2018 Vol. 42, No. 12

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Strong decays of P-wave mixing heavy-light 1+ states
Zhi-Hui Wang, Yi Zhang, Tian-Hong Wang, Yue Jiang, Qiang Li, Guo-Li Wang
2018, 42(12): 123101. doi: 10.1088/1674-1137/42/12/123101
Many P-wave mixing heavy-light 1+ states have not yet been discovered by experiment, while others have been discovered but without width information, or with large uncertainties on the widths. In this paper, the strong decays of the P-wave mixing heavy-light 1+ states D0, D±, Ds±, B0, B± and Bs are studied by the improved Bethe-Salpeter (B-S) method with two conditions of mixing angle θ:one is θ=35.3°; the other is considering a correction to the mixing angle θ=35.3°+θ1. Valuable predictions for the strong decay widths are obtained:Γ(D1'0)=232 MeV, Γ(D10)=21.5 MeV, Γ(D1)=232 MeV, Γ(D1±)=21.5 MeV, Γ(Ds1)=0.0101 MeV, Γ(Ds1±)=0.950 MeV, Γ(B1)=263 MeV, Γ(B1±)=16.8 MeV, Γ(Bs1')=0.01987 MeV and Γ(Bs1)=0.412 MeV. It is found that the decay widths of Ds1± and Bs1 are very sensitive to the mixing angle. The results will provide theoretical assistance to future experiments.
Weak decays of doubly heavy baryons: “decay constants”
Xiao-Hui Hu, Yue-Long Shen, Wei Wang, Zhen-Xing Zhao
2018, 42(12): 123102. doi: 10.1088/1674-1137/42/12/123102
Inspired by the recent observation of the Ξcc++ by the LHCb Collaboration, we explore the "decay constants" of doubly heavy baryons in the framework of QCD sum rules. With the Ξcc, Ξbc, Ξbb, and Ωcc, Ωbc, Ωbb baryons interpolated by three-quark operators, we calculate the correlation functions using the operator product expansion and include the contributions from operators up to dimension six. On the hadron side, we consider both contributions from the lowest-lying states with JP=1/2+ and from negative parity baryons with JP=1/2-. We find that the results are stable and the contaminations from negative parity baryons are not severe. These results are ingredients for the QCD study of weak decays and other properties of doubly-heavy baryons.
Pseudo-rapidity distribution from a perturbative solution of viscous hydrodynamics for heavy ion collisions at RHIC and LHC
Ze-Fang Jiang, C. B. Yang, Chi Ding, Xiang-Yu Wu
2018, 42(12): 123103. doi: 10.1088/1674-1137/42/12/123103
The charged-particle final state spectrum is derived from an analytic perturbative solution for relativistic viscous hydrodynamics. By taking into account the longitudinal acceleration effect in relativistic viscous hydrodynamics, the pseudorapidity spectrum describes the nucleus-nucleus colliding systems at RHIC and the LHC well. Based on both the extracted longitudinal acceleration parameter λ* and a phenomenological description of λ*, the charged-particle pseudorapidity distributions for √sNN=5.44 TeV Xe+Xe collisions are computed from the final state expression in a limited space-time rapidity ηs region.
Charged current quasi-elastic scattering of νμ off 12C
Deepika Grover, Kapil Saraswat, Prashant Shukla, Venktesh Singh
2018, 42(12): 123104. doi: 10.1088/1674-1137/42/12/123104
In this work, we study charged current quasi-elastic scattering (QES) of νμ off nucleon and nucleus using a formalism based on the Llewellyn Smith (LS) model. Parameterizations by Galster et al. are used for electric and magnetic Sach's form factors of the nucleons. We use the Fermi gas model along with the Pauli suppression condition to take into account the nuclear effects in the anti-neutrino—nucleus QES. We calculate νμ - p and νμ -12C charged current quasi-elastic scattering differential and total cross sections for different values of axial mass MA, and compare the results with data from the GGM, SKAT, BNL, NOMAD, MINERνA and MiniBooNE experiments. The present theoretical approach gives a good description of differential cross section data. The calculations with axial mass MA=0.979 and 1.05 GeV are compatible with data from most of the experiments.
