2019 Vol. 43, No. 2

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The Higgs signatures at the CEPC CDR baseline
Hang Zhao, Yong-Feng Zhu, Cheng-Dong Fu, Dan Yu, Man-Qi Ruan
2019, 43(2): 023001. doi: 10.1088/1674-1137/43/2/023001
As a Higgs factory, the CEPC (Circular Electron-Positron Collider) project aims at precision measurements of the Higgs boson properties. A baseline detector concept, APODIS (A PFA Oriented Detector for the HIggS factory), has been proposed for the CEPC CDR (Conceptual Design Report) study. We explore the Higgs signatures for this baseline design with \begin{document}$\nu\bar{\nu}$\end{document} Higgs events. The detector performance for reconstructing charged particles, photons and jets is quantified with \begin{document}$H \to \mu\mu, \gamma\gamma$\end{document} and jet final states, respectively. The resolutions of reconstructed Higgs boson mass are comparable for the different decay modes with jets in the final states. We also analyze the \begin{document}$H \to WW$\end{document} * and ZZ* decay modes, where a clear separation between different decay cascades is observed.
Study of the Standard Model and Majorana neutrino contributions to ${ B}^{{ +}} { \to} { K}^{{ (*){ \pm}}}{ \mu}^{ +}{ \mu}^{{ \mp}}$
Hong-Lei Li, Peng-Cheng Lu, Cong-Feng Qiao, Zong-Guo Si, Ying Wang
2019, 43(2): 023101. doi: 10.1088/1674-1137/43/2/023101
Lepton number violation processes can be induced by the Majorana neutrino exchange, which provide evidence for the Majorana nature of neutrinos. In addition to the natural explanation of the small neutrino masses, Type-I seesaw mechanism predicts the existence of Majorana neutrinos. The aim of this work is to study the B meson rare decays \begin{document}$B^{+} \to K^{(*)+}\mu^+\mu^-$\end{document} in the Standard Model and its extensions, and then to investigate the same-sign decay process \begin{document}$B^{+}\to K^{(*)-}\mu^{+}\mu^+$\end{document} . The corresponding dilepton invariant mass distributions are calculated. It is found that the dilepton angular distributions could shed light on the properties of new interactions induced by Majorana neutrinos.
Scalar quintuplet minimal dark matter with Yukawa interactions: perturbative up to the Planck scale
Zhu Luo, Cheng-feng Cai, Zhao-feng Kang, Zhao-huan Yu, Hong-hao Zhang
2019, 43(2): 023102. doi: 10.1088/1674-1137/43/2/023102
We confront the perturbativity problem in the real scalar quintuplet minimal dark matter model. In the original model, the quintuplet quartic self-coupling inevitably hits a Landau pole at a scale ~1014 GeV, far below the Planck scale. In order to push up this Landau pole scale, we extend the model with a fermionic quintuplet and three fermionic singlets which couple to the scalar quintuplet via Yukawa interactions. Involving such Yukawa interactions at a scale ~1010 GeV can not only keep all couplings perturbative up to the Planck scale, but can also explain the smallness of neutrino masses via the type-I seesaw mechanism. Furthermore, we identify the parameter regions favored by the condition that perturbativity and vacuum stability are both maintained up to the Planck scale.
A model to explain the angular distribution of $ {{{J /\psi}}} $ and $ {{\psi(2S)}} $ decay into $ {\Lambda \overline{\Lambda}} $ and ${\Sigma^0 \overline{\Sigma^0}} $
M. Alekseev, A. Amoroso, R. Baldini Ferroli, I. Balossino, M. Bertani, D. Bettoni, F. Bianchi, J. Chai, G. Cibinetto, F. Cossio, F. De Mori, M. Destefanis, R. Farinelli, L. Fava, G. Felici, I. Garzia, M. Greco, L. Lavezzi, C. Leng, M. Maggiora, A. Mangoni, S. Marcello, G. Mezzadri, S. Pacetti, P. Patteri, A. Rivetti, M. Da Rocha Rolo, M. Savrié, S. Sosio, S. Spataro, L. Yan
2019, 43(2): 023103. doi: 10.1088/1674-1137/43/2/023103
BESIII data show a particular angular distribution for the decay of \begin{document}$ J/\psi $\end{document} and \begin{document}$ \psi(2S) $\end{document} mesons into \begin{document}$ \Lambda \overline \Lambda $\end{document} and \begin{document}$ \Sigma^0 {\overline \Sigma}{}^0 $\end{document} hyperons: the angular distribution of the decay \begin{document}$ {{\psi(2S)}} \to {\Sigma^0\overline{\Sigma}{}^0} $\end{document} exhibits an opposite trend with respect to the other three channels: \begin{document}$ J/\psi \to \Lambda \overline \Lambda $\end{document} , \begin{document}$ J/\psi \to \Sigma^0 {\overline \Sigma}{}^0 $\end{document} and \begin{document}$ \psi(2S) \to \Lambda \overline \Lambda $\end{document} . We define a model to explain the origin of this phenomenon.
