bosons are produced in association with a pair of leptons, dominantly mediated by the ZH production process. The statistical uncertainty of the signal cross section is estimated to be about 1% in the \begin{document}$H \to b\bar b$\end{document} final state, and approximately 5%-10% in the \begin{document}$H \to c\bar c/gg$\end{document} final states. In addition, the main sources of the systematic uncertainties and their impacts to the measurements of branching fractions are discussed. This study demonstrates the potential of precise measurement of the hadronic final states of the Higgs boson decay at the CEPC, and will provide key information to understand the Yukawa couplings between the Higgs boson and quarks, which are predicted to be the origin of quarks’ masses in the standard model.
2020, 44(1): 013002. doi: 10.1088/1674-1137/44/1/013002
Abstract:
Measurements of decay asymmetry parameters of charmed baryons, e.g., \begin{document}$\Xi_c$\end{document}, provide more data to test the W-emission and W-exchange mechanisms controlled by strong and weak interactions. Taking advantage of the spin polarization in charmed baryon decays, we investigate the possibility to measure weak decay asymmetry parameters in the \begin{document}$e^{+}e^{-}\to \Xi_c^0\bar\Xi_c^0$\end{document} process. We analyze the transverse polarization spontaneously produced in this process and the spin transfer in the subsequent \begin{document}$\Xi_c$\end{document} decays. The sensitivity to measure the asymmetry parameters is estimated for the decay \begin{document}$\Xi_c\to\Xi \pi$\end{document}.
2020, 44(1): 013101. doi: 10.1088/1674-1137/44/1/013101
Abstract:
The heavy quark effective field theory (HQEFT) provides an effective way to deal with heavy meson decays. In this paper, we adopt two different correlators to derive the light-cone sum rules (LCSR) for the \begin{document}$B \to \pi$\end{document} transition form factors (TFFs) in the framework of HQEFT. We label the two LCSR results as LCSR-\begin{document}${\cal U}$\end{document} and LCSR-\begin{document}${\cal R}$\end{document}, which stand for the conventional correlator and the right-handed correlator. We observe that the correlation parameter \begin{document}$|\rho_{\rm RU}|$\end{document} for the branching ratio \begin{document}${\cal B}(B \to \pi l \nu_{l})$\end{document} is \begin{document}$\sim 0.85$\end{document}, implying a consistency of LCSRs with the other correlators. Furthermore, we obtain \begin{document}$|V_{ub}| _{{\rm LCSR}-{\cal U}} = (3.45^{+0.28}_{-0.20}\pm{0.13}_{\rm{exp}})\times10^{-3}$\end{document} and \begin{document}$|V_{ub}| _{{\rm LCSR}-\cal{R}} = (3.38^{+0.22}_{-0.16} \pm{0.12}_{\rm{exp}})\times10^{-3}$\end{document}. We also obtain \begin{document}${\cal{R}}_{\pi}| _{{\rm LCSR}-\cal{U}} = 0.68^{+0.10}_{-0.09}$\end{document} and \begin{document}${\cal{R}}_{\pi}| _{{\rm LCSR}-\cal{R}} = 0.65^{+0.13}_{-0.11}$\end{document}, both of which agree with the lattice QCD predictions. Thus, HQEFT provides a useful framework for studying B meson decays. Moreover, by using the right-handed correlator, the twist-2 terms are dominant in TFF \begin{document}$f^+(q^2)$\end{document}, as their contribution is over ~97% in the whole \begin{document}$q^2$\end{document} region, while the large twist-3 uncertainty of the conventional correlator is greatly suppressed. Hence, the LCSR-\begin{document}${\cal R}$\end{document} predictions can be used to test the properties of the various models for the pion twist-2 distribution amplitudes.
