Publications (277)602.53 Total impact
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ABSTRACT: The Casimir effect is a general phenomenon in physics, which arises when the vacuum fluctuation of an arbitrary field is modified by static or slowly varying boundary. However, its spin version is rarely addressed, mainly due to the fact that a macroscopic boundary in quantum spin systems is hard to define. In this article, we explore the spin Casimir effect induced by the zeropoint fluctuation of spin waves in a general noncollinear ordered quantum antiferromagnet. This spin Casimir effect results in a spin torque between local spins and further causes various singular and divergent results in the framework of spinwave theory, which invalidate the standard $1/S$ expansion procedure. To avoid this dilemma, we develop a selfconsistent spinwave expansion approach, which preserves the spinwave expansion away from singularities and divergence. A detailed spinwave analysis of the antiferromagnetic spin1/2 Heisenberg model on a spatially anisotropic triangular lattice is undertaken within our approach. Our results indicate that the spiral order is only stable in the region $0.5<\alpha<1.2$, where $\alpha$ is the ratio of the coupling constants. In addition, the instability in the region $1.2<\alpha<2$ is owing to the spin Casimir effect instead of the vanishing sublattice magnetization. And this extended spiral instable region may host some quantum disordered phases besides the quantum order by disorder induced Neel phase. Furthermore, our method provides an efficient and convenient tool that can estimate the correct exchange parameters and outline the quantum phase diagrams, which can be useful for experimental fitting processes in frustrated quantum magnets.  [Show abstract] [Hide abstract]
ABSTRACT: Based on a sample of $1.31 \times 10^9$ $J/\psi$ events collected with the BESIII detector at the BEPCII collider, Dalitz plot analyses of selected 79,625 $\eta\rightarrow\pi^{+}\pi^{}\pi^0$ events, 33,908 $\eta\rightarrow\pi^0\pi^0\pi^0$ events and 1,888 $\eta^{\prime}\rightarrow\pi^0\pi^0\pi^0$ events are performed. The measured matrix elements of $\eta\rightarrow\pi^+\pi^\pi^0$ are in reasonable agreement with previous measurements. The Dalitz plot slope parameters of $\eta\rightarrow\pi^0\pi^0\pi^0$ and $\eta^{\prime}\rightarrow\pi^0\pi^0\pi^0$ are determined to be $0.055 \pm 0.014 \pm 0.004$ and $0.640 \pm 0.046 \pm 0.047$, respectively, where the first uncertainties are statistical and the second systematic. Both values are consistent with previous measurements, while the precision of the latter one is improved by a factor of three. Final state interactions are found to have an important role in those decays.  [Show abstract] [Hide abstract]
ABSTRACT: We report an observation of the process $J/\psi\rightarrow\gamma X(1835)\rightarrow\gamma K^0_S K^0_S\eta$ at low $K^0_S K^0_S$ mass with a statistical significance larger than 12.9$\sigma$ using a data sample of $1.31 \times 10^{9}$ $J/\psi$ events collected with the BESIII detector. In this region of phase space the $K^0_S K^0_S$ system is dominantly produced through the $f_0(980)$. By performing a partial wave analysis, we determine the spinparity of the $X(1835)$ to be $J^{PC}=0^{+}$. The mass and width of the observed $X(1835)$ are $1844\pm9(\text{stat})^{+16}_{25}(\text{syst})$~\MeV~and $192^{+20}_{17}(\text{stat})^{+62}_{43}(\text{syst})$~MeV, respectively, which are consistent with the results obtained by BESIII in the channel $J/\psi\rightarrow\gamma\pi^+\pi^\eta^{\prime}$.  [Show abstract] [Hide abstract]
