## 2021 Vol. 45, No. 4

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2021, 45(4): 041001. doi: 10.1088/1674-1137/abde2e
Abstract:
The global \begin{document}$SU(3)$\end{document} color symmetry and its physical consequences are discussed. The Nöther current is actually governed by the conserved matter current of color charges if the color field generated by this charge is properly polarized. The color field strength of a charge can have a uniform part due to the nontrivial QCD vacuum field and the nonzero gluon condensate, which implies that the self-energy of a system with a net color charge is infinite and, therefore, cannot exist as a free state. This is precisely what color confinement means. Accordingly, the Cornell type potential with the feature of Casimir scaling is derived for a color singlet system composed of a static color charge and an anti-charge. The uniform color field also implies that a hadron has a minimal size and minimal energy. Furthermore, the global \begin{document}$SU(3)$\end{document} color symmetry requires that the minimal irreducible color singlet systems can only be \begin{document}$q\bar{q}$\end{document}, \begin{document}$qqq$\end{document}, \begin{document}$gg$\end{document}, \begin{document}$ggg$\end{document}, \begin{document}$q\bar{q}g$\end{document}, \begin{document}$qqqg$\end{document}, \begin{document}$\bar{q}\bar{q}\bar{q}g$\end{document}, etc., therefore a multi-quark system can only exist as a molecular configuration if there are no other binding mechanisms.
2021, 45(4): 041002. doi: 10.1088/1674-1137/abdfbe
Abstract:
We investigate the exotic \begin{document}$\Omega\Omega$\end{document} dibaryon states with \begin{document}$J^P=0^+$\end{document} and \begin{document}$2^+$\end{document} in a molecular picture. We construct a tensor \begin{document}$\Omega$\end{document}\begin{document}$\Omega$\end{document} molecular interpolating current and calculate the two-point correlation function within the method of QCD sum rules. Our calculations indicate that the masses of the scalar and tensor dibaryon states are \begin{document}$m_{\Omega\Omega, \, 0^+} =$\end{document} \begin{document}$(3.33\pm 0.51) \,{\rm{GeV}}$\end{document} and \begin{document}$m_{\Omega\Omega,\, 2^+}=(3.15\pm0.33)\, {\rm{GeV}}$\end{document}, respectively, which are below the \begin{document}$2m_\Omega$\end{document} threshold. Within error, these results do not negate the existence of loosely bound molecular \begin{document}$\Omega\Omega$\end{document} dibaryon states. These exotic strangeness \begin{document}$S=-6$\end{document} and doubly-charged \begin{document}$\Omega\Omega$\end{document} dibaryons, if they exist, may be identified in heavy-ion collision processes in the future.
2021, 45(4): 041003. doi: 10.1088/1674-1137/abe03c
Abstract:
In this study, we analyze the direct-detection constraints of light dark matter in the next-to minimal supersymmetric standard model (NMSSM) with non-universal Higgs masses (NUHM); we specially focus on the correlation between higgsino asymmetry and spin-dependent (SD) cross section. We draw the following conclusions. (i) The SD cross section is proportional to the square of higgsino asymmetry in dark matter \begin{document}$\tilde{\chi}^0_1$\end{document} in the NMSSM-NUHM, and hence, it is small for highly singlino-dominated dark matter. (ii) The higgsino-mass parameter \begin{document}$\mu_{\rm{eff}}$\end{document} is smaller than approximately \begin{document}$335\;{\rm{GeV}}$\end{document} in the NMSSM-NUHM due to the current muon g-2 constraint, but our scenario with light dark matter can still be alive under current constraints including the direct detection of dark matter in the spin-dependent channel. (iii) With a sizeable higgsino component in the light dark matter, the higgsino asymmetry and SD cross section can also be sizeable, but dark matter relic density is always small; thus, it can escape the direct detections. (iv) Light dark matter in the \begin{document}$h_2$\end{document}- and Z-funnel annihilation channels with sufficient relic density can be covered by future LUX-ZEPLIN (LZ) 7-ton in SD detections. (v) The spin-independent (SI) cross section is dominated by \begin{document}$h_1$\end{document}- and \begin{document}$h_2$\end{document}-exchanging channels, which can even cancel each other in some samples, leaving an SI cross section smaller by a few orders of magnitude than that of one individual channel.
2021, 45(4): 041004. doi: 10.1088/1674-1137/abe03d
Abstract:
Many experiments have confirmed spectral hardening at a few hundred GeV in the spectra of cosmic ray (CR) nuclei. Three different origins have been proposed: primary source acceleration, propagation, and the superposition of different kinds of sources. In this work, a broken power law has been employed to fit each of the spectra of cosmic ray nuclei from AMS-02 directly, for rigidities greater than 45 GeV. The fitting results of the break rigidity and the spectral index differences less than and greater than the break rigidity show complicated relationships among different nuclear species, which cannot be reproduced naturally by a simple primary source scenario or a propagation scenario. However, with a natural and simple assumption, the superposition of different kinds of sources could have the potential to explain the fitting results successfully. Spectra of CR nuclei from a single future experiment, such as DAMPE, will provide us the opportunity to do cross checks and reveal the properties of the different kinds of sources.
2021, 45(4): 041005. doi: 10.1088/1674-1137/abe110
Abstract:
By globally analyzing nuclear Drell-Yan data including all incident energies, the nuclear effects of nuclear parton distribution functions (nPDFs) and initial-state parton energy loss are investigated. Based on the Landau-Pomeranchuk-Migdal (LPM) regime, the calculations are carried out by means of analytic parametrizations of quenching weights derived from the Baier-Dokshitzer-Mueller-Peign\begin{document}$\acute{e}$\end{document}-Schiff (BDMPS) formalism and using the new EPPS16 nPDFs. It is found that the results are in good agreement with the data and the role of the energy loss effect in the suppression of Drell-Yan ratios is prominent, especially for low-mass Drell-Yan measurements. The nuclear effects of nPDFs become more obvious with increasing nuclear mass number A, the same as the energy loss effect. By a global fit, the transport coefficient extracted is \begin{document}$\hat{q} = 0.26\pm0.04$\end{document} GeV2/fm. In addition, to avoid diminishing the QCD NLO correction to the data form of Drell-Yan ratios, separate calculations of the Compton differential cross section ratios \begin{document}$R_{\rm Fe(W)/C}(x_{\rm F})$\end{document} at 120 GeV are performed, which provides a feasible way to better distinguish the gluon energy loss in Compton scattering. It is found that the role of the initial-state gluon energy loss in the suppression of Compton scattering ratios is not very important and disappears with the increase of \begin{document}$x_{\rm F}$\end{document}.