2020, 44(1): 013102. doi: 10.1088/1674-1137/44/1/013102
Abstract:
Mass spectra and wave functions of the doubly heavy baryons are computed assuming that the two heavy quarks inside a baryon form a compact heavy ‘diquark core’ in a color anti-triplet, and bind with the remaining light quark into a colorless baryon. The two reduced two-body problems are described by the relativistic Bethe-Salpeter equations (BSEs) with the relevant QCD inspired kernels. We focus on the doubly heavy baryons with \begin{document}$1^+$\end{document} heavy diquark cores. After solving BSEs in the instantaneous approximation, we present the mass spectra and the relativistic wave functions of the diquark cores, and of the low-lying baryon states \begin{document}$J^P=\frac{1}{2}^+$\end{document} and \begin{document}$\frac{3}{2}^+$\end{document} with flavors \begin{document}$(ccq)$\end{document}, \begin{document}$(bcq)$\end{document} and \begin{document}$(bbq)$\end{document}. A comparison with other approaches is also made.
2020, 44(1): 013103. doi: 10.1088/1674-1137/44/1/013103
Abstract:
Theta-dependent gauge theories can be studied using holographic duality through string theory in certain spacetimes. By this correspondence we consider a stack of N0 dynamical D0-branes as D-instantons in the background sourced by Nc coincident non-extreme black D4-branes. According to the gauge-gravity duality, this D0-D4 brane system corresponds to Yang-Mills theory with a theta angle at finite temperature. We solve the IIA supergravity action by taking account into a sufficiently small backreaction of the Dinstantons and obtain an analytical solution for our D0-D4-brane configuration. Subsequently, the dual theory in the large Nc limit can be holographically investigated with the gravity solution. In the dual field theory, we find that the coupling constant exhibits asymptotic freedom, as is expected in QCD. The contribution of the theta-dependence to the free energy gets suppressed at high temperatures, which is basically consistent with the calculation using the Yang-Mills instanton. The topological susceptibility in the large Nc limit vanishes, and this behavior remarkably agrees with the implications from the simulation results at finite temperature. Moreover, we finally find a geometrical interpretation of the theta-dependence in this holographic system.
2020, 44(1): 014001. doi: 10.1088/1674-1137/44/1/014001
Abstract:
We use the latest results of the ultra-high accuracy 1S-2S transition experiments in the hydrogen atom to constrain the forms of the deformed dispersion relation in the non-relativistic limit. For the leading correction of the non-relativistic limit, the experiment sets a limit at an order of magnitude for the desired Planck-scale level, thereby providing another example of the Planck-scale sensitivity in the study of the dispersion relation in controlled laboratory experiments. For the next-to-leading term, the bound is two orders of magnitude away from the Planck scale, however it still amounts to the best limit, in contrast to the previously obtained bound in the non-relativistic limit from the cold-atom-recoil experiments.
2020, 44(1): 014002. doi: 10.1088/1674-1137/44/1/014002
Abstract:
We propose the transverse velocity (\begin{document}$\beta_T$\end{document}) dependence of the anti-deuteron to deuteron ratio as a new observable to search for the QCD critical point in heavy-ion collisions. The QCD critical point can attract the system evolution trajectory in the QCD phase diagram, which is known as the focusing effect. To quantify this effect, we employ the thermal and hadronic transport model to simulate the dynamical particle emission along a hypothetical focusing trajectory near the critical point. We found that the focusing effect can lead to anomalous \begin{document}$\beta_T$\end{document} dependence on \begin{document}$\bar{p}/p$\end{document}, \begin{document}$\bar{d}/d$\end{document} and \begin{document}$^3\overline{\rm{He}}/^3{\rm{He}}$\end{document} ratios. We examined the \begin{document}$\beta_T$\end{document} dependence of \begin{document}$\bar{p}/p$\end{document} and \begin{document}$\bar{d}/d$\end{document} ratios of central Au+Au collisions at \begin{document}$\sqrt {s_{\rm{NN}}} =$\end{document} 7.7 to 200 GeV measured by the STAR experiment at RHIC. Surprisingly, we only observe a negative slope in \begin{document}$\beta_T$\end{document} dependence of \begin{document}$\bar{d}/d$\end{document} ratio at \begin{document}$\sqrt {s_{\rm{NN}}} =$\end{document} 19.6 GeV, which indicates the trajectory evolution has passed through the critical region. In the future, we could constrain the location of the critical point and/or width of the critical region by conducting precise measurements on the \begin{document}$\beta_T$\end{document} dependence of the \begin{document}$\bar{d}/d$\end{document} ratio at different energies and rapidity.
