Xue-Qian Li

Nankai University, T’ien-ching-shih, Tianjin Shi, China

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Publications (191)310.16 Total impact

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    Hong-Wei Ke, Xue-Qian Li
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    ABSTRACT: Observing the CKM matrix elements written in different parametrization schemes, one can notice obvious relations among the sine-values of the CP phases in those schemes. Using the relations, we establish a few parametrization-independent equations, by which the matrix elements of the CKM matrix can be completely fixed up to a universal parameter. If it is true, we expect that there should exist a hidden symmetry in the nature which determines the relations. Moreover, it requires a universal parameter, naturally it would be the famous Jarlskog invariant which is also parametrization independent. Thus the four parameters (three mixing angles and one CP phase) of the CKM matrix are not free, but determined by the symmetry and the universal parameter. As we generalize the rules to the PMNS matrix for neutrino mixing, the CP phase of the lepton sector is predicted to be within a range of $0\sim 59^\circ$ centered at $39^\circ$ (in the P$_a$ parametrization) which will be tested in the future experiments.
    11/2014;
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    Hong-Wei Ke, Jia-Hui Zhou, Xue-Qian Li
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    ABSTRACT: The observed resonance peak around 2.86 GeV has been carefully reexamined by the LHCb collaboration and it is found that under the peak there reside two states $D^*_{s1}(2860)$ and $D^*_{s3}(2860)$ which are considered as $1^3D_1(c\bar s)$ and $1^3D_3(c\bar s)$ with slightly different masses and total widths. Thus, the earlier assumption that the resonance $D^*_{s1}(2710)$ was a $1D$ state should not be right. We suggest to measure the partial widths of radiative decays of $D^*_{sJ}(2860)$ and $D^*_{s1}(2710)$ to confirm their quantum numbers. We would consider $D^*_{s1}(2710)$ as $2^3S_1$ or a pure $1^3D_1$ state, or their mixture and respectively calculate the corresponding branching ratios as well as those of $D^*_{sJ}(2860)$. The future precise measurement would provide us information to help identifying the structures of those resonances .
    11/2014;
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    ABSTRACT: In this work, we use the Born-Oppenheimer approximation where the potential between atoms can be approximated as a function of distance between the two nuclei to study the four-quark bound states. By the approximation, Heitler and London calculated the spectrum of hydrogen molecule which includes two protons (heavy) and two electrons (light). Generally, the observed exotic mesons $Z_b(10610)$, $Z_b(10650)$, $Z_c(3900)$ and $Z_c(4025)$($Z_c(4020)$) may be molecular states of two physical mesons and/or in diquark-anti-diquark structures. In analog to the Heitler-London method for calculating the mass of hydrogen molecule, we investigate whether there exist energy minima for these two structures. By contrary to the hydrogen molecule case where only the spin-triplet possesses an energy minimum, there exist minima for both of them. It implies that both molecule and tetraquark states can be stable objects. But since they have the same quantum numbers, the two states may mix to result in physical states. A consequence would be that one may expect to experimentally observe partner exotic states co-existing with $Z_b(10610)$, $Z_b(10650)$, $Z_c(3900)$ and $Z_c(4025)$($Z_c(4020)$).
    09/2014;
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    Hong-Wei Ke, Tan Liu, Xue-Qian Li
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    ABSTRACT: It is suggested that there is an underlying symmetry which relates the quark and lepton sectors. Namely, among the mixing matrix elements of CKM for quarks and PMNS for leptons there exist complementarity relations at a high energy scale (such as the see-saw or even the GUT scales). Assuming that the relations would remain during the matrix elements running down to the EW scale. Observable breaking of the rational relation is attributed to existence of sterile neutrinos which mix with the active neutrino to result in the observable PMNS matrix. We show that involvement of a sterile in the (3+1) model, induces that $|U_{e4}|^2= 0.040$, $|U_{\mu4}|^2= 0.009$ and $\sin^2 2\alpha=0.067$. We also find a new self-complementarity $\vartheta_{12}+\vartheta_{23}+\vartheta_{13}+\alpha\approx90^\circ$. The numbers are generally consistent with those obtained by fitting recent measurements, especially in this scenario, the existence of a sterile neutrino does not upset the LEP data i.e. the number of neutrino types is very close to 3.
