arXiv subjects

C. Chen

Publications and source records attributed to C. Chen.

At least 127 records · Page 7Linked to original sources

arXiv2024

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

We report an improved study of the semileptonic decay $D^0 \rightarrow \bar{K}^0π^-e^+ν_{e}$ based on a sample of $7.9~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data collected at a center-of-mass energy of 3.773~GeV with the BESIII detector at the BEPCII collider. The branching fraction of this decay is measured to be $\mathcal{B}(D^0\rightarrow \bar{K}^0π^-e^+ν_{e}) = (1.444 \pm 0.022_{\rm stat} \pm 0.024_{\rm syst})\%$, which is the most precise to date, where the first uncertainty is statistical and the second is systematic. Based on investigation of the decay dynamics, we find that the decay is dominated by the $K^{*}(892)^-$ component and present an improved measurement of its branching fraction to be $\mathcal{B}(D^0\rightarrow K^{*}(892)^-e^+ν_e) = (2.039 \pm 0.032_{\rm stat} \pm 0.034_{\rm syst})\%$. We also determine the ratios of the hadronic form factors for the $K^{*}(892)^-e^+ν_e$ decay to be $r_{V} = V(0)/A_1(0) = 1.48 \pm 0.05_{\rm stat} \pm 0.02_{\rm syst}$ and $r_{2} = A_2(0)/A_1(0) = 0.70 \pm 0.04_{\rm stat} \pm 0.02_{\rm syst}$, where $V(0)$ is the vector form factor and $A_{1,2}(0)$ are the axial form factors. In addition, the $\bar{K}^0π^-$ $\mathcal{S}$-wave component is found to account for $(5.87 \pm 0.32_{\rm stat} \pm 0.16_{\rm syst})\%$ of the total decay rate, corresponding to a branching fraction of $\mathcal{B}[D^0\rightarrow (\bar{K}^0π^-)_{S-{\rm wave}}e^+ν_e] = (0.085 \pm 0.005_{\rm stat} \pm 0.003_{\rm syst})\%$.

hep-ex↗

arXiv2024

Measurement of the integrated luminosity of the data collected at 3.773 GeV by BESIII from 2021 to 2024

We present a measurement of the integrated luminosity of $e^+e^-$ collision data collected with the BESIII detector at the BEPCII collider at a center-of-mass energy of $E_{\rm cm} = 3.773$~GeV. The integrated luminosities of the data sets taken from December 2021 to June 2022, from November 2022 to June 2023, and from October 2023 to February 2024 are determined to be $4.995 \pm 0.019$~fb$^{-1}$, $8.157 \pm 0.031$~fb$^{-1}$, and $4.191 \pm 0.016$~fb$^{-1}$, respectively, by analyzing large angle Bhabha scattering events. The uncertainties are dominated by systematic effects and the statistical uncertainties are negligible. Our results provide essential input for future analyses and precision measurements.

hep-ex↗

arXiv2024

Study of the decay ψ(3686) \to Σ^{0}\barΣ^{0}ϕ

Using $(27.12\pm 0.14)\times 10^{8}$ $ψ(3686)$ events collected with the BESIII detector operating at the BEPCII collider, the decay $ψ(3686)\toΣ^{0}\barΣ^{0}ϕ$ is observed for the first time with a statistical significance of 7.6$σ$. Its branching fraction is measured to be $(2.64 \pm 0.32_{\textrm{stat}} \pm 0.12_{\textrm{sys}}) \times 10^{-6}$, where the first uncertainty is statistical and the second is systematic. In addition, we search for potential intermediate states in the $Σ^{0}ϕ$($\barΣ^{0}ϕ$) invariant mass distribution and a possible threshold enhancement in the $Σ^{0}\barΣ^{0}$ system, but no conclusive evidence of is observed.

