2019 Vol. 43, No. 7

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Probing the CP violating Hγγ coupling using interferometry
Xia Wan, You-Kai Wang
2019, 43(7): 073101. doi: 10.1088/1674-1137/43/7/073101
The diphoton invariant mass distribution from the interference between \begin{document}$gg\to H \to \gamma\gamma$\end{document} and \begin{document}$gg\to \gamma\gamma$\end{document} is almost antisymmetric around the Higgs mass \begin{document}$M_H$\end{document}. We propose a new observable \begin{document}$A_{\rm{int}}$\end{document}, the ratio of the sign-reversed integral around \begin{document}$M_H$\end{document} (e.g. \begin{document}$\int^{M_H}_{M_H-5~\rm{GeV}} -\int_{M_H}^{M_H+5~\rm{GeV}}$\end{document}) and the cross-section of the Higgs signal, to quantify this effect. We study \begin{document}$A_{\rm{int}}$\end{document} both in the Standard Model (SM) and new physics with various CP violating \begin{document}$H\gamma\gamma$\end{document} couplings. \begin{document}$A_{\rm{int}}$\end{document} in SM could reach a value of 10%, while for CP violating \begin{document}$H\gamma\gamma$\end{document} coupling \begin{document}$A_{\rm{int}}$\end{document} could range from 10% to −10%, which could probably be detected in the HL-LHC experiments. \begin{document}$A_{\rm{int}}$\end{document} with both CP violating \begin{document}$H\gamma\gamma$\end{document} and \begin{document}$Hgg$\end{document} couplings is also studied, and its range of values is found to be slightly larger.
New physics search in the doubly weak decay ${{\overline B}^0 \to K^+ \pi^- }$
Faisal Munir Bhutta, Ying Li, Cai-Dian Lü, Yue-Hong Xie
2019, 43(7): 073102. doi: 10.1088/1674-1137/43/7/073102
The doubly weak transition \begin{document}$b\to dd{\bar s}$\end{document} is highly suppressed in the Standard Model, which makes it a potential channel for exploring new physics signals. We present a study of the exclusive two-body wrong sign weak decay \begin{document}$\smash{\overline B}^0\to K^+\pi^-$\end{document} , which belongs to this class, in the perturbative QCD framework. We perform a model independent analysis for various effective dimension-6 operators for which large effects are possible. We further analyze the considered process in the Randall-Sundrum model, including the custodially protected and the bulk-Higgs Randall-Sundrum models. Exploring the experimentally favored parameter space of these models leads to a large and significant enhancement of the decay rate compared to the Standard Model, which might be accessible in future experiments. We propose to search for the wrong sign decay \begin{document}$\smash{\overline B}^0\to K^+\pi^-$\end{document} via flavor-tagged time-dependent analyses, which can be performed at LHCb and Belle-II.
S-wave contributions to ${{{\bar B}_s^0\to (D^0,{\bar D}^0)\pi^+\pi^-}}$ in the perturbative QCD framework
Ye Xing, Zhi-Peng Xing
2019, 43(7): 073103. doi: 10.1088/1674-1137/43/7/073103
\begin{document}$\bar B_s^0\to (D^0,\bar D^0) \pi^+\pi^-$\end{document} is induced by the \begin{document}$b\to c \bar us$\end{document}/\begin{document}$b \to u\bar cs$\end{document} transitions, which can interfere if a CP-eigenstate \begin{document}$D_{\rm CP}$\end{document} is formed. The interference contribution is sensitive to the CKM angle \begin{document}$\gamma$\end{document}. In this work, we study the S-wave \begin{document}$\pi^+\pi^-$\end{document} contributions to the process in the perturbative QCD factorization. In the factorization framework, we adopt two-meson light-cone distribution amplitudes, whose normalization is parametrized by the S-wave time-like two-pion form factor with resonance contributions from \begin{document}$f_0(500)$\end{document}, \begin{document}$f_0(980),f_0(1500),f_0(1790)$\end{document}. We find that the branching ratio of \begin{document}$\bar B_s^0\to (D^0,\bar D^0) (\pi^+\pi^-)_S$\end{document} is of the order of \begin{document}$10^{-6}$\end{document}, and that significant interference exists in \begin{document}$\bar B_s^0\to D_{\rm CP} (\pi^+\pi^-)_S$\end{document}. Future measurement could not only provide useful constraints on the CKM angle \begin{document}$\gamma$\end{document}, but would also be helpful for exploring the multi-body decay mechanism of heavy mesons.
