arXiv subjects

G. Chen

Publications and source records attributed to G. Chen.

At least 595 records · Page 33Linked to original sources

arXiv2021

Comparison of $pp$ and $p \bar{p}$ differential elastic cross sections and observation of the exchange of a colorless $C$-odd gluonic compound

We describe an analysis comparing the $p\bar{p}$ elastic cross section as measured by the D0 Collaboration at a center-of-mass energy of 1.96 TeV to that in $pp$ collisions as measured by the TOTEM Collaboration at 2.76, 7, 8, and 13 TeV using a model-independent approach. The TOTEM cross sections extrapolated to a center-of-mass energy of $\sqrt{s} =$ 1.96 TeV are compared with the D0 measurement in the region of the diffractive minimum and the second maximum of the $pp$ cross section. The two data sets disagree at the 3.4$σ$ level and thus provide evidence for the $t$-channel exchange of a colorless, $C$-odd gluonic compound, also known as the odderon. We combine these results with a TOTEM analysis of the same $C$-odd exchange based on the total cross section and the ratio of the real to imaginary parts of the forward elastic scattering amplitude in $pp$ scattering. The combined significance of these results is larger than 5$σ$ and is interpreted as the first observation of the exchange of a colorless, $C$-odd gluonic compound.

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arXiv2021

Study of $e^+e^- \rightarrow π^{0}X(3872)γ$ and search for $Z_c(4020)^{0}\rightarrow X(3872)γ$

Using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.178 to 4.600 GeV, we study the process $e^+e^-\rightarrowπ^{0}X(3872)γ$ and search for $Z_c(4020)^{0}\rightarrow X(3872)γ$. We find no significant signal and set upper limits on $σ(e^+e^-\rightarrowπ^{0}X(3872)γ)\cdot\mathcal{B}(X(3872)\rightarrowπ^{+}π^{-}J/ψ)$ and $σ(e^+e^-\rightarrowπ^{0}Z_c(4020)^{0})\cdot\mathcal{B}(Z_c(4020)^{0}\rightarrow X(3872)γ)\cdot\mathcal{B}(X(3872)\rightarrowπ^{+}π^{-}J/ψ)$ for each energy point at $90\%$ confidence level, which is of the order of several tenths pb.

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arXiv2021

Detection of Galactic and Extragalactic Millimeter-Wavelength Transient Sources with SPT-3G

High-angular-resolution cosmic microwave background experiments provide a unique opportunity to conduct a survey of time-variable sources at millimeter wavelengths, a population which has primarily been understood through follow-up measurements of detections in other bands. Here we report the first results of an astronomical transient survey with the South Pole Telescope (SPT) using the SPT-3G camera to observe 1500 square degrees of the southern sky. The observations took place from March to November 2020 in three bands centered at 95, 150, and 220 GHz. This survey yielded the detection of fifteen transient events from sources not previously detected by the SPT. The majority are associated with variable stars of different types, expanding the number of such detected flares by more than a factor of two. The stellar flares are unpolarized and bright, in some cases exceeding 1 Jy, and have durations from a few minutes to several hours. Another population of detected events last for 2--3 weeks and appear to be extragalactic in origin. Though data availability at other wavelengths is limited, we find evidence for concurrent optical activity for two of the stellar flares. Future data from SPT-3G and forthcoming instruments will provide real-time detection of millimeter-wave transients on timescales of minutes to months.

astro-ph.HE↗

arXiv2021

Measurement of the doubly Cabibbo-suppressed decay $D^+\to K^+π^+π^-π^0$ with semileptonic tags

Using an $e^+e^-$ annihilation data sample corresponding to an integrated luminosity of $2.93\,\rm fb^{-1}$ collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, the doubly Cabibbo-suppressed decay $D^+\to K^+π^+π^-π^0$ is studied with a semileptonic tag method. After removing the decays containing narrow intermediate resonances, $D^+\to K^+η$, $D^+\to K^+ω$, and $D^+\to K^+ϕ$, the branching fraction for the decay $D^+\to K^+π^+π^-π^0$ is determined to be $(1.03 \pm 0.12_{\rm stat} \pm 0.06_{\rm syst})\times 10^{-3}$. The ratio of the branching fraction for $D^+\to K^+π^+π^-π^0$ to its Cabibbo-favored counterpart $D^+\to K^-π^+π^+π^0$ is measured to be $ (1.65\pm0.21)\%$, corresponding to $(5.73\pm0.73)\tan^4θ_C$, where $θ_C$ is the Cabibbo mixing angle. These results are consistent with our previous measurement with hadronic tags but are significantly larger than other doubly Cabibbo-suppressed decays in the charm sector.

