2018 Vol. 42, No. 7

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A minimal model for two-component FIMP dark matter: A basic search
Peyman Zakeri, Mohammad Moosavi, Mohammadreza Zakeri, Yaser Ayazi
2018, 42(7): 073101. doi: 10.1088/1674-1137/42/7/073101
In the multi-component configurations of dark matter phenomenology, we propose a minimal two-component configuration which is an extension of the Standard Model with only three new fields; one scalar and one fermion interact with the thermal soup through Higgs portal, mediated by the other scalar in such a way that the stabilities of dark matter candidates are made simultaneously by an explicit Z2 symmetry. Against the most common freeze-out framework, we look for dark matter particle signatures in the freeze-in scenario by evaluating the relic density and detection signals. A simple distinguishing feature of the model is the lack of dark matter conversion, so the dark matter components act individually and the model can be adapted entirely to both singlet scalar and singlet fermionic models, separately. We find dark matter self-interaction as the most promising approach to probe such feeble models. Although the scalar component satisfies this constraint, the fermionic one refuses it even in the resonant region.
Decay constants of pseudoscalar and vector mesons with improved holographic wavefunction
Qin Chang, Xiao-Nan Li, Xin-Qiang Li, Fang Su
2018, 42(7): 073102. doi: 10.1088/1674-1137/42/7/073102
We calculate the decay constants of light and heavy-light pseudoscalar and vector mesons with improved soft-wall holographic wavefuntions, which take into account the effects of both quark masses and dynamical spins. We find that the predicted decay constants, especially for the ratio fV/fP, based on light-front holographic QCD, can be significantly improved, once the dynamical spin effects are taken into account by introducing the helicity-dependent wavefunctions. We also perform detailed χ2 analyses for the holographic parameters (i.e. the mass-scale parameter κ and the quark masses), by confronting our predictions with the data for the charged-meson decay constants and the meson spectra. The fitted values for these parameters are generally in agreement with those obtained by fitting to the Regge trajectories. At the same time, most of our results for the decay constants and their ratios agree with the data as well as the predictions based on lattice QCD and QCD sum rule approaches, with only a few exceptions observed.
Pair production of Higgs boson in NMSSM at the LHC with the next-to-lightest CP-even Higgs boson being SM-like
Zhaoxia Heng, Xue Gong, Haijing Zhou
2018, 42(7): 073103. doi: 10.1088/1674-1137/42/7/073103
The next-to-minimal supersymmetric standard model (NMSSM) more naturally accommodates a Higgs boson with a mass of approximately 125 GeV than the minimal supersymmetric standard model (MSSM). In this work, we assume that the next-to-lightest CP-even Higgs boson h2 is the SM-like Higgs boson h, whereas the lightest CP-even Higgs boson h1 is dominantly singlet-like. We discuss the h1h1, h2h2, and h1h2 pair production processes via gluon-gluon fusion at the LHC for an collision energy of 14 TeV, and we consider the cases in which one Higgs boson decays to bb and the other decays to γγ or τ+τ-. We find that, for mh1≲ 62 GeV, the cross section of the ggh1h1 process is relatively large and maximally reaches 5400 fb, and the production rate of the h1h1bbτ+τ-final state can reach 1500 fb, which make the detection of this final state possible for future searches of an integrated luminosity of 300 and 3000 fb-1. This is mainly due to the contributions from the resonant production process pph2h1h1 and the relatively large branching ratio of h1bb and h1τ+τ-. The cross sections of the pph2h2 and pph1h2 production processes maximally reach 28 fb and 133 fb, respectively.
Angular distribution measurement for 12C fragmentation via 12C + 12C scattering at 100 MeV/u
Wei-Wei Qu, Gao-Long Zhang, Guo-Yu Tian, Zhi-Qiang Chen, Shou-Ping Xu, Royichi Wada
2018, 42(7): 074001. doi: 10.1088/1674-1137/42/7/074001
The angular distributions and energy spectra of 11B, 10B, and 9Be fragments of 12C in the angular range from 1.0° to 7.5° at 100 MeV/u were obtained via 12C + 12C scattering. Detailed comparisons are presented between the experimental data and the modified antisymmetrized molecular dynamics (AMD-FM), binary intranuclear cascade model (BIC) and Liège intranuclear cascade model (INCL++). The experimental angular distributions and energy spectra are well reproduced by the AMD-FM calculations but fail to be reproduced by the physical models installed in the Geant4 program, including the BIC and INCL++ models.