hep-ex↗

arXiv2024

Measurement of $CP$ asymmetries in $B^0\toη'K^0_s$ decays at Belle II

We describe a measurement of charge-parity ($CP$) violation asymmetries in $B^0\toη'K^0_S$ decays using Belle II data. We consider $η'\toη(\toγγ)π^+π^-$ and $η'\toρ(\toπ^+π^-)γ$ decays. The data were collected at the SuperKEKB asymmetric-energy $e^+e^-$ collider between the years 2019 and 2022, and contain $(387\pm 6) \times 10^6$ bottom-antibottom meson pairs. We reconstruct $829\pm35$ signal decays and extract the $CP$ violating parameters from a fit to the distribution of the proper-decay-time difference between the two $B$ mesons. The measured direct and mixing-induced $CP$ asymmetries are $\text{C}_{η'K^0_S} = -0.19 \pm 0.08 \pm 0.03 $ and $\text{S}_{η'K^0_S} = +0.67 \pm 0.10 \pm 0.04 $, respectively, where the first uncertainties are statistical and the second are systematic. These results are in agreement with current world averages and standard model predictions.

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arXiv2024

Search for lepton-flavor-violating $τ^- \to μ^-μ^+μ^-$ decays at Belle II

We present the result of a search for the charged-lepton-flavor violating decay $τ^- \to μ^-μ^+μ^-$ using a $424fb^{-1}$ sample of data recorded by the Belle II experiment at the SuperKEKB $e^{-}e^{+}$ collider. The selection of $e^{-}e^{+}\toτ^+τ^-$ events is based on an inclusive reconstruction of the non-signal tau decay, and on a boosted decision tree to suppress background. We observe one signal candidate, which is compatible with the expectation from background processes. We set a $90\%$ confidence level upper limit of $1.9 \times 10^{-8}$ on the branching fraction of the \taumu decay, which is the most stringent bound to date.

hep-ex↗

arXiv2024

Thickness-dependent Topological Phases and Flat Bands in Rhombohedral Multilayer Graphene

Rhombohedral multilayer graphene has emerged as an extraordinary platform for investigating exotic quantum states, such as superconductivity and fractional quantum anomalous Hall effects, mainly due to the existence of topological surface flatbands. Despite extensive research efforts, a systematic spectroscopic investigation on the evolution of its electronic structure from thin layers to bulk remains elusive. Using state-of-the-art angle-resolved photoemission spectroscopy with submicron spatial resolution, we directly probe and trace the thickness evolution of the topological electronic structures of rhombohedral multilayer graphene. As the layer number increases, the gapped subbands transform into the 3D Dirac nodes that spirals in the momentum space; while the flatbands are constantly observed around Fermi level, and eventually evolve into the topological drumhead surface states. This unique thickness-dependent topological phase transition can be well captured by the 3D generalization of 1D Su-Schrieffer-Heeger chain in thin layers, to the topological Dirac nodal spiral semimetal in the bulk limit. Our findings establish a solid foundation for exploring the exotic quantum phases with nontrivial topology and correlation effects in rhombohedral multilayer graphene.

cond-mat.mes-hall↗

arXiv2024

Search for lepton number violating decays of $D_s^+\to h^-h^0e^+e^+$

Based on 7.33 fb$^{-1}$ of $e^+e^-$ collision data collected by the BESIII detector operating at the BEPCII collider at center-of-mass energies from 4.128 to 4.226 GeV, a search for the Majorana neutrino $ν_m$ is conducted in the lepton-number-violating decays of $D_s^+\to h^-h^0e^+e^+$. Here, $h^-$ represents a $K^-$ or $π^-$, and $h^0$ represents a $π^0$, $K_S^0$ or $ϕ$. No significant signal is observed, and the upper limits of their branching fractions at the 90\% confidence level are determined to be $\mathcal{B}(D_s^+\to ϕπ^-e^+e^+) < 6.9 \times 10^{-5}$, $\mathcal{B}(D_s^+\to ϕK^-e^+e^+) < 9.9 \times 10^{-5}$, $\mathcal{B}(D_s^+\to K_S^0π^-e^+e^+) < 1.3 \times 10^{-5}$, $\mathcal{B}(D_s^+\to K_S^0K^-e^+e^+) < 2.9 \times 10^{-5}$, $\mathcal{B}(D_s^+\to π^-π^0e^+e^+) < 2.9 \times 10^{-5}$ and $\mathcal{B}(D_s^+\to K^-π^0e^+e^+) < 3.4 \times 10^{-5}$. The Majorana neutrino is searched for with different mass assumptions within the range [0.20, 0.80] GeV$/c^2$ in the decay of $D_s^+\toϕe^+ν_m$ with $ν_m\toπ^-e^+$, and the upper limits of the branching fractions at the 90\% confidence level are at the level of $10^{-5}-10^{-2}$, depending on the mass of the Majorana neutrino.