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arXiv2021

Cross section measurement of $e^{+}e^{-} \to K_{S}^{0}K_{L}^{0}$ at $\sqrt{s}=2.00-3.08~{\rm GeV}$

The cross sections of the process $e^{+}e^{-} \to K_{S}^{0}K_{L}^{0}$ are measured at fifteen center-of-mass energies $\sqrt{s}$ from $2.00$ to $3.08~{\rm GeV}$ with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results are found to be consistent with those obtained by BaBar. A resonant structure around $2.2~{\rm GeV}$ is observed, with a mass and width of $2273.7 \pm 5.7 \pm 19.3~{\rm MeV}/c^2$ and $86 \pm 44 \pm 51~{\rm MeV}$, respectively, where the first uncertainties are statistical and the second ones are systematic. The product of its radiative width ($Γ_{e^+e^-}$) with its branching fraction to $K_{S}^{0}K_{L}^{0}$ ($Br_{K_{S}^{0}K_{L}^{0}}$) is $0.9 \pm 0.6 \pm 0.7~{\rm eV}$.

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arXiv2021

Weak phases and CP-symmetry tests in sequential decays of entangled double-strange baryons

Using a sample of $1.31\times10^9$ $J/ψ$ events collected with the BESIII detector at the electron-positron collider BEPCII, we analyse the full $J/ψ\to$ $Ξ^-\overlineΞ^+$, $Ξ^-\to Λπ^-$, $Λ\to pπ^-$, $\overlineΞ^+\to\overlineΛπ^+$, $\overlineΛ\to\overline{p}π^+$ decay chain. A new method, exploiting the fact that the $Ξ^-\overlineΞ^+$ pair is entangled and sequentially decaying, and where the complete decay chains are reconstructed, is applied for the first time. This enables precision measurements of the decay parameters for the $Ξ^-\toΛπ^-$ decay ($α_Ξ$, $ϕ_Ξ$) as well as the $\overlineΞ^+\to\overlineΛπ^+$ decay ($\overlineα_Ξ$, $\overlineϕ_Ξ$). From the decay parameters, two independent CP tests were performed, quantified by the observables $A_{\rm CP}^Ξ$ and $Δϕ_Ξ$. Our results, $A_{\rm CP}^Ξ$ = $(6.0\pm13.4\pm5.6)\times10^{-3}$ and $Δϕ_Ξ= (-4.8\pm13.7\pm2.9)\times10^{-3}~{\rm rad}$, are consistent with CP symmetry. Furthermore, our method enables a separation of strong and weak $Ξ\toΛπ$ decay amplitudes. This results in the first direct measurement of the weak phase difference for any baryon decay. The result is found to be $(ξ_{P} - ξ_{S}) = (1.2\pm3.4\pm0.8)\times10^{-2}$ rad and is one of the most precise tests of CP symmetry for strange baryons. The strong phase difference is measured to be $(δ_P - δ_S) = (-4.0\pm3.3\pm1.7)\times10^{-2}$ rad. In addition, we provide an independent measurement of the recently debated $Λ$ decay parameter, $α_Λ = 0.757 \pm 0.011 \pm 0.008 $. The $Λ\overlineΛ$ asymmetry is measured to be $A_{\rm CP}^Λ = (-3.7\pm11.7\pm9.0)\times10^{-3}$.

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arXiv2021

Search for new decay modes of the $ψ_2(3823)$ and the process $e^+e^-\rightarrowπ^0π^0ψ_2(3823)$

The decays $ψ_2(3823)\rightarrowγχ_{c0,1,2}, π^+π^-J/ψ, π^0π^0J/ψ, ηJ/ψ$, and $π^0J/ψ$ are searched for using the reaction $e^+e^-\rightarrowπ^+π^-ψ_2(3823)$ in a 19 fb$^{-1}$ data sample collected at center-of-mass energies between 4.1 and 4.7 GeV with the BESIII detector. The process $ψ_2(3823)\rightarrowγχ_{c1}$ is observed in a 9 fb$^{-1}$ data sample in the center-of-mass energy range 4.3 to 4.7 GeV, which confirms a previous observation but with a higher significance of $11.8σ$, and evidence for $ψ_2(3823)\rightarrowγχ_{c2}$ is found with a significance of $3.2σ$ for the first time. The branching-fraction ratio $\frac{\mathcal{B}(ψ_2(3823)\rightarrowγχ_{c2})}{\mathcal{B}(ψ_2(3823)\rightarrowγχ_{c1})}$ is determined. No significant $ψ_2(3823)$ signals are observed for any of the other decay channels. Upper limits of branching-fraction ratios for $ψ_2(3823)\rightarrowπ^+π^-J/ψ, π^0π^0J/ψ, ηJ/ψ, π^0J/ψ, γχ_{c0}$ relative to $ψ_2(3823)\rightarrowγχ_{c1}$ are reported. The process $e^+e^-\rightarrowπ^0π^0ψ_2(3823)$ is also searched for, and we find evidence for the process with a significance of $4.3σ$. The average cross-section ratio $\frac{σ(e^+e^-\rightarrowπ^0π^0ψ_2(3823))}{σ(e^+e^-\rightarrowπ^+π^-ψ_2(3823))}$ is also determined.

