arXiv subjects

G. Chen

Publications and source records attributed to G. Chen.

At least 775 records · Page 43Linked to original sources

arXiv2018

Observation of $ψ(3686) \to η' e^+ e^- $

Using a data sample of $448.1 \times 10^6$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay $ψ(3686) \to η' e^+ e^-$, with significances of 7.0$σ$ and 6.3$σ$ when reconstructing the $η'$ meson via its decay modes $η'\toγπ^+ π^-$ and $η'\toπ^+π^-η$ ($η\to γγ$), respectively. The weighted average branching fraction is determined to be $\mathcal{B}(ψ(3686) \to η' e^+ e^-)= (1.90 \pm 0.25 \pm 0.11) \times 10^{-6}$, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2018

Insight-HXMT observations of the New Black Hole Candidate MAXI J1535-571: timing analysis

We present the X-ray timing results of the new black hole candidate (BHC) MAXI J1535-571 during its 2017 outburst from Hard X-ray Modulation Telescope (\emph{Insight}-HXMT) observations taken from 2017 September 6 to 23. Following the definitions given by \citet{Belloni2010}, we find that the source exhibits state transitions from Low/Hard state (LHS) to Hard Intermediate state (HIMS) and eventually to Soft Intermediate state (SIMS). Quasi-periodic oscillations (QPOs) are found in the intermediate states, which suggest different types of QPOs. With the large effective area of \emph{Insight}-HXMT at high energies, we are able to present the energy dependence of the QPO amplitude and centroid frequency up to 100 keV which is rarely explored by previous satellites. We also find that the phase lag at the type-C QPOs centroid frequency is negative (soft lags) and strongly correlated with the centroid frequency. By assuming a geometrical origin of type-C QPOs, the source is consistent with being a high inclination system.

astro-ph.HE↗

arXiv2018

Observation of $ψ(3686) \to n\bar{n}$ and improved measurement of $ψ(3686) \to p \bar{p}$

We observe the decay $ψ(3686) \to n \bar{n}$ for the first time and measure $ψ(3686) \to p \bar{p}$ with improved accuracy by using $1.07\times 10^8$ $ψ(3686)$ events collected with the BESIII detector. The measured branching fractions are $\mathcal{B}(ψ(3686) \to n \bar{n}) = (3.06 \pm 0.06 \pm 0.14)\times 10^{-4}$ and $\mathcal{B}(ψ(3686) \to p \bar{p}) = (3.05 \pm 0.02 \pm 0.12) \times 10^{-4}$. Here, the first uncertainties are statistical and the second ones systematic. With the hypothesis that the polar angular distributions of the neutron and proton in the center-of-mass system obey $1+α\cos^2θ$, we determine the $α$ parameters to be $α_{n\bar{n}} = 0.68 \pm 0.12 \pm 0.11$ and $α_{p\bar{p}} = 1.03 \pm 0.06 \pm 0.03$ for $ψ(3686)\to n\bar{n}$ and $ψ(3686)\to p\bar{p}$, respectively.

hep-ex↗

arXiv2018

Search for invisible decays of $ω$ and $ϕ$ with $J/ψ$ data at BESIII

Using a data sample of $(1310.6 \pm 7.0)\times 10^6$ $J/ψ$ events collected with the BESIII detector operating at the BEPCII collider, we perform the first experimental search for invisible decays of a light vector meson ($V=ω,ϕ$) via $J/ψ\to V η$ decays. The decay of $η\to π^+π^-π^0$ is utilized to tag the $V$ meson decaying into the invisible final state. No evidence for a significant invisible signal is observed, and the upper limits on the ratio of branching fractions at the 90\% confidence level are determined to be $\frac{\mathcal{B}(ω\rightarrow \rm{invisible})}{\mathcal{B}(ω\to π^+π^-π^0)} < 8.1 \times 10^{-5}$ and $\frac{\mathcal{B}(ϕ\to \rm{invisible})}{\mathcal{B}(ϕ\to K^+K^-)} < 3.4\times 10^{-4}$. By using the world average values of $\mathcal{B}(ω\to π^+π^-π^0)$ and $\mathcal{B}(ϕ\to K^+K^-)$, the upper limits on the decay branching fractions at the $90\%$ confidence level are set as $\mathcal{B}(ω\to \rm{invisible})< 7.3 \times 10^{-5}$ and $\mathcal{B}(ϕ\to \rm{invisible})< 1.7\times 10^{-4}$, respectively.

