arXiv subjects

G. Chen

Publications and source records attributed to G. Chen.

At least 829 records · Page 46Linked to original sources

arXiv2017

Observation of $ψ(3686) \rightarrow e^{+}e^{-}χ_{cJ}$ and $χ_{cJ} \rightarrow e^{+}e^{-}J/ψ$

Using $4.479 \times 10^{8}$ $ψ(3686)$ events collected with the BESIII detector, we search for the decays $ψ(3686) \rightarrow e^{+}e^{-}χ_{c0,1,2}$ and $χ_{c0,1,2} \rightarrow e^{+}e^{-}J/ψ$. The decays $ψ(3686) \rightarrow e^{+}e^{-}χ_{c0,1,2}$ and $χ_{c0,1,2} \rightarrow e^{+}e^{-}J/ψ$ are observed for the first time. The measured branching fractions are $\mathcal{B}(ψ(3686) \rightarrow e^{+}e^{-}χ_{c0,1,2}) = (11.7 \pm 2.5 \pm 1.0)\times10^{-4}$, $(8.6 \pm 0.3 \pm 0.6)\times10^{-4}$, $(6.9 \pm 0.5 \pm 0.6)\times10^{-4}$, and $\mathcal{B}(χ_{c0,1,2} \rightarrow e^{+}e^{-}J/ψ) = (1.51 \pm 0.30 \pm 0.13)\times10^{-4}$, $(3.73 \pm 0.09 \pm 0.25)\times10^{-3}$, $(2.48 \pm 0.08 \pm 0.16)\times10^{-3}$. The ratios of the branching fractions $\frac{\mathcal{B}(ψ(3686) \rightarrow e^{+}e^{-}χ_{c0,1,2})}{\mathcal{B}(ψ(3686) \rightarrow γχ_{c0,1,2})}$ and $\frac{\mathcal{B}(χ_{c0,1,2} \rightarrow e^{+}e^{-}J/ψ)}{\mathcal{B}(χ_{c0,1,2} \rightarrow γJ/ψ)}$ are also reported.

hep-ex↗

arXiv2017

Amplitude analysis of $D^{0} \rightarrow K^{-} π^{+} π^{+} π^{-}$

We present an amplitude analysis of the decay $D^{0} \rightarrow K^{-} π^{+} π^{+} π^{-}$ based on a data sample of 2.93 ${\mbox{\,fb}^{-1}}$ acquired by the BESIII detector at the $ψ(3770)$ resonance. With a nearly background free sample of about 16000 events, we investigate the substructure of the decay and determine the relative fractions and the phases among the different intermediate processes. Our amplitude model includes the two-body decays $D^{0} \rightarrow \bar{K}^{*0}ρ^{0}$, $D^{0} \rightarrow K^{-}a_{1}^{+}(1260)$ and $D^{0} \rightarrow K_{1}^{-}(1270)π^{+}$, the three-body decays $D^{0} \rightarrow \bar{K}^{*0}π^{+}π^{-}$ and $D^{0} \rightarrow K^{-}π^{+}ρ^{0}$, as well as the four-body decay $D^{0} \rightarrow K^{-}π^{+}π^{+}π^{-}$. The dominant intermediate process is $D^{0} \rightarrow K^{-}a_{1}^{+}(1260)$, accounting for a fit fraction of $54.6\%$.

hep-ex↗

arXiv2017

Improved measurements of branching fractions for $η_c\toϕϕ$ and $ωϕ$

Using $(223.7\pm1.4)\times10^6$ J/$ψ$ events accumulated with the BESIII detector, we study $η_c$ decays to $ϕϕ$ and $ωϕ$ final states. The branching fraction of $η_c\toϕϕ$ is measured to be $Br(η_c\toϕϕ)=(2.5\pm0.3^{+0.3}_{-0.7}\pm0.6)\times10^{-3}$, where the first uncertainty is statistical, the second is systematic, and the third is from the uncertainty of $Br(J/ψ\toγη_c)$. No significant signal for the double OZI-suppressed decay of $η_c\toωϕ$ is observed, and the upper limit on the branching fraction is determined to be $Br(η_c\toωϕ)<2.5\times 10^{-4}$ at the 90\% confidence level.

hep-ex↗

arXiv2017

Measurement of higher-order multipole amplitudes in $ψ(3686)\rightarrowγχ_{c1,2}$ with $χ_{c1,2}\toγJ/ψ$ and search for the transition $η_{c}(2S)\toγJ/ψ$

