arXiv subjects

J. Chai

Publications and source records attributed to J. Chai.

At least 37 records · Page 2Linked to original sources

arXiv2019

Observation of the Semileptonic $D^+$ Transition into an Axial-Vector Meson $\bar K_1(1270)^0$

By analyzing a 2.93~$\rm fb^{-1}$ data sample of $e^+e^-$ collisions, recorded at a center-of-mass energy of 3.773 $\rm \,GeV$ with the BESIII detector operated at the BEPCII collider, we have searched for the semileptonic $D^+$ transition into the axial-vector meson ${\bar{K}}_{1}(1270)^{0}$. The $D^{+} \rightarrow {\bar{K}}_{1}(1270)^{0}e^{+}ν_{e}$ decay is observed for the first time with a statistical significance greater than $10σ$. Its decay branching fraction is determined to be ${\mathcal B}[D^+\to \bar K_1(1270)^0 e^+ν_e]=(2.30\pm0.26\pm 0.18 \pm 0.25)\times10^{-3}$, where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of ${\bar{K}}_{1}(1270)^{0} \rightarrow K^{-} π^{+} π^{0}$.

hep-ex↗

arXiv2019

Measurement of Branching Fractions of $ψ(3686)\rightarrowϕη^\prime, ϕf_1(1285)$ and $ϕη(1405)$

Using a sample of $448.1\times10^6$ $ψ(3686)$ events collected with the BESIII detector, we perform a study of the decay $ψ(3686) \rightarrow ϕπ^{+}π^{-}η$. The branching fraction of $ψ(3686)\rightarrowϕη^\prime$ is determined to be $(1.51\pm0.16\pm0.12)\times 10^{-5}$, which is consistent with the previous measurement but with significantly improved precision. The resonances $f_{1}(1285)$ and $η(1405)$ are clearly observed in the $π^{+}π^{-}η$ mass spectrum with statistical significances of $18σ$ and $9.7σ$, respectively. The corresponding product branching fractions are measured to be $\mathcal{B}(ψ(3686)\rightarrowϕf_{1}(1285),f_{1}(1285)\rightarrowπ^{+}π^{-}η) =(1.03\pm0.10\pm0.09)\times 10^{-5}$ and $\mathcal{B}(ψ(3686)\rightarrowϕη(1405),η(1405)\rightarrowπ^{+}π^{-}η) =(8.46\pm1.37\pm0.92)\times 10^{-6}$.

hep-ex↗

arXiv2019

Observation of the leptonic decay $D^+ \to τ^+ ν_τ$

We report the first observation of $D^+\toτ^+ν_τ$ with a significance of $5.1σ$. We measure ${\cal B}(D^+\toτ^+ν_τ) = (1.20\pm0.24_{\text{stat.}}\pm0.12_{\text{syst.}})\times10^{-3}$. Taking the world average ${\cal B}(D^+\toμ^+ν_μ) = (3.74\pm0.17)\times10^{-4}$, we obtain $R_{τ/μ} =Γ(D^+\toτ^+ν_τ)/Γ(D^+\toμ^+ν_μ) = 3.21\pm0.64_{\text{stat.}}\pm0.43_{\text{syst.}}$, which is consistent with the Standard Model expectation of lepton flavor universality. Using external inputs, our results give values for the $D^+$ decay constant $f_{D^+}$ and the CKM matrix element $|V_{cd}|$ that are consistent with, but less precise than, other determinations.

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arXiv2019

Partial-wave analysis of $J/ψ\to K^+K^-π^0$

A partial-wave analysis of the decay $J/ψ\to K^+K^-π^0$ has been made using $(223.7\pm1.4)\times 10^{6}$ $J/ψ$ events collected with the BESIII detector in 2009. The analysis, which is performed within the isobar-model approach, reveals contributions from $K^*_2(1430)^\pm$, $K^*_2(1980)^\pm$ and $K^*_4(2045)^\pm$ decaying to $K^\pmπ^0$. The two latter states are observed in $J/ψ$ decays for the first time. Two resonance signals decaying to $K^+K^-$ are also observed. These contributions can not be reliably identified and their possible interpretations are discussed. The measured branching fraction $B(J/ψ\to K^+K^-π^0)$ of $(2.88\pm0.01\pm0.12)\times10^{-3}$ is more precise than previous results. Branching fractions for the reported contributions are presented as well. The results of the partial-wave analysis differ significantly from those previously obtained by BESII and BABAR.

