arXiv subjects

C. Geng

Publications and source records attributed to C. Geng.

At least 199 records · Page 11Linked to original sources

arXiv2015

Observation of the electromagnetic doubly OZI-suppressed decay $J/ψ\rightarrow ϕπ^{0}$

Using a sample of $1.31$ billion $J/ψ$ events accumulated with the BESIII detector at the BEPCII collider, we report the observation of the decay $J/ψ\rightarrow ϕπ^{0}$, which is the first evidence for a doubly Okubo-Zweig-Iizuka suppressed electromagnetic $J/ψ$ 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 $J/ψ\rightarrow ϕπ^{0}$ and $J/ψ\rightarrow K^{+}K^{-}π^{0}$ decays. Due to this interference, two possible solutions are found. The corresponding measured values of the branching fraction of $J/ψ\to ϕπ^{0}$ are $[2.94 \pm 0.16\text{(stat.)} \pm 0.16\text{(syst.)}] \times 10^{-6}$ and $[1.24 \pm 0.33\text{(stat.)} \pm 0.30\text{(syst.)}] \times 10^{-7}$.

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arXiv2015

Measurement of the proton form factor by studying $e^{+} e^{-}\rightarrow p\bar{p}$

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 center-of-mass 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.

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arXiv2015

Measurement of $\mathcal B(ψ(3770)\toγχ_{c1})$ and search for $ψ(3770)\toγχ_{c2}$

We report a measurement of the branching fraction of $ψ(3770)\toγχ_{c1}$ and search for the transition $ψ(3770)\rightarrow γχ_{c2}$ 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 $ψ(3770) \rightarrow γχ_{c1}$ is $\mathcal B(ψ(3770) \rightarrow γχ_{c1})=(2.48 \pm 0.15 \pm 0.23) \times 10^{-3}$, which is the most precise measurement to date. The upper limit on the branching fraction of $ψ(3770)\rightarrow γχ_{c2}$ at a $90\%$ confidence level is $\mathcal B(ψ(3770) \rightarrow γχ_{c2})<0.64 \times 10^{-3}$. The corresponding partial widths are $Γ(ψ(3770) \to γχ_{c1}) =(67.5\pm 4.1\pm 6.7)$~keV and $Γ(ψ(3770) \to γχ_{c2}) < 17.4$~keV.

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arXiv2015

Observation of the $ψ(1^3D_2)$ state in $e^+e^-\toπ^+π^-γχ_{c1}$ at BESIII

We report the observation of the $X(3823)$ in the process $e^+e^-\to π^+π^-X(3823) \to π^+π^-γχ_{c1}$ with a statistical significance of $6.2σ$, in data samples at center-of-mass 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 $e^+e^-\to π^+π^-X(3823)$ and the branching ratio $\mathcal{B}[X(3823)\to γχ_{c1,c2}]$ are also measured. These measurements are in good agreement with the assignment of the $X(3823)$ as the $ψ(1^3D_2)$ charmonium state.

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arXiv2015

An Improved Limit for Gamma_ee of X(3872) and Gamma_ee Measurement of psi(3686)

Using the data sets taken at center-of-mass 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+pi-J/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 next-to-leading 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+pi-Jψ) < 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.

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arXiv2015

Observation of the Dalitz Decay $η' \to γe^+e^-$

We report the first observation of the Dalitz decay $η' \to γe^+e^-$, based on a data sample of 1.31 billion $J/ψ$ events collected with the BESIII detector. The $η'$ mesons are produced via the $J/ψ\to γη'$ decay process. The ratio $Γ(η' \to γe^+ e^-)/Γ(η'\toγγ)$ is measured to be $(2.13\pm0.09(\text{stat.})\pm0.07(\text{sys.}))\times10^{-2}$. This corresponds to a branching fraction ${\cal B}(η' \to γe^+e^-)= (4.69 \pm0.20(\text{stat.})\pm0.23(\text{sys.}))\times10^{-4}$. 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.

