2018 Vol. 42, No. 5

Display Method:          |     

Discovery potentials of doubly charmed baryons
Fu-Sheng Yu, Hua-Yu Jiang, Run-Hui Li, Cai-Dian Lü, Wei Wang, Zhen-Xing Zhao
2018, 42(5): 051001. doi: 10.1088/1674-1137/42/5/051001
The existence of doubly heavy flavor baryons has not been well established experimentally so far. In this Letter we systematically investigate the weak decays of the doubly charmed baryons, Ξcc++ and Ξcc+, which should be helpful for experimental searches for these particles. The long-distance contributions are first studied in the doubly heavy baryon decays, and found to be significantly enhanced. Comparing all the processes, Ξcc++→ Λc+K-π+π+ and Ξc+π+ are the most favorable decay modes for experiments to search for doubly heavy baryons.
Measurement of H→μ+ μ- production in association with a Z boson at the CEPC
Zhen-Wei Cui, Qiang Li, Gang Li, Man-Qi Ruan, Lei Wang, Da-Neng Yang
2018, 42(5): 053001. doi: 10.1088/1674-1137/42/5/053001
The Circular Electron-Positron Collider (CEPC) is a future Higgs factory proposed by the Chinese high energy physics community. It is planned to operate at a center-of-mass energy of 240-250 GeV and is expected to accumulate an integrated luminosity of 5 ab-1 over ten years of operation. At the CEPC, Higgs bosons will be dominantly produced from the ZH associated process. The vast number of Higgs events collected will enable precise studies of its properties, including Yukawa couplings to massive particles. With GEANT4-based simulation of detector effects, we study the feasibility of measuring the Higgs boson decaying into a pair of muons at the CEPC. The results with and without information from the Z boson decay products are provided, showing that a signal significance of over 10 standard deviations can be achieved and the H-μ-μ coupling can be measured within 10% accuracy.
An optimal scheme for top quark mass measurement near the tt threshold at future e+e- colliders
Wei-Guo Chen, Xia Wan, You-Kai Wang
2018, 42(5): 053002. doi: 10.1088/1674-1137/42/5/053002
A top quark mass measurement scheme near the tt production threshold in future e+e- colliders, e.g.the Circular Electron Positron Collider (CEPC), is simulated. A χ2 fitting method is adopted to determine the number of energy points to be taken and their locations. Our results show that the optimal energy point is located near the largest slope of the cross section v. beam energy plot, and the most efficient scheme is to concentrate all luminosity on this single energy point in the case of one-parameter top mass fitting. This suggests that the so-called data-driven method could be the best choice for future real experimental measurements. Conveniently, the top mass statistical uncertainty can also be calculated directly by the error matrix even without any sampling and fitting. The agreement of the above two optimization methods has been checked. Our conclusion is that by taking 50 fb-1 total effective integrated luminosity data, the statistical uncertainty of the top potential subtracted mass can be suppressed to about 7 MeV and the total uncertainty is about 30 MeV. This precision will help to identify the stability of the electroweak vacuum at the Planck scale.
Spectroscopy of the Ωccb baryon in the hypercentral constituent quark model
Zalak Shah, Ajay Kumar Rai
2018, 42(5): 053101. doi: 10.1088/1674-1137/42/5/053101
We extract the mass spectrum of the triply heavy baryon Ωccb using the hypercentral constituent quark model. The first order correction is also added to the potential term of the Hamiltonian. The radial and orbital excited state masses are determined, and the Regge trajectories and magnetic moments for this baryon are also given.
