arXiv subjects

Q. An

Publications and source records attributed to Q. An.

At least 685 records · Page 38Linked to original sources

arXiv2018

Observation of the $W$-Annihilation Decay $D^{+}_{s} \rightarrow ωπ^{+}$ and Evidence for $D^{+}_{s} \rightarrow ωK^{+}$

We report on the observation of the $W$-annihilation decay $D^{+}_{s} \rightarrow ωπ^{+}$ and the evidence for $D_{s}^{+} \rightarrow ωK^{+}$ with a data sample corresponding to an integrated luminosity of 3.19 fb$^{-1}$ collected with the BESIII detector at the center-of-mass energy $\sqrt{s} = 4.178$ GeV. We obtain the branching fractions $\mathcal{B}(D^{+}_{s} \rightarrow ωπ^{+}) = (1.77\pm0.32_{\rm stat.}\pm0.11_{\rm sys.}) \times 10^{-3}$ and $\mathcal{B}(D^{+}_{s} \rightarrow ωK^{+}) = (0.87\pm0.24_{\rm stat.}\pm0.07_{\rm sys.}) \times 10^{-3}$, respectively.

hep-ex↗

arXiv2018

Measurement of the Branching Fraction For the Semi-Leptonic Decays $D^{0(+)}\to π^{-(0)}μ^+ν_μ$ and Test of Lepton Flavor Universality

Using a data sample corresponding to an integrated luminosity of $2.93\,\rm fb^{-1}$ taken at a center-of-mass energy of 3.773\,GeV with the BESIII detector operated at the BEPCII collider, we perform an analysis of the semi-leptonic decays $D^{0(+)}\to π^{-(0)}μ^+ν_μ$. The branching fractions of $D^0\to π^-μ^+ν_μ$ and $D^+\to π^0μ^+ν_μ$ are measured to be $(0.272 \pm 0.008_{\rm stat.} \pm 0.006_{\rm syst.})\%$ and $(0.350 \pm 0.011_{\rm stat.} \pm 0.010_{\rm syst.})\%$, respectively, where the former is of much improved precision compared to previous results and the latter is determined for the first time. Using these results along with previous BESIII measurements of $D^{0(+)}\to π^{-(0)}e^+ν_e$, we calculate the branching fraction ratios to be ${\mathcal R}^0\equiv {\mathcal B}_{D^{0}\to π^{-}μ^+ν_μ}/{\mathcal B}_{D^{0}\to π^{-}e^+ν_e}=0.922\pm 0.030_{\rm stat.}\pm0.022_{\rm syst.}$ and ${\mathcal R}^+\equiv {\mathcal B}_{D^{+}\to π^{0}μ^+ν_μ}/{\mathcal B}_{D^{+}\to π^{0}e^+ν_e}=0.964\pm 0.037_{\rm stat.}\pm0.026_{\rm syst.}$, which are compatible with the theoretical expectation of lepton flavor universality within $1.7σ$ and $0.5σ$, respectively. We also examine the branching fraction ratios in different four-momentum transfer square regions, and find no significant deviations from the standard model predictions.

hep-ex↗

arXiv2018

Observation of $h_1(1380)$ in the $J/ψ\to η^{\prime} K\bar K π$ Decay

Using $1.31 \times 10^9$ $J/ψ$ events collected by the BESIII detector at the BEPCII $e^+e^-$ collider, we report the first observation of the $h_1(1380)$ in $J/ψ\to η^{\prime} h_1(1380)$ with a significance of more than ten standard deviations. The mass and width of the possible axial-vector strangeonium candidate $h_1(1380)$ are measured to be $M = (1423.2 \pm 2.1 \pm 7.3)\mevcc$ and $Γ= (90.3 \pm 9.8 \pm 17.5)\mev$. The product branching fractions, assuming no interference, are determined to be $\mathcal{B}(J/ψ\to η^{\prime}h_1(1380)) \times \mathcal{B}(h_1(1380) \to K^{*}(892)^{+} K^{-} +c.c.) = (1.51 \pm 0.09 \pm 0.21) \times 10^{-4}$ in $η^{\prime}K^+K^-π^0$ mode and $\mathcal{B}(J/ψ\to η^{\prime}h_1(1380)) \times \mathcal{B}(h_1(1380) \to K^{*}(892)\bar K +c.c.) = (2.16 \pm 0.12 \pm 0.29) \times 10^{-4}$ in $η^{\prime}K_S^0K^{\pm}π^{\mp}$ mode. The first uncertainties are statistical and the second are systematic. Isospin symmetry violation is observed in the decays $h_1(1380) \to K^{*}(892)^{+} K^{-} +c.c.$ and $h_1(1380) \to K^{*}(892)^{0}\bar K^{0} +c.c.$. Based on the measured $h_1(1380)$ mass, the mixing angle between the states $h_1(1170)$ and $h_1(1380)$ is determined to be $(35.9\pm2.6)^{\circ}$, consistent with theoretical expectations.