2021, 45(4): 041006. doi: 10.1088/1674-1137/abe197
Abstract:
In this work, the existence of Borromean states is discussed for bosonic and fermionic cases in both the relativistic and non-relativistic limits from the 3-momentum shell renormalization. With the linear bosonic model, we check the existence of Efimov-like states in the bosonic system. In both limits a geometric series of singularities is found in the 3-boson interaction vertex, while the energy ratio is reduced by around 70% in the relativistic limit because of the anti-particle contribution. Motivated by the quark-diquark model in heavy baryon studies, we have carefully examined the p-wave quark-diquark interaction and found an isolated Borromean pole at finite energy scale. This may indicate a special baryonic state of light quarks in high energy quark matter. In other cases, trivial results are obtained as expected. In the relativistic limit, for both bosonic and fermionic cases, potential Borromean states are independent of the mass, which means the results would also be valid even in the zero-mass limit.
2021, 45(4): 043001. doi: 10.1088/1674-1137/abdf40
Abstract:
A search for the rare decay \begin{document}$B^0\to J/ \psi\phi$\end{document} is performed using \begin{document}$pp$\end{document} collision data collected with the LHCb dete-ctor at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. No significant signal of the decay is observed and an upper limit of \begin{document}$1.1 \times 10^{-7}$\end{document} at 90% confidence level is set on the branching fraction.
2021, 45(4): 043101. doi: 10.1088/1674-1137/abde2d
Abstract:
It is well-known that direct analytic continuation of the DGLAP evolution kernel (splitting functions) from space-like to time-like kinematics breaks down at three loops. We identify the origin of this breakdown as due to splitting functions not being analytic functions of external momenta. However, splitting functions can be constructed from the squares of (generalized) splitting amplitudes. We establish the rules of analytic continuation for splitting amplitudes, and use them to determine the analytic continuation of certain holomorphic and anti-holomorphic part of splitting functions and transverse-momentum dependent distributions. In this way we derive the time-like splitting functions at three loops without ambiguity. We also propose a reciprocity relation for singlet splitting functions, and provide non-trivial evidence that it holds in QCD at least through three loops.
2021, 45(4): 043102. doi: 10.1088/1674-1137/abde2f
Abstract:
We calculate the masses of the \begin{document}$QQ\bar{q}\bar{q}$\end{document} (\begin{document}$Q=c,b$\end{document}; \begin{document}$q=u,d,s$\end{document}) tetraquark states with the aid of heavy diquark-antiquark symmetry (HDAS) and the chromomagnetic interaction (CMI) model. The masses of the highest-spin (\begin{document}$J=2$\end{document}) tetraquarks that have only the \begin{document}$(QQ)_{\bar{3}_c}(\bar{q}\bar{q})_{3_c}$\end{document}color structure are related with those of conventional hadrons using HDAS. Thereafter, the masses of their partner states are determined with the mass splittings in the CMI model. Our numerical results reveal that (i) the lightest \begin{document}$cc\bar{n}\bar{n}$\end{document} (\begin{document}$n=u,d$\end{document}) is an \begin{document}$I(J^P)=0(1^+)$\end{document} state around 3929 MeV (53 MeV above the \begin{document}$DD^*$\end{document} threshold), and none of the double-charm tetraquarks are stable; (ii) the stable double-bottom tetraquarks are the lowest \begin{document}$0(1^+)$\end{document} \begin{document}$bb\bar{n}\bar{n}$\end{document} around 10488 MeV (\begin{document}$\approx116$\end{document} MeV below the \begin{document}$\bar{B}\bar{B}^*$\end{document} threshold) and the lowest \begin{document}$1/2(1^+)$\end{document} \begin{document}$bb\bar{n}\bar{s}$\end{document} around 10671 MeV (\begin{document}$\approx20$\end{document} MeV below the \begin{document}$\bar{B}\bar{B}_s^*/\bar{B}_s\bar{B}^*$\end{document} threshold); and (iii) the two lowest \begin{document}$bc\bar{n}\bar{n}$\end{document} tetraquarks, namely the lowest \begin{document}$0(0^+)$\end{document} around 7167 MeV and the lowest \begin{document}$0(1^+)$\end{document} around 7223 MeV, are in the near-threshold states. Moreover, we discuss the constraints on the masses of double-heavy hadrons. Specifically, for the lowest nonstrange tetraquarks, we obtain \begin{document}$T_{cc} < 3965$\end{document} MeV, \begin{document}$T_{bb} < 10627$\end{document} MeV, and \begin{document}$T_{bc} < 7199$\end{document} MeV.
