arXiv subjects

W. Cheng

Publications and source records attributed to W. Cheng.

At least 73 records · Page 4Linked to original sources

arXiv2019

A fast and parametric digitization for triple-GEM detectors

Triple-GEM detectors are a well known technology in high energy physics. In order to have a complete understanding of their behavior, in parallel with on beam testing, a Monte Carlo code has to be developed to simulate their response to the passage of particles. The software must take into account all the physical processes involved from the primary ionization up to the signal formation, e.g. the avalanche multiplication and the effect of the diffusion on the electrons. In the case of gas detectors, existing software such as Garfield already perform a very detailed simulation but are CPU time consuming. A description of a reliable but faster simulation is presented here: it uses a parametric description of the variables of interest obtained by suitable preliminary Garfield simulations and tuned to the test beam data. It can reproduce the real values of the charge measured by the strip, needed to reconstruct the position with the Charge Centroid method. In addition, particular attention was put to the simulation of the timing information, which permits to apply also the micro-Time Projection Chamber position reconstruction, for the first time on a triple-GEM. A comparison between simulation and experimental values of some sentinel variables in different conditions of magnetic field, high voltage settings and incident angle will be shown.

physics.ins-det↗

arXiv2019

Search for the decay $D_s^+\rightarrow γe^+ν_e$

A search for the rare radiative leptonic decay $D_s^+\toγe^+ν_e$ is performed for the first time using electron-positron collision data corresponding to an integrated luminosity of 3.19 fb$^{-1}$, collected with the BESIII detector at a center-of-mass energy of 4.178 GeV. No evidence for the $D_s^+\toγe^+ν_e$ decay is seen and an upper limit of $\mathcal B(D_s^+\toγe^+ν_e)<1.3\times 10^{-4}$ is set on the partial branching fraction at a 90\% confidence level for radiative photon energies $E_γ^*>0.01$~GeV.

hep-ex↗

arXiv2019

Measurement of the Dynamics of the Decays ${ D_s^+ \rightarrow η^{(\prime)} e^{+} ν_e}$

Using $e^+e^-$ annihilation data corresponding to an integrated luminosity of 3.19\,fb$^{-1}$ collected at a center-of-mass energy of 4.178~GeV with the BESIII detector, we measure the absolute branching fractions $\mathcal{B}_{D_s^+ \rightarrow ηe^{+} ν_e }$ = $(2.323\pm0.063_{\rm stat}\pm0.063_{\rm syst})\%$ and $\mathcal{B}_{D_s^+ \rightarrow η^{\prime} e^{+} ν_e}$ = $(0.824\pm0.073_{\rm stat}\pm0.027_{\rm syst})\%$ via a tagged analysis technique, where one $D_s$ is fully reconstructed in a hadronic mode. Combining these measurements with previous BESIII measurements of $\mathcal{B}_{D^+\toη^{(\prime)} e^{+} ν_e}$, the $η-η^\prime$ mixing angle in the quark flavour basis is determined to be $ϕ_{\rm P} = (40.1\pm2.1_{\rm stat}\pm0.7_{\rm syst})^\circ$. From the first measurements of the dynamics of $D^+_s\to η^{(\prime)}e^+ν_e$ decays, the products of the hadronic form factors $f_+^{η^{(\prime)}}(0)$ and the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cs}|$ are determined with different form factor parameterizations. For the two-parameter series expansion, the results are $f^η_+(0)|V_{cs}| = 0.4455\pm0.0053_{\rm stat}\pm0.0044_{\rm syst}$ and $f^{η^{\prime}}_+(0)|V_{cs}| = 0.477\pm0.049_{\rm stat}\pm0.011_{\rm syst}$.