hep-ex↗

arXiv2018

Measurements of $e^+e^- \to K_{S}^{0}K^{\pm}π^{\mp}π^0$ and $K_{S}^{0}K^{\pm}π^{\mp}η$ at center-of-mass energies from $3.90$ to $4.60~\mathrm{GeV}$

Using $5.2 \ \mathrm{fb}^{-1}$ $e^+ e^-$ annihilation data samples collected with the BESIII detector, we measure the cross sections of $e^+e^- \to K_S^0 K^\pm π^\mp π^0$ and $K_{S}^{0}K^{\pm}π^{\mp}η$ at center-of-mass energies from $3.90$ to $4.60$ GeV. In addition, we search for the charmonium-like resonance $Y(4260)$ decays into $K_{S}^{0}K^{\pm}π^{\mp}π^0$ and $K_{S}^{0}K^{\pm}π^{\mp}η$, and $Z_c^{0,\pm}(3900)$ decays into $K_{S}^{0}K^{\pm}π^{\mp,0}$ and $K_{S}^{0}K^{\pm}η$. Corresponding upper limits are provided since no clear signal is observed.

hep-ex↗

arXiv2018

First measurement of $e^+ e^- \to pK^{0}_{S}\bar{n}K^{-} + c.c.$ above open charm threshold

The process $e^+e^-\rightarrow pK^{0}_{S}\bar{n}K^{-} + c.c.$ and its intermediate processes are studied for the first time, using data samples collected with the BESIII detector at BEPCII at center-of-mass energies of 3.773, 4.008, 4.226, 4.258, 4.358, 4.416, and 4.600 GeV, with a total integrated luminosity of 7.4 fb$^{-1}$. The Born cross section of $e^+e^- \to p K^{0}_S\bar{n}K^- + c.c.$ is measured at each center-of-mass energy, but no significant resonant structure in the measured cross-section line shape between 3.773 and 4.600 GeV is observed. No evident structure is detected in the $pK^-$, $nK^{0}_S$, $pK^0_{S}$, $nK^+$, $p\bar{n}$, or $K^{0}_S K^-$ invariant mass distributions except for $Λ(1520)$. The Born cross sections of $e^+e^-\rightarrowΛ(1520)\bar{n}K^{0}_{S} + c.c.$ and $e^+e^-\rightarrow Λ(1520)\bar{p}K^{+} + c.c.$ are measured, and the 90\% confidence level upper limits on the Born cross sections of $e^+e^-\rightarrowΛ(1520)\barΛ(1520)$ are determined at the seven center-of-mass energies.

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arXiv2018

Polarization and Entanglement in Baryon-Antibaryon Pair Production in Electron-Positron Annihilation

Using a sample of $1.31\times 10^9$ $J/ψ$ events collected with the BESIII detector, we report the first observation of spin polarization of $Λ$ and $\barΛ$ hyperons from the coherent production in the $J/ψ\toΛ\barΛ$ decay. We measure the phase between the hadronic form factors to be $ΔΦ=(42.4\pm0.6\pm0.5)^\circ$. The decay parameters for $Λ\to pπ^-$ ($α_-$), $\barΛ\to\bar pπ^+$ ($α_+$) and $\barΛ\to\bar nπ^0$ ($\barα_0$) are measured to be $α_-=0.750\pm0.009\pm0.004$, $α_+=-0.758\pm0.010\pm0.007$ and $\barα_0=-0.692\pm0.016\pm0.006$, respectively. The obtained value of $α_-$ is higher by $(17\pm 3)\%$ than the current world average. In addition, the $CP$ asymmetry of $-0.006\pm0.012\pm0.007$ is extracted with substantially improved precision. The ratio $\barα_0/α_{+} = 0.913\pm 0.028 \pm 0.012$ is also measured.

