arXiv subjects
Publications and source records attributed to G. Chen.
Using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider, we search for the lepton number violation decay $ϕ\to π^+ π^+ e^- e^-$ via $J/ψ\to ϕη$. No signal is found and the upper limit on the branching fraction of $ϕ\to π^+ π^+ e^- e^-$ is set to be $9.7\times10^{-6}$ at the 90\% confidence level.
The Born cross sections and effective form factors of the process $e^+e^-\toΛ\barΣ^0 + c.c.$ are measured at 14 center-of-mass energy points from 2.3094 to 3.0800 GeV, based on data corresponding to an integrated luminosity of $(478.5 \pm 4.8)\ \text{pb}^{-1}$ collected with the BESIII detector. A non-zero Born cross section is observed at the center-of-mass energy of 2.3094 GeV with a statistical significance of more than five standard deviations, and the cross sections at other energies are obtained with improved precision compared to earlier measurements from the BaBar Collaboration. The Born cross-section lineshape is described better by a shape with a plateau near the threshold than by a pQCD motivated functional form.
Based on $e^+e^-$ collision data corresponding to an integrated luminosity of 4.5 $fb^{-1}$ collected at the center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII, the absolute branching fraction of the inclusive decay $Λ^{+}_{c}\to n + X$, where $X$ refers to any possible final state particles, is measured. The absolute branching fraction is determined to be $\mathcal{B}(Λ^{+}_{c}\to n + X) = (32.4 \pm 0.7 \pm 1.5)\% $, where the first uncertainty is statistical and the second systematic. Assuming $CP$ symmetry, the measurement indicates that about one-fourth of $Λ^{+}_{c}$ ($\barΛ_{c}^-$) decay modes with a neutron (an anti-neutron) in the final state have not been observed.
Using 2.93 $\rm{fb}^{-1}$ of $e^+e^-$ collision data collected with the BESIII detector at the center-of-mass energy 3.773\,GeV, we perform the first amplitude analysis of the decay $D^+\to K_S^0π^+π^0π^0$ and determine the relative magnitudes and phases of different intermediate processes. The absolute branching fraction of $D^+\to K_S^0π^+π^0π^0$ is measured to be $(2.888\pm0.058_{\rm stat.}\pm0.069_{\rm syst.})\%$. The dominant intermediate processes are $D^+\to K_S^0a_1(1260)^+(\to ρ^+π^0)$ and $D^+\to \bar{K}^{*0}ρ^+$, with branching fractions of $(8.66\pm1.04_{\rm stat.}\pm1.39_{\rm syst.})\!\times \!10^{-3}$ and $(9.70\pm0.81_{\rm stat.}\pm0.53_{\rm syst.})\!\times \!10^{-3}$, respectively.
Using an $e^+ e^-$ collision data sample with a total integrated luminosity of $3.19$ fb$^{-1}$ collected with the BESIII detector at a center-of-mass energy of 4.178 GeV, the branching fraction of the inclusive decay of the $D_s^+$ meson to final states including at least three charged pions is measured for the first time to be ${\cal B}(D_s^+\toπ^+ π^+ π^- X) = (32.81 \pm 0.35_{\rm stat} \pm {0.63_{\rm syst}})\%$. In this measurement the charged pions from $K_S^0$ meson decays are excluded. The partial branching fractions of $D_s^+\toπ^+ π^+ π^- X$ are also measured as a function of the $π^+ π^+ π^-$ invariant mass.
A determination of the $C\!P$-even fraction $F_+$ in the decay $D^0 \to K^+K^-π^+π^-$ is presented. Using $2.93$ fb$^{-1}$ of $e^+e^-\toψ(3770)\to D\bar{D}$ data collected by the BESIII detector, one charm meson is reconstructed in the signal mode and the other in a $C\!P$ eigenstate or the decay $D\to K_{S, L}^0π^+π^-$. Analysis of the relative rates of these double-tagged events yields the result $F_+ = 0.730 \pm 0.037 \pm 0.021$, where the first uncertainty is statistical and the second is systematic. This is the first model-independent measurement of $F_+$ in $D^0 \to K^+K^-π^+π^-$ decays.