A light scalar in the Minimal Dilaton Model in light of the LHC constraints
Lijia Liu, Haoxue Qiao, Kun Wang, Jingya Zhu
2019, 43(2): 023104. doi: 10.1088/1674-1137/43/2/023104
Whether an additional light scalar exists is an interesting topic in particle physics beyond the Standard Model (SM), as we do not know as yet the nature of physics beyond the SM in the low mass region in view of the inconsistent results of the ATLAS and CMS collaborations in their search for light resonances around 95 GeV in the diphoton channel. We study a light scalar in the Minimal Dilaton Model (MDM). Under the theoretical and the latest experimental constraints, we sort the selected data samples into two scenarios according to the diphoton rate of the light scalar: the large-diphoton scenario (with \begin{document}$\sigma_{\gamma\gamma}/{\rm SM}\gtrsim0.2$\end{document} ) and the small-diphoton scenario (with \begin{document}$\sigma_{\gamma\gamma}/{\rm SM}\lesssim0.2$\end{document} ), which are favored by the CMS and ATLAS results, respectively. We compare the two scenarios, test the characteristics of the model parameters, the scalar couplings, production and decay, and consider how they could be further discerned at colliders. We draw the following conclusions for the two scenarios: (i) The large-diphoton scenario has in general a small Higgs-dilaton mixing angle ( \begin{document}$|\sin\theta_S|\lesssim0.2$\end{document} ) and a small dilaton vacuum expectation value (VEV) \begin{document}$f$\end{document} ( \begin{document}$0.5\lesssim\eta\equiv v/f\lesssim1$\end{document} ), and the small-diphoton scenario has large mixing ( \begin{document}$|\sin\theta_S|\gtrsim0.4$\end{document} ) or large VEV ( \begin{document}$\eta\equiv v/f\lesssim0.3$\end{document} ). (ii) The large-diphoton scenario in general predicts small \begin{document}$s\gamma\gamma$\end{document} coupling ( \begin{document}$|C_{s\gamma\gamma}/{\rm SM}|\lesssim0.3$\end{document} ) and large \begin{document}$sgg$\end{document} coupling ( \begin{document}$0.6\lesssim|C_{sgg}/{\rm SM}|\lesssim1.2$\end{document} ), while the small-diphoton scenario predicts small \begin{document}$sgg$\end{document} coupling ( \begin{document}$|C_{sgg}/{\rm SM}|\lesssim0.5$\end{document} ). (iii) The large-diphoton scenario can interpret the small diphoton excess seen by CMS at its central value, when \begin{document}$m_s\simeq95$\end{document} GeV, \begin{document}$\eta\simeq0.6$\end{document} and \begin{document}$|\sin\theta_S|\simeq0$\end{document} . (iv) The large-diphoton scenario in general predicts a negative correlation between the Higgs couplings \begin{document}$|C_{h\gamma\gamma}/{\rm SM}|$\end{document} and \begin{document}$|C_{hgg}/{\rm SM}|$\end{document} , while the small-diphoton scenario predicts that both couplings are smaller than 1, or \begin{document}$|C_{h\gamma\gamma}/{\rm SM}|\lesssim0.9 \lesssim|C_{hgg}/{\rm SM}|$\end{document} .
Criticality of QCD in a holographic QCD model with critical end point
Xun Chen, Danning Li, Mei Huang
2019, 43(2): 023105. doi: 10.1088/1674-1137/43/2/023105
The thermodynamics of strongly interacting matter near the critical end point are investigated in a holographic QCD model, which can describe the QCD phase diagram in \begin{document}$ T-\mu $\end{document} plane qualitatively. Critical exponents along different axes ( \begin{document}$ \alpha,\beta,\gamma,\delta $\end{document} ) are extracted numerically. It is given that \begin{document}$ \alpha\approx 0$\end{document} , \begin{document}$\beta\approx 0.54 $\end{document} , \begin{document}$\gamma \approx 1.04$\end{document} , and \begin{document}$\delta \approx 2.97$\end{document} , which is similar to the three-dimensional Ising mean-field approximation and previous holographic QCD model calculations. We also discuss the possibilities to go beyond the mean field approximation by including the full back-reaction of the chiral dynamics in the holographic framework.