hep-ex↗

arXiv2019

Precision measurement of the branching fractions of $η^\prime$ decays

Based on a sample of $(1310.6 \pm 7.0) \times 10^6~J/ψ$ events collected with the BESIII detector, we present measurements of $J/ψ$ and $η^\prime$ absolute branching fractions using the process $J/ψ\rightarrowγη^\prime$. By analyzing events where the radiative photon converts into an $e^+e^-$ pair, the branching fraction for $J/ψ\rightarrow γη^\prime$ is measured to be $(5.27\pm0.03\pm0.05)\times 10^{-3}$. The absolute branching fractions of the five dominant decay channels of the $η^\prime$ are then measured independently for the first time and are determined to be $\mathcal{B}(η^\prime \rightarrow γπ^{+} π^{-})$ = (29.90$\pm$0.03$\pm$0.55)%, $\mathcal{B}(η^\prime \rightarrow ηπ^{+} π^{-})$ = (41.24$\pm$0.08$\pm$1.24)%, $\mathcal{B}(η^\prime \rightarrow ηπ^{0} π^{0})$ = (21.36$\pm$0.10$\pm$0.92)%, $\mathcal{B}(η^\prime \rightarrow γω)$ = (2.489$\pm$0.018$\pm$0.074)%, and $\mathcal{B}(η^\prime \rightarrow γγ)$ = (2.331$\pm$0.012$\pm$0.035)%, where the first uncertainties are statistical and the second systematic.

hep-ex↗

arXiv2019

Complete measurement of $Λ$ electromagnetic form factors

The exclusive process $e^+e^-\rightarrowΛ\barΛ$, with $Λ\to pπ^-$ and $\barΛ \to \bar{p}π^+$, has been studied at $\sqrt{s} =$ 2.396 GeV for measurement of the $Λ$ electric and magnetic form factors, $G_E$ and $G_M$. A data sample, corresponding to an integrated luminosity of 66.9 pb$^{-1}$, was collected with the BESIII detector for this purpose. A multi-dimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio $R=|G_E/G_M|$ and, for the first time for any baryon, the relative phase $ΔΦ=Φ_E-Φ_M$. The resulting values are obtained using the recent and most precise measured value of the asymmetry parameter $α_Λ$ = $0.750~\pm~0.010$ to be $R~=~0.96\pm0.14~(\rm stat.)\pm~0.02~(\rm sys.)$ and $ΔΦ=37^{\mathrm{o}}\pm~12^{\mathrm{o}}~(\rm stat.)\pm~6^{\mathrm{o}}~(\rm sys.)$, respectively. In addition, the cross section is measured with unprecedented precision to be $σ= 118.7~\pm~5.3~(\rm stat.)\pm~5.1~(\rm sys.)$ pb, which corresponds to an effective form factor of $|G|=0.123~\pm~0.003~(\rm stat.)\pm~0.003~(\rm sys.)$. The contribution from two-photon exchange is found to be negligible. Our result enables the first complete determination of baryon time-like electromagnetic form factors.

hep-ex↗

arXiv2019

Observation of $e^{+}e^{-}\rightarrow π^{+}π^{-}ψ(3770)$ and $D_{1}(2420)^{0}\bar{D}^{0} + c.c.$

Several intermediate states of the reaction channels $e^{+}e^{-} \rightarrow π^{+} π^{-} D^{0} \bar{D}^{0}$ and $e^{+}e^{-} \rightarrow π^{+} π^{-} D^{+}D^{-}$ are studied using the data samples collected with the BESIII detector at center-of-mass energies above 4.08 GeV. For the first time in this final state, a $ψ(3770)$ signal is seen in the $D\bar{D}$ invariant mass spectrum, with a statistical significance of $5.2σ$ at $\sqrt{s} = 4.42$ GeV. There is also evidence for this resonance at $\sqrt{s}$ = 4.26 and 4.36 GeV with statistical significance of 3.2$σ$ and 3.3$σ$, respectively. In addition, the Born cross section of $e^{+}e^{-}\to π^{+}π^{-}ψ(3770)$ is measured. The proposed heavy-quark-spin-symmetry partner of the $X(3872)$, the state $X_{2}(4013)$, is also searched for in the $D\bar{D}$ invariant mass spectra. No obvious signal is found. The upper limit of the Born cross section of the process $e^{+}e^{-}\to ρ^{0}X_{2}(4013)$ combined with the branching fraction is measured. Also, the processes $e^{+}e^{-}\to D_{1}(2420)\bar{D} + c.c.$ are investigated. The neutral mode with $D_{1}(2420)^{0}\to D^{0}π^{+}π^{-}$ is reported with statistical significance of 7.4$σ$ at $\sqrt{s} = 4.42$ GeV for the first time, and evidence with statistical significance of 3.2$σ$ and 3.3$σ$ at $\sqrt{s}$ = 4.36 and 4.60 GeV is seen, respectively. No evident signal for the process $e^{+}e^{-}\to D_{1}(2420)^{0}\bar{D}^{0} + c.c., D_{1}(2420)^{0}\to D^{*+}π^{-}$ is reported. Evidence for $e^{+}e^{-}\to D_{1}(2420)^{+}D^{-} +~c.c., D_{1}(2420)^{+}\to D^{+}π^{+}π^{-}$ is reported with statistical significance of 3.1$σ$ and 3.0$σ$ at $\sqrt{s}$ = 4.36 and 4.42 GeV, respectively.