    Physical Review D 08/2014; 90(5). · 4.86 Impact Factor
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    ABSTRACT: The China Dark Matter Experiment (CDEX) is located at the China Jinping underground laboratory (CJPL) and aims to directly detect the WIMP flux with high sensitivity in the low mass region. Here we present a study of the predicted photon and electron backgrounds including the background contribution of the structure materials of the germanium detector, the passive shielding materials, and the intrinsic radioactivity of the liquid argon that serves as an anti-Compton active shielding detector. A detailed geometry is modeled and the background contribution has been simulated based on the measured radioactivities of all possible components within the GEANT4 program. Then the photon and electron background level in the energy region of interest (<10^-2 events kg-1 day-1 keV-1 (cpkkd)) is predicted based on Monte Carlo simulations. The simulated result is consistent with the design goal of CDEX-10 experiment, 0.1 cpkkd, which shows that the active and passive shield design of CDEX-10 is effective and feasible.
    02/2014;
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    ABSTRACT: The supersymmetry (SUSY) may be the most favorable extension of the standard model, however, so far at LHC no evidence of the SUSY particles were observed. An obvious question is whether they have already emerged, but escaped from our detection or do not exist at all. We propose that at future ILC which may provide sufficient energy to produce SUSY particles if they are not too heavy as suggested by many authors and low background environment. The superflavor symmetry associates baryons with mesons as long as both of them contain a heavy constituent and a light one. Thus in this work, we are able to calculate the production rate of SUSY baryons near their production threshold in terms of the $B\bar B$ production data. Our analysis unambiguously indicates that the future ILC data would determine if the SUSY particles with a mass below $\sqrt s/2$ ($\sqrt s$ is the ILC energy) indeed exist.
    01/2014;
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    Hong-Wei Ke, Tan Liu, Xue-Qian Li
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    ABSTRACT: The LHCb Collaboration has systematically measured the rates of Bc→J /ψK, Bc→J/ψDs, Bc→J /ψDs*, and Bc→ψ(2S)π. The new data enable us to study relevant theoretical models and further determine the model parameters. In this work, we calculate the form factors for the transitions Bc→J /ψ and Bc→ψ(2S) numerically and then determine the partial widths of the semileptonic and nonleptonic decays. The theoretical predictions on the ratios of Γ(Bc→J/ψK)/Γ(Bc→J/ψπ), Γ(Bc→J/ψDs)/Γ(Bc→J/ψπ), and Γ(Bc→J/ψDs*)/Γ(Bc→J/ψπ) are consistent with data within only 1σ. Especially, for calculating Γ(Bc→ψ(2S)X) the modified harmonic oscillator wave function which we developed in early works is employed, and the results indicate that the modified harmonic oscillator wave function works well.
    Physical Review D 12/2013; 89(1). · 4.86 Impact Factor
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    ABSTRACT: In contrast with $B^0-\bar B^0$, $B_s-\bar B_s$ mixing where the standard model (SM) contributions overwhelm that of new physics beyond standard model (BSM), a measured relatively large $D^0-\bar D^0$ mixing where the SM contribution is negligible, definitely implies the existence of new physics BSM. It is natural to consider that the rare decays of D meson might be more sensitive to new physics, and the rare decay $D^0\to \mu^+\mu^-$ could be an ideal area to search for new physics because it is a flavor changing process. In this work we look for a trace of new physics BSM in the leptonic decays of $D^0$, concretely we discuss the contributions of unparticle or an extra gauge boson $Z'$ while imposing the constraints set by fitting the $D^0-\bar D^0$ mixing data. We find that the long-distance SM effects for $D^0\to l\bar l$ still exceed those contributions of the BSM under consideration, but for a double-flavor changing process such as $D^0\to \mu^{\pm}e^{\mp}$, the new physics contribution would be significant.