Using a data sample of $(10087\pm44)\times 10^6$ $J/ψ$ events collected by the BESIII detector in 2009, 2012, 2018 and 2019, the electromagnetic Dalitz process $J/ψ\to e^+ e^- η(1405)$ is observed via the decay $η(1405) \to π^0 f_0(980)$, $f_0(980) \to π^+ π^-$, with a significance of about $9.6σ$. The branching fraction of this decay is measured to be ${\mathcal B}(J/ψ\to e^+ e^- π^0 η(1405) \to e^+ e^- π^0 f_0(980) \to e^+ e^- π^0 π^+ π^-)=(2.02\pm0.24(\rm{stat.})\pm0.09(\rm{syst.}))\times 10^{-7}$. The branching-fraction ratio ${\mathcal B}(J/ψ\to e^+ e^- η(1405))$/${\mathcal B}(J/ψ\to γη(1405))$ is determined to be $(1.35\pm0.19(\rm{stat.})\pm0.06(\rm{syst.}))\times10^{-2}$. Furthermore, an $e^+e^-$ invariant-mass dependent transition form factor of $J/ψ\to e^+ e^-η(1405)$ is presented for the first time. The obtained result provides input for different theoretical models, and is valuable for the improved understanding the intrinsic structure of the $η(1405)$ meson.
The $D^+_s\to K^+K^-μ^+ν_μ$ decay is studied based on 7.33 fb$^{-1}$ of $e^+e^-$ collision data collected with the BESIII detector at center-of-mass energies in the range from 4.128 to 4.226 GeV. The absolute branching fraction is measured as ${\mathcal B}(D^+_s\to ϕμ^+ν_μ) = (2.25\pm 0.09 \pm 0.07) \times10^{-2}$, the most precise measurement to date. Combining with the world average of ${\mathcal B}(D^+_s\to ϕe^+ν_e)$, the ratio of the branching fractions obtained is$\frac{{\mathcal B}(D^+_s\to ϕμ^+ν_μ)}{{\mathcal B}(D^+_s\to ϕe^+ν_e)} = 0.94\pm0.08$, in agreement with lepton universality. By performing a partial wave analysis, the hadronic form factor ratios at $q^{2}=0$ are extracted, finding $r_{V}=\frac{V(0)}{A_{1}(0)}=1.58\pm0.17\pm0.02$ and $r_{2}=\frac{A_{2}(0)}{A_{1}(0)}=0.71\pm0.14\pm0.02$, where the first uncertainties are statistical and the second are systematic. No significant $S$-wave contribution from $f_0(980)\to K^+K^-$ is found. The upper limit $\mathcal{B}(D_s^+\to f_0(980)μ^{+}ν_μ) \cdot{\mathcal B}(f_0(980)\to K^+K^-) < 5.45 \times 10^{-4}$ is set at 90\% confidence level.
A 218 MHz quarter wave niobium cavity has been fabricated for the purpose of demonstrating Nb3Sn technology on a low-beta accelerator cavity. Niobiumtin has been established as a promising next generation SRF material, but development has focused primarily in high-beta elliptical cell cavities. This material has a significantly higher TC than niobium, allowing for design of higher frequency quarter wave cavities (that are subsequently smaller) as well as for significantly lowered cooling requirements (possibly leading to cryocooler based designs). The fabrication, initial cold testing, and Nb3Sn coating are discussed as well as test plans and details of future applications.