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arXiv2021

Measurements of the branching fractions of $ψ(3686)\rightarrow\barΣ^{0}Λ+c.c.$ and $χ_{cJ (J = 0,1,2)} \rightarrow Λ\barΛ$

Based on $4.481\times10^8$ $ψ(3686)$ events collected with the BESIII detector at BEPCII, the branching fraction of the isospin violating decay $ψ(3686)\rightarrow\barΣ^{0}Λ+c.c.$ is measured to be $(1.60 \pm 0.31 \pm 0.13~\pm~0.58) \times 10^{-6}$, where the first uncertainty is statistical, the second is systematic, and the third is the uncertainty arising from interference with the continuum. This result is significantly smaller than the measurement based on CLEO-c data sets. The decays $χ_{cJ} \rightarrowΛ\barΛ$ are measured via $ψ(3686)\rightarrowγχ_{cJ}$, and the branching fractions are determined to be $\mathcal{B}\left(χ_{c0}\rightarrowΛ\barΛ\right)=(3.64 \pm 0.10 \pm 0.10 \pm 0.07)\times 10^{-4}$, $\mathcal{B}\left(χ_{c1}\rightarrowΛ\barΛ\right)=(1.31\pm0.06 \pm 0.06 \pm0.03)\times 10^{-4}$, $\mathcal{B}\left(χ_{c2}\rightarrowΛ\barΛ\right)=(1.91\pm0.08 \pm 0.17 \pm0.04)\times 10^{-4}$, where the third uncertainties are systematic due to the $ψ(3686) \rightarrow γχ_{c J}$ branching fractions.

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arXiv2021

Measurement of the absolute branching fraction of inclusive semielectronic $D_s^+$ decays

We measure the inclusive semielectronic decay branching fraction of the $D_s^+$ meson. A double-tag technique is applied to $e^+e^-$ annihilation data collected by the BESIII experiment at the BEPCII collider, operating in the center-of-mass energy range $4.178 - 4.230$ GeV. We select positrons from $D_s^+\rightarrow Xe^{+}ν_e$ with momenta greater than 200 MeV/$c$, and determine the laboratory momentum spectrum, accounting for the effects of detector efficiency and resolution. The total positron yield and semielectronic branching fraction are determined by extrapolating this spectrum below the momentum cutoff. We measure the $D_s^+$ semielectronic branching fraction to be $\mathcal{B}\left(D_s^+\rightarrow Xe^{+}ν_e\right)=\left(6.30\pm0.13\;(\text{stat.})\pm 0.10\;(\text{syst.})\right)\%$, showing no evidence for unobserved exclusive semielectronic modes. We combine this result with external data taken from literature to determine the ratio of the $D_s^+$ and $D^0$ semielectronic widths, $\frac{Γ(D_{s}^{+}\rightarrow Xe^+ν_e)}{Γ(D^0\rightarrow Xe^+ν_e)}=0.790\pm 0.016\;(\text{stat.})\pm0.020\;(\text{syst.})$. Our results are consistent with and more precise than previous measurements.

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arXiv2021

Measurement of the Branching Fraction of and Search for a CP-Violating Asymmetry in $η' \to π^+ π^- e^+ e^-$ at BESIII

The rare decay $η' \to π^+ π^- e^+ e^-$ is studied using a sample of $1.3 \times 10^9$ $J/ψ$ events collected with the BESIII detector at BEPCII in 2009 and 2012. The branching fraction is measured with improved precision to be $\left( 2.42\pm0.05_{stat.}\pm0.08_{syst.} \right) \times 10^{-3}$. Due to the inclusion of new data, this result supersedes the last BESIII result on this branching fraction. In addition, the CP-violating asymmetry in the angle between the decay planes of the $π^+π^-$-pair and the $e^+e^-$-pair is investigated. A measurable value would indicate physics beyond the standard model; the result is $\mathcal{A}_{CP} = \left(2.9\pm3.7_{stat.}\pm1.1_{syst.} \right)\%$, which is consistent with the standard model expectation of no CP-violation. The precision is comparable to the asymmetry measurement in the $K^0_L\toπ^+π^-e^+e^-$ decay where the observed $(14\pm2)\%$ effect is driven by a standard model mechanism.