    12/2013;
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    Lian-Bao Jia, Xue-Qian Li
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    ABSTRACT: The new observation of CDMS II favors low mass WIMPs. Taking the CDMS II new results as input and following the literature we consider a SM singlet: the darkon as the dark matter candidate, which can be either scalar, fermion or vector. It is found that the simplest scenario of DM+SM conflicts with the stringent constraint set by the LHC data. New physics beyond the SM is needed as many authors suggested. In this work, we discuss an extended standard model $SU_L(2)\otimes U_Y(1)\otimes U(1)'$ where $U(1)'$ only couples to the darkon. The new gauge symmetry is broken into $U_{em}(1)$ and two neutral bosons $Z^0$ and $Z'$ which are mixtures of $W^3_{\mu},\; B_{\mu}\; X_{\mu}$ are resulted in, where $Z^0$ is very close to the $Z$ boson of the standard model. Following the literature and based on the CDMS data, we make a complete analysis to testify the validity of the model. The cross section of the elastic scattering between darkon and nucleon is calculated, and the DM relic density is evaluated in the extended scenario as well. It is found that considering the constraints from both cosmology and collider experiments, only if $Z'$ is lighter than $Z^0$, one can reconcile all the presently available data.
    Physical Review D 09/2013; 89(3). · 4.86 Impact Factor
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    ABSTRACT: We calculate the forward backward asymmetry of the top-pair production at TEVATRON up to next to leading order (NLO) in the little Higgs model (LHM). We find that the contribution of $Z_H$ can be large enough to make up the gap between standard model (SM) prediction and data. With the database of $7.65\pm0.20\pm0.36$ pb, therefore, the parameter space for flavor-changing coupling of $Z_H$ is constrained. Thus this model can result in the required asymmetry while the total cross section of top-pair production remaining consistent with data.
    Chinese Physics C 09/2013; 38(11). · 0.82 Impact Factor
  • Hong-Wei Ke, Ya-Zheng Chen, Xue-Qian Li
    Chinese Physics Letters 09/2013; 30(9):099901. · 0.92 Impact Factor
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    Hong-Wei Ke, Zheng-Tao Wei, Xue-Qian Li
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    ABSTRACT: Assuming the newly observed $Z_c(3900)$ to be a molecular state of $D\bar D^*(D^{*} \bar D)$, we calculate the partial widths of $Z_c(3900)\to J/\psi+\pi;\; \psi'+\pi;\; \eta_c+\rho$ and $D\bar D^*$ within the light front model (LFM). $Z_c(3900)\to J/\psi+\pi$ is the channel by which $Z_c(3900)$ was observed, our calculation indicates that it is indeed one of the dominant modes whose width can be in the range of a few MeV depending on the model parameters. Similar to $Z_b$ and $Z_b'$, Voloshin suggested that there should be a resonance $Z_c'$ at 4030 MeV which can be a molecular state of $D^*\bar D^*$. Then we go on calculating its decay rates to all the aforementioned final states and as well the $D^*\bar D^*$. It is found that if $Z_c(3900)$ is a molecular state of ${1\over\sqrt 2}(D\bar D^*+D^*\bar D)$, the partial width of $Z_c(3900)\to D\bar D^*$ is rather small, but the rate of $Z_c(3900)\to\psi(2s)\pi$ is even larger than $Z_c(3900)\to J/\psi\pi$. The implications are discussed and it is indicated that with the luminosity of BES and BELLE, the experiments may finally determine if $Z_c(3900)$ is a molecular state or a tetraquark.
    07/2013;
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    ABSTRACT: Considering the CP violating phases, we analyze the neutron electric dipole moment (EDM) in a CP violating supersymmetric extension of the standard model where baryon and lepton numbers are local gauge symmetries(BLMSSM). The contributions from the one loop diagrams and the Weinberg operators are taken into account. Adopting some assumptions on the relevant parameter space, we give the numerical results analysis. The numerical results for neutron EDM can reach $1.05\times 10^{-25}(e.cm)$, which is about the experimental upper limit.