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arXiv2019

Observation of the decays $χ_{cJ} \to ϕϕη$

Using a data sample of $(448.1\pm2.9)\times10^{6}$ $ψ(3686)$ decays collected by the BESIII detector at the Beijing Electron Positron Collider (BEPCII), we observe the decays $χ_{cJ}\to ϕϕη~(J=0,~1,~2)$, where the $χ_{cJ}$ are produced via the radiative processes $ψ(3686)\toγχ_{cJ}$. The branching fractions are measured to be $\mathcal B(χ_{c0}\toϕϕη)=(8.41\pm0.74\pm0.62)\times10^{-4}$, $\mathcal B(χ_{c1}\toϕϕη)=(2.96\pm0.43\pm0.22)\times 10^{-4}$, and $\mathcal B(χ_{c2} \to ϕϕη)=(5.33\pm0.52\pm0.39) \times 10^{-4}$, where the first uncertainties are statistical and the second are systematic. We also search for intermediate states in the $ϕϕ$ or $ηϕ$ combinations, but no significant structure is seen due to the limited statistics.

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arXiv2019

Measurement of branching fractions for $D$ meson decaying into $ϕ$ meson and a pseudoscalar meson

The four decay modes $D^{0}\toϕπ^{0}$, $D^{0}\toϕη$, $D^{+}\toϕπ^{+}$, and $D^{+}\toϕK^{+}$ are studied by using a data sample taken at the centre-of-mass energy $\sqrt{s} = 3.773$~GeV~with the BESIII detector, corresponding to an integrated luminosity of 2.93 fb$^{-1}$. The branching fractions of the first three decay modes are measured to be ${\cal B}(D^{0}\toϕπ^{0})=(1.168\pm0.028\pm0.028)\times10^{-3}$, ${\cal B}(D^{0}\toϕη)=(1.81\pm0.46\pm0.06)\times10^{-4}$, and ${\cal B}(D^{+}\toϕπ^{+})=(5.70\pm0.05\pm0.13)\times10^{-3}$, respectively, where the first uncertainties are statistical and the second are systematic. No significant signal is observed of the decay $D^+\toϕ{K^+}$ and the upper limit of its branching fraction is set for the first time, to be $2.1\times10^{-5}$ at the $90\%$ confidence level. The ratio of ${\cal B}(D^0\toϕπ^0)$ to $\cal B(D^+\toϕπ^+)$ is calculated to be $(20.49\pm0.50\pm0.45)\%$, which is consistent with the theoretical prediction based on isospin symmetry between these two decay modes.

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arXiv2019

Study of the decays $ψ(3686)\rightarrowγχ_{cJ}\rightarrowγ\bar{p}K^{+}Λ+c.c.$ and $ψ(3686)\rightarrow\bar{p}K^{+}Λ+c.c.$

Based on the data sample of $448.1\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector at BEPCII, we present a study of the decays $ψ(3686)\rightarrowγχ_{cJ}\rightarrowγ\bar{p}K^{*+}Λ+c.c.$ and $ψ(3686)\rightarrow\bar{p}K^{*+}Λ+c.c.$. The branching fractions of $χ_{cJ}\rightarrow\bar{p}K^{*+}Λ+c.c.$ ($J$=0, 1, 2) are measured to be $(4.8\pm0.7\pm0.5)\times10^{-4}$, $(5.0\pm0.5\pm0.4)\times10^{-4}$, and $(8.2\pm0.9\pm0.7)\times10^{-4}$, respectively, where the first uncertainties are statistical and the second systematic. The branching fraction of $ψ(3686)\rightarrow\bar{p}K^{*+}Λ+c.c.$ is measured to be $(6.3\pm0.5\pm0.5)\times10^{-5}$. All these decay modes are observed for the first time.

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arXiv2019

Observation of $ψ(3686)\rightarrowΞ(1530)^{-}\barΞ(1530)^{+}$ and $Ξ(1530)^{-}\barΞ^{+}$