Tsallis' quantum q-fields
A. Plastino, M. C. Rocca
2018, 42(5): 053102. doi: 10.1088/1674-1137/42/5/053102
We generalize several well known quantum equations to a Tsallis' q-scenario, and provide a quantum version of some classical fields associated with them in the recent literature. We refer to the q-Schrödinger, q-Klein-Gordon, q-Dirac, and q-Proca equations advanced in, respectively, Phys. Rev. Lett. 106, 140601 (2011), EPL 118, 61004 (2017) and references therein. We also introduce here equations corresponding to q-Yang-Mills fields, both in the Abelian and non-Abelian instances. We show how to define the q-quantum field theories corresponding to the above equations, introduce the pertinent actions, and obtain equations of motion via the minimum action principle. These q-fields are meaningful at very high energies (TeV scale) for q=1.15, high energies (GeV scale) for q=1.001, and low energies (MeV scale) for q=1.000001[Nucl. Phys. A 955 (2016) 16 and references therein]. (See the ALICE experiment at the LHC). Surprisingly enough, these q-fields are simultaneously q-exponential functions of the usual linear fields' logarithms.
Super-light baryo-photons, weak gravity conjecture and exotic instantons in neutron-antineutron transitions
Andrea Addazi
2018, 42(5): 053103. doi: 10.1088/1674-1137/42/5/053103
In companion papers A. Addazi, Nuovo Cim. C, 38(1):21 (2015), A. Addazi, Z. Berezhiani, and Y. Kamyshkov, arXiv:1607.00348, we have discussed current bounds on a new super-light baryo-photon, associated with a U(1)B-L gauge, from current neutron-antineutron data, which are competitive with Eötvös-type experiments. Here, we discuss the implications of possible baryo-photon detection in string theory and quantum gravity. The discovery of a very light gauge boson should imply violation of the weak gravity conjecture, carrying deep consequences for our understanding of holography, quantum gravity and black holes. We also show how the detection of a baryo-photon would exclude the generation of all B-L violating operators from exotic stringy instantons. We will argue against the common statement in the literature that neutron-antineutron data may indirectly test at least the 300-1000 TeV scale. Searches for baryo-photons can provide indirect information on the Planck (or string) scale (quantum black holes, holography and non-perturbative stringy effects). This strongly motivates new neutron-antineutron experiments with adjustable magnetic fields dedicated to the detection of super-light baryo-photons.
Supersymmetric AdS4 vacua in N=3 gauged supergravity
Zhen-Bin Cao
2018, 42(5): 053104. doi: 10.1088/1674-1137/42/5/053104
We study the maximally supersymmetric AdS backgrounds of matter-coupled N=3 gauged supergravity in four dimensions. We find that to admit supersymmetric AdS vacua, the gauge group can only be of the form G0×HSO(3,n) with G0=SO(3), SO(3,1) or SL(3,R) and H a compact group of dimension n+3-dim(G0). We also show that these AdS vacua have no moduli, namely they correspond to critical points in field space.
The DD* interaction with isospin zero in an extended hidden gauge symmetry approach
Bao-Xi Sun, Da-Ming Wan, Si-Yu Zhao
2018, 42(5): 053105. doi: 10.1088/1674-1137/42/5/053105
The DD* interaction via a ρ or ω exchange is constructed within an extended hidden gauge symmetry approach, where the strange quark is replaced by the charm quark in the SU(3) flavor space. With this DD* interaction, a bound state slightly lower than the DD* threshold is generated dynamically in the isospin zero sector by solving the Bethe-Salpeter equation in the coupled-channel approximation, which might correspond to the X(3872) particle announced by many collaborations. This formulism is also used to study the BB* interaction, and a BB* bound state with isospin zero is generated dynamically, which has no counterpart listed in the review of the Particle Data Group. Furthermore, the one-pion exchange between the D meson and the D* is analyzed precisely, and we do not think the one-pion exchange potential need be considered when the Bethe-Salpeter equation is solved.