Chiral criticality and glue dynamics
Wei-Jie Fu
2019, 43(7): 074101. doi: 10.1088/1674-1137/43/7/074101
The chiral order-parameter σ field and its higher-order cumulants of fluctuations are calculated within the functional renormalization group approach by adopting the local potential approximation in this study. The influence of glue dynamics on fluctuations of the σ field is investigated, and we find that they are weakly affected. This is in sharp contrast to the baryon number fluctuations, which are sensitive to the glue dynamics and involve information on the color confinement. The implications of our calculated results are discussed from the viewpoint of the theoretical and experimental efforts in the search for the QCD critical end point.
Search for decay modes of heavy and superheavy nuclei
A. Soylu
2019, 43(7): 074102. doi: 10.1088/1674-1137/43/7/074102
Spontaneous fission (SF) with a new formula based on a liquid drop model is proposed and used in the calculation of the SF half-lives of heavy and superheavy nuclei (Z = 90–120). The predicted half-lives are in agreement with the experimental SF half-lives. The half-lives of \begin{document}$ \alpha $\end{document} decay (AD) for the same nuclei are obtained by using the Wentzel-Kramers-Brillouin (WKB) method together with Bohr-Sommerfeld (BS) quantization condition considering the isospin-dependent effects for the cosh potential. The decay modes and branching ratios of superheavy nuclei (Z = 104-118) with experimental decay modes are obtained, and the modes are compared with the experimental ones and with the predictions found in the literature. Although some nuclei have predicted decay modes that are different from their experimental decay modes, decay modes same as the experimental ones are predicted for many nuclei. The SF and AD half-lives, branching ratios, and decay modes are obtained for superheavy nuclei (Z = 119–120) with unknown decay modes and compared with the predictions obtained in a previous study. The present results provide useful information for future experimental studies performed on both the AD and SF of superheavy nuclei.
Cross-section prediction for isotopes near neutron drip line in 70, 80Zn projectile fragmentation reactions
Hui-Ling Wei, Yi-Dan Song, Chun-Wang Ma, Zhi-Hong Li, Jun Su
2019, 43(7): 074103. doi: 10.1088/1674-1137/43/7/074103
The cross sections for 59, 60Ca, recently measured in the 345 A MeV \begin{document}$^{70}{\rm{Zn}}+^{9}{\rm{Be}}$\end{document} reaction, were estimated using the FRACS parametrization and an empirical formula, which are in good agreement. The FRACS parametrization and the empirical formula are combined to predict the cross sections for extreme calcium isotopes \begin{document}$^{66, 70}{\rm{Ca}}$\end{document} in the \begin{document}$^{70, 80}{\rm{Zn}}+^{9}{\rm{Be}}$\end{document} reactions at the incident energies of 60, 80, and 345 A MeV. The dependence of emperical formula parameters on the reaction system, as well as the incident energy, are discussed. The results indicate that \begin{document}$^{66, 70}{\rm{Ca}}$\end{document} can be discovered in reactions of 60, 80 A MeV \begin{document}$^{80}{\rm{Zn}}+^{9}{\rm{Be}}$\end{document}. The predicted binding energy for extreme neutron-rich isotopes by the spherical relativistic continuum Hartree-Bogoliubov theory was adopted in the calculation. Hence, the planned Beijing Isotope-Separation-On Line Neutron-Rich Beam Facility (BISOL), which is a third generation radioactive ion beam facility, could provide the opportunity to discover \begin{document}$^{66, 70}{\rm{Ca}}$\end{document} and neighboring neutron-drip line nuclei.