Using 448.1 $\times$ $10^{6}$ $ψ(3686)$ events collected with the BESIII detector at BEPCII, we employ a single-baryon tagging technique to make the first observation of $ψ(3686)\rightarrowΞ(1530)^{-}\barΞ(1530)^{+}$ and $Ξ(1530)^{-}\barΞ^{+}$ decays with a statistical significance of more than 10$σ$ and 5.0$σ$, respectively. The branching fractions are measured to be $\cal{B}$$[ψ(3686)\rightarrowΞ(1530)^{-}\barΞ(1530)^{+}] $ = (11.45 $\pm$ 0.40 $\pm$ 0.59) $\times$ $10^{-5}$ and $\cal{B}$$[ψ(3686)\rightarrowΞ(1530)^{-}\barΞ^{+}]$ = (0.70 $\pm$ 0.11 $\pm$ 0.04) $\times$ $10^{-5}$. The angular distribution parameter for $ψ(3686)\rightarrowΞ(1530)^{-}\barΞ(1530)^{+}$ is determined to be $α$ = 0.40 $\pm$ 0.24 $\pm$ 0.06, which agrees with the theoretical predictions within 1$σ$. The first uncertainties are statistical, and the second systematic.

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arXiv2019

First observation of the decay $χ_{cJ}\to Σ^{+}\bar{p}K_{S}^{0}+c.c. ~(J = 0, 1, 2)$

Using E1 radiative transitions $ψ(3686) \to γχ_{cJ}$ from a sample of $(448.1 \pm 2.9)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector, the decays $χ_{cJ}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.~(J = 0, 1, 2)$ are studied. The decay branching fractions are measured to be $\mathcal{B}(χ_{c0}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.) = (3.52 \pm 0.19\pm 0.21)\times10^{-4}$, $\mathcal{B}(χ_{c1}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.) = (1.53 \pm 0.10\pm 0.08)\times10^{-4}$, and $\mathcal{B}(χ_{c2}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.) = (8.25 \pm 0.83 \pm 0.49)\times10^{-5}$, where the first and second uncertainties are the statistical and systematic ones, respectively. No evident intermediate resonances are observed in the studied processes.

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arXiv2019

Triple GEM performance in magnetic field

Performance of triple GEM prototypes in strong magnetic field has been evaluated bymeans of a muon beam at the H4 line of the SPS test area at CERN. Data have been reconstructedand analyzed offline with two reconstruction methods: the charge centroid and the micro-Time-Projection-Chamber exploiting the charge and the time measurement respectively. A combinationof the two reconstruction methods is capable to guarantee a spatial resolution better than 150μmin magnetic field up to a 1 T.

physics.ins-det↗

arXiv2019

Search for the rare decay $η'\rightarrowπ^{0}π^{0}π^{0}π^{0}$ at BESIII

Based on a sample of 1.31 billion $J/ψ$ events collected with the BESIII detector, we perform a search for the rare decay $η'\rightarrow 4π^{0}$ via $J/ψ\rightarrowγη'$. No significant $η'$ signal is observed in the invariant mass spectrum of 4$π^{0}$. With a Bayesian approach, the upper limit on the branching fraction of $η'\rightarrow 4π^{0}$ is determined to be $\mathcal{B}(η'\rightarrow 4π^{0})$ $< 4.94\times10^{-5}$ at the 90\% confidence level, which is a factor of six smaller than the previous experimental limit.

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arXiv2019

Evidence for the decays of $Λ^+_{c}\toΣ^+η$ and $Σ^+η^\prime$

We study the hadronic decays of $Λ_{c}^{+}$ to the final states $Σ^{+}η$ and $Σ^+η^\prime$, using an $e^{+}e^{-}$ annihilation data sample of 567 pb$^{-1}$ taken at a center-of-mass energy of 4.6 GeV with the BESIII detector at the BEPCII collider. We find evidence for the decays $Λ_{c}^{+}\rightarrowΣ^{+}η$ and $Σ^+η^\prime$ with statistical significance of $2.5σ$ and $3.2σ$, respectively. Normalizing to the reference decays $Λ_c^+\toΣ^+π^0$ and $Σ^+ω$, we obtain the ratios of the branching fractions $\frac{{\mathcal B}(Λ_c^+\toΣ^+η)}{{\mathcal B}(Λ_c^+\toΣ^+π^0)}$ and $\frac{{\mathcal B}(Λ_c^+\toΣ^+η^\prime)}{{\mathcal B}(Λ_c^+\toΣ^+ω)}$ to be $0.35 \pm 0.16 \pm 0.03$ and $0.86 \pm 0.34 \pm 0.07$, respectively. The upper limits at the 90\% confidence level are set to be $\frac{{\mathcal B}(Λ_c^+\toΣ^+η)}{{\mathcal B}(Λ_c^+\toΣ^+π^0)}<0.58$ and $\frac{{\mathcal B}(Λ_c^+\toΣ^+η^\prime)}{{\mathcal B}(Λ_c^+\toΣ^+ω)}<1.2$. Using BESIII measurements of the branching fractions of the reference decays, we determine $\mathcal B({Λ_{c}^{+}\rightarrowΣ^{+}η})=(0.41\pm0.19\pm0.05)\%$ ($<0.68\%$) and $\mathcal B({Λ_{c}^{+}\rightarrowΣ^{+}η'})=(1.34\pm0.53\pm0.21)\%$ ($<1.9\%$). Here, the first uncertainties are statistical and the second systematic. The obtained branching fraction of $Λ_c^+\toΣ^+η$ is consistent with the previous measurement, and the branching fraction of $Λ_{c}^{+}\rightarrowΣ^{+}η^{\prime}$ is measured for the first time.

