arXiv subjects

Y. K. Heng

Publications and source records attributed to Y. K. Heng.

At least 91 records · Page 5Linked 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

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

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

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↗

arXiv2017

Improved Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay

A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9~GW$_{\mathrm{th}}$ nuclear reactors and detected by eight antineutrino detectors deployed in two near (560~m and 600~m flux-weighted baselines) and one far (1640~m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be $0.946\pm0.020$ ($0.992\pm0.021$) for the Huber+Mueller (ILL+Vogel) model. A 2.9~$σ$ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4-6~MeV was found in the measured spectrum, with a local significance of 4.4~$σ$. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.

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

Measurement of the Absolute Branching Fraction for $Λ_c^+\rightarrow Λμ^+ν_μ$

We report the first measurement of the absolute branching fraction for $Λ^+_{c}\rightarrow Λμ^+ν_μ$. This measurement is based on a sample of $e^+e^-$ annihilation data at a center-of-mass energy of $\sqrt{s}=4.6$ GeV collected with the BESIII detector at the BEPCII storage rings. The sample corresponds to an integrated luminosity of 567 pb$^{-1}$. The branching fraction is determined to be $\mathcal B({Λ^+_c\rightarrow Λμ^+ν_μ})=(3.49\pm0.46({\rm stat})\pm0.27({\rm syst}))\%$. In addition, we calculate the ratio $\mathcal{B}(Λ^+_c\rightarrow Λμ^+ν_μ)/\mathcal{B}(Λ^+_c\rightarrow Λe^+ν_{e})$ to be $0.96\pm0.16({\rm stat})\pm0.04({\rm syst})$.

hep-ex↗

arXiv2016

Limits on Active to Sterile Neutrino Oscillations from Disappearance Searches in the MINOS, Daya Bay, and Bugey-3 Experiments

Searches for a light sterile neutrino have been performed independently by the MINOS and the Daya Bay experiments using the muon (anti)neutrino and electron antineutrino disappearance channels, respectively. In this Letter, results from both experiments are combined with those from the Bugey-3 reactor neutrino experiment to constrain oscillations into light sterile neutrinos. The three experiments are sensitive to complementary regions of parameter space, enabling the combined analysis to probe regions allowed by the LSND and MiniBooNE experiments in a minimally extended four-neutrino flavor framework. Stringent limits on $\sin^2 2θ_{μe}$ are set over 6 orders of magnitude in the sterile mass-squared splitting $Δm^2_{41}$. The sterile-neutrino mixing phase space allowed by the LSND and MiniBooNE experiments is excluded for $Δm^2_{41} < 0.8$ eV$^2$ at 95% CL$_s$.

hep-ex↗

arXiv2016

Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment

A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GW$_{\rm th}$ nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of $\overlineν_{e}$'s. Comparison of the $\overlineν_{e}$ rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors ($\sim$1500-1950 m) relative to detectors near the reactors ($\sim$350-600 m) allowed a precise measurement of $\overlineν_{e}$ disappearance. More than 2.5 million $\overlineν_{e}$ inverse beta decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (Dec. 2011--Jul. 2012) with a subsequent 1013 days using the complete configuration of eight detectors (Oct. 2012--Jul. 2015). The $\overlineν_{e}$ rate observed at the far detectors relative to the near detectors showed a significant deficit, $R=0.949 \pm 0.002(\mathrm{stat.}) \pm 0.002(\mathrm{syst.})$. The energy dependence of $\overlineν_{e}$ disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle $\sin^22θ_{13}=0.0841 \pm 0.0027(\mathrm{stat.}) \pm 0.0019(\mathrm{syst.})$ and the effective neutrino mass-squared difference of $\left|Δm^2_{\mathrm{ee}}\right|=(2.50 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$. Analysis using the exact three-flavor probability found $Δm^2_{32}=(2.45 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$ assuming the normal neutrino mass hierarchy and $Δm^2_{32}=(-2.56 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$ for the inverted hierarchy.

hep-ex↗

arXiv2016

Measurement of the $D_s^+ \to \ell^+ν_\ell$ branching fractions and the decay constant $f_{D_s^+}$

Using 482~pb$^{-1}$ of $e^+e^-$ collision data collected at a center-of-mass energy of $\sqrt{s} = 4.009$ GeV with the BESIII detector, we measure the branching fractions of the decays $D_s^+\toμ^+ν_μ$ and $D_s^+\toτ^+ν_τ$. By constraining the ratio of decay rates of $D_s^+$ to $τ^+ν_τ$ and to $μ^+ν_μ$ to the Standard Model prediction, the branching fractions are determined to be $\mathcal{B}(D_s^+ \to μ^+ν_μ) = (0.495 \pm 0.067 \pm 0.026)\%$ and $\mathcal{B}(D_s^+ \to τ^+ν_τ) = (4.83 \pm 0.65 \pm 0.26)\%$. Using these branching fractions, we obtain a value for the decay constant $f_{D_s^+}$ of $(241.0 \pm 16.3 \pm 6.5)~\text{MeV}$, where the first error is statistical and the second systematic.

hep-ex↗

arXiv2016

Improved Search for a Light Sterile Neutrino with the Full Configuration of the Daya Bay Experiment