The processes $e^{+}e^{-} \to Δ^{++}\barΔ^{--}$ and $e^{+}e^{-}\to Δ^{++} \bar{p} π^{-} + c.c.$ are studied for the first time with $179~{\rm pb}^{-1}$ of $e^{+}e^{-}$ annihilation data collected with the BESIII detector at center-of-mass energies from $2.3094$ GeV to $2.6464$ GeV. No significant signal for the $e^{+}e^{-}\to Δ^{++}\barΔ^{--}$ process is observed and the upper limit of the Born cross section is estimated at each energy point. For the process $e^{+}e^{-} \to Δ^{++} \bar{p} π^{-} + c.c.$, a significant signal is observed at center-of-mass energies near 2.6454 GeV and the corresponding Born cross section is reported.
We study the process $e^{+}e^{-}\toΛ_{c}^{+}\barΛ_c^{-}$ at twelve center-of-mass energies from $4.6119$ to $4.9509~\mathrm{GeV}$ using data samples collected by the BESIII detector at the BEPCII collider. The Born cross sections and effective form factors ($|G_{\mathrm{eff}}|$) are determined with unprecedented precision after combining the single and double-tag methods based on the decay process $Λ_{c}^{+}\to pK^{-}π^{+}$. Flat cross sections around $4.63~\mathrm{GeV}$ are obtained and no indication of the resonant structure $Y(4630)$, as reported by Belle, is found. In addition, no oscillatory behavior is discerned in the $|G_{\mathrm{eff}}|$ energy-dependence of $Λ_{c}^{+}$, in contrast to what is seen for the proton and neutron cases. Analyzing the cross section together with the polar-angle distribution of the $Λ_{c}^{+}$ baryon at each energy point, the moduli of electric and magnetic form factors ($|G_{E}|$ and $|G_{M}|$) are extracted and separated. For the first time, the energy-dependence of the form factor ratio $|G_{E}/G_{M}|$ is observed, which can be well described by an oscillatory function.
The $Ξ^0$ asymmetry parameters are measured using entangled quantum $Ξ^0$-$\barΞ^0$ pairs from a sample of $(448.1 \pm 2.9) \times 10^6$ $ψ(3686)$ events collected with the BESIII detector at BEPCII. The relative phase between the transition amplitudes of the $Ξ^0 \barΞ^0$ helicity states is measured to be $ΔΦ= -0.050 \pm 0.150 \pm 0.020$~rad, which implies that there is no obvious polarization at the current level of statistics. The decay parameters of the $Ξ^0$ hyperon $(α_{Ξ^0}, α_{\barΞ^0}, ϕ_{Ξ^0}, ϕ_{\barΞ^0})$ and the angular distribution parameter $(α_{ψ(3686)})$ and $ΔΦ$ are measured simultaneously for the first time. In addition, the $CP$ asymmetry observables are determined to be $A^{Ξ^0}_{CP} = (α_{Ξ^0} + α_{\barΞ^0})/(α_{Ξ^0} - α_{\barΞ^0})$ $= -0.007$ $\pm$ 0.082 $\pm$ 0.025 and $Δϕ^{Ξ^0}_{CP} = (ϕ_{Ξ^0} + ϕ_{\barΞ^0})/2$ $= -0.079$ $\pm$ 0.082 $\pm$ 0.010 rad, which are consistent with $CP$ conservation.
Using $e^+e^-$ collision datasets corresponding to total integrated luminosity of 21.7 fb$^{-1}$ collected with the BESIII detector at the BEPCII collider at center-of-mass energies ranging from 4.009 GeV to 4.951 GeV, the energy-dependent cross sections of $e^+e^-\to pK^-\barΛ+c.c.$ are measured for the first time. By fitting these energy-dependent cross sections, we search for the excited $ψ$ states $ψ(4160)$ and $ψ(4415)$, and the vector charmonium-like states $ψ(4230)$, $ψ(4360)$, and $ψ(4660)$. No evidence for these is observed and the upper limits on the branching fractions of these states decaying into $pK^-\bar Λ+c.c.$ are set at the 90\% confidence level.