ABSTRACT: An amplitude analysis of the $\pi^{0}\pi^{0}$ system produced in radiative $J/\psi$ decays is presented. In particular, a piecewise function that describes the dynamics of the $\pi^{0}\pi^{0}$ system is determined as a function of $M_{\pi^{0}\pi^{0}}$ from an analysis of the $(1.311\pm0.011)\times10^{9}$ $J/\psi$ decays collected by the BESIII detector. The goal of this analysis is to provide a description of the scalar and tensor components of the $\pi^0\pi^0$ system while making minimal assumptions about the properties or number of poles in the amplitude. Such a modelindependent description allows one to integrate these results with other related results from complementary reactions in the development of phenomenological models, which can then be used to directly fit experimental data to obtain parameters of interest. The branching fraction of $J/\psi \to \gamma \pi^{0}\pi^{0}$ is determined to be $(1.15\pm0.05)\times10^{3}$, where the uncertainty is systematic only and the statistical uncertainty is negligible.  [Show abstract] [Hide abstract]
ABSTRACT: Using a sample of 1.31 billion $J/\psi$ events collected with the BESIII detector at the BEPCII collider, the decays $J/\psi \to \phi \pi^{+}\pi^{}\pi^{0}$ and $J/\psi \to \phi \pi^{0}\pi^{0}\pi^{0}$ are investigated. The isospin violating decay $J/\psi \to \phi \pi^{0} f_{0}(980)$ with $f_{0}(980) \to \pi\pi$, is observed for the first time. The width of the $f_{0}(980)$ obtained from the dipion mass spectrum is found to be much smaller than the world average value. In the $\pi^{0} f_{0}(980)$ mass spectrum, there is evidence of $f_1(1285)$ production. By studying the decay $J/\psi \to \phi\eta'$, the branching fractions of $\eta' \to \pi^{+}\pi^{}\pi^{0}$ and $\eta' \to \pi^{0}\pi^{0}\pi^{0}$, as well as their ratio, are also measured.  [Show abstract] [Hide abstract]
ABSTRACT: Using $2.92$ fb$^{1}$ of electronpositron annihilation data collected at $\sqrt{s} = 3.773$~GeV with the BESIII detector, we report the results of a search for the flavorchanging neutral current process $D^0\to\gamma\gamma$ using a doubletag technique. We find no signal and set an upper limit at $90\%$ confidence level for the branching fraction of $B(D^0\to\gamma\gamma) < 3.8\times10^{6}$. We also investigate $D^0$meson decay into two neutral pions, obtaining a branching fraction of $B(D^0\to\pi^0\pi^0) = (8.24\pm0.21(\text{stat.})\pm0.30(\text{syst.}))\times10^{4}$, the most precise measurement to date and consistent with the current world average  [Show abstract] [Hide abstract]
ABSTRACT: Using the data sets taken at centerofmass energies above 4 GeV by the BESIII detector at the BEPCII storage ring, we search for the reaction e+e > gamma_ISR X(3872) > gamma_ISR pi+piJ/psi via the Initial State Radiation technique. The production of a resonance with quantum numbers J^PC = 1^++ such as the X(3872) via single photon e+e annihilation is forbidden, but is allowed by a nexttoleading order box diagram. We do not observe a significant signal of X(3872), and therefore give an upper limit for the electronic width times the branching fraction Gamma_ee^X(3872)Br(X(3872) > pi+piJ\psi) < 0.13 eV at the 90% confidence level. This measurement improves upon existing limits by a factor of 46. Using the same final state, we also measure the electronic width of the psi(3686) to be Gamma_ee^psi(3686) = 2231 + 18 + 99 eV.  [Show abstract] [Hide abstract]
ABSTRACT: Using data samples collected at center of mass energies of $\sqrt{s}$ = 4.009, 4.226, 4.257, 4.358, 4.416 and 4.599 GeV with the BESIII detector operating at the BEPCII storage ring, we search for the isospin violating decay $Y(4260)\rightarrow J/\psi \eta \pi^{0}$. No signal is observed, and upper limits on the cross section $\sigma(e^{+}e^{}\rightarrow J/\psi \eta \pi^{0})$ at the 90\% confidence level are determined to be 3.6, 1.7, 2.4, 1.4, 0.9 and 1.9 pb, respectively.  [Show abstract] [Hide abstract]