Cross-section measurement for the 93Nb(n, 2n)92gNb reaction at the neutron energy of 14.6 MeV by the AMS method
Guo-Zhu He, Bin Shi, Ming He, Zhen-Yu Li, Shi-Long Liu, Xiong-Jun Chen, Xi-Chao Ruan, Qi-Wei Zhang, Qi-Wen Fan, Heng Li, Shao-Yong Wu, Shan Jiang, Zu-Ying Zhou
2018, 42(7): 074002. doi: 10.1088/1674-1137/42/7/074002
The cross-section for the 93Nb(n, 2n)92gNb reaction has been measured at the neutron energy of 14.6 MeV using neutron activation and accelerator mass spectrometry (AMS) determination of the long-lived product nuclide 92gNb. The neutron energy was generated from the D+T neutron source at the China Institute of Atomic Energy (CIAE). The neutron flux was monitored by measuring the activity of 92mNb produced in the competing reaction channel of 93Nb(n, 2n)92mNb. At the neutron energy of 14.6 MeV, the 93Nb(n, 2n)92gNb reaction cross-section of (736±220) mb was obtained for the first time.
Investigation of the near-threshold cluster resonance in 14C
Hong-Liang Zang, Yan-Lin Ye, Zhi-Huan Li, Jian-Song Wang, Jian-Ling Lou, Qi-Te Li, Yu-Cheng Ge, Xiao-Fei Yang, Jing Li, Wei Jiang, Jun Feng, Qiang Liu, Biao Yang, Zhi-Qiang Chen, Yang Liu, Hong-Yi Wu, Chen-Yang Niu, Chen-Guang Li, Chun-Guang Wang, Xiang Wang, Wei Liu, Jian Gao, Han-Zhou Yu, Jun-Bin Ma, Peng Ma, Zhen Bai, Yan-Yun Yang, Shi-Lun Jin, Fei Lu
2018, 42(7): 074003. doi: 10.1088/1674-1137/42/7/074003
An experiment for m p(14C},14C*10Be+α)p inelastic excitation and decay was performed in inverse kinematics at a beam energy of 25.3 MeV/u. A series of 14C excited states, including a new one at 18.3(1) MeV, were observed which decay to various states of the final nucleus of 10Be. A specially designed telescope system, installed around zero degrees, played an essential role in detecting the resonant states near the α-separation threshold. A state at 14.1(1) MeV is clearly identified, being consistent with the predicted band-head of the molecular rotational band characterized by the π-bond linear chain configuration. Further clarification of the properties of this exotic state is suggested by using appropriate reaction tools.
An energy sum constraint of event mixing for Bose-Einstein correlations in reactions with ππX final states around 1 GeV
Qing-Hua He
2018, 42(7): 074004. doi: 10.1088/1674-1137/42/7/074004
We present a new event mixing technique for measuring two-pion Bose-Einstein correlations (BEC) in reactions with only two identical bosons among three final state particles. This new mixing method contains a missing mass consistency (MMC) cut and an energy sum order (ESO) cut. Unlike the previous proposed pion energy cut, which abandons nearly half the original events, the ESO cut does not eliminate any original events and hence improves the statistics of both original events and mixed events. Numerical tests using the γp→π0π0p events around 1 GeV are carried out to verify the validity of the ESO cut. This cut is able to reproduce the relative momentum distribution of the original events in the absence of BEC effects. In addition, its ability to observe BEC effects is tested by an event sample in the presence of BEC effects. Simulation results show the BEC effects can be observed clearly as an enhancement in the correlation function, and the BEC parameters extracted by this event mixing cut are consistent with the input BEC parameters.
An analytical formula for fluctuations in nuclear charge density
A. R. Abdulghany
2018, 42(7): 074101. doi: 10.1088/1674-1137/42/7/074101
The experimental charge densities of atomic nuclei show fluctuations in their distributions. This paper investigates the limits of accuracy of two-parameter Fermi and three-parameter Fermi distributions in describing the charge density. An improved analytical function for density distribution is proposed, which allows for density fluctuation. The experimental charge densities of 40Ca, 60Ni, 100Mo, 152Sm and 208Pb, representing the various shapes of density fluctuation, are used to assess the accuracy of the proposed formula. The proposed function reproduces the experimental charge densities with significant improvement in accuracy over other commonly used formulae. A compilation of charge density distribution parameters of 73 nuclei is presented based on the proposed formula.