2021, 45(4): 043103. doi: 10.1088/1674-1137/abdeab
Abstract:
In this paper, we consider a set of new symmetries in the SM: diagonal reflection symmetries \begin{document}$R \, m_{u,\nu}^{*} \, R = m_{u,\nu}, m_{d,e}^{*} = m_{d,e}$\end{document} with \begin{document}$R =$\end{document} diag \begin{document}$(-1,1,1)$\end{document}. These generalized \begin{document}$CP$\end{document} symmetries predict the Majorana phases to be \begin{document}$\alpha_{2,3} /2 \sim 0$\end{document} or \begin{document}$\pi /2$\end{document}. Realization of diagonal reflection symmetries implies a broken chiral \begin{document}$U(1)_{\rm{PQ}}$\end{document} symmetry only for the first generation. The axion scale is suggested to be \begin{document}$\langle {\theta_{u,d}} \rangle \sim \Lambda_{\rm{GUT}} \, \sqrt{m_{u,d} \, m_{c,s}} / v \sim 10^{12}$\end{document} [GeV]. By combining the symmetries with the four-zero texture, the mass eigenvalues and mixing matrices of quarks and leptons are reproduced well. This scheme predicts the normal hierarchy, the Dirac phase \begin{document}$\delta _{CP} \simeq 203^{\circ},$\end{document} and \begin{document}$|m_{1}| \simeq 2.5$\end{document} or \begin{document}$6.2$\end{document} [meV]. In this scheme, the type-I seesaw mechanism and a given neutrino Yukawa matrix \begin{document}$Y_{\nu}$\end{document} completely determine the structure of the right-handed neutrino mass \begin{document}$M_{R}$\end{document}. A \begin{document}$u-\nu$\end{document} unification predicts the mass eigenvalues to be \begin{document}$(M_{R1} \, , M_{R2} \, , M_{R3}) = (O (10^{5}) \, , O (10^{9}) \, , O (10^{14}))$\end{document} [GeV].
2021, 45(4): 043104. doi: 10.1088/1674-1137/abdea7
Abstract:
We investigate the dynamics of a strong first-order quark-hadron transition driven by cubic interactions via homogeneous bubble nucleation in the Friedberg-Lee model. The one-loop effective thermodynamic potential of the model and the critical bubble profiles have been calculated at different temperatures and chemical potentials. By taking the temperature and the chemical potential as variables, the evolutions of the surface tension, the typical radius of the critical bubble, and the shift in the coarse-grained free energy in the presence of a nucleation bubble are obtained, and the limit on the reliability of the thin-wall approximation is also addressed accordingly. Our results are compared to those obtained for a weak first-order quark-hadron phase transition; in particular, the spinodal decomposition is relevant.
2021, 45(4): 043105. doi: 10.1088/1674-1137/abdea9
Abstract:
Electro-production of several pentaquark states is investigated in this study. The eSTARlight package is adapted to study the electro-production of \begin{document}$J/\psi$\end{document} and \begin{document}$\Upsilon (1S)$\end{document} via pentaquark \begin{document}$P_c$\end{document} and \begin{document}$P_b$\end{document} resonance channels in \begin{document}$e p \to e J/\psi p$\end{document} and \begin{document}$e p \to e \Upsilon(1S) p$\end{document} scattering processes at the proposed electron-ion colliders (EICs). The results obtained in this study are compared to those of non-resonance t-channels, which are described in the pomeron exchange model developed in our studies. Some pseudo-rapidity and rapidity distributions of \begin{document}$J/\psi$\end{document} and \begin{document}$\Upsilon(1S)$\end{document} are presented for the proposed EICs, including EicC and EIC-US. It is found that EicC is a good platform to identify \begin{document}$P_b$\end{document} states in the future.
2021, 45(4): 043106. doi: 10.1088/1674-1137/abdfbf
Abstract:
We investigate the thermodynamics and stability of the horizons in warped anti-de Sitter black holes of the new massive gravity under the scattering of a massive scalar field. Under scattering, conserved quantities can be transferred from the scalar field to the black hole, thereby changing the state of the black hole. We determine that the changes in the black hole are well coincident with the laws of thermodynamics. In particular, the Hawking temperature of the black hole cannot be zero in the process as per the third law of thermodynamics. Furthermore, the black hole cannot be overspun beyond the extremal condition under the scattering of any mode of the scalar field.
2021, 45(4): 043107. doi: 10.1088/1674-1137/abe03b
Abstract:
We studied the condensate mass of QCD vacuum through the duality approach via dilaton wall background in the presence of the parameter \begin{document}$c$\end{document}, which represents the condensation in a holographic set up. First, from Wilson line calculation, we found \begin{document}$m_0^2$\end{document} (i.e., the condensate parameter in mixed non-local condensation), whose behavior mimics that of QCD. The value of \begin{document}$m_0^2$\end{document} that we found by this approach is in agreement with QCD data. Second, we considered the produced mass \begin{document}$m$\end{document} via the Schwinger effect mechanism in the presence of the parameter \begin{document}$c$\end{document}. We show that vacuum condensation generally contributes the mass dominantly and that the produced mass via Schwinger effect is suppressed by \begin{document}$m_0$\end{document}.
2021, 45(4): 043108. doi: 10.1088/1674-1137/abe0bc
Abstract:
The discovery of \begin{document}$\Xi_{cc}^{++}$\end{document} has inspired new interest in studying doubly heavy baryons. In this study, the weak decays of a doubly charmed baryon \begin{document}${\cal B}_{cc}$\end{document} to a light baryon \begin{document}${\cal B}$\end{document} and a charm meson \begin{document}$D^{(*)}$\end{document} (either a pseudoscalar or a vector one) are calculated. Following our previous work, we calculate the short distance contributions under the factorization hypothesis, whereas the long distance contributions are modeled as the final state interactions, which are calculated with the one particle exchange model. We find that the \begin{document}${\cal B}_{cc}\to {\cal B} D^{*}$\end{document} decays' branching ratios are obviously larger, as they receive contributions of more polarization states. Among the decays that we investigate, the following have the largest branching fractions: \begin{document}${\cal BR}(\Xi_{cc}^{++}\rightarrow\Sigma^{+}D^{*+}) \in [0.46 \%, 3.33 \%]$\end{document} estimated with \begin{document}$\tau_{\Xi_{cc}^{++}} = 256$\end{document} fs; \begin{document}${\cal BR}(\Xi_{cc}^{+}\rightarrow\Lambda D^{*+}) \in [0.38 \%, 2.63 \%]$\end{document} and \begin{document}${\cal BR}(\Xi_{cc}^{+}\rightarrow\Sigma^{0} D^{*+}) \in [0.45 \%, 3.16 \%]$\end{document} with \begin{document}$\tau_{\Xi_{cc}^+} = 45$\end{document} fs; and \begin{document}${\cal BR}(\Omega_{cc}^{+}\rightarrow \Xi^{0} D^{*+}) \in [0.27 \%, 1.03 \%]$\end{document}, \begin{document}${\cal BR}(\Omega_{cc}^{+}\rightarrow\Xi^{0} D^{+}) \in [0.07 \%, 0.44 \%]$\end{document}, and \begin{document}${\cal BR}(\Omega_{cc}^{+}\rightarrow\Sigma^{0} D^{*+}) \in [0.06 \%, 0.45 \%]$\end{document} with \begin{document}$\tau_{\Omega_{cc}^+} = 75$\end{document} fs. By comparing the decay widths of pure color commensurate channels with those of pure bow-tie ones, we find that the bow-tie mechanism plays an important role in charm decays.