Discussion of thermodynamic features within the PNJL model
Jin-Li Zhang, Cheng-Ming Li, Hong-Shi Zong
2018, 42(12): 123105. doi: 10.1088/1674-1137/42/12/123105
We discuss some thermodynamical features of a QCD system within the two-flavor Polyakov loop extended Nambu—Jona-Lasinio (PNJL) model. Several thermodynamical quantities of interest (pressure, energy density, specific heat, speed of sound, etc.) are investigated and discussed in detail with two different forms of Polyakov loop potential. The effective coupling strength G incorporating a quark feedback (quark condensate) through operator product expansion is also discussed, as well as the relationship between color deconfinement and chiral phase crossover. We find that some thermodynamical quantities have quite different behavior for different Polyakov loop potentials. By changing the characteristic temperature T0 of the pure Yang-Mills field, we find that when T0 becomes small, color deconfinement might happen earlier than chiral phase crossover, while their relationship can be determined via some thermodynamical quantities. Furthermore, the behavior of the thermodynamical quantities is quite different in the two different forms of Polyakov loop potential studied. Especially, one of the potentials, specific heat, has two peaks, which correspond to color deconfinement and chiral phase crossover respectively. This interesting phenomenon may shed some light on whether the inflection points of the chiral condensate and deconfinement transitions happen at the same temperature or not for lattice QCD and experimental studies.
A model with flavor-dependent gauged U(1)B-L1×U(1)B-L2-L3 symmetry
Linping Mu, Hiroshi Okada, Chao-Qiang Geng
2018, 42(12): 123106. doi: 10.1088/1674-1137/42/12/123106
We propose a new model with flavor-dependent gauged U(1)B-L1×U(1)B-L2-L3 symmetry in addition to the flavor-blind symmetry in the Standard Model. The model contains three right-handed neutrinos to cancel gauge anomalies and several Higgs bosons to construct the measured fermion masses. We show the generic features of the model and explore its phenomenology. In particular, we discuss the current bounds on the extra gauge bosons from the K and B meson mixings as well as the LEP and LHC data, and focus on their contributions to the lepton flavor violating processes of li+1liγ (i=1,2).
Probing top-quark couplings indirectly at Higgs factories
Gauthier Durieux, Jiayin Gu, Eleni Vryonidou, Cen Zhang
2018, 42(12): 123107. doi: 10.1088/1674-1137/42/12/123107
We perform a global effective-field-theory analysis to assess the combined precision of Higgs couplings, triple gauge-boson couplings, and top-quark couplings, at future circular e+e- colliders, with a focus on runs below the tt production threshold. Deviations in the top-quark sector entering as one-loop corrections are consistently taken into account in the Higgs and diboson processes. We find that future lepton colliders running at center-of-mass energies below the tt production threshold can still provide useful information on top-quark couplings, by measuring virtual top-quark effects. With rate and differential measurements, the indirect individual sensitivity achievable is better than at the high-luminosity LHC. However, strong correlations between the extracted top-quark and Higgs couplings are also present and lead to much weaker global constraints on top-quark couplings. This implies that a direct probe of top-quark couplings above the tt production threshold is also helpful for the determination of Higgs and triple-gauge-boson couplings. In addition, we find that below the e+e-tth production threshold, the top-quark Yukawa coupling can be determined by its loop corrections to all Higgs production and decay channels. Degeneracy with the ggh coupling can be resolved, and even a global limit is competitive with the prospects of a linear collider above the threshold. This provides an additional means of determining the top-quark Yukawa coupling indirectly at lepton colliders.
Correlation of normal neutrino mass ordering with upper octant of θ23 and third quadrant of δ via RGE-induced μ-τ symmetry breaking
Guo-yuan Huang, Zhi-zhong Xing, Jing-yu Zhu
2018, 42(12): 123108. doi: 10.1088/1674-1137/42/12/123108
The recent global analysis of three-flavor neutrino oscillation data indicates that the normal neutrino mass ordering is favored over the inverted one at the 3σ level, and the best-fit values of the largest neutrino mixing angle θ23 and the Dirac CP-violating phase δ are located in the higher octant and third quadrant, respectively. We show that all these important issues can be naturally explained by the μ-τ reflection symmetry breaking of massive neutrinos from a superhigh energy scale down to the electroweak scale owing to the one-loop renormalization-group equations (RGEs) in the minimal supersymmetric standard model (MSSM). The complete parameter space is explored for the first time in both the Majorana and Dirac cases, by allowing the smallest neutrino mass m1 and the MSSM parameter tanβ to vary within their reasonable regions.
R4 corrections to holographic Schwinger effect
Fei Li, Zi-qiang Zhang, Gang Chen
2018, 42(12): 123109. doi: 10.1088/1674-1137/42/12/123109
We consider R4 corrections to the holographic Schwinger effect in an AdS black hole background and a confining D3-brane background. The potential between a test particle pair are performed for both backgrounds. We find there is no potential barrier in the critical electric field, which means that the system becomes catastrophically unstable. It is shown that for both backgrounds, increasing the inverse't Hooft coupling parameter 1/λ enhances the Schwinger effect. We also discuss the possible relation between the Schwinger effect and the viscosity-entropy ratio η/s in strong coupling.