Predictions for cross sections of light proton-rich isotopesin the 40Ca + 9Be reaction
Yi-Dan Song, Hui-Ling Wei, Chun-Wang Ma
2018, 42(7): 074102. doi: 10.1088/1674-1137/42/7/074102
The cross sections for Z=10-19 with isotopes Tz=-3/2 to -5 in the 140A MeV 40Ca + 9Be projectile fragmentation reaction have been predicted. An empirical formula based on the correlation between the cross section and average binding energy of an isotope has been adopted to predict the cross section. The binding energies in the AME16, WS4, and the theoretical prediction by the spherical relativistic continuum Hartree-Bogoliubov theory have been used. Meanwhile, the FRACS parametrization and the modified statistical abrasion-ablation model are also used to predict the cross sections for the proton-rich isotopes. The predicted cross sections for the Tz=-3 isotopes are close to 10-10 mb, which hopefully can be studied experimentally. In addition, based on the predicted cross sections, Z=14 is suggested to be a new magic number in the light proton-rich nuclei with Tz ≤ -3/2, for which the phenomenon is much more evident than it is from the average binding energy per nucleon.
α particle preformation and shell effect for heavy andsuperheavy nuclei
Yan-Wei Zhao, Shu-Qing Guo, Hong-Fei Zhang
2018, 42(7): 074103. doi: 10.1088/1674-1137/42/7/074103
The α particle preformation factor is extracted within a generalized liquid drop model for Z=84-92 isotopes and N=126, 128, 152, 162, 176, 184 isotones. The calculated results show clearly that the shell effects play a key role in α particle preformation. The closer the proton and neutron numbers are to the magic numbers, the more difficult the formation of the α cluster inside the mother nucleus is. The preformation factors of the isotopes reflect that N=126 is a magic number for Po, Rn, Ra, and Th isotopes, but for U isotopes the weakening of the influence of the N=126 shell closure is evident. The trend of the factors for N=126 and N=128 isotones also support this conclusion. We extend the calculations for N=152, 162, 176, 184 isotones to explore the magic numbers for heavy and superheavy nuclei, which are probably present near Z=108 to N=152, 162 isotones and Z=116 to N=176, 184 isotones. The results also show that another subshell closure may exist after Z=124 in the superheavy nuclei. This is useful for future experiments.
Poisson baseline of net-charge fluctuations in relativisticheavy ion collisions
Xue Pan, Yu-Fu Lin, Li-Zhu Chen, Ming-Mei Xu, Yuan-Fang Wu
2018, 42(7): 074104. doi: 10.1088/1674-1137/42/7/074104
Taking doubly charged particles, positive-negative charge pair production and the effects of volume fluctuations into account, the Poisson baseline of the fluctuations of net-charge is studied. Within the Poisson baseline, the cumulants of net-charge are derived. Comparing to the Skellam baseline of net-charge, we infer that doubly charged particles broaden the distributions of net-charge, while positive-negative charge pairs narrow the distributions. Using the ratios of doubly charged particles and positive-negative charge pairs from neutral resonance decays to the total positive charges from THERMINATOR 2, the first four orders of moments and the corresponding moment products are calculated in the Poisson baseline for Au + Au collisions at √sNN=200 GeV at RHIC/STAR. We find that the standard deviation is mainly influenced by the resonance decay, while the third and fourth order moments and corresponding moment products are mainly modified and fit the data of RHIC/STAR much better after including the effects of volume fluctuations.
Possible candidate nuclei for chirality-parity quartet bands
Chen Liu, Shou-Yu Wang, Bin Qi, Hui Jia
2018, 42(7): 074105. doi: 10.1088/1674-1137/42/7/074105
The potential energy surfaces of the even-even 68-92Se, 112-150Ba, and 208-230Ra isotopes are calculated using the macroscopic-microscopic method in a multidimensional space {αλ,μ} including quadrupole (λ=2, μ=0, 2) and octupole (λ=3, μ=0, 1, 2, 3) degrees of freedom. The calculated results show that the even-even isotopes 92Se, 112,114,144-150Ba and 220-228Ra can exhibit the coexistence of triaxial and octupole deformations, thereby leading to simultaneous chiral and reflected symmetry breaking. Therefore, chirality-parity quartet bands are expected in these and their neighboring odd-A/odd-odd nuclei.