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arXiv2015

Measurements of $ψ(3686) \to K^{-} Λ\barΞ^{+} +c.c.$ and $ψ(3686) \to γK^{-} Λ\barΞ^{+} +c.c$

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, $Ξ(1690)^-$ and $Ξ(1820)^-$, in the $K^-Λ$ invariant mass distribution in the decay $\klx+c.c.$ with significances of $4.9 σ$ and $6.2 σ$, respectively. The branching fractions of $\klx+c.c.$, $\ksx+c.c.$, $\psip\toγχ_{cJ}\to γK^- Λ\barΞ^+ +c.c.$ $(J=0,\ 1,\ 2)$, and $\psip\to Ξ(1690/1820)^{-} \barΞ^++c.c$ with subsequent decay $Ξ(1690/1820)^-\to K^-Λ$ are measured for the first time.

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arXiv2015

Measurement of the $e^{+}e^{-} \to ηJ/ψ$ cross section and search for $e^{+}e^{-} \to π^{0} J/ψ$ at center-of-mass energies between 3.810 and 4.600~GeV

Using data samples collected with the BESIII detector operating at the BEPCII collider at center-of-mass energies from 3.810 to 4.600 GeV, we perform a study of $e^{+}e^{-} \to ηJ/ψ$ and $π^0 J/ψ$. Statistically significant signals of $e^{+}e^{-} \to ηJ/ψ$ 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 $e^{+}e^{-} \to π^{0} J/ψ$ are observed. The measured energy-dependent Born cross section for $e^{+}e^{-} \to ηJ/ψ$ shows an enhancement around 4.2~GeV. The measurement is compatible with an earlier measurement by Belle, but with a significantly improved precision.

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arXiv2015

Precision measurement of the integrated luminosity of the data taken by BESIII at center of mass energies between 3.810 GeV and 4.600 GeV

From December 2011 to May 2014, about 5 $\rm fb^{-1}$ of data were taken with the BESIII detector at center-of-mass 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 large-angle Bhabha scattering process.

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arXiv2015

Study of $ψ(3686)\toπ^0 h_c, h_c\toγη_c$ via $η_c$ exclusive decays

The process $ψ(3686) \to π^0 h_c, h_c \to γη_c$ has been studied with a data sample of $106 \pm 4$ million $ψ(3686)$ events collected with the BESIII detector at the BEPCII storage ring. The mass and width of the $P$-wave charmonium spin-singlet state $h_c(^1P_1)$ are determined by simultaneously fitting distributions of the $π^0$ recoil mass for 16 exclusive $η_c$ decay modes. The results, $M(\hc) = 3525.31 \pm 0.11 {\rm (stat.)} \pm 0.14 {\rm (syst.)}$\,MeV/$c^2$ and $Γ(\hc) = 0.70 \pm 0.28 \pm 0.22$\,MeV, are consistent with and more precise than previous measurements. We also determine the branching ratios for the 16 exclusive $η_c$ decay modes, five of which have not been measured previously. New measurements of the $η_c$ line-shape parameters in the $E1$ transition $h_c\toγη_c$ are made by selecting candidates in the $h_c$ signal sample and simultaneously fitting the hadronic mass spectra for the 16 $η_c$ decay channels. The resulting $η_c$ mass and width values are $M(η_c) = 2984.49 \pm 1.16 \pm 0.52$\,MeV/$c^2$ and $Γ(η_c) = 36.4 \pm 3.2 \pm 1.7$\,MeV.

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arXiv2015

Search for the $η_c(2S)/h_c\to p\bar{p}$ decays and measurements of the $χ_{cJ}\to p\bar{p}$ branching fractions