Conformal field theory on the horizon of a BTZ black hole
Jing-Bo Wang, Chao-Guang Huang
2018, 42(12): 123110. doi: 10.1088/1674-1137/42/12/123110
In a three-dimensional spacetime with negative cosmological constant, general relativity can be written as two copies of SO(2,1) Chern-Simons theory. On a manifold with a boundary, the Chern-Simons theory induces a conformal field theory—Wess-Zumino-Witten theory on the boundary. In this paper, it is shown that with suitable boundary conditions for a Banados-Teitelboim-Zanelli black hole, the Wess-Zumino-Witten theory can reduce to a chiral massless scalar field on the horizon.
Double differential cross sections of light charged particle production for the n+238U reaction
Hai-Rui Guo, Yin-Lu Han, Chong-Hai Cai
2018, 42(12): 124101. doi: 10.1088/1674-1137/42/12/124101
Production of light complex particles from the n+238U reaction is analyzed with the exciton model including the improved Iwamoto-Harada pickup mechanism for the preequilibrium process. It is allowed that some of the nucleons forming the complex ejectile come from levels below the Fermi energy, and the intrinsic structure of the emitted particle is taken into account. The equilibrium-state emissions are also considered by using Hauser-Feshbach theory with the width fluctuation correction and the evaporation model. Moreover, all cross sections, angular distributions, energy spectra and double differential cross sections of neutron, proton, deuteron, triton and alpha emissions for the n+238U reaction are consistently calculated and analyzed with nuclear theoretical models in the energy range En ≤ 150 MeV. ENDF-formatted nuclear data including information about the production of light charged particles are obtained.
Woods-Saxon-Gaussian potential and alpha-cluster structures ofalpha + closed shell nuclei
Dong Bai, Zhongzhou Ren
2018, 42(12): 124102. doi: 10.1088/1674-1137/42/12/124102
The Woods-Saxon-Gaussian (WSG) potential is proposed as a new phenomenological potential to systematically describe the level scheme, electromagnetic transitions, and alpha-decay half-lives of the alpha-cluster structures in various alpha + closed shell nuclei. It modifies the original Woods-Saxon (WS) potential with a shifted Gaussian factor centered at the nuclear surface. The free parameters in the WSG potential are determined by reproducing the correct level scheme of 212Po=208Pb+α. It is found that the resulting WSG potential matches the M3Y double-folding potential at the surface region and makes corrections to the inner part of the cluster-core potential. It was also determined that the WSG potential, with nearly identical parameters to that of 212Po (except for a rescaled radius), could also be used to describe alpha-cluster structures in 20Ne=16O+α and 44Ti=40Ca+α. In all three cases, the calculated values of the level schemes, electromagnetic transitions, and alpha-decay half-lives agree with the experimental data, which indicates that the WSG potential could indeed capture many important features of the alpha-cluster structures in alpha + closed shell nuclei. This study is a useful complement to the existing cluster-core potentials in literature. The Gaussian form factor centered at the nuclear surface might also help to improve our understanding of the alpha-cluster formation, which occurs in the same general region.
The study of gluon energy loss in cold nuclear matter from J/ψ production
Li-Hua Song, Lin-Wan Yan, Shang-Fei Xin
2018, 42(12): 124103. doi: 10.1088/1674-1137/42/12/124103
The energy loss effects of the incident quark, gluon, and the color octet cc on J/ψ suppression in p-A collisions are studied by means of the experimental data at E866, RHIC, and LHC energy. We extracted the transport coefficient for gluon energy loss from the E866 experimental data in the middle xF region (0.20 < xF < 0.65) based on the Salgado-Wiedemann (SW) quenching weights and the recent EPPS16 nuclear parton distribution functions together with nCTEQ15. It was determined that the difference between the values of the transport coefficient for light quark, gluon, and heavy quark in cold nuclear matter is very small. The theoretical results modified by the parton energy loss effects are consistent with the experimental data for E866 and RHIC energy, and the gluon energy loss plays a remarkable role on J/ψ suppression in a broad variable range. Because the corrections of the nuclear parton distribution functions in the J/ψ channel are significant at LHC energy level, the nuclear modification due to the parton energy loss is minimal. It is worth noting that we use the color evaporation model (CEM) at leading order to compute the p-p baseline, and the conclusion in this paper is CEM model dependent.
