2018 Vol. 42, No. 2

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Determination of the number of ψ (3686) events at BESⅢ
M. Ablikim, et al
2018, 42(2): 023001. doi: 10.1088/1674-1137/42/2/023001
The numbers of ψ(3686) events accumulated by the BESⅢ detector for the data taken during 2009 and 2012 are determined to be (107.0±0.8)×106 and (341.1±2.1)×106, respectively, by counting inclusive hadronic events, where the uncertainties are systematic and the statistical uncertainties are negligible. The number of events for the sample taken in 2009 is consistent with that of the previous measurement. The total number of ψ(3686) events for the two data taking periods is (448.1±2.9)×106.
Limits on light WIMPs with a 1 kg-scale germanium detector at 160 eVee physics threshold at the China Jinping Underground Laboratory
Li-Tao Yang, et al
2018, 42(2): 023002. doi: 10.1088/1674-1137/42/2/023002
We report results of a search for light weakly interacting massive particle (WIMP) dark matter from the CDEX-1 experiment at the China Jinping Underground Laboratory (CJPL). Constraints on WIMP-nucleon spin-independent (SI) and spin-dependent (SD) couplings are derived with a physics threshold of 160 eVee, from an exposure of 737.1 kg-days. The SI and SD limits extend the lower reach of light WIMPs to 2 GeV and improve over our earlier bounds at WIMP mass less than 6 GeV.
Chiral crossover transition in a finite volume
Chao Shi, Wenbao Jia, An Sun, Liping Zhang, Hongshi Zong
2018, 42(2): 023101. doi: 10.1088/1674-1137/42/2/023101
Finite volume effects on the chiral crossover transition of strong interactions at finite temperature are studied by solving the quark gap equation within a cubic volume of finite size L. With the anti-periodic boundary condition, our calculation shows the chiral quark condensate, which characterizes the strength of dynamical chiral symmetry breaking, decreases as L decreases below 2.5 fm. We further study the finite volume effects on the pseudo-transition temperature Tc of the crossover, showing a significant decrease in Tc as L decreases below 3 fm.
Phenomenological aspects of possible vacua of a neutrino flavor model
Takuya Morozumi, Hideaki Okane, Hiroki Sakamoto, Yusuke Shimizu, Kenta Takagi, Hiroyuki Umeeda
2018, 42(2): 023102. doi: 10.1088/1674-1137/42/2/023102
We discuss a supersymmetric model with discrete flavor symmetry A4×Z3. The additional scalar fields which contribute masses of leptons in the Yukawa terms are introduced in this model. We analyze their scalar potential and find that they have various vacuum structures. We show the relations among 24 different vacua and classify them into two types. We derive expressions of the lepton mixing angles, Dirac CP violating phase and Majorana phases for the two types. The model parameters which are allowed by the experimental data of the lepton mixing angles are different for each type. We also study the constraints on the model parameters which are related to Majorana phases. The different allowed regions of the model parameters for the two types are shown numerically for a given region of two combinations of the CP violating phases.
Testing the electroweak phase transition in scalar extension models at lepton colliders
Qing-Hong Cao, Fa-Peng Huang, Ke-Pan Xie, Xinmin Zhang
2018, 42(2): 023103. doi: 10.1088/1674-1137/42/2/023103
We study the electroweak phase transition in three scalar extension models beyond the Standard Model. Assuming new scalars are decoupled at some heavy scale, we use the covariant derivative expansion method to derive all of the dimension-6 effective operators, whose coefficients are highly correlated in a specific model. We provide bounds to the complete set of dimension-6 operators by including the electroweak precision test and recent Higgs measurements. We find that the parameter space of strong first-order phase transitions (induced by the|H|6 operator) can be probed extensively in Zh production at future electron-positron colliders.
Constraining qqtt operators from four-top production: a case for enhanced EFT sensitivity
Cen Zhang
2018, 42(2): 023104. doi: 10.1088/1674-1137/42/2/023104
Recently, experimental collaborations have reported O(10) upper limits on the signal strength of four-top production at the LHC. Surprisingly, we find that the constraining power of four-top production on the qqtt type of operators is already competitive with the measurements of top-pair production, even though the precision level of the latter is more than two orders of magnitude better. This is explained by the enhanced sensitivity of the four-top cross section to qqtt operators, due to multiple insertion of operators in the squared amplitude, and to the large threshold energy of four-top production. We point out that even though the dominant contribution beyond the standard model comes from the O(C44/Λ8) terms, the effective field theory expansion remains valid for a wide range of underlying theories. Considering the possible improvements of this measurement with higher integrated luminosity, we believe that this process will become even more crucial for probing and testing the standard model deviations in the top-quark sector, and will eventually provide valuable information about the top-quark properties, leading to significant improvements in precision top physics.