2021, 45(4): 043109. doi: 10.1088/1674-1137/abe0be
Abstract:
In this study, light-by-light (LBL) scattering with initial polarized Compton backscattered photons at the CLIC, induced by axion-like particles (ALPs), is investigated. The total cross sections are calculated assuming CP-even coupling of the pseudoscalar ALP to photons. The 95% C.L. exclusion region for the ALP mass \begin{document}$m_a$\end{document} and its coupling constant f is presented. The results are compared with CLIC bounds previously obtained for the unpolarized case. It is shown that the bounds on f for the polarized beams in the region \begin{document}$m_a = 1000 - 2000 \;{\rm{GeV}}$\end{document} with collision energy of 3000 GeV and integrated luminosity of 4000 fb\begin{document}$^{-1}$\end{document} are on average 1.5 times stronger than the bounds for the unpolarized beams. Moreover, our CLIC bounds are stronger than those for all current exclusion regions for \begin{document}$m_a > 80$\end{document} GeV. In particular, they are more restrictive than the limits that follow from the ALP-mediated LBL scattering at the LHC.
2021, 45(4): 043110. doi: 10.1088/1674-1137/abe0c0
Abstract:
We investigate the prospect of discovering the Flavour Changing Neutral Current (FCNC) \begin{document}$tqZ$\end{document} couplings via two production processes yielding trilepton signals: top quark pair production \begin{document}$pp\to t\bar{t}$\end{document} with one top quark decaying to the Z boson and one light jet and the anomalous single top quark plus Z boson production process \begin{document}$pp\to tZ$\end{document}. We study these channels at various successors of the Large Hadron Collider (LHC), i.e., the approved High-Luminosity LHC (HL-LHC) as well as the proposed High-Energy LHC (HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh). We perform a full simulation for the signals and the relevant Standard Model (SM) backgrounds and obtain limits on the Branching Ratios (BRs) of \begin{document}$t\to qZ\; (q = u,c)$\end{document}, eventually yielding a trilepton final state through the decay modes \begin{document}$t\to b W^{+}\to b\ell^{+}\nu_{\ell}$\end{document} and \begin{document}$Z\to \ell^{+}\ell^{-}$\end{document}. The upper limits on these FCNC BRs at 95% Confidence Level (CL) are obtained at the HL-LHC with \begin{document}$\sqrt s = 14$\end{document} TeV and 3 ab−1, at the HE-LHC with \begin{document}$\sqrt s = 27$\end{document} TeV and 15 ab−1, and at the FCC-hh with \begin{document}$\sqrt s = 100$\end{document} TeV and 30 ab−1.
2021, 45(4): 043111. doi: 10.1088/1674-1137/abe198
Abstract:
In this paper, we consider \begin{document}$(n+1)$\end{document}-dimensional topological dilaton de Sitter black holes with a power-Maxwell field as thermodynamic systems. The thermodynamic quantities corresponding to the black hole horizon and the cosmological horizon are interrelated. Therefore, the total entropy of the space-time should be the sum of the entropies of the black hole horizon and the cosmological horizon plus a correction term which is produced by the association of the two horizons. We analyze the entropic force produced by the correction term at given temperatures, which is affected by the parameters and dimensions of the space-time. It is shown that the change of entropic force with the position ratio of the two horizons in some regions is similar to that of the variation of the Lennard-Jones force with the position of particles. If the effect of entropic force is similar to that of the Lennard-Jones force, and other forces are absent, the motion of the cosmological horizon relative to the black hole horizon should have an oscillating process. The entropic force between the two horizons is probably one of the participants in driving the evolution of the universe.
2021, 45(4): 043112. doi: 10.1088/1674-1137/abe1c7
Abstract:
A multiscalar and nonrenormalizable \begin{document}$B-L$\end{document} extension of the standard model (SM) with \begin{document}$S_4$\end{document} symmetry which successfully explains the recently observed neutrino oscillation data is proposed. The tiny neutrino masses and their hierarchies are generated via the type-I seesaw mechanism. The model reproduces the recent experiments of neutrino mixing angles and Dirac CP violating phase in which the atmospheric angle \begin{document}$(\theta_{23})$\end{document} and the reactor angle \begin{document}$(\theta_{13})$\end{document} get the best-fit values while the solar angle \begin{document}$(\theta_{12})$\end{document} and Dirac CP violating phase (\begin{document}$\delta$\end{document}) are in \begin{document}$3\, \sigma$\end{document} range of the best-fit value for the normal hierarchy (NH). For the inverted hierarchy (IH), \begin{document}$\theta_{13}$\end{document} gets the best-fit value and \begin{document}$\theta_{23}$\end{document} together with \begin{document}$\delta$\end{document} are in the \begin{document}$1\, \sigma$\end{document} range, while \begin{document}$\theta_{12}$\end{document} is in \begin{document}$3\, \sigma$\end{document} range of the best-fit value. The effective neutrino masses are predicted to be \begin{document}$\langle m_{ee}\rangle=6.81 \,\, {\rm{meV}}$\end{document} for the NH and \begin{document}$\langle m_{ee}\rangle=48.48\,\, {\rm{meV}}$\end{document} for the IH, in good agreement with the most recent experimental data.