hep-ex↗

arXiv2019

Amplitude Analysis and Branching Fraction Measurement of $D^0\rightarrow K^-π^+π^0π^0$

Utilizing the dataset corresponding to an integrated luminosity of $2.93$ fb$^{-1}$ at $\sqrt{s}=3.773$ GeV collected by the BESIII detector, we report the first amplitude analysis and branching fraction measurement of the $D^0\rightarrow K^-π^+π^0π^0$ decay. We investigate the sub-structures and determine the relative fractions and the phases among the different intermediate processes. Our results are used to provide an accurate detection efficiency and allow measurement of ${\cal B}(D^0\rightarrow K^-π^+π^0π^0) \,=\, (8.86 \pm 0.13(\text{stat}) \pm 0.19(\text{syst}))\%$.

hep-ex↗

arXiv2019

Amplitude analysis of $D_{s}^{+} \rightarrow π^{+}π^{0}η$ and first observation of the pure $W$-annihilation decays $D_{s}^{+} \rightarrow a_{0}(980)^{+}π^{0}$ and $D_{s}^{+} \rightarrow a_{0}(980)^{0}π^{+}$

We present the first amplitude analysis of the decay $D^{+}_{s} \rightarrow π^{+}π^{0}η$. We use an $e^{+}e^{-}$ collision data sample corresponding to an integrated luminosity of 3.19~${\mbox{\,fb}^{-1}}$ collected with the BESIII detector at a center-of-mass energy of $4.178$ GeV. We observe for the first time the pure $W$-annihilation decays $D_{s}^{+} \rightarrow a_{0}(980)^{+}π^{0}$ and $D_{s}^{+} \rightarrow a_{0}(980)^{0}π^{+}$. We measure the absolute branching fractions $\mathcal{B}(D_{s}^{+} \rightarrow a_{0}(980)^{+(0)}π^{0^(+)}, a_{0}(980)^{+(0)} \to π^{+(0)}η) = (1.46\pm0.15_{\rm stat.}\pm0.23_{\rm sys.})$\%, which is larger than the branching fractions of other measured pure $W$-annihilation decays by at least one order of magnitude. In addition, we measure the branching fraction of $D_{s}^{+} \rightarrow π^{+}π^{0}η$ with significantly improved precision.

hep-ex↗

arXiv2019

Observation of $ψ(3686)\to p\bar{p}ϕ$

Using a data sample of $4.48\times10^{8}$ $\psip$ events collected with the BESIII detector, we present a first observation of $ψ(3686)\to p\bar{p}ϕ$, and we measure its branching fraction to be $[6.06\pm0.38 ($stat.$) \pm 0.48 ($syst.$)]\times10^{-6}$. In contrast to the earlier discovery of a threshold enhancement in the $p\bar{p}$-mass spectrum of the channel $J/ψ\toγp\bar p$, denoted as $X(p\bar{p})$, we do not find a similar enhancement in $ψ(3686)\to p\bar{p}ϕ$. An upper limit of $1.82\times10^{-7}$ at the $90\%$ confidence level on the branching fraction of $ψ(3686)\to X(p\bar{p})ϕ\to p\bar{p}ϕ$ is obtained.