hep-ex↗

arXiv2024

Discovery of an Antiferromagnetic Topological Nodal-line Kondo Semimetal

The symbiosis of strong interactions, flat bands, topology and symmetry has led to the discovery of exotic phases of matter, including fractional Chern insulators, correlated moiré topological superconductors, and Dirac and Weyl semimetals. Correlated metals, such as those present in Kondo lattices, rely on the screening of local moments by a sea of non-magnetic conduction electrons. Here, we report on a unique topological Kondo lattice compound, CeCo2P2, where the Kondo effect - whose existence under the magnetic Co phase is protected by PT symmetry - coexists with antiferromagnetic order emerging from the flat bands associated with the Co atoms. Remarkably, this is the only known Kondo lattice compound where magnetic order occurs in non-heavy electrons, and puzzlingly, at a temperature significantly higher than that of the Kondo effect. Furthermore, at low temperatures, the emergence of the Kondo effect, in conjunction with a glide-mirror-z symmetry, results in a nodal line protected by bulk topology near the Fermi energy. These unusual properties, arising from the interplay between itinerant and correlated electrons from different constituent elements, lead to novel quantum phases beyond the celebrated topological Kondo insulators and Weyl Kondo semimetals. CeCo2P2 thus provides an ideal platform for investigating narrow bands, topology, magnetism, and the Kondo effect in strongly correlated electron systems.

cond-mat.str-el↗

arXiv2024

Model-independent determination of the strong-phase difference between $D^0$ and $\bar{D}^0 \to π^+π^-π^+π^-$ decays

Measurements of the strong-phase difference between $D^0$ and $\bar{D}^0\toπ^+π^-π^+π^-$ are performed in bins of phase space. The study exploits a sample of quantum-correlated $D\bar{D}$ mesons collected by the BESIII experiment in $e^+e^-$ collisions at a center-of-mass energy of 3.773~GeV, corresponding to an integrated luminosity of 2.93~fb$^{-1}$. Here, $D$ denotes a neutral charm meson in a superposition of flavor eigenstates. The reported results are valuable for measurements of the $C\!P$-violating phase $γ$ (also denoted $ϕ_3$) in $B^\pm \to DK^\pm$, $D \to π^+π^-π^+π^-$ decays, and the binning schemes are designed to provide good statistical sensitivity to this parameter. The expected uncertainty on $γ$ arising from the precision of the strong-phase measurements, when applied to very large samples of $B$-meson decays, is around $1.5^\circ$ or $2^\circ$, depending on the binning scheme. The binned strong-phase parameters are combined to give a value of $F_+^{4π} = 0.746 \pm 0.010 \pm 0.004$ for the $C\!P$-even fraction of $D^0 \to π^+π^-π^+π^-$ decays, which is around 30\% more precise than the previous best measurement of this quantity.

hep-ex↗

arXiv2024

Observation of $D^+\to f_0(500)μ^+ν_μ$ and study of $D^+\to π^+π^-\ell^+ν_\ell$ decay dynamics