hep-ex↗

arXiv2018

Measurement of e+e- --> D Dbar Cross Sections at the psi(3770) Resonance

We report new measurements of the cross sections for the production of D Dbar final states at the psi(3770) resonance. Our data sample consists of an integrated luminosity of 2.93/fb of e+e- annihilation data produced by the BEPCII collider and collected and analyzed with the BESIII detector. We exclusively reconstruct three D0 and six D+ hadronic decay modes and use the ratio of the yield of fully reconstructed D Dbar events ("double tags") to the yield of all reconstructed D or Dbar mesons ("single tags") to determine the number of D0 D0bar and D+D- events, benefiting from the cancellation of many systematic uncertainties. Combining these yields with an independent determination of the integrated luminosity of the data sample, we find the cross sections to be σ(e+e- --> D0 D0bar)=(3.615 +- 0.010 +- 0.038) nb and σ(e+e- --> D+D-)=(2.830 +- 0.011 +- 0.026) nb, where the uncertainties are statistical and systematic, respectively.

hep-ex↗

arXiv2018

Observation of $a^{0}_{0}(980)$-$f_{0}(980)$ Mixing

We report the first observation of $a^{0}_{0}(980)$-$f_{0}(980)$ mixing in the decays of $J/ψ\toϕf_{0}(980)\toϕa^{0}_{0}(980)\toϕηπ^{0}$ and $χ_{c1}\to a^{0}_{0}(980)π^{0}\to f_{0}(980)π^{0}\toπ^{+}π^{-}π^{0}$, using data samples of $1.31\times10^{9}$ $J/ψ$ events and $4.48\times10^{8}$ $ψ(3686)$ events accumulated with the BESIII detector. The signals of $f_{0}(980)\to a^{0}_{0}(980)$ and $a^{0}_{0}(980)\to f_{0}(980)$ mixing are observed at levels of statistical significance of $7.4σ$ and $5.5σ$, respectively. The corresponding branching fractions and mixing intensities are measured and the constraint regions on the coupling constants, $g_{a_{0}K^{+}K^{-}}$ and $g_{f_{0}K^{+}K^{-}}$, are estimated. The results improve the understanding of the nature of $a^{0}_{0}(980)$ and $f_{0}(980)$.

hep-ex↗

arXiv2018

Precision Study of $η^\prime\rightarrowγπ^+π^-$ Decay Dynamics

Using a low background data sample of $9.7\times10^{5}$ $Jψ\rightarrowγη^\prime$, $η^\prime\rightarrowγπ^+π^-$ events, which are 2 orders of magnitude larger than those from the previous experiments, recorded with the BESIII detector at BEPCII, the decay dynamics of $η^\prime\rightarrowγπ^+π^-$ are studied with both model-dependent and model-independent approaches. The contributions of $ω$ and the $ρ(770)-ω$ interference are observed for the first time in the decays $η^\prime\rightarrowγπ^+π^-$ in both approaches. Additionally, a contribution from the box anomaly or the $ρ(1450)$ resonance is required in the model-dependent approach, while the process specific part of the decay amplitude is determined in the model-independent approach.

hep-ex↗

arXiv2018

Measurements of Absolute Branching Fractions for $Λ^+_c\toΞ^0K^+$ and $Ξ(1530)^0K^+$