ABSTRACT: We report a measurement of the branching fraction of $\psi(3770)\to\gamma\chi_{c1}$ and search for the transition $\psi(3770)\rightarrow \gamma \chi_{c2}$ based on 2.92~fb$^{1}$ of $e^+e^$ data accumulated at $\sqrt{s}=3.773$~GeV with the BESIII detector at the BEPCII collider. The measured branching fraction of $\psi(3770) \rightarrow \gamma \chi_{c1}$ is $\mathcal B(\psi(3770) \rightarrow \gamma \chi_{c1})=(2.48 \pm 0.15 \pm 0.23) \times 10^{3}$, which is the most precise measurement to date. The upper limit on the branching fraction of $\psi(3770)\rightarrow \gamma \chi_{c2}$ at a $90\%$ confidence level is $\mathcal B(\psi(3770) \rightarrow \gamma \chi_{c2})<0.64 \times 10^{3}$. The corresponding partial widths are $\Gamma(\psi(3770) \to \gamma \chi_{c1}) =(67.5\pm 4.1\pm 6.7)$~keV and $\Gamma(\psi(3770) \to \gamma \chi_{c2}) < 17.4$~keV.  [Show abstract] [Hide abstract]
ABSTRACT: We report the first observation of the Dalitz decay $\eta' \to \gamma e^+e^$, based on a data sample of 1.31 billion $J/\psi$ events collected with the BESIII detector. The $\eta'$ mesons are produced via the $J/\psi \to \gamma \eta'$ decay process. The ratio $\Gamma(\eta' \to \gamma e^+ e^)/\Gamma(\eta'\to\gamma\gamma)$ is measured to be $(2.13\pm0.09(\text{stat.})\pm0.07(\text{sys.}))\times10^{2}$. This corresponds to a branching fraction ${\cal B}(\eta' \to \gamma e^+e^)= (4.69 \pm0.20(\text{stat.})\pm0.23(\text{sys.}))\times10^{4}$. The transition form factor is extracted and different expressions are compared to the measured dependence on the $e^+e^$ invariant mass. The results are consistent with the prediction of the Vector Meson Dominance model.  [Show abstract] [Hide abstract]
ABSTRACT: Using data samples collected with the BESIII detector at the BEPCII collider, we measure the Born cross section of $e^{+}e^{}\rightarrow p\bar{p}$ at 12 centerofmass energies from 2232.4 to 3671.0 MeV. The corresponding effective electromagnetic form factor of the proton is deduced under the assumption that the electric and magnetic form factors are equal $(G_{E}= G_{M})$. In addition, the ratio of electric to magnetic form factors, $G_{E}/G_{M}$, and $G_{M}$ are extracted by fitting the polar angle distribution of the proton for the data samples with larger statistics, namely at $\sqrt{s}=$ 2232.4 and 2400.0 MeV and a combined sample at $\sqrt{s}$ = 3050.0, 3060.0 and 3080.0 MeV, respectively. The measured cross sections are in agreement with recent results from BaBar, improving the overall uncertainty by about 30\%. The $G_{E}/G_{M}$ ratios are close to unity and consistent with BaBar results in the same $q^{2}$ region, which indicates the data are consistent with the assumption that $G_{E}=G_{M}$ within uncertainties. 
Article: Observation of the electromagnetic doubly OZIsuppressed decay $J/\psi \rightarrow \phi \pi^{0}$
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ABSTRACT: Using a sample of $1.31$ billion $J/\psi$ events accumulated with the BESIII detector at the BEPCII collider, we report the observation of the decay $J/\psi \rightarrow \phi\pi^{0}$, which is the first evidence for a doubly OkuboZweigIizuka suppressed electromagnetic $J/\psi$ decay. A clear structure is observed in the $K^{+} K^{}$ mass spectrum around 1.02 GeV/$c^2$, which can be attributed to interference between $J/\psi \rightarrow \phi\pi^{0}$ and $J/\psi \rightarrow K^{+}K^{}\pi^{0}$ decays. Due to this interference, two possible solutions are found. The corresponding measured values of the branching fraction of $J/\psi \to \phi\pi^{0}$ are $[2.94 \pm 0.16\text{(stat.)} \pm 0.16\text{(syst.)}] \times 10^{6}$ and $[1.24 \pm 0.33\text{(stat.)} \pm 0.30\text{(syst.)}] \times 10^{7}$.  [Show abstract] [Hide abstract]