    Journal of High Energy Physics 06/2013; 10(2013):020. · 6.22 Impact Factor
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    ABSTRACT: The CDEX Collaboration has been established for direct detection of light dark matter particles, using ultra-low energy threshold p-type point-contact germanium detectors, in China JinPing underground Laboratory (CJPL). The first 1 kg point-contact germanium detector with a sub-keV energy threshold has been tested in a passive shielding system located in CJPL. The outputs from both the point-contact p+ electrode and the outside n+ electrode make it possible to scan the lower energy range of less than 1 keV and at the same time to detect the higher energy range up to 3 MeV. The outputs from both p+ and n+ electrode may also provide a more powerful method for signal discrimination for dark matter experiment. Some key parameters, including energy resolution, dead time, decay times of internal X-rays, and system stability, have been tested and measured. The results show that the 1 kg point-contact germanium detector, together with its shielding system and electronics, can run smoothly with good performances. This detector system will be deployed for dark matter search experiments.
    Chinese Physics C 05/2013; 37(12). · 0.82 Impact Factor
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    Hong-Wei Ke, Xue-Qian Li, Yan-Liang Shi
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    ABSTRACT: The radiative decay is believed to be an ideal lab to study the hadronic structure of newly observed resonances because the reactions are governed by only the electromagnetic interaction (tree level). However, to obtain correct theoretical values, one has to properly deal with the nonperturbative QCD effects in the wave function and hadronization. In this work, we derive the formulas for the radiative decays of 0++ and 1-+ heavy mesons in the light-front quark model. Because B(χc0→J/ψγ) is well-measured, the theoretical evaluation of the transition rate can be used to test our approach. Within this theoretical framework, the width of χb0→Υ(1S)γ is evaluated. The formulas can be applied to identify the inner structures of new resonances, for example the isospin of hc(b) and the structure of Ds(2317), via processes hc→ηcγ, hb→ηbγ and Ds(2317)→Ds*+γ.
    Physical review D: Particles and fields 03/2013; 87(5).
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    Bin Wang, Jian Tang, Xue-Qian Li
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    ABSTRACT: The PMNS matrix displays an obvious symmetry, but not exact. There are several textures proposed in literature, which possess various symmetry patterns and seem to originate from different physics scenarios at high energy scales. To be consistent with the experimental measurement, all of the regularities slightly decline, i.e. the symmetry must be broken. Following the schemes given in literature, we modify the matrices (9 in total) to gain the real PMNS matrix by perturbative rotations. The transformations may provide hints about the underlying physics at high energies and the breaking mechanisms which apply during the evolution to the low energy scale, especially the results may be useful for the future model builders.
    Physical Review D 03/2013; 88(7). · 4.86 Impact Factor
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    ABSTRACT: Weakly Interacting Massive Particles (WIMPs) are the candidates of dark matter in our universe. Up to now any direct interaction of WIMP with nuclei has not been observed yet. The exclusion limits of the spin-independent cross section of WIMP-nucleon which have been experimentally obtained is about 10^{-7}pb at high mass region and only 10^{-5}pb} at low mass region. China Jin-Ping underground laboratory CJPL is the deepest underground lab in the world and provides a very promising environment for direct observation of dark matter. The China Dark Matter Experiment (CDEX) experiment is going to directly detect the WIMP flux with high sensitivity in the low mass region. Both CJPL and CDEX have achieved a remarkable progress in recent two years. The CDEX employs a point-contact germanium semi-conductor detector PCGe whose detection threshold is less than 300 eV. We report the measurement results of Muon flux, monitoring of radioactivity and Radon concentration carried out in CJPL, as well describe the structure and performance of the 1 kg PCGe detector CDEX-1 and 10kg detector array CDEX-10 including the detectors, electronics, shielding and cooling systems. Finally we discuss the physics goals of the CDEX-1, CDEX-10 and the future CDEX-1T detectors.