Using $2.93~\mathrm{fb}^{-1}$ of $e^+e^-$ collision data collected with the BESIII detector at the center-of-mass energy of 3.773 GeV,we investigate the semileptonic decays $D^+\to π^+π^- \ell^+ν_\ell$ ($\ell=e$ and $μ$). The $D^+\to f_0(500)μ^+ν_μ$ decay is observed for the first time. By analyzing simultaneously the differential decay rates of $D^+\to f_0(500) μ^+ν_μ$ and $D^+\to f_0(500) e^+ν_e$ in different $\ell^+ν_\ell$ four-momentum transfer intervals, the product of the relevant hadronic form factor $f^{f_0}_{+}(0)$ and the magnitude of the $c\to d$ Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|$ is determined to be $f_{+}^{f_0} (0)|V_{cd}|=0.143\pm0.014_{\rm stat}\pm0.011_{\rm syst}$ for the first time. With the input of $|V_{cd}|$ from the global fit in the standard model, we determine $f_{+}^{f_0} (0)=0.63\pm0.06_{\rm stat}\pm0.05_{\rm syst}$. The absolute branching fractions of $D^+\to f_0(500)_{(π^+π^-)}μ^+ν_μ$ and $D^+\to ρ^0_{(π^+π^-)} μ^+ν_μ$ are determined as $(0.72\pm0.13_{\rm stat}\pm0.08_{\rm syst})\times10^{-3}$ and $(1.64\pm0.13_{\rm stat}\pm0.10_{\rm syst})\times 10^{-3}$. Combining these results with those of previous BESIII measurements on their semielectronic counterparts from the same data sample, we test lepton flavor universality by measuring the branching fraction ratios ${\mathcal B}_{D^+\to ρ^0 μ^+ν_μ}/{\mathcal B}_{D^+\to ρ^0 e^+ν_e}=0.88\pm0.10$ and ${\mathcal B}_{D^+\to f_0(500) μ^+ν_μ}/{\mathcal B}_{D^+\to f_0(500) e^+ν_e}=1.14\pm0.26$, which are compatible with the standard model expectation.

hep-ex↗

arXiv2024

Measurement of Born cross sections of $e^+e^-\toΞ^0\barΞ^0$ and search for charmonium(-like) states at $\sqrt{s}$ = 3.51-4.95 GeV

Using $e^+e^-$ collision data collected by the BESIII detector at BEPCII corresponding to an integrated luminosity of 30 $\rm fb^{-1}$, we measure Born cross sections and effective form factors for the process $e^+e^-\toΞ^0\barΞ^0$ at forty-five center-of-mass energies between 3.51 and 4.95 GeV. The dressed cross section is fitted, assuming a power-law function plus a charmonium(-like) state, i.e., $ψ(3770)$, $ψ(4040)$, $ψ(4160)$, $ψ(4230)$, $ψ(4360)$, $ψ(4415)$ or $ψ(4660)$. No significant charmonium(-like) state decaying into $Ξ^0\barΞ^0$ is observed. Upper limits at the 90% confidence level on the product of the branching fraction and the electronic partial width are provided for each decay. In addition, ratios of the Born cross sections and the effective form factors for $e^+e^-\toΞ^0\barΞ^0$ and $e^+e^-\toΞ^-\barΞ^+$ are also presented to test isospin symmetry and the vector meson dominance model.

hep-ex↗

arXiv2024

Search for $η_c(2S)\to p\bar{p}$ and branching fraction measurements of $χ_{cJ} \to p\bar{p}$ via $ψ(2S)$ radiative decays

Using $(27.12\pm0.14) \times 10^{8}$ $ψ(2S)$ events collected by the BESIII detector operating at BEPCII, we search for the decay $η_c(2S)\to p\bar{p}$ via the process $ψ(2S)\to γη_c(2S)$, and only find a signal with a significance of $1.7\,σ$. The upper limit of the product branching fraction at the 90% confidence level is determined to be $\mathcal{B}(ψ(2S)\to γη_c(2S))\times \mathcal{B}(η_c(2S)\to p\bar{p})<2.4\times 10^{-7}$. The branching fractions of $χ_{cJ}\to p\bar{p}~(J=0,1,2)$ are also measured to be $\mathcal{B}(χ_{c0}\to p\bar{p})=(2.51\pm0.02\pm0.08)\times 10^{-4}$, $\mathcal{B}(χ_{c1}\to p\bar{p})=(8.16\pm0.09\pm0.25)\times 10^{-4}$, and $\mathcal{B}(χ_{c2}\to p\bar{p})=(8.33\pm0.09\pm0.22)\times 10^{-4}$, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2024

