Using 58×106J/ψ events collected with the Beijing Spectrometer (BESII) at the Beijing Electron Positron Collider (BEPC), the branching fractions of J/ψ to pp¯η and pp¯η′ are determined. The ratio ...Γ(J/ψ→pp¯η)Γ(J/ψ→pp¯) obtained by this analysis agrees with expectations based on soft-pion theorem calculations.
Phys.Rev.Lett. 131 (2023) 12, 121801 We report the first search for $\bar\Lambda$--$\Lambda$ oscillations in the
decay $J/\psi \to p K^- \bar{\Lambda} + c.c.$ by analyzing $1.31\times10^9$
$J/\psi$ ...events accumulated with the BESIII detector at the BEPCII collider.
The $J/\psi$ events are produced using $e^+e^-$ collisions at a center of mass
energy $\sqrt{s}= 3.097$~GeV. No evidence for hyperon oscillations is observed.
The upper limit for the oscillation rate of $\bar\Lambda$ to $\Lambda$ hyperons
is determined to be $\mathcal{P}(\Lambda)=\frac{\mathcal{B}(J/\psi\to
pK^-\Lambda+c.c.)}{\mathcal{B}(J/\psi\to
pK^-\bar\Lambda+c.c.)}<4.4\times10^{-6}$ corresponding to an oscillation
parameter $\delta m_{\Lambda\bar\Lambda}$ of less than $3.8\times10^{-18}$~GeV
at the 90\% confidence level.
Phys. Rev. D 106, 112002 (2022) Using a data sample of $(448.1 \pm 2.9)\times10^6 ~\psi(3686)$ decays
collected at an $e^+ e^-$ center-of-mass energy of $3.686~\rm{GeV}$ by the
BESIII detector at ...BEPCII, we report an observation of the hindered
electromagnetic Dalitz decay $\psi(3686) \to e^+ e^- \eta_c$ with a
significance of $7.9\sigma$. The branching fraction is determined to be
$\mathcal{B} (\psi(3686) \to e^+ e^- \eta_c) = (3.77 \pm 0.40_{\rm stat.} \pm
0.18_{\rm syst.})\times 10^{-5}$, agreeing well with the prediction of the
vector meson dominance model. This is the first measurement of the
electromagnetic Dalitz transition between the $\psi(3686)$ and the $\eta_c$,
which provides new insight into the electromagnetic properties of this decay,
and offers new opportunities to measure the absolute branching fractions of
$\eta_c$ decays.
Phys. Rev. D 106, 092004 (2022) A measurement of the $C\!P$-even fraction of the decay
$D^{0}\to\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ is performed with a quantum-correlated
$\psi(3770)\to D\bar{D}$ data ...sample collected by the BESIII experiment,
corresponding to an integrated luminosity of 2.93 $\textrm{fb}^{-1}$. Using a
combination of $C\!P$ eigenstates, $D \to \pi^+\pi^-\pi^0$ and $D \to
K_{S,L}^0\pi^{+}\pi^{-}$ as tagging modes, the $C\!P$-even fraction is measured
to be $F_{+}^{4\pi} = 0.735 \pm 0.015 \pm 0.005$, where the first uncertainty
is statistical and the second is systematic. This is the most precise
determination of this quantity to date. It provides valuable model-independent
input for the measurement of the CKM angle $\gamma$ with $B^\pm\to D K^\pm$
decays, and for time-dependent studies of $C\!P$ violation and mixing in the
$D^{0}$-$\bar{D}^{0}$ system.
Eur. Phys. J. C 82, 1009 (2022) The decay $D\to K^-\pi^+$ is studied in a sample of quantum-correlated
$D\bar{D}$ pairs, based on a data set corresponding to an integrated luminosity
of ...2.93\,fb$^{-1}$ collected at the $\psi(3770)$ resonance by the BESIII
experiment. The asymmetry between $C\!P$-odd and $C\!P$-even eigenstate decays
into $K^-\pi^+$ is determined to be ${\cal A}_{K\pi} = 0.132 \pm 0.011 \pm
0.007$, where the first uncertainty is statistical and the second is
systematic. This measurement is an update of an earlier study exploiting
additional tagging modes, including several decay modes involving a $K^0_L$
meson. The branching fractions of the $K^0_L$ modes are determined as input to
the analysis in a manner that is independent of any strong phase uncertainty.
Using the predominantly $C\!P$-even tag $D\to \pi^+\pi^-\pi^0$ and the ensemble
of $C\!P$-odd eigenstate tags, the observable ${\cal A}_{K\pi}^{\pi\pi\pi^0}$
is measured to be $0.130 \pm 0.012 \pm 0.008$. The two asymmetries are
sensitive to $r_D^{K\pi} \cos \delta_D^{K\pi}$, where $r_D^{K\pi}$ and
$\delta_D^{K\pi}$ are the ratio of amplitudes and phase difference,
respectively, between the doubly Cabibbo-suppressed and Cabibbo-favoured
decays. In addition, events containing $D \to K^-\pi^+$ tagged by $D \to
K^0_{S,L} \pi^+\pi^-$ are studied in bins of phase space of the three-body
decays. This analysis has sensitivity to both $r_D^{K\pi} \cos \delta_D^{K\pi}$
and $r_D^{K\pi} \sin \delta_D^{K\pi}$. A fit to ${\cal A}_{K\pi}$, ${\cal
A}_{K\pi}^{\pi\pi\pi^0}$ and the phase-space distribution of the $D \to
K^0_{S,L} \pi^+\pi^-$ tags yields $\delta_D^{K\pi}= \left( 187.6
{^{+8.9}_{-9.7}}{^{+5.4}_{-6.4}} \right)$ degrees, where external constraints
are applied for $r_D^{K\pi}$ and other relevant parameters. This is the most
precise measurement of $\delta_D^{K\pi}$ in quantum-correlated $D\bar{D}$
decays.