Calculation of multidimensional potential energy surfaces for even-even transuranium nuclei:systematic investigation of the triaxiality effect on the fission barrier
Qing-Zhen Chai, Wei-Juan Zhao, Min-Liang Liu, Hua-Lei Wang
2018, 42(5): 054101. doi: 10.1088/1674-1137/42/5/054101
Static fission barriers for 95 even-even transuranium nuclei with charge number Z=94-118 have been systematically investigated by means of pairing self-consistent Woods-Saxon-Strutinsky calculations using the potential energy surface approach in multidimensional (β2, γ, β4) deformation space. Taking the heavier 252Cf nucleus (with the available fission barrier from experiment) as an example, the formation of the fission barrier and the influence of macroscopic, shell and pairing correction energies on it are analyzed. The results of the present calculated β2 values and barrier heights are compared with previous calculations and available experiments. The role of triaxiality in the region of the first saddle is discussed. It is found that the second fission barrier is also considerably affected by the triaxial deformation degree of freedom in some nuclei (e.g., the Z=112-118 isotopes). Based on the potential energy curves, general trends of the evolution of the fission barrier heights and widths as a function of the nucleon numbers are investigated. In addition, the effects of Woods-Saxon potential parameter modifications (e.g., the strength of the spin-orbit coupling and the nuclear surface diffuseness) on the fission barrier are briefly discussed.
Estimation of the chiral magnetic effect considering the magnetic field response of the QGP medium
Sheng-Qin Feng, Xin Ai, Lei Pei, Fei Sun, Yang Zhong, Zhong-Bao Yin
2018, 42(5): 054102. doi: 10.1088/1674-1137/42/5/054102
The magnetic field plays a major role in searching for the chiral magnetic effect in relativistic heavy-ion collisions. If the lifetime of the magnetic field is too short, as predicted by simulations of the field in vacuum, the chiral magnetic effect will be largely suppressed. However, the lifetime of the magnetic field will become longer when the QGP medium response is considered. We give an estimate of the effect, especially considering the magnetic field response of the QGP medium, and compare it with the experimental results for the background-subtracted correlator H at RHIC and LHC energies. The results show that our method explains the experimental results better at the top RHIC energy than at the LHC energy.
Crust-core properties of neutron stars in the Nambu-Jona-Lasinio model
Si-Na Wei, Rong-Yao Yang, Wei-Zhou Jiang
2018, 42(5): 054103. doi: 10.1088/1674-1137/42/5/054103
We adopt the Nambu-Jona-Lasinio (NJL) model to study the crust-core transition properties in neutron stars (NSs). For a given momentum cutoff and symmetry energy of saturation density in the NJL model, decreasing the slope of the symmetry energy gives rise to an increase in the crust-core transition density and transition pressure. Given the slope of the symmetry energy at saturation density, the transition density and corresponding transition pressure increase with increasing symmetry energy. The increasing trend between the fraction of the crustal moment of inertia and the slope of symmetry energy at saturation density indicates that a relatively large momentum cutoff of the NJL model is preferred. For a momentum cutoff of 500 MeV, the fraction of the crustal moment of inertia clearly increases with the slope of symmetry energy at saturation density. Thus, at the required fraction (7%) of the crustal moment of inertia, the NJL model with momentum cutoff of 500 MeV and a large slope of the symmetry energy of saturation density can give the upper limit of the mass of the Vela pulsar to be above 1.40 M.
Band head spin assignment of superdeformed bands in Hg isotopes through power index formula
Honey Sharma, H. M. Mittal
2018, 42(5): 054104. doi: 10.1088/1674-1137/42/5/054104
The power index formula has been used to obtain the band head spin (I0) of all the superdeformed (SD) bands in Hg isotopes. A least squares fitting approach is used. The root mean square deviations between the determined and the observed transition energies are calculated by extracting the model parameters using the power index formula. Whenever definite spins are available, the determined and the observed transition energies are in accordance with each other. The computed values of dynamic moment of inertia J(2) obtained by using the power index formula and its deviation with the rotational frequency is also studied. Excellent agreement is shown between the calculated and the experimental results for J(2) versus the rotational frequency. Hence, the power index formula works very well for all the SD bands in Hg isotopes expect for 195Hg(2, 3, 4).