    Frontiers of Physics 03/2013; 8(4). · 1.36 Impact Factor
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    ABSTRACT: Motivated by the measurement on the asymmetry at TEVATRON and relevant theoretical interpretations, in this work we calculate the forward-backward asymmetry ($A_{FB}$) in processes $e^+e^-\rightarrow t\bar t$ and $b\bar{b}$ up to the next-to-leading order (NLO) in both the Standard Model (SM) and the little Higgs model (LHM) which is one of the models beyond the SM (BSM). We carefully analyze the contributions of the SM and LHM to the $A_{FB}$ for $t\bar t$ and $b\bar b$ and find that to reconcile the theoretical predictions on $A_{FB}$ and the data of LEP I and II, the model parameter $a$ (see the text to find its definition) is constrained in a rather narrow region. The $A_{FB}$ will be more precisely measured at the proposed ILC and Z-factory. By a comparison with data, we can testify the validity degree of LHM and the theoretical results may be useful for designing future experiments.
    02/2013;
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    ABSTRACT: Because at the tree level Bs→K+K- is Cabibbo triple suppressed, so its branching ratio should be smaller than that of Bs→π+K-. The measurements present a reversed ratio as R=B(Bs→π+K-)/ B(Bs→K+K-)∼4.9/33. Therefore, it has been suggested that the transition Bs→K+K- is dominated by the penguin mechanism, which is proportional to VcbVcs*. In this work, we show that an extra contribution from the final state interaction to Bs→K+K- via sequential processes Bs→D(s)(*)D̅ s(*)→K+K- is also substantial and should be superposed on the penguin contribution. Indeed, taking into account the final state interaction effects, the theoretical prediction on R is well consistent with the data.
    Physical review D: Particles and fields 01/2013; 87(1).
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    ABSTRACT: The successful operation of the LHC provides a great opportunity to study the processes where heavy baryons are involved. In this work we mainly study the weak transitions of Σb→Σc. Assuming the reasonable quark-diquark structure, where the two light quarks constitute an axial vector, we calculate the widths of semileptonic decay Σb→Σceνe and nonleptonic decay modes Σb→Σc+M (light mesons) in terms of the light-front quark model. We first construct the vertex function for the concerned baryons and then deduce the form factors which are related to two Isgur-Wise functions for the Σb→Σc transition under the heavy quark limit. Our numerical results indicate that Γ(Σb→Σceνe) is about 1.60±0.28×1010 s-1 and Γ(Σb→Σc+M) is slightly below 1×1010 s-1, which may be accessed at the LHCb detector. By the flavor SU(3) symmetry, we estimate the rates of Ωb→Ωc. We suggest measuring weak decays of Ωb→Ωc, because Ωb does not decay via strong interactions, creating an obvious advantage.
    Physical review D: Particles and fields 12/2012; 86(11).

Publication Stats

1k Citations
310.16 Total Impact Points

Institutions

  • 1994–2014
    • Nankai University
      • Department of Physics
      T’ien-ching-shih, Tianjin Shi, China
  • 2010–2011
    • Northeast Institute of Geography and Agroecology
      • Department of Physics
      Peping, Beijing, China
    • Guangxi Normal University
      Ling-ch’uan, Guangxi Zhuangzu Zizhiqu, China
  • 2007
    • Peking University
      • Department of Physics
      Peping, Beijing, China
  • 2005
    • National Taiwan University
      • Department of Physics
      T’ai-pei, Taipei, Taiwan
  • 2004
    • Chinese Academy of Sciences
      • Institute of Theoretical Physics
      Peping, Beijing, China
  • 2002
    • University of Adelaide
      • Special Research Centre for the Subatomic Structure of Matter
      Tarndarnya, South Australia, Australia
  • 1999
    • University of Milan
      • Department of Physics
      Milano, Lombardy, Italy
  • 1990–1997
    • Academia Sinica
      T’ai-pei, Taipei, Taiwan