We report the first measurements of absolute branching fractions for the $W$-exchange-only processes $Λ^+_c\toΞ^0K^+$ and $Λ^+_c\toΞ(1530)^0K^+$ with the double-tag technique, by analyzing an $e^{+}e^{-}$ collision data sample, that corresponds to an integrated luminosity of 567 pb$^{-1}$ collected at a center-of-mass energy of 4.6 GeV by the BESIII detector. The branching fractions are measured to be $\mathcal{B}(Λ^+_c\toΞ^0K^+)=(5.90\pm0.86\pm0.39)\times10^{-3}$ and $\mathcal{B}(Λ^+_c\toΞ(1530)^0K^+)=(5.02\pm0.99\pm0.31)\times10^{-3}$, where the first uncertainties are statistical and the second systematic. Our results are more precise than the previous relative measurements.

hep-ex↗

arXiv2018

The GTC exoplanet transit spectroscopy survey IX. Detection of Haze, Na, K, and Li in the super-Neptune WASP-127b

Exoplanets with relatively clear atmospheres are prime targets for detailed studies of chemical compositions and abundances in their atmospheres. Alkali metals have long been suggested to exhibit broad wings due to pressure broadening, but most of the alkali detections only show very narrow absorption cores, probably because of the presence of clouds. We report the strong detection of the pressure-broadened spectral profiles of Na, K, and Li absorption in the atmosphere of the super-Neptune WASP-127b, at 4.1$σ$, 5.0$σ$, and 3.4$σ$, respectively. We performed a spectral retrieval modeling on the high-quality optical transmission spectrum newly acquired with the 10.4 m Gran Telescopio Canarias (GTC), in combination with the re-analyzed optical transmission spectrum obtained with the 2.5 m Nordic Optical Telescope (NOT). By assuming a patchy cloudy model, we retrieved the abundances of Na, K, and Li, which are super-solar at 3.7$σ$ for K and 5.1$σ$ for Li (and only 1.8$σ$ for Na). We constrained the presence of haze coverage to be around 52%. We also found a hint of water absorption, but cannot constrain it with the global retrieval owing to larger uncertainties in the probed wavelengths. WASP-127b will be extremely valuable for atmospheric characterization in the era of James Webb Space Telescope.

astro-ph.EP↗

arXiv2018

Measurement of the absolute branching fraction of the inclusive semileptonic $Λ_c^+$ decay

Using a data sample corresponding to an integrated luminosity of 567 pb$^{-1}$ collected at a center-of-mass energy of $\sqrt{s}=4.6$ GeV with the BESIII detector, we measure the absolute branching fraction of the inclusive semileptonic $Λ_c^+$ decay with a double-tag method. We obtain $\mathcal{B}(Λ_c^+ \rightarrow X e^+ ν_e) = (3.95\pm0.34\pm0.09)\%$, where the first uncertainty is statistical and the second systematic. Using the known $Λ_c^+$ lifetime and the charge-averaged semileptonic decay width of nonstrange charmed measons ($D^0$ and $D^+$), we obtain the ratio of the inclusive semileptonic decay widths $Γ(Λ_c^+ \rightarrow X e^+ ν_e)/\barΓ(D\rightarrow X e^+ ν_e)= 1.26\pm0.12$.

hep-ex↗

arXiv2018

Measurement of the Integrated Luminosities of Cross-section Scan Data Samples Around the $ψ(3770)$ Mass Region

To investigate the nature of the $ψ(3770)$ resonance and to measure the cross section for $e^+e^- \to D\bar{D}$, a cross-section scan data sample, distributed among 41 center-of-mass energy points from 3.73 to 3.89~GeV, was taken with the BESIII detector operated at the BEPCII collider in the year 2010. By analyzing the large angle Bhabha scattering events, we measure the integrated luminosity of the data sample at each center-of-mass energy point. The total integrated luminosity of the data sample is $76.16\pm0.04\pm0.61$~pb$^{-1}$, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2018