Using 106~million $ψ(3686)$ events collected with the BESIII detector, we measure multipole amplitudes for the decay $ψ(3686)\rightarrowγχ_{c1,2}\toγγJ/ψ$ beyond the dominant electric-dipole amplitudes. The normalized magnetic-quadrupole amplitude for $ψ(3686)\rightarrowγχ_{c1,2}\rightarrowγγJ/ψ$ and the normalized electric-octupole amplitudes for $ψ(3686)rightarrowγχ_{c2}$,~$χ_{c2}\rightarrowγJ/ψ$ are determined. The M2 amplitudes for $ψ(3686)\rightarrowγχ_{c1}$ and $χ_{c1,2}\rightarrowγJ/ψ$ are found to differ significantly from zero and are consistent with theoretical predictions. We also obtain the ratios of M2 contributions of $ψ(3686)$ and $J/ψ$ decays to $χ_{c1,2}$, $b_{2}^{1}/b_{2}^{2} = 1.35\pm0.72$ and $a_{2}^{1}/a_{2}^{2} = 0.617\pm0.083$, which agree well with theoretical expectations. By considering the multipole contributions of $χ_{c1,2}$, we measure the product branching fractions for the cascade decays $ψ(3686)\rightarrowγχ_{c0,1,2}\toγγJ/ψ$ and search for the process $η_{c}(2S)\toγJ/ψ$ through $ψ(3686)\rightarrowγη_{c}(2S)$. The product branching fraction for $ψ(3686)\rightarrowγχ_{c0}\toγγJ/ψ$ is 3$σ$ larger than published measurements, while those of $ψ(3686)rightarrowγχ_{c1,2}\toγγJ/ψ$ are consistent. No significant signal for the decay $ψ(3686)\toγη_c(2S)\toγγJ/ψ$ is observed, and the upper limit of the product branching fraction at the 90\% confidence level is determined.

hep-ex↗

arXiv2017

Study of $J/ψ$ and $ψ(3686)$ decay to $Λ\barΛ$ and $Σ^0\barΣ^0$ final states

Using $1310.6\times10^6$ $J/ψ$ and $447.9\times10^6$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII $e^{+}e^{-}$ collider, the branching fractions and the angular distributions of $J/ψ$ and $ψ(3686)$ decays to $Λ\barΛ$ and $Σ^0\barΣ^0$ final states are measured. The branching fractions are in agreement with, and much more precise than, the averages of previously published results. The polar angular distributions of $ψ(3686)$ decays are measured for the first time, while those of $J/ψ$ decays are measured with much improved precision. In addition, the ratios of branching fractions $\frac{\mathcal{B}(ψ(3686)\toΛ\barΛ)}{\mathcal{B}(J/ψ\toΛ\barΛ)}$ and $\frac{\mathcal{B}(ψ(3686)\toΣ^0\barΣ^0)}{\mathcal{B}(J/ψ\toΣ^0\barΣ^0)}$ are determined to test the "12\% rule".

hep-ex↗

arXiv2017

Analysis of $D^+\to\bar K^0e^+ν_e$ and $D^+\toπ^0e^+ν_e$ Semileptonic Decays

Using 2.93~fb$^{-1}$ of data taken at 3.773 GeV with the BESIII detector operated at the BEPCII collider, we study the semileptonic decays $D^+ \to \bar K^0e^+ν_e$ and $D^+ \to π^0 e^+ν_e$. We measure the absolute decay branching fractions $\mathcal B(D^+ \to \bar K^0e^+ν_e)=(8.60\pm0.06\pm 0.15)\times10^{-2}$ and $\mathcal B(D^+ \to π^0e^+ν_e)=(3.63\pm0.08\pm0.05)\times10^{-3}$, where the first uncertainties are statistical and the second systematic. We also measure the differential decay rates and study the form factors of these two decays. With the values of $|V_{cs}|$ and $|V_{cd}|$ from Particle Data Group fits assuming CKM unitarity, we obtain the values of the form factors at $q^2=0$, $f^K_+(0) = 0.725\pm0.004\pm 0.012$ and $f^π_+(0) = 0.622\pm0.012\pm 0.003$. Taking input from recent lattice QCD calculations of these form factors, we determine values of the CKM matrix elements $|V_{cs}|=0.944 \pm 0.005 \pm 0.015 \pm 0.024$ and $|V_{cd}|=0.210 \pm 0.004 \pm 0.001 \pm 0.009$, where the third uncertainties are theoretical.

hep-ex↗

arXiv2017

The GTC exoplanet transit spectroscopy survey. VII. Detection of sodium in WASP-52b's cloudy atmosphere

