2017 Vol. 41, No. 11
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To study the nature of the state Y(2175), a dedicated data set of m e+ e- collision data was collected at the center-of-mass energy of 2.125 GeV with the BESⅢ detector at the BEPCⅡ collider. By analyzing large-angle Bhabha scattering events, the integrated luminosity of this data set is determined to be 108.49±0.02±0.85 pb-1, where the first uncertainty is statistical and the second one is systematic. In addition, the center-of-mass energy of the data set is determined with radiative dimuon events to be 2126.55±0.03±0.85 MeV, where the first uncertainty is statistical and the second one is systematic.
We have studied Yang-Baxter deformations of supercoset sigma models with Z4m grading. The deformations are specified by a skew-symmetric classical r-matrix satisfying the classical Yang-Baxter equations. The deformed action is constructed and the Lax pair is also presented. When m=1, our results reduce to those of the type ⅡB Green-Schwarz superstring on AdS5×S5 background recently given by Kawaguchi, Matsumoto and Yoshida.
The universality of the weak interactions can be tested in semileptonic b → c transitions, and in particular in the ratios R (D*)) Γ(B → D*) τν)/Γ(B→ D*) lν) (where l=μ or e). Due to the recent differences between the experimental measurements of these observables by BaBar, Belle and LHCb on the one hand and the Standard Model predicted values on the other hand, we study the predicted ratios R (D*))=Γ(B → D*)τ +"missing")/Γ(B → D*) lν) in scenarios with an additional sterile heavy neutrino of mass~1 GeV. Further, we evaluate the newly defined ratio R(0) Γ(B →τ +"missing")/Γ(B →μν) in such scenarios, in view of the future possibilities of measuring the quantity at Belle-Ⅱ.
In this paper, we apply the Maximum Entropy Method to estimate the proton radius and determine the valence quark distributions in the proton at extremely low resolution scale Q02. Using the simplest functional form of the valence quark distribution and standard deviations of quark distribution functions in the estimation of the proton radius, we obtain a quadratic polynomial for the relationship between the proton radius and the momentum fraction of other non-perturbative components in the proton. The proton radii are approximately equal to the muonic hydrogen experimental result rp=0.841 fm and the CODATA analysis rp=0.877 fm when the other non-perturbative components account for 17.5% and 22.3% respectively. We propose "ghost matter" to explain the difference in other non-perturbative components (4.8%) that the electron can detect.
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We study the impact of recent measurements of charm cross section H1-ZEUS combined data on simultaneous determination of parton distribution functions (PDFs) and the strong coupling, αs(MZ2), in two different schemes. We perform several fits based on Thorne-Roberts (RT) and Thorne-Roberts optimal (RTOPT) schemes at next-to-leading order (NLO). We show that adding charm cross section H1-ZEUS combined data reduces the uncertainty of the gluon distribution and improves the fit quality up to ~0.4% and ~0.9%, without and with the charm contribution, from the RT scheme to the RTOPT scheme, respectively. We also emphasise the central role of the strong coupling, αs(MZ2), in revealing the impact of charm flavour contribution, when it is considered as an extra free parameter. We show that in going from the RT scheme to the RT OPT scheme, we get~0.9% and~2.0% improvement in the value of αs(MZ2), without and with the charm flavour contribution respectively.
In the framework of the canonical seesaw model, we present a simple but viable scenario to explicitly break an S3L×S3R flavor symmetry in the leptonic sector. It turns out that the leptonic flavor mixing matrix is completely determined by the mass ratios of the charged leptons (i.e., me/mμ and mμ/mτ) and those of light neutrinos (i.e., m1/m2 and m2/m3). The latest global-fit results of the three neutrino mixing angles θ12, θ13, θ23 and two neutrino mass-squared differences △ m212, △ m312 at the 3σ level are used to constrain the parameter space of m1/m2, m2/m3. The predictions for the mass spectrum and flavor mixing are highlighted:(1) the neutrino mass spectrum shows a hierarchical pattern and a normal ordering, e.g., m1 ≈ 2.2 meV, m2 ≈ 8.8 meV and m3 ≈ 52.7 meV; (2) only the first octant of θ23 is allowed, namely, 41.8° ≤ θ23 ≤ 43.3° (3) the Dirac CP-violating phase δ ≈ -22° deviates significantly from the maximal value -90°. All these predictions are ready to be tested in ongoing and forthcoming neutrino oscillation experiments. Moreover, we demonstrate that the cosmological matter-antimatter asymmetry can be explained via resonant leptogenesis, including the individual lepton-flavor effects. In our scenario, leptonic CP violation at low-and high-energy scales is closely connected.
While quantum-classical correspondence for a system is a very fundamental problem in modern physics, the understanding of its mechanism is often elusive, so the methods used and the results of detailed theoretical analysis have been accompanied by active debate. In this study, the differences and similarities between quantum and classical behavior for an inverted oscillator have been analyzed based on the description of a complete generalized Airy function-type quantum wave solution. The inverted oscillator model plays an important role in several branches of cosmology and particle physics. The quantum wave packet of the system is composed of many sub-packets that are localized at different positions with regular intervals between them. It is shown from illustrations of the probability density that, although the quantum trajectory of the wave propagation is somewhat different from the corresponding classical one, the difference becomes relatively small when the classical excitation is sufficiently high. We have confirmed that a quantum wave packet moving along a positive or negative direction accelerates over time like a classical wave. From these main interpretations and others in the text, we conclude that our theory exquisitely illustrates quantum and classical correspondence for the system, which is a crucial concept in quantum mechanics.