hep-ex↗

arXiv2018

Amplitude analysis of the $K_{S}K_{S}$ system produced in radiative $J/ψ$ decays

An amplitude analysis of the $K_{S}K_{S}$ system produced in radiative $J/ψ$ decays is performed using the $(1310.6\pm7.0)\times10^{6}$ $J/ψ$ decays collected by the BESIII detector. Two approaches are presented. A mass-dependent analysis is performed by parameterizing the $K_{S}K_{S}$ invariant mass spectrum as a sum of Breit-Wigner line shapes. Additionally, a mass-independent analysis is performed to extract a piecewise function that describes the dynamics of the $K_{S}K_{S}$ system while making minimal assumptions about the properties and number of poles in the amplitude. The dominant amplitudes in the mass-dependent analysis include the $f_{0}(1710)$, $f_{0}(2200)$, and $f_{2}^\prime(1525)$. The mass-independent results, which are made available as input for further studies, are consistent with those of the mass-dependent analysis and are useful for a systematic study of hadronic interactions. The branching fraction of radiative $J/ψ$ decays to $K_{S}K_{S}$ is measured to be $(8.1 \pm 0.4) \times 10^{-4}$, where the uncertainty is systematic and the statistical uncertainty is negligible.

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arXiv2018

Observation of $ψ(3686) \to η' e^+ e^- $

Using a data sample of $448.1 \times 10^6$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay $ψ(3686) \to η' e^+ e^-$, with significances of 7.0$σ$ and 6.3$σ$ when reconstructing the $η'$ meson via its decay modes $η'\toγπ^+ π^-$ and $η'\toπ^+π^-η$ ($η\to γγ$), respectively. The weighted average branching fraction is determined to be $\mathcal{B}(ψ(3686) \to η' e^+ e^-)= (1.90 \pm 0.25 \pm 0.11) \times 10^{-6}$, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2018

Observation of $ψ(3686) \to n\bar{n}$ and improved measurement of $ψ(3686) \to p \bar{p}$

We observe the decay $ψ(3686) \to n \bar{n}$ for the first time and measure $ψ(3686) \to p \bar{p}$ with improved accuracy by using $1.07\times 10^8$ $ψ(3686)$ events collected with the BESIII detector. The measured branching fractions are $\mathcal{B}(ψ(3686) \to n \bar{n}) = (3.06 \pm 0.06 \pm 0.14)\times 10^{-4}$ and $\mathcal{B}(ψ(3686) \to p \bar{p}) = (3.05 \pm 0.02 \pm 0.12) \times 10^{-4}$. Here, the first uncertainties are statistical and the second ones systematic. With the hypothesis that the polar angular distributions of the neutron and proton in the center-of-mass system obey $1+α\cos^2θ$, we determine the $α$ parameters to be $α_{n\bar{n}} = 0.68 \pm 0.12 \pm 0.11$ and $α_{p\bar{p}} = 1.03 \pm 0.06 \pm 0.03$ for $ψ(3686)\to n\bar{n}$ and $ψ(3686)\to p\bar{p}$, respectively.

hep-ex↗

arXiv2018

Search for invisible decays of $ω$ and $ϕ$ with $J/ψ$ data at BESIII

Using a data sample of $(1310.6 \pm 7.0)\times 10^6$ $J/ψ$ events collected with the BESIII detector operating at the BEPCII collider, we perform the first experimental search for invisible decays of a light vector meson ($V=ω,ϕ$) via $J/ψ\to V η$ decays. The decay of $η\to π^+π^-π^0$ is utilized to tag the $V$ meson decaying into the invisible final state. No evidence for a significant invisible signal is observed, and the upper limits on the ratio of branching fractions at the 90\% confidence level are determined to be $\frac{\mathcal{B}(ω\rightarrow \rm{invisible})}{\mathcal{B}(ω\to π^+π^-π^0)} < 8.1 \times 10^{-5}$ and $\frac{\mathcal{B}(ϕ\to \rm{invisible})}{\mathcal{B}(ϕ\to K^+K^-)} < 3.4\times 10^{-4}$. By using the world average values of $\mathcal{B}(ω\to π^+π^-π^0)$ and $\mathcal{B}(ϕ\to K^+K^-)$, the upper limits on the decay branching fractions at the $90\%$ confidence level are set as $\mathcal{B}(ω\to \rm{invisible})< 7.3 \times 10^{-5}$ and $\mathcal{B}(ϕ\to \rm{invisible})< 1.7\times 10^{-4}$, respectively.