2020, 44(1): 014003. doi: 10.1088/1674-1137/44/1/014003
Abstract:
The 6Li(n, t)4He reaction was measured as the first experiment involving neutron-induced charged particle emission reactions at the CSNS (China Spallation Neutron Source) Back-n white neutron source. The differential cross-sections of the 6Li(n, t)4He reaction at 15 detection angles ranging from 19.2° to 160.8° are obtained from 1.0 eV to 3.0 MeV at 80 neutron energy points; for 50 energy points below 0.1 MeV they are reported for the first time. The results indicate that the anisotropy of the emitted tritium is noticeable above En = 100 eV. The angle-integrated cross-sections are also obtained. The present differential cross-sections agree in general with the previous evaluations, but there are some differences in the details. More importantly, the present results indicate that the cross-sections of the 6Li(n, t)4He reaction might be overestimated by most evaluations in the 0.5 − 3.0 MeV region, although they are recommended as standards below 1.0 MeV.
2020, 44(1): 014101. doi: 10.1088/1674-1137/44/1/014101
Abstract:
We show that the \begin{document}$p_{T}$\end{document} spectra of \begin{document}$\Omega^{-}$\end{document} and \begin{document}$\phi$\end{document} at midrapidity in the inelastic events in \begin{document}$pp$\end{document} collisions at \begin{document}$\sqrt{s}=$\end{document} 13 TeV exhibit a constituent quark number scaling property, which is a clear signal of quark combination mechanism at hadronization. We use a quark combination model with equal velocity combination approximation to systematically study the production of identified hadrons in \begin{document}$pp$\end{document} collisions at \begin{document}$\sqrt{s}$\end{document}= 13 TeV. The midrapidity \begin{document}$p_{T}$\end{document} spectra for protons, \begin{document}$\Lambda$\end{document}, \begin{document}$\Xi^{-}$\end{document}, \begin{document}$\Omega^{-}$\end{document}, \begin{document}$\phi$\end{document} and \begin{document}$K^{*}$\end{document} in the inelastic events are simultaneously fitted by the model. The multiplicity dependence of the yields of these hadrons are also well understood. The strong \begin{document}$p_{T}$\end{document} dependence of the \begin{document}$p/\phi$\end{document} ratio is well explained by the model, which further suggests that the production of two hadrons with similar masses is determined by their quark content at hadronization. The \begin{document}$p_{T}$\end{document} spectra of strange hadrons at midrapidity in different multiplicity classes in \begin{document}$pp$\end{document} collisions at \begin{document}$\sqrt{s}=$\end{document} 13 TeV are predicted for further tests of the model. The midrapidity \begin{document}$p_{T}$\end{document} spectra of soft (\begin{document}$p_T < 2$\end{document} GeV/c) strange quarks and up/down quarks at hadronization in \begin{document}$pp$\end{document} collisions at \begin{document}$\sqrt{s}=$\end{document} 13 TeV are extracted.
2020, 44(1): 014102. doi: 10.1088/1674-1137/44/1/014102
Abstract:
Within the framework of the Lanzhou quantum molecular dynamics model, the deep subthreshold antiproton production in heavy-ion collisions has been investigated thoroughly. The elastic scattering, annihilation and charge exchange reactions associated with antiproton channels are implemented in the model. The attractive antiproton potential extracted from the G-parity transformation of nucleon selfenergies reduces the threshold energies in meson-baryon and baryon-baryon collisions, and consequently enhances the antiproton yields to some extent. The calculated invariant spectra are consistent with the available experimental data. The primordial antiproton yields increase with the mass number of the colliding system. However, annihilation reactions reduce the antiproton production which becomes independent of the colliding partners. Anti-flow phenomena of antiprotons correlated with the mean field potential and annihilation mechanism is found by comparing them with the proton flows. Possible experiments at the high-intensity heavy-ion accelerator facility (HIAF) in China are discussed.