Na I and H$α$ absorption features in the atmosphere of MASCARA-2b/KELT-20b

We have used the HARPS-North high resolution spectrograph ($\mathcal{R}$=115 000) at TNG to observe one transit of the highly irradiated planet MASCARA-2b/KELT-20b. Using only one transit observation, we are able to clearly resolve the spectral features of the atomic sodium (Na I) doublet and the H$α$ line in its atmosphere, measuring absorption depths of 0.17$\pm$0.03$\%$ and 0.59$\pm$0.08$\%$ for a 0.75 $Å$ passband, respectively. These absorptions are corroborated with the transmission measured from their respective transmission light curves, which show a large Rossiter-McLaughlin effect. In case of H$α$, this absorption corresponds to an effective radius of $R_λ/R_P$=1.20$\pm$0.04. While the S/N of the final transmission spectrum is not sufficient to adjust different temperature profiles to the lines, we find that higher temperatures than the equilibrium are needed to explain the lines contrast. Particularly, we find that the Na I lines core require a temperature of T=4210$\pm$180K and that H$α$ requires T=4330$\pm$520K. MASCARA-2b, like other planets orbiting A-type stars, receives a large amount of UV energy from its host star. This energy excites the atomic hydrogen and produces H$α$ absorption, leading to the expansion and abrasion of the atmosphere. The study of other Balmer lines in the transmission spectrum would allow the determination of the atmospheric temperature profile and the calculation of the lifetime of the atmosphere. In the case of MASCARA-2b, residual features are observed in the H$β$ and H$γ$ lines, but they are not statistically significant. More transit observations are needed to confirm our findings in Na I and H$α$, and to build up enough S/N to explore the presence of H$β$ and H$γ$ planetary absorptions.

astro-ph.EP↗

arXiv2018

Search for the rare decays $D\to h(h')e^+e^-$

We search for rare decays of $D$ mesons to hadrons accompany with an electron-positron pair (h(h')$e^+e^-$), using an $e^+e^-$ collision sample corresponding to an integrated luminosity of 2.93 fb$^{-1}$ collected with the BESIII detector at $\sqrt{s}$ = 3.773 GeV. No significant signals are observed, and the corresponding upper limits on the branching fractions at the $90\%$ confidence level are determined. The sensitivities of the results are at the level of $10^{-5} \sim 10^{-6}$, providing a large improvement over previous searches.

hep-ex↗

arXiv2018

Measurement of Singly Cabibbo-Suppressed Decays $D^{0}\toπ^{0}π^{0}π^{0}$, $π^{0}π^{0}η$, $π^{0}ηη$ and $ηηη$

Using a data sample of $e^+e^-$ collision data corresponding to an integrated luminosity of 2.93 $fb^{-1}$ collected with the BESIII detector at a center-of-mass energy of $\sqrt{s}= 3.773~GeV$,we search for the singly Cabibbo-suppressed decays $D^{0}\toπ^{0}π^{0}π^{0}$, $π^{0}π^{0}η$, $π^{0}ηη$ and $ηηη$ using the double tag method. The absolute branching fractions are measured to be $\mathcal{B}(D^{0}\toπ^{0}π^{0}π^{0}) = (2.0 \pm 0.4 \pm 0.3)\times 10^{-4}$, $\mathcal{B}(D^{0}\toπ^{0}π^{0}η) = (3.8 \pm 1.1 \pm 0.7)\times 10^{-4}$ and $\mathcal{B}(D^{0}\toπ^{0}ηη) = (7.3 \pm 1.6 \pm 1.5)\times 10^{-4}$ with the statistical significances of $4.8σ$, $3.8σ$ and $5.5σ$, respectively, where the first uncertainties are statistical and the second ones systematic. No significant signal of $D^{0}\toηηη$ is found, and the upper limit on its decay branching fraction is set to be $\mathcal{B}(D^{0}\toηηη) < 1.3 \times 10^{-4}$ at the $90\%$ confidence level.