Mass predictions of the relativistic continuum Hartree-Bogoliubov model with radial basis function approach
Min Shi, Zhong-Ming Niu, Hao-Zhao Liang
2019, 43(7): 074104. doi: 10.1088/1674-1137/43/7/074104
The radial basis function (RBF) approach is a powerful tool to improve nuclear mass predictions. By combining the RBF approach with the latest relativistic continuum Hartree-Bogoliubov (RCHB) model, the local systematic deviations between the RCHB mass predictions and the experimental data are eliminated, and the root-mean-square (rms) mass deviation is significantly reduced from 7.923 MeV to 0.386 MeV. However, systematic deviations between the RBF improved mass predictions and the experimental data remain for nuclei with four different odd-even parities, i.e. (even Z, even N), (even Z, odd N), (odd Z, even N), and (odd Z, odd N). They can be reduced by separately training RBF for the four groups of nuclei, and the resulting rms deviation decreases to 0.229 MeV. It is found that the RBF approach can describe the deformation effects neglected in the present RCHB mass calculations, and also improves the description of the shell effect and the pairing effect.
Squeezed back-to-back correlations of K +K in d + Au collisions at ${\sqrt{{s_{NN}}}}$=200 GeV and Au + Au collisions at ${\sqrt{{s_{NN}}}}$ = 62.4 GeV
Yong Zhang, Jing Yang, Weihua Wu
2019, 43(7): 074105. doi: 10.1088/1674-1137/43/7/074105
We investigate the squeezed back-to-back correlations (BBC) of \begin{document}$ K^+ $\end{document}\begin{document}$ K^- $\end{document}, caused by the mass modification of particles in the dense medium formed in d + Au collisions at \begin{document}$ \sqrt{s_{NN}} = 200 $\end{document} GeV and Au + Au collisions at \begin{document}$ \sqrt{s_{NN}} = 62.4 $\end{document} GeV. Considering that some kaons may not be affected by the medium, we further study the BBC functions of \begin{document}$ K^+ $\end{document}\begin{document}$ K^- $\end{document} when parts of all kaons have a mass-shift. Our results indicate that the BBC functions of \begin{document}$ K^+ $\end{document}\begin{document}$ K^- $\end{document} can be observed when only ~10% of all kaons have a mass-shift in d + Au collisions at \begin{document}$ \sqrt{s_{NN}} = 200 $\end{document} GeV and the peripheral collisions of Au + Au at \begin{document}$ \sqrt{s_{NN}} = 62.4 $\end{document} GeV. Since the BBC function is caused by the mass-shift due to the interactions between the particle and the medium, the successful detection of the BBC function indirectly marks that the dense medium has formed in these collision systems. We suggest the experimental measurement of the BBC function of \begin{document}$ K^+ $\end{document}\begin{document}$ K^- $\end{document} in d + Au collisions at \begin{document}$ \sqrt{s_{NN}} = 200 $\end{document} GeV and peripheral collisions of Au + Au at \begin{document}$ \sqrt{s_{NN}} = 62.4 $\end{document} GeV.
A close look at the competition of isovector and isoscalar pairing in A=18 and 20 even-even NZ nuclei
Feng Pan, Dan Zhou, Siyu Yang, Grigor Sargsyan, Yingwen He, Kristina D. Launey, Jerry P. Draayer
2019, 43(7): 074106. doi: 10.1088/1674-1137/43/7/074106
The competition of isovector and isoscalar pairing in A=18 and 20 even-even NZ nuclei is analyzed in the framework of the mean-field plus the dynamic quadurpole-quadurpole, pairing and particle-hole interactions, whose Hamiltonian is diagonalized in the basis \begin{document}${ U}(24) \supset ({ U}(6)\supset {{SU}}(3)\supset {{SO}}(3)) \otimes ({ U}(4)\supset{ {SU}}_S(2)\otimes {{SU}}_T(2)) $\end{document} in the L = 0 configuration subspace. Besides the pairing interaction, it is observed that the quadurpole-quadurpole and particle-hole interactions also play a significant role in determining the relative positions of low-lying excited 0+ and 1+ levels and their energy gaps, which can result in the ground state first-order quantum phase transition from J = 0 to J = 1. The strengths of the isovector and isoscalar pairing interactions in these even-even nuclei are estimated with respect to the energy gap and the total contribution to the binding energy. Most importantly, it is shown that although the mechanism of the particle-hole contribution to the binding energy is different, it is indirectly related to the Wigner term in the binding energy.