Measurement of the branching fractions of the decays $Λ_{c}^{+}\rightarrowΛK_{S}^{0}K^{+}$, $Λ_{c}^{+}\rightarrowΛK_{S}^{0}π^{+}$ and $Λ_{c}^{+}\rightarrowΛK^{*+}$

Studies are performed of the Cabibbo-favored decay $Λ_{c}^{+}\toΛK_{S}^{0}K^+$ and the singly Cabibbo-suppressed decay $Λ_{c}^{+}\toΛK_{S}^{0}π^+$, based on a sample of $e^{+}e^{-}$ collision data, corresponding to an integrated luminosity of 4.5 fb$^{-1}$, accumulated at center-of-mass energies between $4599.53$ MeV and $4698.82$ MeV with the BESIII detector. The decay $Λ_{c}^{+}\toΛK_{S}^{0}π^+$ is observed for the first time. The branching fractions of $Λ_{c}^{+}\toΛK_{S}^{0}K^+$ and $Λ_{c}^{+}\toΛK_{S}^{0}π^+$ are measured to be $(3.04\pm0.30\pm0.16)\times 10^{-3}$ and $(1.73\pm0.27\pm0.10)\times 10^{-3}$, respectively, where the first uncertainties are statistical and the second are systematic. These results correspond to the most precise measurement of these quantities for both decays. Evidence of a $K^{*+}$ contribution in the $Λ_{c}^{+}\toΛK_{S}^{0}π^+$ decay is found with a statistical significance of $4.7σ$. The branching fraction of $Λ_{c}^{+}\toΛK^{*+}$ is calculated under three possible interference scenarios.

hep-ex↗

arXiv2024

Simultaneous study of acoustic and optic phonon scattering of electrons and holes in undoped $\mathrm{GaAs}$/$\mathrm{Al_{x} Ga_{1-x} As}$ heterostructures

The study of phonon coupling in doped semiconductors via electrical transport measurements is challenging due to unwanted temperature-induced effects such as dopant ionisation and parallel conduction. Here, we study phonon scattering in 2D electrons and holes in the $1.6-92.5$K range without the use of extrinsic doping, where both acoustic and longitudinal optic (LO) phonons come into effect. We use undoped GaAs/$\mathrm{Al_{x} Ga_{1-x} As}$ heterostructures and examine the temperature dependence of the sample resistivity, extracting phonon coupling constants and the LO activation energy. Our results are consistent with results obtained through approaches other than transport measurements, and highlight the benefit of this approach for studying electron-phonon and hole-phonon coupling.

cond-mat.mes-hall↗

arXiv2024

Observation of $χ_{c0}\toΣ^{+}\barΣ^{-}η$ and evidence for $χ_{c1,2}\toΣ^{+}\barΣ^{-}η$

Using $(27.12\pm 0.14)\times10^{8}$ $ψ(3686)$ events collected with the BESIII detector, the decay $χ_{c0}\toΣ^{+}\barΣ^{-}η$ is observed for the first time with a statistical significance of $7.0σ$, and evidence for $χ_{c1}\toΣ^{+}\barΣ^{-}η$ and $χ_{c2}\toΣ^{+}\barΣ^{-}η$ is found with statistical significances of $4.3σ$ and $4.6σ$, respectively. The branching fractions are determined to be $\mathcal{B}(χ_{c0}\toΣ^{+}\barΣ^{-}η)=({1.26 \pm 0.20 \pm 0.13}) \times 10^{-4}, ~\mathcal{B}(χ_{c1}\toΣ^{+}\barΣ^{-}η)=({5.10 \pm 1.21 \pm 0.67}) \times 10^{-5}$, and $\mathcal{B}(χ_{c2}\toΣ^{+}\barΣ^{-}η)=({5.46 \pm 1.18 \pm 0.50}) \times 10^{-5}$, where the first uncertainties are statistical, and the second ones are systematic.