Limiting majoron self-interactions from gravitational wave experiments
Andrea Addazi, Antonino Marcianò
2018, 42(2): 023105. doi: 10.1088/1674-1137/42/2/023105
We show how majoron models may be tested/limited in gravitational wave experiments. In particular, the majoron self-interaction potential may induce a first order phase transition, producing gravitational waves from bubble collisions. We dub such a new scenario the violent majoron model, because it would be associated with a violent phase transition in the early Universe. Sphaleron constraints can be avoided if the global U(1)B-L is broken at scales lower than the electroweak scale, provided that the B-L spontaneously breaking scale is lower than 10 {TeV} in order to satisfy the cosmological mass density bound. The possibility of a sub-electroweak phase transition is practically unconstrained by cosmological bounds and it may be detected within the sensitivity of the next generation of gravitational wave experiments:eLISA, DECIGO and BBO. We also comment on its possible detection in the next generation of electron-positron colliders, where majoron production can be observed from the Higgs portals in missing transverse energy channels.
Exploratory study of possible resonances in heavy meson-heavy baryon coupled-channel interactions
Chao-Wei Shen, Deborah Rönchen, Ulf-G. Meißner, Bing-Song Zou
2018, 42(2): 023106. doi: 10.1088/1674-1137/42/2/023106
We use a unitary coupled-channel model to study the D Λc-D Σc interactions. In our calculation, SU(3) flavor symmetry is applied to determine the coupling constants. Several resonant and bound states with different spin and parity are dynamically generated in the mass range of the recently observed pentaquarks. The approach is also extended to the hidden beauty sector to study the m B Λb-B Σb interactions. As the m b-quark mass is heavier than the m c-quark mass, there are more resonances observed for the m B Λb-B Σb interactions and they are more tightly bound.
Gravitational waves from dark first order phase transitions and dark photons
Andrea Addazi, Antonino Marcianò
2018, 42(2): 023107. doi: 10.1088/1674-1137/42/2/023107
Cold Dark Matter particles may interact with ordinary particles through a dark photon, which acquires a mass thanks to a spontaneous symmetry breaking mechanism. We discuss a dark photon model in which the scalar singlet associated to the spontaneous symmetry breaking has an effective potential that induces a first order phase transition in the early Universe. Such a scenario provides a rich phenomenology for electron-positron colliders and gravitational waves interferometers, and may be tested in several different channels. The hidden first order phase transition implies the emission of gravitational waves signals, which may constrain the dark photon's space of parameters. Compared limits from electron-positron colliders, astrophysics, cosmology and future gravitational waves interferometers such as eLISA, U-DECIGO and BBO are discussed. This highly motivates a cross-checking strategy of data arising from experiments dedicated to gravitational waves, meson factories, the International Linear Collider (ILC), the Circular Electron Positron Collider (CEPC) and other underground direct detection experiments of cold dark matter candidates.
New model of kaon regeneration
V. I. Nazaruk
2018, 42(2): 023108. doi: 10.1088/1674-1137/42/2/023108
It is shown that in the standard model of KS0 regeneration a system of non-coupled equations of motion is used instead of the coupled ones. A model alternative to the standard one is proposed. A calculation performed by means of the diagram technique agrees with that based on exact solution of the equations of motion.
A data-driven approach to π0, η and η' single and double Dalitz decays
Rafel Escribano, Sergi González-Solís
2018, 42(2): 023109. doi: 10.1088/1674-1137/42/2/023109
The dilepton invariant mass spectra and integrated branching ratios of the single and double Dalitz decays P→l+l-γ and P→l+l-l+l- (P0, η, η'; l=e or μ) are predicted by means of a data-driven approach based on the use of rational approximants applied to π0, η and η' transition form factor experimental data in the space-like region.
Finite-size behaviour of generalized susceptibilities in the whole phase plane of the Potts model
Xue Pan, Yanhua Zhang, Lizhu Chen, Mingmei Xu, Yuanfang Wu
2018, 42(2): 023110. doi: 10.1088/1674-1137/42/2/023110
We study the sign distribution of generalized magnetic susceptibilities in the temperature-external magnetic field plane using the three-dimensional three-state Potts model. We find that the sign of odd-order susceptibility is opposite in the symmetric (disorder) and broken (order) phases, but that of the even-order one remains positive when it is far away from the phase boundary. When the critical point is approached from the crossover side, negative fourth-order magnetic susceptibility is observable. It is also demonstrated that non-monotonic behavior occurs in the temperature dependence of the generalized susceptibilities of the energy. The finite-size scaling behavior of the specific heat in this model is mainly controlled by the critical exponent of the magnetic susceptibility in the three-dimensional Ising universality class.