Phys. Rev. D 107, 012002 (2023) Using a data sample of $(1.0087\pm0.0044)\times10^{10}$ $J/\psi$ decay events
collected with the BESIII detector at the center-of-mass energy of
$\sqrt{s}=3.097$ GeV, ...we present a search for the hyperon semileptonic decay
$\Xi^{0}\to\Sigma^{-}e^{+}\nu_{e}$ which violates the $\Delta S=\Delta Q$ rule.
No significant signal is observed, and the upper limit on the branching
fraction $\mathcal{B}(\Xi^{0}\to\Sigma^{-}e^{+}\nu_{e})$ is determined to be
$1.6\times10^{-4}$ at the 90% confidence level. This result improves the
previous upper limit result by about one order of magnitude.
Physical Review D 107, 092004 (2023) Using an $e^+e^-$ collision data sample of $(27.08 \pm 0.14) \times 10^{8}$
$\psi(3686)$ events collected by the BESIII detector, we report the first
observation ...of $\chi_{cJ} \to \Omega^- \bar{\Omega}^+$ ($J=0,\,1,\,2$) decays
with significances of $5.6\sigma$, $6.4\sigma$, and $18\sigma$, respectively,
where the $\chi_{cJ}$ mesons are produced in the radiative $\psi(3686)$ decays.
The branching fractions are determined to be $\mathcal{B}(\chi_{c0} \to
\Omega^- \bar{\Omega}^+) = (3.51 \pm 0.54 \pm 0.29) \times 10^{-5}$,
$\mathcal{B}(\chi_{c1} \to \Omega^- \bar{\Omega}^+) = (1.49 \pm 0.23 \pm 0.10)
\times 10^{-5}$, and $\mathcal{B}(\chi_{c2} \to \Omega^- \bar{\Omega}^+) =
(4.52 \pm 0.24 \pm 0.18) \times 10^{-5}$, where the first and second
uncertainties are statistical and systematic, respectively.
This paper reports the study of $D_s^+\to \tau^+\nu$ via
$\tau^+\to\pi^+\bar{\nu}_\tau$ using a boosted decision tree method, with
$7.33$ fb$^{-1}$ of $e^{+}e^{-}$ collision data collected by the ...BESIII
detector at center-of-mass energies between $4.128$ and $4.226$~GeV. The
branching fraction of $D_s^+\to \tau^+\nu_\tau$ is determined to be
$(5.44\pm0.17_{\rm stat}\pm0.13_{\rm syst})\%$. The product of the $D_s^+$
decay constant $f_{D_s^+}$ and the CKM matrix element $|V_{cs}|$ is
$f_{D_s^+}|V_{cs}| = (248.3\pm3.9_{\rm stat}\pm3.1_{\rm syst}\pm1.0_{\rm
input})~\mathrm{MeV}$. Combining with the $|V_{cs}|$ value obtained from the
Standard Model global fit or the $f_{D_s^+}$ from the lattice quantum
chromodynamics, we determine $|V_{cs}| = 0.993\pm0.015_{\rm stat}\pm0.012_{\rm
syst}\pm0.004_{\rm input}$ and $f_{D_s^+} = (255.0\pm4.0_{\rm stat}\pm3.2_{\rm
syst}\pm1.0_{\rm input})~\text{MeV}$. The first uncertainty is statistical, the
second one is systematic and the third one is due to the input parameters,
mainly the lifetime of $D_s^+$. All results obtained in this work supersede the
BESIII previous results based on 6.32 fb$^{-1}$ of $e^+e^-$ collision data
taken at center-of-mass energies between $4.178$ and $4.226$~GeV.
Phys. Rev. D 108, L011101 (2023) The $\Xi^0$ asymmetry parameters are measured using entangled quantum
$\Xi^0$-$\bar{\Xi}^0$ pairs from a sample of $(448.1 \pm 2.9) \times 10^6$
$\psi(3686)$ events ...collected with the BESIII detector at BEPCII. The relative
phase between the transition amplitudes of the $\Xi^0 \bar{\Xi}^0$ helicity
states is measured to be $\Delta \Phi = -0.050 \pm 0.150 \pm 0.020$~rad, which
implies that there is no obvious polarization at the current level of
statistics. The decay parameters of the $\Xi^0$ hyperon $(\alpha_{\Xi^0},
\alpha_{\bar{\Xi}^0}, \phi_{\Xi^0}, \phi_{\bar{\Xi}^0})$ and the angular
distribution parameter $(\alpha_{\psi(3686)})$ and $\Delta \Phi$ are measured
simultaneously for the first time. In addition, the $CP$ asymmetry observables
are determined to be $A^{\Xi^0}_{CP} = (\alpha_{\Xi^0} +
\alpha_{\bar{\Xi}^0})/(\alpha_{\Xi^0} -
\alpha_{\bar{\Xi}^0})$ $= -0.007$ $\pm$ 0.082 $\pm$ 0.025 and $\Delta
\phi^{\Xi^0}_{CP} = (\phi_{\Xi^0} + \phi_{\bar{\Xi}^0})/2$ $= -0.079$ $\pm$
0.082 $\pm$ 0.010 rad, which are consistent with $CP$ conservation.
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