Estimating the production rates of D -wave charmed mesons via the semileptonic decays of bottom mesons
Kan Chen, Hong-Wei Ke, Xiang Liu, Takayuki Matsuki
2019, 43(2): 023106. doi: 10.1088/1674-1137/43/2/023106
Using the covariant light-front approach with conventional vertex functions, we estimate the production rates of D -wave charmed/charmed-strange mesons via the \begin{document}$B_{(s)}$\end{document} semileptonic decays. As the calculated production rates are significant, it seems possible to experimentally search for D -wave charmed/charmed-strange mesons via semileptonic decays, which may provide an additional approach for exploring D -wave charmed/charmed-strange mesons.
Different production sources of light nuclei inultra-relativistic heavy-ion collisions
Rui-Qin Wang, Jun Song, Gang Li, Feng-Lan Shao
2019, 43(2): 024101. doi: 10.1088/1674-1137/43/2/024101
We systematically study different production sources of light nuclei in ultra-relativistic heavy-ion collisions with a new method, an exclusive quark combination model + an inclusive hadron recombination model. We take deuterons and 3He produced in Pb-Pb collisions at \begin{document}$\sqrt{s_{NN}}=2.76$\end{document} TeV as examples to show the contribution of different production sources by studying their rapidity densities \begin{document}${\rm d}N/{\rm d}y$\end{document} , yield ratios and transverse momentum ( \begin{document}$p_T$\end{document} ) spectra just after hadronization and at the final kinetic freeze-out. We find that about a half of \begin{document}$d$\end{document} and a fourth of 3He created just after hadronization can survive after the hadronic evolution process. Nucleons from \begin{document}$\Delta$\end{document} resonance decays make a much larger contribution to the regeneration of light nuclei at the hadronic phase stage, and this contribution is about 77% and 90% for \begin{document}$d$\end{document} and 3He, respectively, calculated at the final kinetic freeze-out. In addition, we give an explanation for the constant behaviors of yield ratios \begin{document}$d/p$\end{document} and 3He \begin{document}$/p$\end{document} as a function of the averaged charged multiplicity in Pb-Pb collisions and also provide a possible explanation for the observation that \begin{document}$d/p$\end{document} in Pb-Pb collisions is larger by a factor of about two than in pp collisions at LHC energies.
Cross sections for inelastic 2-to-2 meson-meson scattering in hadronic matter
Ting-Ting Wang, Xiao-Ming Xu
2019, 43(2): 024102. doi: 10.1088/1674-1137/43/2/024102
With quark-antiquark annihilation and creation in the first Born approximation, we study the reactions: \begin{document}$K \bar {K} \to K \bar {K}^\ast$\end{document} , \begin{document}$K \bar{K} \to K^* \bar{K}$\end{document} , \begin{document}$\pi K \to \pi K^\ast$\end{document} , \begin{document}$\pi K \to \rho K$\end{document} , \begin{document}$\pi \pi \to K \bar{K}^\ast$\end{document} , \begin{document}$\pi \pi \to K^\ast \bar{K}$\end{document} , \begin{document}$\pi \pi \to K^\ast \bar{K}^\ast$\end{document} , \begin{document}$\pi \rho \to K \bar{K}$\end{document} , \begin{document}$\pi \rho \to K^\ast \bar{K}^\ast$\end{document} , \begin{document}$\rho \rho \to K^\ast \bar{K}^\ast$\end{document} , \begin{document}$K \bar{K}^\ast \to \rho \rho$\end{document} , and \begin{document}$K^* \bar{K} \to \rho \rho$\end{document} . Unpolarized cross sections for the reactions are obtained from transition amplitudes that are composed of mesonic quark-antiquark relative-motion wave functions and the transition potential for quark-antiquark annihilation and creation. Using a quark-antiquark potential that is equivalent to the transition potential, we prove that the total spin of the two final mesons may not be equal to the total spin of the two initial mesons. Based on flavor matrix elements, cross sections for some isospin channels of reactions can be obtained from other isospin channels of the reactions. Remarkable temperature dependence of the cross sections was observed.
A dynamical description of the 136Xe + p spallation at 1000 MeV/nucleon
Fan Zhang, Jun Su
2019, 43(2): 024103. doi: 10.1088/1674-1137/43/2/024103
We propose a dynamical description of the 136Xe + p spallation at 1000 MeV/nucleon with the aim of probing the mechanism which rules the production of intermediate-mass fragments (IMF). The isospin-dependent quantum molecular dynamics (IQMD) model is used to describe the dynamical process of spallation until hot fragments with excitation energy less than a certain value Estop are formed. The statistical code GEMINI is applied to simulate the light-particle evaporation from hot fragments. It is found that IMF production is well described by the model when Estop = 2 MeV/nucleon is used. Comparison of the calculated mean neutron-to-proton ratio and the experimental data indicates that Estop should be 3 MeV/nucleon.