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arXiv2019

Cross section measurements of $e^{+}e^{-} \to K^{+}K^{-}K^{+}K^{-} $ and $ ϕK^{+}K^{-}$ at center-of-mass energies from 2.10 to 3.08 GeV

We measure the Born cross sections of the process $e^{+}e^{-} \to K^{+}K^{-}K^{+}K^{-}$ at center-of-mass (c.m.) energies, $\sqrt{s}$, between 2.100 and 3.080 GeV. The data were collected using the BESIII detector at the BEPCII collider. An enhancement at $\sqrt{s}= 2.232$ GeV is observed, very close to the $e^{+}e^{-} \to Λ\overlineΛ$ production threshold. A similar enhancement at the same c.m. energy is observed in the $e^{+}e^{-} \to ϕK^{+}K^{-}$ cross section. The energy dependence of the $K^{+}K^{-}K^{+}K^{-}$ and $ϕK^{+}K^{-}$ cross sections differs significantly from that of $e^{+}e^{-} \to ϕπ^{+}π^{-}$.

hep-ex↗

arXiv2019

Search for the decay $η'\toγγη$

Using a data sample of $1.31\times10^{9} ~J/ψ$ events collected with the BESIII detector, a search for $η'\toγγη$ via $J/ψ\toγη'$ is performed for the first time. No significant $η'$ signal is observed in the $γγη$ invariant mass spectrum, and the %upper limit of the branching fraction of $η'\toγγη$ is determined to be less than $1.33 \times 10^{-4}$ at the 90$\%$ confidence level.

hep-ex↗

arXiv2019

Observation and study of the decay $J/ψ\rightarrowϕηη'$

We report the observation and study of the decay $J/ψ\rightarrowϕηη'$ using $1.3\times{10^9}$ $J/ψ$ events collected with the BESIII detector. Its branching fraction, including all possible intermediate states, is measured to be $(2.32\pm0.06\pm0.16)\times{10^{-4}}$. We also report evidence for a structure, denoted as $X$, in the $ϕη'$ mass spectrum in the $2.0-2.1$ GeV/$c^2$ region. Using two decay modes of the $η'$ meson ($γπ^+π^-$ and $ηπ^+π^-$), a simultaneous fit to the $ϕη'$ mass spectra is performed. Assuming the quantum numbers of the $X$ to be $J^P = 1^-$, its significance is found to be 4.4$σ$, with a mass and width of $(2002.1 \pm 27.5 \pm 21.4)$ MeV/$c^2$ and $(129 \pm 17 \pm 9)$ MeV, respectively, and a product branching fraction $\mathcal{B}(J/ψ\rightarrowηX)\times{}\mathcal{B}(X\rightarrowϕη')=(9.8 \pm 1.2 \pm 1.7)\times10^{-5}$. Alternatively, assuming $J^P = 1^+$, the significance is 3.8$σ$, with a mass and width of $(2062.8 \pm 13.1 \pm 7.2)$ MeV/$c^2$ and $(177 \pm 36 \pm 35)$ MeV, respectively, and a product branching fraction $\mathcal{B}(J/ψ\rightarrowηX)\times{}\mathcal{B}(X\rightarrowϕη')=(9.6 \pm 1.4 \pm 2.0)\times10^{-5}$. The angular distribution of $J/ψ\rightarrowηX$ is studied and the two $J^P$ assumptions of the $X$ cannot be clearly distinguished due to the limited statistics. In all measurements the first uncertainties are statistical and the second systematic.

hep-ex↗

arXiv2019

Search for heavy Majorana neutrino in lepton number violating decays of D-> K pi e+ e+