We report the first detection of sodium absorption in the atmosphere of the hot Jupiter WASP-52b. We observed one transit of WASP-52b with the low-resolution Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at the 10.4 m Gran Telescopio Canarias (GTC). The resulting transmission spectrum, covering the wavelength range from 522 nm to 903 nm, is flat and featureless, except for the significant narrow absorption signature at the sodium doublet, which can be explained by an atmosphere in solar composition with clouds at 1 mbar. A cloud-free atmosphere is stringently ruled out. By assessing the absorption depths of sodium in various bin widths, we find that temperature increases towards lower atmospheric pressure levels, with a positive temperature gradient of 0.88 +/- 0.65 K/km, possibly indicative of upper atmospheric heating and a temperature inversion.

astro-ph.EP↗

arXiv2017

Observation of $Λ^+_{c}\to nK^0_Sπ^+$

We report the first direct measurement of decays of the $Λ^+_c$ baryon involving the neutron. The analysis is performed using 567 pb$^{-1}$ of $e^+e^-$ collision data collected at $\sqrt{s}=4.599$ GeV with the BESIII detector at the BEPCII collider. We observe the decay $Λ^+_{c}\rightarrow n K^0_Sπ^+$ and measure the absolute branching fraction to be $\mathcal{B}({Λ^+_{c}\rightarrow n K^0_Sπ^+})=(1.82\pm0.23({\rm stat})\pm0.11({\rm syst}))\%$. A comparison to $\mathcal{B}({Λ^+_{c}\rightarrow p(\bar{K}π)^0})$ provides an important test of isospin symmetry and final state interactions.

hep-ex↗

arXiv2017

The GTC exoplanet transit spectroscopy survey. VI. A spectrally-resolved Rayleigh scattering slope in GJ 3470b

Aims. As a sub-Uranus-mass low-density planet, GJ 3470b has been found to show a flat featureless transmission spectrum in the infrared and a tentative Rayleigh scattering slope in the optical. We conducted an optical transmission spectroscopy project to assess the impacts of stellar activity and to determine whether or not GJ 3470b hosts a hydrogen-rich gas envelop. Methods. We observed three transits with the low-resolution OSIRIS spectrograph at the 10.4 m Gran Telescopio Canarias, and one transit with the high-resolution UVES spectrograph at the 8.2 m Very Large Telescope. Results. From the high-resolution data, we find that the difference of the Ca II H+K lines in- and out-of-transit is only 0.67 +/- 0.22%, and determine a magnetic filling factor of about 10-15%. From the low-resolution data, we present the first optical transmission spectrum in the 435-755 nm band, which shows a slope consistent with Rayleigh scattering. Conclusions. After exploring the potential impacts of stellar activity in our observations, we confirm that Rayleigh scattering in an extended hydrogen/helium atmosphere is currently the best explanation. Further high-precision observations that simultaneously cover optical and infrared bands are required to answer whether or not clouds and hazes exist at high-altitude.

astro-ph.EP↗

arXiv2017

Evidence of Two Resonant Structures in $e^+ e^- \to π^+ π^- h_c$

The cross sections of $e^{+}e^{-}\toπ^{+}π^{-}h_c$ at center-of-mass energies from 3.896 to 4.600 GeV are measured using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The cross sections are found to be of the same order of magnitude as those of $e^{+}e^{-}\toπ^{+}π^{-}J/ψ$ and $e^{+}e^{-}\toπ^{+}π^{-}ψ(2S)$, but the line shape is inconsistent with the $Y$ states observed in the latter two modes. Two structures are observed in the $e^{+}e^{-}\toπ^{+}π^{-}h_c$ cross sections around 4.22 and 4.39 GeV/$c^{2}$, which we call $Y(4220)$ and $Y(4390)$, respectively. A fit with a coherent sum of two Breit-Wigner functions results in a mass of $(4218.4^{+5.5}_{-4.5}\pm0.9)$ MeV/$c^{2}$ and a width of $(66.0^{+12.3}_{-8.3}\pm0.4)$ MeV for the $Y(4220)$, and a mass of $(4391.6^{+6.3}_{-6.8}\pm1.0)$ MeV/$c^{2}$ and a width of $(139.5^{+16.2}_{-20.6}\pm0.6)$ MeV for the $Y(4390)$, where the first uncertainties are statistical and the second ones systematic. The statistical significance of $Y(4220)$ and $Y(4390)$ is 10$σ$ over one structure assumption.

