LHCb

Abstract:

A stringent test of $CP$ symmetry in hyperon decays is performed using $1.0\times {10}^{10}J/\psi$ events and $2.7\times {10}^9\psi (3686)$ events collected by the BESIII experiment. The $CP$ asymmetry in the two-body nonleptonic weak decays ${\mathrm{\Sigma }}^{+}\to p{\pi }^0$ and ${\overline{\mathrm{\Sigma }}}^{-}\to \overline{p}{\pi }^0$ is determined to be $A_{CP}=-0.0118\pm 0.0083(\mathrm{stat})\pm 0.0028(\mathrm{syst})$ , consistent with $CP$ conservation. The average decay parameter $⟨{\alpha }_0⟩=-0.9869\pm 0.0011(\mathrm{stat})\pm 0.0016(\mathrm{syst})$ represents the most precise measurement in the baryon sector to date. A model-independent analysis of the hyperon polarization is performed for the first time at $J/\psi$ and $\psi (3686)$ resonances, revealing a clear sign reversal and offering new insight into SU(3) symmetry breaking and baryon internal structure. These results provide the most stringent constraints on $CP$ violation in $\mathrm{\Sigma }$ decays and establish a benchmark for future precision studies.

Abstract:

Lepton number violation decay is searched for via using a data sample of events collected via the BESIII detector at the BEPCII collider. No significant signal is observed, and the upper limit on the branching fraction of at the 90% confidence level is determined for the first time to be .

Abstract:

The lifetimes of the Ωc0 and Ξc0 baryons are measured using a pp collision dataset collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. The charm baryons are produced in the fully reconstructed decay chains Ωb−→Ωc0→pK−K−π+π− and Ξb−→Ξc0→pK−K−π+π−. The measurement uses topologically and kinematically similar B− → D0(→ K−K+π−π+)π− decays for normalisation. The measured lifetimes areτΩc0=276.3±19.4stat±1.8syst±0.7τD0fs, τΞc0=149.2±2.5stat±0.9syst±0.4τD0fs, where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the D0 lifetime. These results are consistent with previous measurements performed by the LHCb experiment.

Abstract:

We report a study of the semileptonic decay $D^0\to {\overline{K}}^0{\pi }^{-}{\mu }^{+}{\nu }_{\mu }$ 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 the decay is measured for the first time to be $\mathcal{B}(D^0\to {\overline{K}}^0{\pi }^{-}{\mu }^{+}{\nu }_{\mu })=(1.373\pm 0.020_{\mathrm{stat}}\pm 0.023_{\mathrm{syst}})\%$ , where the first uncertainty is statistical and the second is systematic. Based on the investigation of the decay dynamics, we find that the decay is dominated by the $K^{*}(892{)}^{-}$ resonance with the branching fraction measured to be $\mathcal{B}(D^0\to K^{*}(892{)}^{-}{\mu }^{+}{\nu }_{\mu })=(1.948\pm 0.033_{\mathrm{stat}}\pm 0.036_{\mathrm{syst}})\%$ . We also determine the hadronic form factors for the $D^0\to K^{*}(892{)}^{-}{\mu }^{+}{\nu }_{\mu }$ decay to be $r_V=V(0)/A_1(0)=1.46\pm 0.11_{\mathrm{stat}}\pm 0.04_{\mathrm{syst}}$ , $r_2=A_2(0)/A_1(0)=0.71\pm 0.08_{\mathrm{stat}}\pm 0.03_{\mathrm{syst}}$ , and $A_1(0)=0.609\pm 0.008_{\mathrm{stat}}\pm 0.008_{\mathrm{syst}}$ , where $V(0)$ is the vector form factor and $A_{1,2}(0)$ are the axial-vector form factors evaluated at $q^2=0$ . The $A_1(0)$ is measured for the first time in $D^0\to K^{*}(892{)}^{-}{\mu }^{+}{\nu }_{\mu }$ decay. Averaging the form factor parameters that we reported previously in $D^0\to K^{*}(892{)}^{-}(\to {\overline{K}}^0{\pi }^{-})e^{+}{\nu }_e$ and $D^0\to K^{*}(892{)}^{-}(\to K^{-}{\pi }^0){\mu }^{+}{\nu }_{\mu }$ decays, we obtain $r_V=1.456\pm 0.040_{\mathrm{stat}}\pm 0.016_{\mathrm{syst}}$ , $r_2=0.715\pm 0.031_{\mathrm{stat}}\pm 0.014_{\mathrm{stat}}$ , and $A_1(0)=0.614\pm 0.005_{\mathrm{stat}}\pm 0.004_{\mathrm{syst}}$ . This is the most precise determination of the form factor parameters to date measured in $D\to K^{*}(892)$ transitions, which provide the most stringent test on various theoretical models.

Abstract:

By analyzing a data sample containing events taken with the BESIII detector at the BEPCII storage ring in 2009, the resonance parameters are precisely measured using events. The mass of is determined to be ) MeV/ , and its full width is , where the first uncertainty is statistical, the second systematic, and the third for mass comes from mass uncertainty. These measurements improve the precision of mass by a factor of four and width by one order of magnitude over the previous individual measurements, and significantly boost our knowledge about the charmonium spectrum. Together with additional data events taken in 2012, the decay branching fractions of are measured as well, with precision improved by a factor of three compared to previous measurements. These decay branching fractions provide important inputs for the study of glueballs.