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:

The substructure of jets in quantum chromodynamics (QCD) has garnered significant attention with the advent of infrared- and collinear-safe clustering algorithms and observables. A key question emerging from these studies is how in-jet emissions at soft and hard energy scales, across collinear and wide angles relative to the emitter, differ with the mass of the emitting parton. The Lund jet plane (LJP) is a perturbatively well-defined substructure observable that maps the radiation pattern of jets onto a plane, visually distinguishing emissions with different kinematic properties. Comparing LJP for jets containing hadrons of low versus high mass enables the testing of QCD splitting functions from first-principles calculations across both soft and hard regimes and at different radiation angles. This article presents the first measurement of the LJP for light-quark-enriched and beauty-initiated jets at a center-of-mass energy of 13 TeV at LHCb. This marks the first direct observation of the dead-cone effect in beauty-quark jets, measured in the collinear region of the LJP.

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.