hep-ex↗

arXiv2018

Precision measurement of the $e^{+}e^{-}~\rightarrow~Λ_{c}^{+} \barΛ_{c}^{-}$ cross section near threshold

The Born cross section of the $e^{+}e^{-}~\rightarrow~Λ_{c}^{+} \barΛ_{c}^{-}$ process is measured with unprecedented precision using data collected with the BESIII detector at $\sqrt{s}=4574.5$, $45580.0$, $4590.0$ and $4599.5$ $\mathrm{MeV}$. The non-zero cross section near the $Λ_{c}^{+} \barΛ_{c}^{-}$ production threshold is discerned. At center-of-mass energies $\sqrt{s}=4574.5$ and $4599.5 $ $\mathrm{MeV}$, the higher statistics data enable us to measure the $Λ_{c}$ polar angle distributions. From these, the ratio between the $Λ_{c}$ electric and magnetic form factors ($|G_{E}/G_{M}|$) is measured for the first time. They are found to be $1.14\pm0.14\pm0.07$ and $1.23\pm0.05\pm0.03$ respectively, where the first uncertainties are statistical and the second are systematic.

hep-ex↗

arXiv2018

A fully implicit, conservative, non-linear, electromagnetic hybrid particle-ion/fluid-electron algorithm

The quasi-neutral hybrid model with kinetic ions and fluid electrons is a promising approach for bridging the inherent multi-scale nature of many problems in space and laboratory plasmas. Here, a novel, implicit, particle-in-cell based scheme for the hybrid model is derived for multi-dimensional electromagnetic problems with multiple ion species, which features global mass, momentum and energy conservation. The scheme includes sub-cycling and orbit averaging of the ions, with cell-centered finite differences and implicit midpoint time advance. To reduce discrete particle noise, the scheme allows arbitrary-order shape functions for the particle-mesh interpolations and the application of conservative binomial smoothing. The algorithm is verified for a number of test problems to demonstrate the correctness of the implementation, the unique conservation properties, and the favorable stability properties of the new scheme. In particular, there is no indication of unstable growth of the finite-grid instability for a population of cold ions drifting through a uniform spatial mesh, in a set-up where several commonly used non-conservative schemes are highly unstable.

physics.plasm-ph↗

arXiv2018

Search for $h_{c}\rightarrowπ^+π^-J/ψ$ via $ψ(3686)\rightarrow π^0π^+π^-J/ψ$

Using a data sample of $448.1\times10^6$ $ψ(3686)$ events collected with the BESIII detector operating at the BEPCII, we perform search for the hadronic transition $h_c\rightarrowπ^+π^-J/ψ$ via $ψ(3686)\rightarrowπ^0h_c$. No signals of the transition are observed, and the upper limit on the product branching fraction $\mathcal{B}(ψ(3686)\rightarrowπ^0h_c)\mathcal{B}(h_c\rightarrowπ^+π^-J/ψ)$ at the 90% confidence level is determined to be $2.0\times10^{-6}$. This is the most stringent upper limit to date.

hep-ex↗

arXiv2018

Study of the decays $D^+\rightarrowη^{(\prime)} e^+ν_{e}$

The charm semileptonic decays $D^+\toηe^+ν_{e}$ and $D^+\toη'e^+ν_{e}$ are studied with a sample of $e^+e^-$ collision data corresponding to an integrated luminosity of 2.93 fb$^{-1}$ collected at $\sqrt{s}$ = 3.773 GeV with the BESIII detector. We measure the branching fractions for $D^+\toηe^+ν_{e}$ to be $(10.74\pm0.81\pm0.51)\times10^{-4}$, and for $D^+\toη'e^+ν_{e}$ to be $(1.91\pm0.51\pm0.13)\times10^{-4}$, where the uncertainties are statistical and systematic, respectively. In addition, we perform a measurement of the form factor in the decay $D^+\toηe^+ν_{e}$. All the results are consistent with those obtained by the CLEO-c experiment.

hep-ex↗