ABSTRACT: Using a sample of $1.06\times10^8\ \psip$ events produced in $e^+e^$ collisions at $\sqrt{s}$ = 3.686 GeV and collected with the BESIII detector at the BEPCII collider, we present studies of the decays $\klx+c.c.$ and $\gklx+c.c.$. We observe two hyperons, $\Xi(1690)^$ and $\Xi(1820)^$, in the $K^\Lambda$ invariant mass distribution in the decay $\klx+c.c.$ with significances of $4.9 \sigma$ and $6.2 \sigma$, respectively. The branching fractions of $\klx+c.c.$, $\ksx+c.c.$, $\psip\to\gamma \chi_{cJ}\to \gamma K^ \Lambda \bar{\Xi}^+ +c.c.$ $(J=0,\ 1,\ 2)$, and $\psip\to \Xi(1690/1820)^{} \bar{\Xi}^++c.c$ with subsequent decay $\Xi(1690/1820)^\to K^\Lambda$ are measured for the first time.  [Show abstract] [Hide abstract]
ABSTRACT: We report the observation of the $X(3823)$ in the process $e^+e^\to \pi^+\pi^X(3823) \to \pi^+\pi^\gamma\chi_{c1}$ with a statistical significance of $6.2\sigma$, in data samples at centerofmass energies $\sqrt{s}=$4.230, 4.260, 4.360, 4.420 and 4.600~GeV collected with the BESIII detector at the BEPCII electron positron collider. The measured mass of the $X(3823)$ is $(3821.7\pm 1.3\pm 0.7)$~MeV/$c^2$, where the first error is statistical and the second systematic, and the width is less than $16$~MeV at the 90\% confidence level. The products of the Born cross sections for $e^+e^\to \pi^+\pi^X(3823)$ and the branching ratio $\mathcal{B}[X(3823)\to \gamma\chi_{c1,c2}]$ are also measured. These measurements are in good agreement with the assignment of the $X(3823)$ as the $\psi(1^3D_2)$ charmonium state.  [Show abstract] [Hide abstract]
ABSTRACT: Using data samples collected with the BESIII detector operating at the BEPCII collider at centerofmass energies from 3.810 to 4.600 GeV, we perform a study of $e^{+}e^{} \to \eta J/\psi$ and $\pi^0 J/\psi$. Statistically significant signals of $e^{+}e^{} \to \eta J/\psi$ are observed at $\sqrt{s}$ = 4.190, 4.210, 4.220, 4.230, 4.245, 4.260, 4.360 and 4.420 GeV, while no signals of $e^{+}e^{} \to \pi^{0} J/\psi$ are observed. The measured energydependent Born cross section for $e^{+}e^{} \to \eta J/\psi$ shows an enhancement around 4.2~GeV. The measurement is compatible with an earlier measurement by Belle, but with a significantly improved precision.  [Show abstract] [Hide abstract]
ABSTRACT: Using a data sample of 106 million $\psi(3686)$ events collected with the BESIII detector operated at the BEPCII storage ring, we study for the first time the decay $\chi_{cJ}\to\phi K^{0}_S K^{\pm}\pi^{\mp}$ and $\chi_{cJ}\to\phi K^{+} K^{}\pi^{0}$ in the E1 radiative transition $\psi(3686)\to\gamma\chi_{cJ}$. The decays are dominated by the threebody decay $\chi_{cJ}\to \phi K^*(892)\bar{K}$. We measure branching fractions for this reaction via the neutral and charged $K^*(892)$ and find them consistent with each other within the expectation of isospin symmetry. In the $K\bar{K}\pi$ invariant mass distribution a structure near the $K^*(892)\bar{K}$ mass threshold is observed, and the corresponding mass and width are measured to be $1412\pm4(\mathrm{stat.})\pm8(\mathrm{sys.}) \mathrm{MeV}/c^2$ and $\Gamma$ = $84\pm12(\mathrm{stat.})\pm40(\mathrm{sys.}) \mathrm{MeV}$, respectively. The observed state favors an assignment to the $h_1(1380)$, considering its possible $J^{PC}$ and comparing its mass, width and decay mode to those reported in the Particle Data Group.  [Show abstract] [Hide abstract]
ABSTRACT: From December 2011 to May 2014, about 5 $\rm fb^{1}$ of data were taken with the BESIII detector at centerofmass energies between 3.810 GeV and 4.600 GeV to study the charmoniumlike states and higher excited charmonium states. The time integrated luminosity of the collected data sample is measured to a precision of 1% by analyzing events produced by the largeangle Bhabha scattering process.  [Show abstract] [Hide abstract]