hep-ex↗

arXiv2019

Study of electromagnetic Dalitz decays $χ_{cJ} \rightarrow μ^{+}μ^{-}J/ψ$

Using $4.48 \times 10^{8}$ $ψ(3686)$ events collected with the BESIII detector, we search for the decays $χ_{cJ} \rightarrow μ^{+}μ^{-}J/ψ$ through the radiative decays $ψ(3686) \rightarrow γχ_{cJ}$, where $J=0,1,2$. The decays $χ_{c1,2} \rightarrow μ^{+}μ^{-}J/ψ$ are observed, and the corresponding branching fractions are measured to be $\mathcal{B}(χ_{c1} \rightarrow μ^{+}μ^{-}J/ψ) = (2.51 \pm 0.18 \pm 0.20)\times10^{-4}$ and $\mathcal{B}(χ_{c2} \rightarrow μ^{+}μ^{-}J/ψ) = (2.33 \pm 0.18 \pm 0.29)\times10^{-4}$, where the first uncertainty is statistical and the second one systematic. No significant $χ_{c0} \rightarrow μ^{+}μ^{-}J/ψ$ decay is observed, and the upper limit on the branching fraction is determined to be $2.0\times10^{-5}$ at 90% confidence level. Also, we present a study of di-muon invariant mass dependent transition form factor for the decays $χ_{c1,2} \rightarrow μ^{+}μ^{-}J/ψ$.

hep-ex↗

arXiv2019

Measurement of the absolute branching fractions of $Λ_{c}^{+}\toΛηπ^{+}$ and $Σ(1385)^{+}η$

We study the decays $Λ_{c}^{+}\toΛηπ^{+}$ and $Σ(1385)^{+}η$ based on $Λ_{c}^{+}\barΛ_{c}^{-}$ pairs produced in $e^+e^-$ collisions at a center-of-mass energy of $\sqrt{s}=4.6~\mbox{GeV}$, corresponding to an integrated luminosity of $567\;\mbox{pb$^{-1}$}$. The data sample was accumulated with the BESIII detector at the BEPCII collider. The branching fractions are measured to be $\mathcal{B}(Λ_{c}^{+} \to Ληπ^{+})=(1.84\pm0.21({\rm{stat.}})\pm0.15({\rm{syst.}}))\%$ and $\mathcal{B}(Λ_{c}^{+} \to Σ(1385)^{+}η)=(0.91\pm0.18({\rm{stat.}})\pm0.09({\rm{syst.}}))\%$, constituting the most precise measurements to date.

hep-ex↗

arXiv2019

Observation of $D^+ \to f_0(500) e^+ν_e$ and Improved Measurements of $D \toρe^+ν_e$

Using a data sample corresponding to an integrated luminosity of 2.93~fb$^{-1}$ recorded by the BESIII detector at a center-of-mass energy of $3.773$ GeV, we present an analysis of the decays $\bar{D}^0\toπ^+π^0 e^-\barν_e$ and $D^+\toπ^-π^+ e^+ν_e$. By performing a partial wave analysis, the $π^+π^-$ $S$-wave contribution to $D^+\toπ^-π^+ e^+ν_e$ is observed to be $(25.7\pm1.6\pm1.1)$% with a statistical significance greater than 10$σ$, besides the dominant $P$-wave contribution. This is the first observation of the $S$-wave contribution. We measure the branching fractions $\mathcal{B}(D^{0} \to ρ^- e^+ ν_e) = (1.445\pm 0.058 \pm 0.039) \times10^{-3}$, $\mathcal{B}(D^{+} \to ρ^0 e^+ ν_e) = (1.860\pm 0.070 \pm 0.061) \times10^{-3}$, and $\mathcal{B}(D^{+} \to f_0(500) e^+ ν_e, f_0(500)\toπ^+π^-) = (6.30\pm 0.43 \pm 0.32) \times10^{-4}$. An upper limit of $\mathcal{B}(D^{+} \to f_0(980) e^+ ν_e, f_0(980)\toπ^+π^-) < 2.8 \times10^{-5}$ is set at the 90% confidence level. We also obtain the hadronic form factor ratios of $D\to ρe^+ν_e$ at $q^{2}=0$ assuming the single-pole dominance parameterization: $r_{V}=\frac{V(0)}{A_{1}(0)}=1.695\pm0.083\pm0.051$, $r_{2}=\frac{A_{2}(0)}{A_{1}(0)}=0.845\pm0.056\pm0.039$.