Using a sample of $1.06\times10^{8}~ψ(3686)$ events collected with the BESIII detector at BEPCII, the decays $η_{c}(2S)\to p\bar{p}$ and $h_{c}\to p\bar{p}$ are searched for, where $η_c(2S)$ and $h_c$ are reconstructed in the decay chains $ψ(3686)\toγη_{c}(2S)$, $η_{c}(2S)\to p\bar{p}$ and $ψ(3686)\toπ^{0}h_{c}$, $h_{c}\to p\bar{p}$, respectively. No significant signals are observed. The upper limits of the product branching fractions are determined to be $\mathcal{B}(ψ(3686)\toγη_c(2S))\times\mathcal{B}(η_{c}(2S)\to p\bar{p})<1.4\times10^{-6}$ and $\mathcal{B}(ψ(3686)\toπ^0h_c)\times\mathcal{B}(h_{c}\to p\bar{p})<1.3\times10^{-7}$ at the 90% C.L.. The branching fractions for $χ_{cJ}\to p\bar{p}$ $(J=0,~1,~2)$ are also measured to be $(24.5\pm0.8\pm1.3,~8.6\pm0.5\pm0.5,~8.4\pm0.5\pm0.5)\times10^{-5}$, which are the world's most precise measurements.

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arXiv2014

Search for C-parity violation in $J/ ψ\to γγ$ and $ γϕ$

Using $1.06\times10^8$ $ψ(3686)$ events recorded in $e^{+}e^{-}$ collisions at $\sqrt{s}=$ 3.686 GeV with the BESIII at the BEPCII collider, we present searches for C-parity violation in $J/ψ\to γγ$ and $ γϕ$ decays via $ψ(3686) \to J/ψπ^+π^-$. No significant signals are observed in either channel. Upper limits on the branching fractions are set to be $\mathcal{B}(J/ψ\to γγ) < 2.7 \times 10^{-7}$ and $\mathcal{B}(J/ψ\to γϕ) < 1.4 \times 10^{-6}$ at the 90\% confidence level. The former is one order of magnitude more stringent than the previous upper limit, and the latter represents the first limit on this decay channel.

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arXiv2014

Observation of $J/ψ\rightarrow p\bar{p}a_{0}(980)$ at BESIII

Using $2.25\times10^{8}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage rings, we observe for the first time the process $J/ψ\rightarrow p\bar{p}a_{0}(980)$, $a_{0}(980)\rightarrow π^{0}η$ with a significance of $6.5σ$ ($3.2σ$ including systematic uncertainties). The product branching fraction of $J/ψ\rightarrow p\bar{p}a_{0}(980)\rightarrow p\bar{p}π^{0}η$ is measured to be $(6.8\pm1.2\pm1.3)\times 10^{-5}$, where the first error is statistical and the second is systematic. This measurement provides information on the $a_{0}$ production near threshold coupling to $p\bar{p}$ and improves the understanding of the dynamics of $J/ψ$ decays to four body processes.

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arXiv2014

Study of e$^+$e$^-$ $\rightarrow \text{p} \overline{\text{p}}π^0$ in the Vicinity of the $ψ\text{(3770)}$

The process $e^+e^-\rightarrow p\overline{p}π^0$ has been studied by analyzing data collected at $\sqrt{s}=3.773$ GeV, at $\sqrt{s}=3.650$ GeV, and during a $ψ(3770)$ line shape scan with the BESIII detector at the BEPCII collider. The Born cross section of $p \overline{p} π^0$ in the vicinity of the $ψ(3770)$ is measured and the Born cross section of $ψ(3770)\rightarrow p \overline{p} π^0$ is extracted considering interference between resonant and continuum production amplitudes. Two solutions with the same probability and a significance of 1.5$σ$ are found, and the Born cross section of $ψ(3770)\rightarrow p \overline{p} π^0$ is determined to be less than 0.22 pb at 90% confidence level and $33.8\pm1.8\pm2.1$ pb, respectively. Using the estimated cross section and a constant decay amplitude approximation, the cross section $σ(p\overline{p} \rightarrow ψ(3770) π^0)$ is calculated for the kinematic situation of the planned $\overline{\text{P}}\text{ANDA}$ experiment. The maximum cross section corresponding to the two solutions is expected to be less than $0.79$ nb at 90% confidence level and $122\pm10$ nb at a center of mass energy of 5.26 GeV.