hep-ex↗

arXiv2018

Measurement of e+e- --> D Dbar Cross Sections at the psi(3770) Resonance

We report new measurements of the cross sections for the production of D Dbar final states at the psi(3770) resonance. Our data sample consists of an integrated luminosity of 2.93/fb of e+e- annihilation data produced by the BEPCII collider and collected and analyzed with the BESIII detector. We exclusively reconstruct three D0 and six D+ hadronic decay modes and use the ratio of the yield of fully reconstructed D Dbar events ("double tags") to the yield of all reconstructed D or Dbar mesons ("single tags") to determine the number of D0 D0bar and D+D- events, benefiting from the cancellation of many systematic uncertainties. Combining these yields with an independent determination of the integrated luminosity of the data sample, we find the cross sections to be σ(e+e- --> D0 D0bar)=(3.615 +- 0.010 +- 0.038) nb and σ(e+e- --> D+D-)=(2.830 +- 0.011 +- 0.026) nb, where the uncertainties are statistical and systematic, respectively.

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arXiv2018

T0 Fan-out for Back-n White Neutron Facility at CSNS

the main physics goal for Back-n white neutron facility at China Spallation Neutron Source (CSNS) is to measure nuclear data. The energy of neutrons is one of the most important parameters for measuring nuclear data. Method of time of flight (TOF) is used to obtain the energy of neutrons. The time when proton bunches hit the thick tungsten target is considered as the start point of TOF. T0 signal, generated from the CSNS accelerator, represents this start time. Besides, the T0 signal is also used as the gate control signal that triggers the readout electronics. Obviously, the timing precision of T0 directly affects the measurement precision of TOF and controls the running or readout electronics. In this paper, the T0 fan-out for Back-n white neutron facility at CSNS is proposed. The T0 signal travelling from the CSNS accelerator is fanned out to the two underground experiment stations respectively over long cables. To guarantee the timing precision, T0 signal is conditioned with good signal edge. Furthermore, techniques of signal pre-emphasizing and equalizing are used to improve signal quality after T0 being transmitted over long cables with about 100 m length. Experiments show that the T0 fan-out works well, the T0 signal transmitted over 100 m remains a good time resolution with a standard deviation of 25 ps. It absolutely meets the required accuracy of the measurement of TOF.

physics.ins-det↗

arXiv2018

Design of Prototype Front-end Digital Module for Direct Dark Matter Detection based on LAr

Liquid argon (LAr) with a high light yield of approximately 40 photons per keV is an attractive target for the direct detection of weakly interacting massive particles (WIMPs), which are well motivated galactic dark matter candidates. We studies a front-end electronics design for a LAr dark matter detector with the scintillation read out by PMT, which has an input dynamic range from 5pC to 1nC, and high resolution that single photoelectron can be distinguished. In this paper, we present the design of front-end digital module (FDM) which is the important portion of electronics. The prototype FDM is equipped with 14-bit 1-GSPS analog-to-digital converters (ADC), and the performance of prototype FDM had been test in lab (e.g. ENOB is 10.40 bits @298 MHz). Moreover, this prototype FDM had been tested with LAr detector collaboratively and test results are also presented.

physics.ins-det↗

arXiv2018

Electronics of Time-of-flight Measurement for Back-n at CSNS

Back-n is a white neutron experimental facility at China Spallation Neutron Source (CSNS). The time structure of the primary proton beam make it fully applicable to use TOF (time-of-flight) method for neutron energy measuring. We implement the electronics of TOF measurement on the general-purpose readout electronics designed for all of the seven detectors in Back-n. The electronics is based on PXIe (Peripheral Component Interconnect Express eXtensions for Instrumentation) platform, which is composed of FDM (Field Digitizer Modules), TCM (Trigger and Clock Module), and SCM (Signal Conditioning Module). T0 signal synchronous to the CSNS accelerator represents the neutron emission from the target. It is the start of time stamp. The trigger and clock module (TCM) receives, synchronizes and distributes the T0 signal to each FDM based on the PXIe backplane bus. Meantime, detector signals after being conditioned are fed into FDMs for waveform digitizing. First sample point of the signal is the stop of time stamp. According to the start, stop time stamp and the time of signal over threshold, the total TOF can be obtained. FPGA-based (Field Programmable Gate Array) TDC is implemented on TCM to accurately acquire the time interval between the asynchronous T0 signal and the global synchronous clock phase. There is also an FPGA-based TDC on FDM to accurately acquire the time interval between T0 arriving at FDM and the first sample point of the detector signal, the over threshold time of signal is obtained offline. This method for TOF measurement is efficient and not needed for additional modules. Test result shows the accuracy of TOF is sub-nanosecond and can meet the requirement for Back-n at CSNS.