Cosmic ray electron spectrum due to the dispersion ofinjection spectrum
Tian-Lu Chen, Wei Liu, Qi Gao, Mao-Yuan Liu, Hai-Jin Li, Danzengluobu, Ying Shi
2018, 42(7): 075001. doi: 10.1088/1674-1137/42/7/075001
The cosmic-ray total electron spectrum (electrons plus positrons) has been measured precisely up to TeV energies, with more interesting features found. Exhaustive analyses of the electron spectrum strongly support a spectral hardening above 100 GeV, rather than a featureless single power-law, which is confirmed by the most recent observations. Meanwhile, the measurements of the DAMPE satellite have verified the presence of a knee-like structure around 1 TeV in the electron spectrum, resembling the cosmic-ray knee. In this paper, we establish a physical model in which the observed electron spectrum is composed of a superposition of CR sources with various spectral indices and high-energy cutoffs. The dispersion of the power index is assumed to be Gaussian, while the cutoff energy Ec follows a power-law distribution. These simple ideas can account naturally for both the hundred-GeV excess and the TeV spectral break.
Doubly coupled matter fields in massive bigravity
Xian Gao, Lavinia Heisenberg
2018, 42(7): 075101. doi: 10.1088/1674-1137/42/7/075101
In the context of massive (bi-)gravity, non-minimal matter couplings have been proposed. These couplings are special in the sense that they are free of the Boulware-Deser ghost below the strong coupling scale and can be used consistently as an effective field theory. Furthermore, they enrich the phenomenology of massive gravity. We consider these couplings in the framework of bimetric gravity and study the cosmological implications for background and linear tensor, vector, and scalar Previous works have investigated special branches of solutions. Here we perform a complete perturbation analysis for the general background equations of motion, completing previous analyses.
Dynamical interactions of dark energy and dark matter: Yang-Mills condensate and QCD axions
Andrea Addazi, Pietro Donà, Antonino Marcianò
2018, 42(7): 075102. doi: 10.1088/1674-1137/42/7/075102
We analyze a model of cold axion dark matter weakly coupled with a dark gluon condensate, reproducing dark energy. We first review how to recover the dark energy behavior using the functional renormalization group approach, and ground our study in the properties of the effective Lagrangian, to be determined non-perturbatively. Then, within the context of GSM×SU(2)D×U(1)PQ, we consider Yang-Mills condensate (YMC) interactions with QCD axions. We predict a transfer of dark energy density into dark matter density, that can be tested in the next generation of experiments dedicated to dark energy measurements. We obtain new bounds on the interactions between the Yang-Mills condensate and axion dark matter from Planck data:the new physics interaction scale related to the axion/gluon condensate mixing is constrained to be higher than the 106 GeV energy scale.
On the knee of Galactic cosmic rays in light of sub-TeV spectral hardenings
Yi-Qing Guo, Qiang Yuan
2018, 42(7): 075103. doi: 10.1088/1674-1137/42/7/075103
More than fifty years after the discovery of the knee in the cosmic ray (CR) spectra, its physical origin remains a mystery. This is partly due to the ambiguity of the energy spectra of individual components. Recently, direct measurements from several space experiments found significant spectral hardenings of CR nuclei at ~200 GV. A joint modeling of the direct and indirect measurements may help to understand the experimental systematics and the physics of the knee. In this work, we update the phenomenological "poly-gonato" model to include the spectral hardenings, with a changing spectral index of γ + β·logE. This modification gives a reasonable description of the CR spectra in a wide energy range. However, the fits to different data sets give different results. We find that the fit to the AMS-02 and CREAM data slightly favors a relatively low energy knee of the light components. In such a case, the expected all-particle spectra under-shoot the data, which may require an extra component of CRs. The fits to AMS-02 data and the light component (H+He) data from the Tibet ASγ/ARGO-YBJ/WFCTA and KASCADE experiments give consistent results with the all-particle spectra. We further propose a possible physical realization of such a "modified poly-gonato" model of spectral hardenings by means of spatially-dependent diffusion of CRs. We find reasonably good agreement between the model predictions and the data for CR spectra, the secondary-to-primary ratios, and the amplitude of anisotropies.