Description of the critical point symmetry in 124Te by IBM-2
Da-Li Zhang, Cheng-Fu Mu
2019, 43(2): 024104. doi: 10.1088/1674-1137/43/2/024104
Based on the neutron and proton degrees of freedom, low-lying energy levels, \begin{document}$ E2 $\end{document} , \begin{document}$ M1 $\end{document} , and \begin{document}$ E0 $\end{document} transition strengths of nucleus 124Te have been calculated by the neutron-proton interacting boson model. The calculated results are reasonably consistent with the experimental data. By comparing the key observables of the states at the critical point of \begin{document}$ {\rm U}_{\pi \nu}(5) $\end{document} - \begin{document}$ {\rm O}_{\pi \nu}(6) $\end{document} transition with the experimental data and calculated results, we show that the 124Te is a possible nucleus at the critical point of the second-order phase transition from vibration to unstable rotation, and such a critical point exhibits slight triaxial rotation. The 0 \begin{document}$_2^ + $\end{document} state of 124Te can be interpreted as the lowest state of the first-excited family of the intrinsic levels in the critical point symmetry.
In-medium NN→NΔ cross section and its dependence on effective Lagrange parameters in isospin-asymmetric nuclear matter
Ying Cui, Ying-Xun Zhang, Zhu-Xia Li
2019, 43(2): 024105. doi: 10.1088/1674-1137/43/2/024105
The in-medium \begin{document}$ NN\rightarrow N\Delta $\end{document} cross sections and its differential cross sections in isospin asymmetric nuclear medium are investigated in the framework of the one-boson exchange model by including isovector mesons, i.e., \begin{document}$ \delta $\end{document} and \begin{document}$ \rho $\end{document} mesons. Our results show that the in-medium \begin{document}$ NN\rightarrow N\Delta $\end{document} cross sections are suppressed when the density increases, and the differential cross sections become isotropic with an increase in the density around the \begin{document}$ \Delta $\end{document} threshold energy. The isospin splitting on the medium correction factor, \begin{document}$ R=\sigma_{ NN\rightarrow N\Delta}^*/\sigma_{NN\rightarrow N\Delta}^{\rm{free}} $\end{document} is observed for different channels of \begin{document}$ NN\to N\Delta $\end{document} , especially around the threshold energy for all the effective Lagrangian parameters. By analyzing the selected effective Lagrangian parameters, our results show that the larger effective mass is, the weaker medium correction \begin{document}$ R $\end{document} is.
Simple black holes with anisotropic fluid
Inyong Cho, Hyeong-Chan Kim
2019, 43(2): 025101. doi: 10.1088/1674-1137/43/2/025101
We study a spherically symmetric spacetime made of an anisotropic fluid whose radial equation-of-state is given by \begin{document}$ p_1 = -\rho $\end{document} . This case allows analytic solutions and is a good example for studying the static configuration of a black hole plus matter. For a given equation-of-state parameter \begin{document}$ w_2 = p_2/\rho $\end{document} for angular directions, we find the exact solutions of the Einstein equation described by two parameters. We classify the solutions into six types based on the behavior of the metric function. Depending on the parameters, the solutions can have event and cosmological horizons. One of the solution types corresponds to a generalization of the Reissner-Nordström black hole, the thermodynamic properties for which are obtained in a simple form. The solutions are stable under radial perturbations.
Observational constraints on running vacuum model
Jin-Jun Zhang, Chung-Chi Lee, Chao-Qiang Geng
2019, 43(2): 025102. doi: 10.1088/1674-1137/43/2/025102
We investigate the power spectra of the CMB temperature and matter density in the running vacuum model (RVM) with the time-dependent cosmological constant of \begin{document}$ \Lambda = 3 \nu H^2 + \Lambda_0 $\end{document} , where \begin{document}$ H $\end{document} is the Hubble parameter. In this model, dark energy decreases in time and decays to both matter and radiation. By using the Markov chain Monte Carlo method, we constrain the model parameter \begin{document}$ \nu $\end{document} as well as the cosmological observables. Explicitly, we obtain \begin{document}$ \nu \leqslant 1.54 \times 10^{-4} $\end{document} (68% confidence level) in the RVM with the best-fit \begin{document}$\chi^2_{\mathrm{RVM}} = 13968.8$\end{document} , which is slightly smaller than \begin{document}$\chi^2_{\Lambda \mathrm{CDM}} = 13969.8$\end{document} in the \begin{document}$\Lambda{\rm{CDM}}$\end{document} model of \begin{document}$ \nu=0 $\end{document} .