We make use of Manton's analytical method to investigate the force between kinks and anti-kinks at large distances in 1+1 dimensional field theory. The related potential has infinite order corrections of exponential pattern, and the coefficients for each order are determined. These coefficients can also be obtained by solving the equation of the fluctuations around the vacuum. At the lowest order, the kink lattice represents the Toda lattice. With higher order correction terms, the kink lattice can represent one kind of generic Toda lattice. With only two sites, the kink lattice is classically integrable. If the number of sites of the lattice is larger than two, the kink lattice is not integrable but is a near integrable system. We make use of Flaschka's variables to study the Lax pair of the kink lattice. These Flaschka's variables have interesting algebraic relations and non-integrability can be manifested. We also discuss the higher Hamiltonians for the deformed open Toda lattice, which has a similar result to the ordinary deformed Toda.
The statistical uncertainties of 13 model parameters in the Weizsäcker-Skyrme (WS*) mass model are investigated for the first time with an efficient approach, and the propagated errors in the predicted masses are estimated. The discrepancies between the predicted masses and the experimental data, including the new data in AME2016, are almost all smaller than the model errors. For neutron-rich heavy nuclei, the model errors increase considerably, and go up to a few MeV when the nucleus approaches the neutron drip line. The most sensitive model parameter which causes the largest statistical error is analyzed for all bound nuclei. We find that the two coefficients of symmetry energy term significantly influence the mass predictions of extremely neutron-rich nuclei, and the deformation energy coefficients play a key role for well-deformed nuclei around the β-stability line.
We have investigated the effect of tensor correlations on the depletion of the nuclear Fermi sea in symmetric nuclear matter within the framework of the extended Brueckner-Hartree-Fock approach by adopting the AV18 two-body interaction and a microscopic three-body force. The contributions from various partial wave channels including the isospin-singlet T=0 channel, the isospin-triplet T=1 channel and the T=0 tensor 3SD1 channel have been calculated. The T=0 neutron-proton correlations play a dominant role in causing the depletion of nuclear Fermi sea. The T=0 correlation-induced depletion turns out to stem almost completely from the 3SD1 tensor channel. The isospin-singlet T=0 3SD1 tensor correlations are shown to be responsible for most of the depletion, which amounts to more than 70 percent of the total depletion in the density region considered. The three-body force turns out to lead to an enhancement of the depletion at high densities well above the empirical saturation density and its effect increases as a function of density.
The stability of super heavy nuclei (SHN) from Z=104 to Z=126 is analyzed systematically, associated with the following theoretical mass tables:FRDM2012[At. Data Nucl. Data Tables 109-110(2016)], WS2010[Phys. Rev. C 82, 044304(2010)], WS-LZ-RBF[J. Phys. G:Nucl. Part. Phys. 42, 095107(2015)] and the updated experimental data AME2016[Chinese Physics C 41, 040002(2017)]. The nucleus with the biggest mean binding energy in each isotopic chain shows systematic regular behavior, indicating that the mean binding energy is a good criterion to classify SHN by their stability. Based on binding energy, the α-decay energy Qα, two-proton separation energy S2p, and two-neutron separation energy S2n are extracted and analyzed. It is found that N=152 and N=162 are sub-magic numbers, N=184 is a neutron magic number, and Z=114 is a proton magic number, which may provide useful information for the synthesis and identification of SHN.
Very neutron-deficient nuclei are investigated with Woods-Saxon potentials, especially the newly measured A=2Z-1 nucleus 65As[X.L. Tu et al., Phys. Rev. Lett. 106, 112501 (2011)], where the experimental proton separation energy is obtained as -90(85) keV for the first time. Careful consideration is given to quasibound protons with outgoing Coulomb wave boundary conditions. The observed proton halos in the first excited state of 17F and in the ground states of 26,27,28P are reproduced well, and predictions of proton halos are made for the ground states of 56,57Cu and 65As. The sensitivity of the results to the proton separation energy is discussed in detail, together with the effect of the l=1 centrifugal barrier on proton halos.
We present calculations of coherent photoproduction of vector mesons (J/ψ and Υ) with leading-order parton distribution functions to check new kinds of corrections of the DGLAP equations and nuclear modifications. The input gluon distribution of the proton is the dynamical parton model from the DGLAP equations with GLR-MQ-ZRS (Gribov-Levin-Ryskin, Mueller-Qiu, Zhu-Ruan-Shen) modifications. From comparison between several other gluon distribution models, we find that the dynamical gluon distribution fits with the results of meson photoproduction experiments in the high energy region. The calculation of the differential cross sections using dynamical and other gluon distributions is compared with the experimental data from the HERA, ZEUS and LHCb Collaborations. Although there is little data for the rapidity distribution of vector meson photoproduction near zero rapidity, the dynamical gluon distribution works well with the data in the large rapidity region.
Dirac and Pauli form factors are investigated in the relativistic chiral effective Lagrangian. The octet and decuplet intermediate states are included in the one-loop calculation. The 4-dimensional regulator is introduced to deal with the divergence. Different from the non-relativistic case, this 4-dimensional regulator is generated from the nonlocal Lagrangian with the gauge link, which guarantees local gauge invariance. As a result, additional diagrams appear which ensure electric charge 1 and 0 for proton and neutron respectively. The obtained Dirac and Pauli form factors of the nucleons are all reasonable up to relatively large Q2.
We study the properties of two-flavor quark matter in the Dyson-Schwinger model and investigate the possible consequences for hybrid neutron stars, with particular regard to the two-solar-mass limit. We find that with some extreme values of the model parameters, the mass fraction of two-flavor quark matter in heavy neutron stars can be as high as 30 percent and the possible energy release during the conversion from nucleonic neutron stars to hybrid stars can reach 1052 erg.
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