A. Balboni — Page 9

arXiv2025

Measurement of $ϕ(1020)$ meson production in fixed-target $\textit{p}$Ne collisions at $\sqrt{s_{NN}}$ = 68.5 GeV

The first measurement of $ϕ(1020)$ meson production in fixed-target $p$Ne collisions at $\sqrt{s_{NN}}=68.5$ GeV is presented. The $ϕ(1020)$ mesons are reconstructed in their $K^{+}K^{-}$ decay in a data sample consisting of proton collisions on neon nuclei at rest, corresponding to an integrated luminosity of $21.7 \pm 1.4$ nb$^{-1}$, collected by the LHCb detector at CERN. The $ϕ(1020)$ production cross-section in the centre-of-mass rapidity range of $-1.8<y^*<0$ and transverse momentum range of $800<p_{T}<6500$ MeV/c is found to be $σ=182.7\pm2.7~\text{(stat.)}\pm14.1~\text{(syst)}~μ$b/nucleon. A double-differential measurement of the cross-section is also provided in four regions of rapidity and six regions of transverse momentum of the $ϕ(1020)$ meson and compared with the predictions from Pythia and EPOS4, which are found to underestimate the experimental values.

hep-ex↗

arXiv2025

First evidence for direct CP violation in beauty to charmonium decays

The $C\!P$ asymmetry and branching fraction of the CKM-suppressed decay $B^+\!\to J\mskip -3mu/\mskip -2muψ\,π^+$ are precisely measured relative to the favoured decay $B^+\!\to J\mskip -3mu/\mskip -2muψ\,K^+$, using a sample of proton-proton collision data corresponding to an integrated luminosity of $5.4~\mathrm{fb}^{-1}$ recorded at center-of-mass energy of $13~\mathrm{TeV}$ during 2016--2018. The results of the $C\!P$ asymmetry difference and branching fraction ratio are \begin{align*} Δ\mathcal{A}^{C\!P} &\equiv \mathcal{A}^{C\!P}(B^+ \to J\mskip -3mu/\mskip -2muψ\,π^+) - \mathcal{A}^{C\!P}(B^+ \to J\mskip -3mu/\mskip -2muψ\,K^+) = (1.29 \pm 0.49 \pm 0.08) \times 10^{-2}, \end{align*} \begin{equation*} \mathcal{R}_{π/K} \equiv \frac{\mathcal{B}(B^+ \!\to J\mskip -3mu/\mskip -2muψ\,π^+)}{\mathcal{B}(B^+ \!\to J\mskip -3mu/\mskip -2muψ\,K^+)} = (3.852 \pm 0.022 \pm 0.018) \times 10^{-2}. \end{equation*} where the first uncertainties are statistical and the second systematic. A combination with previous LHCb results based on data collected at $7$ and $8~\mathrm{TeV}$ in 2011 and 2012 yields $Δ\mathcal{A}^{C\!P} = (1.42 \pm 0.43 \pm 0.08) \times 10^{-2}$ and $\mathcal{R}_{π/K} = (3.846 \pm 0.018 \pm 0.018) \times 10^{-2}$. The combined $Δ\mathcal{A}^{C\!P}$ value deviates from zero by 3.2 standard deviations, providing the first evidence for direct $C\!P$ violation in the amplitudes of beauty decays to charmonium final states.

hep-ex↗