Effects of mean-field and softening of equation of state on elliptic flow in Au+Au collisions at √sNN=5 GeV from the JAM model
Jiamin Chen, Xiaofeng Luo, Feng Liu, Yasushi Nara
2018, 42(2): 024001. doi: 10.1088/1674-1137/42/2/024001
We perform a systematic study of elliptic flow (v2) in Au+Au collisions at √sNN=5 GeV by using a microscopic transport model, JAM. The centrality, pseudorapidity, transverse momentum and beam energy dependence of v2 for charged as well as identified hadrons are studied. We investigate the effects of both the hadronic mean-field and the softening of equation of state (EoS) on elliptic flow. The softening of the EoS is realized by imposing attractive orbits in two body scattering, which can reduce the pressure of the system. We found that the softening of the EoS leads to the enhancement of v2, while the hadronic mean-field suppresses v2 relative to the cascade mode. It indicates that elliptic flow at high baryon density regions is highly sensitive to the EoS and the enhancement of v2 may probe the signature of a first-order phase transition in heavy-ion collisions at beam energies of a strong baryon stopping region.
Relativistic interpretation of the nature of the nuclear tensor force
Yao-Yao Zong, Bao-Yuan Sun
2018, 42(2): 024101. doi: 10.1088/1674-1137/42/2/024101
The spin-dependent nature of the nuclear tensor force is studied in detail within the relativistic Hartree-Fock approach. The relativistic formalism for the tensor force is supplemented with an additional Lorentz-invariant tensor formalism in the σ-scalar channel, so as to take into account almost fully the nature of the tensor force brought about by the Fock diagrams in realistic nuclei. Specifically, the tensor sum rules are tested for the spin and pseudo-spin partners with and without nodes, to further understand the nature of the tensor force within the relativistic model. It is shown that the interference between the two components of nucleon spinors causes distinct violations of the tensor sum rules in realistic nuclei, mainly due to the opposite signs on the κ quantities of the upper and lower components, as well as the nodal difference. However, the sum rules can be precisely reproduced if the same radial wave functions are taken for the spin/pseudo-spin partners in addition to neglecting the lower/upper components, revealing clearly the nature of the tensor force.
Ground-state properties of light kaonic nuclei signaling symmetry energy at high densities
Rongyao Yang, Sina Wei, Weizhou Jiang
2018, 42(2): 024102. doi: 10.1088/1674-1137/42/2/024102
A sensitive correlation between the ground-state properties of light kaonic nuclei and the symmetry energy at high densities is constructed under the framework of relativistic mean-field theory. Taking oxygen isotopes as an example, we see that a high-density core is produced in kaonic oxygen nuclei, due to the strongly attractive antikaon-nucleon interaction. It is found that the 1S1/2 state energy in the high-density core of kaonic nuclei can directly probe the variation of the symmetry energy at supranormal nuclear density, and a sensitive correlation between the neutron skin thickness and the symmetry energy at supranormal density is established directly. Meanwhile, the sensitivity of the neutron skin thickness to the low-density slope of the symmetry energy is greatly increased in the corresponding kaonic nuclei. These sensitive relationships are established upon the fact that the isovector potential in the central region of kaonic nuclei becomes very sensitive to the variation of the symmetry energy. These findings might provide another perspective to constrain high-density symmetry energy, and await experimental verification in the future.
Massive neutron stars and Λ-hypernuclei in relativistic mean field models
Ting-Ting Sun, Cheng-Jun Xia, Shi-Sheng Zhang, M. S. Smith
2018, 42(2): 025101. doi: 10.1088/1674-1137/42/2/025101
Based on relativistic mean field (RMF) models, we study finite Λ-hypernuclei and massive neutron stars. The effective m N-m N interactions PK1 and TM1 are adopted, while the m N-Λ interactions are constrained by reproducing the binding energy of Λ-hyperon at 1s orbit of Λ40Ca. It is found that the Λ-meson couplings follow a simple relation, indicating a fixed Λ potential well for symmetric nuclear matter at saturation densities, i.e., around VΛ=-29.786 MeV. With those interactions, a large mass range of Λ-hypernuclei can be described well. Furthermore, the masses of PSR J1614-2230 and PSR J0348+0432 can be attained adopting the Λ-meson couplings gσΛ/gσN≳ 0.73, gωΛ/gωN≳0.80 for PK1 and gσΛ/gσN≳ 0.81, gωΛ/gωN≳ 0.90 for TM1, respectively. This resolves the hyperon puzzle without introducing any additional degrees of freedom.
Searching for γ-ray emission from Reticulum Ⅱ by Fermi-LAT
Yi Zhao, Xiao-Jun Bi, Peng-Fei Yin, Xinmin Zhang
2018, 42(2): 025102. doi: 10.1088/1674-1137/42/2/025102
Recently, many new dwarf spheroidal satellites (dSphs) have been discovered by the Dark Energy Survey (DES). These dSphs are ideal candidates for probing for gamma-ray emissions from dark matter (DM) annihilation. However, no significant signature has been found by the Fermi-LAT dSph observations. In this work, we reanalyze the Fermi-LAT Pass 8 data from the direction of Reticulum Ⅱ, where a slight excess has been reported by some previous studies. We treat Reticulum Ⅱ (DES J0335.6-5403) as a spatially extended source, and find that no significant gamma-ray signature is observed. Based on this result, we set upper-limits on the DM annihilation cross section.