Direct production of $J/\psi \phi$ vector mesons at the LHCb experiment without additional activity

The first study of the production of $J/\psi\phi$ vector meson pairs with no additional activity in the LHCb detector is presented. This analysis is based on data from proton-proton collisions at a center-of-mass energy of $\sqrt{s} = 13\text{\,TeV}$ collected during Run 2 of LHC (2016-2018), which corresponds to a single-interaction integrated luminosity of $1.73 \ \text{fb}^{-1}$. The $J/\psi\phi$ candidates are reconstructed from the decays of $J/\psi$ and $\phi$ into pairs of muons and kaons, respectively, detected within the pseudorapidity region $2<\eta<5$ and with $p_{\mathrm{T}}>200\text{\,MeV}$. 989 candidate events are selected. The $J/\psi(\to\mu^+\mu^-)\phi(\to K^+K^-)$ production fiducial cross-section for $m(J/\psi\phi)<6000\ \text{MeV}/c^2$ is measured to be \begin{equation*} \sigma_{J/\psi\phi} = (2.66 \pm 0.08 \pm 0.13 \pm 0.08)\text{\,pb} \end{equation*} where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity determination. Furthermore, information from the \textsc{HeRSCheL} subdetector is used to estimate the fraction of exclusively produced events, which is found to be about $32\%$. A five-resonance model is fitted to the data with a combined significance of $8.6\sigma$ compared to a resonance-free model. The mass and width parameters are fixed for three resonances, $X(4140)$, $X(4685)$ and $X(4700)$, while the parameters of the other two resonances, $X(4274)$ and $X(4500)$, are determined in this analysis. Additionally, this thesis presents two separate contributions to the LHCb Upgrade I, which was performed during LHC's Long Shutdown 2 (2019-2022). The first one concerns contributions made in 2019 to the validation of the new VELO modules that are currently installed in the LHCb for the Run 3 data-taking period (2022-2025). The second one concerns contributions made in 2022 to the RTA project, which is responsible for the developing and maintaining LHCb's new fully-software trigger.