2021, 45(4): 044001. doi: 10.1088/1674-1137/abdea8
Abstract:
With the help of the gas-filled recoil spectrometer SHANS and a digital data acquisition system, the fine structure of the \begin{document}$\alpha$\end{document} decay for \begin{document}$^{222}$\end{document}Pa was studied. The nuclides were produced through the 1p3n evaporation channel via the heavy-ion induced fusion evaporation reaction \begin{document}$^{40}$\end{document}Ar + \begin{document}$^{186}$\end{document}W. Based on the ER-\begin{document}$\alpha 1$\end{document}-\begin{document}$\alpha 2$\end{document}-\begin{document}$\alpha 3$\end{document} and \begin{document}$\alpha$\end{document}-\begin{document}$\gamma$\end{document} correlation measurement, three new \begin{document}$\alpha$\end{document} decays were observed in addition to the three branches known previously. The one with the largest \begin{document}$\alpha$\end{document} decay energy was regarded as the ground state to ground state transition. The newly measured \begin{document}$\alpha$\end{document} decay properties of \begin{document}$^{222}$\end{document}Pa were examined in a framework of reduced width.
2021, 45(4): 044002. doi: 10.1088/1674-1137/abdf3f
Abstract:
Dihadron azimuthal correlations containing a high transverse momentum (\begin{document}$p_{T}$\end{document}) trigger particle are sensitive to the properties of the nuclear medium created at RHIC through the strong interactions occurring between the traversing parton and the medium, i.e. jet-quenching. Previous measurements revealed a strong modification to dihadron azimuthal correlations in Au+Au collisions with respect to p+p and d+Au collisions. The modification increases with the collision centrality, suggesting a path-length or energy density dependence to the jet-quenching effect. This paper reports STAR measurements of dihadron azimuthal correlations in mid-central (20%-60%) Au+Au collisions at \begin{document}$\sqrt{s_{\rm{NN}}} = 200$\end{document} GeV as a function of the trigger particle's azimuthal angle relative to the event plane, \begin{document}$\phi_{s} = | \phi_{t}- \psi_{{\rm{EP}}}|$\end{document}. The azimuthal correlation is studied as a function of both the trigger and associated particle \begin{document}$p_{T}$\end{document}. The subtractions of the combinatorial background and anisotropic flow, assuming Zero Yield At Minimum (ZYAM), are described. The correlation results are first discussed with subtraction of the even harmonic (elliptic and quadrangular) flow backgrounds. The away-side correlation is strongly modified, and the modification varies with \begin{document}$\phi_{s}$\end{document}, with a double-peak structure for out-of-plane trigger particles. The near-side ridge (long range pseudo-rapidity \begin{document}$\Delta\eta$\end{document} correlation) appears to drop with increasing \begin{document}$\phi_{s}$\end{document} while the jet-like component remains approximately constant. The correlation functions are further studied with the subtraction of odd harmonic triangular flow background arising from fluctuations. It is found that the triangular flow, while responsible for the majority of the amplitudes, is not sufficient to explain the \begin{document}$\phi_{s}$\end{document}-dependence of the ridge or the away-side double-peak structure. The dropping ridge with \begin{document}$\phi_{s}$\end{document} could be attributed to a \begin{document}$\phi_{s}$\end{document}-dependent elliptic anisotropy; however, the physics mechanism of the ridge remains an open question. Even with a \begin{document}$\phi_{s}$\end{document}-dependent elliptic flow, the away-side correlation structure is robust. These results, with extensive systematic studies of the dihadron correlations as a function of \begin{document}$\phi_{s}$\end{document}, trigger and associated particle \begin{document}$p_{T}$\end{document}, and the pseudo-rapidity range \begin{document}$\Delta\eta$\end{document}, should provide stringent inputs to help understand the underlying physics mechanisms of jet-medium interactions in high energy nuclear collisions.
2021, 45(4): 044003. doi: 10.1088/1674-1137/abe0bd
Abstract:
In this study, 218Ac and 221Th nuclides were produced via the heavy-ion induced fusion evaporation reaction 40Ar + 186W. Their decay properties were studied with the help of the gas-filled recoil spectrometer SHANS and a digital data acquisition system. The cross section ratio between 222Pa and 218Ac was extracted experimentally, with measured value 0.69(9). Two new possible α decay branches to 221Th are suggested. The valence neutron configurations for the daughter 217Ra are discussed in terms of the hindrance factors.
2021, 45(4): 044004. doi: 10.1088/1674-1137/abe196
Abstract:
The cross sections of the 59Co(n, x) reaction in the average energy range of 15.2-37.2 MeV were measured using activation and an off-line γ-ray spectrometric technique. The neutrons were generated from the 9Be(p, n) reaction with proton beam energies of 25-45 MeV at the MC-50 Cyclotron facility of the Korean Institute of Radiological and Medical Sciences (KIRAMS). Theoretical calculations of neutron–induced reactions on 59Co were performed using the nuclear model code TALYS-1.9. The results for the 59Co(n, x) reactions were compared with the theoretical values obtained using TALYS-1.9 and the literature data provided in EXFOR and the TENDL 2019 nuclear data library. The theoretical values obtained using TALYS-1.9 with adjusted parameters are comparable to the experimental data. The measured reaction cross sections of a few radionuclides are new, and the others are comparable to the literature data, and thus, they can strengthen the database. The present study on cross sections leads to useful insight into the mechanisms of 59Co(n, x) reactions.
2021, 45(4): 044101. doi: 10.1088/1674-1137/abde31
Abstract:
A nucleon-nucleus dynamics model was developed to investigate the proton-, neutron-, and deuteron-induced reactions at hundreds of MeV/nucleon. In this model, the trajectory of incident nucleon is described by classical mechanics, and the probability of reaction between the nucleon and nucleus is calculated by exponential damping. It is shown that the total reaction cross sections calculated by the model agree in general with the predictions by the CDCC and the experimental data. The model was applied to investigate the nucleon stripping in deuteron-induced reactions and its symmetry energy dependence.