hep-ex↗

arXiv2017

Search for the Radiative Leptonic Decay $D^{+}\to γe^{+} ν_{e}$

Using an electron-positron collision data sample of 2.93 fb$^{-1}$ collected at a center-of-mass energy of $\sqrt{s}=3.773$ GeV with the BESIII detector, we present the first search for the radiative leptonic decay $D^{+} \rightarrow γe^{+}ν_{e}$. The analysis is performed with a double tag method. We do not observe a significant $D^{+} \rightarrow γe^{+}ν_{e}$ signal, and obtain an upper limit on the branching fraction of $D^{+} \rightarrow γe^{+}ν_{e}$ decay with the energy of radiative photon larger than 10 MeV of $3.0\times10^{-5}$ at the 90% confidence level.

hep-ex↗

arXiv2017

Amplitude analysis of the $χ_{c1} \to ηπ^+π^-$ decays

Using $448.0 \times 10^6$~$ψ(3686)$ events collected with the BESIII detector, an amplitude analysis is performed for $ψ(3686)\toγχ_{c1}$, $χ_{c1}\toηπ^+π^-$ decays. The most dominant two-body structure observed is $a_0(980)^{\pm}π^{\mp}$; $a_0(980)^{\pm}\toηπ^{\pm}$. The $a_0(980)$ line shape is modeled using a dispersion relation, and a significant non-zero $a_0(980)$ coupling to the $η^{\prime}π$ channel is measured. We observe $χ_{c1}\to a_2(1700)π$ production for the first time, with a significance larger than 17$σ$. The production of mesons with exotic quantum numbers, $J^{PC}=1^{-+}$, is investigated, and upper limits for the branching fractions $χ_{c1}\to π_1(1400)^{\pm}π^{\mp}$, $χ_{c1}\to π_1(1600)^{\pm}π^{\mp}$, and $χ_{c1}\toπ_1(2015)^{\pm}π^{\mp}$, with subsequent $π_1(X)^{\pm} \to ηπ^{\pm}$ decay, are determined.

hep-ex↗

arXiv2017

Luminosity measurements for the R scan experiment at BESIII

By analyzing the large-angle Bhabha scattering events $e^{+}e^{-}$ $\to$ ($γ$)$e^{+}e^{-}$ and diphoton events $e^{+}e^{-}$ $\to$ $γγ$ for the data sets collected at center-of-mass (c.m.) energies between 2.2324 and 4.5900 GeV (131 energy points in total) with the upgraded Beijing Spectrometer (BESIII) at the Beijing Electron-Positron Collider (BEPCII), the integrated luminosities have been measured at the different c.m. energies, individually. The results are the important inputs for R value and $J/ψ$ resonance parameter measurements.

hep-ex↗

arXiv2017

Precise measurement of the $e^+e^-\to π^+π^-J/ψ$ cross section at center-of-mass energies from 3.77 to 4.60 GeV

The cross section for the process $e^+e^-\to π^+π^-J/ψ$ is measured precisely at center-of-mass energies from 3.77 to 4.60~GeV using 9~fb$^{-1}$ of data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in a fit to the cross section. The first resonance has a mass of $(4222.0\pm 3.1\pm 1.4)$~MeV/$c^2$ and a width of $(44.1\pm 4.3\pm 2.0)$~MeV, while the second one has a mass of $(4320.0\pm 10.4 \pm 7.0)$~MeV/$c^2$ and a width of $(101.4^{+25.3}_{-19.7}\pm 10.2)$~MeV, where the first errors are statistical and second ones are systematic. The first resonance agrees with the $Y(4260)$ resonance reported by previous experiments. The precision of its resonant parameters is improved significantly. The second resonance is observed in $e^+e^-\to π^+π^-J/ψ$ for the first time. The statistical significance of this resonance is estimated to be larger than $7.6σ$. The mass and width of the second resonance agree with the $Y(4360)$ resonance reported by the $BABAR$ and Belle experiments within errors. Finally, the $Y(4008)$ resonance previously observed by the Belle experiment is not confirmed in the description of the BESIII data.

hep-ex↗

arXiv2017

Cross section measurements of $e^{+}e^{-}\rightarrow p \bar{p} π^{0}$ at center-of-mass energies between 4.008 and 4.600 GeV

Based on $e^+e^-$ annihilation data samples collected with the BESIII detector at the BEPCII collider at 13 center of mass energies from 4.008 to 4.600 GeV, measurements of the Born cross section of $e^{+}e^{-}\rightarrow p \bar{p} π^{0}$ are performed. No significant resonant structure is observed in the measured energy-dependent cross section. The upper limit on the Born cross section of $e^{+}e^{-}\rightarrow Y(4260) \rightarrow p \bar{p} π^{0}$ at the 90\% C.L. is determined to be 0.01 pb.