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arXiv2021

Measurement of the absolute branching fraction of $Λ_c^+\to p K^0_{\mathrm{S}}η$ decays

Based on 586 $\rm{pb^{-1}}$ of $e^+e^-$ annihilation data collected at a center-of-mass energy of $\sqrt{s}=4.6~\rm{GeV}$ with the BESIII detector at the BEPCII collider, the absolute branching fraction of $Λ_c^+ \to p K^0_{\mathrm{S}}η$ decays is measured for the first time to be $\mathcal{B}(Λ_c^+ \to p K^0_{\mathrm{S}}η) = (0.414 \pm 0.084 \pm 0.028)\%$, where the first uncertainty is statistical and the second is systematic. The result is compatible with a previous CLEO result on the relative branching fraction $\frac{\mathcal{B}(Λ_c^+ \to p K^0_{\mathrm{S}}η)}{\mathcal{B}(Λ_c^+ \to p K^-π^+)}$, and consistent with theoretical predictions of SU(3) flavor symmetry.

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arXiv2021

New Features in the Electromagnetic Structure of the Neutron

Here we present new results for the Born cross section and the effective form factor of the neutron at the center-of-mass energies ${\bf \sqrt{s}}$ between 2.0 and 3.08 GeV, using 18 data sets corresponding to an integrated luminosity of 647.9 pb${\bf ^{-1}}$ from e${\bf ^+}$e${\bf ^-}$ annihilation reactions collected at the BESIII experiment. The process $e^{+}e^{-}\to n\bar{n}$ is analyzed with three individual categories to improve the efficiency of $n\bar{n}$ reconstruction. The cross section of $e^{+}e^{-}\to n\bar{n}$ is measured at 18 c.m. energies where the best precision is 8.1\% at $\sqrt{s}=2.396$ GeV. The corresponding effective form factors are extracted under the assumption $|G_{E}|=|G_{M}|$. Our results improve the statistical precision on the neutron form factor by more than a factor of 60 over previous measurements from the FENICE and DM2 experiments and usher in a new era where neutron form factor data from annihilation in the time-like regime is on par with that from electron scattering experiments. In addition, an oscillatory behavior of the effective form factor observed for the proton is discussed for the neutron.

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arXiv2021

Determination of the $Λ_c^+$ spin via the reaction $e^+e^-\toΛ_c^+\barΛ_c^-$

We report on a comparison of two possible $Λ_c^+$ spin hypotheses, $J=\frac{1}{2}$ and $\frac{3}{2}$, via the process $e^+e^-\toΛ_c^+\barΛ_c^-$, using the angular distributions of $Λ_c^+$ decays into $pK_S^0$, $Λπ^+$, $Σ^0π^+$, and $Σ^+π^0$. The data were recorded at $\sqrt s = 4.6$ GeV with the BESIII detector and correspond to an integrated luminosity of 587 pb$^{-1}$. The $Λ_c^+$ spin is determined to be $J=\frac{1}{2}$, with this value favored over the $\frac{3}{2}$ hypothesis with a significance corresponding to more than 6 Gaussian standard deviations.

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arXiv2021

HXMT Identification of a non-thermal X-ray burst from SGR J1935+2154 and with FRB 200428

Fast radio bursts (FRBs) are short pulses observed in radio band from cosmological distances. One class of models invoke soft gamma-ray repeaters (SGRs), or magnetars, as the sources of FRBs. Some radio pulses have been observed from some magnetars, however, no FRB-like events had been detected in association any magnetar burst, including one giant flare. Recently, a pair of FRB-like bursts (FRB 200428 hereafter) separated by milliseconds (ms) were detected from the general direction of the Galactic magnetar SGR J1935+2154. Here we report the detection of a non-thermal X-ray burst in the 1-250 keV energy band with the Insight-HXMT satellite, which we identify as emitted from SGR J1935+2154. The burst showed two hard peaks with a separation of 34 ms, broadly consistent with that of the two bursts in FRB 200428. The delay time between the double radio and X-ray peaks is about 8.57 s, fully consistent with the dispersion delay of FRB 200428. We thus identify the non-thermal X-ray burst is associated with FRB 200428 whose high energy counterpart is the two hard peaks in X-ray. Our results suggest that the non-thermal X-ray burst and FRB 200428 share the same physical origin in an explosive event from SGR J1935+2154.