2020, 44(1): 014103. doi: 10.1088/1674-1137/44/1/014103
Abstract:
The skyrmion stability at finite isospin chemical potential \begin{document}$\mu_I$\end{document} is studied using the Skyrme Lagrangian with a finite pion mass \begin{document}$m_{\pi}$\end{document}. A critical value \begin{document}$\mu_{I{\rm c}}=\sqrt{3/2}m_{\pi}$\end{document} , above which a stable soliton does not exist, is found. We also explore some properties of the skyrmion as function of \begin{document}$\mu_{I}$\end{document}, i.e., the isoscalar rms radius and the isoscalar magnetic rms radius. Finally, considering the finite temperature effect on the skyrmion mass, we obtain a critical temperature \begin{document}$T_{\rm c}$\end{document}, using the profile function of the skyrmion, above which the skyrmion mass does not have a minimum, which can be interpreted as the occurrence of the deconfinement phase transition.
2020, 44(1): 014104. doi: 10.1088/1674-1137/44/1/014104
Abstract:
The Bayesian neural network (BNN) method is proposed to predict the isotopic cross-sections in proton induced spallation reactions. Learning from more than 4000 data sets of isotopic cross-sections from 19 experimental measurements and 5 theoretical predictions with the SPACS parametrization, in which the mass of the spallation system ranges from 36 to 238, and the incident energy from 200 MeV/u to 1500 MeV/u, it is demonstrated that the BNN method can provide good predictions of the residue fragment cross-sections in spallation reactions.
2020, 44(1): 015101. doi: 10.1088/1674-1137/44/1/015101
Abstract:
The weak cosmic censorship conjecture in the near-extremal BTZ black hole has been tested using test particles and fields. It has been claimed that such a black hole can be overspun. In this paper, we review the thermodynamics and weak cosmic censorship conjecture in BTZ black holes using the scattering of a scalar field. The first law of thermodynamics in the non-extremal BTZ black hole is recovered. For the extremal and near-extremal black holes, due to the divergence of the variation of entropy, we test the weak cosmic censorship conjecture by evaluating the minimum of the function f, and find that both the extremal and near-extremal black holes cannot be overspun.
2020, 44(1): 015102. doi: 10.1088/1674-1137/44/1/015102
Abstract:
In this paper, we investigate the quantum scalar fields in a massive BTZ black hole background. We study the entropy of the system by evaluating the entanglement entropy using a discretized approach. Specifically, we fit the results with a log -modified formula of the black hole entropy, which is introduced by quantum correction. The coefficients of leading and sub-leading terms affected by the mass of graviton are numerically analyzed.
2020, 44(1): 015103. doi: 10.1088/1674-1137/44/1/015103
Abstract:
We study reheating in some one and two field realizations of fibre inflation. We find that reheating begins with a phase of preheating in which long wavelength fluctuation modes are excited. In two field models there is a danger that the parametric amplification of infrared fluctuations in the second scalar field - associated with an entropy mode - might induce an instability of the curvature fluctuations. We show that, at least in the models we consider, the entropy mode has a sufficiently large mass to prevent this instability. Hence, from the point of view of reheating the models we consider are well-behaved.
2020, 44(1): 015104. doi: 10.1088/1674-1137/44/1/015104
Abstract:
This study set out to investigate charged vector particles tunneling via horizons of a pair of accelerating rotating charged NUT black holes under the influence of quantum gravity. To this end, we use the modified Proca equation incorporating generalized uncertainty principle. Applying the WKB approximation to the field equation, we obtain a modified tunneling rate and the corresponding corrected Hawking temperature for this black hole. Moreover, we analyze the graphical behavior of the corrected Hawking temperature \begin{document}$T'_{H}$\end{document} with respect to the event horizon for the given black hole. By considering quantum gravitational effects on Hawking temperatures, we discuss the stability analysis of this black hole. For a pair of black holes, the temperature \begin{document}$T'_{H}$\end{document} increases with the increase in rotation parameters a and \begin{document}$\omega$\end{document}, correction parameter \begin{document}$\beta$\end{document}, black hole acceleration \begin{document}$\alpha$\end{document}, and arbitrary parameter k, and decreases with the increase in electric e and magnetic charges g.