hep-ex↗

arXiv2017

Amplitude Analysis of the Decays $η^\prime \rightarrow π^+π^-π^0$ and $η^\prime \rightarrow π^0π^0π^0$

Based on a sample of $1.31 \times 10^9$ $J/ψ$ events collected with the BESIII detector, an amplitude analysis of the isospin-violating decays $η^\prime \rightarrow π^+π^-π^0$ and $η^\prime \rightarrow π^0π^0π^0$ is performed. A significant $P$-wave contribution from $η^\prime \rightarrow ρ^{\pm} π^{\mp}$ is observed for the first time in $η^\prime \rightarrow π^+π^-π^0$. The branching fraction is determined to be ${\mathcal B}(η^\prime \rightarrow ρ^{\pm}π^{\mp})=(7.44\pm0.60\pm1.26\pm1.84)\times 10^{-4}$, where the first uncertainty is statistical, the second systematic, and the third model dependent. In addition to the nonresonant $S$-wave component, there is a significant $σ$ meson component. The branching fractions of the combined $S$-wave components are determined to be ${\mathcal B}(η^\prime \rightarrow π^+π^-π^0)_S=(37.63\pm0.77\pm2.22\pm4.48)\times 10^{-4}$ and ${\mathcal B}(η^\prime \rightarrow π^0π^0π^0)=(35.22\pm0.82\pm2.54)\times 10^{-4}$, respectively. The latter one is consistent with previous BESIII measurements.

hep-ex↗

arXiv2016

Measurements of the absolute branching fractions for $D_{s}^{+}\rightarrowηe^{+}ν_{e}$ and $D_{s}^{+}\rightarrowη^{\prime} e^{+}ν_{e}$

By analyzing 482 pb$^{-1}$ of $e^+e^-$ collision data collected at $\sqrt s=4.009$ GeV with the BESIII detector at the BEPCII collider, we measure the absolute branching fractions for the semileptonic decays $D_{s}^{+}\toηe^{+}ν_{e}$ and $D_{s}^{+}\to η'e^{+}ν_{e}$ to be ${B}(D_{s}^{+}\rightarrowηe^{+}ν_{e})=(2.30\pm0.31\pm0.08)$\% and ${B}(D_{s}^{+}\rightarrowη'e^{+} ν_{e}) = (0.93\pm0.30\pm0.05)$\%, respectively, and their ratio $\frac{{B}(D_{s}^{+}\rightarrowη'e^{+}ν_{e})} {{B}(D_{s}^{+}\rightarrowηe^{+}ν_{e})}=0.40\pm0.14\pm0.02$, where the first uncertainties are statistical and the second ones are systematic. The results are in good agreement with previous measurements within uncertainties; they can be used to determine the $η-η'$ mixing angle and improve upon the $D_s^+$ semileptonic branching ratio precision.

hep-ex↗

arXiv2016

Measurements of the branching fractions for $D^+\to K^0_SK^0_SK^+$, $K^0_SK^0_Sπ^+$ and $D^0\to K^0_SK^0_S$, $K^0_SK^0_SK^0_S$

By analyzing $2.93\ \rm fb^{-1}$ of data taken at the $ψ(3770)$ resonance peak with the BESIII detector, we measure the branching fractions for the hadronic decays $D^+\to K^0_SK^0_S K^+$, $D^+\to K^0_SK^0_S π^+$, $D^0\to K^0_S K^0_S$ and $D^0\to K^0_SK^0_SK^0_S$. They are determined to be ${\mathcal B}(D^+\to K^0_SK^0_SK^+)=(2.54 \pm 0.05_{\rm stat.} \pm 0.12_{\rm sys.})\times 10^{-3}$, ${\mathcal B}(D^+\to K^0_SK^0_Sπ^+)=(2.70 \pm 0.05_{\rm stat.} \pm 0.12_{\rm sys.})\times 10^{-3}$, ${\mathcal B}(D^0\to K^0_SK^0_S)=(1.67 \pm 0.11_{\rm stat.} \pm 0.11_{\rm sys.})\times 10^{-4}$ and ${\mathcal B}(D^0\to K^0_SK^0_SK^0_S)=(7.21 \pm 0.33_{\rm stat.} \pm 0.44_{\rm sys.})\times 10^{-4}$, where the second one is measured for the first time and the others are measured with significantly improved precision over the previous measurements.

hep-ex↗