hep-ex↗

arXiv2024

Observation of the Singly Cabibbo-Suppressed Decay $Λ_c^{+}\to pπ^0$

Utilizing 4.5${~\rm{fb}}^{-1}$ of $e^+e^-$ annihilation data collected with the BESIII detector at the BEPCII collider at center-of-mass energies between 4.600 and 4.699 GeV, the first observation of the singly Cabibbo-suppressed decay $Λ_c^{+}\to pπ^0$ is presented, with a statistical significance of $5.4σ$. The ratio of the branching fractions of $Λ_c^{+}\to pπ^0$ and $Λ_c^{+}\to pη$ is measured as $\mathcal{B}(Λ_c^{+}\to pπ^0)/\mathcal{B}(Λ_c^{+}\to pη)=(0.120\pm0.026_{\rm stat.}\pm0.007_{\rm syst.})$. This result resolves the longstanding discrepancy between earlier experimental searches, providing both a decisive conclusion and valuable input for QCD-inspired theoretical models. A sophisticated deep learning approach using a Transformer-based architecture is employed to distinguish the signal from the prevalent hadronic backgrounds, complemented by thorough validation and systematic uncertainty quantification.

hep-ex↗

arXiv2024

Search for $η_c(2S)\to 2(π^+π^-)$ and improved measurement of $χ_{cJ}\to 2(π^+π^-)$

We search for the hadronic decay $η_c(2S)\to 2(π^+π^-)$ in the $ψ(3686)\toγη_c(2S)$ radiative decay using $(27.12\pm 0.14)\times 10^8$ $ψ(3686)$ events collected by the BESIII detector at the BEPCII collider. No significant signal is found, and the upper limit of $\mathcal{B}[ψ(3686)\toγη_c(2S)]\mathcal{B}[η_c(2S)\to 2(π^+π^-)]$ is determined to be $0.78\times 10^{-6}$ at the 90\% confidence level. Using $ψ(3686)\toγχ_{cJ}$ transitions, we also measure the branching fractions of $\mathcal{B}[χ_{cJ(J=0,1,2)}\to 2(π^+π^-)]$, which are $\mathcal{B}[χ_{c0}\to 2(π^+π^-)]=(2.127\pm 0.002~(\mathrm{stat.})\pm 0.101~(\mathrm{syst.}))$\%, $\mathcal{B}[χ_{c1}\to 2(π^+π^-)]=(0.685\pm 0.001~(\mathrm{stat.})\pm 0.031~\mathrm{syst.}))$\%, and $\mathcal{B}[χ_{c2}\to 2(π^+π^-)]=(1.153\pm 0.001~(\mathrm{stat.})\pm 0.063~(\mathrm{syst.}))$\%.

hep-ex↗

arXiv2024

Search for $e^{+}e^{-} \to ϕχ_{c0}$ and $ϕη_{c2}(1D)$ at center-of-mass energies from 4.47 to 4.95 GeV

Utilizing a data set of $6.7$ fb$^{-1}$ from electron-positron collisions recorded by the BESIII detector at the BEPCII storage ring, a search is conducted for the processes $e^{+}e^{-} \to ϕχ_{c0}$ and $ϕη_{c2}(1D)$ across center-of-mass energies from 4.47 to 4.95 GeV. In the absence of any significant signals, upper limits are set. These include limits on the Born cross sections for $e^{+}e^{-} \to ϕχ_{c0}$, as well as the product of the Born cross section for $e^{+}e^{-} \to ϕη_{c2}(1D)$ and a sum of five branching fractions. Furthermore, the product of the electronic width of $Y(4660)$ and the branching fraction of the $Y(4660) \to ϕχ_{c0}$, denoted as $Γ^{Y(4660)}_{e^{+}e^{-}} \mathcal{B}_{Y(4660) \to ϕχ_{c0}}$, is determined to be $< 0.40$ eV at the 90\% confidence level.

hep-ex↗