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arXiv2014

Study of $e^+e^- \rightarrow p\bar{p}$ in the vicinity of $ψ(3770)$

Using 2917 $\rm{pb}^{-1}$ of data accumulated at 3.773~$\rm{GeV}$, 44.5~$\rm{pb}^{-1}$ of data accumulated at 3.65~$\rm{GeV}$ and data accumulated during a $ψ(3770)$ line-shape scan with the BESIII detector, the reaction $e^+e^-\rightarrow p\bar{p}$ is studied considering a possible interference between resonant and continuum amplitudes. The cross section of $e^+e^-\rightarrowψ(3770)\rightarrow p\bar{p}$, $σ(e^+e^-\rightarrowψ(3770)\rightarrow p\bar{p})$, is found to have two solutions, determined to be ($0.059\pm0.032\pm0.012$) pb with the phase angle $ϕ= (255.8\pm37.9\pm4.8)^\circ$ ($<$0.11 pb at the 90% confidence level), or $σ(e^+e^-\rightarrowψ(3770)\rightarrow p\bar{p}) = (2.57\pm0.12\pm0.12$) pb with $ϕ= (266.9\pm6.1\pm0.9)^\circ$ both of which agree with a destructive interference. Using the obtained cross section of $ψ(3770)\rightarrow p\bar{p}$, the cross section of $p\bar{p}\rightarrow ψ(3770)$, which is useful information for the future PANDA experiment, is estimated to be either ($9.8\pm5.7$) nb ($<17.2$ nb at 90% C.L.) or $(425.6\pm42.9)$ nb.

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arXiv2014

Observation of $χ_{c1}$ decays into vector meson pairs $ϕϕ$, $ωω$, and $ωϕ$

Decays of $χ_{c1}$ to vector meson pairs $ϕϕ$, $ωω$ and $ωϕ$ are observed for the first time using $(106\pm4)\times 10^6$ $\psip$ events accumulated at the BESIII detector at the BEPCII $e^+e^-$ collider. The branching fractions are measured to be $(4.4\pm 0.3\pm 0.5)\times 10^{-4}$, $(6.0\pm 0.3\pm 0.7)\times 10^{-4}$, and $(2.2\pm 0.6\pm 0.2)\times 10^{-5}$, for $χ_{c1}\to ϕϕ$, $ωω$, and $ωϕ$, respectively. The observation of $χ_{c1}$ decays into a pair of vector mesons $ϕϕ$, $ωω$ and $ωϕ$ indicates that the hadron helicity selection rule is significantly violated in $χ_{cJ}$ decays. In addition, the measurement of $χ_{cJ}\to ωϕ$ gives the rate of doubly OZI-suppressed decay. Branching fractions for $χ_{c0}$ and $χ_{c2}$ decays into other vector meson pairs are also measured with improved precision.

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arXiv2014

Measurement of $χ_{cJ}$ decaying into $η^{\prime}K^+K^-$

Using $(106.41\pm 0.86) \times 10^{6}$ $ψ(3686)$ events collected with the BESIII detector at BEPCII, we study for the first time the decay $χ_{cJ}\toη'K^+K^-$, where $η'\toγρ^{0}$ and $η'\toηπ^+π^-$. A partial wave analysis in the covariant tensor amplitude formalism is performed for the decay $χ_{c1}\toη'K^+K^-$. Intermediate processes $χ_{c1}\toη' f_0(980)$, $χ_{c1}\toη' f_0(1710)$, $χ_{c1}\toη' f_2'(1525)$ and $χ_{c1}\to K^*_0(1430)^{\pm}K^{\mp}$ ($K^*_0(1430)^{\pm}\toη' K^{\pm}$) are observed with statistical significances larger than 5$σ$, and their branching fractions are measured.

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arXiv2014

Precision Measurement of the Mass of the $τ$ Lepton

An energy scan near the $τ$ pair production threshold has been performed using the BESIII detector. About $24$ pb$^{-1}$ of data, distributed over four scan points, was collected. This analysis is based on $τ$ pair decays to $ee$, $eμ$, $eh$, $μμ$, $μh$, $hh$, $eρ$, $μρ$ and $πρ$ final states, where $h$ denotes a charged $π$ or $K$. The mass of the $τ$ lepton is measured from a maximum likelihood fit to the $τ$ pair production cross section data to be $m_τ = (1776.91\pm0.12 ^{+0.10}_{-0.13}$) MeV/$c^2$, which is currently the most precise value in a single measurement.

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