Restoration of pseudo-spin symmetry in N = 32 and N = 34 isotonesdescribed by relativistic Hartree-Fock theory
Zheng-Zheng Li, Shi-Yao Chang, Qiang Zhao, Wen-Hui Long, Yi-Fei Niu
2019, 43(7): 074107. doi: 10.1088/1674-1137/43/7/074107
The restoration of pseudo-spin symmetry (PSS) along the \begin{document}$ N = 32 $\end{document} and \begin{document}$ N =34 $\end{document} isotonic chains and the physics behind are studied by applying the relativistic Hartree-Fock theory with the effective Lagrangian PKA1. Taking the proton pseudo-spin partners \begin{document}$ (\pi2s_{1/2},\pi1d_{3/2}) $\end{document} as candidates, the systematic restoration of PSS along both isotonic chains is found from sulphur (S) to nickel (Ni), while an obvious PSS violation from silicon (Si) to sulphur is discovered near the drip lines. The effects of the tensor force components are investigated, introduced naturally by the Fock terms, which can only partially interpret the systematics from calcium to nickel, whereas they fail for the overall trends. Further analysis following the Schrödinger-like equation of the lower component of Dirac spinor shows that contributions from the Hartree terms dominate the overall systematics of the PSS restoration. Such effects can be self-consistently interpreted by the evolution of the proton central density profiles along both isotonic chains. In particular, the PSS violation is found to tightly relate to the dramatic changes from the bubble-like density profiles in silicon to the central-bumped ones in sulphur.
Expected energy spectrum of cosmic ray protons and helium below 4 PeV measured by LHAASO
L. Q. Yin, S. S. Zhang, Z. Cao, B. Y. Bi, C. Wang, J. L. Liu, L. L. Ma, M. J. Yang, Tiina Suomijärvi, Y. Zhang, Z. Y. You, Z. Z. Zong, (for the LHAASO Collaboration)
2019, 43(7): 075001. doi: 10.1088/1674-1137/43/7/075001
The Large High Altitude Air Shower Observatory (LHAASO) is a composite cosmic ray observatory consisting of three detector arrays: kilometer square array (KM2A), which includes the electromagnetic detector array and muon detector array, water Cherenkov detector array (WCDA) and wide field-of-view Cherenkov telescope array (WFCTA). One of the main scientific objectives of LHAASO is to precisely measure the cosmic rays energy spectrum of individual components from \begin{document}$ 10^{14} $\end{document} eV to \begin{document}$ 10^{18} $\end{document} eV. The hybrid observation will be employed by the LHAASO experiment, in which the lateral and longitudinal distributions of extensive air shower can be observed simultaneously. Thus, many kinds of parameters can be used for primary nuclei identification. In this paper, high purity cosmic ray simulation samples of the light nuclei component are obtained using multi-variable analysis. The apertures of 1/4 LHAASO array for pure proton and mixed proton and helium (H&He) samples are \begin{document}$ 900 \rm\ m^{2}Sr $\end{document} and \begin{document}$ 1800 \rm\ m^{2}Sr $\end{document} , respectively. Prospect of obtaining proton and H&He spectra from 100 TeV to 4 PeV is discussed.