2021, 45(4): 044102. doi: 10.1088/1674-1137/abdf41
Abstract:
We studied coupled dynamics of hydrodynamic fields and order parameter in the presence of nontrivial longitudinal flow using the chiral fluid dynamics model. We found that longitudinal expansion provides an effective relaxation for the order parameter, which equilibrates in an oscillatory fashion. Similar oscillations are also visible in hydrodynamic degrees of freedom through coupled dynamics. The oscillations are reduced when dissipation is present. We also found that the quark density, which initially peaked at the boundary of the boost invariant region, evolves toward forward rapidity with the peak velocity correlated with the velocity of longitudinal expansion. The peak broadens during this evolution. The corresponding chemical potential rises due to simultaneous decrease of density and temperature. We compared the cases with and without dissipation for the order parameter and also the standard hydrodynamics without order parameter. We found that the corresponding effects on temperature and chemical potential can be understood from the conservation laws and different speeds of equilibration of the order parameter in the three cases.
2021, 45(4): 044103. doi: 10.1088/1674-1137/abdf42
Abstract:
Nuclear \begin{document}$\beta$\end{document}-decay half-lives are predicted based on an empirical formula and the mass predictions from various nuclear models. It is found that the empirical formula can reproduce the nuclear \begin{document}$\beta$\end{document}-decay half-lives well, especially for short-lived nuclei with \begin{document}$T_{1/2}< 1$\end{document} s. The theoretical half-life uncertainties from \begin{document}$\beta$\end{document}-decay energies and the parameters of the empirical formula are further investigated. It is found that the uncertainties of the half-lives are relatively large for heavy nuclei and nuclei near the neutron-drip line. For nuclei on the r-process path, the uncertainties for those with \begin{document}$N = 126$\end{document} are about one order of magnitude, which are much larger than the uncertainties for those with \begin{document}$N = 50$\end{document} and \begin{document}$82$\end{document}. However, theoretical uncertainties from the parameters of the empirical formula are relatively small for the nuclei on the r-process path, which indicates that the empirical formula is very suitable for predicting the \begin{document}$\beta$\end{document}-decay half-lives in r-process simulations.
2021, 45(4): 044104. doi: 10.1088/1674-1137/abdf43
Abstract:
We investigate the chiral phase structure of quark matter with spheroidal momentum-space anisotropy specified by one anisotropy parameter \begin{document}$\xi$\end{document} in the 2+1 flavor quark-meson model. We find that the chiral phase diagram and the location of the critical endpoint (CEP) are significantly affected by the value of \begin{document}$\xi$\end{document}. With an increase in \begin{document}$\xi$\end{document}, the CEP is shifted to lower temperatures and higher quark chemical potentials. In addition, the temperature of the CEP is more sensitive to the anisotropy parameter than the corresponding quark chemical potential, which is the opposite to that from the finite system volume effect. The effects of the momentum anisotropy on the thermodynamic properties and scalar (pseudoscalar) meson masses are also studied at the vanishing quark chemical potential. The numerical results reveal that an increase in \begin{document}$\xi$\end{document} can hinder the restoration of chiral symmetry. We also find that shear viscosity and electrical conductivity decrease as \begin{document}$\xi$\end{document} increases. However, the bulk viscosity exhibits a significant non-trivial behavior with \begin{document}$\xi$\end{document} in the entire temperature domain of interest.
2021, 45(4): 044105. doi: 10.1088/1674-1137/abdfbc
Abstract:
The isovector giant dipole resonances (IVGDR) in proton-rich Ar and Ca isotopes have been systematically investigated using the resonant continuum Hartree-Fock+BCS (HF+BCS) and quasiparticle random phase approximation (QRPA) methods. The Skyrme SLy5 and density-dependent contact pairing interactions are employed in the calculations. In addition to the giant dipole resonances at energy around 18 MeV, pygmy dipole resonances (PDR) are found to be located in the energy region below 12 MeV. The calculated energy-weighted moments of PDR in nuclei close to the proton drip-line exhaust about 4% of the TRK sum rule. The strengths decrease with increasing mass number in each isotopic chain. The transition densities of the PDR states show that motions of protons and neutrons are in phase in the interiors of nuclei, while the protons give the main contribution at the surface. By analyzing the QRPA amplitudes of proton and neutron 2-quasiparticle configurations for a given low-lying state, we find that only a few proton configurations give significant contributions. They contribute about 95% to the total QRPA amplitudes, which indicates that the collectivity of PDR states is not strong in proton-rich nuclei in the present study.
2021, 45(4): 044106. doi: 10.1088/1674-1137/abdfc0
Abstract:
A model for cold-fusion reactions related to the synthesis of super-heavy nuclei in collisions of heavy projectile-nuclei with a 208Pb target nucleus is discussed. In the framework of this model, the production of the compound nucleus by two paths, the di-nuclear system path and the fusion path, are taken into account simultaneously. The formation of the compound nucleus in the framework of the di-nuclear system is related to the transfer of nucleons from the light nucleus to the heavy one. The fusion path is linked to the sequential evolution of the nuclear shape from the system of contacting nuclei to the compound nucleus. It is shown that the compound nucleus is mainly formed by the fusion path in cold-fusion reactions. The landscape of the potential energy related to the fusion path is discussed in detail. This landscape for very heavy nucleus-nucleus systems has an intermediate state, which is linked to the formation of both the compound nucleus and the quasi-fission fragments. The decay of the intermediate state is taken into account in the calculation of the compound nucleus production cross sections and the quasi-fission cross sections. The values of the cold-fusion cross sections obtained in the model agree well with the experimental data.