We search for the semi-leptonic decays $Λ_c^+ \to Λπ^+ π^- e^+ ν_e$ and $Λ_c^+ \to p K_S^0 π^- e^+ ν_e$ in a sample of 4.5 $\mathrm{fb}^{-1}$ of $e^{+}e^{-}$ annihilation data collected in the center-of-mass energy region between 4.600 GeV and 4.699 GeV by the BESIII detector at the BEPCII. No significant signals are observed, and the upper limits on the decay branching fractions are set to be $\mathcal{B}(Λ_c^+ \to Λπ^+ π^- e^+ ν_e)<3.9\times10^{-4}$ and $\mathcal{B}(Λ_c^+ \to p K_S^0 π^- e^+ ν_e)<3.3\times10^{-4}$ at the 90% confidence level, respectively.
Gravitational-wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is a space-borne instrument dedicated to monitoring high-energy transients, including Terrestrial Gamma-ray Flashes (TGFs) and Terrestrial Electron Beams (TEBs). We implemented a TGF/TEB search algorithm for GECAM, with which 147 bright TGFs, 2 typical TEBs and 2 special TEB-like events are identified during an effective observation time of $\sim$9 months. We show that, with gamma-ray and charged particle detectors, GECAM can effectively identify and distinguish TGFs and TEBs, and measure their temporal and spectral properties in detail. A very high TGF-lightning association rate of $\sim$80\% is obtained between GECAM and GLD360 in east Asia region.
Based on electron positron collision data collected with the BESIII detector operating at the BEPCII storage rings, the differential cross sections of inclusive $π^0$ and $K^0_S$ production as a function of hadron momentum, normalized by the total cross section of the $e^{+}e^{-} \to$ hadrons process, are measured at six center-of-mass energies from 2.2324 to 3.6710 GeV. Our results with a relative hadron energy coverage from 0.1 to 0.9 significantly deviate from several theoretical calculations based on existing fragmentation functions, especially at lower energies.
The measurement of the Cabibbo-favored semileptonic decay $Λ_c^+\rightarrow Λμ^+ν_μ$ is reported using $4.5~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data collected at center-of-mass energies ranging from 4.600~GeV to 4.699~GeV. The branching fraction of the decay is measured to be $\mathcal{B}(Λ_c^+\rightarrow Λμ^+ν_μ)=(3.48\pm0.14_{\rm stat.}\pm0.10_{\rm syst.})\%$, three times more precise than the prior world average result. Tests of lepton flavor universality using $Λ_c^+\rightarrow Λ\ell^+ν_{\ell}$ ($\ell=e, μ$) decays are reported for the first time, based on measurements of the differential decay rates and the forward-backward asymmetries in separate four-momentum transfer regions. The results are compatible with Standard Model predictions. Furthermore, we improve the determination of the form-factor parameters in $Λ_c^+\rightarrow Λ\ell^+ν_{\ell}$ decays, which provide stringent tests and calibration for lattice quantum chromodynamics (LQCD) calculations.
Exoplanet atmospheres are the key to understanding the nature of exoplanets. To this end, transit spectrophotometry provides us opportunities to investigate the physical properties and chemical compositions of exoplanet atmospheres. We aim to detect potential atmospheric signatures in 12 gaseous giant exoplanets using transit spectrophotometry and we try to constrain their atmospheric properties. The targets of interest were observed using transit spectrophotometry with the GTC OSIRIS instrument. We estimated the transit parameters and obtained the optical transmission spectra of the target planets using a Bayesian framework. We analyzed the spectral features in the transmission spectra based on atmospheric retrievals. Most of the observed transmission spectra were found to be featureless, with only the spectrum of CoRoT-1b showing strong evidence for atmospheric features. However, in combination with the previously published near-infrared transmission spectrum, we found multiple interpretations for the atmosphere of CoRoT-1b due to the lack of decisive evidence for alkali metals or optical absorbers. Featureless spectra are not necessarily indicative of cloudy atmospheres if they poorly constrain the altitudes of cloud decks. Precise constraints on the models of hazes and clouds strongly depend on the significance of the observed spectral features. Further investigations on these exoplanets, especially CoRoT-1b, are required to confirm the properties of their atmospheres.