astro-ph.HE↗

arXiv2021

Amplitude analysis and branching-fraction measurement of \boldmath $D_{s}^{+} \to K^0_{S}π^{+}π^{0}$

Utilizing a data set corresponding to an integrated luminosity of 6.32~$\rm fb^{-1}$, recorded by the BESIII detector at center-of-mass energies between 4.178 and 4.226~GeV, we perform an amplitude analysis of the decay $D_{s}^{+} \to K_{S}^{0}π^{+}π^{0}$ and determine the relative fractions and phase differences of different intermediate processes, which include $K_{S}^{0}ρ(770)^{+}$, $K_{S}^{0}ρ(1450)^{+}$, $K^{*}(892)^{0}π^{+}$, $K^{*}(892)^{+}π^{0}$, and $K^{*}(1410)^{0}π^{+}$. Using a double-tag technique, and making an efficiency correction that relies on our knowledge of the phase-space distribution of the decays coming from the amplitude analysis, the absolute branching fraction is measured to be $\mathcal{B}(D_{s}^{+} \to K_{S}^{0}π^{+}π^{0})=(5.43\pm0.30_{\text{stat}}\pm 0.15_{\text{syst}})\times 10^{-3}$.

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arXiv2021

Constraints on $Λ$CDM Extensions from the SPT-3G 2018 $EE$ and $TE$ Power Spectra

We present constraints on extensions to the $Λ$CDM cosmological model from measurements of the $E$-mode polarization auto-power spectrum and the temperature-$E$-mode cross-power spectrum of the cosmic microwave background (CMB) made using 2018 SPT-3G data. The extensions considered vary the primordial helium abundance, the effective number of relativistic degrees of freedom, the sum of neutrino masses, the relativistic energy density and mass of a sterile neutrino, and the mean spatial curvature. We do not find clear evidence for any of these extensions, from either the SPT-3G 2018 dataset alone or in combination with baryon acoustic oscillation and \textit{Planck} data. None of these model extensions significantly relax the tension between Hubble-constant, $H_0$, constraints from the CMB and from distance-ladder measurements using Cepheids and supernovae. The addition of the SPT-3G 2018 data to \textit{Planck} reduces the square-root of the determinants of the parameter covariance matrices by factors of $1.3 - 2.0$ across these models, signaling a substantial reduction in the allowed parameter volume. We also explore CMB-based constraints on $H_0$ from combined SPT, \textit{Planck}, and ACT DR4 datasets. While individual experiments see some indications of different $H_0$ values between the $TT$, $TE$, and $EE$ spectra, the combined $H_0$ constraints are consistent between the three spectra. For the full combined datasets, we report $H_0 = 67.49 \pm 0.53\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$, which is the tightest constraint on $H_0$ from CMB power spectra to date and in $4.1\,σ$ tension with the most precise distance-ladder-based measurement of $H_0$. The SPT-3G survey is planned to continue through at least 2023, with existing maps of combined 2019 and 2020 data already having $\sim3.5\times$ lower noise than the maps used in this analysis.

astro-ph.CO↗

arXiv2021

Search for the decay $D_s^+\to a_0(980)^0e^+ν_e$

Using 6.32 fb$^{-1}$ of electron-positron collision data recorded by the BESIII detector at center-of-mass energies between 4.178 and 4.226~GeV, we present the first search for the decay $D_s^+\to a_0(980)^0 e^+ν_e,\,a_0(980)^0\rightarrow π^0η$, which could proceed via $a_0(980)$-$f_0(980)$ mixing. No significant signal is observed. An upper limit of $1.2 \times 10^{-4}$ at the $90\%$ confidence level is set on the product of the branching fractions of $D_{s}^{+}\to a_0(980)^0 e^+ν_e$ and $a_0(980)^0\rightarrow π^0η$ decays.

hep-ex↗

arXiv2021

Study of $e^+e^- \to 2(p\bar{p})$ at center-of-mass energies between 4.0 and 4.6 GeV

Using data taken at 23 center-of-mass energies between 4.0 and 4.6 GeV with the BESIII detector at the BEPCII collider and with a total integrated luminosity of approximately $15$ fb$^{-1}$, the process $e^+e^-\to 2(p \bar{p})$ is studied for the first time. The Born cross sections for $e^+e^-\to 2(p \bar{p})$ are measured, and no significant structure is observed in the lineshape. The baryon pair ($pp$ and $\bar{p}\bar{p}$) invariant mass spectra are consistent with phase space, therefore no hexaquark or di-baryon state is found.

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