This Letter reports an improved search for light sterile neutrino mixing in the electron antineutrino disappearance channel with the full configuration of the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data collected in eight antineutrino detectors, this search benefits from 3.6 times the statistics available to the previous publication, as well as from improvements in energy calibration and background reduction. A relative comparison of the rate and energy spectrum of reactor antineutrinos in the three experimental halls yields no evidence of sterile neutrino mixing in the $2\times10^{-4} \lesssim |Δm^{2}_{41}| \lesssim 0.3$ eV$^{2}$ mass range. The resulting limits on $\sin^{2}2θ_{14}$ are improved by approximately a factor of 2 over previous results and constitute the most stringent constraints to date in the $|Δm^{2}_{41}| \lesssim 0.2$ eV$^{2}$ region.

hep-ex↗

arXiv2016

Observation of $J/ψ\to γηπ^{0}$

We present the first study of the process $J/ψ\rightarrow γηπ^{0}$ using $(223.7\pm1.4)\times10^{6}$ $J/ψ$ events accumulated with the BESIII detector at the BEPCII facility. The branching fraction for $J/ψ\rightarrow γηπ^{0}$ is measured to be $\mathcal{B}(J/ψ\rightarrow γηπ^{0}) =(2.14\pm0.18(stat)\pm0.25(syst))\times10^{-5}$. With a Bayesian approach, the upper limits of the branching fractions $\mathcal{B}(J/ψ\rightarrow γa_{0}(980),a_0(980)\rightarrowηπ^0)$ and $\mathcal{B}(J/ψ\rightarrow γa_{2}(1320),a_2(1320)\rightarrowηπ^0)$ are determined to be $2.5\times10^{-6}$ and $6.6\times10^{-6}$ at the 95\% confidence level, respectively. All of these measurements are given for the first time.

hep-ex↗

arXiv2016

Measurement of the leptonic decay width of $J/ψ$ using initial state radiation

Using a data set of 2.93 fb$^{-1}$ taken at a center-of-mass energy of $\sqrt{s}$ = 3.773 GeV with the BESIII detector at the BEPCII collider, we measure the process $e^+e^-\rightarrow J/ψγ\rightarrow μ^+μ^-γ$ and determine the product of the branching fraction and the electronic width $\mathcal B_{μμ}\cdot Γ_{ee} = (333.4 \pm 2.5_{\rm stat} \pm 4.4_{\rm sys})$~eV. Using the earlier-published BESIII result for $\mathcal B_{μμ}$ = (5.973 $\pm$ 0.007$_{\rm stat}$ $\pm$ 0.037$_{\rm sys}$)\%, we derive the $J/ψ$ electronic width $Γ_{ee}$~= (5.58 $\pm$ 0.05$_{\rm stat}$ $\pm$ 0.08$_{\rm sys}$) keV.

hep-ex↗

arXiv2016

Study of $D^{+} \to K^{-} π^+ e^+ ν_e$

We present an analysis of the decay $D^{+} \to K^{-} π^+ e^+ ν_e$ based on data collected by the BESIII experiment at the $ψ(3770)$ resonance. Using a nearly background-free sample of 18262 events, we measure the branching fraction $\mathcal{B}(D^{+} \to K^{-} π^+ e^+ ν_e) = (3.71 \pm 0.03 \pm 0.08)\%$. For $0.8<m_{Kπ}<1.0$ GeV/$c^{2}$ the partial branching fraction is $\mathcal{B}(D^{+} \to K^{-} π^+ e^+ ν_e)_{[0.8,1]} = (3.33 \pm 0.03 \pm 0.07)\%$. A partial wave analysis shows that the dominant $\bar K^{*}(892)^{0}$ component is accompanied by an \emph{S}-wave contribution accounting for $(6.05\pm0.22\pm0.18)\%$ of the total rate and that other components are negligible. The parameters of the $\bar K^{*}(892)^{0}$ resonance and of the form factors based on the spectroscopic pole dominance predictions are also measured. We also present a measurement of the $\bar K^{*}(892)^{0}$ helicity basis form factors in a model-independent way.

hep-ex↗

arXiv2016

Study of the wave packet treatment of neutrino oscillation at Daya Bay

The disappearance of reactor $\barν_e$ observed by the Daya Bay experiment is examined in the framework of a model in which the neutrino is described by a wave packet with a relative intrinsic momentum dispersion $σ_\text{rel}$. Three pairs of nuclear reactors and eight antineutrino detectors, each with good energy resolution, distributed among three experimental halls, supply a high-statistics sample of $\barν_e$ acquired at nine different baselines. This provides a unique platform to test the effects which arise from the wave packet treatment of neutrino oscillation. The modified survival probability formula was used to fit Daya Bay data, providing the first experimental limits: $2.38 \cdot 10^{-17} < σ_{\rm rel} < 0.23$. Treating the dimensions of the reactor cores and detectors as constraints, the limits are improved: $10^{-14} \lesssim σ_{\rm rel} < 0.23$, and an upper limit of $σ_{\rm rel} <0.20$ is obtained. All limits correspond to a 95\% C.L. Furthermore, the effect due to the wave packet nature of neutrino oscillation is found to be insignificant for reactor antineutrinos detected by the Daya Bay experiment thus ensuring an unbiased measurement of the oscillation parameters $\sin^22θ_{13}$ and $Δm^2_{32}$ within the plane wave model.

hep-ex↗