hep-ex↗

arXiv2019

Observation of OZI suppressed decays $χ_{cJ}\toωϕ$

Decays $χ_{cJ}~(J=0,1,2)\toωϕ$ are studied using $(448.1\pm2.9)\times 10^{6} ~ψ(3686)$ events collected with the BESIII detector in 2009 and 2012. In addition to the previously established $χ_{c0}\toωϕ$, first observation of $χ_{c1} \to ωϕ$ is reported in this paper. The measured product branching fractions are ${\cal{B}}(ψ(3686)\toγχ_{c0})\times{\cal{B}}(χ_{c0}\toωϕ)=(13.83\pm 0.70\pm 1.01)\times10^{-6}$ and ${\cal{B}}(ψ(3686)\toγχ_{c1})\times{\cal{B}}(χ_{c1}\toωϕ)=(2.67\pm 0.31\pm 0.27)\times10^{-6}$, and the absolute branching fractions are ${\cal{B}}(χ_{c0}\toωϕ)=(13.84\pm 0.70\pm 1.08)\times10^{-5}$ and ${\cal{B}}(χ_{c1}\toωϕ)=(2.80\pm 0.32\pm 0.30)\times10^{-5}$. We also find a strong evidence for $χ_{c2}\toωϕ$ with a statistical significance of 4.8$σ$, and the corresponding product and absolute branching fractions are measured to be ${\cal{B}}(ψ(3686)\toγχ_{c2})\times{\cal{B}}(χ_{c2}\toωϕ)=(0.91\pm0.23\pm0.12)\times10^{-6} $ and ${\cal{B}}(χ_{c2}\toωϕ)=(1.00\pm0.25\pm0.14)\times10^{-5}$. Here, the first errors are statistical and the second ones systematic.

hep-ex↗

arXiv2019

Study of the decay $D^0\rightarrow \bar{K}^0π^-e^+ν_e$

We report a study of the decay $D^0 \rightarrow \bar{K}^0π^-e^+ν_{e}$ based on a sample of $2.93~\mathrm{fb}^{-1}$ $e^+e^-$ annihilation data collected at the center-of-mass energy of 3.773~GeV with the BESIII detector at the BEPCII collider. The total branching fraction is determined to be $\mathcal{B}(D^0\rightarrow \bar{K}^0π^-e^+ν_{e})=(1.434\pm0.029({\rm stat.})\pm0.032({\rm syst.}))\%$, which is the most precise to date. According to a detailed analysis of the involved dynamics, we find this decay is dominated with the $K^{*}(892)^-$ contribution and present an improved measurement of its branching fraction to be $\mathcal{B}(D^0\rightarrow K^{*}(892)^-e^+ν_e)=(2.033\pm0.046({\rm stat.})\pm0.047({\rm syst.}))\%$. We further access their hadronic form-factor ratios for the first time as $r_{V}=V(0)/A_1(0)=1.46\pm0.07({\rm stat.})\pm0.02({\rm syst.})$ and $r_{2}=A_2(0)/A_1(0)=0.67\pm0.06({\rm stat.})\pm0.01({\rm syst.})$. In addition, we observe a significant $\bar{K}^0π^-$ $S$-wave component accounting for $(5.51\pm0.97({\rm stat.})\pm0.62({\rm syst.}))\%$ of the total decay rate.

hep-ex↗

arXiv2019

First measurement of the form factors in $D^+_{s}\rightarrow K^0 e^+ν_e$ and $D^+_{s}\rightarrow K^{*0} e^+ν_e$ decays