2021, 45(4): 044107. doi: 10.1088/1674-1137/abe03e
Abstract:
This investigation aims to find an appropriate dinuclear system for the formation of \begin{document}${}^{296}$\end{document}119 superheavy compound nucleus. By studying the driving potential and measuring the capture cross section of the reactions, the evolution of the dinuclear system can be understood. In this study, we obtained capture, fusion, and evaporation residue cross sections and survival probability at energies near the Coulomb barrier for four reactions, namely \begin{document}$^{45}$\end{document}Sc + \begin{document}$^{251}$\end{document}Cf, \begin{document}$^{42}$\end{document}Ca + \begin{document}$^{254}$\end{document}Es, \begin{document}$^{39}$\end{document}K + \begin{document}$^{257}$\end{document}Fm, and \begin{document}$^{38}$\end{document}Ar + \begin{document}$^{258}$\end{document}Md. Our calculations show that the reaction \begin{document}$^{38}$\end{document}Ar + \begin{document}$^{258}$\end{document}Md is a suitable choice for the formation of an element with 119 protons among the studied reactions from a theoretical viewpoint.
2021, 45(4): 044108. doi: 10.1088/1674-1137/abe03f
Abstract:
The dependence of proton emission half-lives on the nuclear asymmetry parameter is investigated using the WKB method and two types of empirical formula. Using the single-folding formalism with asymmetry-dependent nuclear radius and surface diffuseness of nuclear matter, the nuclear potential and consequently the half-life are functions of the asymmetry factor. Despite small values of asymmetry in neutron-deficient proton emitters, noticeable changes in the half-lives are observed. The addition of an asymmetry parameter term to the two forms of empirical formulas leads to a reduction in the rms error for ground state and isomeric transitions. A noticeable reduction of about 43% is obtained for isomeric transitions in the second form of the empirical formula. Considering ground state transitions in two categories, odd-even and odd-odd emitters, and adopting deformation and asymmetry-dependent empirical formulas, the rms decreases remarkably. The lowest values of rms errors, viz. 0.1492, 0.2312, and 0.1999, are obtained for the aforementioned empirical formulas for ground state transitions of odd-even and odd-odd emitters and for all isomeric transitions, respectively.
2021, 45(4): 044109. doi: 10.1088/1674-1137/abe10e
Abstract:
Transport models cannot simultaneously explain very recent data on pion multiplicities and pion charged ratios from central collision of Sn+Sn at 0.27 A GeV. This stimulates further investigations on the pion dispersion relation, in-medium \begin{document}$N\pi\to \Delta$\end{document} cross sections, and \begin{document}$\Delta \to N \pi$\end{document} decay widths near the threshold energy or at subthreshold energy of pion production in isospin asymmetric nuclear matter. In this study, the pion dispersion relation, in-medium \begin{document}$N\pi\to \Delta$\end{document} cross section, and \begin{document}$\Delta \to N \pi$\end{document} decay width near the threshold energy are investigated in isospin asymmetric nuclear matter by using the one-boson-exchange model. With the consideration of the energy conservation effect, the in-medium \begin{document}$N\pi\to\Delta$\end{document} cross sections are enhanced at \begin{document}$s^{1/2}<1.11$\end{document} GeV in a nuclear medium. The prediction of pion multiplicity and \begin{document}$\pi^-/\pi^+$\end{document} ratios near the threshold energy could be modified if this effect is considered in transport model simulations.
2021, 45(4): 044110. doi: 10.1088/1674-1137/abe10f
Abstract:
In this study, based on the Gamow-like model, we systematically analyze two-proton (\begin{document}$2p$\end{document}) radioactivity half-lives of nuclei near or beyond the proton drip line. It is found that the calculated results can reproduce experimental data well. Furthermore, using this model, we predict the half-lives of possible \begin{document}$2p$\end{document} radioactivity candidates whose \begin{document}$2p$\end{document} radioactivity is energetically allowed or observed but not yet quantified in the latest table of evaluated nuclear properties, i.e., NUBASE2016. The predicted results are in good agreement with those from other theoretical models and empirical formulas, namely the effective liquid drop model (ELDM), generalized liquid drop model (GLDM), Sreeja formula, and Liu formula.
2021, 45(4): 044111. doi: 10.1088/1674-1137/abe112
Abstract:
An improved semi-empirical relationship for cluster radioactivity half-lives is proposed by introducing an accurate charge radius formula and an analytic expression of the preformation probability. Moreover, the cluster radioactivity half-lives for the daughter nuclei around 208Pb or its neighbors and the 12C radioactivity half-life of 114Ba are calculated within the improved semi-empirical relationship. It is shown that the accuracy of the new relationship is improved significantly compared to its predecessor. In addition, the cluster radioactivity half-lives that are experimentally unavailable for the trans-lead and trans-tin nuclei are predicted by the new semi-empirical formula. These predictions might be useful for searching for the new cluster emitters of the two islands in future experiments.
2021, 45(4): 044112. doi: 10.1088/1674-1137/abe199
Abstract:
Correlations of conserved charges, i.e., the baryon number, electric charge, and strangeness, are calculated at finite temperature and chemical potentials up to the fourth order. The calculations are done in a 2+1 flavor low energy effective theory, in which the quantum and thermal fluctuations are encoded through the evolution of flow equations within the functional renormalization group approach. Strangeness neutrality and a fixed ratio of the electric charge to the baryon number density are implemented throughout the computation. We find that higher-order correlations incorporate more sensitive critical dynamics than the quadratic ones. In addition, a non-monotonic dependence of the fourth-order correlations between the baryon number and strangeness, i.e., \begin{document}$-\chi^{BS}_{31}/\chi^{S}_{2}$\end{document} and \begin{document}$\chi^{BS}_{22}/\chi^{S}_{2}$\end{document}, on the collision energy is also observed.
2021, 45(4): 045001. doi: 10.1088/1674-1137/abde30
Abstract:
The current-mode-counting method is a new approach to observing transient processes, especially in transient nuclear fusion, based on the non-homogeneous Poisson process (NHPP) model. In this paper, a new measurement process model of the pulsed radiation field produced by transient nuclear fusion is built based on the NHPP. A simulated measurement is performed using the model, and the current signal from the detector is obtained by simulation based on Poisson process thinning. The neutron time spectrum is reconstructed and is in good agreement with the theoretical value, with its maximum error of a characteristic parameter less than 2.3%. Verification experiments were carried out on a CPNG-6 device at the China Institute of Atomic Energy, with a detection system with a nanosecond response time. The experimental charge amplitude spectra are in good agreement with those obtained by the traditional counting mode, and the characteristic parameters of the time spectrum are in good agreement with the theoretical values. This shows that the current-mode-counting method is effective for the observation of transient nuclear fusion processes.