Analytical description of shape transition in nuclearalternating parity bands
E. V. Mardyban, T. M. Shneidman, E. A. Kolganova, R. V. Jolos, S. -G. Zhou
2018, 42(12): 124104. doi: 10.1088/1674-1137/42/12/124104
The angular momentum dependencies of parity splitting and electric dipole transitions in the alternating parity bands of heavy nuclei have been analyzed. It is shown that these dependencies can be treated in a universal manner with a single critical angular momentum parameter, which characterizes phase transition from octupole vibrations to the stable octupole deformation. Using the simple but useful model of axially-symmetric reflection-asymmetric mode, the analytical expressions for parity splitting and electric dipole transitional moment have been obtained. The findings are in good agreement with the experimental data for various isotopes of Ra, Th, U, and Pu.
Systematic description of nuclear electric quadrupole moments
Xiao-Jun Sun, Chun-Xing Chen, Ning Wang, Hou-Bing Zhou
2018, 42(12): 124105. doi: 10.1088/1674-1137/42/12/124105
The nuclear electric quadrupole moment (NQM) is one of the fundamental bulk properties of the nucleus with which nuclear deformations can be investigated. The number of measured NQMs is significantly less than that of known masses, and there is still no global NQM formula for all bound nuclei. In this paper, we propose an analytical formula, which includes the shell corrections and which is the function of the charge number, mass number, spin, charge radius, and nuclear deformation, for calculating the NQMs of all bound nuclei. Our calculated NQMs of 524 nuclei in their ground states are reasonable compared to the experimental data based on the nuclear deformation parameters derived from the Weizsäcker-Skyrme (WS) nuclear mass models. Smaller rms deviations between the calculated NQMs and experimental data indicate that the deformation parameters predicted from the WS mass models are reasonable. In addition, 161 unmeasured NQMs with known spins are also predicted with the proposed formula.
Isospin effect in peripheral heavy-ion collisions at Fermi energies
Ya-Fei Guo, Peng-Hui Chen, Fei Niu, Zhao-Qing Feng
2018, 42(12): 124106. doi: 10.1088/1674-1137/42/12/124106
The isospin effect in peripheral heavy-ion collisions was thoroughly investigated within the framework of the Lanzhou quantum molecular dynamics (LQMD) transport model. A coalescence approach was used to recognize the primary fragments formed in nucleus-nucleus collisions. The secondary decay process of these fragments was described using the statistical code GEMINI. The production mechanism and isospin effect of the projectile-like and target-like fragments were analyzed using the combined approach. It was found that the isospin migration from the high-isospin density to the low-density matter occurred in the neutron-rich nuclear reactions, i.e., 48Ca+208Pb, 86Kr+48Ca/208Pb/124Sn, 136Xe+208Pb, 124Sn+124Sn, and 136Xe+136Xe. A hard symmetry energy was available for creating the neutron-rich fragments, particularly in the medium-mass region. The isospin effect of the neutron-to-proton (n/p) ratio of the complex fragments was reduced when the secondary decay process was included. However, a soft symmetry energy enhanced the n/p ratio of the light particles, particularly at kinetic energies greater than 15 MeV/nucleon.
Analysis of Forbush decreases observed using a muon telescope in Antarctica starting on 21 June 2015
De-Hong Huang, Hong-Qiao Hu, Ji-Long Zhang, Hong Lu, Da-Li Zhang, Bin-Shen Xue, Jing-Tian Lu
2018, 42(12): 125001. doi: 10.1088/1674-1137/42/12/125001
A cosmic-ray muon telescope has been collecting data since the end of 2014, which was shortly after the telescope was built in the Zhongshan Station of Antarctica. The telescope is the first observation device to be built by Chinese scientists in Antarctica. The pressure change is very strong in Zhongshan station. The count rate of the pressure correction results shows that the large variations in the count rate are likely caused by pressure fluctuations. During the period from 18 June to 22 June 2015, four halo coronal mass ejections (CMEs) were ejected from the Sun. These CMEs initiated a series of Forbush decreases (FD) when they reached the Earth. We conducted a comprehensive study of the intensity fluctuations of galactic cosmic rays recorded during FDs. The intensity fluctuations used in this study were collected by cosmic ray detectors of multiple stations (Zhongshan, McMurdo, South Polar, and Nagoya), and the solar wind measurements were collected by ACE and WIND. The profile of the FD of 22 June demonstrated a four-step decrease. The traditional one- or two-step FD classification method does not adequately explain the FD profile results. The interaction between the faster CME that occurred on 21 June 2015 and the two slow CMEs of the earlier few days should be considered. The cosmic ray intensities of the South Pole, McMurdo, and Zhongshan stations have similar hourly variations, whereas the galactic cosmic rays recorded between polar and non-polar locations are distinct. The FD pre-increase of 22 June 2015 for the Nagoya muon telescope (non-polar location) lags those of the McMurdo and Zhongshan stations (polar locations) by 1 h. The FD onset of 22 June 2015 for the Nagoya muon telescope lags those of the polar locations by 1 h.