We report on new measurements of Cabibbo-suppressed semileptonic $D_s^+$ decays using $3.19~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data sample collected at a center-of-mass energy of 4.178~GeV with the BESIII detector at the BEPCII collider. Our results include branching fractions $\mathcal B({D^+_s\rightarrow K^0 e^+ν_{e}})=(3.25\pm0.38({\rm stat.})\pm0.16({\rm syst.}))\times10^{-3}$ and $\mathcal B({D^+_s\rightarrow K^{*0} e^+ν_{e}})=(2.37\pm0.26({\rm stat.})\pm0.20({\rm syst.}))\times10^{-3}$ which are much improved relative to previous measurements, and the first measurements of the hadronic form-factor parameters for these decays. For $D^+_s\rightarrow K^0 e^+ν_{e}$, we obtain $f_+(0)=0.720\pm0.084({\rm stat.})\pm0.013({\rm syst.})$, and for $D^+_s\rightarrow K^{*0} e^+ν_{e}$, we find form-factor ratios $r_V=V(0)/A_1(0)=1.67\pm0.34({\rm stat.})\pm0.16({\rm syst.})$ and $r_2=A_2(0)/A_1(0)=0.77\pm0.28({\rm stat.})\pm0.07({\rm syst.})$.

hep-ex↗

arXiv2019

Search for rare decay $J/ ψ\to ϕe^+ e^-$

Using a data sample of $448.1\times10^6$ $ψ(3686)$ events collected at $\sqrt{s}=$ 3.686 GeV with the BESIII detector at the BEPCII, we search for the rare decay $J/ψ\to ϕe^+ e^-$ via $ψ(3686) \to π^+π^- J/ψ$. No signal events are observed and the upper limit on the branching fraction is set to be $\mathcal{B}(J/ψ\to ϕe^+ e^-) < 1.2 \times 10^{-7}$ at the 90\% confidence level, which is still about one order of magnitude higher than the Standard Model prediction.

hep-ex↗

arXiv2019

Measurement of $\mathcal{B}(J/ψ\to η' e^+ e^- $) and search for a dark photon

Using a data sample of $(1310.6\pm7.0)\times10^{6}$ $J/ψ$ decay events collected with the BESIII detector at BEPCII, we study the electromagnetic Dalitz decay $J/ψ\to η' e^+e^-$ with two dominant $η'$ decay modes, $η' \to γπ^+ π^-$ and $η' \to π^+π^-η$. The branching fraction is determined to be $\mathcal{B}(J/ψ\to η' e^+e^-) = (6.59\pm0.07\pm0.17) \times 10^{-5}$, which improves in precision by a factor of 2 over the previous BESIII measurement. A search for the dark photon ($γ'$) is performed via $J/ψ\toη' γ', γ' \to e^{+}e^{-}$. Excluding the $ω$ and $ϕ$ mass regions, no significant signal is observed in the mass range from 0.1 to 2.1 GeV/$c^{2}$. We set upper limits at the 90\% confidence level on $\mathcal{B}(J/ψ\to η' γ')\times\mathcal{B}(γ' \to e^+e^-)$, $\mathcal{B}(J/ψ\toη' γ'$) and the mixing strength as a function of dark photon mass. This is among the first searches for dark photons in charmonium decays.

hep-ex↗

arXiv2019

Observation of $χ_{cJ}\to4K_{S}^{0}$

By analyzing $(448.1\pm2.9)\times10^6$ $ψ(3686)$ events collected with the BESIII detector operating at the BEPCII collider, the decays of $χ_{cJ} \to 4K_S^0$ ($J=0,1,2$) are observed for the first time with statistical significances of 26.5$σ$, 5.9$σ$ and 11.4$σ$, respectively. The product branching fractions of $ψ(3686)\toγχ_{cJ}$, $χ_{cJ}\to4K_{S}^{0}$ are presented and the branching fractions of $χ_{cJ}\to4K_{S}^{0}$ decays are determined to be $\mathcal{B}_{χ_{c0}\to 4K_S^0}$=$(5.76\pm0.34\pm0.38)$$\times10^{-4}$, $\mathcal{B}_{χ_{c1}\to 4K_S^0}$=$(0.35\pm0.09\pm0.03)$$\times10^{-4}$ and $\mathcal{B}_{χ_{c2}\to 4K_S^0}$=$(1.14\pm0.15\pm0.08)$$\times10^{-4}$, where the first uncertainties are statistical and the second are systematic, respectively.

hep-ex↗