2021, 45(4): 045002. doi: 10.1088/1674-1137/abe195
Abstract:
Direct detection experiments tend to lose sensitivity in searches for sub-MeV light dark matter candidates due to the threshold of recoil energy. However, such light dark matter particles could be accelerated by energetic cosmic rays, such that they could be detected with existing detectors. We derive constraints on the scattering of a boosted light dark matter particle and electron from the XENON100/1T experiment. We illustrate that the energy dependence of the cross section plays a crucial role in improving both the detection sensitivity and also the complementarity of direct detection and other experiments.
2021, 45(4): 045101. doi: 10.1088/1674-1137/abdeaa
Abstract:
The LHAASO-WFCTA experiment, which aims to observe cosmic rays in the sub-EeV range using the fluorescence technique, uses a new generation of high-performance telescopes. To ensure that the experiment has excellent detection capability associated with the measurement of the energy spectrum, the primary composition of cosmic rays, and so on, an accurate geometrical reconstruction of air-shower events is fundamental. This paper describes the development and testing of geometrical reconstruction for stereo viewed events using the WFCTA (Wide Field of view Cherenkov/Fluorescence Telescope Array) detectors. Two approaches, which take full advantage of the WFCTA detectors, are investigated. One is the stereo-angular method, which uses the pointing of triggered SiPMs in the shower trajectory, and the other is the stereo-timing method, which uses the triggering time of the fired SiPMs. The results show that both methods have good geometrical resolution; the resolution of the stereo-timing method is slightly better than the stereo-angular method because the resolution of the latter is slightly limited by the shower track length.
2021, 45(4): 045102. doi: 10.1088/1674-1137/abdfbd
Abstract:
This work suggests a new model for anisotropic compact stars with quintessence in \begin{document}$f(T)$\end{document} gravity by using the off-diagonal tetrad and the power-law as \begin{document}$f(T)=\beta T^n$\end{document}, where T is the scalar torsion and \begin{document}$\beta$\end{document} and n are real constants. The acquired field equations incorporating the anisotropic matter source along with the quintessence field, in \begin{document}$f(T)$\end{document} gravity, are investigated by making use of the specific character of the scalar torsion T for the observed stars \begin{document}${\rm{PSRJ1614}}-2230$\end{document}, \begin{document}$4U 1608-52$\end{document}, \begin{document}${\rm{Cen}} X-3$\end{document}, \begin{document}${\rm{EXO1785}}-248$\end{document}, and \begin{document}$SMC X-1$\end{document}. It is suggested that all the stellar structures under examination are advantageously independent of any central singularity and are stable. Comprehensive graphical analysis shows that various physical features which are crucially important for the emergence of the stellar structures are conferred.
2021, 45(4): 045103. doi: 10.1088/1674-1137/abe0bf
Abstract:
In this paper, we study three scalar fields, namely the quintessence, phantom, and tachyon fields, to explore the source of dark energy via the Gaussian processes method from the background and perturbation growth rate data. The corresponding reconstructions suggest that the dark energy should be dynamical. Moreover, the quintom field, which is a combination of the quintessence and phantom fields, is powerfully favored by the reconstruction. The mean values indicate that the potential \begin{document}$V(\phi)$\end{document} in the quintessence field is a double exponential function, whereas \begin{document}$V(\phi)$\end{document} in the phantom field is a double Gaussian function. This reconstruction can provide an important reference for the scalar field study. The two types of data employed reveal that the tachyon field is disadvantageous for describing the cosmic acceleration.
2021, 45(4): 045104. doi: 10.1088/1674-1137/abe111
Abstract:
In this paper, we study the dynamics of k-essence in loop quantum cosmology (LQC). The study indicates that the loop quantum gravity (LQG) effect plays a key role only in the early epoch of the universe and is diluted in the later stages. The fixed points in LQC are basically consistent with those in standard Friedmann-Robertson-Walker (FRW) cosmology. For most of the attractor solutions, the stability conditions in LQC are in agreement with those for the standard FRW universe. For some special fixed points, however, tighter constraints are imposed thanks to the LQG effect.
2021, 45(4): 045105. doi: 10.1088/1674-1137/abe19a
Abstract:
In four-dimensional Einstein-Gauss-Bonnet (EGB) gravity, we consider the thermodynamic and phase transitions of (charged) AdS black holes. For the negative GB coefficient \begin{document}$\alpha<0$\end{document}, the system allows two physical critical points, corresponding to the reentrant phase transition, when the charge \begin{document}$Q>2\sqrt{-\alpha}$\end{document}. For arbitrary \begin{document}$\alpha>0$\end{document}, the system always leads to a van der Waals phase transition. We then study the quasinormal modes (QNMs) of massless scalar perturbations to probe the van der Waals-like phase transition between small and large black holes (SBH/LBH) for (charged) AdS black holes. We find that the signature of this SBH/LBH phase transition in the isobaric process can be detected since the slopes of the QNM frequencies change dramatically in small and large black holes near the critical point. The obtained results further support that QNMs can be a dynamic probe of thermodynamic properties in black holes.
2021, 45(4): 045106. doi: 10.1088/1674-1137/abe19b
Abstract:
In this work, we study the implications of Higgs precision measurements at future Higgs factories for the MSSM parameter space, focusing on the dominant stop sector contributions. We perform a multi-variable fit to both the signal strength for various Higgs decay channels at Higgs factories and the Higgs mass. The χ2 fit results show sensitivity to mA, tan β, stop mass parameter mSUSY , and the stop left-right mixing parameter Xt. We also study the impact of the Higgs mass prediction on the MSSM and compare the sensitivities of different Higgs factories.