Lateral distribution of EAS muons measured for the primary cosmic ray energy around 100 TeV
You-Liang Feng, Yi Zhang, Tian-Lu Chen, Yi-Qing Guo, Hong-Bo Hu, Cheng Liu, Guang-Guang Xin, Yu-Hua Yao, Zhen Wang, , Qi Gao, Mao-Yuan Liu, Shi-Ping Zhao, Bing-Qiang Qiao, Ying-Ying Guo, Hui Cai
2019, 43(7): 075002. doi: 10.1088/1674-1137/43/7/075002
The muonic component of the extensive air showers (EAS) is of great importance for the astroparticle physics. It carries the information about the properties of primary cosmic ray (CR) particles, such as their mass, and electromagnetic and hadronic nature. It provides a sensitive test for the hadronic interaction models, which are inevitable for describing the cascade shower development of cosmic rays in EAS experiments. The YangBaJing Hybrid Array (YBJ-HA) experiment has been in operation since the end of 2016. Surface detectors are used for the measurements of primary energy, angular direction and core position of a shower event, while underground muon detectors are used for measuring the density of muons at various locations. Using the data obtained by the YBJ-HA experiment, this work reports the first measurement of the lateral muon distribution for the primary cosmic ray energy in the 100 TeV region. The punch-through effect is evaluated via MC simulation.
Non-parametric reconstruction of dark energy and cosmic expansion from the Pantheon compilation of type Ia supernovae
Hai-Nan Lin, Xin Li, Li Tang
2019, 43(7): 075101. doi: 10.1088/1674-1137/43/7/075101
The equation of state (EoS) of dark energy plays an important role in the evolution of the universe and has attracted considerable interest in the recent years. With the progress in observational technique, a precise constraint on the EoS of dark energy can be obtained. In this study, we reconstruct the EoS of dark energy and cosmic expansion using Gaussian processes (GP) from the most up-to-date Pantheon compilation of type Ia supernovae (SNe Ia), which consists of 1048 finely calibrated SNe Ia. The reconstructed EoS of dark energy has a large uncertainty owing to its dependence on the second-order derivative of the construction. Adding the direct measurements of Hubble parameters \begin{document}$H(z)$\end{document} as an additional constraint on the first-order derivative can partially reduce the uncertainty; however, it is still not sufficiently precise to distinguish between the evolving and the constant dark energy. Moreover, the results heavily rely on the prior of the Hubble constant \begin{document}$H_0$\end{document}. The \begin{document}$H_0$\end{document} value inferred from SNe+\begin{document}$H(z)$\end{document} without prior is \begin{document}$H_0=70.5\pm 0.5~{\rm km~s^{-1}~Mpc^{-1}}$\end{document}. Moreover, the matter density \begin{document}$\Omega_M$\end{document} has a non-negligible effect on the reconstruction of dark energy. Therefore, more accurate determinations on \begin{document}$H_0$\end{document} and \begin{document}$\Omega_M$\end{document} are required to tightly constrain the EoS of dark energy.
The prospects of using gravitational waves for constraining the anisotropy of the Universe
Zhi-Chao Zhao, Hai-Nan Lin, Zhe Chang
2019, 43(7): 075102. doi: 10.1088/1674-1137/43/7/075102
The observation of GW150914 gave a new independent measurement of the luminosity distance of a gravitational wave event. In this paper, we constrain the anisotropy of the Universe by using gravitational wave events. We simulate hundreds of events of binary neutron star merger that may be observed by the Einstein Telescope. Full simulation of the production process of gravitational wave data is employed. We find that 200 binary neutron star merging events with the redshift in (0,1) observed by the Einstein Telescope may constrain the anisotropy with an accuracy comparable to that from the Union2.1 supernovae. This result shows that gravitational waves can be a powerful tool for investigating cosmological anisotropy.
Primordial perturbations and non-gaussianities in Hořava-Lifshitz gravity
Xian Gao
2019, 43(7): 075103. doi: 10.1088/1674-1137/43/7/075103
We investigate primordial perturbations and non-gaussianities in the Hořava-Lifshitz theory of gravitation. In the UV limit, the scalar perturbation in the Hořava theory is naturally scale-invariant, ignoring the details of the expansion of the Universe. One may thus relax the exponential inflation and the slow-roll conditions for the inflaton field. As a result, it is possible that the primordial non-gaussianities, which are " slow-roll suppressed” in the standard scenarios, become large. We calculate the non-gaussianities from the bispectrum of the perturbation and find that the equilateral-type non-gaussianity is of the order of unity, while the local-type non-gaussianity remains small, as in the usual single-field slow-roll inflation model in general relativity. Our result is a new constraint on Hořava-Lifshitz gravity.