ABSTRACT: Based on data samples collected with the BESIII detector at the BEPCII collider at nine center of mass energies from 4.21 to 4.42 GeV, we search for the production of e^{+}e^{}â†’Ï‰Ï‡_{cJ} (J=0, 1, 2). The process e^{+}e^{}â†’Ï‰Ï‡_{c0} is observed for the first time, and the Born cross sections at sqrt[s]=4.23 and 4.26 GeV are measured to be (55.4Â±6.0Â±5.9) and (23.7Â±5.3Â±3.5) pb, respectively, where the first uncertainties are statistical and the second are systematic. The Ï‰Ï‡_{c0} signals at the other seven energies and the e^{+}e^{}â†’Ï‰Ï‡_{c1} and Ï‰Ï‡_{c2} signals are not significant, and the upper limits on the cross sections are determined. By examining the Ï‰Ï‡_{c0} cross section as a function of center of mass energy, we find that it is inconsistent with the line shape of the Y(4260) observed in e^{+}e^{}â†’Ï€^{+}Ï€^{}J/Ïˆ. Assuming the Ï‰Ï‡_{c0} signals come from a single resonance, we extract the mass and width of the resonance to be (4230Â±8Â±6) MeV/c^{2} and (38Â±12Â±2) MeV, respectively, and the statistical significance is more than 9Ïƒ.Physical Review Letters 03/2015; 114(9):092003. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We report the detailed electronic structure of WTe$_2$ by high resolution angleresolved photoemission spectroscopy. Unlike the simple one electron plus one hole pocket type of Fermi surface topology reported before, we resolved a rather complicated Fermi surface of WTe$_2$. Specifically, there are totally nine Fermi pockets, including one hole pocket at the Brillouin zone center $\Gamma$, and two hole pockets and two electron pockets on each side of $\Gamma$ along the $\Gamma$$X$ direction. Remarkably, we have observed circular dichroism in our photoemission spectra, which suggests that the orbital angular momentum exhibits a rich texture at various sections of the Fermi surface. As reported previously for topological insulators and Rashiba systems, such a circular dichroism is a signature for spinorbital coupling (SOC). This is further confirmed by our density functional theory calculations, where the spin texture is qualitatively reproduced as the conjugate consequence of SOC. Since the backscattering processes are directly involved with the resistivity, our data suggest that the SOC and the related spin and orbital angular momentum textures may be considered in the understanding of the anomalous magnetoresistance of WTe$_2$.  [Show abstract] [Hide abstract]
ABSTRACT: We present the first upperlimit measurement of the branching fractions of the isospinviolating transitions $\chi_{c0,2} \rightarrow \pi^{0} \eta_{c}$. The measurements are performed using $106\times 10^{6}$ $\psi(3686)$ events accumulated with the BESIII detector at the BEPCII $e^{+}e^{}$ collider at a centerofmass energy corresponding to the $\psi(3686)$ mass. We obtained upper limits on the branching fractions at a 90\% confidence level of $B(\chi_{c0} \rightarrow \pi^{0} \eta_{c}) < 1.6 \times 10^{3}$ and $B(\chi_{c2} \rightarrow \pi^{0} \eta_{c}) < 3.2 \times 10^{3}$.
Publication Stats
2k  Citations  
602.53  Total Impact Points  
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Institutions

2009–2015

Nanjing University
 Department of Physics
Nanching, Jiangsu Sheng, China


2008–2012

Institute of physics china
Peping, Beijing, China 
University of Toronto
Toronto, Ontario, Canada


2010

RuhrUniversitÃ¤t Bochum
Bochum, North RhineWestphalia, Germany


2005–2010

Government of the People's Republic of China
Peping, Beijing, China


1984–2010

Nankai University
Tâ€™ienchingshih, Tianjin Shi, China


2001

Colorado State University
 Department of Physics
Fort Collins, Colorado, United States


1999

National Tsing Hua University
 Nuclear Science and Technology Development Center
Hsinchuhsien, Taiwan, Taiwan


1998

Hangzhou University
Shanghai, Shanghai Shi, China
