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Abstract:

Using (2712.4 ± 14.3) × 106ψ(3686) candidates collected by the BESIII detector operating at the BEPCII storage ring, the decays χcJJ=012→pp¯ηη are observed for the first time through the radiative transition ψ(3686) → γχcJ. The statistical significances for χcJ signals are all larger than 5σ. The branching fractions of χc0, 1, 2→pp¯ηη are determined to be (5.75 ± 0.59 ± 0.42) × 10−5, (1.40 ± 0.33 ± 0.17) × 10−5, and (2.64 ± 0.40 ± 0.27) × 10−5, respectively, where the first uncertainties are statistical and the second systematic. No evident resonant structures are found in the pp¯ and pη/p¯η systems.

Abstract:

Using (2712 ± 14) × 106ψ(3686) events collected with the BESIII detector, we perform the first amplitude analysis of the radiative decay ψ3686→γKS0KS0$$ \psi (3686)\to \gamma {K}_S^0{K}_S^0 $$ within the mass region MKS0KS0<2.8$$ {M}_{K_S^0{K}_S^0}<2.8 $$ GeV/c2. Employing a one-channel K-matrix approach for the description of the dynamics of the KS0KS0$$ {K}_S^0{K}_S^0 $$ system, the data sample is well described with four poles for the f0-wave and three poles for the f2-wave. The determined pole positions are consistent with those of well-established resonance states. The observed f0 and f2 states are found to be in agreement with those produced in radiative J/ψ decays. The production behaviors of f0 and f2 poles in ψ3686→γKS0KS0$$ \psi (3686)\to \gamma {K}_S^0{K}_S^0 $$ are qualified with their residues and the converted branching fractions. By comparing with J/ψ→γKS0KS0$$ J/\psi \to \gamma {K}_S^0{K}_S^0 $$ decay, the ratios Bψ3686→γf0,2BJ/ψ→γf0,2$$ \frac{\mathcal{B}\left(\psi (3686)\to \gamma {f}_{0,2}\right)}{\mathcal{B}\left(J/\psi \to \gamma {f}_{0,2}\right)} $$ are determined, which provides crucial experimental inputs on the internal structure of the f0,2 states, especially their potential mixing with glueball components.

Abstract:

This article presents doubly differential measurements of the asymmetries in production rates between mesons containing a charm quark and those containing an anti-charm quark in proton-proton collisions at a centre-of-mass energy of s=13.6 TeV using data recorded by the LHCb experiment. The asymmetries of D0, D+ and Ds+ mesons are measured for two-dimensional intervals in transverse momentum and pseudorapidity, within the range 2.5 < pT< 25.0 GeV/c and 2.0 < η < 4.5. No significant production asymmetries are observed. Comparisons to the Pythia 8 and Herwig 7 event generators are also presented, and their agreement with the data is evaluated. These measurements constitute the first measurements of production asymmetries at this centre-of-mass energy of colliding beams, and the first measurements with the LHCb Run 3 detector.

Abstract:

A stringent test of $CP$ symmetry in hyperon decays is performed using $1.0×{10}^{10}J/\mathrm{ψ}$ events and $2.7×{10}^9\mathrm{ψ}(3686)$ events collected by the BESIII experiment. The $CP$ asymmetry in the two-body nonleptonic weak decays ${\mathrm{Î\pounds }}^{+}→p{\mathrm{Ï€}}^0$ and ${\stackrel{¯}{\mathrm{Î\pounds }}}^{−}→\stackrel{¯}{p}{\mathrm{Ï€}}^0$ is determined to be $A_{CP}=−0.0118Â\pm 0.0083(\mathrm{stat})Â\pm 0.0028(\mathrm{syst})$ , consistent with $CP$ conservation. The average decay parameter $⟨{\mathrm{Î\pm }}_0âŸ\copyright =−0.9869Â\pm 0.0011(\mathrm{stat})Â\pm 0.0016(\mathrm{syst})$ 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 $J/\mathrm{ψ}$ and $\mathrm{ψ}(3686)$ 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 $\mathrm{Î\pounds }$ 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.