arXiv subjects

S. Chen

Publications and source records attributed to S. Chen.

At least 217 records · Page 12Linked to original sources

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

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

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

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 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↗

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

Search for the rare decay $K^+\toμ^+ν\barνν$

Evidence of the $K^+\toμ^+ν\barνν$ decay was searched for using E949 experimental data with an exposure of $1.70\times 10^{12}$ stopped kaons. The data sample is dominated by the backgrond process $K^+\toμ^+ν_μγ$. An upper limit on the decay rate $Γ(K^+\toμ^+ν\barνν)< 2.4\times 10^{-6}Γ(K^+\to all)$ at 90% confidence level was set assuming the Standard Model muon spectrum. The data are presented in such a way as to allow calculation of rates for any assumed $μ^+$ spectrum.

hep-ex↗

arXiv2016

Optical Nonlinear Dark X-Waves

We introduce spatiotemporal optical dark X solitary waves of the (2+1)D {hyperbolic} nonlinear Schrödinger equation (NLSE), that rules wave propagation in a self-focusing and normally dispersive medium. These analytical solutions are derived by exploiting the connection between such NLSE and a well known equation of hydrodynamics, namely the type II Kadomtsev-Petviashvili (KP-II) equation. As a result, families of shallow water X soliton solutions of the KP-II equation are mapped into optical dark X solitary wave solutions of the NLSE. Numerical simulations show that optical dark X solitary waves may propagate for long distances (tens of nonlinear lengths) before they eventually break up, owing to the modulation instability of the continuous wave background. This finding opens a novel path for the excitation and control of X solitary waves in nonlinear optics.

nlin.PS↗

arXiv2016

Observation of $h_{c}$ radiative decay $h_{c} \rightarrow γη'$ and evidence for $h_{c} \rightarrow γη$

A search for radiative decays of the $P$-wave spin singlet charmonium resonance $h_c$ is performed based on $4.48 \times 10^{8}$ $ψ'$ events collected with the BESIII detector operating at the BEPCII storage ring. Events of the reaction channels $h_{c} \rightarrow γη'$ and $γη$ are observed with a statistical significance of $8.4 σ$ and $4.0 σ$, respectively, for the first time. The branching fractions of $h_{c} \rightarrow γη'$ and $h_{c} \rightarrow γη$ are measured to be $\mathcal{B}(h_{c} \rightarrow γη')=(1.52 \pm 0.27 \pm 0.29)\times10^{-3}$ and $\mathcal{B}(h_{c} \rightarrow γη)=(4.7 \pm 1.5 \pm 1.4)\times10^{-4}$, respectively, where the first errors are statistical and the second are systematic uncertainties.

hep-ex↗

arXiv2016

Improved measurement of the absolute branching fraction of $D^{+}\rightarrow \bar K^0 μ^{+}ν_μ$

By analyzing 2.93 fb$^{-1}$ of data collected at $\sqrt s=3.773$ GeV with the BESIII detector, we measure the absolute branching fraction ${\mathcal B}(D^{+}\rightarrow\bar K^0μ^{+}ν_μ)=(8.72 \pm 0.07_{\rm stat.} \pm 0.18_{\rm sys.})\%$, which is consistent with previous measurements within uncertainties but with significantly improved precision. Combining the Particle Data Group values of ${\mathcal B}(D^0\to K^-μ^+ν_μ)$, ${\mathcal B}(D^{+}\rightarrow\bar K^0 e^{+}ν_{e})$, and the lifetimes of the $D^0$ and $D^+$ mesons with the value of ${\mathcal B}(D^{+}\rightarrow\bar K^0 μ^{+}ν_μ)$ measured in this work, we determine the following ratios of partial widths: $Γ(D^0\to K^-μ^+ν_μ)/Γ(D^{+}\rightarrow\bar K^0μ^{+}ν_μ)=0.963\pm0.044$ and $Γ(D^{+}\rightarrow\bar K^0 μ^{+}ν_μ)/Γ(D^{+}\rightarrow\bar K^0 e^{+}ν_{e})=0.988\pm0.033$.

hep-ex↗

arXiv2016

Silicide Induced Surface Defects in FePt nanoParticle fcc-to-fct Thermally Activated Phase Transition

Magnetic nanoparticles (MnPs) are relevant to a wide range of applications including high density information storage and magnetic resonance imaging to name but a few. Among the materials available to prepare MnPs, FePt is attracting growing attention. However, to harvest the strongest magnetic properties of FePt MnPs, a thermal annealing is often required to convert face-centered cubic as synthesized nPs into its tetragonal phase. Rarely addressed are the potential side effects of such treatments on the magnetic properties. In this study, we focus on the impact of silica shells often used in strategies aiming at overcoming MnP coalescence during the thermal annealing. While we show that this shell does prevent sintering, and that fcc-to-fct conversion does occur, we also reveal the formation of silicide, which can prevent the stronger magnetic properties of fct-FePt MnPs from being fully realised. This report therefore sheds lights on poorly investigated and understood interfacial phenomena occurring during the thermal annealing of MnPs and, by doing so, also highlights the benefits of developing new strategies to avoid silicide formation.

cond-mat.mtrl-sci↗