Using the data sample of an integrated luminosity of 2.93 fb$^{-1}$ taken at the center-of-mass energy of 3.773 GeV, we search for the Majorana neutrino in the lepton number violating decays $D\to K πe^+ e^+$. No significant signal is observed, and the upper limits on the branching fraction at the 90\% confidence level are set to be $\mathcal{B}\,(D^0 \to K^- π^- e^+ e^+)<2.8\times10^{-6}$, $\mathcal{B}\,(D^+ \to K_S^0 π^- e^+ e^+)<3.3\times10^{-6}$ and $\mathcal{B}\,(D^+ \to K^- π^0 e^+ e^+)<8.5\times10^{-6}$. The Majorana neutrino is searched for with different mass assumptions ranging from 0.25 to 1.0 GeV/$c^2$ in the decays $D^0\to K^- e^+ ν_N(π^- e^+)$ and $D^+\to K_S^0 e^+ ν_N(π^- e^+)$, and the upper limits on the branching fraction at the 90\% confidence level are extracted to be at the level of $10^{-7} \sim 10^{-6}$, depending on the mass of Majorana neutrino. The constraints on the mixing matrix element $|V_{eN}|^2$ are also evaluated.

hep-ex↗

arXiv2019

Observation of $η_c\toωω$ in $J/ψ\toγωω$

Using a sample of $(1310.6\pm7.0)\times10^6$ $J/ψ$ events recorded with the BESIII detector at the symmetric electron positron collider BEPCII, we report the observation of the decay of the $(1^1 S_0)$ charmonium state $η_c$ into a pair of $ω$ mesons in the process $J/ψ\toγωω$. The branching fraction is measured for the first time to be $\mathcal{B}(η_c\toωω)= (2.88\pm0.10\pm0.46\pm0.68)\times10^{-3}$, where the first uncertainty is statistical, the second systematic and the third is from the uncertainty of $\mathcal{B}(J/ψ\toγη_c)$. The mass and width of the $η_c$ are determined as $M=(2985.9\pm0.7\pm2.1)\,$MeV/$c^2$ and $Γ=(33.8\pm1.6\pm4.1)\,$MeV.

hep-ex↗

arXiv2019

Study of the Decays $D_{s}^{+} \rightarrow K_{S}^{0}K^{+}$ and $K_{L}^{0}K^{+}$

Using an $e^{+}e^{-}$ annihilation data sample corresponding to an integrated luminosity of $3.19~\mathrm{fb}^{-1}$ and collected at a center-of-mass energy $\sqrt{s} = 4.178~\mathrm{GeV}$ with the BESIII detector, we measure the absolute branching fractions $\mathcal{B}(D_{s}^{+} \rightarrow K_{S}^{0}K^{+}) = (1.425\pm0.038_{\rm stat.}\pm0.031_{\rm syst.})\%$ and $\mathcal{B}(D_{s}^{+} \rightarrow K_{L}^{0}K^{+}) =(1.485\pm0.039_{\rm stat.}\pm0.046_{\rm syst.})\%$. The branching fraction of $D_{s}^{+} \rightarrow K_{S}^{0}K^{+}$ is compatible with the world average and that of $D_{s}^{+} \rightarrow K_{L}^{0}K^{+}$ is measured for the first time. We present the first measurement of the $K_{S}^{0}$-$K_{L}^{0}$ asymmetry in the decays $D_{s}^{+} \rightarrow K_{S,L}^{0}K^{+}$, and $R(D_{s}^{+} \rightarrow K_{S,L}^{0}K^{+})=\frac{\mathcal{B}(D_{s}^{+} \rightarrow K_{S}^{0}K^{+}) -\mathcal{B}(D_{s}^{+} \rightarrow K_{L}^{0}K^{+})}{\mathcal{B}(D_{s}^{+} \rightarrow K_{S}^{0}K^{+}) +\mathcal{B}(D_{s}^{+} \rightarrow K_{L}^{0}K^{+})}= (-2.1\pm1.9_{\rm stat.}\pm1.6_{\rm syst.})\%$. In addition, we measure the direct $CP$ asymmetries $A_{\rm CP}(D_{s}^{\pm} \rightarrow K_{S}^{0}K^{\pm}) = (0.6\pm2.8_{\rm stat.}\pm0.6_{\rm syst.})\%$ and $A_{\rm CP}(D_{s}^{\pm} \rightarrow K_{L}^{0}K^{\pm}) = (-1.1\pm2.6_{\rm stat.}\pm0.6_{\rm syst.})\%$.

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