Backbendings of superdeformed bands in 36,40Ar
Xu-Hui Xiang, Xiao-Tao He
2018, 42(5): 054105. doi: 10.1088/1674-1137/42/5/054105
Experimentally observed superdeformed (SD) rotational bands in 36Ar and 40Ar are studied by the cranked shell model (CSM) with the pairing correlations treated by a particle-number-conserving (PNC) method. This is the first time that PNC-CSM calculations have been performed on the light nuclear mass region around A=40. The experimental kinematic moments of inertia J(1) versus rotational frequency are reproduced well. The backbending of the SD band at frequency around =1.5 MeV in 36Ar is attributed to the sharp rise of the simultaneous alignments of the neutron and proton 1d5/2[202]5/2 pairs and 1f7/2[321]3/2 pairs, which is a consequence of the band crossing between the 1d5/2[202]5/2 and 1f7/2[321]3/2 configuration states. The gentle upbending at low frequency of the SD band in 40Ar is mainly affected by the alignments of the neutron 1f7/2[321]3/2 pairs and proton 1d5/2[202]5/2 pairs. The PNC-CSM calculations show that besides the diagonal parts, the off-diagonal parts of the alignments play an important role in the rotational behavior of the SD bands.
Screening effects on 12C+12C fusion reaction
F. Koyuncu, A. Soylu
2018, 42(5): 054106. doi: 10.1088/1674-1137/42/5/054106
One of the important reactions for nucleosynthesis in the carbon burning phase in high-mass stars is the 12C+12C fusion reaction. In this study, we investigate the influences of the nuclear potentials and screening effect on astrophysically interesting 12C+12C fusion reaction observables at sub-barrier energies by using the microscopic α-α double folding cluster (DFC) potential and the proximity potential. In order to model the screening effects on the experimental data, a more general exponential cosine screened Coulomb (MGECSC) potential including Debye and quantum plasma cases has been considered in the calculations for the 12C+12C fusion reaction. In the calculations of the reaction observables, the semi-classical Wentzel-Kramers-Brillouin (WKB) approach and coupled channel (CC) formalism have been used. Moreover, in order to investigate how the potentials between 12C nuclei produce molecular cluster states of 24Mg, the normalized resonant energy states of 24Mg cluster bands have been calculated for the DFC potential. By analyzing the results produced from the fusion of 12C+12C, it is found that taking into account the screening effects in terms of MGECSC is important for explaining the 12C+12C fusion data, and the microscopic DFC potential is better than the proximity potential in explaining the experimental data, also considering that clustering is dominant for the structure of the 24Mg nucleus.
Fragment distribution in 78,86Kr+181Ta reactions
Dong-Hong Zhang, Feng-Shou Zhang
2018, 42(5): 054107. doi: 10.1088/1674-1137/42/5/054107
Within the framework of the isospin-dependent quantum molecular dynamics model, along with the GEMINI model, the 86Kr+181Ta reaction at 80, 120 and 160 MeV/nucleon and the 78Kr+181Ta reaction at 160 MeV/nucleon are studied, and the production cross sections of the generated fragments are calculated. More intermediate and large mass fragments can be produced in the reactions with a large range of impact parameter. The production cross sections of nuclei such as the isotopes of Si and P generally decrease with increasing incident energy. Isotopes near the neutron drip line are produced more in the neutron-rich system 86Kr+181Ta.
Relativistic compact stars with charged anisotropic matter
S. K. Maurya, Ayan Banerjee, Phongpichit Channuie
2018, 42(5): 055101. doi: 10.1088/1674-1137/42/5/055101
In this article, we perform a detailed theoretical analysis of new exact solutions with anisotropic fluid distribution of matter for compact objects subject to hydrostatic equilibrium. We present a family solution to the Einstein-Maxwell equations describing a spherically symmetric, static distribution of a fluid with pressure anisotropy. We implement an embedding class one condition to obtain a relation between the metric functions. We generalize the properties of a spherical star with hydrostatic equilibrium using the generalised Tolman-Oppenheimer-Volkoff (TOV) equation. We match the interior solution to an exterior Reissner-Nordström one, and study the energy conditions, speed of sound, and mass-radius relation of the star. We also show that the obtained solutions are compatible with observational data for the compact object Her X-1. Regarding our results, the physical behaviour of the present model may serve for the modeling of ultra compact objects.