physics.ins-det↗

arXiv2018

Observation of $a^{0}_{0}(980)$-$f_{0}(980)$ Mixing

We report the first observation of $a^{0}_{0}(980)$-$f_{0}(980)$ mixing in the decays of $J/ψ\toϕf_{0}(980)\toϕa^{0}_{0}(980)\toϕηπ^{0}$ and $χ_{c1}\to a^{0}_{0}(980)π^{0}\to f_{0}(980)π^{0}\toπ^{+}π^{-}π^{0}$, using data samples of $1.31\times10^{9}$ $J/ψ$ events and $4.48\times10^{8}$ $ψ(3686)$ events accumulated with the BESIII detector. The signals of $f_{0}(980)\to a^{0}_{0}(980)$ and $a^{0}_{0}(980)\to f_{0}(980)$ mixing are observed at levels of statistical significance of $7.4σ$ and $5.5σ$, respectively. The corresponding branching fractions and mixing intensities are measured and the constraint regions on the coupling constants, $g_{a_{0}K^{+}K^{-}}$ and $g_{f_{0}K^{+}K^{-}}$, are estimated. The results improve the understanding of the nature of $a^{0}_{0}(980)$ and $f_{0}(980)$.

hep-ex↗

arXiv2018

Precision Study of $η^\prime\rightarrowγπ^+π^-$ Decay Dynamics

Using a low background data sample of $9.7\times10^{5}$ $Jψ\rightarrowγη^\prime$, $η^\prime\rightarrowγπ^+π^-$ events, which are 2 orders of magnitude larger than those from the previous experiments, recorded with the BESIII detector at BEPCII, the decay dynamics of $η^\prime\rightarrowγπ^+π^-$ are studied with both model-dependent and model-independent approaches. The contributions of $ω$ and the $ρ(770)-ω$ interference are observed for the first time in the decays $η^\prime\rightarrowγπ^+π^-$ in both approaches. Additionally, a contribution from the box anomaly or the $ρ(1450)$ resonance is required in the model-dependent approach, while the process specific part of the decay amplitude is determined in the model-independent approach.

hep-ex↗

arXiv2018

Measurements of Absolute Branching Fractions for $Λ^+_c\toΞ^0K^+$ and $Ξ(1530)^0K^+$

We report the first measurements of absolute branching fractions for the $W$-exchange-only processes $Λ^+_c\toΞ^0K^+$ and $Λ^+_c\toΞ(1530)^0K^+$ with the double-tag technique, by analyzing an $e^{+}e^{-}$ collision data sample, that corresponds to an integrated luminosity of 567 pb$^{-1}$ collected at a center-of-mass energy of 4.6 GeV by the BESIII detector. The branching fractions are measured to be $\mathcal{B}(Λ^+_c\toΞ^0K^+)=(5.90\pm0.86\pm0.39)\times10^{-3}$ and $\mathcal{B}(Λ^+_c\toΞ(1530)^0K^+)=(5.02\pm0.99\pm0.31)\times10^{-3}$, where the first uncertainties are statistical and the second systematic. Our results are more precise than the previous relative measurements.

hep-ex↗

arXiv2018

Measurement of the absolute branching fraction of the inclusive semileptonic $Λ_c^+$ decay

Using a data sample corresponding to an integrated luminosity of 567 pb$^{-1}$ collected at a center-of-mass energy of $\sqrt{s}=4.6$ GeV with the BESIII detector, we measure the absolute branching fraction of the inclusive semileptonic $Λ_c^+$ decay with a double-tag method. We obtain $\mathcal{B}(Λ_c^+ \rightarrow X e^+ ν_e) = (3.95\pm0.34\pm0.09)\%$, where the first uncertainty is statistical and the second systematic. Using the known $Λ_c^+$ lifetime and the charge-averaged semileptonic decay width of nonstrange charmed measons ($D^0$ and $D^+$), we obtain the ratio of the inclusive semileptonic decay widths $Γ(Λ_c^+ \rightarrow X e^+ ν_e)/\barΓ(D\rightarrow X e^+ ν_e)= 1.26\pm0.12$.

hep-ex↗